Aims

The aim of this study was to determine whether the rates of revision for metal-on-metal (MoM) total hip arthroplasties (THAs) with Pinnacle components varied according to the year of the initial operation, and compare these with the rates of revision for other designs of MoM THA.

This study utilized data from the NJR dataset on all Corail/Pinnacle total hip replacements (THR) to determine (a) the level of unit variation of the Corail/Pinnacle 36mm Metal On Metal THR within England and Wales; (b) patient, implant and surgeon factors that may be associated with higher revision rates; (c) Account for the influence of the MHRA announcement in 2010.

The national Revision Rate (RR) for the Corail / Pinnacle MOM THR was 10.77% (OR:1.46; CI:1.17–1.81). This was significantly greater than other articulation combinations (MOP 1.72%, COP 1.36%, COC 2.19%).

The 2010 MHRA announcement did not increase rate of revision (X²=1649.63, df=13, p<.001).

Patient factors associated with significantly increased revision rates included, female gender (OR 1.38 (CI 1.17–1.63, p<.001) and younger age OR 0.99 (CI 0.98–0.99), p<.001). Implant factor analysis demonstrated an inverse relationship between cup size and revision. As head length increased RR increased – highest risk of revision +12.5 (OR 1.69 (CI 1.12–2.55), p=0.13). Coxa vara, high offset stems had a higher risk of revision compared to standard offset stems (OR:1.41 (CI 1.15–1.74; p<.001). As stem size increased risk of revision decreased (OR 0.89 (CI 0.85–0.93); p<.001). Surgeon grade did not influence RR.

There was significant variation in RR between hospitals with 7 units (7/61 excluding low volume centres, <50 implants) identified as having significant higher rates of revision. However, for each of these units there was a greater proportion of higher risk patients (female, cup size 50–54, stem type).

This study has provided insight into unit variation, risk factors and the long term outcome of the Corail/Pinnacle 36mm MOMTHR. Future aims are to use these results to develop a risk stratified algorithm for the long term follow of these patients to minimize patient inconvenience and excess use of limited NHS resources.

Using a femoral head from one manufacturer on the stem of another manufacturer poses the risk that the taper interface between the components do not contact correctly and the performance of the joint will be impaired. The cohorts in this study are a combination of modular Birmingham Hip Resurfacing (BHR) and Adept femoral heads on CPT stems. The study reviews the geometry of the taper interfaces to establish if the taper clearance angles was outside of the normal range for other taper interfaces. In addition the rates of material loss from the bearings and taper and a ranking of the stem damage were reviewed to determine if the levels of loss were above that seen for other similar joints.

The material loss analysis demonstrated that the rates or levels of loss from the bearings, taper and stem are no different to levels published for manufacturer matched joints and in many cases are lower. The results demonstrate that the taper clearance angles for the mixed manufacturer joints (BHR-CPT: 0.067 to −0.116, Adept-CPT: 0.101 to −0.056) were within the range of other studies and manufacturer matched clearances (0.134 to −0.149).

Using components from different manufacturers has not in this instance increased the level of material loss from the joints, when compared to other similar manufacturer matched joints.

The aim of this study was to assess the effect of frictional torque and bending moment on fretting corrosion at the taper interface of a modular femoral component and to investigate whether different combinations of material also had an effect. The combinations we examined were 1) cobalt–chromium (CoCr) heads on CoCr stems 2) CoCr heads on titanium alloy (Ti) stems and 3) ceramic heads on CoCr stems.

In test 1 increasing torque was imposed by offsetting the stem in the anteroposterior plane in increments of 0 mm, 4 mm, 6 mm and 8 mm when the torque generated was equivalent to 0 Nm, 9 Nm, 14 Nm and 18 Nm.

In test 2 we investigated the effect of increasing the bending moment by offsetting the application of axial load from the midline in the mediolateral plane. Increments of offset equivalent to head + 0 mm, head + 7 mm and head + 14 mm were used.

Significantly higher currents and amplitudes were seen with increasing torque for all combinations of material. However, Ti stems showed the highest corrosion currents. Increased bending moments associated with using larger offset heads produced more corrosion: Ti stems generally performed worse than CoCr stems. Using ceramic heads did not prevent corrosion, but reduced it significantly in all loading configurations.

Cite this article: Bone Joint J 2015;97-B:463–72.

This study reports the mid-term results of a large bearing uncemented metal on metal total hip replacement (MOMHTHR) matched series using the Synergy stem and Birmingham modular head in 36 hips (mean follow up 61 months). All patients underwent clinical, metal ion and MRI assessment. Wear analysis was performed on retrieved heads using Redlux non-contact optical profilometry.

Seven patients (19%) have undergone revision surgery. All revisions had two or more of either symptoms, high metal ions or an MRI suggestive of an adverse reaction to metal debris (ARMD). There was no evidence of component malposition or impingement. Frank staining of tissues together with high volume dark brown fluid collections were found in all cases. All stems and cups were well fixed. In 4 cases pubic and ischial lysis (adjacent to the inferior fins) was observed. All 7 cases had radiological, intraoperative and histological evidence of ARMD (Figure 1). The failure cohort had significantly higher whole blood cobalt ion levels and OHS (p = 0.001), but no significant difference in cup size (p = 0.77), gender predominance, stem offset or cup position (p = 0.12). Sleeves had been used in all revision cases

Wear analysis (n = 4) demonstrated increased wear at the trunnion/sleeve interface in a distribution compatible with micromotion (Figure 2). There was normal wear at the articulating surface.

