Aims

The aim of this study was to perform the first population-based description of the epidemiological and health economic burden of fracture-related infection (FRI).

There is an increasing incidence of revision for periprosthetic joint infection. The addition of vancomycin to beta-lactam antimicrobial prophylaxis in joint arthroplasty may reduce surgical site infections, however, the efficacy and safety have not been established.

This was a multicenter, double-blind, superiority, placebo-controlled trial. We randomized 4239 adult patients undergoing joint arthroplasty surgery to receive 1.5g vancomycin or normal saline placebo, in addition to standard cefazolin antimicrobial prophylaxis. The primary outcome was surgical site infection at 90-days from index surgery. Perioperative carriage of Staphylococcus species was also assessed.

In the 4113 patients included in the modified intention-to-treat population, surgical site infections occurred in 72/2069 (3.5%) in the placebo group and 91/2044 (4. 5%) in the vancomycin group (risk ratio 1.28; 95% confidence interval 0.94 to 1.73; p value 0.11). No difference was observed between the two groups for primary hip arthroplasty procedures. A higher proportion of infections occurred in knee arthroplasty patients in the vancomycin group (63/1109 [4.7%]) compared with the placebo group (42/1124 [3.7%]; risk ratio 1.52; 95% confidence interval 1.04 to 2.23; p value 0.031). Hypersensitivity reactions occurred in 11 (0.5%) patients in the placebo group and 24 (1.2%) in the vancomycin group (risk ratio 2.20; 95% confidence interval 1.08, 4.49) and acute kidney injury in 74 (3.7%) patients in the placebo group and 42 (2.1%) in the vancomycin group (risk ratio 0.57; 95% confidence interval 0.39, 0.83). Perioperative Staphylococcus aureus carriage was detected in 1089/3748 (29.1%) of patients.

This is the first randomized controlled trial examining the addition of a glycopeptide antimicrobial to standard beta-lactam surgical antimicrobial prophylaxis in joint arthroplasty. The addition of vancomycin to standard cefazolin prophylaxis was not superior to placebo for the prevention of surgical site infections in hip and knee arthroplasty surgery.

Local antimicrobial therapy is an integral aspect of treating orthopaedic device related infection (ODRI), which is conventionally administered via polymethylmethacrylate (PMMA) bone cement. PMMA, however, is limited by a suboptimal antibiotic release profile and a lack of biodegradability.

In this study, we compare the efficacy of PMMA versus an antibioticloaded hydrogel in a single- stage revision for chronic methicillin-resistant Staphylococcus aureus (MRSA) ODRI in

sheep. Antibiofilm activity of the antibiotic combination (gentamicin and vancomycin) was determined in vitro. Swiss alpine sheep underwent a single-stage revision of a tibial intramedullary nail with MRSA infection. Local gentamicin and vancomycin therapy was delivered via hydrogel or PMMA (n = 5 per group), in conjunction with systemic antibiotic therapy. In vivo observations included: local antibiotic tissue concentration, renal and liver function tests, and quantitative microbiology on tissues and hardware post-mortem.

There was a nonsignificant reduction in biofilm with an increasing antibiotic concentration in vitro (p = 0.12), confirming the antibiotic tolerance of the MRSA biofilm. In the in vivo study, four out of five sheep from each treatment group were culture negative. Antibiotic delivery via hydrogel resulted in 10–100 times greater local concentrations for the first 2–3 days compared with PMMA and were comparable thereafter. Systemic concentrations of gentamicin were minimal or undetectable in both groups, while renal and liver function tests were within normal limits.

This study shows that a single-stage revision with hydrogel or PMMA is equally effective, although the hydrogel offers certain practical benefits over PMMA, which make it an attractive proposition for clinical use.

Aims

Cauda equina syndrome (CES) can be associated with chronic severe lower back pain and long-term autonomic dysfunction. This study assesses the recently defined core outcome set for CES in a cohort of patients using validated questionnaires.

The MAGnetic Expansion Control (MAGEC) system is used increasingly in the management of early-onset scoliosis. Good results have been published, but there have been recent reports identifying implant failures that may be associated with significant metallosis surrounding the implants. This article aims to present the current knowledge regarding the performance of this implant, and the potential implications and strategies that may be employed to identify and limit any problems.

We urge surgeons to apply caution to patient and construct selection; engage in prospective patient registration using a spine registry; ensure close clinical monitoring until growth has ceased; and send all explanted MAGEC rods for independent analysis.

The MAGEC system may be a good instrumentation system for the treatment of early-onset scoliosis. However, it is innovative and like all new technology, especially when deployed in a paediatric population, robust systems to assess long-term outcome are required to ensure that patient safety is maintained.

Cite this article: Bone Joint J 2017;99-B:708–13.

Purpose:

To produce objective evidence that lifting is more comfortable in lumbar flexion than lumbar extension.

Traditionally, lifting is taught in lumbar extension (“straight back”) but in our experience is more comfortable and stronger in flexion with backward lumbar tilt.

Aim:

An analysis of significant neuromonitoring changes (NMCs) and evaluation of the efficacy of multimodality neuromonitoring in spinal deformity surgery.

Introduction:

The risk for late periprosthetic fractures is higher in patients treated for a neck of femur fracture compared to those treated for osteoarthritis. It has been hypothesised that osteopenia and consequent decreased stiffness of the proximal femur are responsible for this. We investigated if a femoral component with a bigger body would increase the torque to failure in a biaxially loaded composite sawbone model.

Introduction:

In an attempt to reduce stress shielding in the proximal femur multiple new shorter stem design have become available. We investigated the load to fracture of a new polished tapered cemented short stem in comparison to the conventional polished tapered Exeter stem.

Introduction

The Exeter cemented polished tapered stem design was introduced into clinical practice in the early 1970's. [i] Design and cement visco-elastic properties define clinical results [ii]; a recent study by Carrington et al. reported the Exeter stem has 100% survivorship at 7 years. [iii] Exeter stems with offsets 37.5–56 mm have length 150 mm (shoulder to tip). Shorter stems, lengths 95–125 mm, exist in offsets 30–35.5 mm. The Australian National Joint Replacement Registry recently published that at 7 years the shorter stems are performing as well as longer stems on the registry [iv]. Clinical observation indicates in some cases of shorter, narrower femora that fully seating a 150 mm stem's rasp in the canal can be difficult, which may affect procedural efficiency. This study investigates the comparative risk of rasp distal contact for the Exeter 150 mm stem or a 125 mm stem.

Aim:

This prospective cohort study investigated whether the use of preoperative anticoagulants is an independent risk factor for the outcomes of surgical treatment of patients with a neck of femur fracture.

There has been much discussion and controversy in the media recently regarding metal toxicity following large head metal on metal (MoM) total hip replacement (THR). Patients have been reported as having hugely elevated levels of metal ions with, at times, devastating systemic, neurolgical and/or orthopaedic sequelae.

However, no direct correlation between metal ion level and severity of metallosis has yet been defined. Normative levels of metal ions in well functioning, non Cobalt-Chrome hips have also not been defined to date.

The Exeter total hip replacement contains no Cobalt-Chrome (Co-Cr) as it is made entirely from stainless steel. However, small levels of these metals may be present in the modular head of the prosthesis, and their effect on metal ion levels in the well functioning patient has not been investigated.

We proposed to define the “normal” levels of metal ions detected by blood test in 20 well functioning patients at a minimum 1 year post primary Exeter total hip replacement, where the patient had had only one joint replaced.

Presently, accepted normal levels of blood Chromium are 10–100 nmol/L and plasma Cobalt are 0–20 nmol/L. The UK Modern Humanities Research Association (MHRA) has suggested that levels of either Cobalt or Chromium above 7 ppb (equivalent to 135 nmol/L for Chromium and 120 nmol/L for Cobalt) may be significant. Below this level it is indicated that significant soft tissue reaction and tissue damage is less likely and the risk of implant failure is reduced.

Hips were a mixture of cemented and hybrid procedures performed by two experienced orthopaedic consultants. Seventy percent were female, with a mixture of head sizes used.

In our cohort, there were no cases where the blood Chromium levels were above the normal range, and in more than 70% of cases, levels were below recordable levels. There were also no cases of elevated plasma Cobalt levels, and in 35% of cases, levels were negligible.

We conclude that the implantation with an Exeter total hip replacement does not lead to elevation of blood metal ion levels.

Bleeding related wound complications including deep infection, superficial infection and haematoma cause significant morbidity in lower limb joint arthroplasty surgery. It has been observed anecdotally that patients requiring therapeutic anti-coagulation within the peri-operative period have higher rates of bleeding related complications and those requiring intravenous heparin particularly appear to do poorly.

The aim of this study is to investigate the relationship between post-operative bleeding and wound complications in the patient requiring therapeutic warfarin, plus or minus heparin, in total hip arthroplasty surgery.

This is a retrospective cohort study reviewing 1047 primary total hip replacements performed in a single centre over a five year period and comparing outcomes of the patients on warfarin (89) with a double-matched control group of patients not on warfarin (179). Outcomes included rates of deep infection, excessive wound ooze or haematoma, superficial infection, return to OT for washout and need for revision operation. The study group was then sub analysed comparing those on IV heparin plus oral warfarin, to those on warfarin alone.

The warfarin group had significantly higher risk of deep joint infection (9% vs 2.2% p= 0.023), haematoma/wound ooze (28% vs 4% p < 0.001) and superficial infection (13.5% vs 2.2% p < 0.001) compared to the control group. In the sub analysis of the study group, those on IV heparin had significantly higher risk of haematoma/wound ooze (44% vs 28% p= 0.023) than those on warfarin alone.

The requirement of therapeutic anti-coagulation in the peri-operative period is a tenuous balance between the complications of thrombo-embolic disease and bleeding-related morbidity. In the past, perhaps the full burden of bleeding related complications has not been appreciated, but now improved understanding will enable the both the surgeon and the patient to make more informed decisions regarding therapeutic anticoagulation in elective arthroplasty surgery.

Favourable long-term results have been reported with the standard Exeter cemented stem. We report our experience with a version for use in smaller femora, the Exeter 35.5 mm stem. Although, also a collarless polished taper, the stem is slimmer and 25 mm shorter than a standard stem.

Between August 1988 and August 2003, 192 primary hip arthroplasties were performed in 165 patients using the Exeter 35.5 mm stem. Clinical and operative data were collected prospectively. Clinical evaluation was by the Charnley, Harris and Oxford hip scores and radiographs were analysed post-operatively and at latest follow up.

The mean age at time of operation was 53 years (18 to 86), with 73 patients under the age of 50 years. The diagnosis was osteoarthritis in 91, hip dysplasia in 77, inflammatory arthritis in 18, septic arthritis of the hip in three, secondary to Perthes disease in two and avascular necrosis of the hip in one patient. The fate of every implant is known.

At a median follow-up of 8 years (5 to 19), survivorship with revision of the femoral stem for aseptic loosening as the endpoint was 100%. Fifteen cases (7.8%) underwent further surgery 11 for acetabular revision, one for stem fracture and three others.

Although, smaller than a standard Exeter Universal polished tapered cemented stem—with a shorter, slimmer taper—the performance of the Exeter 35.5 mm stem was equally good even in this young, diverse group of patients.

Impaction bone grafting (IBG) of the acetabulum in cemented primary total hip replacement is a useful technique in the management of acetabular deficiencies. It has the capacity to restore anatomy and bone stock with good long-term outcome. We present 125 consecutive cases of IBG with a cemented polyethylene component. All patients who received full IBG of the acetabulum in primary cemented Exeter total hip replacements and who underwent surgery between August 1995 and August 2003 were identified. All operative and follow-up data was collected prospectively and no patients were lost to follow-up. All patients underwent pre-operative and regular post-operative hip scores with the Harris, Oxford and the modified Charnley scoring systems. Data on indication, surgical technique, socket position and migration and revision was reviewed at a mean follow-up of 7.6 (range 5 to13.4) years.

