Aims

This cross-sectional study aimed to investigate the in vivo ankle kinetic alterations in patients with concomitant chronic ankle instability (CAI) and osteochondral lesion of the talus (OLT), which may offer opportunities for clinician intervention in treatment and rehabilitation.

We report a new surgical technique for the treatment of traumatic dislocation of the carpometacarpal (CMC) joint of the thumb. This is a tenodesis which uses part of the flexor carpi radialis.

Between January 2010 and August 2013, 13 patients with traumatic instability of the CMC joint of the thumb were treated using this technique. The mean time interval between injury and ligament reconstruction was 13 days (0 to 42). The mean age of the patients at surgery was 38 years: all were male.

At a mean final follow-up of 26 months (24 to 29), no patient experienced any residual instability. The mean total palmar abduction of the CMC joint of the thumb was 61° and the mean radial abduction 65° The mean measurements for the uninjured hand were 66° (60° to 73°) and 68° (60° to 75°), respectively. The mean Kapandji thumb opposition score was 8.5° (8° to 9°). The mean pinch and grip strengths of the hand were 6.7 kg (3.4 to 8.2) and 40 kg (25 to 49), respectively. The mean Disabilities of the Arm, Shoulder, and Hand questionnaire score was 3 (1 to 6). Based on the Smith and Cooney score, we obtained a mean score of 85 (75 to 95), which included four excellent, seven good, and two fair results.

Our technique offers an alternative method of treating traumatic dislocation of the CMC joint of the thumb: it produces a stable joint and acceptable hand function.

Cite this article: Bone Joint J 2015;97-B:1533–8.

We report a new surgical technique of open carpal tunnel release with subneural reconstruction of the transverse carpal ligament and compare this with isolated open and endoscopic carpal tunnel release.

Between December 2007 and October 2011, 213 patients with carpal tunnel syndrome (70 male, 143 female; mean age 45.6 years; 29 to 67) were recruited from three different centres and were randomly allocated to three groups: group A, open carpal tunnel release with subneural reconstruction of the transverse carpal ligament (n = 68); group B, isolated open carpal tunnel release (n = 92); and group C, endoscopic carpal tunnel release (n = 53).

At a mean final follow-up of 24 months (22 to 26), we found no significant difference between the groups in terms of severity of symptoms or lateral grip strength. Compared with groups B and C, group A had significantly better functional status, cylindrical grip strength and pinch grip strength. There were significant differences in Michigan Hand Outcome scores between groups A and B, A and C, and B and C. Group A had the best functional status, cylindrical grip strength, pinch grip strength and Michigan Hand Outcome score.

Subneural reconstruction of the transverse carpal ligament during carpal tunnel decompression maximises hand strength by stabilising the transverse carpal arch.

Cite this article: Bone Joint J 2015;97-B:221–8

Summary Statement

An autologous thrombin activated 3-fold PRP, mixed with a biphasic calcium phosphate at a 1mL:1cc ratio, is beneficial for early bone healing in older age sheep.

Summary Statement

Combination of sorafenib with irradiation achieved synergistic effect with dose reduction in both 143B and HOS cell lines. This demonstrated the potential application of sorafenib in the treatment of osteosarcoma metastasis and radiation resistance.

Introduction

Post-arthroscopic glenohumeral chondrolysis (PAGCL) is a rare, but significant, complication of arthroscopic shoulder surgery that may lead to arthroplasty. Exact causal factors and pathways associated with the development of PAGCL are unknown however a number of patient factors and surgical factors have been implicated. Suture is one of these potential causal factors and currently little is known about the body's immune response to commonly used orthopaedic sutures. The aim of this project is to examine the biological response to 3 commonly used orthopaedic sutures (Ethibond, Fibrewire, and Orthocord) in a murine airpouch model. It was hypothesised that different sutures would elicit a different histological response and that suture wear-debris would induce an increased inflammatory reaction compared to intact suture.