This series further demonstrates unacceptable failure rates in LHMOMTHR in a series where a compatible stem for the BHR modular head was used. Use of a CoCr sleeve within a CoCr head taper appears to contribute to abnormal wear and therefore potential ARMD and subsequent failure.

Background

Large diameter chrome cobalt modular heads in hip replacement surgery have caused one of the biggest challenges to face orthopaedic surgeons, manufacturers and regulators in a generation. Increasing numbers of retrieved implants offer the opportunity to look in detail at the modes of failure of these devices.

Introduction:

High failure rates with large diameter, metal on metal hip replacements have highlighted a potential issue with the head/stem taper junction as one of the significant sources of metal ion release. Postulated reasons as to why this may be such a problem with large head metal on metal hip replacements is due to the increased torque achieved by the larger head size. This may be responsible for applying greater micromotion between the head and stem taper and consequently greater amounts of fretting corrosion. The aim of this study was to perform short term in vitro electrochemical tests to assess the effect of increasing head diameter and torque on the fretting corrosion susceptibility of the head/stem taper interface and to investigate its effect on different material combinations.

Introduction

Metal on metal hip arthroplasty continues to be controversial. Emerging evidence suggests that there are multiple modes of failure, and that the results of revision surgery are influenced by host and implant factors.

Introduction:

Cemented femoral components have been used in hip replacement surgery since its inception. For many patients this works well, but recent retrieval studies^1–4 and more fundamental studies^{5, 6} have highlighted the issues of damage and material loss from the both matt and polished cemented stems.

The poor outcome of large head metal on metal total hip replacements (LHMOMTHR) in the absence of abnormal articulating surface wear has focussed attention on the trunnion / taper interface. The RedLux ultra-precision 3D form profiler provides a novel indirect optical method to detect small changes in form and surface finish of the head taper as well as quantitative assessment of wear volume. This study aimed to assess and compare qualitatively tapers from small and large diameter MOMTHR's. Tapers from 3 retrieval groups were analysed. Group 1: 28mm CoCr heads from MOMTHRs (n=5); Group 2: Large diameter CoCr heads from LHMOMTHRs (n=5); Gp 3 (control): 28mm heads from metal on polyethylene (MOP) THRs; n=3). Clinical data on the retrievals was collated. RedLux profiling of tapers produced a taper angle and 3D surface maps. The taper angles were compared to those obtained using CMM measurements. There was no difference between groups in mean 12/14 taper angles or bearing surface volumetric and linear wear. Only LHMOMs showed transfer of pattern from stem trunnion to head taper, with clear demarcation of contact and damaged areas.3D surface mapping demonstrated wear patterns compatible with motion or deformations between taper and trunnion in the LHMOM group. These appearances were not seen in tapers from small diameter MOM and MOP THRs. Differences in appearance of the taper surface between poorly functioning LHMOMTHRs and well functioning MOP or MOM small diameter devices highlight an area of concern and potential contributor to the mode of early failure.

The poor outcome of large head metal on metal total hip replacements (LHMOMTHR) in the absence of abnormal wear at the articulating surfaces has focussed attention on the trunnion / taper interface. The RedLux ultra-precision 3D form profiler provides a novel indirect optical method to detect small changes in the form and surface finish of the head taper as well as a quantitative assessment of wear volume. This study aimed to assess and compare qualitatively the tapers from well functioning small diameter, with poorly functioning LHMOMTHR's using the above technique.

Pseudotumour formation is being reported with increasing frequency in failing metal-on-metal hip resurfacings and replacements. This mode of failure complication has also been reported with metal-on-polyethylene bearing bearings when it is usually associated with evidence of surface corrosion and no apparent wear at the head–neck taper.

We present a case with evidence of taper wear and damage secondary to corrosion in an uncemented total hip replacement with a metal on polyethylene articulation (TMZF (Titanium, Molybdenum, Zirconium and Ferrous) Accolade® stem, Trident® HA coated acetabular shell, Low Friction Ion Treatment (LFIT™) Cobalt-Chrome anatomic head (40 mm), X3® polyethylene liner)

The aim of this study was to perform a comprehensive evaluation of the changes in function from pre- to post-surgery in total and unilateral knee arthroplasty (UKA/TKA) patients. Twenty healthy (age 62.4 ±5.9, 11 male), 14 UKA (age 60.9 ±10.1, 8 male) and 17 TKA (age 67.2 ±8.1, 9 male) patients were studied. KA patients were assessed four weeks pre- and six months post-operation. Measures of perceived pain and function were collected using Oxford Knee Score (OKS) questionnaire. Tests of objective function included joint range of motion (RoM), ultrasound imaging, and 3-D motion analysis/inverse modelling from gait and sit-stand. An optimal set of variables was used to classify KA function using the Cardiff DST method. Pre-KA and healthy individuals were accurately classified (96%). Post-operation questionnaire measures of function improved for both UKA and TKA groups. However, observed measures of RoM, muscle atrophy and gait had only limited gains. This resulted in 57% of UKA and only 27% of TKA patients being classified as healthy post-operation. The results of this study show that 6 months post-surgery UKA patients had higher function than TKA. Using statistical approaches to combine functional assessments has provided an accurate platform to classify function and estimate changes from pre- to post-surgery. The clinical application of this tool requires further investigation and comparison to commonly used clinical techniques.

