Aims

The COVID-19 pandemic posed significant challenges to healthcare systems across the globe in 2020. There were concerns surrounding early reports of increased mortality among patients undergoing emergency or non-urgent surgery. We report the morbidity and mortality in patients who underwent arthroplasty procedures during the UK first stage of the pandemic.

Introduction

Many worldwide regulatory authorities recommend regular surveillance of metal-on-metal hip arthroplasty patients given high failure rates. However concerns have been raised about whether such regular surveillance, which includes asymptomatic patients, is evidence-based and cost-effective. We determined: (1) the cost of implementing the 2015 MHRA surveillance in “at-risk” Birmingham Hip Resurfacing (BHR) patients, and (2) how many asymptomatic hips with adverse reactions to metal debris (ARMD) would have been missed if patients were not recalled.

Introduction

We investigated predictors of poor outcomes following metal-on-metal hip arthroplasty (MoMHA) revision surgery performed for adverse reactions to metal debris (ARMD), to help inform the revision threshold and type of reconstruction.

Background

Following endosteal uncemented orthopaedic device implantation, the initial implant/bone interface retains spaces and deficiencies further exacerbated by pressure necrosis and resultant bone resorption. This implant-bone space requires native bone infill through the process of de novo osteogenesis. New appositional bone formation on the implant surface is known as contact osteogenesis and is generated by osteogenic cells, including skeletal stem cells (SSCs), colonising the implant surface and depositing the extracellular bone matrix. Surface nanotopographies provide physical cues capable of triggering SSC differentiation into osteoblasts, thus inducing contact osteogenesis, translated clinically into enhanced osseointegration and attainment of secondary stability. The current study has investigated the in vitro and in vivo effects of unique nanotopographical pillar substrates on SSC phenotype and function.

Introduction

We investigated whether blood metal ions could effectively identify bilateral metal-on-metal hip patients at risk of adverse reactions to metal debris (ARMD).

Background

In 2012, the National Joint Registry recorded 86,488 primary total hip replacements (THR) and 9,678 revisions (1). To date aseptic loosening remains the most common cause of revision in hip and knee arthroplasty, accounting for 40% and 32% of all cases respectively and emphasising the need to optimise osseointegration in order to reduce revisions. Clinically, osseointegration results in asymptomatic stable durable fixation of orthopaedic implants. Osseointegration is a complex process involving a number of distinct mechanisms affected by the implant surface topography, which is defined by surface orientation and surface roughness. Micro- and nano-topography levels have discrete effects on implant osseointegration and yet the role on cell function and subsequent bone implant function is unknown. Nanotopography such as collagen banding is a critical component influencing the SSC niche in vivo and has been shown to influence a range of cell behaviours in vitro (2,3). We have used unique fabricated nanotopographical pillar substrates to examine the function of human bone stem cells on titanium surfaces.

There is a large variability associated with hip stem designs, patient anatomy, bone mechanical property, surgical procedure, loading, etc. Designers and orthopaedists aim at improving the performance of hip stems and reducing their sensitivity to this variability. This study focuses on the primary stability of a cementless short stem across the spectrum of patient morphology using a total of 109 femoral reconstructions, based on segmentation of patient CT scan data. A statistical approach is proposed for assessing the variability in bone shape and density [Blanc, 2012]. For each gender, a thousand new femur geometries were generated using a subset of principal components required to capture 95% of the variance in both female and male training datasets [Bah, 2013]. A computational tool (Figure 1) is then developed that automatically selects and positions the most suitable implant (distal diameter 6–17 mm, low and high offset, 126° and 133° CCD angle) to best match each CT-based 3D femur model (75 males and 34 females), following detailed measurements of key anatomical parameters. Finite Element contact models of reconstructed hips, subjected to physiologically-based boundary constraints and peak loads of walking mode [Speirs, 2007] were simulated using a coefficient of fricition of 0.4 and an interference-fit of 50μm [Abdul-Kadir, 2008]. Results showed that the maximum and average implant micromotions across the subpopulation were 100±7μm and 7±5μm with ranges [15μm, 350μm] and [1μm, 25μm], respectively. The computed percentage of implant area with micromotions greater than reported critical values of 50μm, 100μm and 150μm never exceeded 14%, 8% and 7%, respectively. To explore the possible correlations between anatomy and implant performance, response surface models for micromotion metrics were constructed using the so-called Kriging regression methodology, based on Gaussian processes. A clear nonlinear decreasing trend was revealed between implant average micromotion and the metaphyseal canal flare indexes (MCFI) measured in the medial-lateral (ML), anterio-posterior (AP) and femoral neck-oriented directions but also the average bone density in each Gruen zone. In contrast, no clear influence of the remaining clinically important parameters (neck length and offsets, femoral anteversion and CCD angle, standard canal flares, patient BMI and weight or stem size) to implant average micromotion was found. In conclusion, the present study demonstrates that the primary stability and tolerance of the short stem to variability in patient anatomy were high, suggesting no need for patient stratification. The developed methodology, based on detailed morphological analysis, accurate implant selection and positioning, prediction of implant micromotion and primary stability, is a novel and valuable tool to support implant design and planning of femoral reconstructive surgery.