Between August 1995 and August 2003, 113 patients (85 females) with an average age of 67.8 (range 22.9–99.2) years underwent 125 primary Exeter cemented total hip replacements with IBG of acetabular defects. Acetabular defects were classified according to the AAOS classification as cavitatory in 62 hips and as segmental, requiring application of a rim mesh prior to IBG, in 63 hips. Life tables were constructed demonstrating 86.4% survival of the acetabular component at 13.4 years with revision for any reason as the endpoint and 89.3% survival with revision for aseptic loosening as the endpoint. Of the seven patients who underwent revision for aseptic loosening, all had pre-operative segmental acetabular defects requiring application of a rim mesh. No patient who underwent IBG for a cavitatory defect required revision surgery for aseptic loosening. Survival of the Exeter cemented femoral component was 100% at 13.4 years with revision for aseptic loosening as the endpoint. There were 11 radiographic failures of the acetabular component, which have not been revised at latest review. One of these is symptomatic but not fit for revision surgery, two were asymptomatic at time of death and eight are asymptomatic but under review.

This is the largest series of IBG in the acetabulum in cemented primary THR. Our results suggest that the medium term survival of this technique is good, particularly when used for cavitatory defects. Although there were radiographic failures, these are largely asymptomatic and may not require revision.

The cement in cement technique for revision total hip arthroplasty (THA) has shown good results in selected cases. However, results of its use in the revision of hemiarthroplasty to THA has not been previously reported.

Between May 1994 and May 2007 28 (20 Thompson's and 8 Exeter bipolar) hip hemiarthroplasties were revised to THA in 28 patients using the cement in cement technique. All had an Exeter stem inserted at the time of revision. Clinical and operative data were collected prospectively. Clinical evaluation was by the Charnley, Harris and Oxford. Hip scores and radiographs were analysed post-operatively and at latest follow up.

The mean age at time of hemiarthroplasty revision was 80 (35 to 93) years. The reason for revision was acetabular erosion in 12 (43%), recurrent dislocation in eight (29%), aseptic stem loosening in four (14%), periprosthetic fracture in two (7%) and infection in a further two (7%) patients. No patient has been lost to follow up. Three patients died within three months of surgery. The mean follow up of the remainder was 50 (16 to 119) months. Survivorship with revision of the femoral stem for aseptic loosening as the endpoint was 100%. Three cases (11%) have since undergone further revision, one for recurrent dislocation, one for infection, and one for periprosthetic fracture.

The cement in cement technique can be successfully applied to revision of hip hemiarthroplasty to THA. It has a number of advantages in this elderly population including minimising bone loss, blood loss and operative time.

Removal of well-fixed cement at the time of revision THA for sepsis is time consuming and risks bone stock loss, femoral perforation or fracture. We report our experience of two-stage revision for infection in a series of cases in which we have retained well-fixed femoral cement.

All patients underwent two-stage revision for infection. At the first stage the prostheses and acetabular cement were removed but when the femoral cement mantle demonstrated good osseo-integration it was left in-situ. Following Girdlestone excision arthroplasty (GEA), patients received local antibiotics delivered by cement spacers, as well as systemic antibiotics. At the second stage the existing cement mantle was reamed, washed and dried and then a femoral component was cemented into the old mantle.

Sixteen patients (M:F 5:11) had at least three years follow-up (mean 80 months – range 43 to 91). One patient died of an unrelated cause at 53 months. Recurrence of infection was not suspected in this case. The mean time to first stage revision was 57 months (3 to 155). The mean time between first and second stages was nine months (1 to 35). Organisms were identified in 14 (87.5%) cases (5 Staphylococcus Aureas, 4 Group B Streptococcus, 2 Coagulase negative Staphylococcus, 2 Enterococcus Faecalis, 1 Escheria Coli). At second stage, five (31.2%) acetabulae were uncemented and 11 (68.8%) were cemented. There were two complications; one patient dislocated 41 days post-operatively and a second patient required an acetabular revision at 44 days for failure of fixation. No evidence of infection was found at re-revision. One patient (1/16, 7%) has been re-revised for recurrent infection. Currently no other patients are suspected of having a recurrence of infection (93%).

Retention of a well-fixed femoral cement mantle during two-stage revision for infection and subsequent cement-in-cement reconstruction appears safe with a success rate of 93%. Advantages include a shorter operating time, reduced loss of bone stock, improved component fixation and a technically easier second stage procedure.

Surgery for degenerative lumbar spondylolisthesis may entail both decompression and fusion. The knee-chest position facilitates the decompression, but fixation in this position risks fusion in kyphosis. This can be avoided by intra-operative re-positioning to the prone position. The aim of this study was to quantify the restoration of lordosis achieved by intra-operative repositioning and to assess the clinical and radiological outcome.

A total of forty consecutive patients with degenerative lumbar spondylolisthesis and stenosis were treated by posterior decompression and interbody fusion with pedicle screw fixation. The screw insertion, decompression and interbody grafting were performed with the patient in the knee-chest position. The patient was then re-positioned to the fully prone position for fusion. Sagittal plane angles were measured pre-, intra- and post-operatively. Clinical assessment was performed using SF-36 scores and visual analogue scores for back and leg pain.

The sagittal plane angle increased from median 16.0 degrees pre-operatively to 23.1 degrees post-operatively (p<0.01) and this was maintained at the last follow-up (mean 21 months). The SF-36 scores improved for 7 out of 8 domains and the physical score improved from 29% to 40% (p<0.05). The mean pain scores improved significantly from 7.5 to 3.8 for back pain and from 7.6 to 3.7 for leg pain (p<0.001).

Lumbar spondylolisthesis was found to be associated with a reduction of normal lumbar lordosis and the knee-chest position exacerbates this loss of lordosis. Intra-operative repositioning restored lordosis to greater than the pre-operative angle and was associated with a good clinical outcome.

Data from recent AOANJRR shows a higher incidence of acetabular revision for dislocation of THA in uncemented compared to cemented THA (RR 1.59). We hypothesized that a difference in accuracy of component placement may be a factor. We aimed to assess any difference in accuracy between these 2 types of THA.

Patients undergoing navigated THA were prospectively recruited. Choice of uncemented or cemented THA was based on individual surgeon’s routine practice and preference and no adjustments were made for this study. All THAs (Cemented Exeter-21 and uncemented Trident/Secur fit-20) were performed through a posterior approach.

Statistical analysis: the mean and 95% confidence intervals (or median and interquartile range (IQR) for non parametric data) for each measure in both groups. ANOVA and nonparametric Mann-Whitney U test (significance level 5%). Levene’s test for homogeneity, Comparison of frequencies with chi-squared test or Fishers Exact test. Bonferroni correction where necessary.

We demonstrated a significant difference in reproducibility between components. Four of 20 (20%) uncemented cups deviated from the target inclination by 5 degrees or more compared to none of 21 in the cemented group (p=0.048). Seven of the 20 (35%) of the uncemented cups deviated from the target version by 5 degrees or more compared to none of 21 in the cemented group (p=0.003). There was a significant difference between the groups with regard to deviation from planned leg length (p< 0.001). Deviation from target leg length of greater than 5mm was found in 36.4% of the uncemented cases as compared to 8.3% of the cemented cases although due to the small numbers this was not statistically significant (p=0.16).

Statistically significant reduced accuracy of cup placement is demonstrated with uncemented compared to cemented implants. It is harder to control implant positioning in uncemented implants than cemented implants.

Objective: We prospectively compared the techniques of skip laminectomy and laminoplasty for the treatment of cervical spondolytic myelopathy in terms extent of decompression achieved, axial pain, postoperative range of cervical motion, patient and surgical outcomes.

Methods and results: We studied fifty consecutive patients operated on for cervical spondolytic myelopathy and spinal cord compression as demonstrated on MRI between the levels C3–4 to C6–7. Each patient had a minimum follow-up of two years (2.2 – 4.3 years). Twenty-five patients underwent skip laminectomy and twenty-five patients underwent laminoplasty. Decompression was assessed by pre- and post-operative MRI. Cervical range of motion was assessed by pre- and postoperative flexion and extension radiographs. Patient outcomes were assessed by evaluation of pre-and postoperative neurology and SF12 scores for mental health, physical health and axial pain.

Less blood loss and operative times were found with skip laminectomy. Similar degrees of decompression with both techniques. Significantly improved axial pain scores with skip laminectomy. Significantly improved preservation of range of movement with skip laminectomy.

Conclusion: Skip laminectomy is an effective procedure for reducing the incidence of postoperative morbidities, such as persisting axial pain, and restriction of neck motion often seen after laminoplasty, and provides adequate decompression of the spinal cord as demonstrated on MRI for a minimum follow-up of two years.

Tissue engineering is a rapidly expanding field of research. Bone and cartilage engineering are being undertaken in an attempt to treat osteoarthritis and repair bone defects. In spite of extensive research little successful clinical application of this work has been seen. There are however many advances in the field that one day may have therapeutic interest. One particular area of interest is the potential for using osteophyte tissue in repairing osteoarthritic defects. Osteophytes represent an attempt by the body to regenerate bone and cartilage. They present an obvious source of cells for tissue engineering. Research ay QUT has shown that cells within the osteophytes are a better source of bone and cartilage regeneration in the laboratory than matched patient’s bone marrow stem cells.

Osteoarthritis remains the ultimate challenge for orthopaedic tissue engineering. Understanding the chemical and mechanical signals occurring in osteoarthritis presents opportunities for targeted drug delivery and potential slowing of disease. We have identified changes within the MMP profile of cells at the osteochondral junction. Subchondral sclerosis appears to be associated with changes in the nature of chondrocytes deep within the cartilage layer. This transformation of chondrocytes into osteoblast-like tissue in many ways mimics the changes seen in the growth plate once maturity is reached. Understanding the parallels between these processes may help answer some of the mechanisms of the development of osteoarthritis.

This talk will discuss the above topics as well as other areas of interest to an orthopaedic surgeon working within a group of 10 cell biologists.

Introduction: It is well known that the fate of biomaterials is determined by the distribution of proteins attached to the surface from the initial contact with blood or serum. This profile determines wether a material is inert, creates a foreign body response or is bioactive. Bioinert materials, such as polyethylene completely denature surface proteins, whilst materials inducing inflammatory responses are predisposed to complement protein attachment. Bioactive materials such autologous tissue grafts adsorb, but do not denature serum proteins such as fibronectin and Von Willebrand’s factor. This does not interfere with the healing cascade. This aim of this study is to prepare a synthetic bone graft substitute that activates the body’s autologous healing cascade by activating platelets, without activating a complement response through the controlled adsorption of serum proteins.

Methods: Polymers composed of varied concentration of acrylic acid (AA) and comonomers (methyl, ethyl and butyl methacrylates (MMA, EMA, BMA)) were prepared in glass vials by free radical polymerisation. Fresh blood was collected from a healthy donor and pipetted immediately into each chamber. Glass was used as a control. The chambers were incubated at 37o C for 2 hours. The surface morphology was examined using Scanning Electron Microscopy (SEM). Concentration of complement protein C5a and prothrombin fragments 1 and 2 were determined using commercial ELISA kits. Foreign body reaction (FBR) initiated by the biomaterial was estimated by counting leukocytes on clot sections using immunofluorescence.

Results: Extent of coagulation was correlated with plasma concentrations of Prothrombin fragments 1 and 2. These measurements show blood incubated with various polymers composed of different comonomers all promoted the formation of blood clots. It was found that the leukocyte population towards the interface of clot and polymer (AA:MMA) decreased with increasing surface acid concentration (65%AA:MMA 30 leukocytes/0.25mm2, glass 70 leukocytes/0.25mm2 (p< 0.05)). FBR is induced by the activation of complement system. The percentage of C5a concentration detected in blood incubated with various polymers composed of different comonomers relative to normal serum level of C5a (35ng/mL). No significant elevations of C5a were measured from polymer 65% AA:MMA and 65% AA:EMA. Glass induced vigorous complement response as expected. The synergistic combination of surface acid concentration and comonomers had a significant effect on extent of FBR. Increased acid concentration resulted in decreased C5a level with MMA and ET but increased level with BMA.

Discussion: The functional groups exposed on the surface of a material influence whether leukocyte or platelet activation is responsible for the subsequent physiological response. By modifying the combinations of surface acid concentrations and comonomers, we show that a biomaterial with an appropriate surface chemistry promotes the platelet plug formation and coagulation but down regulated foreign body reaction. This study shows that that a biomaterial with the appropriate surface chemistry to evoke the same coagulation response as damaged tissue, mediated through platelet activation and intrinsic and extrinsic coagulation, initiates the initial pathways of the bone healing cascade. This material is a realistic candidate for biomaterial induced bone regeneration.