The poor outcome of large head metal on metal total hip replacements (LHMOMTHR) in the absence of abnormal wear at the articulating surfaces has focussed attention on the trunnion/taper interface. The RedLux ultra-precision 3D form profiler provides a novel indirect optical method to detect small changes in form and surface finish of the head taper as well as a quantitative assessment of wear volume. This study aimed to assess and compare qualitatively the tapers from small diameter with LHMOMTHR's. 3 groups of retrieval tapers were analysed (Group 1: 28mm CoCr heads from MOMTHRs (n=5); Group 2: Large diameter CoCr heads from LHMOMTHRs (n=5); Group 3: 28mm heads from metal on polyethylene (MOP) THRs; n=3). Clinical data on the retrievals was collated. Both bearing surfaces and head tapers were measured for wear using the Redlux profiling non contact measurement system. Measurements included taper angle and 3D surface maps. Taper angles obtained with the Redlux method were compared to those obtained using CMM measurement on 3 parts. The Redlux profiling, including imprints, was also repeated 3 times to gauge potential errors. There was no difference in mean 12/14 taper angles between groups. There was no difference in volumetric and linear wear at the bearing surface between groups. Only the LHMOMs showed transfer of pattern from the stem to the internal head taper, with clear demarcation of the contact and damaged area between head taper and stem trunnion. 3D surface mapping demonstrated wear patterns compatible with motion or deformations between taper and trunnion in the LHMOM group alone. Discussion: Differences in appearance of the taper surface between LHMOMTHRs and MOP or MOM small diameter devices highlight an area of concern and potential contributor to the mode of early failure. Further work is required to fully qualify the Redlux method capabilities.

This study reports the mid-term results of a large bearing hybrid metal on metal total hip replacement (MOMHTHR) in 199 hips (185 patients) with mean follow up of 62 months. Clinical, radiological, metal ion and retrieval analysis were performed.

Seventeen patients (8.6%) had undergone revision, and a further fourteen are awaiting surgery (defined in combination as failures). Twenty one (68%) failures were females. All revisions and ten (71%) awaiting revision were symptomatic. Twenty four failures (86%) showed progressive radiological changes.

Fourteen revision cases showed evidence of adverse reactions to metal debris (ARMD). The failure cohort had significantly higher whole blood cobalt ion levels (p=0.001), but no significant difference in cup size (p=0.77), inclination (p=0.38) or cup version (p=0.12) compared to the non revised cohort. Female gender was associated with increased risk of failure (p=0.04). Multifactorial analysis demonstrated isolated raised Co levels in the absence of symptoms or XR changes were not predictive of failure (p=0.675). However the presence of pain (p<0.001) and XR changes (p<0.001) in isolation were significant predictors of failure. Wear analysis (n=5) demonstrated increased wear at the trunnion/head interface (mean out of roundness measurements 34.5 microns (normal range 8–10 microns) with normal wear levels at the articulating surfaces. Macroscopically corrosion was evident at the proximal and distal stem surfaces. Cumulative survival rate, with revision for any reason was 92.4% (95%CI: 87.4–95.4) at 5 years. Including those awaiting surgery, the revision rate would be 15.1% with 89.6% (95% CI: 83.9–93.4). Cumulative survival at 5 years.

This MOMHTHR series has demonstrated unacceptable high failure rates with evidence of high wear at the head/trunnion interface and passive corrosion to the stem surface. Female gender was an independent risk factor of failure. Metal ion levels remain a useful aspect of the investigation work up but in isolation are not predictive of failure.

This study utilised NJR primary hip data from the 6^th Annual Report to determine the rate and indication for revision between cemented, uncemented, hybrid and resurfacing prosthetic groups. Regression analysis was performed to identify the influence of gender and ASA grade on these revision rates. Validity of the data was interrogated by exploring for episodes of misclassification.

Background

Since 1991 to 2008 approximately 800,000 Exeter stems have been sold worldwide with 80 reported cases of fracture (neck or stem). This study aimed to determine factors predisposing to fracture.

This study reports the mid-term results of a large bearing hybrid metal on metal total hip replacement (MOMHTHR) in 199 hips (185 patients) with mean follow up of 62 months. Clinical, radiological outcome, metal ion levels and retrieval analysis were performed.

Seventeen patients (8.6%) had undergone revision, and a further fourteen are awaiting surgery (defined in combination as failures). Twenty one (68%) failures were females. All revisions and ten (71%) of those awaiting revision were symptomatic. Twenty four failures (86%) showed progressive radiological changes.

Fourteen revision cases showed evidence of adverse reactions to metal debris (ARMD). The failure cohort had significantly higher whole blood cobalt ion levels (p=0.001), but no significant difference in cup size (p=0.77), inclination (p=0.38) or cup version (p=0.12) in comparison to the non revised cohort. Female gender was associated with an increased risk of failure (chi squared p=0.04). Multifactorial analysis demonstrated isolated raised Co levels in the absence of either symptoms or XR changes was not predictive of failure (p=0.675). However both the presence of pain (p<0.001) and XR changes (p<0.001) in isolation were both significant predictors of failure. Wear analysis (n=5) demonstrated increased wear at the trunnion/head interface (mean out of roundness measurements of 34.5 microns +/−13.3 (+/−2SD, normal range 8-10 microns) with normal levels of wear at the articulating surfaces. There was evidence of corrosion at the proximal and distal stem surfaces. The cumulative survival rate, with revision for any reason was 92.4% (95%CI: 87.4-95.4) at 5 years. Including those awaiting surgery, the revision rate would be 15.1% with cumulative survival at 5 years of 89.6% (95% CI: 83.9-93.4).