Introduction

The need for regeneration and repair of bone presents itself in a variety of clinical situations. The current gold standard of treatment is autograft harvested from the iliac crest or local bone. Inherent disadvantages associated with the use of autogenous bone include limited supply, increased operating time and donor site morbidity. This study utilized a challenging model of posterolateral fusion to evaluate the in vivo response of an engineered collagen carrier combined with nano-structured hydroxyapatite (NanOss Bioactive 3D, Pioneer Surgical) compared to a collagen porous beta-tricalcium phosphate bone void filler (Vitoss BA, Orthovita).

The purpose of this study was to understand the effects of terminal sterilisation and residual calcium on human demineralised bone matrix (DBM) in ectopic bone formation in nude rat.

The intramuscular implantation of human DBM prepared by the Queensland Bone Bank (QBB) from four donors into eight male athymic rats was used to assess osteoinductivity. The DBM contained different levels of residual calcium and treated with or without gamma-irradiation at 11kGy. At 6 weeks post-implantation, calcium deposition was assessed by manual palpitation and radiological imaging. Tissue morphology and cellular interactions was analysed using various histological staining methods whilst protein expression of anabolic and catabolic biomarkers were examined through immunohistochemistry. All results were then analysed in qualitative, semi-quantitative and quantitative manners and tested for statistical significance.

Bone formation was observed in all specimens at the gross level. This was confirmed by histology which revealed bony capsules surrounded by soft tissue in the muscle pockets and differences in tissue components. On a cellular level, variations in osteoclast expression were found between the two groups as well as amongst individual donors through statistical analysis which resulted in an imbalance of the expression of anabolic and catabolic markers. Furthermore, a positive relationship between residual calcium and new bone formation in gamma irradiated DBM samples was found. To date, no studies have compared the effect of calcium in gamma irradiated DBM.

Our results suggest that gamma irradiation even at low doses and residual calcium may affect new bone formation. Taken together, this study stresses the importance of selecting ideal conditions for graft processing and the need to identify an optimal level of irradiation and remaining calcium levels that confers a balance between osteoinductivity and sterility.

To set up an osteosarcoma mouse model with spontaneous lung metastasis and to identify a marker of osteosarcoma metastasis and to inhibit the marker against the invasive ability of an osteosarcoma cell line.

A human osteosarcoma orthotopic mouse model was set up by injecting 143B human osteosarcoma cells into mouse tibia. Type I insulin-like growth factor receptor (IGF-1R) and its downstream signalling factors were measured in samples from the primary tumor and the lung secondaries by immunohistochemistry. Human Alu mRNA expression was tested using in situ hybridization assay. A Matrigel assay was used to assess cell invasion ability under the interference of a MEK/ERK pathway specific inhibitor, U0126.

All fifteen mice showed tumour mass at the left tibia and lung metastasis. Human Alu expression in the primary and secondary tumours confirmed human origin of the tumour cells. Total IGF-1R, MEK, Akt, p38 and phosphorylated MEK (p-MEK), but not p-Akt and p-p38, were positive in both local tumours and lung secondaries. Leiomyosarcoma controls expressed p-Akt and p-MEK, but not p-p38. The 143B cells treated with U0126 had significantly lower in vitro invasion ability compared with controls.

The IGF-1R-MEK signalling pathway, particularly Ras/Raf/MEK/ERK, may play an important role in osteosarcoma lung metastasis, and the targeting MEK/ERK by its specific inhibitor may have a potential use in the effective treatment of osteosarcoma.

Animal studies examining tendon-bone healing have demonstrated that the overall structure, composition, and organization of direct type entheses are not regenerated following repair. We examined the effect of Low-Intensity Pulsed Ultrasound (LIPUS) on tendon-bone healing. LIPUS may accelerate and augment the tendon-bone healing process through alteration of critical molecular expressions.

