Introduction: Transcutaneous Amputation Prosthesis (ITAP) is an alternative for transfemoral amputees to conventional stump-socket prostheses which have many problems. These include: poor fit, stump pressure sores, pain, infections and unnatural gait. ITAP aims to overcome these by being osseointegrated into the femoral medulla with a pin protruding through the skin to which the external prosthesis attaches. Thus, the forces normally encountered by the stump soft tissues are now transferred directly to the skeleton. However, the transcutaneous pin produces a route for infection from the external to internal environment. Therefore, a key feature to the success of the ITAP is to produce a biological seal at the transcutaneous interface. Epithelial cells have been shown to attach to dental transcutaneous titanium devices via hemidesmosomes (HD).2 Focal contacts (FC) are also important in cell adhesion and to the underlying substratum.3 We grew human keratinocytes on different titanium surfaces to assess their morphology, ability to proliferate and produce HD and FC. Hypothesis: Surface topography influences keratinocytes morphology and proliferative capacity and expression of HD and FC.

Materials and Methods: 4 titanium alloy (Ti6Al4V) surface topographies were used (10mm x 4mm discs): polished, machine finished, sandblasted and hydrofluoric acid etched (HF) and a control – plastic thermanox. Surface roughness profiling of titanium discs were measured (Mitutoyo Surftest SV-400). HaCaT keratinocytes were grown on disc surfaces in wells of culture medium at +37oC, 5% CO2 and analysed at 1, 2, 3 and 4 days. Cells were processed to visualise HD with fluorescence microscopy using antibodies to the 6-integrin and plec-tin. Anti-vinculin antibodies were used to visualise FC. Fluorescein isothiocyanate (FITC) secondary antibodies enabled counting of structures (all product: Sigma-Aldrich, UK). Alamar blue (Serotec, UK) measured cell proliferation and SEM (surface morphology, cell area) and TEM were also performed. Cells grown on polished, machined and thermanox discs supported a regular, confluent layer with many cytoplasmic processes and dividing cells. HF and sandblasted discs grew an irregularly layer with fewer cytoplasmic processes and fewer dividing cells (not quantified). Day 3 TEM revealed HD, FC and desmosomes; cells on polished and thermanox were more closely packed and in layers.

Conclusion: Keratinocytes are significantly influenced by titanium surface topography. Smooth polished titanium alloy may be the ideal surface for a transcutaneous pin in the ITAP. Further experiments into isolating favourable biological components needed to encourage keratinocytes to attach onto titanium should be carried out.

Results: No significant difference shown in cell proliferation between titanium discs but cells on thermanox grew significantly more (p< 0.05). FC and HD numbers increased on all surfaces (days 1–3); a negative correlation between surface roughness and HD and FC numbers observed (lower Ra values = more HD and FC expressed).

Introduction: Conservative hip replacements are advantageous because resection of bone in the proximal femur is minimised. This study investigated a new design of conservative hip in the goat model where the femoral head was resected and two hydroxyapatite coated ‘pegs’ were introduced into the femoral neck. The hypothesis was that the ‘pegs’ would provide a direct method of transmitting forces within the femoral neck thus resulting in less adverse bone remodelling and reduced loosening. Bone stock is also preserved should subsequent revision be required.

Methods: Eight unilateral implants were inserted into the right femur of adult female goats for 1 year. Retrieved specimens were analysed radiographically and histologically. Image analysis was used to quantify bone attachment and total bone area adjacent to the implant. Tetracycline bone markers quantified bone turnover. Operated hips were compared with non-operated hips. The students t-test was used for comparative statistical analysis where p< 0.05 were classified as significant.

Results: Radiographic analysis demonstrated bone loss beneath the cup with increased bone density at the distal end of the pins (fig.1). Light microscopy revealed areas of new and mature bone adjacent to the implant. Osseointegration to the HA coating was observed. Bone markers established significantly decreased bone formation rates (p< 0.05) in bone adjacent to the implant in the operated versus control hips.

Image analysis results demonstrated an average bone attachment of 30.94% to the implant surface (fig 2). Greatest bone attachment occurred at the end of the pins (78.99%) contributing 22% of overall attachment to the implant. Least attachment occurred beneath the prosthetic cup (13.82%) and in the medial aspect adjacent to the central pin. Greater total bone area was measured in control hips and no significant correlation between bone attachment to the ‘pegs’ and bone area beneath the prosthetic cup was identified.

Discussion: From this study we have concluded that despite the resorption of bone beneath the prosthetic cup, the conservatve hip design investigated remained well fixed in the femur during the 1 year in vivo period. It appears that an implant design that resurfaces the femoral head with two pins used to transmit forces into the femoral neck is a useful approach in conservative hip design.