This MOMHTHR series has demonstrated unacceptable high failure rates with evidence of high wear at the head/trunnion interface and passive corrosion to the stem surface. This raises concern with the use of large heads on conventional 12/14 tapers. Female gender was an independent risk factor of failure. Metal ion levels remain a useful aspect of the investigation work up but in isolation are not predictive of failure.

Objective

To determine the use of oral anti-inflammatory drugs use in the year before and the two years after primary total hip (THR) or knee (TKR) replacement, and to assess whether this varied according to the Body mass Index (BMI).

Introduction and aim

One of the suggested advantages of hip resurfacing arthroplasty is that it offers the possibility of straightforward revision. As the femoral canal is not violated during the resurfacing procedure, it is postulated that the outcome of revision surgery should be equivalent to that of a primary hip arthroplasty. The purpose of this study was to investigate whether revision was as straightforward and as successful as has been suggested.

Introduction: Functional Foot Orthoses (FFO’s) have been shown to improve one element of balance, postural sway, when prescribed for patients with ankle injuries. Little is known, however, about the effect of these devices on ankle stability/proprioception, or the changes which might occur as the patient becomes habituated to using the device. We studied these effects from the time of initial application of the FFO through to regular usage at six weeks.

Methods: Patients with musculoskeletal conditions affecting the lower limb that required custom made FFO’s were evaluated. A standardised protocol, using the Biodex stability system (a balance platform), to assess several stability indices was performed. Patients were assessed before fitting the orthosis, at the time of fitting and six weeks later. The American Orthopaedic Foot and ankle Society (AOFAS) score was also used to evaluate the progress of these patients.

Results: There were 13 male and seven female patients, aged 10 to 64 years. Patients had a range of orthopaedic conditions and all been assessed by orthopaedic specialist and podiatrist as having correctable foot biomechanics. In 6 patients, proprioception deteriorated on initial application of FFO’s. However, all patients exhibited improved over-all stability by a mean of 2.5 points (Normal range 0.82–3.35) at 6 weeks evaluation. The mean AOFAS on presentation was 72 and the final mean score was 97, both of which were clinically and statistically significant (t test, p< 0.05). Eighteen patients had complete resolution of symptoms of pain and instability.

Conclusions: FFO’s alter foot biomechanics, and in doing so appear also to improve balance and proprioception. Proprioception deteriorated in 30% of cases on initial application of orthotics, but pain and instability improved in more than 90% of patients on extended use of foot orthotics, with this improvement becoming manifest by 6 weeks after starting use of the device.

Introduction: One of the main factors in the success of impaction bone grafting (IBG) in revision hip surgery is its ability to resist shear and to form a stable construct. Bone marrow contains multipotent skeletal stem cells and we propose that in combination with allograft will produce a living composite with biological and mechanical potential. In this study we looked at whether coating of the allograft with type 1 collagen followed by seeding with human bone marrow stromal cells (hBMSC) would enhance the grafts mechanical and biological properties.

Methods: A control group of plain allograft and three experimental groups where used to determine the effects that collagen and hBMSC have on IBG. The samples where impacted in standardised fashion previously validated to replicate femoral IBG, and cultured in vitro for 2 weeks. The samples then underwent mechanical shear testing and biochemical analysis for DNA content and Osteogenic activity.

Results: Collagen coating of the allograft prior to seeding with hBMSC significantly enhanced the mechanical properties of the construct compared to the ‘gold standard’ of plain allograft with a 22% increase in shear strength (p=0.002). The collagen coated group also showed increased osteogenic differentiation of the stromal cells (Alkaline Phospatase specific activity: 124 +/− 18.6 vs 54.6 +/− 9.6 nM pNPP/Hr/ngDNA p= < 0.01).

Discussion: This study has shown a role in the improvement of the biomechanical properties of IBG by coating with collagen and seeding with hBMSC. Collagen coating of IBG is a simple process and translation of the technique into the theatre setting feasible. The improvement in shear strength and cohesion could lead to earlier weight bearing for the patients and allow quicker recovery. The therapeutic implications of such composites auger well for orthopaedic applications. We are currently strengthening the above findings with an in vivo study.

Introduction: Revision hip surgery is predicted to rise significantly over the coming decades. There is therefore likely to be an increasing need to overcome the large bone loss and cavitatory defects encountered in failed primary hip replacements. Impaction bone grafting (IBG) is a recognised technique for replacing lost bone stock. Achieving optimal graft impaction is a difficult surgical skill with a significant learning curve, balancing the need to achieve sufficient compaction to provide primary stability versus the need to keep impaction forces to a minimum to prevent iatrogenic fracture. In this study we have developed a revision acetabular model to test the hypothesis that the use of vibration and drainage with a new custom made perforated tamp could reduce the peak stresses imparted to the acetabulum during the impaction process and also improve the reliability and reproducibility of the impaction technique

Methods: Composite Sawbone hemi Pelvis models were used, with identical contained cavitatory defects created (Paprosky Type 2a). A strain gauge was attached to the medial wall of each hemi pelvis. A custom set of IBG tamps were made, and coupled a pneumatic hammer used to generate the vibrations. A standard impaction technique was used for the control group and the new vibration impaction for the experimental group. The cavity was progressively filled with morsellised allograft in 6 set steps for both groups with strain gauge readings taken during all impaction to monitor peak stresses. A standard Exeter Contemporary cup was then cemented into the graft bed for both groups. The models were mechanically loaded according to the protocol developed by Westphal et al at the angle of the joint reaction force during heel strike for a total of 50 000 cycles. 3D assessment of any micro motion post mechanical testing and degree of graft compaction was done with high resolution micro CT.