Eight skeletally mature wethers, randomly allocated to either control group (n=4) or LIPUS group (n=4), underwent rotator cuff surgery following injury to the infraspinatus tendon. All animals were sacrificed 28 days post surgery to allow examination of early effects of LIPUS. Humeral head – infraspinatus tendon constructs were harvested and processed for histology and immunohistochemical staining for BMP2, Smad4, VEGF and RUNX2. All the growth factors were semiquantitative evaluated. T-tests were used to examine differences which were considered significant at p < 0.05. Levene's Test (p < 0.05) was used to confirm variance homogeneity of the populations.

The surgery and LIPUS treatment were well tolerated by all animals. Placement of LIPUS sensor did not unsettle the animals. Histologic appearance at the tendon-bone interface in LIPUS treated group demonstrated general improvement in appearance compared to controls. Generally a thicker region of newly formed woven bone, morphologically resembling trabecular bone, was noted at the tendon-bone interface in the LIPUS-treated group compared to the controls. Structurally, treatment group also showed evidence of a mature interface between tendon and bone as indicated by alignment of collagen fibres as visualized under polarized light. Immunohistochemistry revealed an increase in the protein expression patterns of VEGF (p = 0.038), RUNX2 (p = 0.02) and Smad4 (p = 0.05) in the treatment group. There was no statistical difference found in the expression patterns of BMP2. VEGF was positively stained within osteoblasts in newly formed bone, endothelial cells and some fibroblasts at the interface and focally within fibroblasts around the newly formed vessels. Expression patterns of RUNX2 were similar to that of BMP-2; the staining was noted in active fibroblasts found at the interface as well as in osteoblast-like cells and osteoprogenitor cells. Immunostaining of Smad4 was present in all cell types at the healing interface.

The results of this study indicate that LIPUS may aid in tendon to bone healing process in patients who have undergone rotator cuff repair. This treatment may also be beneficial following other types of reconstructive surgeries involving the tendon-bone interface.

Fibrocartilaginous entheses are formed through endochondral ossification and characterized by four zones morphologically separated into tendon, uncalcified fibrocartilage, calcified fibrocartilage and bone [1]. These zones are not successfully regenerated following surgical repair. Demineralized Bone (DBM) presented at the tendon bone interface may improve healing between tendon and bone.

Fifty six female nude rats were randomly allocated into either a control reconstruction or treatment group (DBM at the tendon-bone healing site). A modified rodent model of anterior cruciate ligament reconstruction was adopted [2]. Animals were sacrificed at 2, 4 and 6 weeks following surgery. Four rats per group were prepared for histology at each time point while eight rats were culled for biomechanical testing at 4 and 6 week time points. ANOVA and post hoc tests were used to examine differences which were considered significant at p < 0.05.

The surgical procedure was well tolerated. Macroscopic dissection did not reveal any infection and all joint surfaces appeared normal. An intra-articular graft between the femur and tibia was present in all specimens. Mechanical differences were noted between groups. Peak loads were significantly higher in treatment group at 4 and 6 weeks (6.0 ± 3.6N and 9.1 ± 2.6 N, respectively) compared to controls (2.9 ± 1.9 N and 5.8 ± 2.7 N). No statistical differences were found in graft stiffness between the groups at 4 or 6 week time points. Histology showed an initial influx of inflammatory cells coupled with formation of a loose disorganized fibrovascular interface layer between tendon and bone in both groups. By the 6 weeks the interface layer in the DBM group fused into the newly formed bone to create a continuum between the tendon and bone, in an interdigitated fashion, containing Sharpy's like fibres. In the control group the continuum was less apparent with evidence of large areas of discontinuity between the two zones. A thicker region of newly formed woven bone with increased osteoblast activity along the bone tunnel was evident in the DBM group.

DBM has the potential to increase the quality of repair following surgical procedures involving reattachment of tendon to bone.

The biological properties of morselised bone allograft treated with either a supercritical fluid process or low-dose (15 kGy) gamma irradiation were compared using radiological, histological and immunohistological techniques. The aims were to investigate any differences in the biological properties of supercritical fluid treated allograft and low-dose gamma irradiated allograft in-vivo.