Introduction: The use of uncemented arthroplasty in joint replacement surgery requires osseointegration of the prosthesis to maximise function and longevity. It has been demonstrated that osteoblast-like cells will preferentially proliferate, differentiate and produce mineralised matrix in pits and grooves on non-biological surfaces, of similar dimensions to those of Howslip’s lacunae produced by osteoclasts in vitro. The hypotheses of this study were that a photochemically etched titanium alloy surface would 1) induce proliferation and differentiation in osteoblast-like cells; 2) induce osteoblastic differentiation of human mesenchymal stem cells and 3) induce greater bone to implant contact in a caprine model.

Methods: Three microgrooved titanium alloy surfaces (fine, medium & coarse) were created by photochemical etching, with dimensions of 200 to 515 microns. Human Mesenchymal stem cells (MSC) and Human Osteosarcoma (HOS) cells (TE-85) were seeded onto these surfaces and cultured in standard media; in the case of MSC, with and without the addition of osteogenic supplements. At intervals of time each surface and cell type were assessed for proliferation by Alamar blue assay and osteoblastic differentiation by Alkaline Phosphatase expression. A polished titanium surface was used as a control. A plate of each surface dimension was placed into a femoral condyle of ten adult male goats. The animals were euthanased at 6 and 12 weeks post-implantation. The specimens were histologically processed and examined under light and backscattered electron microscopy to establish the percentage of bone to implant contact and the presence of new bone within the grooves.

Results: In vitro, all cells showed an increase in proliferation with time, the greatest occurring on the coarse surface. Alkaline phosphatase expression showed a rise with time on all surfaces, the greatest being on the coarse surface seeded with HOS cells (p< 0.05). MSC could not be induced to differentiate to an osteogenic lineage by these surface textures alone. On addition of osteogenic supplements their results followed the trends of HOS cells. In vivo, histomorphometric analysis showed significantly greater bone implant contact on the coarse surface at both 6 and 12 weeks (p< 0.05). In a number of cases there were signs of osteogenesis occurring deep within the pits and grooves.

Discussion: This study confirms that a photochemically etched surface topography mimicking that created by osteoclasts will increase the proliferation and differentiation of osteoblastic cells in vitro. The rate of differentiation of these cells increased significantly in relation to the size of the grooves. When implanted in vivo these same surfaces were shown to support osseointegration. This surface has the potential to improve the function of uncemented arthroplasties in the future.

Introduction: Bone marrow derived stromal stem cells (BMSSC’s) have the ability to differentiate into a variety of mesenchymal tissues including bone. The objective of this study was to evaluate the use a hydroxyapatite – BMSSC (HA-BMSSC) composite graft for posterior spinal fusion in a rabbit model.

Method: The HA- BMSSC composite graft was prepared by seeding rabbit marrow derived BMSSC’s onto 5 grams of HA granules which were cultured for a further 7 days prior to implantation. Bilateral posterior L4–L5 interlamina spinal fusion was performed using the HA- BMSSC composite graft (4 Rabbits), hydroxyapatite(HA) granules (6 rabbits) or autologous bone graft obtained from the iliac crest (6 rabbits). Rabbits were sacrificed at 5 weeks. Fusion was assessed by manual palpation. Quantitative histological analysis of cartilage, fibrous tissue and bone in the mid portion of the graft was performed using image analysis software.

Results: Three of four of the HA- BMSSC grafts fused successfully compared to 5 of 6 of the autologous bone grafts and 0 of 6 of the HA control grafts. The fusion rate was significantly higher in the iliac crest and HA- BMSSC groups than the HA control group (p< 0.05). In both the HA control and HA stem cell composite grafts there was ingrowth of new bone and encasement of HA granules by new trabecular bone at the graft – host interface. Within the mid region of the grafts there was bone formation in 2 of four fusion masses in the HA- BMSSC group comprising 26% and 45% of tissue in the area examined. In contrast bone formation was seen in the centre of only one of the six 6 HA fusion masses and amounted to only 2% of tissue. There was no significant difference in average percentage area of new bone, cartilage or fibrous tissue within the central region of the HA and HA-BMSSC grafts. There was a higher mean percentage area of new bone formation within the autologous bone graft (27%) than the HA control group (0.3%). p< 0.02.

Discussion: The BMSSC –HA composite was as effective as autologous graft and superior to HA in promoting fusion, but HA when used alone was ineffective. A positive finding to support the osteogenic potential of the stem cell loaded HA granules was the presence of moderate amounts of enchondral new bone isolated within the central regions of the graft away from the graft host interface in 2 of 4 fusion masses. In contrast the HA control grafts only supported significant amounts of bone formation in the periphery, adjacent to the host bed.