Introduction: The biological activity of autologous grafts is due to a number of proteins (growth factors) that control bone cell differentiation, proliferation and expression. Several of these have been isolated including; bone morphogenetic proteins 2 and 7. These are commercially available and regularly used with the intention of accelerating fracture healing, repairing critical sized defects and combating bone mineral loss. Whilst it is commonly recognised that multiple growth factors are present at differing times in the healing cascade, the usual delivery, both in the clinic and the laboratory, is of one growth factor delivered over a very short and early time period. Commonly growth factors are delivered in solution or from a collagen sponge and are quickly metabolised in the proteolytic wound healing environment. The physiological need for BMPs is later than the acute delivery at the time of surgery. The aim of this study is to develop a granular protein delivery system that enables controlled release of multiple proteins at a variety of time points.

Methods: A series of homogenous polymer granules 8mm3 were prepared by photo-polymerising 12uL of mixtures of methacrylated adipic acid anhydride (MAAA) and methyl methacrylate (MMA) or MAAA and butyl methacrylate (BMA) with molar ratios ranging from 100- 55 % (MSAA). Into each granule 5ug of a model drug, carmoisine was loaded and 1%w/w of 2,2-dimethoxy-2-phenyl-acetophenone (DMPA) photoinitiator was added per granule. The granules were exposed to UV light at 390nm for 14 minutes. Multilayered granules were prepared photo-polymerising 4uL layers of different monomer compositions in a similar method to the single layered method above. The composition of the multilayered granules was chosen to optimise the release profile. Carmoisine release profiles were determined by UV-visible spectroscopy.

Results: Homogenous granules composed of 100% MAAA released 90% of their payload by 24hrs, those composed of 90:10 MAAA:MMA released by 48hrs those composed of 70:30 MAAA:MMA released by 80hrs those composed of 60:40 MAAA:MMA released by 170hrs those composed of 70:30 MAAA: BMA released by 288hrs and those composed of 60:40 MAAA:BMA released by 456hrs. The multilayered granule had a sustained release of the model drug over the test period of 19 days.

Discussion: The limitation of most drug delivery systems, such as microspheres or collagen, is poor control over the release profile. The drug is ether released instantly or well after it is required. This multilayered composite drug delivery system enables the controlled release of different bioactive compounds at different time points between 0 and 19 days. By altering the drug loading in each layer we were able to sustain the release of one compound over this time period. This technology enables us to switch compounds at a given time points for example delivery of angiogenic factors for one week, proliferative factors for the second week and differentiation factors for the third week. This technology enables the pre-programmed release of multiple growth factors at times in the healing cascade when they meet the physiological need. A controlled release of growth factors at the appropriate time should improve bone healing rates.

Introduction: Acute neurological damage from spinal cord injuries is believed to be localised, however it initiates a cascade of secondary events which usually leads to extensive and permanent neurological deficit. The secondary damage begins with the disruption of the blood-spinal cord barrier which unleashes a protracted inflammatory response. This prolonged inflammatory response is the catalyst for the secondary neurodegeneration and limited repair response that occurs in the chronic phase of a spinal cord injury. In this study it was proposed that the acute delivery of the angiogenic growth factors vascular endothelial growth factor (VEGF) and platelet derived growth factor (PDGF) would mediate inflammation and restore the blood spinal cord barrier. This would minimise the formation of glial scar and reduce the extent of secondary degeneration caudal and cranial to the lesion site.

Methods: Adult male Wistar rats (400g) were anesthetised. Complete laminectomies were performed at T10 and the animals were subjected to T10 hemisection. Animals were randomised to a treatment group (Lesion Control (LC), Gel Control (GC) and Angiogenic Gel (AG)) after the spinal cord was cut. Each treatment group had 6 animals sacrificed 3 months post injury. Sections were stained with antibodies to neurofilament 200, glial fibrillary acidic protein, smooth muscle actin (SMA), and fluorescent secondary antibodies and mounted with DAPI. The lesion size was measured from horizontal histological sections of the midline from 5 animals in each group using Axiovision version 4.6.1.0 (Carl Zeiss Imaging Solutions, Germany).

Results: The mean lesion size for the lesion control group was 2.09mm2, 1.97mm2 for the gel control group and 0.45mm2 for the active gel group. A t-test was used to confirm that the differences between the active gel and the two control groups were statistically significant (AG vs LC p= 0.021 AG vs GC p= 0.026). Histology showed a marked improvement of the morphology of the astrocytes in the treatment group over the control groups indicating that the treatment affected the population of reactive astrocytes. SMA staining showed an increased level of revascularisation in the treated lesions.

Discussion: Spinal cords do not heal because of prolonged inflammation which leads to secondary necrotic events, scar formation and the inhibition of regeneration. In this study we present a method for regulating the post lesion inflammatory signals, significantly reducing post-lesion scar formation. We propose the delivery of VEGF/PDGF significantly increases the permeability of the blood spinal cord barrier to neutrophils and macrophages and promotes angiogenesis observed in the lesion site. This may have two major effects on the progression of the spinal cord injury. Firstly, by increasing the initial influx of inflammatory cells it enables the faster removal of damaged tissue and phagocytosis of apoptotic cells thereby restoring the balance in favour of regulated inflammation and results in a finite and reduced inflammation time. Secondly, combination of VEGF and PDGF provides a robust angiogenic response and reduces ischemia, the population of reactive astrocytes and the capacity to form glial scars. These growth factors appear to moderate the secondary degenerative changes that result from the prolonged inflammation and thus promote the inherent capacity for regeneration.

This presentation introduces a new tool to be used in the cementing of acetabular components in total hip arthroplasty, the ‘Rim Cutter’. The Rim Cutter is designed to cut a ledge in the rim of the acetabulum into which a flanged cup can be cemented. The flange is trimmed such that it fits precisely into the ledge cut in the acetabulum. We present the in vitro pilot study of the effect of using this tool on the intra-acetabular cement mantle pressure during cup insertion and also the effect on the depth of cement penetration as the cup is inserted. A significant improvement in both cement pressure and cement penetration over conventional flanged and unflanged cups is noted. Improved cement penetration around the rim of the acetabulum in THR has implications for reducing the rate of aseptic loosening. The pilot study also suggests other beneficial features of using the rim cutter such as improved cup centralisation, control of orientation and the prevention of the cup ‘bottoming out’. Further in vivo studies are required to better assess its efficacy.

To regenerate the complex tissue such as bone-cartilage construct using tissue engineering approaches, controllable differentiation of mesenchymal stem cells (BMSCs) into chondrogenic and osteogenic lineages is crucially important. Although bilayered scaffolds have been investigated in vitro and in vivo, no culture system is available to test BMSCs differentiation into bone and cartilage simultaneously in bilayered scaffolds. This study investigated a defined culture media, which supported osteoblast and chondrocyte differentiation depending on growth factors implemented in biomaterials. In 2-dimensional culture, BMSCs differentiated to chondrocytes when transforming growth factor-beta 3 (TGF-β3) was added to the defined media, whereas osteogenic differentiation was induced by adding bone morphogenetic protein 7 (BMP-7). BMSC differentiation to osteogenic and chondrogenic lineages was further strengthen in 3-dimensional culture. Proteoglycan formation, type II collagen, and aggrecan were upregulated in the defined media when BMSCs were mixed with fibrin gel impregnated with TGF-β3. Mineralization and the expression of osteogenic markers such as alkaline phosphatase, osteopontin, and osteoclacin were noticeable when BMSCs cultured in hydroxyapatite-tricalcium phosphate (HA/TCP) scaffolds coated with BMP-7.

This study generated and tested a growth media, which could induce osteogenic and chondrogenic differentiation of BMSCs in one culture system. These results will help the development of tissue substitutes for multi-complexed tissues such as subchondral replacement.

Bone Tissue Engineering Program, Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, Australia

Adult mesenchymal stem cells (MSCs) are a topic of immense research interest in the field of tissue engineering. Since, depletion of multipotent cells has been implicated in degenerative joint diseases, cell based therapies have been proposed for tissue regeneration, especially for cartilage repair. The aim of the present study is to focus on the possibility of deriving and expanding multipotential MSCs from the heterogeneous bone marrow stromal samples of patients with osteoarthritis (OA) by characterising MSCs at the single cell level.

Single cell clonal cultures were established by limiting dilution of marrow stromal cells from three OA patients. A total of 14 clones with a wide variation in their cell doubling time were isolated. The clones were grouped into fast-growing and slow-growing clones. All except one of the fast-growing clones were tripotential. However the slow-growing clones showed limited differentiation potential and morphological changes associated with cellular senescence with extended duration in culture. Flow cytometric analysis did not depict any difference in the expression of the selected putative MSC cell surface markers CD29, CD44, CD90, CD105 and CD166 between fast-growing and slow-growing clones indicating a strong need to investigate for novel cell-surface markers. Further, proteomic analysis to understand the sub-cellular processes responsible for the existence of varying sub-populations identified 11 differentially expressed proteins. These proteins were reported to be associated with cellular organization, signal transduction, energy pathways and stress related proteins. Identification of signaling pathway proteins and cell cycle related proteins, such as calmodulin and caldesmon in the clonal populations, suggest that high-throughput proteomic technologies like two dimensional liquid chromatography (2D LC) coupled with mass spectrometry (MS) may facilitate the discovery of therapeutically useful biomarkers.

This study demonstrated the existence of a fast-growing multipotential MSC population from bone marrow samples of patients with OA. Therefore, despite a supposedly smaller stem cell compartment in these patients, we demonstrate here that they can still yield a potentially therapeutically useful source of syngeneic MSCs.

Synthetic biodegradable polymers have been utilized increasingly in pharmaceutical, medical and biomedical engineering. Control of the interaction of living cells and biomaterials surfaces is one of the major goals in the design and development of new polymeric biomaterials in tissue engineering.

In this study, a novel amphiphilic tri-block copolymer, methoxy-terminated poly (ethylene glycol) (MPEG) – polyL-lactide (PLLA) – polylysine (PLL) was synthesized. Various molecular compositions of tri-block copolymers were prepared via optimising the parameters and characterized through Nuclear Magnetic Resonance and Gel Permeation Chromatography. The tri-block copolymer was then mixed with high molecular weight PLLA to form a flat film. The surface properties measured by X-ray Photoelectron Spectroscopy and Atomic Force Microscopy demonstrated high content of the PLL on the surface of PLLA film, which indicated self-segregation of MPEG-b-PLLA-b-PLL on PLLA surface. No cytotoxicity was detected in triblock copolymers, and compared to pure PLLA and diblock copolymers, the triblock copolymers were much more effective for cell adhesion and proliferation. It was noted that the hydrophilic chain of PEG and PLL stretched out and formed an outer layer, especially under the aqueous environment, which resulted in enhanced cell attachment and proliferation. The self-segregation behaviour of MPEG-b-PLLA-b-PLL triblock copolymer shows a potential application in scaffold preparation of tissue engineering.

Interactions between cells and polymers are mediated by proteins, which are either secreted by cells and immobilized on the biomaterial surface, or absorbed from the medium. Poly (lactic acid) (PLA) is widely used in tissue engineering as a scaffold material, however anchorage-dependent cells such as osteoblasts do not attach, grow, and differentiate well on a hydrophobic surface. In this study, a hydrophilic polymer-poly (ethylene glycol) (PEG) was used to develop diblock polymers, Methoxy-terminated poly (ethylene glycol)-Poly (lactic acid) (MPEG-PLA) to investigate cell-biomaterial interactions. Osteoblasts were cultured on different composition of PEG-PLA films in serum free or serum condition. Lactate dehydrogense (LDH) assay was used to assess the cytotoxicity of the copolymers and cell attachment and proliferation on the polymer surfaces; furthermore cell morphology was visualized by Crystal Violet stain.