Rabbit allograft were cleaned of all soft tissue, cartilage and processed into ‘corticancellous crunch’ using a Noviomagus Bone Mill. Pooled samples were either gamma irradiated (15 kGy) or treated by NovaSterilis using super critical carbon dioxide. A well-reported tibial defect model in ten rabbits was used to examine the in vivo response of the different treatments at two and four weeks following surgery (n=5 per time point). Radiographic (x-ray, CT and micro CT), histology and immunohistochemistry was used to assess the in vivo response.

Radiographic results revealed an initial response to the gamma-irradiated samples compared to SCF. Histology confirmed this reaction to be inflammatory in nature at two weeks that continued at four weeks for the gamma irradiated samples. In contrast, the SCF treated sample demonstrated new bone formation while the inflammatory reaction was muted compared to the gamma irradiated samples. Four week x-rays and histology confirmed new bone formation in both groups while the lack of significant inflammatory response in the SCF group was noted.

Allograft sterilisation techniques do not result in the same initial response when evaluated in vivo. Removal of lipids and cellular debris following SCF treatment may influence the in vivo response. While both techniques can provide a sterile product, the in vivo response requires further investigation.

Posterolateral spinal fusion using autograft in adult rabbits has been reported by many groups using the Boden model. Age in general has an adverse effect on skeletal healing; although, its role in posterolateral fusion is not well understood. This study examined the influence of animal age on spinal fusion using a standard model and experimental endpoints. We hypothesised that fusion quality and quantity would be less with increasing age.

A single level posterolateral fusion between the fifth and sixth lumbar segments were performed in six-month and two-year-old New Zealand white rabbits (n=6 per group) using morcelized iliac crest autograft. All animals were sacrificed at 12 weeks following surgery. Posteroanterior Faxitron radiographs and CT scans were taken and DICOM data was analysed (MIMICS Version 12, Materialise, Belgium). Axial, sagittal, coronal and three-dimensional models were created to visualise the fusion masses. Bone mineral density (BMD) of the fusion mass was measured using a Lunar DPXL Dexa machine. An MTS Bionix testing machine was then used to assess peak load and stiffness. Sagittal and coronal plane histology was evaluated in a blinded fashion using H&E, Tetrachrome and Pentachrome stains. Assessment included overall bony response on and between the transverse processes. Radiographs and CT confirmed a more robust healing response in younger animals. Radiographic union rates decreased from 83% to 50% in the aged animals. A neo- cortex surrounding the fusion mass was observed in the younger group but absent in the aged animals. Fusion mass BMD and that of the vertebral body was decreased in the older animals (P<0.05). Tensile mechanical data revealed a 30% reduction in peak load (P=0.024) and 34% reduction in stiffness (P=0.073) in the two-year-old animals compared with the six-month-old animals. Histological evaluation demonstrated a reduction in overall biological activity in the two-year-old animals. This reduction in activity was observed in the more challenging intertransverse space as well as adjacent to the transverse processes and vertebral bodies at the decortication sites. Numerous sites of new bone formation was present in the middle of the fusion mass in the six-month-old animals while the bone graft in the two-year- old animals were less viable.

Skeletal healing is complex and mediated by both local and systemic factors. This study demonstrated that ageing leads to an impaired and delayed skeletal repair.

Where autograft is utilised, diminished graft osteoinductivity and reduced levels of growth factors and nutritional supply in the surrounding milieu explains our observations. The aged rabbit posterolateral spinal fusion model has not been previously described but would be a useful to evaluate new treatment modalities in a more challenging host environment.

Single level posterolateral spinal fusion in rabbits is the accepted preclinical model for evaluating bone graft substitutes or treatments to enhance/augment healing. This study aimed to improve preclinical testing by developing a multi-level unilateral fusion model that could be used as a screening tool prior to larger scale preclinical experiments.

A four level unilateral posterolateral fusion was performed in nine animals. The materials were randomly allocated and placed between the decorticated surfaces of the transverse processes and vertebral bodies. Animals were euthanised at three, six and 12 weeks. The materials were (1) 25 kGy y-irradiated rabbit allograft chips (RAC), (2) SCF RAC, (3) 60% tri-calcium phosphate, 40% hydroxyapatite formagraft (BiOstetic) (4) Autograft (1.5 cc morsellised to 1-2.5 mm granules). The autograft was harvested from the iliac crest using the L5-L6 incision. Endpoints included x-ray, CT, micro CT and histology.

