The primary aim of this study was to compare the clinical outcomes of osteoid osteoma (OO) between the group of patients with the presence of nidus on biopsy samples from radiofrequency ablation (RFA) with those without nidus. Secondly, we aimed to examine other factors that may affect the outcomes of OO reflecting our experience as a tertiary orthopaedic oncology centre.

We retrospectively reviewed 88 consecutive patients diagnosed with OO treated with RFA between November 2005 and March 2015, consisting of 63 males (72%) and 25 females (28%). Sixty-six patients (75%) had nidus present in their biopsy samples. Patients’ mean age was 17.6 years (4-53). Median duration of follow-up was 12.5 months (6-20.8). Lesions were located in the appendicular skeleton in seventy-nine patients (90%) while nine patients (10%) had an OO in the axial skeleton. Outcomes assessed were based on patients’ pain alleviation (partial, complete, or no pain improvement) and the need for further interventions.

Pain improvement in the patient group with nidus in histology sample was significantly better than the group without nidus (OR 7.4, CI 1.35-41.4, p=0.021). The patient group with nidus on biopsy demonstrated less likelihood of having a repeat procedure compared to the group without nidus (OR 0.092, CI 0.016-0.542, p=0.008). Our study showed significantly better outcomes in pain improvement in appendicular lesions compared to the axially located lesions (p = 0.005). Patients with spinal lesions tend to have relatively poor pain relief than those with appendicular or pelvic lesions (p=0.007).

Patients with nidus on histology had better pain alleviation compared to patients without nidus. The histological presence of nidus significantly reduces the chance of repeat interventions. The pain alleviation of OO following RFA is better in patients with appendicular lesions than spinal or axially located lesions.

Aims

Current literature suggests that survival outcomes and local recurrence rates of primary soft-tissue sarcoma diagnosed in the very elderly age range, (over 90 years), are comparable with those in patients diagnosed under the age of 75 years. Our aim is to quantify these outcomes with a view to rationalizing management and follow-up for very elderly patients.

Aims

Proximal femoral endoprosthetic replacements (PFEPRs) are the most common reconstruction option for osseous defects following primary and metastatic tumour resection. This study aimed to compare the rate of implant failure between PFEPRs with monopolar and bipolar hemiarthroplasties and acetabular arthroplasties, and determine the optimum articulation for revision PFEPRs.

Aims

While a centralized system for the care of patients with a sarcoma has been advocated for decades, regional variations in survival remain unclear. The aim of this study was to investigate regional variations in survival and the impact of national policies in patients with a soft-tissue sarcoma (STS) in the UK.

Aims

Chondrosarcoma is the second most common primary sarcoma of bone: conventional chondrosarcoma accounts for 85% of all cases. Conventional chondrosarcoma may be central or peripheral. Most studies group central and peripheral chondrosarcomas together, although there is growing evidence that their clinical behaviour and prognosis differ. The aims of this study were to analyze any differences in characteristics between central and peripheral chondrosarcomas and to investigate the incidence and role of different syndromes.

Aims

Urgent referral to a specialist centre for patients with a soft-tissue sarcoma (STS) has been recommended by the National Institute for Health and Care Excellence (NICE) in the UK since 2006. However, the impact of this recommendation on the prognosis for these patients remains unclear. We aimed to determine the impact of the NICE guidelines on the disease-specific survival (DSS) of patients with an STS.

Aims

Although chondrosarcomas (CSs) display true malignant features, including local recurrence (LR) and metastases, their behaviour in the hands and feet is thought to differ from that in other parts of the axial and appendicular skeleton by having a lower metastatic potential. The purpose of this study was to investigate the disease-specific and surgical factors that affect the local and systemic prognosis of CS of the hands and feet.

Aims

Malignancy and surgery are risk factors for venous thromboembolism (VTE). We undertook a systematic review of the literature concerning the prophylactic management of VTE in orthopaedic oncology patients.

Aims

The existing clinical guidelines do not describe a clear indication for adjuvant radiotherapy (RT) in the treatment of superficial soft tissue sarcomas (STSs). We aimed to determine the efficacy of adjuvant RT for superficial STSs.

Aims

The aim of this study was to report the results of custom-made endoprostheses with extracortical plates plus or minus a short, intramedullary stem aimed at preserving the physis after resection of bone sarcomas in children.

Objectives

Investigate the incorporation of an antibiotic in bone cement using liposomes (a drug delivery system) with the potential to promote osseointegration at the bone cement interface whilst maintaining antibiotic elution, anti-microbiological efficacy and cement mechanical properties.

Prosthetic joint infection and aseptic loosening are associated with significant morbidity. Antibiotic loaded bone cement is commonly used and successfully reduces infection rates; however, there is increasing resistance to the commonly used gentamicin.

Previous studies have shown gentamicin incorporated into bone cement using liposomes can maintain the cement's mechanical properties and improve antibiotic elution.

The phospholipid phosphatidyl-l-serine has been postulated to encourage surface osteoblast attachment and in a liposome could improve osseointegration, thereby reducing aseptic loosening.

Preliminary clinical isolate testing showed excellent antimicrobial action with amoxicillin therefore the study aims were to test amoxicillin incorporated into bone cement using liposomes containing phosphatidyl-l-serine in terms of antibiotic elution, microbiological profile and mechanical properties.

Aims

Preserving growth following limb-salvage surgery of the upper limb in children remains a challenge. Vascularized autografts may provide rapid biological incorporation with the potential for growth and longevity. In this study, we aimed to describe the outcomes following proximal humeral reconstruction with a vascularized fibular epiphyseal transfer in children with a primary sarcoma of bone. We also aimed to quantify the hypertrophy of the graft and the annual growth, and to determine the functional outcomes of the neoglenofibular joint.

