Bone marrow cells are well known for improving healing. Recent studies report that stromal cell-derived factor-1 (SDF-1) and its receptor CXC chemokine receptor 4 (CXCR4) play roles in stem cell homing and are related to short-term and long-term engraftment. SDF-1 secreted from an injured organ can pass the endothelium barrier in a CXCR4-dependent manner into the bone marrow and recruit hematopoietic progenitors to the circulation. There is evidence to show that SDF-1 also has chemoat-tractive effects and is able to recruit mesenchymal stem cells and osteoprogenitors. Our previous study also showed that SDF-1 has an enhanced effect on osteoblas-tic differentiation of human mesenchymal stem cells. The purpose of this study is to investigate the effects of genetically modified bone marrow cells that overexpress SDF-1 on bone fracture healing in rat model. The hypothesis is that genetically modified rat bone marrow cells (rBMCs) that over expresses SDF-1 will enhance the fracture healing process compared to non-treated groups or to groups treated with only rBMCs. rBMCs were harvested from femora of young male Wistar rats. rBMCs were expanded ex vivo, and cells of passage 3 were used in the experiment. SDF-1 over-expressing rBMCs (rBMC-SDF-1) were engineered by infection of adenovirus carrying human SDF-1 gene at the multiplicity of infection (MOI) 500. Eighteen adult female Wistar rats were divided into three groups with 6 rats in each group:

rBMC-SDF-1,

A 3mm gap in the middle of femur was created during surgery and stabilized by an external fixator. In two groups three hundred thousand rBMCs or rBMCs-SDF-1 were seeded into a collagen sponge and transplanted into the gap. For the control group, sponges without cells were used. Rats were sacrificed 3 weeks after operation and the femora were harvested. Bone mineral content within the gap was measured immediately after operation and compared with the bone mineral content within the same gap at the third week by dual energy X-ray absorptiometry (DEXA) scanning. The area of new bone formation was measured using histomorphometery on H& E stained sections and quantified by imaging analysis system. In the present study, the rBMC-SDF-1 group showed the most dominant influence in both new bone formation and bone mineral increase. rBMC-SDF-1 not only increases new bone formation but also has higher bone mineral content after 3 weeks compare with the rBMC only. This bone healing progress may due to the enhanced local SDF-1/CXCR4 interaction that recruited more host’s stem cells into the fracture site. The control group showed an increased new bone formation in the histological analysis but a reduced bone mineral content after 3 weeks whereas in comparison the rBMC group showed a similar new bone area to the control group but a significantly higher bone mineral content. This may indicate a faster bone repairing ability with the BMCs. Both rBMC and rBMC-SDF-1 groups have a higher bone mineral content and a more compact new bone structure that may indicate an accelerate effect of rBMC in the bone mineralization. In this study, we show that SDF-1 induces improved bone formation in early fracture healing.

We investigated the hypothesis that autologous bone marrow stromal cells (BMSC) sprayed on the surface of acetabular cups would improve bone formation and bone implant contact.

Total hip replacements were implanted in 11 sheep, randomly assigned to receive either acetabular implants sprayed with autologous BMSCs suspended in fibrin (study group) or fibrin only (control group). Sheep were sacrificed after six months and the acetabulum with the implant was retrieved and prepared for undcalcified histology. Implant bone contact in both groups was compared, by microscopically noting the presence or absence of new bone or fibrous tissue along the implant at 35 consecutive points (every 1000 μm). The observers undertaking the histological analysis were blinded.

Significantly increased bone implant contact was noted in the BMSC treated group 30.71% ± 2.95 compared to the control group 5.14% ± 1.67 (p = 0.014). The mean thickness of fibrous tissue in contact with the implant was greater at the periphery 887.21mm ± 158.89 and the dome 902.45mm ± 80.67 of the implant in the control group compared to the BMSC treated group (327.49mm ± 20.38 at the periphery and 739.1 mm ±173.72 at the centre). Conversely direct bone contact with the implant surface was significantly greater around the cups with stem cells.

BMSC sprayed on surface of implants improves bone implant contact. Spraying acetabular cups using stem cells could be used in humans where acetabular bone contact is compromised such as in revision procedures.