The results showed that MPEG-PLA films induced early osteoblast attachment in serum free condition and the higher content of PEG in the MPEG-PLA films the more cell attachment was noticed. No significant difference of cell attachment was observed on MPEG-PLA films between serum free and 10% serum culture condition. Crystal Violet stain demonstrated the same trend in the cell-spreading characteristics on the polymer surface.

In conclusion MPEG-PLA copolymer can enhance osteoblast attachment under serum-free condition, which implies a potential application in cell delivery therapy due to the restriction in animal products for human therapeutically goods.

In both physiological and pathological processes, periosteum plays a determinant role in both bone formation and fracture healing. However, no specific reports are available so far focusing on the detailed structural and major cellular differences between the periostea covering different bone surface areas in relation to ageing. The aim of this study is to compare the structural and cellular differences in diaphyseal and epiphyseal periostea in different-aged rats using histological and immunohistochemical methods.

Four female Lewis rats from each group of juvenile (7-week old), mature (7-month old) and aged groups (2-year old) were sacrificed and the right femur of each rat was retrieved, fixed, decalcified and embedded. 5μm thick serial sagittal sections were cut and stained with Hematoxylin and Eosin, Stro-1 (stem cell marker), F4/80 (macrophage marker), TRAP (osteoclast marker) and vWF (endothelial cell marker). 1mm length of middle diaphyseal and epiphyseal periosteum were selected for observation. The thickness, total cell number and positive cell number for each antibody in each periosteal area and different-aged groups were measured and compared. The results were subjected to ANOVA and SNK-q tests.

The results showed that the thickness and cell number in diaphyseal periosteum decreased with age (p< 0.001). In comparison with diaphyseal area, the thickness and cell number in epiphyseal periosteum were much higher (p< 0.001). There were no significant differences between the juvenile and aged groups in the thickness and cell number in cambial layer of epiphyseal periosteum (p> 0.05). However, the juvenile rats had more Stro1+, F4/80+ cells and blood vessels and few TRAP+ cells in different periosteal areas compared with other groups(p< 0.001). The aged rats showed much less Stro1+ cells, but more F4/80+,TRAP+ cells and blood vessels in the cambial layer of epiphyseal periosteum (p< 0.001).

In conclusion, the age-related structure and cell population in diaphyseal and epiphyseal periostea are different, especially in aged rats. The epiphyseal periosteum of aged rats seems more destructive than diaphyseal part and other age groups. Macrophages in the periosteum play a dual important role in osteogenesis and osteoclastogenesis.

Bone Tissue Engineering Program, Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, QLD 4059, Australia.

Osteophytes are the most remarkable and consistently distinct feature of osteoarthritis (OA). Their formation may be related to pluripotential cells in the periosteum responding to stimulus during OA. This study aimed to isolate stem cells from osteophyte tissues, and characterise their phenotype, proliferation and differentiation potential, and immuno-modulatory properties.

Osteophyte derived cells were isolated from five osteophyte tissue samples collected during knee replacement surgery. These cells were characterised by the expression of cell surface antigens, differentiation potential into mesenchymal lineages, growth kinetics and modulation of allo-immune responses.

Multipotential stem cells (MSCs) were identified from all osteophyte samples namely osteophyte derived MSCs (oMSCs). The surface antigen expression of oMSCs was consistent with that of mesenchymal stem cells, such as lacking the haematopoietic and common leukocyte markers (CD34, CD45) while expressing those related to adhesion (CD29, CD166, CD44) and stem cells (CD90, CD105, CD73). The longevity of oMSCs in culture was superior to that of bone marrow derived MSC (bMSCs), and they readily differentiated into tissues of the mesenchymal lineages. oMSCs also demonstrated the ability to suppress allogeneic T-cell proliferation, which was associated with the expression of tryptophan degrading enzyme indoleamine 2,3 dioxygenase (IDO).

Our results showed that osteophyte derived cells had similar properties to mesenchymal stem cells in the expression of antigen phenotype, differential potential and suppression of allo-immune response. Furthermore, when compared to bMSCs, oMSCs maintained a higher proliferative capacity, which may offer an alternative source for therapeutic stem cell based tissue regeneration.

Introduction: Although there are several accepted methods of surgical treatment for single level cervical radiculopathy, the choice depends on the surgeon’s preference. The techniques may vary in perioperative morbidity, short and long term outcome, but no study so far has analysed their cost-effectiveness. To compare the outcome and cost-effectiveness of four techniques commonly used for degenerative cervical disc pathology.

Methods: We conducted a observational cohort study from two spinal units. Between 1999 and 2004, 60 patients underwent surgery for single level anterior cervical disc pathology. Out of this 30 patients underwent their surgery in centre A the other 30 in centre B. Centre A used two ACDF techniques-group 1- plate and tricortical graft, group 2- plate, cage and bone substitute (BCP granules). Centre B used two other techniques- group 3- cage alone with autologous locally harvested graft, group 4- disc arthroplasty. We had 15 patients in each of the above four groups. Operating time, blood loss, duration of stay, donor site morbidity, analgesia requirements, and total cost incurred per patient were recorded. All patients were followed up at 6 weeks, 3 months, 6 months, 1 year and 2 years. The clinical outcome and pain assessment were done using the SF12 and VAS.

Results: The three Fusion groups had a similar radiological outcome. With appropriate statistical analysis, there were no differences in physical and mental domains of the SF12 or pain scores between the groups. The average operative time in the group 1 was 160 minutes, group 2 was 100 minutes, group 3 was 90 minutes and group 4 was 105 minutes. Average blood loss was minimal in all groups. The average hospital stay was of 5, 2.7, 2.5, 2 days for groups 1–4 respectively. The average total cost per patient in the group 1 (surgery+stay+plate) was £2790, group 2 (surgery+stay+plate+cage+BCP) was £2400, group 3 (surgery+stay+cage) was £1900, and group 4(surgery+stay+disc implant) was £2350.

Conclusion: All the techniques gave similarly satisfactory clinical outcomes but using cages alone could be more cost-effective than using iliac crest auto-graft for fusion. The disc arthroplasty was comparable to cage with bone substitute and plate in terms of outcome and may giev the surgeon an alternative choice in patients who are not keen on/ unfit for fusion.

AIM: To compare the outcomes between two different surgical techniques for cervical myelopathy (skip laminectomy vs laminoplasty).

METHODS: Cervical skip laminectomy is a new technique described by Japanese surgeons in 2000. The advantage of this procedure over the other conventional techniques is it addresses multilevel problem in a least traumatic way without need for instrumentation.

We are comparing the above two techniques with 25 patients in each group operated by 3 surgeons. The first group had conventional laminoplasty and the second group underwent the skip laminectomy. The groups were comparable in age, sex, pathology and clinical presentation. Both these group had clinical outcome measurements using SF 12 questionnaires, pre and postoperative clinical assessment with standard tools performed by independent surgeon and a specialist spinal physiotherapist. We also routinely performed pre and postoperative MRI scans to assess the adequacy of decompression.

RESULTS & CONCLUSION: There was no significant difference in the outcome of these patients in terms of the operative technique, hospital stay, clinical and radiological outcome. However skip laminectomy is relatively a easier procedure to perform, while the laminoplasty does need instrumentation.

Introduction: Dislocation remains one of the most common orthopaedic complications of hip replacement. Surgical technique, implant design and patient factors have been suggested as risk factors. The 2005 AOA Joint Registry recorded data on 101, 952 hip procedures between 1999 and 2004. We analyzed risk factors for early revision in this group of patients.

Methods: Ethics approval was obtained then a formal application was made to the Australian Joint Registry to release the required data. All primary hip replacements between 1/09/1999 – 31/12/2004 were studied. Statistical analyses of traditional risk factors including initial diagnosis, sex, age and head size were performed. We also studied the effect of fixation method on revision for dislocation.

Results: A total of 65,992 primary hip replacements across all diagnoses groups recorded were investigated with regard to diagnosis. The only initial diagnoses with significantly increased relative risk (RR) of revision for dislocation compared to osteoarthritis was fractured neck of femur (RR 2.25, p< 0.0001) and rheumatoid arthritis (RR 1.9, p< 0.01).

58,109 primary hip replacements for osteoarthritis were investigated for effect of age group, sex and fixation method. Age group and sex were not significant risk factors in revision for dislocation. Studying fixation method, cementless acetabular components were implanted more frequently (49,027, 84%) than cemented (9,082, 15.6%). In total, there were 428 (0.7%) revisions for dislocation, 369(0.8%) with a cementless acetabulum and 59 (0.6%) with cemented. Relative risk (cementless v cemented acetabulum adjusted for age group, sex and head size) of 1.59 (CI 1.19 to 2.12, p< 0.01). Head sizes of > 30mm, 28mm, 26mm and 22mm had significantly increasing relative risk (p< 0.001).

Discussion: The results from this large database indicate rheumatoid patients and those after fractured neck of femur have increased risk of revision for dislocation compared to osteoarthritis. Many of the traditional groups thought to be at higher risk of dislocation were not associated with an increased risk of revision for dislocation. These included age group, sex, avascular necrosis, developmental dysplasia and failed internal fixation. Cementless acetabuli have a higher rate of revision for dislocation. This has not been previously reported. Further investigation is needed to identify the cause of this finding.

Introduction/Aims: Early results of a prospective randomised control trial suggested improved position of components implanted during primary hip replacement. The aim of this study is to definitively show the benefit of computer aided navigation in hip arthroplasty with regard to acetabular component position, stem position and leg length.

Method: Eighty consecutive patients were prospectively recruited. Patients were quasi-randomised, on an alternating basis, to undergo hip arthroplasty conventionally or with imageless computer navigation. Postoperatively, a CT scan was performed of the pelvis and lower limb. Using a dynamic CT planning software package, the cup and stem position was measured and compared to the position expected by the three operating surgeons in control cases and the position given by the navigation unit in the study group. Change in leg length was measured clinically and compared with the navigation predicted leg length change. Statistical analysis was performed by a statistician.

Results: Thirty nine navigated hips (29 female, 10 male) and forty one control hips (26 female, 15 male) were recruited. In the navigated group, the mean age was 65.7 and mean BMI was 29.1. In the control group, the mean age was 64.7 and the mean BMI was 29.4 in the control group. Uncemented, securfit/trident hips were used in 18 navigated cases and 20 control cases, with all other cases being cemented Exeter stems and contemporary cups. None of these differences were significant using the Mann-Whitney test. The mean operating time was 128 minutes for navigated hips and 84 minutes for controls, the difference significant at p< 0.005 using t-test.

There was no significant correlation between clinical leg length change, measured in the operating theatre and the leg length change predicted by navigation. Accuracy of cup and stem placement was assessed by comparison of the homogeneity of variances, the Levene statistic, in the navigated and control groups. The range of cup inclination, cup version and stem version was significantly narrowed in the navigation group (p< 0.05).

Conclusion: Computer navigation improves the accuracy of component placement in hip arthroplasty with respect to cup version, cup inclination and stem version with either cemented or uncemented hips.

Purpose: To compare two different techniques of inter-body fusion in treatment for single level degenerative spondylolisthesis with symptomatic spinal stenosis.

Methods: Retrospective review of patients with degenerative spondylolisthesis and spinal stenosis treated with decompression and instrumented posterior interbody fusion with and without cages. Between 1996 and 2003 there were 59 patients with single level degenerative spondylolisthesis and spinal stenosis. Of these 32 were treated with complete laminectomy, interbody grafting and pedicle screw fixation. In the second group of 27 patients, the technique was modified by the incorporation of an interbody cage in an attempt to improve the restoration of lordosis. Both groups were comparable in terms of pathology, age, sex, intraoperative technique and were treated by the same surgeon. All patients were followed up at 6, 12, 26 and 52 weeks with radiographs and were assessed for fusion and maintenance of lordosis at a minimum of 1 year.

Results: There was a statistically significant difference between pre and postoperative lordotic angles in both groups. There was no significant difference in clinical outcomes between the two groups, nor was there a statistical difference in postoperative lordotic angles at the end of 1 year between the two groups. We had 2 deep infections in the cage group. There was one implant failure in the no cage group.

Conclusion: We did not find any advantage in using interbody cages in treating single level degenerative spondylolisthesis.

Aim: To compare the outcomes between two different surgical techniques for cervical myelopathy (skip laminectomy vs laminoplasty).