Aims

Following the resection of an extensive amount of bone in the treatment of a tumour, the residual segment may be insufficient to accept a standard length intramedullary cemented stem. Short-stemmed endoprostheses conceivably have an increased risk of aseptic loosening. Extra-cortical plates have been added to minimise this risk by supplementing fixation. The aim of this study was to investigate the survivorship of short-stemmed endoprostheses and extra-cortical plates.

Background

Devices are frequently used to gain sufficient purchase in a bone so that the bone itself can be manipulated to move or rupture soft tissue attachments. During hip surgery, several different extraction corkscrews are available to remove the femoral head, each with a different screw design with no evidence to suggest which is most effective. Additionally during the use of corkscrew devices, often due to the low bone density, stripping of the screw threads out of the femoral head can occur prior to its extraction, thus requiring reinsertion. The aims of this project were to measure the primary pullout and reinsertional forces of five commercially available corkscrews.

Aim

Compare clinical outcomes following staged revision arthroplasty for periprosthetic joint infection (PJI) secondary to either multidrug resistant (MDR) bacteria or non-MDR (NMDR) bacteria.

25–40% of unicompartmental knee replacement (UKR) revisions are performed for unexplained pain possibly secondary to elevated proximal tibial bone strain. This study investigates the effect of tibial component metal backing and polyethylene thickness on cancellous bone strain in a finite element model (FEM) of a cemented fixed bearing medial UKR, validated using previously published acoustic emission data (AE).

FEMs of composite tibiae implanted with an all-polyethylene tibial component (AP) and a metal backed one (MB) were created. Polyethylene of thickness 6–10mm in 2mm increments was loaded to a medial load of 2500N. The volume of cancellous bone exposed to <−3000 (pathological overloading) and <−7000 (failure limit) minimum principal (compressive) microstrain (µ∊) and >3000 and >7000 maximum principal (tensile) microstrain was measured.

Linear regression analysis showed good correlation between measured AE hits and volume of cancellous bone elements with compressive strain <−3000µ∊: correlation coefficients (R= 0.947, R2 = 0.847), standard error of the estimate (12.6 AE hits) and percentage error (12.5%) (p<0.001). AP implants displayed greater cancellous bone strains than MB implants for all strain variables at all loads. Patterns of strain differed between implants: MB concentrations at the lateral edge; AP concentrations at the keel, peg and at the region of load application. AP implants had 2.2 (10mm) to 3.2 (6mm) times the volume of cancellous bone compressively strained <−7000µ∊ than the MB implants. Altering MB polyethylene insert thickness had no effect. We advocate using caution with all-polyethylene UKR implants especially in large or active patients where loads are higher.

Introduction

Bone tumours of the foot are rare, representing 3–6% of all bone tumours. Of these 15–25% are thought to be malignant. Obtaining clear surgical margins remains an important factor in improving outcome from tumours. However, the anatomical complexity of the foot can lead to an inadequate resection, particularly if the operating surgeon is attempting to preserve function. The aim of this paper is to identify the clinical course of patients suffering from malignant bone tumours of the foot.

The management of spinal deformity in children with univentricular cardiac pathology poses significant challenges to the surgical and anaesthetic teams. To date, only posterior instrumented fusion techniques have been used in these children and these are associated with a high rate of complications. We reviewed our experience of both growing rod instrumentation and posterior instrumented fusion in children with a univentricular circulation.

Six children underwent spinal corrective surgery, two with cavopulmonary shunts and four following completion of a Fontan procedure. Three underwent growing rod instrumentation, two had a posterior fusion and one had spinal growth arrest. There were no complications following surgery, and the children undergoing growing rod instrumentation were successfully lengthened. We noted a trend for greater blood loss and haemodynamic instability in those whose surgery was undertaken following completion of a Fontan procedure. At a median follow-up of 87.6 months (interquartile range (IQR) 62.9 to 96.5) the median correction of deformity was 24.2% (64.5° (IQR 46° to 80°) vs 50.5° (IQR 36° to 63°)).

We believe that early surgical intervention with growing rod instrumentation systems allows staged correction of the spinal deformity and reduces the haemodynamic insult to these physiologically compromised children. Due to the haemodynamic changes that occur with the completed Fontan circulation, the initial scoliosis surgery should ideally be undertaken when in the cavopulmonary shunt stage.

Cite this article: Bone Joint J 2014;96-B:94–9.

Joint registries report that 25–40% of UKR revisions are performed for pain. Proximal tibial strain and microdamage are possible causes of this “unexplained” pain. The aim of this study was to examine the effect of UKR implant design and material on proximal tibial cortical strain and cancellous microdamage.

Composite Sawbone tibias were implanted with cemented UKR components: 5 fixed bearing all-polyethylene (FB-AP), 5 fixed bearing metal backed (FB-MB), and 5 mobile bearing metal backed implants (MB-MB). Five intact tibias were used as controls. Tibias were loaded in 500N increments to 2500N. Cortical surface strain was measured using digital image correlation (DIC). Cancellous microdamage was measured using acoustic emission (AE), a technique which detects elastic waves produced by the rapid release of energy during microdamage events.

DIC showed significant differences in anteromedial cortical strain between implants at 1500N and 2500N in the proximal 10mm only (p<0.001) with strain shielding in metal backed implants. AE showed significant differences in cancellous microdamage (AE hits), between implants at all loads (p=0.001). FB-AP implants displayed significantly more hits at all loads than both controls and metal backed implants (p<0.001). FB-AP implants also differed significantly by displaying AE hits on unloading (p=0.01), reflecting a lack of implant stiffness. Compared to controls, the FB-AP implant displayed 15x the total AE hits, the FB-MB 6x and the MB-MB 2.7x. All-polyethylene medial UKR implants are associated with greater cancellous bone microdamage than metal backed implants even at low loads.