Results: Vibration impaction lead to a significant reduction in the peak stresses during the impaction process throughout the 6 steps (e.g. Step 1: 34.6 vs 110.8 MPa p=0.03). There was also far less variability in the peak stresses in the vibration group compared to standard impaction both in sequential impactions by the same surgeon and between different surgeons. One medial wall fracture occurred in the control group only. There was no difference in the degree of graft compaction or in the subsidence of the implant post cyclical loading.

Conclusion: Impaction bone grafting can be a difficult surgical skill with a significant learning curve. We believe that this new technique of applying vibration coupled with drainage to the IBG process in the acetabulum can reduce the risk of intraoperative fracture whilst achieving good graft compaction and implant stability. This technique therefore has the potential to widen the ‘safety margins’ of IBG and reduce the learning curve allowing more widespread adoption of the technique for replacing lost bone stock.

Introduction: Impaction bone grafting (IBG) using fresh frozen morsellised allograft is considered by many as the method of choice for replacing lost bone stock encountered during revision hip surgery. Bone marrow contains multipotent skeletal stem cells which have the potential to differentiate down a number of different cell lineages including osteoblasts, chondrocytes and adipocytes. In IBG it is desirable for as many as possible to go on to form bone rather than fibrous tissue to form a solid osseous construct. Whilst it is possible to push cells down the osteogenic lineage in vitro, some of these methods (e.g. the addition of Dexamethasone) are not translatable to clinical practice due to undesirable side effects. In this study we test the hypothesis that by coating the allograft with type 1 Collagen prior to seeding with human bone marrow stromal cells (hBMSC), the cellular adhesion and proliferation down an osteogenic lineage can be increased, leading to improved mechanical and biological properties of the IBG composite.

Methods: A control group of plain allograft and three experimental groups where used to determine the effects that collagen and hBMSC have on IBG (both individually and in combination). The samples where impacted in standardised fashion previously validated to replicate Femoral IBG, and cultured in vitro for 2 weeks. The samples then underwent mechanical shear testing giving a family of stress strain curves for each group, from which a Mohr coulomb failure curve can be plotted. Using the Mohr Coulomb failure equation τ = σ tanΦ + c, the shear strength (τ), Internal friction angle (tanΦ) and inter particulate cohesion (c) can then be calculated. Biochemical analysis was also performed for DNA content and Osteogenic activity.

Results: Mechanical shear testing demonstrated a significant improvement (p=0.002) in the grafts ability to resist shear with the coating of Collagen and seeding with hBMSC (245 vs 299 kPa) as well as improved cohesion between the bone graft particles (46 vs 144 kPa). Regression analysis of the shear strength showed a linear increase with compressive stress (R2 > 0.98) for all groups, indicating that the grafts satisfied the Mohr Coulomb failure law. In the two groups seeded with cells, the collagen coated group also showed increased osteogenic cell activity compared to the plain allograft.

Conclusion: This study has shown a role in the improvement of the mechanical and biological properties of IBG coated with type 1 Collagen and seeded with hBMSC. Collagen coating of IBG is a facile process and translation of the technique into the theatre setting feasible. The improvement in shear strength and cohesion could lead to earlier weight bearing for the patients and allow quicker recovery. The therapeutic implications of such composites auger well for orthopaedic applications. We are currently strengthening the above findings with an in vivo study.

Introduction: Impaction bone grafting (IBG) for revision hip surgery can be a difficult surgical skill with a fine line between construct failure from insufficient compaction and intraoperative fracture from high impaction forces. Following on from our experience in the femur, in this study we used an acetabular model to test the hypothesis that the use of vibration for IBG could reduce the peak stresses thus reducing the intraoperative fracture risk and also improve the reliability and reproducibility of the impaction technique.

Methods: Revision hemi pelvis models were made (Pra-prosky Type 2a). A standard impaction technique was used for the control group, and the impactor tamps were coupled with a pneumatic hammer for the vibration group. The cavity was filled in 6 set steps with strain gauge readings taken throughout. The pelvis construct was then mechanically loaded. Graft compaction and micro motion post mechanical testing was assessed with micro CT.

Results: Vibration impaction led to a significant reduction (p=0.03) in the peak stresses during the impaction process. There was also significantly less variability in peak stresses for the vibration group compared to standard, both in sequential impactions by the same surgeon and between different surgeons. One medial wall fracture occurred in the control group only, similar to fractures encountered in the clinical situation. There was no significant difference in the degree of graft compaction or in the subsidence of the cup.

Discussion: We believe that this new technique of applying vibration to the IBG process can reduce the risk of intraoperative fracture whilst achieving good graft compaction and implant stability. This technique therefore has the potential to widen the ‘safety margins’ of IBG and reduce the learning curve allowing more widespread adoption of the technique for replacing lost bone stock.