This work was motivated by the need to capture the spectrum of anatomical shape variability rather than relying on analyses of single bones. A novel tool was developed that combines image-based modelling with statistical shape analysis to automatically generate new femur geometries and measure anatomical parameters to capture the variability across the population. To demonstrate the feasibility of the approach, the study used data from 62 Caucasian subjects (31 female and 31 male) aged between 43 and 106 years, with CT voxel size ranging 0.488 × 0.488 × 1.5 mm to 0.7422 × 0.7422 × 0.97 mm.

The scans were divided into female and male subgroups and high-quality subject-specific tetrahedral finite element (FE) meshes resulting from segmented femurs formed the so-called training samples. A source mesh of a segmented femur (25580 nodes, 51156 triangles) from the Visible Human dataset [Spitzer, 1996] was used for elastic surface registration of each considered target male and female subjects, followed by applying a mesh morphing strategy.

To represent the variations in bone morphology across the population, gender-based Statistical Shape Models (SSM) were developed, using Principal Component Analysis. These were then sampled using the principal components required to capture 95% of the variance in each training dataset to generate 1000 new anatomical shapes [Bryan, 2010; Blanc, 2012] and to automatically measure key anatomical parameters known to critically influence the biomechanics after hip replacement (Figure 1).

Analysis of the female and male training datasets revealed the following data for the five considered anatomical parameters: anteversion angle (12.6 ± 6.4° vs. 6.2 ± 7.5°), CCD angle (124.8 ± 4.7° vs. 126.3 ± 4.6°), femoral neck length (48.7 ± 3.8 mm vs. 52 ± 5 mm), femoral head radius (21.5 ± 1.3 mm vs. 24.9 ± 1.5 mm) and femur length (431.0 ± 17.6 mm vs. 474.5 ± 26.3 mm). However, using the SSM generated pool of 1000 femurs, the following data were computed for females against males: anteversion angle (10.5 ± 14.3° vs. 7.6 ± 7.2°), CCD angle (123.9 ± 5.8° vs. 126.7 ± 4°), femoral neck length (46.7 ± 7.7 mm vs. 51.5 ± 4.4 mm), femoral head radius (21.4 ± 1.2 mm vs. 24.9 ± 1.4 mm) and femur length (430.2 ± 16.1 mm vs. 473.9 ± 25.9 mm).

The highest variability was found in the anteversion of the females where the standard deviation in the SSM-based sample was increased to 14.3° from 6.4° in the original training dataset (Figures 2 & 3). The mean values for both females (10.5°) and males (7.6 °) were found close to the values of 10° and 7° reported in [Mishra, 2009] in 31 females and 112 males with a [2°, 25°] and [2°, 35°] range, respectively.

Femoral neck length of the female (male) subjects was 47.3 ± 6.2 mm (51.8 ± 4.1 mm) compared to 48.7 ± 3.8 mm (52 ± 5 mm) in the training dataset and 63.65 ± 5.15 mm in [Blanc, 2012] with n = 142, 54% female, 46% male and a [50.32–75.50 mm] range. For the measured CCD angle in both female (123.9 ± 5.8°) and male (126.7 ± 4°) subjects, a good correlation was found with reported values of 128.4 ± 4.75° [Atilla, 2007], 124.7 ± 7.4° [Noble, 1988] and 129.82 + 5.37° [Blanc, 2012].

In conclusion, the present study demonstrates that the proposed methodology based on gender-specific statistical shape modelling can be a valuable tool for automatically generating a large specific population of femurs to support implant design and planning of femoral reconstructive surgery.

Recently, the osteoregenerative properties of allograft have been enhanced by addition of autogenous skeletal stem cells to treat orthopaedic conditions characterised by lost bone stock. There are multiple disadvantages to allograft, and trabecular tantalum represents a potential alternative. This metal is widely used, although in applications where there is poor initial stability, or when it is used in conjunction with bone grafting, loading may need to be limited until sound integration has occurred. Strategies to speed up implant incorporation to surrounding bone are therefore required. This may improve patient outcomes, extending the clinical applications of tantalum as a substitute for allograft.

Background

Impaction bone grafting with milled human allograft is the gold standard for replacing lost bone stock during revision hip surgery. Problems surrounding the use of allograft include cost, availability, disease transmission and stem subsidence (usually due to shear failure of the surrounding allograft). Aims. To investigate various polymers for use as substitute allograft. The ideal graft would be a composite with similar mechanical characteristics as allograft, and with the ability to form de novo bone.

Background

Replacing bone lost as a consequence of trauma or disease is a major challenge in the treatment of musculoskeletal disorders. Tissue engineering strategies seek to harness the potential of stem cells to regenerate lost or damaged tissue. Bone marrow aspirate (BMA) provides a promising autologous source of skeletal stem cells (SSCs) however, previous studies have demonstrated that the concentration of SSCs required for robust tissue regeneration is below levels present in iliac crest BMA, emphasising the need for cell enrichment strategies prior to clinical application.