Introduction

We present our experience of the coned hemi-pelvis (‘ice-cream’ cone) implant, using an extended posterior approach to the hip joint, in the management of pelvic bone loss and pelvic discontinuity.

Aim/Purpose

Review our unique experience in the management of 29 consecutive casualties who survived open pelvic fractures following a blast mechanism.

The aim of this study is to review our unique experience in the management of 29 consecutive casualties who survived open pelvic fractures following a blast mechanism, in order to determine the injury pattern, clinical management and outcome of these devastating injuries.

All patients were serving soldiers who were injured whilst on operations in Afghanistan. The median New Injury Severity Score (NISS) was 41. Mean blood requirement in the 1^st 24 hours was 60.3 units. In addition to their orthopaedic injury, 6 (21%) had an associated vascular injury, 7(24%) had a bowel injury, 11 (38%) had a genital injury and 7(24%) had a bladder injury. 8 (28%) fractures were managed definitively with external fixation, and 7 (24%) fractures required ORIF. Of those patients who underwent ORIF, 4 (57%) required removal of metalwork for infection. Faecal diversion was performed on 9 (31%) casualties. Median length of stay was 70.2 days, and mean total operative time was 29.6 hours. At a mean 20.3 months follow-up, 24 (83%) were able to ambulate, and 26 (90%) had clinical and radiological evidence of pelvic ring stability.

The “Global War on Terror” has resulted in incidents that were previously confined exclusively to conflict areas can now occur anywhere, and surgeons who are involved in trauma care may be required to manage similar injuries from terrorist attacks. Our study clearly demonstrates that the management of this injury pattern is extremely resource intensive with the need for significant multi-disciplinary input. Given the nature of the soft tissue injury, we would advocate an approach of minimal internal fixation in the management of these fractures. With the advent of emerging wound and faecal management techniques, we do not believe that faecal diversion is mandated in all cases.

This study was undertaken to assess for equivalence or superiority in tendon reconstruction techniques. This is an in vitro analysis of several, different, reconstruction techniques for chronic Achilles tendon ruptures. The surgical techniques have been borne out of surgical preference rather than biomechanical principles with little published research into their comparability. Surgical preferences are a result of the supposed benefits of reduced operative time, single operative incision and decreased morbidity. An animal model, after human cadaveric tissue dissection to guide the specimen construction, was used to compare the different techniques using bovine bone and tendon and tested using a material testing machine. Ultimate load to failure was recorded for all specimens and statistical analysis of the results was undertaken.

A statistically significant difference was shown between all the techniques by analysis of variance. This will guide clinical application of these techniques. The use of bone tunnels, through which the flexor hallucis longus tendon can be passed, were found to be biomechanically superior, with regard to ultimate load to failure, to either bone anchors or end-to-end tendon suture techniques. Interference screws were found to have a large range in their ultimate load suggesting a lack of consistency in the results. The mean of the bone tunnel group (482.8N, SD 83.6N) is significantly (p < 0.01) higher than the mean of the bone anchor group (180.2N, SD 19.3N), which is, in turn, significantly (p < 0.01) higher than the mean of the Bunnell group (73.7N, SD 20.9N). This study is larger than any previous study found in the literature with regard to number of study groups and allows the techniques to be compared side by side.

Background

Patients with fractured neck of femur have historically received less attention than they deserve and have high morbidity and mortality. Literature suggests that speed to theatre reduces length of in-patient stay and complications.

The fixation of comminuted femoral fractures with intramedullary nails is commonplace but there remains little work on the mechanical ability of the different diameters of nail available to resist bending. What previous work there is has produced conflicting conclusions. The bending stiffness against the intramedullary nail diameter and the extent of the comminuted fracture is clinically important due to the impact on fracture healing and implant failure.

Intramedullary nails of differing diameters (10 mm, 11 mm and 13 mm) were loaded axially in fourth generation composite femurs with increasing mid shaft bone defects, namely 3cm, 5cm, 8cm and 10cm bones. The loading versus the displacement was recorded for each nail.

A one-way ANOVA analysis demonstrated a significant difference between intramedullary nail diameters and the bending stiffness, with p values of less than 0.012; 3cm mean 12.26 (CI 9.06-15.46) mm, p=0.012; 5 cm mean 10.63 (CI 8.35-12.92) mm, p=<0.001; 8 cm mean 11.04 (CI 8.35-13.74) mm, p=<0.001; 10 cm mean 11.68 (CI 7.86-15.50) mm, p=<0.001. For the 11 mm diameter intramedullary nail, failure occurred at around two times the body weight of an average individual or 1400 to 1800 N. A repeated measure ANOVA analysis of the effect of the increasing bone defect showed a mixed picture, with a significant difference between the 5 cm and 8 cm gap and only a trend towards significance between 5 cm and 10 cm.

Caution should be advised when considering using a cannulated femoral intramedullary nail in a patient with a fracture gap of greater than 5 cm. Further, the mechanical effect of comminuted fractures treated with nails suggests reduced stiffness with increasing length of fracture gap although the picture is complex and explains the divergence of research conclusions.

One reason why NICE (National Institute for Clinical Excellence) does not support operations by the NHS to heal hyaline cartilage lesions using a patients own cells is because there is no clear evidence to show that these operations are beneficial and cost-effective in the long term. Specifically, NICE identified a deficiency of high quality cartilage being produced in repaired joints. The presence of high quality cartilage is linked to long-lasting and functional repair of cartilage. The benchmark for quality, NICE stipulate, is repair cartilage that is stiff and strong and looks similar to the normal tissue surrounding it, i.e. mature hyaline articular cartilage.