The animals tolerated the surgery well. Radiographic data provided a useful method to differentiate between groups. Micro CT however was extremely valuable demonstrating new bone formation as early as three weeks across the groups. Gamma irradiated samples demonstrated an initial inflammatory reaction while the autograft, SCF allograft and synthetic TCP did not show this response. As expected, time was an important factor demonstrating the maturity in the fusions. These materials responded in a similar fashion in this model as observed in a single level fusion.

A unilateral multi-level fusion can be performed in rabbits to provide a useful screening for different materials. Gamma irradiated allograft has an initial inflammatory reaction that may be related to the presence of residual cellular material whereas SCF and synthetic materials do not.

Introduction: Monobutyrin (MB) has been shown to be a potent angiogenic factor for adipose tissue. It is one of the many compounds secreted from adipocytes adding to the knowledge that adipose tissue is not merely a storage unit but has an endocrine function. Adipocytes and osteoblasts share a common precursor. In osteoporosis the proportion of fat in bone increases. As both are present at a fracture site the addition of MB may enhance fracture healing by stimulating angiogenesis.

Method: 138 Sprague Dawley rodents were ovarect-omised at 12 weeks of age. After a further 24 weeks each animal underwent a right closed femoral fracture stabilized with a retrograde k-wire using a standard model (Walsh et al. 1997). Animals were randomised into control (empty or substrate only) or MB of varying concentrations (2.5μg, 7.5μg, 25μg, 75μg). A percutaneous injection of 0.2mls of each of the above was then injected into the fracture site. Animals were culled at 1, 3 and 6 week time points post surgery. The right and left femurs were dissected out and analyzed using radiographic, mechanical testing, micro computed tomography and histology endpoints. Statistical analysis was perfomed with SPSS for windows.

Results: All animals recovered well from the procedure and no adverse reactions were noted following the addition of MB. A progression to union was seen with time in all groups. Mechanical testing did not result in a statistical difference between groups, however the trend showed improved healing in the 7.5μg Monobutyrin group. Radiographic grading again showed no statistical difference however, interestingly micro CT data showed an increasing trend in both trabecular number and bone surface area to volume with increasing concentrations of MB.

The histology results implied a potential acceleration in the early stage of fracture healing in the high dose (75 μg) MB group. However progression to union following this initial early phase acceleration was delayed as callus volume increased rather than union according to micro CT and histological data.

Discussion: The ability to augment fracture healing has significant clinical implications considering the “greying of society”. This study investigated the possibility of improving fracture healing by incorporating the angiogenic factor, Monobutyrin in an estrogen deficient animal model. Although the results do not conclusively demonstrate an improvement in fracture healing, they do imply that MB does affect the early phase of fracture healing in the estrogen deficient model. This study is limited in that the effects of MB on fracture healing in a non-estrogen deficient model was not considered. The ideal release kinetics for Monobutyrin as well as other factors remains unknown.

Introduction: The use of bioabsorbable devices in sports medicine surgery in the shoulder and knee continues to evolve as new designs, devices and materials become available. Concerns over potential problems associated with metal artifacts and permanent metal devices continue to motivate the development and use of polymeric based devices. Calaxo interference screws (Smith & Nephew Endoscopy, Andover, MA) are composed of a novel bioabsorbable material blend of poly DL- lactide – co – glycolide 85:15 (65%) and calcium carbonate (35%). These screws have been shown to be osteoconductive when placed in the centre of a 4 stranded tendon graft in an ovine ACL reconstruction [1]. The screws are fully resorbed at 26 weeks with new bone formation in the tunnel. In general, osteoconductive materials are often more effective when placed adjacent to a bony bed. This study investigated whether positioning the Calaxo screw adjacent to the bone tunnel was superior to screw placement within the tendon as in our previous study [1].