Introduction: One of the main factors in the success of impaction bone grafting (IBG) in revision hip surgery is its ability to resist shear and to form a stable construct. Bone marrow contains multipotent skeletal stem cells and we propose that in combination with allograft will produce a living composite with biological and mechanical potential. In this study we looked at whether coating of the allograft with type 1 collagen followed by seeding with human bone marrow stromal cells (hBMSC) would enhance the grafts mechanical and biological properties.

Methods: A control group of plain allograft and three experimental groups where used to determine the effects that collagen and hBMSC have on IBG. The samples where impacted in standardised fashion previously validated to replicate femoral IBG, and cultured in vitro for 2 weeks. The samples then underwent mechanical shear testing and biochemical analysis for DNA content and Osteogenic activity.

Results: In isolation, both Collagen coating and seeding with hBMSC significantly enhanced the mechanical properties of the construct compared to the ‘gold standard’ of plain allograft. This was further enhanced (p=0.002) when the two processes are combined both with shear strength (245 vs. 299 kPa) and cohesion between the graft particles (46 vs. 144 kPa). The collagen coated group also showed increased osteogenic cell proliferation.

Discussion: This study has shown a role in the improvement of the mechanical properties of IBG coated with collagen and seeded with hBMSC. Collagen coating of IBG is a simple process and translation of the technique into the theatre setting feasible. The improvement in shear strength and cohesion could lead to earlier weight bearing for the patients and allow quicker recovery. The therapeutic implications of such composites auger well for orthopaedic applications. We are currently strengthening the above findings with an in vivo study.

Quantification and 3D visualization of new vessel networks in vivo remains a major unresolved issue in tissue engineering constructs. This study has examined the potential of combining the use of a radio opaque dye and micro-CT to visualize and quantify microvascular networks in 3D in vivo. We have applied this technique to the study of neoangiogenesis in a bone impaction graft model in vivo as proof of concept. Tissue engineered constructs were created with natural (morsellised allograft) and synthetic grafts (Poly Lactic Acid, PLA)

Culture expanded human bone marrow stromal cells (HBMSC) labeled with a fluorescent probe (Cell Tracker Green, CTG) to measure cell viability, were seeded onto prepared scaffolds (morsellised allograft or PLA) and impacted with a force equivalent to a standard femoral impaction (474J/m2). The impacted HBMSC / scaffolds and scaffolds alone were contained within capsules and implanted subcutaneously into severely compromised immunodeficient mice. Radiopaque dye was infused into all vessels via cardiac cannulation prior to removal of implants. Micro CT imaging and immunohistochemistry was performed in all samples.

Cell survival was evident by abundant fluorescent staining. The average number of blood vessels penetrating the capsules were 16.33 in the allograft / HBMSC constructs compared to 3.5 (p=0.001) in the allograft alone samples and 32.67 in the PLA / HBMSC constructs compared to 7.67 (p=0.001) in the PLA alone samples. The average total vessel volume within the capsules was 0.43mm3 in the allograft / HBMSC constructs compared to 0.04mm3 (p=0.05) in the allograft alone samples and 1.19mm3 in the PLA / HBMSC constructs compared to 0.12mm3 (p=0.004) in the PLA alone samples. Extensive staining for Type 1 Collagen, new matrix and Von Willebrand factor in living tissue engineered constructs confirmed osteogenic cell phenotype, and new blood vessel formation respectively.

In summary, these studies demonstrate, HBMSC combined with either morsellised allograft or PLA can survive the forces of femoral impaction, differentiate along the osteogenic lineage and promote neovascularisation in vivo. Successful combined neovascularisation and bone formation in impacted tissue engineered constructs in vivo augers well for their potential use in IBG.

This novel technique utilising contrast enhanced 3D reconstructions in combination with immunohistochemistry enables quantification of neovascularisation and new bone formation in impacted tissue engineered constructs with widespread experimental application in regenerative medicine and tissue engineering analysis.

Impaction bone grafting with morsellised allograft is a recognized technique to reconstitute loss of bone stock often encountered during revision hip surgery. Concerns over disease transmission, high costs and limited supply has led to interest in synthetic grafts. Poly (lactic acid) (PLA) grafts are attractive to the tissue engineering community as a consequence of their biocompatibility, ease of processing into three-dimensional structures, their established safety as suture materials and the versatility that they offer for producing chemically defined substrates for bone graft matrices. This study set out to examine the potential of PLA scaffolds augmented with human bone marrow stromal cells in impaction bone grafting (IBG).

Methods: In vitro and in vivo studies were performed on impacted morsellised PLA seeded with human bone marrow stromal cells (HBMSC) and compared to PLA alone. In vitro samples were incubated under osteogenic conditions and in vivo samples were implanted subcutaneously into severely compromised immunodeficient mice, both for 4 weeks. In vitro samples were analysed for cell viability, DNA content, specific alkaline phosphatase activity, immunohistochemistry and mechanical shear testing using a cam shear tester. In vivo samples were analysed for cell viability, immunohistochemistry and evidence of neovascularisation and new bone formation using contrast enhance micro computer tomography.