Biopsy material from autologous cartilage implantation surgical procedures has the appearance of immature articular cartilage and is frequently a mixture of hyaline and fibrocartilage. Osteoarthritic cartilage, in its early stages, also exhibits characteristics of immature articular cartilage in that it expresses proteins found in embryonic and foetal developmental stages, and is highly cellular as evidenced through the presence of chondrocyte clusters. Therefore, an ability to modulate the phenotype and the structure of the extracellular matrix of articular cartilage could positively affect the course of repair and regeneration of articular cartilage lesions. In order to do this, the biochemical stimuli that induce the transition of an essentially unstructured amorphous cartilage mass (immature articular cartilage) to one that is highly structured and ordered, and biomechanically adapted to its particular function (mature articular cartilage) has to be identified.

We show for the first time, that fibroblast growth factor-2 and transforming growth factor beta-1 induce precocious maturation of immature articular cartilage. Our data demonstrates that it is possible to significantly enhance maturation of cartilage tissue using growth factor stimulation; consequently this may have applications in transplantation therapy, or through phenotypic modulation of osteoarthritic chondrocytes in diseased cartilage in order to stimulate growth and maturation of repair tissue.

The open blast fracture of the pelvis is considered to be the most severe injury within the spectrum of battlefield trauma. We report our experience of 29 consecutive patients who had sustained this injury in Afghanistan between 2008 and 2010. Their median new injury severity score (NISS) was 41 (8 to 75), and mean blood requirement in the first 24 hours was 60.3 units (0 to 224). In addition to their orthopaedic injury, six had an associated vascular injury, seven had a bowel injury, 11 had a genital injury and seven had a bladder injury. In all, eight fractures were managed definitively with external fixation and seven required internal fixation. Of those patients who underwent internal fixation, four required removal of metalwork for infection. Faecal diversion was performed in nine cases. The median length of hospital stay following emergency repatriation to the United Kingdom was 70.5 days (5 to 357) and the mean total operating time was 29.6 hours (5 to 187). At a mean follow-up of 20.3 months (13.2 to 29.9), 24 patients (82.8%) were able to walk and 26 (89.7%) had clinical and radiological evidence of stability of the pelvic ring.

As a result of the increase in terrorism, injuries that were previously confined exclusively to warfare can now occur anywhere, with civilian surgeons who are involved in trauma care potentially required to manage similar injuries. Our study demonstrates that the management of this injury pattern demands huge resources and significant multidisciplinary input. Given the nature of the soft-tissue injury, we would advocate external fixation as the preferred management of these fractures. With the advent of emerging wound and faecal management techniques, we do not believe that faecal diversion is necessary in all cases.

Patient specific knee modelling has the potential to help understand the development of the mechanically induced degenerative disease, Osteoarthritis. A full joint contact model of the knee involves modelling the bones, ligaments, articular cartilage (AC) and meniscus, as well as, the kinematics and geometry of real joints. These finite element models will inevitably require great computational resource to run and it is desirable to find resource effective material model formulations which can accurately describe the mechanical behaviour of the soft tissues. Biphasic models (BIMs) have long been established as an effective formulation for modelling AC. However, the swelling behaviour caused by changes in the ionic phase is a major recovery mechanism and is neglected in the BIMs. It is therefore believed that BIMs alone are insufficient to fully describe the mechanical behaviour of AC. Instead, a thermal analogy method which is generically a BIM that includes the swelling behaviour has been thought to be suitable and has been validated against literature data using material parameters optimized to match the numerical and experimental results. To ensure the model is suitable for patient specific modelling where it will have the ability to reflect the individual AC material properties of the patients in the mechanical behaviour it predicts, two experiments have been planned and are currently being carried out using bovine AC. The first experiment is to investigate the diffusivity of the tissue in solutions of different molarity by measuring the change in tissue weight over time. Eleven explants are taken from the same bovine articular joint using a 6mm biopsy punch and are left in 10mM of PBS overnight to ensure ionic equilibrium has been reached before experiments are carried out. The explants are then placed in PBS solutions of molarities ranging from 0mM to 10mM and weighed at regular time intervals. In the final stage, the explants are then lyophilized and weighed for determining the volume of water in the tissues. Using Archimedes principle, the change in porosity of the tissue is found. A preliminary study has shown that explants submerged in a solution of 5mM has an approximately 4% change in weight after the first 24h and a further 1.73% change in the following 24h. Control specimens left in a solution of 10mM had a 0% change in weight. The second experiment is to carry out mechanical loading on the AC specimens while submerged in a solution of different ion concentrations. Experiments with various loading conditions are being investigated to explore their efficacy for validation. Preliminary compression tests have been carried out where steps of 1% strain was applied, giving a total of 10% strain. Between each step, strain was held constant until full relaxation has been achieved. The reaction force measured from the second experiment in conjunction with data collected from the first experiment will be compared to results predicted in the numerical model. This will allow the determination of whether thermal analogy is adequate or whether more complex triphasic models need to be considered. Furthermore, the development of these experimental methods will contribute to the validation of other AC material models in the future.

Introduction

Iatrogenic proximal femur hoop-stress fracture is a recognised complication of uncemented hip arthroplasty. It has a reported incidence of two to three percent and increases patient morbidity. We describe a novel technology that predicts fracture in real-time by less than one minute.

Excessive implant migration and micromotion have been related to eventual implant loosening. The aim of this project is to develop a computational tool that will be able to predict the mechanical performance of a cementless implant in the presence of uncertainty, for example through variations in implant alignment or bone quality. To achieve this aim, a computational model has to be developed and implemented. However, to gain confidence in the model, it should be verified experimentally. To this end, the present work investigated the behavior of a cementless implant experimentally, and compared the results with a computational model of the same test setup.