Materials and Methods: An intra-articular anterior cruciate ligament (ACL) reconstruction model using 2 doubled over tendon autografts whip stitched and inserted into the right hind limb of 8 sheep were used. Animals were culled at 26 or 52 weeks following surgery (n=4 per time point) and data was compared using the same surgical model but with screws placed in the center of the 4 stranded graft (Walsh et al., 2006). The tibias were CT scanned and processed for paraffin histology along the axis of the bone tunnel. Three dimensional models using the DICOM data obtained from the CT where made using MIMICS (Materialise, Belgium).

Result & Discussion: Results showed excellent biocompatibility of the screws with no adverse reactions at 26 and 52 weeks as in our previous study [1]. The screws were fully resorbed by 26 weeks with new bone replacing the PLC material. Similarly, the screws were not detectable at 52 weeks with new bone formation where the screw had previously resided. The intra-articular portion of the graft, articular cartilage and synovium was normal at 26 and 52 weeks as previously reported [1]. Tendon – bone healing proximal to the screw progressed in a normal fashion. No calcification of the intraarticular portion of the graft was noted. Computed tomography, 3D models and histology revealed an osteoconductive response to the PLC material with new bone formation as the material degraded in vivo.

Placement of the screw adjacent to the tendon graft and thus against the bone tunnel appears to provide superior results compared to screw placement in the middle of the graft sleeve device. This effect may be due to direct contact of the osteoconductive material to the adjacent bone bed.

[1] Walsh et al., Arthroscopy 2006, in press.

Introduction: A cosmetic deformity does not always occur after a biceps tenotomy. The anatomical restraints preventing distal excursion of the long head of biceps tendon following tenotomy have not previously been described. This study aims to evaluate the biceps sheath and its potential role as a restraint to distal excursion of the biceps following tenotomy.

Methods: Fifteen fresh cadaveric specimens were dissected free of overlying soft tissues to reveal the rotator cuff, biceps sheath and long head of biceps muscle belly and tendon. Eight specimens were used for gross anatomical analysis. Measurements of the length of the biceps sheath on the humeral (bone) side and tendon side were made using a digital caliper (Mitutoyo, Japan). The long head of biceps tendon was then released from the glenoid labrum and the excursion of the stump relative to the rim of the articular surface measured. The biceps sheaths of two specimens were used for histological analysis.

Seven specimens were used for mechanical analysis. A humeral osteotomy was performed distal to the insertion of pectoralis major, leaving intact the biceps sheath and the muscle belly of long head of biceps. The proximal humerus was attached to a custom-designed jig and the muscle belly of biceps grasped in cryogenic grips. Specimens were loaded on an MTS 858 Bionix mechanical testing machine (MTS Systems, MN) in uniaxial tension at a rate of 1 mm/sec until failure was observed.

Results: The biceps sheath surrounds the long head of biceps tendon and inserts into the bone of the proximal humerus. It is trapezoidal in cross-section, with a mean length of 75.1 mm on the bone side and 49.3 mm on the tendon side. The average excursion of the stump was to within 2.8 mm of the rim of the articular surface.

Histological examination of the biceps sheath revealed membranous tissue consisting of loose soft tissue with fat and blood vessels. Synovial tissue was also identified. The sheath was seen to loosely attach to the biceps tendon, with a more intimate attachment to the periosteum.

The mean force to pull the long head of biceps tendon out of the sheath 102.7 N (range 17.4 N–227.6 N)

Discussion: The biceps sheath is a consistent structure intimately associated with the biceps tendon. It appears to contain blood vessels which provide nutrition to the tendon, similar to the vincula of flexor digitorum pro-fundus. Mechanical testing reveals that a substantial force is sometimes required to pull the biceps tendon from the sheath. This may explain why biceps tenotomy does not routinely result in a “Popeye” biceps.