Background: Osseointegrated amputation prostheses avoid soft tissue complications associated with traditional socket prostheses. Forces are transmitted directly to the skeleton resulting in improved function. However, approximately 50% of transcutaneous implants become infected due to the lack of a successful skin-implant seal. Intraosseous Transcutaneous Amputation Prostheses (ITAP) are designed to integrate with the skin preventing epithelial downgrowth and infection.

Fibronectin adsorption enhances fibroblast adhesion in vitro; however, in vivo, fibronectin becomes desorbed from the implant surface. Covalent attachment of fibronectin by silanisation has been shown to be durable in vitro. The silanisation process for fibronectin includes a stage of passivation with sulphuric acid which alters surface characteristics.

Aims: The aim of this study was to determine if in vitro fibroblast adhesion to silanised fibronectin (SiFn) titanium alloy could be improved by omitting or reducing the length of time of passivation. The study also assessed the effects of SiFn on dermal attachment in vivo comparing the results with adsorbed fibronectin substrates and with uncoated controls.

Methods: Scanning electron microscopy, Ra profilometry and contact angle measurement (n=6) were used for topographical characterization of surfaces. Anti-vinculin antibodies were used to immunolocalize fibroblast adhesion sites after 24 hours. The morphology of fibroblasts on each surface was evaluated using scanning electron microscopy. Subcutaneous plates were implanted onto the tibiae of an ovine model (n=3) in order to evaluate the performance of the modified SiFn surface in vivo. Hydroxyapatite (HA) and adsorption of fibronectin to HA (HAFn) were also tested because HA coatings are currently applied to the dermal section of ITAP in clinical trials. After four weeks, a histological assessment of the percentage of soft-tissue attachment and cell alignment relative to the implant was performed.

Results: Passivation produced rougher, more hydrophobic surfaces with numerous microcracks and was associated with poorer fibroblast adhesion and spreading than un-passivated controls in vitro.

SiFn with passivation resulted in poorer cell adhesion than SiFn without passivation. Reducing the time period for passivation did not reduce the detrimental effects of passivation In vivo, HAFn and SiFn resulted in higher median values for soft-tissue attachment than simple adsorption of fibronectin; however, the differences were not statistically significant. Cell alignment was significantly different for HAFn and SiFn compared with controls (p< 0.05), with cells on the fibro-nectin treated surfaces orientated more perpendicular to the implant surface.

Conclusion: Omission of passivation improves fibro-blast adhesion to SiFn surfaces in vitro. Coating with fibronectin either by silanisation onto titanium alloy or by adsorption onto HA surfaces affected the orientation of cells in vivo, implying that tissue attachment was enhanced. A time course may be of value to determine if fibronectin coatings are lost over time in vivo.

Introduction: Due to uneven distribution of stress between the stump and the socket in amputees pain, infection and necrosis of soft tissue can be problematic (Dudek, Marks, & Marshall 2006)Implants have been developed that allow the external prostheses to attach directly to the skeleton by a percutaneous section by osseointegration that reduces the stresses on the soft tissue alleviating the problems associated with a socket (Lai et al. 1998). It has been postulated that surface coatings can enhance soft tissue attachment and increase the in growth of fibroblastic dermal tissues enhancing the seal at the skin implant interface and reducing infection (Pendegrass et al. 2006). Hydrogenated (acetylene: C2H2) and silanized (tetra methyl silane: TMS) diamond-like-carbon coating (DLC) can be applied to titanium(Ti) alloy to reduce surface energy and hydrophilicity. It was hypothesized that biomaterial surfaces having high surface energy and high hydrophilicity eg, Ti alloy enhance the adhesion and maturation of human dermal fibroblasts when compared with C2H2 and TMS coated substrates in vitro.

Methods: Fibroblasts were cultured on 10 mm diameter Ti alloy, C2H2 and TMS coated Ti alloy discs for 4 hours and 24 hours (2500 cells per disc). Cell area and attachment were analysed using Image Analysis and quantification of immunolocalised vinculin containing adhesion plaques respectively. The number of plaques per cell and cell area were compared between experimental groups and controls at 4 and 24 hours. The change in cell area and number of adhesion plaques between 4 and 24 hours were compared for each substrate type. SPSS version 10 was used for the statistical analysis.