A synthetic bone (item 3406, Sawbones Europe AB, Sweden) was surgically implanted with a Furlong cementless stem (JRI, Sheffield, UK) in a neutral position and subjected to a compression fatigue test of −200 N to −1.6 kN at a frequency of 0.5 Hz for 50000 cycles. Measurements of the micromotion and migration were carried out using two linear variable differential transducers and the strain on the cortex of the femur was measured by a digital image correlation system (Limess Messtechnik & Software Gmbh).

A three-dimensional model was generated from computed tomography scans of the implanted Sawbone and converted to a finite element (FE) model using Simple-ware software (Simpleware Ltd, Exeter, UK). Face-to-face elements were used to generate a contact pair between the Sawbone and the implant. A contact stiffness of 6000 N/m and a friction coefficient of 0.3 were assigned. The analysis simulated a load of −1.6 kN applied to the head of the implant shortly post implantation. The motions and strains recorded in the experiment were compared with the predictions from the computational model. The micromotion (the vertical movement of the implant during a single load cycle), was measured at the proximal shoulder, at the distal tip of the implant and at the bone-implant interface. The maximum value calculated proximally using FE was 61.3 μm compared to the experimental value of 59.6 μm. At the distal end, the maximum micromotion from FE was 168.9 μm compared to 170 μm experimentally. As a point of reference, some authors have suggested that in vivo, fibrous tissue formation may take place at the bone-implant interface when the micromotion is above 150 μm. The maximum micromotion found computationally at this interface was 99 μm which is below the threshold value defined. The longitudinal strain over the surface of the bone was variable and reached values of up to 0.15% computationally and 0.4% experimentally; this may be related to the coordinate systems used. However, it was noted that digital image correlation identified qualitatively similar strain patterns, and has great potential for measuring low level surface strains on bone.

In conclusion, the good correlation between the computational modelling and experimental tests provides confidence in the model for further investigations using probabilistic analyses where more complex configurations (for example change in implant alignment) can be analyzed.

Background: Stress shielding in the proximal femur is a widely recognized sequel of total hip replacement. It is due to a discrepancy in the stiffness between the implant and the proximal femur. The strain characteristics of implants of differing materials on the femur have previously been demonstrated in the laboratory using strain gauges and photo-elastic techniques. These are however relatively crude techniques giving limited results. Finite element analysis has also been used, but this provides only a theoretical analysis. Digital Image Correlation is an extremely accurate technique for strain analysis previously used in micro and nano engineering research.

Methods: A stainless steel, a titanium, and a carbonfibre reinforced plastic (CFRP) femoral prosthesis of the same dimensions, were implanted without cement into 5 prosthetic femora. A 1kN load was applied using a compression device. The process was repeated with 5 other prosthetic control femora. Digital Image Correlation was used to give an extremely detailed 2D strain map of inner cortex of the proximal femora during laboratory simulated static physiological loading conditions.

Results: All implants caused stress shielding in the proximal calcar area. In Gruen zones 6–4, both the stainless steel and titanium implants caused statistically significant stress shielding, whereas the femora implanted with the CFRP prosthesis did not show a statistically different strain pattern from the control group. There was a reduction in strain experienced by the medial cortex of the femora beyond the tip of all of the implants.

Conclusion: Digital Image Correlation is a novel method for strain measurement within Orthopaedic research which produces extremely accurate strain maps and data that can be reliably used for statistical analysis. Using this technique, this laboratory based investigation indicates that a carbon-fibre reinforced plastic stem is a good candidate to avoid stress shielding in total hip replacement surgery.

Aim: To reduce the amount of blood wastage in our unit.

Method: In 72 patients, the number of blood units cross-matched and the haemoglobin/haematocrit fall were audited for primary total shoulder replacement (n=44), primary hemiarthroplasty (n=21), and revision shoulder replacement (n=7) over twelve months (January 2008 to December 2008). The amount of crossmatched blood was compared to the amount of blood transfused, pre-operative haemoglobin and fall in haemoglobin/haematocrit.

Results: 23 of 44 primary total shoulder replacements and 5 of 21 hemiarthroplasties were crossmatched 55 units preoperatively. 4 of the 7 revision arthroplasties were crossmatched 7 units preoperatively. No units were transfused. 4 patients were later transfused 2 units each for symptomatic low haemoglobin at day 3–5 postoperatively from postoperatively crossmatched blood. No correlation existed between preoperative haemoglobin and number of units blood ordered. A haemoglobin reduction of ~2.5 g/dl was seen for both primary and revision surgery. There was significant correlation between low preoperative haemoglobin and need for transfusion (p< 0.05). Nearly all patients in whom blood was crossmatched rather than group and saved, belonged to one consultant. No patients had an adverse outcome due to a lack of immediately available cross-matched blood.

Conclusion: A large amount of blood was crossmatched and no units used in primary and revision shoulder replacement surgery. We recommend group and save only in primary shoulder arthroplasty and crossmatch of 2 units for revision shoulder surgery. Providing pre-operative haemoglobin is > 11.5 g/dl, group and save is safe even for revision shoulder arthroplasty. Wastage of blood could be reduced to zero in our unit. We recommend regular audit as a tool to ensure compliance with guidelines, and for clinical governance purposes ensuring guidelines remain best practice.

Introduction: Unstable inter-trochanteric fractures are increasing in incidence and stable fixation can improve outcome by leading to earlier mobilisation and reduced mortality. The appropriate choice of implant is vital to ensure a satisfactory outcome.

Objectives: The objective of this study was to determine the load at which different intramedullary device constructs failed.

Materials and Methods: Nine identical 3rd generation composite Sawbones were used and prepared with reverse obliquity cuts made to the femoral necks. Three different types of trochanteric entry intramedullary nail were then inserted using manufacturer’s guidelines. The nine constructs were loaded to failure using a Dartec 9500 servo hydraulic testing machine.