Background

Skeletal stem cells (SSCs) have been used for the treatment of osteonecrosis of the femoral head to prevent subsequent collapse. In isolation SSCs do not provide structural support but an innovative case series in Southampton, UK, has used SSCs in combination with impaction bone grafting (IBG) to improve both the biological and mechanical environment and to regenerate new bone at the necrotic site.

Introduction

Controversy exists as to whether the short external rotator tendons and capsule of the hip should be repaired after posterior approach primary total hip arthroplasty (THA). Recent studies using radiopaque markers have demonstrated that reimplantation of these muscle tendons fail early and may not prevent post operative dislocation.

Aims

Disease transmission, availability and economic costs of allograft have resulted in significant efforts into finding an allograft alternative for use in impaction bone grafting (IBG). Biotechnology offers the combination of skeletal stem cells (SSC) with biodegradable polymers as a potential solution. Recently polymers have been identified with both structural strength and SSC compatibility that offer the potential for clinical translation.

The aim of this study was to assess whether increasing the porosity of one such polymer via super critical CO₂ fluid foaming (SCF) enhanced the mechanical and cellular compatibility characteristics for use as an osteogenic alternative to allograft in IBG.

Aims

Impaction bone grafting with milled human allograft is the gold standard for replacing lost bone stock during revision hip surgery. Problems surrounding the use of allograft include cost, availability, disease transmission and stem subsidence (usually due to shear failure of the surrounding allograft).

The aim of this study was to investigate various polymers for use as substitute allograft. The ideal graft would be a composite with similar mechanical characteristics as allograft, and with the ability to form de novo bone.

The osteo-regenerative properties of allograft have recently been enhanced by addition of autogenous skeletal stem cells to treat orthopaedic conditions characterised by lost bone stock. There are however, multiple disadvantages to allograft, including cost, availability, consistency and potential for disease transmission, and trabecular tantalum represents a potential alternative. Tantalum is already in widespread orthopaedic use, although in applications where there is poor initial implant stability, or when tantalum is used in conjunction with bone grafting, loading may need to be limited until sound integration has occurred. Development of enhanced bone-implant integration strategies will improve patient outcomes, extending the clinical applications of tantalum as a substitute for allograft.

The aim of this study was to examine the osteoconductive potential of trabecular tantalum in comparison to human allograft to determine its potential as an alternative to allograft.

Human bone marrow stromal cells (500,000 cells per ml) were cultured on blocks of trabecular tantalum or allograft for 28 days in basal and osteogenic media. Molecular profiling, confocal and scanning electron microscopy, as well as live-dead staining and biochemical assays were used to characterise cell adherence, proliferation and phenotype.

Cells displayed extensive adherence and proliferation throughout trabecular tantalum evidenced by CellTracker immunocytochemistry and SEM. Tantalum-cell constructs cultured in osteogenic conditions displayed extensive matrix production. Electron microscopy confirmed significant cellular growth through the tantalum to a depth of 5mm. In contrast to cells cultured with allograft in both basal and osteogenic conditions, cell proliferation assays showed significantly higher activity with tantalum than with allograft (P<0.01). Alkaline phosphatase (ALP) assay and molecular profiling confirmed no significant difference in expression of ALP, Runx-2, Col-1 and Sox-9 between cells cultured on tantalum and allograft.

These studies demonstrate the ability of trabecular tantalum to support skeletal cell growth and osteogenic differentiation comparable to allograft. Trabecular tantalum represents a good alternative to allograft for tissue engineering osteo-regenerative strategies in the context of lost bone stock. Such clinical scenarios will become increasingly common given the ageing demographic, the projected rates of revision arthroplasty requiring bone stock replacement and the limitations of allograft. Further mechanical testing and in vivo studies are on-going.

Recent approaches have sought to harness the potential of stem cells to regenerate bone lost as a consequence of trauma or disease. Bone marrow aspirate (BMA) provides an autologous source of skeletal stem cells (SSCs) for such applications, however previous studies have demonstrated that the concentration of SSCs present in iliac crest BMA is below that required for robust bone regeneration. Here we present a novel acoustic-facilitated filtration strategy to concentrate BMA for SSCs, clinically applicable for intra-operative orthopaedic use.

The aim of this study was to demonstrate the efficacy of this strategy in concentrating SSCs from iliac crest bone marrow, as well as femoral canal BMA from older patients.

Iliac crest BMA (Lonza, Rockville, MD, USA) and femoral canal BMA was obtained with informed consent from older patients during total hip replacement. 5 to 40ml of BMA was processed via the acoustically-aided exclusion filtration process to obtain 2-8 fold volume reductions. SSC concentration and function was assessed by flow-cytometry, assays for fibroblastic colony-forming units (CFU-F) and multi-lineage differentiation along chondrogenic, osteogenic and adipogenic pathways examined. Seeding efficiency of enriched and unprocessed BMA (normalised to cell number) onto allograft was assessed.