Results: At 4 and 24 hours, the number of adhesion plaques was significantly greater on control and C2H2 compared with TMS (p< 0.001). No significant difference was observed between control and C2H2 discs (p> 0.05). At 4 hours, cell area was significantly greater in control compared to both C2H2 and TMS (p< 0.001). At 4 hours, the cell area in TMS was significantly greater than C2H2 (p< .001). At 24 hours, the cell area on control and C2H2 was significantly greater than TMS(p< 0.001). However, there was no significant difference between cell area on control and C2H2 (p> 0.05). From 4 to 24 hours, the number of adhesion plaques increased significantly on all the surfaces (p< 0.001). Cell area increased significantly on C2H2 and TMS between 4 and 24 hours. No significant increase in the cell area was observed on control substrates

Discussion: This supports the hypothesis that surfaces with high surface energy and high hydrophilicity lead to increased cell attachment and cell area. Thus, it can be concluded that the hydrophilic surfaces with higher surface energies favour the adhesion of dermal fibroblasts.

This case highlights the close association between osteo-fibrous dysplasia (OFD) and adamantinoma, drawing attention to the role for more radical treatment options when treating OFD. We discuss the advancements in joint-sparing endoprostheses using bicortical fixation. Finally we describe a unique biomedical design allowing for manufacture of an end cap to allow amputation through a custom made joint-sparing proximal tibial replacement as opposed to an above knee amputation.

A 37 year old presented 7 years ago having sustained a pathological fracture of her tibia. Subsequent biopsy revealed OFD, curettage with bone graft was performed. She later developed recurrence, two percutaneous biopsies confirmed OFD. 6 years following her initial diagnosis she was referred to RNOH with further recurrence, a biopsy at this stage revealed a de-differentiated adamantinoma. A joint-sparing proximal tibial replacement was performed and adjuvant chemotherapy administered, she remained well for one year. Recurrence was noted at the distal bone-prosthesis interface, histology revealed a high grade dedifferentiated osteosarcoma, limb preservation was not deemed possible and an amputation was performed through the prosthesis. The proximal tibial device was uncoupled leaving a residual 7 cms insitu, a small custom made end cap was attached to the remaining prosthesis and a myocutaneous flap fashioned over it, this ultimately enabled the patient to mobilise well with a below–knee orthotic device.

This case highlights the need for more radical surgery when treating cases of OFD and the relationship between OFD and adamantinoma. It also introduces a joint-sparing proximal tibial device for use in proximal tibial tumours that do not invade the proximal tibial metaphysis. The biomechanical design solution has given us the unique option of preserving the knee joint allowing the patient a below knee amputation whereas previously an above knee amputation would have been performed thereby significantly reducing her functional outcome.

The use of massive endoprostheses following bone tumour resection is well recognised. Where possible, joint salvage rather than joint replacement is usually attempted. However cases arise where there is insufficient bone following tumour resection to allow adequate fixation of a joint sparing prosthesis. We reporta series of 4 patients (aged 4–12), treated between 1994 and 2008, in which irradiated autologous bone has been combined with a diaphyseal or distal femoral replacement in order to preserve the native hip joint.

There were 3 cases of osteosarcoma and 1 case of Ewing‘s sarcoma. After a mean follow-up of 53.5 months (range 9–168), all four patients are alive without evidence of local recurrence or metastases. One implant was revised after 14 years following fracture of the extending component of the growing endoprosthesis. There have been no cases of loosening or periprosthetic fracture.

This is the first report of irradiated autologous bone with joint sparing endoprostheses in skeletally immature patients.

Following resection of tumours in the distal femur, reconstruction with joint-sparing prostheses have shown good short-term functional outcomes. There is however limited literature on the affect of knee-sparing prostheses on function of the distal femoral physis in children of bone growing age.

We discuss two patients, a male (11yrs) and female (10yrs) who had joint-sparing distal femoral prostheses inserted for treatment of Ewing’s sarcoma. The knee joint, along with the distal growth plate, was preserved and fixed to the distal end of the prosthesis using uni-cortical screws positioned distal to the physis. In the female, these screws were removed 6 months postop due to prominence of the screws under the skin. In both patients, we assessed radiographs from immediately post[surgery and the most recent follow-up (20 and 28 months respectively). In each set, for the operated limb, we measured the height and width of the distal femoral epiphysis, the total length of the femur and the length of the proximal femoral bone segment from the femoral head to the proximal bone-prosthesis interface. In addition, postoperative assessments of leg lengths, bilaterally, were documented.