Results: The average failure loads were 3954±952N for the DePuy nail, 2420±281N for the Synthes nail and 3810±377N for the Stryker nail. In eight of the nine constructs the Sawbone failed at the medial side of the fracture. One of the DePuy nails failed at 5041N in the area of the distal locking screws.

The Stryker nail constructs were significantly stronger than the Synthes constructs (p=0.008); although the DePuy constructs were similar in strength to the Stryker constructs (p=0.83) they were not significantly different from the Synthes constructs (p=0.098).

Conclusion: There must be a balance between movement at the fracture site to allow compression but enough stability that the fracture may heal.

Our study showed that the Synthes nail failed at a significantly lower load than the DePuy or the Stryker nails. The Synthes construct failed at a typical walking load, around three times body weight for an 80kg patient.

Introduction: Acrylic bone cement (ABC) manufacturers vary their products by using different proportions of the principle ingredients to optimize handling time or mechanical properties.

There is limited research showing the effect that varying the monomer to polymer ratio (independent from other constituents) has on thermal and mechanical properties of ABC.

Materials and Methods: The formula for CMW1 (DePuy) was reproduced using original ingredients obtained separately from different suppliers. The commercially available CMW1 monomer/polymer ratio is approximately (0.6 ml/gm). Six variants of CMW1 bone cement were prepared with varying monomer/polymer ratio (0.4–1 ml/gm). The specimens were cured and aged in an incubator for 7 days at 37°C.

Thermal characteristics of the polymerization reaction such as maximum polymerization reaction temperature (Tmax) and setting time (ts) were recorded using a Picolog digital data recorder.

Compressive mechanical properties (Young’s modulus and yield stress) were measured using a TestexpertII Universal Testing System from Zwick Roell implementing ISO5833 test criteria.

SPSS 14 for Windows software was used for calculating statistics and data analysis.

Results: An increase in monomer/polymer ratio was associated with a significant (p= 0.00) increase in setting time (5.3–11.3 minutes) with a strong correlation (r2=0.988). However, there seemed to be no effect on Tmax (p=0.792).

Compression tests showed a significant (p=0.022) decrease in E-modulus (2.63 to 2.22 GPa) with a strong Pearson correlation negative coefficient (r2= −0.827).

Similarly, yield compressive stress showed a significant (p=0.002) decrease (121.83–101.19 MPa) with a strong negative correlation (r2= −0.93)

Conclusion: This experimental study shows that varying the ratio of monomer to polymer independently from other constituents in acrylic bone cement significantly affects setting time and compressive mechanical properties. Setting time can be prolonged to increase handling time; however this will occur at the expense of a reduction in compressive stiffness and strength.

We implanted titanium and carbon fibre-reinforced plastic (CFRP) femoral prostheses of the same dimensions into five prosthetic femora. An abductor jig was attached and a 1 kN load applied. This was repeated with five control femora. Digital image correlation was used to give a detailed two-dimensional strain map of the medial cortex of the proximal femur. Both implants caused stress shielding around the calcar. Distally, the titanium implant showed stress shielding, whereas the CFRP prosthesis did not produce a strain pattern which was statistically different from the controls. There was a reduction in strain beyond the tip of both the implants.

This investigation indicates that use of the CFRP stem should avoid stress shielding in total hip replacement.

This study aims to evaluate the accuracy of sheer off self limiting screw drivers and to assess repeatability with age.

It has been reported that overzealous tightening of halo pins is associated with co-morbidity. Our unit has recently received a tertiary referral where the patient over tightened a pin leading to intracranial haematoma, hence our interest in this subject. The torque produced by six new and nine old screw drivers was tested using an Avery Torque Gauge and a Picotech data recorder. These devices are designed to produce a torque of 0.68 Nm, any greater than this is potentially hazardous. Accepted error for each device was +/− 10%. The average torque produced by the new screw drivers was 0.56 Nm with a range of 0.35–0.64 Nm (SD 0.120). The older screw drivers produced an average torque of 0.67 Nm ranging from 0.52–0.85 Nm (SD 0.123).

In conclusion, sheer off self limiting screw drivers are not accurate devices. The older devices are more likely to produce a torque exceeding a safe range and therefore we would recommend the use of new devices only.

Ethics approval: none audit.

Interest statement: none local grant.

Introduction: Restoration of vertebral height for burst fractures can be achieved either anteriorly, posteriorly or combined.

Aim: To biomechanically assess and compare stiffness of 1) posterior pedicle screws with Synex, 2) Synex+ Double screw+rod Ventrofix 3) Synex+ Double screw+ Single rod and 4) Synex+ Single screw+ Single rod in reconstructing an unstable burst fracture following anterior corpectomy.

Method: Fresh frozen calf lumbar spines (L3–L5) were dissected and L4 corpectomy performed. L3 and L5 were mounted on a plate and fixed. Loads were applied as a dead weight of 2Nm. The range of movement was measured using the Qualisys motion analysis system using external marker clusters attached to L3 and L5. Bony landmarks were identified with marker clusters as baseline. The movement was measured between the 2 marker clusters.

Five specimens were implanted for each group 1) with pedicle screw (into L3 and L5) and tested with/without Synex (expandable) cage anteriorly, 2) implanted with a Synex cage and Double screw+rod Ventrofix system, 3) Synex cage and Double screw+ Single rod Ventrofix construct and 4) Synex cage and Single screw+ Single rod Ventrofix system.

Results: Reconstruction of the anterior column with the combination of Synex and double rod Ventrofix produces a stiffer construct than the pedicle screw system in all planes of movement (p= 0.001 in rotation).

The double screw/ single rod system is less effective than the Ventrofix System but is comparable to the pedicle screw construct.