Iliac crest BMA from 15 patients was enriched for SSCs in a processing time of only 15 minutes. Femoral BMA from 15 patients in the elderly cohort was concentrated up to 5-fold with a corresponding enrichment of viable and functional SSCs, confirmed by flow cytometry and assays for CFU-F. Enhanced osteogenic (P<0.05) and chondrogenic (P<0.001) differentiation was observed using concentrated aspirate, as evidenced by biochemical assay and semi-quantitative histological analysis. Furthermore, enhanced cell seeding efficiency onto allograft was seen as an effect of SSC concentration per ml of aspirate (P<0.001), confirming the utility of this approach for application to bone regeneration.

The ability to rapidly enrich BMA demonstrates potential for intra-operative application to enhance bone healing and offers immediate capacity for clinical application to treat many scenarios associated with local bone stock loss. Further in vivo analysis is ongoing prior to clinical tests.

Background

Skeletal stem cells can be combined with human allograft, and impacted to produce a mechanically stable living bone composite. This strategy has been used for the treatment of femoral head avascular necrosis, and has been translated to four patients, of which three remain asymptomatic at up to three year follow-up. In one patient collapse occurred in both hips due to widely distributed and advanced AVN disease, necessitating bilateral hip arthroplasty. However this has provided the opportunity to retrieve the femoral heads and analyse human tissue engineered bone.

Disease transmission, availability and economic costs of allograft have resulted in significant efforts into finding an allograft alternative for use in impaction bone grafting (IBG). Biotechnology offers the combination of skeletal stem cells (SSC) with biodegradable polymers as a potential solution. Recently polymers have been identified with both structural strength and SSC compatibility that offer the potential for clinical translation.

The aim of this study was to assess whether increasing the porosity of one such polymer via super critical CO2 dissolution (SCD) enhanced the mechanical and cellular compatibility characteristics for use as an osteogenic alternative to allograft in IBG.

High molecular weight PLA scaffolds were produced via traditional (solid block) and SCD (porous) techniques, and the differences characterised using scanning electron microscopy (SEM). The polymers were milled, impacted, and mechanical comparison between traditional vs SCD created scaffolds and allograft controls was made using a custom shear testing rig, as well as a novel agitation test to assess cohesion. Cellular compatibility tests for cell number, viability and osteogenic differentiation using WST-1 assays, fluorostaining and ALP assays were determined following 14 day culture with SSCs.

SEM showed increased porosity of the SCD produced PLA scaffolds, with pores between 50-100 micrometres. Shear testing showed the SCD polymer exceeded the shear strength of allograft controls (P<0.001). Agitation testing showed greater cohesion between the particles of the SCD polymer (P<0.05). Cellular studies showed increased cell number, viability and osteogenic differentiation on the SCD polymer compared to traditional polymer (P<0.05) and allograft (P<0.001).

The use of supercritical C02 to generate PLA scaffolds significantly improves the cellular compatibility and cohesion compared to traditional non-porous PLA, without substantial loss of mechanical shear strength. The improved characteristics are critical for clinical translation as a potential osteogenic composite for use in impaction bone grafting.

Impaction bone grafting with milled human allograft is the gold standard for replacing lost bone stock during revision hip surgery. Problems surrounding the use of allograft include cost, availability, disease transmission and stem subsidence (usually due to shear failure of the surrounding allograft).

The aim of this study was to investigate various polymers for use as substitute allograft. The ideal graft would be a composite with similar mechanical characteristics as allograft, and with the ability to form de novo bone.

High and low molecular weight (MW) forms of three different polymers (polylactic acid (PLA), poly (lactic co-glycolic) acid (PLGA) and polycaprolactone (PCL)) were milled, impacted into discs, and then tested in a custom built shear testing rig, and compared to allograft.

A second stage of the experiment involved the addition of skeletal stem cells (SSC) to each of the milled polymers, impaction, 8 days incubation, and then tests for cell viability and number, via fluorostaining and biochemical (WST-1) assays.

The shear strengths of both high/ low MW PLA, and high/low MW PLGA were significantly higher than those of milled allograft (P<0.001, P<0.001, P<0.005 and P<0.005) but high and low MW PCL was poor to impact, and had significantly lower shear strengths (P<0.005, P<0.001). Fluorostaining showed good cell survival on high MW PLA, high MW PCL and high MW PLGA. These findings were confirmed with WST-1 assays.

High MW PLA as well as high MW PLGA performed well both in mechanical testing and cell compatibility studies. These two polymers are good contenders to produce a living composite for use as substitute human allograft in impaction bone grafting, and are currently being optimised for this use via the investigation of different production techniques and in-vivo studies.

With an increasing ageing population and a rise in the number of primary hip arthroplasty, peri-prosthetic fracture (PPF) reconstructive surgery is becoming more commonplace. The Swedish National Hip Registry reported that, in 2002, 5.1% of primary total hip replacements required revision due to PPF. Laboratory studies have indicated that age, bone quality and BMI all contribute to an increased risk of PPF. Osteolysis and aseptic loosening contribute to the formation of loosening zones as described by Gruen, with subsequent increased risk of fracture. The aim of the study was to identify significant risk factors for PPF in patients who have undergone primary total hip replacement (THR).