Introduction and Aims: Adipose-derived stem cells (ADSCs) are capable of osteogenic differentiation under appropriate conditions in vitro (1). In this study we demonstrate the differences and similarities of the healing potential of ADSCs against the bone marrow-derived stem cell population (BMSCs) in the critical size ovine cancellous defect model, healed with culture expanded autologous stem cells from adipose tissue (ADSCs).

Method: Bone marrow aspirates and subcutaneous adipose tissue were harvested from 42 adult wethers. The population of stromal cells was derived from both tissues. Populations of bone marrow cells and adipose stromal cells were expanded in culture and stimulated with osteogenic medium for seven days. Cultured cell populations were harvested, mixed with a hydroxy-apatite carrier (Pro-Osteon 200R) and deposited into bilateral medial femoral condyle confined cancellous defect. Seven groups were examined: Bone graft+ ADSCs, Bone graft+ BMSCs, Carrier + ADSCs, Carrier+ BMSCs, Bone graft, Carrier, Empty defect. Two week, four week and eight week time-points were examined.

Results: All specimens were decalcified and five μm histological slides were stained using H& E and Masson’s Trichrome. Histomorphometry analysis on Masson’s Trichrome stained slides was performed using colour threshold-based software Bioquant Nova 6.50.10. Immunohistochemical staining for BMP4 and BMP7 and their downstream regulators: Smad4 and CBFA1 were evaluated in the defect area and graded in a blind fashion by two trained observers. There was a progressive and time-dependent increase in woven bone formation in the defects treated with ADSCs across all time points. The amount of bone formed in this group was comparable with the amount formed by the use of BMSCs.

Conclusion: The results of this study support the hypothesis that seeding porous hydroxyappatite with ADSCs does enhance bone formation and defect healing.

Purpose: Using the finite element analysis, the authors analyze the effect of the articulating material properties of the total hip arthroplasty to stress and micro-motion of the proximal femur and the femoral stem.

Material and methods: The head (28mm) and the acetabular component (outer diameter = 54mm, liner thickness = 11.4mm) were considered as ceramic on ceramic, cramic on polyethylene, metal on metal, metal on polyethylene and metal on metal-polyethylene. The femur was modeled with different friction coefficients according to the different contact portion of the femoral stem, which was modeled after Omni fit HA #9(Osteonics, Allendale, NJ). Non-linear contact analysis was proceeded in human with body weight 70Kg at one leg standing and stair climbing.

Result: The maximal yield strength was always higher in hard-hard coupling. In one leg standing, the site of maximal yield strength was represented at the contact point of articulation. In stair climbing, the site of maximal yield strength was represented at the same site in hand on hard coupling but at the lateral aspect of the neck in hard-soft couplings. There were no changes in the patterns of stress distribution but the micro-motions were up to the limit of bone in growth in hard-hard coouplings.

Conclusion: The maximal yield strength and the micro-motions revealed different values according to the articulating materials. These findings were considered valuable information to postoperative management and longavity of the total hip prosthesis but requiring the following experimental and clinical study.

Introduction VEGF is a well known angiogenic peptide which has been shown to be central to endochondral ossification. Secondary fracture healing involves a combination of intramembranous and endochondral ossification. VEGF has been recently shown to be chemotactic for osteoblasts and chondroclasts. We therefore set out to examine the temporal and spatial expression of VEGF and its receptors in fracture healing. We report here the preliminary findings of our study.

Methods A closed mid-shaft fracture was produced in the right femora of nine 12 week old Sprague Dawley rats, stabilised by an intramedullary K-wire. The rats were sacrificed at one, two and four weeks. Through the use of immunohistochemistry, RT-PCR and in situ hybridisation.

Results We show that at each of the time points, VEGF is expressed in all of the cell types involved in fracture healing; the inflammatory cells, the osteo-progenitor cells,chondroblasts,chondrocytes,osteoblasts and osteoclasts as well as fibroblasts. We further show that there is persistent expression of VEGF in chondrocytes at four weeks.

Conclusions Our findings are consistent with the hypothesis that events in fracture healing reflect the processes that take place at the growth plate during embryonic development.