Results: HBMSC survival post impaction, as evidenced by cell tracker green staining, was seen throughout the samples in vitro and in vivo. In vitro there was a significant increase in DNA content (P< 0.001) and specific alkaline phosphatase activity (P< 0.001) in PLA / HBMSC samples compared to impacted PLA alone. Mechanical shear testing of in vitro PLA / HBMSC samples demonstrated a significant increase in shear strength and interparticulate cohesion compared to PLA alone. Immunohistochemistry for type I collagen, osteocalcin, confirmed cell differentiation along the osteogenic lineage in vitro and in vivo. In vivo studies showed a significant increase in blood vessel number and volume penetrating the PLA / HBMSC constructs (32.6 vessels, 1.19mm3, p=0.02, p=0.004) compared to PLA alone (7.6vessels, 0.12mm3). There was a significant relative increase in new bone formation in the PLA / hBMSC constructs (0.47mm3) compared to PLA alone (0mm3), further confirmed with positive staining for osteoid using Goldners Trichrome.

Conclusion: HBMSC seeded onto PLA can withstand the forces of femoral impaction and continue to differentiate and proliferate along the osteogenic lineage. Furthermore PLA / hBMSC constructs in vitro offer a mechanical advantage over PLA alone and in vivo induce neovascularisation and new bone formation. From both a biological and mechanical perspective these studies have demonstrated that PLA is a suitable and beneficial bone graft extender for use in IBG.

Background: The use of fresh morsellised allograft in impaction bone grafting for revision hip surgery remains the gold standard. Bone marrow contains osteogenic progenitor cells that arise from multipotent mesenchymal stem cells and we propose that in combination with allograft will produce a living composite with biological and mechanical potential. This study aimed to determine if human bone marrow stromal cells (HBMSC) seeded onto highly washed morsellised allograft could survive the impaction process, differentiate and proliferate along the osteogenic lineage and confer biomechanical advantage in comparison to impacted allograft alone

Methods: HBMSC were isolated and culture expanded in vitro under osteogenic conditions. Cells were seeded onto prepared morsellised allograft and impacted with a force equivalent to a standard femoral impaction (474J/m2). Samples were incubated for either two or four week periods under osteogenic conditions and analysed for cell viability, histology, immunohistochemistry, and biochemical analysis of cell number and osteogenic enzyme activity. Mechanical shear testing, using a Cam shear tester was performed, under three physiological compressive stresses (50N, 150N, 250N) from which the shear strength, internal friction angle and particle interlocking values were derived.

Results: Cell viability of HBMSC post impaction, was confirmed with cell tracker green staining, a marker of viable cells, and observed throughout all samples. There was a significant increase in DNA content and specific alkaline phosphatase activity compared to impacted seeded allograft samples. Immunohistochemical staining for type I collagen confirmed cell differentiation along the osteogenic lineage. Mechanical shear testing demonstrated a statistical significant increase in shear strength and interparticulate cohesion in the allograft/hBMSC group over allograft alone at 2 and 4 week intervals (p< 0.001).

Conclusion: HBMSC seeded onto allograft resulted in the formation of a living composite capable of withstanding the forces equivalent to a standard femoral impaction. HBMSC under osteogenic conditions were observed to differentiate and proliferate along the osteogenic lineage. In addition, an allograft/HBMSC living composite confers a biomechanical advantage over allograft alone These changes resulting in enhancement of biological and mechanical properties of bone graft within impaction bone grafting have implications for translation and future change in orthopaedic practice in an increasing ageing population.

The use of fresh morsellised allograft in impaction bone grafting for revision hip surgery remains the gold standard. Bone marrow contains osteogenic progenitor cells that arise from multipotent mesenchymal stem cells and we propose that in combination with allograft will produce a living composite with biological and mechanical potential. This study aimed to determine if human bone marrow stromal cells (HBMSC) seeded onto highly washed morsellised allograft could survive the impaction process, differentiate and proliferate along the osteogenic lineage and confer biomechanical advantage in comparison to impacted allograft alone. Future work into the development of a bioreactor is planned for the potential safe translation of such a technique into clinical practice.

Methods: HBMSC were isolated and culture expanded in vitro under osteogenic conditions. Cells were seeded onto prepared morsellised allograft and impacted with a force equivalent to a standard femoral impaction (474J/m2). Samples were incubated for either two or four week periods under osteogenic conditions and analysed for cell viability, histology, immunocytochemistry, and biochemical analysis of cell number and osteogenic enzyme activity. Mechanical shear testing, using a Cam shear tester was performed, under three physiological compressive stresses (50N, 150N, 250N) from which the shear strength, internal friction angle and particle interlocking values were derived.

Results: HBMSC survival post impaction, as evidenced by cell tracker green staining, was seen throughout the samples. There was a significant increase in DNA content (P< 0.05) and specific alkaline phosphatase activity (P< 0.05) compared to impacted seeded allograft samples. Immunocytochemistry staining for type I collagen confirmed cell differentiation along the osteogenic lineage. There was no statistical difference in the shear strength, internal friction angle and particulate cohesion between the two groups at 2 and 4 weeks.

Conclusion: HBMSC seeded onto allograft resulted in the formation of a living composite capable of withstanding the forces equivalent to a standard femoral impaction and, under osteogenic conditions, differentiate and proliferate along the osteogenic lineage. In addition, there was no reduction in aggregate shear strength and longer term studies are warranted to examine the biomechanical advantage of a living composite. The therapeutic implications of such composites auger well for orthopaedic applications.

Introduction: Bone is unique with a vast potential for regeneration from cells with stem cell characteristics. With an increasing aging population, clinical imperatives to augment and facilitate tissue repair have highlighted the therapeutic potential of harnessing mes-enchymal populations from bone. We describe laboratory and clinical findings from two clinical cases, where different proximal femoral conditions (AVN, bone cyst) were treated with impacted allograft augmented with marrow-derived allogeneic progenitor cells.