Logbooks of three Consultant hip surgeons were filtered for patients who had THR-PPF fixation subsequent to trauma. Risk factors evaluated included sex, age, bone density (Singhs index), loosening zones, Vancouver classification, prosthesis stem angle relative to the axis of the femur, and length of time from THR to fracture. A control group of uncomplicated primary THR patients was also scrutinised.

Forty-six PPF were identified representing 2.59% of THR workload. The male: female ratios in both groups were not significantly different (1:1.27 and 1:1.14 respectively). Average age of PPF was 72.1, which was significantly older than the control group (54.7, p>0.05). The commonest type of PPF was Vancouver type B. Whilst stem position in the AP plane was similar in both groups, in lateral views the PPF stem angle demonstrated significant antero-grade leg position compared to the non-PPF group (p.0.05). The PPF group demonstrated a greater number of loosening zones in pre-fracture radiographs compared to the control group (2.59 and 1.39 respectively, p>0.05)

Our workload from PPF reflects that seen in Europe. Age, stem position and the degree of stem loosening appear to contribute to the risk of a peri-prosthetic fracture.

AIM

Avascular necrosis (AVN) of the femoral head is a potentially debilitating disease of the hip in young adults. Impaction bone grafting (IBG) of morcellised fresh frozen allograft is used in a number of orthopaedic conditions. This study has examined the potential of skeletal stem cells (SSC) to augment the mechanical properties of impacted bone graft and we translate these findings into clinical practice.

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).

Propionibacteria are organisms of low virulence, although they do cause deep periprosthetic infections. The aim of this study was to show that Propionibacteria do not always cause a significant rise in ESR and CRP.

Between May 2001 and May 2004, we identified 77 patients with prosthetic joint replacements colonised with Propionibacteria, 47 males and 30 females. There were 47 hip joint replacements, 27 knee joint replacements, 2 endoprosthetic replacements of the femur and 1 shoulder joint replacement. We retrieved successfully the medical records of 66 patients in order to identify the number of patients treated for an infected prosthetic joint arthroplasty. The pre-operative values of ESR and CRP were recorded. For the purposes of this study, an ESR rate of 30mm/hr or higher and a CRP level of 10mg/lt or higher were considered to be suggestive of infection and were deemed a positive result.

All of the 77 patients had both ESR and CRP measured pre-operatively. In only 16 (21%) both ESR and CRP were higher than 30mm/hr and 10mg/l respectively. In 33 patients (43%) with prosthetic joint replacements colonised with Propionibacteria, the pre-operative values of ESR and CRP were normal. 23 patients were treated for an infected prosthetic joint arthroplasty. In 7 (30%) of those patients both ESR and CRP were normal.

This suggests that normal pre-operative values of ESR and CRP in suspected failed prosthetic joint replacements might not exclude infection, if the causative organism is of low virulence such as Propionibacteria.

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: Total hip arthroplasty is one of the most frequently performed surgical procedures, with implants usually giving over 90% survival at 10 years. The failure rate is primarily due to aseptic loosening often associated with progressive bone stock loss. Impaction of cancellous morselized allografts with cement can be used for revision total hip arthroplasty in such cases. There is increasing interest in the use of synthetic bone graft substitutes as extenders to allograft due to the shortage and variable quality of allograft. A chemically-pure synthetic calcium phosphate (CaP) allograft extender is compared with allograft alone for acetabular and/or femoral revisions using the Impaction Grafting technique.

Methods: 96 hips in 94 patients underwent revision hip arthroplasty using impaction grafting at 4 sites. Hip revision using impaction grafting was carried out using the Exeter X-Change Instrumentation system, using an Exeter Stem and/or a cemented polyethylene cup. Patients were randomized to receive allograft or CaP plus allograft in a 50:50 volume. Clinical and radiographic assessment was conducted pre-operatively and immediately post-operatively and at 6, 12 and 24 months. Clinical assessments included Harris Hip, Oxford and Charnley modified Merle d’Aubigne scores. Clinical complications were also recorded. Radiographs were assessed for the graft quality, radiolucent lines, lyses or migration, and incorporation of graft. The X-rays were also independently reviewed by an experienced author.

Results: The mean age was 70.2 years (range 41–89 years) with 58 males and 36 females. A total of 40 femoral revisions and 88 acetabular revisions were conducted. There were 46 patients in the ApaPore group, 49 patients in the allograft group and 1 patient who received CaP/allograft and allograft for an acetabular and femoral revision respectively.

No deep infections or adverse events due to the CaP were reported, with no significant difference in complication rates including revision and re-operations. No significant difference in acetabular migration, femoral subsidence, radiolucencies and lyses between the groups was observed. The independent review found no difference between the groups in terms of migration. The bone density was apparently greater for the ApaPore group at 12 months (p=0.001) and 24 months (p=0.012) although the significance of this is unclear. No significant difference in the clinical measures was observed between the groups.

Conclusion: CaP is comparable with allograft in terms of performance and safety when used as an allograft extender for total hip revision arthroplasty using impaction grafting.