We used a knee-sparing distal femoral endoprosthesis in young patients with malignant bone tumours of the distal femur in whom it was possible to resect the tumour and to preserve the distal femoral condyles. The proximal shaft of the endoprosthesis had a coated hydroxyapatite collar, while the distal end had hydroxyapatite-coated extracortical plates to secure it to the small residual femoral condylar fragment. We reviewed the preliminary results of this endoprosthesis in eight patients with primary bone tumours of the distal femur. Their mean age at surgery was 17.years (14 to 21). The mean follow-up was 24 months (20 to 31). At final follow-up the mean flexion at the knee was 102° (20° to 120°) and the mean Musculoskeletal Tumour Society score was 80% (57% to 96.7%).

There was excellent osteointegration at the prosthesis-proximal bone interface with formation of new bone around the hydroxyapatite collar. The prosthesis allowed preservation of the knee and achieved a good functional result. Formation of new bone and remodelling at the interface make the implant more secure. Further follow-up is required to determine the long-term structural integrity of the prosthesis.

Introduction: Many mini compression screws are now available for fixation in procedures such as metatarsal osteotomies or arthrodeses of the foot.

The aim of the current study is to compare the compression forces achieved by the relatively new commercial mini compression screws on cortical and cancellous bone models.

Material and Methods: The screws that were tested are listed in the table below. All screws apart from the AO screws are headless and cannulated; and all screws apart from the AO cortical screw are self-tapping. The compression forces were tested by inserting a pressures load measurement cell between longitudinally-split sheep tibia as a cortical bone model and longitudinally split retrieved femoral heads as a cancellous bone model. The screws were inserted across the 2 halves with gradual compression after allowing the reading of the cell to settle.

Results: The Headed AO 3.5 mm cortical screw gave the best compression force, both in cortical and cancellous bone and the Bold was the weakest both in cortical and cancellous bone. The relative compression forces of the other tested screws were different between cortical and cancellous bone. Compression with the headless screws was lost as soon as the screw penetrated through the cortex in the cortrical bone model.

Conclusions: The indications for using headless self-tapping screws should be reserved for fixation of cancellous bone or of metatarsal or Akin osteotomies where compression is not required for union. When compression is important, such as in MPJ, tarso-metatarsal or talo-navicular arthrodeses, Headed AO 3.5 mm or 2.7 mm cortical or 4 mm cancellous screws, which give better compression, should be used.

We report our early experience with the use of a non-invasive distal femoral expandable endoprosthesis in seven skeletally immature patients with osteosarcoma of the distal femur. The patients had a mean age of 12.1 years (9 to 15) at the time of surgery. The prosthesis was lengthened at appropriate intervals in outpatient clinics, without anaesthesia, using the principle of electromagnetic induction. The patients were functionally evaluated using the Musculoskeletal Tumour Society scoring system. The mean follow-up was 20.2 months (14 to 30). The prostheses were lengthened by a mean of 25 mm (4.25 to 55) and maintained a mean knee flexion of 110° (100° to 120°). The mean Musculoskeletal Tumour Society score was 68% (11 to 29). Complications developed in two patients; one developed a flexion deformity of 25° at the knee joint, which was subsequently overcome and one died of disseminated disease. The early results from patients treated with this device have been encouraging. The implant avoids multiple surgical procedures, general anaesthesia and assists in maintaining leg-length equality.

Introduction: Surgeons in the UK and Europe generally use a thinner cement mantle than their counterparts in the USA for the femoral component in total hip replacement. The aim of this study was to compare the performance of different thicknesses of cement mantle using finite element analysis. A linear-elastic model of the implanted femur is used to give a prediction of the stresses in the cement mantle and in the femoral cortex. These measures give an indication of cement cracking rates and stress shielding. To assess the reliability of our model in representing patients with different bone densities, we use a range of cancellous bone stiffnesses.

Method: Two cadaveric femora from the same donor were sized, reamed and implanted with identical Stanmore Hips. One was prepared using UK rasps, over-reaming by 2mm, the other using US rasps, over-reaming by 5mm. Serial CT-scans were used to create three-dimensional geometric models of the implanted femora. Two finite element meshes were hand-built in MSC.Marc finite element software, incorporating cortical and cancellous bone, bone cement and prosthesis, with a bonded stem-cement interface. Loading conditions were chosen to represent the heel-strike phase of gait. In order to assess the impact of variability in patient bone density, cancellous bone modulus was varied between 0.06 and 2.90 GPa.

Results: Equivalent stress was examined on the external surface of the cortex and the internal surface of the cement mantle. The lowest cortical bone stresses were proximal and the highest cement stresses around the distal tip of the prosthesis. In the proximal cortex, higher equivalent stresses were observed medially and laterally with a thick cement mantle. Distally, lower cement stresses were observed in the thick cement mantle. With the highest cancellous modulus, there was little difference between the two models. As this modulus was reduced, stress differences between the models became more apparent.