Methods: Cervical skip laminectomy is a new technique described by Japanese surgeons in 2000. The advantage of this procedure over the other conventional techniques is it addresses multilevel problem in a least traumatic way without need for instrumentation.

We are comparing the above two techniques with 25 patients in each group operated by 3 surgeons. The first group had conventional laminoplasty and the second group underwent the skip laminectomy. The groups were comparable in age, sex, pathology and clinical presentation. Both these group had clinical outcome measurements using SF 12 questionnaires, pre and postoperative clinical assessment with standard tools performed by independent surgeon and a specialist spinal physiotherapist. We also routinely performed pre and postoperative MRI scans to assess the adequacy of decompression.

Results and Conclusion: here was no significant difference in the outcome of these patients in terms of the operative technique, hospital stay, clinical and radiological outcome. However skip laminectomy is relatively a easier procedure to perform, while the laminoplasty does need instrumentation.

Introduction Anterior column reconstruction and fusion remains the gold standard of treatment for a number of spinal pathologies. One of the challenges of interbody fusions cages is the footprint of the cage reducing the surface area of endplate available for fusion. Biodegradable polymer implants will over time present a greater area for fusion and may help to reduce problems such as stress shielding, particulate debris and retained foreign body response. Resorbable cages have been have been prepared from a number of different materials, including inorganic composites (eg hydroxyapatite / tricalcium phosphate) and polymers (Poly L-lactide-co-D,L-lactide (PDLLA)). However all of the current options for interbody fusion have reported deficiencies or complications. The synthesis, mechanical properties, and degradation behaviour of two novel biopolymers are presented and the applicability for use as materials in interbody fusion devices is discussed.

Methods Methacrylated adipic anhydride (MAA) and methacrylated sebacic anhydride (MSA) pre-polymers were synthesized by melt condensation. Conversion of the acid to the anhydride was confirmed using 1H nuclear magnetic resonance (NMR) (Bruker, Alexandria, NSW) and FT- Infrared spectroscopy (Nicolet, Waltham MA). These pre-polymers were subsequently co-polymerized with methyl methacrylate (MMA) and 0.25 wt% benzoyl peroxide at 65oC for 16hrs and post-cured at 120oC under vacuum for 2 hrs to form biodegradable networks. The co-polymerization behaviour was monitored by FT-Raman spectroscopy. The compressive mechanical properties of the polymer were determined using an Instron 5567 (Bayswater Vic.). The polymer networks were degraded in phosphate buffered saline (PBS) with various amounts of MAA and MSA.

Results The formation of the pre-polymer was confirmed with the observation of NMR peaks at 5.8 and 6.2 ppm and FT-IR peaks at 1637cm-1. Copolymerization was followed with consecutive FT-IR acquisitions with 100% conversion achieved between 10 and 30 hrs depending on the ratio of MMA to MSA or MAA. Increasing the fraction of methacrylated anhydride slowed the reaction rate.

The compressive strength of the MAA and MSA based copolymers was measured as a function of anhydride concentration. Compressive strength for MMA increased (90±9 to 140±10 Mpa) in an approximately linear manner for MAA concentrations from 10 to 40 wt.% but decreased markedly for MAA concentration of 45% (62±14 Mpa). The compressive strength of MSA decreased exponentially for concentrations ranging from 10 to 45 wt.% (140±18 to 39±1 Mpa).

Discussion The use of poly-L-lactic acid in lumbar interbody cages has been shown to be mechanically feasible with the mechanical strength of the cage material reported to be 93 Mpa (1). The material described here has controlled mechanical properties in the required range as well as a degradation behaviour that lends itself better to spinal applications than current materials

Computer aided joint replacement surgery has become very popular during recent years and is being done in increasing numbers all over the world. The accuracy of the system depends to a major extent, on accurate registration and immobility of the tracker attachment devices to the bone. This study was designed to assess the forces needed to displace the tracker attachment devices in the bone simulators.

Bone simulators were used to maintain the uniformity of the bone structure during the study. The fixation devices tested were 3mm diameter self drilling, self tapping threaded pin, 4mm diameter self tapping cortical threaded pin, 5mm diameter self tapping cancellous threaded pin and a triplanar fixation device ‘ortholock’ used with three 3mm pins. All the devices were tested for pull out, translational and rotational forces in unicortical and bicortical fixation modes. Also tested was the normal bang strength and forces generated by leaning on the devices.

The forces required to produce translation increased with the increasing diameter of the pins. These were 105 N, 185 N, and 225 N for the unicortical fixations and 130N, 200N, 225 N for the bicortical fixations for 3mm, 4mm and 5 mm diameter pins respectively. The forces required to pull out the pins were 1475N, 1650N, 2050N for the unicortical, 1020N, 3044N and 3042N for the bicortical fixated 3mm, 4mm and 5mm diameter pins. The ortholock translational and pull out strength was tested to 900N and 920N respectively and still it did not fail. Rotatory forces required to displace the tracker on pins was to the magnitude of 30N before failure. The ortholock device had rotational forces applied up to 135N and still did not fail. The manual leaning forces and the sudden bang forces generated were of the magnitude of 210 N and 150 N respectively.

The strength of the fixation pins increases with increasing diameter from three to five mm for the translational forces. There is no significant difference in pull out forces of four mm and five mm diameter pins though it is more than the three mm diameter pins. This is because of the failure of material at that stage rather than the fixation device. The rotatory forces required to displace the tracker are very small and much less than that can be produced by the accidental leaning or bang produced by the surgeon or assistants in single pins. Although the ortholock device was tested to 135 N in rotation without failing, one has to be very careful not to put any forces during the operation on the tracker devices to ensure the accuracy of the procedure.

The aim of this randomised, controlled in vivo study in an ovine model was to investigate the effect of cylic pneumatic pressure on fracture healing. We performed a transverse osteotomy of the right radius in 37 sheep. They were randomised to a control group or a treatment group where they received cyclic loading of the osteotomy by the application of a pressure cuff around the muscles of the proximal forelimb. Sheep from both groups were killed at four or six weeks. Radiography, ultrasonography, biomechanical testing and histomorphometry were used to assess the differences between the groups. The area of periosteal callus, peak torsional strength, fracture stiffness, energy absorbed over the first 10° of torsion and histomorphometric analysis all showed that the osteotomies treated with the cyclic pneumatic pressure at four weeks were not significantly different from the control osteotomies at six weeks.

Aims: Surgery for degenerative lumbar spondylolisthesis may entail both decompression and fusion. The knee-chest position facilitates decompression, but fixation in this position risks fusion in kyphosis. This can be avoided by intra-operative re-positioning to the prone position. The aim of our study was to quantify restoration of lordosis achieved by intra-operative repositioning and to assess clinical and radiological outcome.

Patients and method: Thirty-six patients with degenerative lumbar spondylolisthesis and stenosis were treated by posterior decompression and interbody fusion with pedicle screw fixation. The decompression, interbody grafting and screw insertion were performed with the patient in the knee-chest position. The patient was repositioned to the prone position for fusion. Sagittal plane angles were measured pre, intra and post-operatively. Clinical assessment was performed using SF-36 scores and visual analogue scores for back and leg pain.

Results: The median pre-operative sagittal angle between fused spinal segments was 16.0 degrees lordosis. Intra-operatively in the knee-chest position the sagittal angle was median 13.5 degrees and after changing to the prone position increased to median 27.1 degrees. On the initial post-operative lumbar radiographs the sagittal angle was 23.1 and this was maintained at 6 months post-operatively (22.5 degrees). Overall there was a mean increase in lordosis angle after repositioning of 7.1 degrees per operative level (p< 0.01). The SF-36 scores improved for 7 out of 8 domains and the physical score improved from 29% to 40% (p< 0.05). Mean pain scores improved from 7.5 to 3.8 for back pain and from 7.6 to 3.7 for leg pain (p< 0.001).

Conclusion: Lumbar spondylolisthesis was found to be associated with a reduction of normal lumbar lordosis. The knee-chest position exacerbates this loss of lordosis. Intra-operative repositioning restores lordosis to greater than the pre-operative angle and was associated with a good clinical outcome.

Introduction and aims: Surgical decompression for lumbar stenosis entails a risk of iatrogenic instability. Consequently, laminectomy has been largely superseded by the more conservative procedure of fenestration, but the decompression may be compromised. We describe an additional technique of undercutting laminectomy, which conserves stability while maximising decompression, and the results are presented.

Method: Forty-nine patients with lumbar spinal stenosis were treated by fenestration, medial facetectomy and removal with curved osteotomes of the ventral aspect of the lamina superior to the involved facets together with the attached ligamentum flavum. The results were assessed at a mean follow-up period of three years and four months using walking distance and a pain analogue scale as outcome measures, and surgical complications were recorded. The radiological results were assessed in 25 patients by measurement on MRI scan of the spinal canal cross-sectional area pre- and post-operatively.

Results: Ten patients had undercutting laminectomy at one level, 19 at two levels, 14 at three levels and four at four levels. Medical co-morbidity was present in most patients; 11 were ASA 1, 25 ASA2 and 11 ASA 3. Pre-operatively, all patients reported leg pain or numbness and 20 patients reported back pain. All but one had limited walking distance, the mean being 564 metres (range 5m–8000m). Post-operatively the mean pain score was 3.3 and the mean walking distance 762 metres. Forty-one patients said they felt the operation had been worthwhile and six said they did not. Surgical complications occurred in five patients, consisting of dural tear in four patients (repaired with no sequelae) and a wound haematoma requiring drainage in one patient. The mean spinal canal cross-sectional area at the level of maximal stenosis pre-operatively was 28mm² and postoperatively was 75mm², giving a mean increase of 133%. No patients had any evidence of iatrogenic instability as judged by the development of degenerative spondylolisthesis or scoliosis.

Conclusion: The technique described achieves excellent decompression of the stenotic lumbar canal as measured radiologically, while largely preserving the facet joints. In relation to published reports on fenestration and medial facetectomy alone, the clinical results are at least as good.

Introduction and Aims: Reinfusion drains have been used to decrease the need for blood transfusion following total knee replacement. The aim of this study was to evaluate the degree of activation of platelets and leucocytes in both the blood that has been salvaged after total knee arthroplasty and the patients’ blood following reinfusion.

Method: A prospective series of 24 consecutive patients undergoing a primary total knee replacement in a case-control study were investigated. Post-operatively 12 patients received salvaged blood reinfusion and as a control, 12 patients underwent TKA with a standard drain. The reinfusion was initiated four hours after the operation. Blood samples were taken from all patients at three and five and a half to six hours post-operatively. A third sample was acquired in the treatment group from salvaged blood after reinfusion. Platelet, platelet-leucocyte and leucocyte activation markers were studied in both the drainage blood and the patients’ blood following reinfusion.

Results: Comparison between platelet, platelet-leucocyte and leucocyte activation markers in patients’ circulation prior to reinfusion compared to salvaged blood showed that almost all markers were significantly increased in salvaged blood. For example the platelet activation markers P-selectin (p< 0.01), Factor V (p< 0.01), CD40L (p< 0.01) and platelet derived microparticles (p< 0.01) were all significantly increased in the drainage blood. All studied platelet-leukocyte and leucocyte activation particles were also significantly increased. Following re-infusion of autologous salvaged blood there was no statistically measurable effect on activation markers of patients’ circulating platelets and leucocytes, but there was a slight drop in platelet count in the reinfused group compared to the control group. Levels of prothrombin fragment F 1+2 increased in the reinfused group compared to control indicating either activation of coagulation or simply the effect of addition of the high levels present in the salvage blood.

Conclusion: Blood from reinfusion drains showed a significant increase in activation of platelets and leukocytes indicating activation of coagulation. The reinfused blood did not lead to a difference in platelet and leukocyte activation but a decrease in platelets and an increase in fragment F1+2 suggests the possibility of activation of coagulation.

Introduction and Aims: To deliver osteogenic cells into bone defects, the crucial steps are cell attachment and migration in cell-delivery biomaterials. The aim of this study was to examine whether complexes comprised of vitronectin (VN), insulin growth factors (IGFs) and insulin growth factor binding proteins (IGFBPs) could enhance human osteoblasts attachment, especially cell migration in three-dimensional (3-D) culture.