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: The senior author undertakes single stage revision hip arthroplasty for cases with no preoperative evidence of infection based on history and examination, ESR and CRP results and negative results from selective aspirations. Despite this a large proportion of intra-operative samples are positive for infection. The purpose of our study is to look at the results of intra-operative histology and microbiology samples in these cases and to assess the subsequent incidence of infection.

Methods: Retrospective case study comprising of 230 single stage revision total hip arthroplasties carried out by a single surgeon over 5 year period (2003–2008). Intra-operatively tissue samples were taken from multiple sites and sent for both histology and microbiology. Microbiology results were reported at 24hrs, 48hrs, 7 days and 21 days and correlated with histology reports.

Results: From a total number of 230 patients, we had 98 left and 132 right hip revision arthroplasties. There were 95 men and 135 women with a mean age of 73 years (range 40–93). Intra-operative microbiology was negative in 108 patients (46.95%), of which 3 patients’ histology samples were consistent with infection. Of the 122 microbiology positive patients (53.04%), there were 8 histology samples consistent with infection. The most frequent growths were of Coagulase negative Staphylococcus (64 cases) and Propionibacterium (18 cases). 3 cases subsequently developed deep infection.

Discussion: This study highlights a significant discrepancy between intra-operative microbiology and intra-operative histology results. There is also a very high discrepancy between pre-operative assessment and intra-operative microbiological findings although the majority of cases subsequently did not show any clinical evidence of infection.

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: The Corail stem is a well proven femoral implant used for the past 22 years. It is the most common uncemented femoral stem used for total hip replacements in the UK. The stem was modified in 2004 with an increased neck taper to allow for an increased range of bearings and modular heads. This study reviews a series of primary total hip replacements using this recently modified Corail stem to assess if this implant is still performing to acceptable standards.

Method: A prospective patient database collated by 2 arthroplasty surgeons recorded data at the time of operation and subsequent follow up. All intra-operative and post-operative complications were recorded. Pre and postoperative oxford hip scores were analysed.

Results: 751 cases were reviewed. The average age was 63 with females accounting for 69%. The pinnacle cup was used in 83% of cases, with a polyethylene bearing in 48%. Survival of the stem at 3 years was 99.9% (1 periprosthetic fracture following a fall), the cup 99.6%, with overall survival of 99.5%. The most common intra operative complication was calcar fracture occurring in 0.9%. Dislocation occurred in 0.5%, subsidence in 0.3%, deep infection in 0.1% and leg length discrepancy requiring shoe raise in 0.1%. Average 3 year oxford hip score was 12.

Discussion: 3 year survival of both the femoral stem and the total hip replacement are above the quoted rates in the National Joint Registry’s 4th annual report for corail and uncemented stems (98.8% and 98.1% respectively), and also exceeds that of cemented stems (99.1%). The same report quotes similar rates of calcar fractures (0.8%), although we recorded no other perioperative complications. We conclude the new generation of Corail stem has excellent 3 year performance.

Introduction: The advantages of metal on metal bearings (MoM) include improved wear characteristics and lower dislocation rate. Metal sensitivity and Aseptic Lymphocyte Dominated Vasculitis Associated Lesion (ALVAL) reaction are becoming increasingly recognised. The BOA has recently issued a statement regarding MoM bearings. They suggested that any revisions for symptoms of pain and soft tissue reaction should be reported to the MHRA and histological specimens forwarded to the Stanmore Retrieval Centre.

Methods and results: We report four patients (all females), who presented with late dislocation of a large diameter MoM bearing (three following total hip replacements and one following resurfacing). They all made good initial recovery with complete relief of pain. They developed pain around groin between one and two years following the surgery. Inflammatory markers were normal. MRI/Ultrasound scanning showed the presence of cystic lesions around the hip. They all presented with relatively late dislocation (26 months to six years). At exploration there was a large joint effusion with necrosis and detachment of the abductors. A characteristic finding was an avascular bare trochanter stripped free of any soft tissues. Histology showed a predominantly histiocytic response in keeping with the findings of Willert and Pandit.

Discussion: In the absence of any obvious causes for dislocation, one should have a high index of suspicion for the possibility of metal hypersensitivity causing joint effusion, muscle necrosis and thereby leading to instability due to the progressive periosteal and soft tissue erosion. These patients should be considered for early revision of the bearing surface to prevent further damage to the muscle and bone. If the abductors are completely detached a more constrained type of bearing should be used to improve the stability. To the best of our knowledge this is the first report of this unusual complication following MoM bearings.

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.

Weight gain is often reported by patients who succumb to impaired activity as a result of progressive osteoarthritis of the hip or knee. Optimistic views of weight loss after joint replacement are often held by patients. We studied the affect of lower limb arthroplasty on body weight.

We reviewed 144 patients having undergone hip and knee arthroplasty and were functionally well. Infected cases were excluded. Average age was 65 years and average follow up was 27 months. The Body Mass Index (BMI) was prospectively measured at follow up and compared to immediate pre-operative BMI.

Our findings demonstrated an average rise in BMI post-operatively which was statistically significant. A rise in post operative BMI was seen in patients who were obese to start with or those who had undergone a total hip replacement (statistically significant). Moderate rises were seen in patients who had underwent hip resurfacing procedures or those who were overweight preoperatively (p=0.06).