Discussion: Proximal stress shielding was greatest in the calcar, in agreement with clinical findings. The thicker cement mantle led to less stress shielding in this region. Cement stresses, highest around the distal tip of the prosthesis, were larger in the thin cement mantle. This suggests a higher rate of both cracking and bone resorption with thin cement mantles, particularly in patients with low bone density.

Introduction Tissue engineering aims to produce a cellular structure in an extracellular matrix, which when implanted heals tissue defects.

To tissue-engineer bone suitable cells need to be grown on a scaffold. In this study we grew human marrow cells as they can differentiate into osteoblasts, on porous hydroxyapatite (HA) scaffolds, as this is osteoconductive, allows cell penetration and in growth of capillaries after implantation.

Increased extravascular perfusion through bone increases new bone formation. So we reproduced these physiological conditions in our novel bioreactor by perfusing scaffolds at 6ml/hr.

Hypotheses 1. Culture in our bioreactor improved cell penetration through HA scaffolds compared to static conditions. 2. Human mesenchymal stem cells (MSCs) cultured in our bioreactor differentiated into osteo-blasts and produced bone extracellular matrix.

Method MSCs were isolated from 8 human bone marrow aspirates taken from patients following informed consent. For each experiment 16 scaffolds were seeded with MSCs and comparisons were made between the two conditions. After 7 days culture the scaffolds were sectioned longitudinally and the number of cells at increasing depths were counted. The scaffolds were observed under SEM & TEM. Osteoblastic markers ALP and type I pro-collagen (PICP) were measured.

Results Penetration of cells through the scaffolds was significantly greater when cultured in the bioreactor.

After 14 days in bioreactor culture the HA was covered with cuboidal cells, consistent with osteoblasts, however in static culture cells remained fibroblastic. TEM results showed that MSCs in the bioreactor produced organised collagen matrix after 21 days and osteoid by 28 days, but no collagen matrix was observed following static culture.

ALP and PICP were significantly greater over 15 days culture when in our bioreactor.

Conclusions These results show that when MSCs were cultured in our bioreactor they attached and penetrated through porous HA scaffolds, whereas in static conditions few cells penetrated below 2mm. Our bioreactor significantly improved 3-dimensional growth, resembling tissue.

Moreover, MSCs grown on HA in the bioreactor produced significantly more ALP and PICP indicating osteoblastic differentiation. Furthermore, bone osteoid was produced.

Therefore this culture method could be use to convert autologous MSCs from human marrow into tissue-engineered bone which could be used to heal defects after tumor excision.

Introduction: Total femoral endoprosthetic replacement can be an alternative to amputation following extensive tumour excision or in cases of severe bone loss. In skeletally immature patients the problem of leg length inequality may be overcome by the use of extendable prostheses. The aim of this study is to assess the functional outcome of patients following total femoral endoprosthetic replacement.

Methods: This is a retrospective, single centre study of 16 patients who underwent consecutive total femoral replacements between 1978 and 1999. Information was collected from the Bone Tumour database, medical records and clinical review. The prostheses were custom made by the Biomedical Engineering Department of University College London and Stanmore Implants Worldwide. The implants are composed of a Titanium alloy shaft with Cobalt-Chrome bearing surfaces, incorporating a SMILES (Stanmore Modular Individualised Lower Extremity System) knee joint. Outcome was assessed using the Musculoskeletal Tumour Society (MTS) rating score.

Sample: Eight patients were male and eight female. Mean age was 35 years (range 5–75 years). Ten patients underwent total femoral replacement as a primary procedure; nine for malignant tumour and one for hydatid disease. Of the patients with malignancy five had metastases at the time of presentation. The other indications were failed distal femoral replacement in four cases and periprosthetic fractures in the remaining two. Four children received extendable prostheses.

Results: Of the patients with malignant disease, all but one had complete tumour excision. Three patients developed local recurrence. Two patients died of metastases within one year of diagnosis and three more died within five years. Three required revision procedures. Two more dislocated at the hip joint. Other complications included infection and lymphoedema. In patients surviving longer than one year the average range of motion at the hip was 85 degrees and at the knee 80 degrees. Using the MTS rating score the mean functional outcome was 60% of normal (range 27–90%). Of the survivors one achieved an excellent result, five were good, four fair and one poor.

Conclusion: Total femoral endoprosthetic replacement can be effective in limb salvage and provide an alternative to amputation. Good functional results can often be achieved. However, the complication rate is high and the outcome extremely varied.