Method: Human osteoblasts derived from alveolar bone chips (passage 4–10) and established human osteoblast cell line SaOS-2 were used. These cells were seeded on scaffolds of type I collagen sponges and poly glycolic acid (PGA) (approx. one millimetre thick, porous structure), which had been coated with VN +/− IGF-I +/− IGFBP-3. Cell attachment and migration were evaluated by cell counting, confocal microscopy, and scanning electron microscopy.

Results: The number of attached human osteoblasts was significantly higher in wells in which pre-bound VN was coated on the polystyrene culture dish or on type I collagen sponges. However, no significant difference of cell attachment was observed when growth factors were bound to these surfaces in the presence of VN. In the two scaffold materials examined, greater cell attachment was found in type I collagen sponges compared to PGA scaffolds. However, coating the scaffolds with complexes comprised of VN + IGF-I or VN + IGFBP-5 + IGF-I enhanced cell attachment on PGA. Moreover, the presence of vitronectin + IGF-I + IGFBP-5 resulted in significantly greater osteoblast migration into deep pore areas as compared to untreated scaffolds or scaffolds treated with different combinations of the VN +/− IGF +/− IGFBP-5.

Conclusion: Complexes of VN + IGFBP-5 + IGF-I enhance the attachment and migration of human osteoblast in three-dimensional culture, which implies that this complex has potential application for use in surface modification of biomaterials for tissue reconstruction.

Introduction and Aims: Decreasing blood loss during total hip replacement (THR) remains a challenge for the orthopaedic surgeon. This study investigated the effects of the antifibrinolytics aprotinin and epsilon aminocaproic acid (EACA) against placebo on blood loss during primary total hip replacement. Their safety and mechanism of action was also investigated.

Method: Forty-five patients undergoing primary unilateral total hip arthroplasty were randomised to receive an infusion of either aprotinin, EACA, or placebo. Intra- and post-operative blood loss was measured, as was the rate of blood transfusion and changes in haemoglobin concentration. Clinical examination and duplex ultrasound was used in all patients to detect thrombotic events. All patients were assessed clinically six weeks post-op to detect adverse events. Platelet function was assessed using P-selectin, Platelet-monocyte aggregates (PMA) and factor V/Va levels. D-dimer activity was recorded as an indicator of fibrinolysis. Non-parametric statistical analysis was employed in the interpretation of results.

Results: There was no difference in demographics or pre-operative platelet function between the groups with the exception of the EACA group which had a lower pre-operative haemoglobin concentration. Intra-operative blood loss was significantly lower in the aprotinin group compared to placebo (p=0.01), similarly there was also a reduction in intra-operative blood loss in the EACA group but this did not reach statistical significance. Post-operative bleeding from closed suction drains was markedly reduced for both aprotinin (60%, p=< 0.01) and EACA (53%, p=< 0.001) compared to placebo. Markedly less haemoglobin was lost in drains in both antifibrinolytic groups, with aprotinin showing a 77% (p=< 0.0001) and EACA a 73% reduction (p=< 0.001) in post-operative haemoglobin loss. Despite this, no difference in the rate of blood transfusion was observed between groups. Total hip arthroplasty surgery led to the activation of platelets as evidenced by P-selectin, PMA and factor V/Va levels. However, platelet function was not affected by either aprotinin or EACA. Both antifibrinolytics showed a similar increase in D-dimer levels indicating a similar efficacy in inhibiting fibrinbolysis. There were no DVTs, PEs or infections recorded in the study, and no increase in adverse events was seen with the use of antifibrinolytics.

Conclusion: Infusion of either aprotinin or EACA reduces blood loss after primary THA. Both agents are equally effective and have a favourable safety profile. The two drugs inhibit fibrinolysis in a similar fashion, and this action appears to be independent of platelets.

Introduction and Aims: Cyclic pneumatic pressure applied to the musculature proximal to a fracture of the distal radius has been shown to produce compressive loading of the fracture. The aim of this randomised controlled in vivo study in an ovine model was to investigate the effect of the pneumatic pressure on fracture healing.

Method: Thirty-seven sheep underwent a transverse osteotomy of the right radius. All sheep were managed in a plaster cast and splint to ensure non-weight bearing during rehabilitation. Nineteen of the sheep were randomised to receive cyclic loading by the application of a pressure cuff around the muscles of the proximal forearm deep to the cast. The other 18 sheep acted as controls. The sheep in the experimental group received 120 cyclic loads over two 10-minute sessions each day starting one week post-osteotomy. Sheep from both groups were sacrificed at either four or six weeks. X-rays, ultrasonography, biomechanical testing and histomorphometry were used to assess differences between the groups.

Results: The area of periosteal callus on lateral and antero-posterior x-ray, the peak torsional strength, the fracture stiffness, the energy absorbed over the first 10 degrees of torsion and histomorphometric analysis all showed that the fractures in the group treated with the cyclic pneumatic pressure achieved the same level of union at four weeks as the control group fractures at six weeks (not significantly different p> 0.05). The density of the woven bone in the periosteal callus of the treated sheep was significantly greater than the controls (p< 0.01). Ultrasonography showed no significant difference (p> 0.05) in the amount of muscle wasting between the treated group and the control group.

Conclusion: This study has shown that the rate of healing is enhanced when cyclic pneumatic pressure is applied to the musculature proximal to a transverse fracture of the distal radius in an adult sheep model. There is potential for this treatment to be used in a human population.

Introduction and Aims: The radiographic appearance of fractures is often used as an evaluative tool when assessing the status of healing fractures. The aim of this study was in the first instance to assess the reliability of orthopaedic surgeons to measure the area of periosteal callus and secondly to compare the area with the biomechanical strength of the fractures.

Method: Thirty-seven sheep underwent a transverse osteotomy of the right radius. All sheep were managed in a plaster cast and splint to ensure non weight-bearing during rehabilitation. Nineteen of the sheep were ran-domised to receive cyclic loading by the application of a pressure cuff around the muscles of the proximal forearm deep to the cast. The other 18 sheep acted as controls. Sheep from both groups were sacrificed at either four or six weeks. Fractures were x-rayed and subjected to biomechanical testing following sacrifice. X-rays were transferred to a Labview program from which the area of callus was measured. Biomechanical testing of the fractures was a torsional test to failure. The peak torque, stiffness and energy absorbed over the first 10 degrees of torsion were measured for each fracture.

Results: The two orthopaedic surgeons who measured the area of callus showed a positive correlation (r = 0.85). When the four-week fractures that were treated with cyclic loading were compared with the four-week control fractures, the periosteal callus measurement along with the peak torque, fracture stiffness and energy absorbed over the first 10 degrees of torsion all showed a significant difference (p < 0.05). In addition, when the six-week fractures that were treated with cyclic loading were compared with the six-week control fractures, the periosteal callus measurement along with the peak torque, fracture stiffness and energy absorbed over the first 10 degrees of torsion were not significantly different (p > 0.05).

Conclusion: The results show that the area of periosteal callus on radiographs can be related to the biomechanical status of a healing fracture. Further research is required to determine if other characteristics of the periosteal callus plus quantification of the callus area is able to accurately predict fracture strength.

Introduction and Aims: Surgery for degenerative lumbar spondylolisthesis may entail both decompression and fusion. The knee-chest position facilitates decompression, but fixation in this position risks fusion in kyphosis. This can be avoided by intra-operative re-positioning to the fully prone position. We aim to quantify restoration of lordosis achieved by this manoeuvre.

Method: Thirty-six patients with degenerative lumbar spondylolisthesis and stenosis were treated by posterior decompression and interbody fusion with pedicle screw fixation (without interbody cages). There were 16 men and 20 women with a mean age of 58.2 years (32–80). The decompression, interbody grafting and screw insertion were performed with the patient in the knee-chest position. The patient was repositioned to the fully prone position for subsequent fusion. The sagittal plane angle was measured on the pre-operative, intra-operative and post-operative x-rays. Short-Form 36 (SF-36) scores and Visual Analogue Scales (VAS) for pain (0 to 10) were determined pre- and post-operatively.

Results: Twenty-eight patients underwent single-level fusion, two patients had two levels, two patients had three levels and four patients had four levels fused. The mean pre-operative sagittal angle between the operated vertebrae was 15.7 degrees lordosis, and the intra-operative angle before re-positioning was 14.9 degrees. The mean immediate post-operative angle was 23.7, and at six-month follow-up the angle was 23.1. Overall there was a mean increase in lordosis angle after repositioning of 8.0 degrees per operative level (p< 0.01). The mean scores of the SF-36 improved in all eight domains and this was significant (p< 0.05) for social functioning (44.4 to 68.9), energy and vitality (36.0 to 49.5), pain (23.8 to 58.3) and general health perception (51.4 to 65.6). Mean VAS pain scores for back pain improved from 7.47 pre-operatively to 3.84 post-operatively (p< 0.001); and for leg pain improved from 7.56 to 3.78 (p< 0.001). No complications attributable to the manoeuvre occurred.

Conclusion: Lumbar spondylolisthesis was found to be associated with reduction of normal lumbar lordosis. The knee-chest position for surgery exacerbates this loss of lordosis. Intra-operative repositioning restores lordosis to greater than the pre-operative angle, which may improve clinical outcome.

Introduction Experimental heterotopic bone formation in the canine urinary bladder has been observed for more than seventy years without revealing the origin of the osteoinductive signals. In 1931, Huggins demonstrated bone formation in a fascial transplant to the urinary bladder. Through an elaborate set of experiments, it was found that proliferating canine transitional epithelial cells from the urinary system act as a source of osteoinduction.

Urist performed a similar series of experiments in guinea pigs as Huggins did in his canine model. After two weeks, mesenchymal cells condensed against the columnar epithelium and membranous bone with haversian systems and marrow began to form juxtapose the basement membrane. At no time was cartilage formation noted, only direct membranous bone formation. They also demonstrated the expression of BMP’s in migrating epithelium and suggested that BMP is the osteoinductive factor in heterotopic bone formation.

Method This study was approved by Institutional Animal Ethics Committee. Six dogs underwent a mid-line laparotomy incision followed by mobilisation of a right sided myoperitioneal vascularised flap based on an inferior epigastric artery pedicle. A sagittal cystotomy is made in the dome of the bladder and the vascularised flap was sutured in place with acryl absorbable, continuous suture. The animals were sacrificed at 6 weeks. The bladder samples were removed and assessed by histology and immunohistochemistry. Sections were incubated with optimal dilution of primary antibody for type I collagen, type III collagen, alkaline phosphatase (ALP), bone morphogenetic protein (BMP)-2 and –4, osteocalcin (OCN), osteopontin (OPN), bone sialoprotein (BSP).

Results The mechanism for bone formation induced by the epithelial-mesenchymal cell interactions is not clear. We were able to demonstrate mature lamellar bone formation 6 weeks after transplanting a portion of the abdominal smooth muscle into the bladder wall. The bone formed immediately adjacent to the proliferating transitional uroepithelium, a prerequisite for bone formation in Huggins’ model. Here we report evidence of cartilage formation and therefore endochondral ossification as well as membranous bone formation. This is very similar histologically to the process of endochondral ossification at the growth plate in the growing skeleton. We propose a mechanism for the expression of BMP by epithelial cells.

Discussion This study demonstrates transitional epithelium induced formation of chondrocytes and osteoblasts in muscle tissue. The sequential expression of bone matrix proteins was related to cell proliferation, differentiation and formation of endochondral and membranous bone. Further information regarding the molecular mechanism of bone formation induced by epithelial-mesenchymal cell interactions will improve understanding of cell differentiation during osteogenesis.

Introduction Over recent years the techniques of femoral and acetabular impaction allografting with fresh frozen morsellised bone have become incressingly popular for revision total hip arthoplasty with osseous defects. In many centres lack of availability or legislation has required surgeons to explore alternatives to fresh frozen bone that may have different structural and biological properties. In this study we compare in vitro the load carrying capacity of irradiated morsellised bone against a control non-irradiated sample.