In both patients, distal femoral epiphyseal height and width in the operated leg showed no significant change following endoprosthetic replacement. In the female, growth did not resume even after removal of the epiphyseal screws. In both patients, lengths of the femur and the proximal bone segment increased significantly following surgery. The patients demonstrated no clinical leg length discrepancy at the most recent follow-up.

This study suggests that the function of the distal femoral growth plate ceases following insertion of joint-sparing distal femoral endoprostheses, probably due to trans-physeal fixation. This does not appear to resume following early removal of distal screws. The proximal growth plate, however, continues to function adequately enough to maintain symmetry in overall leg length.

Purpose: To determine if Cobalt-Chrome (CoCr) femoral components of knee replacement components roughen significantly, and when significant roughening may start.

Methods:

Retrieval study:

14 knee replacement components were retrieved after revision procedures. The average surface roughness (Ra) of the articulating regions of each condyle was measured by surface profilometry and compared to Ra of non-articulating regions, which acted as controls on each implant.

In vitro testing:

Pin-on-plate testing of 6 paired CoCr pins and vacuum γ-irradiated UHMWPE discs was carried out under a force of 2.3kN at 1Hz to investigate how the articular Ra of CoCr pins varied with increasing number of cycles. Ra was measured at 0, 10, 100 and 1000 cycles using surface profilometry.

Results:

Retrieval analysis:

Average medial femoral condyle Ra was significantly greater than control Ra (p=0.040). Average lateral femoral condyle Ra was not significantly greater than control Ra (p=0.158). Significantly higher average Ra was seen on the medial condyles when compared with the lateral condyles (p < 0.05). 8/14 retrieved femoral components had ≥1 significantly roughened condyle (p< 0.05).

In vitro testing:

At 100 and 1000 cycles the Ra of the CoCr pins was significantly greater than Ra at 0 cycles (p< 0.05).

Conclusion: A large proportion of femoral components of knee replacement implants roughen significantly in vivo, a finding supported by our in vitro testing which indicates that roughening may begin very early on. This may have important implications for aseptic loosening of knee replacement components. However, the average Ra of those CoCr surfaces significantly (p< 0.05) roughened was within acceptable limits for orthopaedic implants (0.050μm).

Despite advances in total hip arthroplasty, failure of acetabular cup remains a concern. The role of bone marrow stromal cells (BMSCs) to aid osseointegration of orthopaedic implants have been recently studied. We investigated the hypothesis that autologous BMSCs sprayed on the surface of acetabular cups would improve bone formation and bone implant contact.

Total hip replacements were implanted in 11 sheep, randomly assigned to receive either acetabular implants sprayed with autologous BMSCs suspended in fibrin (study group) or fibrin only (control group). Sheep were sacrificed after six months and the acetabulum with the implant was retrieved and prepared for undecalcified histology. Implant bone contact in both groups was compared microscopically, by noting the presence or absence of new bone or fibrous tissue along the implant at 35 consecutive points (every 1000 μm). The observers undertaking the histological analysis were blinded.

Significantly increased bone implant contact was noted in the BMSC treated group 30.71% ± 2.95 compared to the control group 5.14% ± 1.67 (p = 0.014). The mean thickness of fibrous tissue in contact with the implant was greater at the periphery 887.21mm ± 158.89 and the dome 902.45mm ± 80.67 of the implant in the control group compared to the BMSC treated group (327.49mm ± 20.38 at the periphery and 739.1 mm ± 173.72 at the centre). Conversely, direct bone contact with the implant surface was significantly greater around the cups with BMSCs.

Our data demonstrate that BMSC sprayed on surface of acetabular implants improves bone implant contact. Spraying acetabular cups using stem cells could be used in humans where acetabular bone contact is compromised such as in revision procedures.

Introduction: The non-invasive growing prosthesis continues to be used successfully for the treatment of limb salvage operations in tumour patients. We report our continued experience in 17 skeletally immature patients with osteosarcoma of the distal femur.

Methods: Patients had a mean age of 10.2 years (range 6 to 15) at the time of surgery. The endoprosthesis was lengthened at appropriate intervals in outpatient clinics without anaesthesia using the principle of electromagnetic induction.