These findings are useful in informing patients of achievable expectations following joint replacement surgery and preoperative overweightness should be treated as a separate entity unrelated to co-existing joint degeneration.

Background The exclusion of infection at the site of a painful or failed prosthetic joint replacement is important for pre-operative planning and counselling. A variety of investigations can be used to assist in the diagnosis or exclusion of infection.

An ESR and CRP are widely used as the initial screening investigation to differentiate between aseptic and septic loosening of prosthetic joint replacements¹. Propionobacteria are organisms of low virulence, although they do cause deep peri-prosthetic infections². We believe that Propionobacteria do not always cause a significant rise in ESR and CRP.

Methods Between May 2001 and May 2004, we identified 78 patients with prosthetic joint replacements colonised with Propionobacteria. There were 48 hip joint replacements, 27 knee joint replacements, 2 endoprosthetic replacements of the femur and 1 shoulder joint replacement. There were 48 males and 30 females. The preoperative values of ESR and CRP were recorded. For the purposes of this study, an ESR rate of 30mm/hr or higher and a CRP level of 10mg/lt or higher were considered to be suggestive of infection and were deemed a positive result.

Results All of the 78 patients had both ESR and CRP measured preoperatively. In only 17 patients (22%) both ESR and CRP were higher than 30mm/hr and 10mg/l respectively. In 33 patients (42%) with prosthetic joint replacements colonised with Propionobacteria, the preoperative values of both ESR and CRP were normal.

Conclusion In our study we have shown that 33 out of 78 patients (42%) with prosthetic joint replacements colonised with Propionobacteria had normal preoperative of both ESR and CRP values. This is to suggest that normal preoperative values of ESR and CRP in suspected failed prosthetic joint replacements might not exclude infection, if the causative organism is of low virulence such as Propionobacteria.

Introduction: We have investigated the accuracy of a serological marker to distinguish between septic and aseptic loosening of Total Hip Replacements (THR). We present the preliminary results of our on-going prospective study.

Methods: After obtaining Ethical Committee approval, 46 patients were collected in 3 groups; “control” primary THR, revision THR for aseptic loosening, and revision THR for infection. Serum IgG responses to an exocellular bacterial antigen (Lipid S) were determined by enzyme-linked immunosorbent assay (ELISA).

Results: Our results show that the test can accurately differentiate between the patients with infected joint replacements and the control group. The test, to date, has a specificity of 93% and a sensitivity of 100%.

Discussion and Conclusion: This simple and cheap test can reliably assist in the accurate evaluation of a painful hip arthroplasty, and planning for revision surgery. It will also be useful in the management of patients in whom the microbiology results are either negative or based on a single isolate of an organism, which may be either a contaminant or a possible pathogen. This, in turn, would have implications on financial costs and the optimum use of available resources.

Introduction and Aims: We have investigated the accuracy of a serological marker to distinguish between septic and aseptic loosening of Total Hip Replacements (THR). We present the preliminary results of our ongoing prospective study.

Method: After obtaining Ethical Committee approval, 46 patients were collected in three groups: ‘control’ primary THR, revision THR for aseptic loosening and revision THR for infection. Serum IgG responses to an exocellular bacterial antigen (LipidS) were determined by enzyme-linked immunosorbent assay (ELISA).

Results: Our results show that the test can accurately differentiate between the patients with infected joint replacements and the control group. The test, to date, has a specificity of 93% and a sensitivity of 100%.

Conclusions: This simple and cheap test can reliably assist in the accurate evaluation of a painful hip arthroplasty, and planning for revision surgery. It will also be useful in the management of patients in whom the microbiology results are either negative or based on a single isolate of an organism, which may be either a contaminant or a possible pathogen. This, in turn, would have implications on financial costs and the optimum use of available resources.

Introduction and Aims: The usefulness of bone graft substitutes and growth factors to promote bone graft incorporation and prosthesis fixation in hip replacement should be examined in a loaded model, as results from cortical defect models may not apply. This paper reviews the results of femoral impaction grafting using these materials in an ovine hip replacement model.

Method: At cemented hemiarthroplasty, sheep femurs were impacted with allograft bone (control group n=23) or with allograft mixed with: 1) corglaes bioglass (n=12); 2) a synthetic hydroxyapatite (HA) (n=6) or the bone morpohogenetic protein OP-1 (n=6) (study groups) and implanted with a cemented double taper femoral stem. Sheep were sacrificed at between six and 26 weeks. The primary outcome was femoral stem subsidence, as determined more recently by the development of clinical radiostereometric analysis (RSA) in this model. Femoral fixation, as assessed by ex-vivo mechanical testing, and bone graft incorporation, as assessed by histological review and histoquantitation, were also key outcomes.