Methods Fresh frozen heads were divided in halves with one half irradiated at 25 kGy and the control half left non-irradiated. A custom-built pneumatic loading apparatus applied a force of 1200N at a cycle rate of 1Hz for a total of 1500 cylcles. This loading cycle was chosen to simulate the loads normally experienced by the human femur during walking gait. The reduction in height (subsidence) of each test specimen was measured and statistical analysis performed.

Results Results from each treatment group displayed similar patterns of subsidence, with an initial rapid rate of subsidence occurring up to 50 to 100 load cycles, followed by a more gradual, slower rate as the tests progressed. The results for each treatment (mean ± standard deviation) were −3.59 ± 0.91 mm and −2.98 ± 0.812 mm for the irradiated and non-irradiated groups, respectively (P+0.049). The irradiated specimens demonstrated an increased amount of subsidence compared to the non-irradiated specimens.

Conclusions This study has shown that gamma irradiation of morsellised bone allograft material decreases its load-carrying capacity, as expressed by an increase in subsidence due to an applied cyclic load. The ability for morsellised bone allograft material to bear applied loads in vivo is an important biomechanical parameter and one indicator of a successful clinical outcome. The clinical implications of this result are important when considering the most appropriate methods of treating human bone allograft material.

In relation to the conduct of this study, one or more of the authors is in receipt of a research grant from a commercial source.

Introduction This study aims to improve knee arthroplasty prosthetic alignment by determining if an algorithm based on establishing the most prominent points on the medial and lateral malleolion 3D CT scans can be used to establish the true center of the ankle joint.

Methods Axial, coronal and sagittal multi-planar reconstructions were generated on 20 ankles. Two observers independently identified the most prominent medial and lateral malleolar points, in the coronal plane, and the highest talar dome point, in the sagittal plane. Ratios were calculated comparing total intermalleolar distance to distance to medial and lateral malleolus, and the ratio of medial to lateral distance. The distance from the true center of the joint, in the sagittal plane, to the computer calculated center was determined. Statistical analysis using ANOVA, paired t-tests and regression analysis was performed. There were 17 normal ankles, two arthritic ankles, and one previously fractured ankle.

Results In the coronal plane there was a strong correlation between the measurements of each observer. The mean intermalleolar distance was 70.2 mm (95% CI 68.3–72.0). The strongest correlation was seen in the ratio of lateral distance to total distance (r=0.728) which was 0.57 in normal ankles (95% CI 0.55–0.58). The ratio for arthritic ankles was 0.48 (95% CI 0.46–0.50) and for the fractured ankle 0.57 (95% CI 0.15–0.99). These were significantly different at the five percent level (p< 0.02). The normal ankle ratio was substantiated by regression analysis. There was a poor correlation between the individual measurements in the sagittal plane (r=0.218). The mean distances from the calculated line to the true center were not statistically different with the true center always lying posterior to the calculated line (4.2 mm (95% CI 2.5–5.9) and 2.8 mm (95% CI 1.7–3.8) posterior. For the combined data this means that the mean distance that the true center of the ankle joint’s from a line joining the medial and lateral malleoli is 3.2 mm (95% CI 2.3–4.0 mm). The data was reproducible with a small standard deviation in each plane. Assuming a 300 mm tibial length, angular error in tibial alignment generated by a computer navigation system is less than one degree in both planes.

Conclusions The algorithm presented can give accurate measurements of normal ankle joints in knee navigation surgery.

Introduction: Vertebroplasty using polymethylmethacrylate (PMMA) is an established technique in the treatment of osteoporotic fractures of the vertebra. Complications of vertebroplasty associated with PMMA leakage can include damage to the spinal cord. Previous studies have sought to investigate thermal changes in the paravertebral region, but used smaller volumes of cement than are used clinically¹, or used in vitro experimental techniques.² We have designed an in vivo sheep model to investigate the thermal changes after injection of clinically relevant volumes of PMMA, and to measure change in cord function associated with PMMA extrusion.

Methods: Five sheep were anaesthetised and 1.0ml of PMMA was injected into the spinal canal at the L1 level, with measurement of the temperature by thermocouple. The L2 to L5 vertebral bodies were then exposed and 9 thermocouples placed at points in and around the vertebra (superior and inferior endplate, disc above and below, central body, posterior wall, and spinal canal) to measure paravertebral temperature for a 10- minute period after injecting 6.0mls of PMMA. All animals were then humanely euthanased, and the T12 to L2 vertebrae harvested to examine the effect of temperature on the vertebral body and spinal cord using light microscopy.

Results: The experiments showed significant increases in the paravertebral temperature, especially at the end-plates (mean temperature 51.7°C, mean increase in temperature +16°C). This is contrary to studies using small cement volumes or in vitro conditions. Intradiscal and posterior wall temperature did not significantly rise. Spinal canal temperature reached a mean 75.4°C in the presence of “extruded” cement. Microscopic examination showed thermal damage to the spinal cord.

Discussion: The experiments indicate that neurological complications associated with vertebroplasty are likely to be thermally mediated, and that the analgesic effects of vertebroplasty are likely to be, at least in part, due to thermal damage to endplate neurological structures.

Introduction Unicompartmental knee replacement (UKR) is an increasingly utilised alternative to tibial osteotomy and total knee arthroplasty in patients with single compartment degenerative disease. We report on four fractures of the medial tibial plateau following UKR.

Methods We retrospectively reviewed four cases with periprosthetic tibial plateau fractures following unicompartmental knee replacement. Each arthroplasty, performed between 1999 and 2002, was done in a community teaching hospital by a single orthopaedic surgeon and a senior level assistant. All patients had medial compartment osteoarthritis confirmed both radiographically and arthroscopically prior to arthroplasty surgery. The arthroplasties were performed by four different surgeons and three different arthroplasty systems were used. All cases were reviewed using the documented chart histories and x-ray evaluation. Each surgeon was contacted individually for the relevant case history and x-rays. The study population was composed of four females, and no males with a mean age of 63.5 years (range 58 to 68). Two patients (50%) had simultaneous bilateral UKRs performed. The remaining two patients had unilateral procedures, involving one right and one left knee. Two patients were clinically obese, and one patient had had a previous ipsilateral high tibial osteotomy.

Results The total number of fractures was four, involving three left knees and one right knee. Of the bilateral arthroplasties each patient sustained a unilateral fracture of the left knee. The patient with the previous tibial osteotomy sustained an ipsilateral fracture. Two fractures involved traumatic falls, the remaining fractures had no history of trauma. The mean post-operative period to fracture was 95.75 days with a range of 5 to 195 days. Two patients had revision surgery to total knee arthroplasty. One patient underwent internal fixation of the fracture with retention of the original prosthetic components and exchange of the polyethylene bearing. The remaining patient underwent revision of the tibial component with concurrent internal fixation and was subsequently revised to total knee arthroplasty as the result of failure. Subsequent to the described surgery all fractures have healed with no further surgical intervention.

Conclusions This series, whilst small, demonstrates that tibial periprosthetic fracture following UKR is a previously unreported but important cause of failure. Revision surgery to total knee replacement appears to be a reasonable salvage option.

Introduction Correct component positioning is critical for the stability of the prosthesis in total hip arthroplasty (THA). Malpositioning of either the femoral or acetabular component may lead to impingement or dislocation. This study aims to assess the accuracy of placement of the acetabular component in THA.

Methods Forty-six total hip arthroplasties were studied. The surgeon’s estimates of intra-operative inclination and anteversion of the acetabular component were recorded. Post-operative inclination of the acetabular component was measured from routine plain antero-posterior (AP) radiographs of the pelvis. Planar anteversion of the acetabular component was determined from AP radiographs with the beam centred over the hip using the method described by Pradhan. Planar anteversion was then corrected to ‘true’ anteversion correcting for inclination. The surgeons estimate of intra-operative cup inclination and anteversion and the radiographic position were compared.

Results The mean difference between the estimated and true cup inclination was 1.5° more than planned (range of −13° to 16°, SD 6.75). The mean difference between estimated and true values of anteversion was 1.8° less than planned (range of −32° to 25°, SD 11.07). Allowing plus or minus five degrees of error, 37% of the cups were outside the estimated inclination and 35% outside the estimated anteversion. There was a poor correlation for both inclination (Spearman’s correlation coefficient equals 0.20) and anteversion (Spearman’s correlation coefficient equals 0.25) between perceived and true cup positioning. Using the ‘safe zones’ for inclination and anteversion described by Lewinnek et al for minimising dislocation, 48% of the cups were unsafely positioned in either inclination, anteversion or both.

Conclusions Our study showed that positioning of the ace-tabular component cannot be reliably performed even by experienced surgeons. Acetabular component placement is of high importance for preventing dislocation or impingement. A tool, such as a navigation device, may be beneficial in improving acetabular component placement.

In relation to the conduct of this study, one or more of the authors is in receipt of a research grant from a non-commercial source.

Introduction Component malalignment may result in failure in total knee arthroplasty (TKA). Knee navigation systems assist surgeons with intra-operative component positioning in TKA. We report on the effect of one system on the post-operative mechanical axis of the limb and coronal alignment of femoral and tibial components in TKA.

Methods In a prospective study of 47 total knee replacements we compared 24 cases using conventional techniques to 23 cases using the Stryker Knee Navigation System. Patient groups were matched for sex, weight and age. Postoperative antero-posterior radiographs of the whole leg were used to determine the mechanical axis of the limb and coronal position of the femoral and tibial components.

Results The mean post-operative mechanical axis of the limb in the navigated group was 1.3° varus (range 7° varus to 3.5° valgus, SD=2.6). In the control group the mean mechanical axis was 0.8° varus (range 9.5° varus to 10° valgus, SD=4.4). There was no significant difference in the mean mechanical axis between the groups (p=0.6). There was no significant difference in mean coronal alignment of the femoral (p=0.99) or tibial components, (p=0.98). The 95% confidence interval for the mechanical axis was narrower for the navigated group (2.4° varus to 0.2° varus) than for the control group (2.6° varus to 1.1° valgus). Using Levene’s test (not dependant on normal distribution) the variances for the mechanical axis of the limb, and the coronal alignment of the femoral and tibial components are all significantly less in the navigated than non-navigated groups (p=0.05, 0.001 and 0.004 respectively).

Conclusions This study showed no difference in the overall mean alignment of navigated versus non-navigated knees. However, a significant decrease in the variance of alignment seen with navigation means we are seeing fewer outlying results that may lead to a decrease in mechanical failure in TKA.

In relation to the conduct of this study, one or more of the authors is in receipt of a research grant from a non-commercial source.

Introduction Malposition of the acetabular component in total hip arthroplasty is associated with a number of significant complications. In this study we acertain the accuracy of an imageless computer based surgical navigation system for positioning the acetabular component, using a mechanical hip device.

Methods A mechanical hip device was constructed that allowed accurate measurement of inclination and version, leg length and lateral offset of the acetabular and femoral components. In 31 cases these parameters were varied while a blinded operator would place the cup in the predetermined position in the mechanical hip jig. The values given by the navigation system on the screen were recorded and compared to the measurements obtained directly from the mechanical hip device.

Results The mean difference between value set by an independent person and value read by the navigation system was; inclination of the cup 0.97 ± 0 and the ante-version of the cup 1.58 ± 0.83. The leg length change contributed by the cup showed a mean difference between beforehand set value and read value on the screen of 1.48 ± 1.36 mm and for lateral offset change by the cup of 1.58 ± 0 mm.

Conclusions The accuracy of the hip navigation unit demonstrated in this study is well within the limits that would be required for clinical usage as a surgical aid in total hip arthroplasty and could provide the surgeon with a tool that enables significant improvement in accuracy for acetabular positioning.

Introduction Using a new surgical technique for the first time involves a ‘learning curve’. The aim of this study is to assess the technical errors encountered in the early utilisation of a computer assistance system during total knee arthroplasty and to see if this error rate decreases with experience.

Methods Thirty-two total knee replacement procedures performed by a single surgeon using the Stryker Knee Navigation system for the first time, were monitored. All technical difficulties were documented. We compared the complications encountered in the first five cases against the following 27 cases.