Introduction: Long term performance of total knee replacements is governed by wear of ultra-high molecular weight polyethylene (UHMWPE) which leads to aseptic loosening of the implant. Little has been done to reduce wear due to the femoral component properties in knee joint replacement. Scratching of the femoral component has been identified in retrieved knee replacements. Using a material that has a higher scratch resistance than current metals may reduce the rate of UHMWPE wear in knee replacements. In this study we investigated the effects of using an oxidized Zirconium femoral component has on wear in knee replacements.

Methods: Total knee replacements made of CoCr and oxidised zirconium were tested in a four station, six degrees of motion knee simulator for 4 million cycles. The surface roughness values (Ra, Rz and Sm) for the metal counterfaces was measured through the test. In addition gravimetric wear of the UHMWPE inserts was recorded. Scanning electron microscopy of the two counterface surfaces was performed to provide information on possible mechanisms involved in the wear process.

Results: The starting surface roughness for both CoCr and oxidised zirconium were similar (Ra=0.03m). Oxidised zirconium was significantly more scratch resistant than CoCr; Ra (mean average roughness) of 0.7m compared to 0.43m (p< < 0.01) at end of test, with similar differences in the other surface roughness parameters. This was accompanied by a 4 fold reduction in wear of UHMWPE 49.60mg to 12.48mg (p=0.02).

SEM analysis of the surfaces of the metals revealed large deep scratches of the CoCr implants which were aligned in the A-P sliding direction. Barium sulphate particles were seen embedded in the surface of the femoral component. Voids were seen in the surface of the cobalt chrome and particles of silicate polishing powder were seen in these voids. There was also evidence of scratches originating at these voids. By contrast oxidised zirconium, showed small amounts of superficial scratching with an intact surface and no evidence of third body particles.

Summary and conclusions: Oxidised zirconium leads to a reduction in wear of UHMWPE due to its increased resistance to third body wear. It has the potential to increase the longevity of total knee replacements by reducing wear of UHMWPE. Additionally, polishing powder used in the manufacture of cobalt chrome femoral components of knee joint replacements is a potential source of third body particles.

Introduction and Aims: Retrospective analysis of 25 consecutive metal-on-metal proximal femoral replacements performed at our unit between 1965 and 1979.

Method: Patients were clinically evaluated using the Modified Harris hip and Enneking Scoring Systems and radiologically evaluated using the ISOLOS scoring system. The concentration of Cr, Co, Ti, Al, V, Mo & Ni in whole blood and urine was also measured by High-Resolution Inductively Coupled Mass Spectrometry and compared with controls and patients with other implants.

Retrieved prostheses (in-situ for in excess of 25 years) were analysed for roughness and wear using a Mitutoya form tracer and an electron microscope.

Results: Thirteen patients have since died, nine from metastatic disease and four from other causes. Of the remainder, 11 (44%) are still alive, five still retaining metal-on-metal articulations and one has been lost to follow-up. They have been in-situ for an average of 32 years. The average modified Harris hip score is 76 (53–93) and the average Enneking Score is 74 (63–90).

In the retrieved prostheses the contact zones were found to be smoother (Ra 0.05mm), have fewer and smaller carbides, together with evidence of ‘self-healing’ when compared to the original surface (Ra 0.32mm).

Blood and urine levels of Co & Cr were significantly elevated. Co levels were exceptionally elevated in loose prostheses, but levels quickly fell following revision.

Conclusion: We have shown the potential longevity of metal-on-metal arthroplasty. The wear seen in retrieved specimens is low and we might expect to improve the fixation by reducing the torque with apical bearing and encouraging extra-cortical bone bridging with hydroxy-apatite-coated collars. Elevated serum and urine Co levels may well predict a loose prosthesis and may be useful as a screening tool.

Introduction: Functional outcome following proximal tibial replacement can be impaired by extensor mechanism inefficiency. Current methods used to re-attach the patellar tendon result in varied levels of extensor function. Successful attachment of the patellar tendon requires initial mechanical stability and long-term biological fixation. We have employed a prosthesis, to model patellar tendon re-attachment, to test the hypothesis that biological augmentation of an implant which can provide sufficient mechanical integrity will allow a tendon-implant interface to develop that is similar in function and morphology to a normal tendon-bone interface.

Methods: The right patellar tendon in 24 Skeletally mature Friesland ewes was transfixed between the interlocking spikes of a hydroxyapatite-coated, customized tendon clamp to simulate patellar tendon re-attachment to a proximal tibial replacement. In 12 animals (Autograft group) the clamp attachment was augmented with autologous cancellous bone and marrow graft harvested from the ipsilateral iliac crest at the time of surgery, whilst the remaining animals (HA group) served as un-supplemented controls. Functional outcome was assessed using force plate measurements and two-dimensional optical kinematic gait analysis. Animals were euthanised at 6 and 12 weeks. The specimens were harvested, processed for histology and examined using light microscopy.