Results: In the control groups, there was a consistent response with bone graft incorporation by new bone advancing proximal to distally in the femur and advancing from the endocortex towards the cement mantle. Mineralised bone apposition occurred by six weeks and this was preceeded by partial resorption of the graft. Complete graft incorporation, with subsequent remodelling of bone, was evident proximally by 26 weeks. Bone graft incorporation in femurs impacted with a 1:1 allograft: bioglass mix was minimal and there was often partial or complete resorption of the graft with replacement by fibrous tissue, resorption of endocortical bone and instability of the femoral prosthesis. Supplementation of allograft with OP-1 promotes initial graft resorption, thus hastening bone graft incorporation and remodelling but one case of stem subsidence, that may have been associated with early resorption seen in the OP-1 group, reinforces the need for further studies examining dose response. There was excellent incorporation of the allograft and HA, with new woven bone directly apposing the HA surface and integrated into the larger porous spaces of the HA. There was no adverse response to the HA and there was minimal to no subsidence of the stem at the cement-bone interface, as determined by RSA.

Conclusion: This model is extremely valuable for investigating new biological approaches to reconstruction of major bone deficiency at revision hip replacement and demonstrates clear differences between materials used to supplement allograft, with HA and OP-1 giving encouraging results. RSA is an essential outcomes tool for this model.

To establish the efficacy of femoral impaction grafting in femoral reconstruction following sepsis, we identified and reviewed all cases of two stage hip revision for sepsis in which femoral impaction grafting was used in the second stage, performed in Exeter from 1989 until the end of 1998. All patients underwent a Girdlestone excisional arthroplasty, were prescribed local and systemic antibiotic treatment, and then subsequently underwent surgical reconstruction, using femoral impaction grafting.

These 53 cases represent a subgroup of our patients who had received a two-stage revision for infection during that period. The other patients did not require femoral grafting. 4 patients died within 24 months of surgery.

4 patients became reinfected (7.5%), and 1 patient underwent stem revision for a fracture below the tip of the stem at 10 months, leaving 44 patients with an average of 53 months follow up (range 24 to 122 months). These 44 patients all demonstrated improved clinical scores and satisfactory radiological outcomes.

Our clinical results reveal post-operative scores approaching those for primary arthroplasty. Our intermediate term results justify the use of fresh frozen allograft bone in the second stage of revisional hip surgery for its low incidence of reinfection and loosening, and potential to improve bone stock.

Introduction: The purpose of this study was to evaluate the micromotion of a femoral prosthesis relative to the femur in a revision hip replacement model.

Methods: A series of Ovine hip hemiarthroplasties were mechanically tested to detect micromotion of the femoral prosthesis relative to the femur 12 weeks following implantation. A mechanical testing device utilising muscle simulation of the major groups around the femur was designed. A 3D targeting system was developed using non-contact LASER transducers on the implant referenced to a second target on the overlying femur. Movement of this second target was measured with three LVDT’s (linear variable differential transformers).

Results: The system error was quantified in each femur to a resolution of the order of 15 microns. The mean micromotion, in 3D at two points assuming rigid body mechanics, was less than 50 microns for clinically stable implants. One stem was determined to be clinically loose and had a corresponding mean micromotion of 150 microns.

Conclusion: The method enabled measurement of 3Dmicromotion of a femoral prosthesis within the femur, during a laboratory approximation of normal physiological load cycles. The micromotion values corresponded to clinical outcomes, in a manner consistent with other reports in the literature. This system can be modified to allow targeting of different implants within a variety of bone types.

Introduction: New biological approaches to reconstruction of major bone deficiency such as the use of bone substitutes and growth factors are being developed. This paper reports on the adverse response to the Bioglass in comparison to allograft alone.

Aim: To compare the biological response to femoral impaction grafting and a cemented femoral stem when using allograft bone versus allograft bone plus a synthetic bone graft substitute, Bioactive glass.

Methods: Eighteen merino wethers underwent a left cemented hemi-arthroplasty and were randomised to have impaction allografting of the femur using either allograft alone (allograft group) or a 50:50 mix of allograft and Bioactive glass (Bioglass group). After sacrifice at 12 weeks, histological analysis of the femora at the levels of the proximal, mid and distal femoral stem and distal to the stem was undertaken.

Results: In the allograft group, there was a consistent response with bone graft incorporation being greatest in the proximal femur and occurring progressively less, more distally. Mineralised bone apposition in the graft occurred post-operatively after eight weeks. In contrast, in the Bioglass group, the response was inconsistent. Bone graft incorporation was either minimal, or there was partial or complete resorption of the bone graft with replacement by particulate-laden fibrous tissue and resorption of endocortical bone. Inflammation of the capsule tissue was noted in some cases.

Conclusion: In comparison to allograft alone, the use of Bioglass to supplement allograft for use in impaction grafting in ovine hip arthroplasty gave inferior results.

We report the mid-term results of femoral impaction grafting which was used in 53 patients during the second stage of a two-stage revision for an infected total hip replacement. We reviewed all cases performed between 1989 and 1998. All patients underwent a Girdlestone excision arthroplasty, received local and systemic antibiotics and subsequently underwent reconstruction, using femoral impaction grafting.

Four patients had further infection (7.5%), and four died within 24 months of surgery. One patient underwent revision of the stem for a fracture below its tip at ten months. This left 44 patients with a mean follow-up of 53 months (24 to 122). All had improved clinical scores and a satisfactory radiological outcome.