Results Technical difficulties related to the navigation equipment were noted in four of the 32 cases (12.5%). These included (one case each); errors in tibial pin placement, concern over initial navigation readings, pin loosening, and dropping the navigation shim plate. There was a significant decrease in technical difficulties encountered in the later cases (7%) compared to the first five cases (40 percent, p= 0.041). Additionally, in three of the 32 cases (9%) the surgeon used their clinical judgement to override the navigation readings and recut the bone, to take ligament balancing into account.

Conclusions A steep learning curve is involved when first utilising the Stryker Knee Navigation system. It is recommended that adequate training is undertaken prior to utilising knee navigation. The computer readings should be considered carefully and clinical judgement should not be overridden.

In relation to the conduct of this study, one or more of the authors is in receipt of a research grant from a non-commercial source.

Introduction Concentric interference screw placement has been proposed as having potentially better biological graft integration than eccentric interference screw placement during soft tissue ACL reconstruction. The purpose of this study was to determine whether a wedge shaped concentric screw was at least equivalent to an eccentric screw in stiffness, yield load, ultimate load and mode of failure.

Methods Seven matched pairs of human cadaveric tendon in porcine tibia with titanium wedge shaped screws were randomly allocated to either the eccentric or concentric groups. Bone tunnels were drilled 45° to the long axis of the tibia, akin to standard ACL reconstruction. Tendon diameter was matched to tunnel diameter and a screw one millimetre larger than tunnel diameter was inserted. An Instrom machine was used to pull in the line of the tendon. Tendons were inspected after construct disassembly.

Results The concentric screw configuration showed significantly higher stiffness (p< 0.0085), yield load (p< 0.0135) and ultimate load (p< 0.0075). The mode of failure in the eccentric screw position was slippage at the screw tendon interface in all cases. In the concentric group 88% of cases had a breakage in the tendon and 13% of cases had slippage at the tendon bone interface. However, it was observed during construct disassembly that there was more macroscopic damage to the tendon substance in the concentric group. Failure was mostly by tendon breakage, which reflects the strongest fixation possible with the tendon being the weakest link in the system.

Conclusions Concentric interference screw fixation of soft tissue graft offers superior fixation in single pullout mode when compared to eccentric interference screw fixation.

Introduction The reduced WOMAC function scale has been developed and initial validity performed. However, further validation and recommendations for the treatment of missing values is required. The aim of this study is to further assess the validity of the reduced function scale of the WOMAC and recommend a protocol for the treatment of missing values.

Method Further validation of the reduced scale was performed via a cross-over study of 100 pre-operative total joint replacement patients, each being randomised to receive either the full or reduced scale along with the pain scale, and then the alternate version upon admission. Data utilised in the development of the reduced scale was used to develop a missing value protocol, where the number of valid responses for several protocols was examined, as well as comparison of the means and standard deviations. Of the consenting 100 patients, 66 continued onto admission. The median time between administrations of the questionnaires was 14 days (range zero to 72 days).

Results There was no significant difference between pain scores for each questionnaire using the paired t-test (p=0.56). Similarly, there was no significant difference between the full and reduced function scales (p=0.65). The standard protocol for the full scale is that if there are four or more missing items, the patient’s response is invalid. But when there are one to three items missing, the average value for the sub-scale is substituted in lieu of these missing values. Examining the frequencies of valid responses, means and standard deviations when using different missing value protocols (none missing, zero or one, up to two and up to three missing), indicated that there was no substantial benefit between the ‘up to two’ missing and ‘up to three’ missing response protocols. However, for this small gain, the supposition that the completed items are representative of the missing ones rises from 29% (two of seven items) to 43% (three of seven items) should be considered unacceptable.

Conclusions The reduced WOMAC function scale has been further validated. It is proposed that where three or more responses are missing, the patients response is regarded as invalid. Where there are one or two items missing, the average value for the sub-scale is substituted in lieu of these missing values.

We prospectively investigated a consecutive series of ten patients undergoing a cemented primary total hip replacement (THR) for osteoarthritis in order to establish the elution characteristics of Simplex-tobramycin bone cement (Howmedica, Limerick, Ireland). Specimens of blood, urine and drainage fluid were collected for 72 hours postoperatively. Very high concentrations of tobramycin were found in the drainage fluid, with mean levels at one hour of 103 mg/l, which steadily declined to 15.1 mg/l after 48 hours. The mean serum tobramycin levels reached a peak of 0.94 mg/l at three hours and declined rapidly to 0.2 mg/l by 48 hours. The mean urinary tobramycin levels peaked at 57.8 mg/l at 12 hours with a rapid decline to 12.6 mg/l by 24 hours.

There was a direct correlation between the amount of tobramycin bone cement which was implanted and the amount of tobramycin systemically absorbed. Excellent local delivery was achieved with minimal systemic concentrations. Simplex-tobramycin bone cement is an efficient and safe method for the delivery of antibiotics after THR.

Introduction: The aim of this study was to compare the serum cobalt and chromium levels in patients with Oxford Universal hips and Cenator hips. Both systems are composed of cobalt chromium alloy and have modular cobalt chromium heads, however only the Oxford hip has a sliding mechanism.

Material: The serum levels of chromium and cobalt were measured in 20 patients with Oxford Universal Hip replacement (Group 1). This was compared to the serum levels of chromium and cobalt in 17 patients with Cenator Hip replacement (Group 2) and 20 patients with no implants (Group 3). Patients in Group 1 and 2 were assessed clinically and with plain radiographs. Patients were excluded if there was evidence of loosening, if they had other joint implants or any other known cobalt or chromium implant and if they had impaired renal function. All hip replacements were performed as primary procedures. Specimens were analysed by electrothermal atomization atomic absorption spectrometry.

Results: There was no statistically significant difference in serum cobalt and chromium levels between groups 1 and 2. Patients in groups 1 and 2 had statistically significant higher serum levels of chromium and cobalt than group 3 patients.

Discussion: This study demonstrates that serum levels of chromium and cobalt are elevated in patients with stable hip implants composed of this alloy but not in a normal population. Although it is not known what the long-term effects of chronic low-grade exposure to these ions are, these levels are many order of magnitude below the toxic range. Furthermore, our results show that the Oxford Universal Hip releases no more metal ions into the circulation than an implant without a sliding mechanism.

Purpose: The purpose of the study is to compare the disease severity at the time of surgical intervention between patients undergoing primary joint replacement under the National Health Service and Private Health-care Systems.

Materials: 166 patients were included in the study – 101 NHS and 65 Private. Inclusion criteria were: 1) hip or knee osteoarthritis, 2) primary joint replacement, and 3) informed consent of the patient. Patients with arthropathy of inflammatory, infectious or neoplastic aetiology were excluded. Physician evaluation included medical history, calculation of Charleson Comorbidity Scores, and Knee Society rating. Patients were given self-assessment health questionnaires including WOMAC, SF-36, and Nottingham Health Profile.

Results: Mean age was 69.4 years and did not vary significantly between NHS and Private groups. Charleson Comorbidity Scores were significantly worse in the NHS group than in the private. Health assessment questionnaire scores were all adjusted for age, sex, and comorbidity. In NHS patients undergoing TKR, we demonstrate significantly worse pre-operative comorbidity than in private group for indices of function and pain. Patients undergoing THR showed little difference in pre-operative comorbidity.

Conclusion: NHS patients undergoing primary TKR have significantly more advanced disease than their counterparts who are privately insured. Access to TKR surgery is determined by the healthcare delivery system rather then a threshold level of disease severity. Further follow-up of the outcomes of TKR in these two groups needs to be carried out to determine the long-term effects of accessing surgical care at a more advanced stage of disease.

Temporary immobilisation of joints can lead to permanent ankylosis or fusion. The aim of this study is to demonstrate that treatment of vertebral fractures by single level fusion and 2 level fixation preserves movement in the unfused lower motion segment after removal of metalwork.

12 consecutive thoracolumbar fractures were treated by posterior fixation over two motion segments with fusion of the upper injured segment. Average age 39 years (27–50yrs.) and 6 were male. L2 was most frequently affected (6) then T12 (3), L1(2) and L3(1). Using the Denis classification 9 were Burst type B, 1 was Burst type A and 2 were Compression type B. No patients had abnormal neurology or any other vertebral injury. All operations were performed by one surgeon (RC) within 7 days of injury. Metalwork bridging the injured vertebra was removed at mean 11 months (8–13 * one patient 27 months) and average follow up in this study was 12 months (2–40) after removal of metalwork. A simple pain questionnaire and flexion-extension radiographs were obtained. The average movement in the motion segment previously bridged by metalwork was 5 degrees (0–12). For comparison, the level below moved an average of 7 degrees (2–17). Kyphus angle was 11 degrees (1–18) on presentation corrected to 0 degrees at operation (−6 - +12) returning 1 year after removal of metalwork to 5 degrees (1–16). Pain scores (0–10) were measured retrospectively, prior to the accident mean 0(0–1) and at review 2.6 (0–6).

Only one patient failed to return to previous employment. She had the highest pain score at 6, showed no movement at the bridged motion segment where removal of metalwork was delayed to 27 months.

Introduction: Octacol F15 is a fibrin sealant, derived from human cryoprecipitate, which can be delivered as a spray that seals on contact. Pre-clinical studies have established its safety. The aim of this study was to determine the impact of Octacol F15 on blood loss in patients undergoing THR

Materials and Methods: The effect of Octacol F15 on 81 patients undergoing THR was studied in a randomised, prospective, multi-centres study. 38 patients received Octacol F15 delivered to the soft tissues around the hip at 3 predetermined times throughout the operation. 43 patients received a routine THR. Surgeons were constrained to use their predetermined approach, fixation method, and DVT prophylaxis. Blood loss was measured and transfusion needs recorded along with all adverse events.

Results: Mean blood loss in treatment patients was 699ml v 837ml in controls. Log transformed means adjusted for weight, surgeon and pre-operative haemoglobin showed a significant reduction in blood loss of 197ml or 23.5% (95% CI 5.4% to 38.1%) as an effect of treatment (p=0.014). Intra-operative blood loss was not significantly less in the treatment group (p=0.13) but post-operative blood loss was significantly reduced (p=0.0005). 11 treatment patients received blood transfusions (29%) against 18 controls (42%). This difference in transfusion needs was not significant (p=0.11). There was only one minor complication ‘possibly’ related to the use of Octacol F15.

Conclusion: Octacol F15 significantly reduces blood loss in THR without any increase in the complication rate. Its use in THR, particularly in procedures in which increased bleeding may be encountered, offers important clinical benefits.

We determined the outcome of 56 ‘Oxford’ unicompartmental replacements performed for anteromedial osteoarthritis of the knee between 1982 and 1987. Of these, 24 were in patients who had died without revision, one was lost to follow-up and two had been revised. Of the remaining 29 knees, 26 were examined clinically and radiologically, two were only examined clinically and one patient was contacted by telephone. The mean age of the patients was 80.3 years.

At a mean follow-up of 11.4 years (10 to 14) the measurements of the knee score, range of movement and degree of deformity were not significantly different from those made one to two years after operation, except that the range of flexion had improved. Comparison of fluoroscopically-controlled radiographs at a similar interval of time showed no change in the appearance of the lateral compartments. The retained articular cartilage continued to function for ten or more years which suggests that anteromedial osteoarthritis may be considered as a focal disorder of the knee. This justifies continued efforts to develop methods of treatment which preserve intact joint structures.

We reviewed histologically the incidence and pathogenesis of the deposition of calcium pyrophosphate dihydrate (CPPD) crystals in the pseudocapsule, femoral and acetabular membranes and periprosthetic tissue at revision of 789 cases of failed total hip replacement. In 13, periprosthetic tissues were found to have deposits of CPPD crystals in areas of cartilaginous metaplasia; four also showed evidence of localised deposition of amyloid. None of the patients had a history of chondrocalcinosis in the hip or other joints. Cartilaginous metaplasia and other changes in periprosthetic tissues may predispose to the deposition of CPPD and associated localised amyloid.

We present a case in which the growth of an intraosseous cyst arising from the proximal tibiofibular joint appeared to have been increased by polyethylene wear particles from a medial unicompartmental knee replacement. Histological examination of the cyst wall showed a histiocytic response associated with numerous polyethylene wear particles. This case demonstrates that there is a direct communication between the joint cavity and the cyst. Such communication is probably through openings in the articular cartilage large enough to allow the passage of these particles.