Results: The clamp device provided sufficient mechanical fixation of the patellar tendon to allow immediate weight bearing. Gait analysis showed that the range of movement of the stifle (knee) joint was not compromised by the surgical intervention at 6 or 12 weeks post-operation. An extensor lag observed at 6 weeks in both the Autograft and HA group was seen to fully recover by 12 weeks post-operation. There was a significant increase in functional weight bearing through the operated limb of the Autograft group animals between 6 and 12 weeks, which was not observed in the HA group. The tendon-implant interface in the HA group animals showed a fibrous tissue encapsulation of the HA coated surface, with collagen fibrils running parallel to the implant surface. In the Autograft group at 6 weeks post-operation a soft tissue – bone – HA interface had developed, similar in morphology to that of an indirect-type enthesis. Perpendicular orientated Sharpey’s-like fibres were observed spanning the region between the tendon and the HA coated implant and the bone graft material was seen to be undergoing active remodelling. By 12 weeks post-operation the interface was layered with regions of fibrocartilage clearly visible, more closely resembling the morphology of a direct-type enthesis.

Discussion: The clamp device provided sufficient mechanical fixation of the patellar tendon to allow immediate use the operated limb. The incorporation of a bio-active implant coating and biological augmentation encouraged a neo-enthesis to develop with near normal functional properties, and morphology similar to that of a normal patellar tendon-bone direct-type enthesis.

Introduction: The aim of this study is to develop a novel approach to tissue engineering in vivo, in which the adaptive response of skeletal tissues to the imposed mechanical environment will be utilised to induce a cartilaginous resurfacing of the acetabular articulation in a hemi-arthroplasty model of hip replacement. Our hypothesis was that a cartilaginous resurfacing of subchondral bone can be induced by applying stresses of 0 to 3 MPa to the articular surface of the acetabulum. We used an ovine hemiarthroplasty model where the stresses on the acetabulum were engineered by using different femoral head sizes.

Methods: Three groups of six sheep received unilateral hip hemi-arthroplasties and were sacrificed 24 weeks post-operatively to harvest the acetabula. At operation, acetabular cartilage was removed completely and the subchondral bone was reamed down and left bleeding. Three femoral head sizes, 25, 28, and 32-mm, were used to induce different contact stress levels. Vertical ground reaction force (GRF) data were measured and normalised by body weight for both limbs pre-operatively and every 4 weeks post-operatively. Five specimens from each group and eight unoperated controls were processed and stained with Safranin O and Sirius Red. Cartilage proteoglycans in the regenerated tissues from four specimens in the 25-mm group were detected by immunoblotting using specific monoclonal antibodies.

Results: The operated limbs were subjected to an average of 80 to 90% pre-operative GRF after the eighth post-operative week and maintained till the end of the study. No significant difference was noted during the period between the three groups. A layer of regenerated tissue was noted on all specimens processed and was Sirius positive. Four operated specimens processed in the 25-mm group and three in the 28-mm group were Safranin O positive. The presence of cartilage aggrecan, cartilage link proteins, biglycan, and decorin was confirmed by immunoblotting.

Discussion and Conclusion: We conclude that a cartilaginous resurfacing of acetabulum can be induced in vivo under the mechanical environment imposed by our hemi-arthroplasty model. This approach may be advantageous in clinical practice as a regenerated acetabular cartilaginous surface would avoid the problems associated with wear of the plastic acetabular cup and replacement of the acetabulum.

Introduction: The treatment of bone defects that occurs following fractures, the excision of bone tumours and at revision arthroplasty surgery, often involves the use of either autologous or allogenous bone grafts. However, both grafts have limitations. The aim of tissue engineering is to produce cells within an extracellular matrix that resembles tissue, which can be implanted into a patient to heal a tissue defect. The potential to engineer bone tissue grafts from patients’ autologous cells would improve the treatment of bone defects.

Bone marrow contains cells, known as mesenchymal stem cells (MSCs), which have the ability to differentiate into osteoblasts. To create a 3-dimensional structure necessary for the reconstruction of tissue, cells need to be grown on a scaffold, for which hydroxyapatite (HA) was used, as it is osteoconductive. In living bone, increased extravascular perfusion increases new bone formation. Thus, these physiological conditions were reproduced in our novel bioreactor by perfusing MSCs seeded on porous HA scaffolds at a rate of 6ml/hr. Hypotheses: 1. Culture in this bioreactor improves cell penetration through a HA scaffold. 2. MSCs cultured on HA in this bioreactor differentiated into osteoblasts.