Results: The mean follow-up was 28 months (range 2 to 55). The prostheses were lengthened by a mean of 47.4 mm (range 0.5 to 208) and maintained a mean knee flexion of 110 degrees (range 90 to 120 degrees).

Complications developed in seven patients: two implants failed requiring revision, one peri-prosthetic fracture occurred, one developed a flexion deformity of 25 degrees at the knee joint, which was subsequently overcome and three died of disseminated disease.

Discussion: The medium term results from patients treated with this device have continued to show a promising outcome. Four patients successfully completed desired lengthening, six patients are continuing with ongoing lengthening. The implant avoids multiple surgical procedures, general anaesthesia and assists in maintaining leg-length equality.

Scarf osteotomy is widely used as a surgical treatment for hallux valgus. It is a versatile osteotomy, allowing shortening, depression or medial displacement of the capital fragment but it remains uncertain how stresses within the bone subsequently vary. The aim of this study was to design a computerised model to explore the effect on bone stress of changing the position of bony cuts for a scarf osteotomy.

A computerised image was constructed using finite element analysis. This utilises a mathematical technique to form element equations which represent the effect of applied force to the object appropriate to each finite element. Maximum bone stresses were then measured using different osteotomy variables. The osteotomy variables studied were the length of the longditudinal cut, apex of the distal cut to articular cartilage, resection level of the longditudinal cut and combinations of these variables. A saw bone model was used to test the findings of the study.

The results of this study show that lowering the longditudinal resection level and shortening via the distal cut beyond 6 mm will decrease bone stress. Additionally, raising the longditudinal resection level and shortening via the proximal cut caused an increase in bone stress. A saw bone model confirmed the findings of the study.

In conclusion, our experience is that finite element analysis is a very useful model in studying the bony stresses for a scarf osteotomy and assists in optimising the direction and angle of bony cuts used.

Introduction: Recent studies have shown that MSCs can be isolated from the peripheral blood of many different species. Hematopoietic stem cell (HSC) mobilization from the bone marrow to the circulating bloodstream can be induced using granulocyte colony stimulating factors (G-CSF). As it has been shown that HSCs and MSCs have positive interactions with each other, it may be possible that G-CSF also promotes the release of circulating peripheral blood MSCs (PBMSCs). The hypothesis of this study was that G-CSF would increase the mobilization of peripheral blood-derived stromal-like cells.

Materials and Methods: Six sheep with normal hematological profiles were given 5& #956;g/kg Neupogen& #63721; (filgrastim, G-CSF) subcutaneously for five days. Pre- and post-G-CSF treatment, blood was taken 4, 12, 24, and 2 weeks post-treatment. PBMSCs were isolated from the blood and cells plated at a cell density of 4.0 x 10e4 nucleated cells/cm2. Fibroblastic colony forming units (CFU-F) were counted 7 and 14 days after initial culture. The cells were tested for their multipotency by treating them with osteogenic, adipogenic, and chondrogenic supplements, and staining with the Von Kossa, Oil Red ‘O,’ and Alcian Blue stains, respectively, to show differentiation down the different lineages.

Results: No CFU-F formation was observed in all blood samples taken before G-CSF therapy (0 CFU-F) after 7 and 14 days in culture. After G-CSF treatment, CFU-Fs were observed in blood samples taken 4, 12, and 336 hours (2 weeks) post-G-CSF. The CFU-F count was highest after 14 days in culture in the blood samples obtained 2 weeks post-G-CSF administration (1.027 ± 30.1353 CFU-F/cm2), compared to the lowest count, which was at 12 hours post-G-CSF treatment (0.064 ± 0.064 CFU-F/cm2). Hematology showed an increase in white blood cell (WBC), neutrophil, and eosinophil counts 24 hours after G-CSF administration. Two weeks post-G-CSF treatment, WBC, neutrophil, lymphocyte, and monocyte counts dropped back to normal range values. The highest number of CFU-F/cm2 were observed at this time. When WBC numbers were correlated with CFU-F counts using Pearson’s correlation co-efficient, the result was 0.523, a significant value (p=0.023) indicating that 27.4% of the WBC counts were related to CFU-F counts and vice versa. When time was accounted for as a third variable using the test for partial correlation coefficients, the co-efficient was found to be −0.0063, and was not significant (p=0.492). Expanded cells were fibroblastic in morphology, and upon differentiation were positive for the Von Kossa, Oil Red ‘O,’ and Alican Blue stains, indicating differentiation down the osteogenic, adipogenic, and chondrogenic lineages, respectively.