The single screw/ single rod construct leads to unacceptable movement about the axis of the inferior screw particularly in extension with a ROM much greater than the intact spine (p< 0.001)

Conclusion: Thus biomechanically we recommend Synex and double rod Ventrofix construct to reconstruct the anterior vertebral column following corpectomy for unstable burst fractures.

Introduction and aim: prosthesis displacement while attempting closed reduction of a dislocated total hip or during dislocation itself is a rare but significant complication. We have come across three cases and there are at least six case reports in the literature. The aim of our study is to conduct an in vitro biomechanical study to assess, whether application of bone cement over the shoulder of the stem confers any additional advantage in the pull out strength of the implant.

Materials and Methods: We used fourteen saw bones and cemented seven bones with a standard cementing technique and another seven bones with additional cement over the shoulder of the implant. A tensile testing machine was used to assess the pull out force needed in both groups. A comparision was done between both groups.

Results: The mean pull out force in the routine cementing technique was 2066N(S.D. 256.65) and for the group with the cement on the shoulder was 3220N(S.D. 312.22). The mean difference was 1154N. The results were analysed with two-tailed t- test, unequal variance and the difference was statistically significant with p value of 0.00045.

Conclusion: Our experiment confirms that application of the bone cement over the shoulder of the implant does give additional axial stability and should be practised routinely to reduce this complication.

Our aim was to determine whether abnormalities noted on MRI immediately after reduction for developmental dysplasia of the hip could predict the persistance of dysplasia and aid surgical planning. Scans of 13 hips in which acetabular dysplasia had resolved by the age of four years were compared with those of five which had required pelvic osteotomy for persisting dysplasia. The scans were analysed by two consultant musculoskeletal radiologists who were blinded to the outcome in each child.

The postreduction scans highlighted a number of anatomical abnormalities secondary to developmental dysplasia of the hip, but statistical analysis showed that none were predictive of persisting acetabular dysplasia in the older child, suggesting that the factors which determine the long-term outcome were not visible on these images.

Leucocytes represent a very important host defence against a number of invading pathogens and neoplasia. However, the activity of phagocytic leucocytes has been heavily implicated in the development of ischaemia-reperfusion injury, and as an aetiological factor in the pathology of other clinically important inflammatory conditions. Ischaemia-reperfusion injury occurs in diseases such as stroke and ischaemic heart disease (IHD), and during surgical procedures such as orthopaedic surgery. Investigations presented here employed a model of tourniquet-induced forearm ischaemia-reperfusion injury to investigate the effect on leucocyte adhesion and trapping (n=20). Neutrophil and monocyte leucocyte subpopulations were isolated by density gradient centrifugation techniques. Neutrophil and monocyte cell surface expression of the adhesion molecule CD11b was measured by labelling with fluorescent anti-CD11b monoclonal antibody via flow cytometry. Plasma concentrations of the soluble intercellular adhesion molecule-1 (sICAM-1) and soluble L-selectin (sL-selectin) adhesion molecules were measured using commercially available ELISA kits. Leucocyte trapping was investigated by measuring the concentration of leukocytes in venous blood leaving the arm. During ischaemia-reperfusion there was an increase in CD11b expression on neutrophils (p=0.040) and monocytes (p=0.049), a decrease in sL-selectin (p=0.387) and sICAM-1 (p=0.089) concentrations, and a decrease in peripheral blood leucocyte concentration (p=0.019). Evidence of increased leucocyte adhesion and trapping during ischaemia-reperfusion injury was supported by an increase in CD11b cell surface expression of neutrophils and monocytes. CD11b is expressed on phagocytic leucocytes and binds to ICAM-1 expressed on the surface of vascular endothelium. This increased expression of CD11b on leucocytes may therefore play a central role as the mechanism by which leucocyte trapping in the microcirculation occurs. The measured decrease in plasma concentration of sICAM-1 and sL-selectin suggests that these adhesion molecules retain their functional activity, and may bind to their corresponding cell surface ligands. It is therefore reasonable to believe that ICAM-1 expressed on the endothelium and L-selectin expressed on leucocytes is also binding to their corresponding cell surface ligands. A decrease in the number of leucocytes in the peripheral circulation may be due to increased trapping of leucocytes in the microcirculation. When leucocytes become trapped their concentration in blood leaving the microcirculation decreases, resulting in the measured decrease in leucocyte concentration. In conclusion, this study confirms the important role of leucocytes during ischaemia-reperfusion injury, which could allow for the possibility of future research that may provide therapeutic intervention for inflammatory conditions.

Introduction: Surface replacement of the hip has been proposed as an alternative to total hip replacement, particularly in young active patients. The suggested benefits include preservation of bone stock for future revision surgery and avoidance of proximal femoral stress protection, which can cause bone resorption. However, following femoral head resurfacing, femoral neck fracture can occur.

The aim of this study was to compare the strain pattern in intact and resurfaced femurs using validated third generation composite femurs and rosette strain gauges.

Methods: Rosette strain gauges were applied to an intact and a resurfaced third generation composite femur at three sites; narrowest part of the lateral surface of the neck, narrowest part of the medial surface of the neck and medial surface at the level of lesser trochanter. The femurs were loaded with axial loads of 600N, 800N and 1000N sequentially. The tests were repeated thrice for each femur. Maximum and minimum principal strains were calculated.

Further tests were carried out in which an abductor load was included in the model. Testing was done at 600N and repeated thrice for each femur. The principal strains were calculated and compared with the the principal strains without the abductor load.

Results: The maximum principal strains in the resurfaced femur were approximately 50% higher in the lateral surface of the neck and about 30% higher in the lesser trochanteric region when loaded without including an abductor force. Inclusion of the abductor force decreased the strain particularly at the lateral surface of the neck by approximately 45% in the intact femur and approximately 25% in the implanted femur. Even with the inclusion of the abductor load the strain in the resurfaced femur remained more than 50% higher at the lateral surface of the neck and 20% higher in the lesser trochanteric region.