Method: MSCs were isolated from 8 bone marrow aspirates, which were taken from patients during orthopaedic procedures following informed consent. For each experiment, MSCs from each patient were seeded onto 2 x 1cm³ scaffolds. To test cell penetration, the HA scaffolds were cultured for 7 days, then sectioned longitudinally and the number of cells were counted at increasing depths. Observations of MSCs on HA were compared under scanning (SEM) and transmission (TEM) electron microscopy. The HA scaffolds were cultured with MSCs in the bioreactor for 5, 10 & 15 days, after which time alkaline phosphatase (ALP) and type I pro-collagen protein levels were measured.

Results: Penetration of cells through the porous HA scaffold was significantly greater when the cells had been cultured in the bioreactor (P< 0.05). Observing MSCs after 7 days in bioreactor culture under SEM, adherent fibroblastic cells formed a network over the HA. However, by 14 days the HA was covered with cuboidal cells, consistent with osteoblasts. TEM results showed that MSCs cultured on HA in the bioreactor produced organised collagen matrix after 28 days. Osteoblastic protein levels were significantly greater at each time point when MSCs were cultured in bioreactor conditions: ALP (P< 0.005) and type I pro-collagen (P< 0.05).

Discussion and Conclusions: These results show that when cultured in our novel bioreactor, MSCs penetrated uniformly through the porous HA scaffold, whereas few cells penetrated in static culture conditions. Thus, our bio-reactor significantly improves the 3-dimensional growth of cells, resembling tissue. Moreover, in this study MSCs grown on HA in the bioreactor produced significantly larger amounts of ALP and type I pro-collagen, indicating that the MSCs differentiated into osteoblasts. Observations under TEM showed extracellular collagen matrix production which, when mineralized, produces bone.

Therefore, this culture method could potentially be used to convert MSCs, isolated from patients’ bone marrow, into tissue-engineered bone.

Introduction: Bone grafts are frequently used in orthopaedic operations to augment bone healing. Autologous bone graft is the gold standard for osteogenesis, but the amount available from the patient’s iliac crest is often insufficient to fill the defect and donor site morbidity is a significant complication. Alternatively, allograft can be implanted into patients, however, processing is necessary to reduce the immunicity of the graft and the risk of transmission of infection, but this destroys osteoprogenitor cells and hence reduces the osteogenic properties of the graft. Mesenchymal stem cells (MSCs) are present in bone marrow and have the ability to differentiate into osteoblasts. Therefore our study examined the use of MCSs, from bone marrow, to enhance the osteogenic properties of allograft.

Hypothesis: MSCs cultured on freeze-dried ethylene oxide treated bone allograft differentiate into osteoblasts, thereby increasing the osteogenic nature of the graft material.

Method: After informed consent, bone marrow aspirates were taken from 10 patients during elective orthopaedic operations. MSCs were characterized using Stro-1 antibody and grown on freeze-dried ethylene oxide treated bone allograft in vitro.

The hypothesis was tested on three groups of graft, with eight samples in each group. Firstly, freeze-dried ethylene oxide treated bone graft was tested (group 2). For a negative control, allograft was heated to 70°C to denature the osteogenic proteins (group 1). The final group tested the effect of additional osteogenic supplements (100nM dexamethasone, 0.05mM ascorbic acid and 10mM (-glycerol phosphate) on MSCs on allograft (group 3).

Osteoblastic differentiation of MSCs was observed under scanning (SEM) and transmission (TEM) electron microscopy, and by measuring protein levels: alkaline phosphatase (ALP), osteopontin and type I pro-collagen over 14 days.

Results: SEM confirmed that MSCs could be successfully cultured on bone allograft. Cells grown in groups 2 and 3 were characteristic of metabolically active osteoblasts and collagen extracellular matrix was observed under TEM. The amount of ALP protein produced by MSCs cultured in groups 2 and 3 increased significantly over 14 days (P< 0.05), but there was no increase in group 1. ALP, osteopontin and type I pro-collagen production was significantly greater for group 2 than for group 1 and for group 3 than for group 2 (P< 0.05).

Discussion and Conclusions: ALP, type I pro-collagen and osteopontin proteins are known to be produced by osteoblasts during increasing cell maturation and the levels of each of these proteins increased significantly when MSCs were cultured on allograft for 14 days compared with the negative control. The addition of osteogenic supplements significantly increased production of these proteins. Furthermore, MSCs cultured in groups 2 and 3 produced extracellular collagen matrix. These results are consistent with allograft causing MSCs to differentiate into osteoblasts and that this differentiation increases with additional osteogenic supplements.

This study confirms that MSCs, derived from autologous bone marrow, could be used to increase the osteogenic potential of allograft, thereby increasing bony healing in patients.