Methods: Marrow was aspirated from the posterior superior iliac crest and seeded onto prepared washed morsellised allograft. The seeded graft was left for 40 minutes to allow adherence of the marrow-derived osteoprogenitor cells prior to impaction into the defect. Samples of the impacted graft were taken for in-vitro analysis of cell viability, histology and biochemical analysis of cell number and osteogenic enzyme activity. The total force imparted during impaction was calculated using a load cell, with three independent surgeons performing a laboratory simulation of the impaction technique.

Results: Both patients made a rapid clinical recovery after an overnight stay. Imaging confirmed filling of the defects with increased density on plain radiographs suggesting good impaction of the graft composite. Immu-nohistochemical staining of graft samples demonstrated that a living composite graft with osteogenic activity had been introduced into the defects as evidenced by cell tracker green viability and alkaline phosphatase (osteogenic marker) expression and specific activity. The average peak forces during impaction were 0.7kN corresponding to average peak stresses within the graft of 8.3MPa. Similar forces were seen between operators.

Discussion: Replacement of bone loss remains a major challenge in orthopaedic practice. Although allograft remains the gold standard where large volumes preclude autograft, allograft has little osteoinductive potential. We demonstrate that marrow-derived cells can adhere to highly washed morsellised allograft, survive the impaction process, and are of the osteoblastic phenotype creating a living composite. Thus we conclude, impacted allograft seeded with autologous marrow cells allows the delivery of a biologically active scaffold for the treatment of bone deficiency. In addition this is a novel straightforward technique, surgeon independent and with applications in a number of orthopaedic scenarios.

Background: Impaction bone-grafting in revision hip surgery generates high forces that may be transmitted through the graft to the femoral cortex, generating high surface strains and a concomitant risk of femoral fracture. Concern of inducing fracture may lead to under-compaction of the graft, with subsequent risk of implant migration. Vibration is commonly used in civil engineering applications to increase aggregate compressive and shear strengths. We have therefore examined the hypotheses that vibration-assisted graft compaction would (a) increase graft compaction compared with the standard femoral impaction grafting technique and subsequently reduce prosthesis migration and (b) reduce femoral hoop strains in the production of graft of a given density and mechanical properties.

Method: Physiological composite femurs were adapted to represent femurs encountered in revision hip surgery by widening of the internal diameter and thinning of the outer shell. In the control group, revision with the standard Exeter technique was simulated using highly washed morcellised bone graft from fresh-frozen human femoral heads. In the study group, vibration-assisted graft compaction was used. The femurs were mounted on a 5kN capacity load cell to measure the total force imparted during graft impaction. Strain gauges placed at the medial calcar and midshaft, measured hoop strains generated during the impaction process. On completion of graft impaction, an Exeter stem was cemented in place. Implant subsidence under physiological cyclic loading (5x 105 cycles) and graft density using micro CT were measured after compaction.

Results: There were no significant differences between the two groups in the peak forces (3.8-4.1kN) imparted during the impaction process. Similar peak hoop strains were observed in the both groups (1.2-1.4%). However a greater graft density was seen in the vibration group with minimal implant subsidence under cyclic loading.

Conclusion: The use of vibration during the impaction process allowed improved graft compaction to be achieved without increasing hoop strains in the femoral cortex. This has implications in preventing failure from under impaction without increasing the risk of fracture. Furthermore, this analysis is applicable to the study of novel synthetic grafts / mixtures in the impaction process for orthopaedic application.

Introduction Rheumatoid arthritis commonly produces disabling forefoot deformities. Surgical interventions include hallux metatarsophalangeal (MTP) joint fusion with lesser toe metatarsal head and/or proximal phalanx base excisions. Here we describe our experience of combining first MTP joint fusion using a plate with Weil metatarsal osteotomies (WMO) of the lesser toes. WMO preserve and reduce lesser MTP joints thus enhancing stability and relocating the plantar fat pads. Plate fusion of the first MTP joint protects against recurrent deformity. Our aim was to assess the outcome of this procedure.

Method Twelve female patients (21 feet) underwent the procedure with no loss to follow up. Informed consent was given and ethics approval obtained. American Orthopaedic Foot and Ankle Society (AOFAS) forefoot scale and visual analogue scale scores were recorded post-operatively only. Pre- and post-operative plain radiographs were compared.

Results Mean age at operation was 62.5 years (range 48–75). Mean follow up was 25.9 months (range 2–54). The mean post-operative AOFAS scale score was 70.6/100 (range 34–90).

The mean hallux valgus angle was reduced from 39.6 degrees to 31.8 degrees and the second MTP angle from 28.3 degrees to 19.4 degrees. Pre-operatively 28% of the lesser toe MTP joints were aligned compared with 83% post-operatively. All of the WMOs fused. Two first MTP joint fusions resulted in non-unions and required successful revision surgery. In five cases metalwork was removed from the hallux because of discomfort. In two cases, metalwork was removed because of superficial wound infection. Infection subsequently resolved after a course of oral antibiotics. Nine patients stated they would recommend the procedure.

Conclusion First MTP joint plate arthrodesis and WMOs of the lesser toes provides good symptomatic relief and restoration of forefoot mechanics. It is a useful procedure in delaying more radical and final surgery for this progressive, destructive disease.