Conclusion: Our study suggests that proximal femoral stress protection will not occur following surface replacement of the hip. The increased strain at the lateral surface of the neck could result in fracture, particularly if there is notching of the neck or if abductor function has been compromised, which can happen particularly with the direct lateral approach.

Controversy exists as to whether the biomechanical properties of a 360 lumbar fusion are influenced by the order in which the anterior and posterior components of the procedure are performed.

The fusion technique used Magerl screws to effect the posterior fusion and a Syncage implant (Stratec) to effect the anterior component of the fusion.

Isolated motion segments from calf spines were tested in each of two groups of five. In the first group the posterior fusion was performed first and in the second group the anterior fusion was performed first. Loads were applied as a dead weight of 2Nm in each range of movement of the spine (flexion/extension, lateral flexion and rotation). The range of movement was measured using the Qualisys motion analysis software linked to a set of five cameras, using external marker clusters attached to the vertebral bodies. Each motion segment was tested prior to instrumentation, post anterior or posterior instrumentation and with both anterior and posterior instrumentation.

Ranges of movement following 360 instrumentation were increased in all planes tested when posterior fixation was performed first; flexion/extension 26% v 55% (p=0.020), lateral flexion 18% v 34% (p=0.382), and rotation 18% v 73% (p=0.034).

It was concluded that posterior fixation should not be performed prior to anterior fixation as this results in a significant loss of stability in both flexion/extension and rotation

Objective: Controversy exists as to whether the biomechanical properties of a 360° lumbar fusion are influenced by the order in which the anterior and posterior components of the procedure are performed.

Methods: The fusion technique used Mager screws to effect the posterior fusion and a Syncage implant (Stratec) to effect the anterior component of the fusion. Isolated motion segments from five calf spines were tested in each of two groups. In the first group the posterior fusion was performed first and in the second group the anterior fusion was performed first. Loads were applied as a dead weight of 2Nm in each range of movement of the spine (flexion/extension, lateral flexion and rotation). The range of movement was measured using the Qualisys motion analysis system, using external marker clusters attached to the vertebral bodies. Each motion segment was tested prior to instrumentation, post anterior or posterior instrumentation and with both anterior and posterior instrumentation.

Results: Ranges of movement following 360° instrumentation were decreased in all planes. When posterior fixation was performed first; flexion/extension reduced to 55% compared to 26% with anterior fixation first (p=0.020), in lateral flexion 34% v 18% (p=0.382), and in rotation 73% v 18%(p=0.034).

Conclusions: The 360° fusion construct has reduced range of movement if the anterior first approach is used as compared to posterior first approach. Posterior fixation should not be performed prior to anterior fixation as this results in a significant loss of stability in both flexion/extension and rotation.

Interbody fusion is increasingly widely used as a treatment for intervertebral disc disorders, but the biomechanics of the procedure are not well understood. The compressive loads through the spine are largely carried by the implant or bone graft, which typically rests on a relatively small area of the vertebral body. As the compressive strength of the bone is very low, subsidence of the implants into the vertebral bodies is a common clinical complication.

Previous biomechanical studies of spinal fusion have concentrated on the stiffness of the constructs, which is important in promoting fusion. Preliminary studies have shown that there are large differences in compressive strength between different implant systems, and gave an insight into the biomechanical factors that are important in determining the strength of spinal fusion constructs. This paper reports part of a larger on going study comparing anterior and posterior fusion systems, with various methods of fixation.

A major problem in interpreting the results of these tests is to distinguish between initial settling of the implants and the onset of failure to construct. We have developed a novel technique using acoustic emission monitoring to detect microcracking in the bones, which allows the onset of failure to be distinguished from initial bedding in of the implants.

Two implant systems were tested, the Syncage and the Contact fusion cage. The cages were implanted into porcine lumbar spines at L4-L5, and the implanted motion segment was then dissected out. Steel plates were mounted on each end using bone cement to ensure an even distribution of load through the vertebral body. The complete constructs were then loaded in compression, using acoustic emission sensors to detect microcracking in the bones. The load was cyclically increased in o.5kN steps until failure occurred.

The acoustic emission technique gave a sensitive indication of the onset of damage in the bones and allowed the initial settling of the implant under load to be identified. Using cyclic unloading and reloading, it was possible to accurately identify whether this damage had weakened the construct or increased its strength by redistributing stress concentrations. Initial results indicate that the Contact fusion cage fails at a much lower load than the Syncage in this model; this is ascribed to the very small contact areas between the cage and the vertebral body, which results in high compressive stresses in the bone. Under large compressive loads it appears that the constructs become unstable, and fail by buckling and plastic collapse of the vertebral bodies. Various failure models are therefore possible depending on which part of the vertebral body starts to collapse first.

We measured the proximal migration of 265 acetabular cups over seven years and correlated the findings with clinical outcome and acetabular revision for aseptic loosening. Cups which eventually became aseptically loose were shown to migrate more rapidly than successful cups. The average proximal migration at two years postoperatively for four groups of cups showed a monotonic relationship to the acetabular revision rate for aseptic loosening at 6.5 years. We conclude that acetabular cups which develop aseptic loosening as evidenced by pain, revision or screw fracture show increased proximal migration by one year, and that the 'migration rate' at two years can be used to predict the acetabular revision rate from aseptic loosening at 6.5 years.

Individual components of a total hip replacement are difficult to evaluate and quantify. We have studied the assessment of the acetabular component, and conclude that the measurement of migration allows the comparison of implants, although there is no established link between migration and significant loosening. A method of measurement based on clinical radiographs has been developed, and its limitations estimated. The accuracy of the technique was calculated to be +/- 3 mm.