Background: Interventional MRI provides a novel non-invasive method of in-vivo weight-bearing analysis of the subtalar joint. Preceding in-vivo experimentation with stereophotogammetry of volunteers embedded with tantalum beads has produced valuable data on relative talo-calcaneal motion (Lundberg et al. 1989). However the independent motion of each bone remains unanswered.

Materials and Methods: Six healthy males (mean 28.8 years), with no previous foot pathology, underwent static right foot weight bearing MRI imaging at 0°, 15° inversion, and 15° eversion. Using identifiable radiological markers the absolute and relative rotational and translational motion of the talus and calcaneum were analysed.

Results and Discussion: Inversion: The calcaneum externally rotates, plantar-flexes and angulates into varus. The talus shows greater plantar-flexion with similar varus angulation, with variable axial rotation. Relative talo-calcaneal motion thus involves, 6° relative talar internal rotation, 3.2° flexion and no motion in the frontal plane. Concurrently the talus moves laterally on the calcaneum, by 6.5mm, with variable translations in other planes. This results in posterior facet gapping and riding up of the talus at its posterolateral prominence. Eversion: The calcaneum plantar-flexes, undergoes valgus angulation, and shows variable rotation in the axial plane. The talus plantar-flexes less, externally rotates, and shifts into varus. Relative motion in the axial plane reverses rotations seen during inversion (2.5° talar external rotation). The 8° of relative valgus talo-calcaneal angulation is achieved consistently through considerable varus angulation of the talus, in a direction opposite to the input motion. This phenomenon has not been previously reported. From coronal MRI data, comparative talo-calcaneal motion in inversion is prevented by high bony congruity, whereas during eversion, the taut posterior tibio-talar ligament prevents talar valgus angulation.

Conclusion: We have demonstrated that Interventional MRI scanning is a valuable tool to analysing the weight bearing motion of the talo-calcaneal joint, whilst approaching the diagnostic accuracy of stereophoto-gammetry. We have also demonstrated consistent unexpected talar motion in the frontal plane. Talo-calcaneal motion is highly complex involving simultaneous rotation and translation, and hence calculations of instantaneous axes of rotation cannot effectively describe talo-calcaneal motion. We would suggest that relating individual and relative motion of the talus / calcaneum better describes subtalar kinematics.

Metal-on-metal hip bearings are being implanted into younger patients. The consequence of elevated levels of potentially carcinogenic metal ions is therefore a cause for concern. We have determined the levels of cobalt (Co), chromium (Cr), titanium (Ti) and vanadium (Va) in the urine and whole blood of patients who had had metal-on-metal and metal-on-polyethylene articulations in situ for more than 30 years. We compared these with each other and with the levels for a control group of subjects.

We found significantly elevated levels of whole blood Ti, Va and urinary Cr in all arthroplasty groups. The whole blood and urine levels of Co were grossly elevated, by a factor of 50 and 300 times respectively in patients with loose metal-on-metal articulations when compared with the control group. Stable metal-on-metal articulations showed much lower levels. Elevated levels of whole blood or urinary Co may be useful in identifying metal-on-metal articulations which are loose.

Massive endoprostheses using a cemented intramedullary stem are widely used to allow early resumption of activity after surgery for tumours. The survival of the prosthesis varies with the anatomical site, the type of prosthesis and the mode of fixation. Revision surgery is required in many cases because of aseptic loosening. Insertion of a second cemented endoprosthesis may be difficult because of the poor quality of the remaining bone, and loosening recurs quickly.

We describe a series of 14 patients with triplate fixation in difficult revision or joint-sparing tumour surgery with a minimum follow-up of four years. The triplate design incorporated well within a remodelled cortex to achieve osseomechanical integration with all patients regaining their original level of function within five months.

Our preliminary results suggest that this technique may provide an easy, biomechanically friendly alternative to insertion of a further device with an intramedullary stem, which has a shorter lifespan in revision or joint-sparing tumour surgery. A short segment of bone remaining after resection of a tumour will not accept an intramedullary stem, but may be soundly fixed using this method.

This study investigates the use of porous biphasic ceramics as graft extenders in impaction grafting of the femur during revision hip surgery.

Impaction grafting of the femur was performed in four groups of sheep. Group one received pure allograft, group two 50% allograft and 50% BoneSave, group three 50% allograft and 50% BoneSave type 2 and group four 10% allograft and 90% BoneSave as the graft material. Function was assessed using an index of pre- and post-operative peak vertical ground reaction force ratios. Changes in bone mineral density were measured by dual energy X ray absorptiometry (DEXA) scanning. Loosening and subsidence were assessed radiographically and by histological examination of the explanted specimens.

There was no statistically significant difference between the four groups after 18 months of unrestricted functional loading for all outcome measures.