Discussion and Conclusions: We have shown that PBMSCs can be isolated after G-CSF administration in sheep, and that the numbers of CFU-F increase after WBC levels have returned to normal. A previous in vitro study proposed that the increased BMSC growth observed when co-cultured with CD45+ HSCs was due to positive interactions between HSCs and MSCs, indicating a possible steady-state balance. PBMSCs may have important future applications in bone tissue regeneration.

Introduction: Cell adhesion to titanium alloy implants is important in osseointegration [1,2] and attachment of the soft tissues to skin penetrating implants e.g. external fixator pins and Intraosseous Transcutaneous Amputation Prostheses [3,4]. Cell adhesion can be assessed using cell area data and immunolocalisation of focal contact proteins e.g. vinculin; however no method of assessing biophysical attachment is performed routinely. Cell adhesion can be enhanced with adhesion proteins including fibronectin (Fn)[5]. We have previously shown that covalently binding Fn to titanium also increases cell adhesion, and produces a more robust protein coating [6]. However the strength of adhesion of cells to this coating has not been measured. Our hypothesis was that biophysical cell adhesion measured using novel radial flow apparatus would correlate with cell area and focal contact data and that covalently bound fibronectin substrates would increase cell adhesion compared with adsorbed and uncoated controls.

Method: Dermal fibroblasts were cultured for 1, 4, and 24 hours on 30mm and 10mm diameter polished titanium alloy discs (n = 6). Cells on 30mm discs were calcein stained and subjected to shear stress in a submerged, media filled, custom-made radial flow apparatus at 37¬C at 1.66ml/s for 15s. Cells were fixed in 10% formal saline and photographs were taken using a tangential light source. Fluorescent microscopy was performed at 2mm intervals along two perpendicular diameters. Using image analysis, the central cell free zone was measured and radial distance and shear stress calculated. Cells on 10mm discs were fixed, permeablised and vinculin stained (mouse vinculin antibody (1:200) 2hrs; FITC mouse antibody (1:100)1hr). Images were analyzed with a Zeiss microscope linked to image analysis software and the number of focal contacts were counted per cell area. The medians of the radial flow data were compared with data for cell area and focal contact production at the same time points using Spearman¡s regression correlation. This method was subsequently used to compare cell adhesion at one hour with adsorbed and covalently bound Fn substrates (10¥ìg/disc).

Results/Discussion: The shear strength of cells increased between 4 and 24hrs (p=0.002) on polished untreated control substrates. Attachment values (dynes/cm2) were 84.90 (73.98–97.19), 96.30 (91.66–100.89), and 136.69 (134.68–140.30) for 1, 4 and 24 hours respectively. At 1hr, covalently bound Fn (509.90 dynes/cm2 (490.55–528.49) significantly increased cell adhesion compared with adsorbed Fn(434.45 dynes/cm2(385.25–465.62)) and control substrates(p=0.002). There was significant correlation between shear stress and focal contacts/cell (1.00(p< 0.01)) and focal contacts/cell area (0.900(p=0.037)), but not cell area (0.600(p=0.285)).

Conclusion: Radial flow measurement is a useful direct method to quantify cell adhesion to orthopaedic implants and correlates well with other methods of measurement. Covalently bound Fn significantly increases biophysical cell attachment compared with adsorbed and uncoated controls.

Introduction: Aseptic loosening at the bone-implant interface of THA acetabular components is a significant cause of implant failure. This loosening has been attributed either to wear particle-induced osteolysis or to the effects of joint fluid-pressure. It may be possible to prevent the loosening of implants by improving fixation between the bone and implant, or promoting the growth of a biological bony seal, in order to prevent the influx of wear particles or pressurized joint fluid. Additionally in revision implants it is important to promote osseointegration in situations where bone stock may be limited. The hypothesis of this study was spraying autologous BMSCs in fibrin glue onto the surface of HA-coated acetabular components would increase bone formation around the implant and improve bone-implant contact.

Materials and Methods: Bone marrow was aspirated from the iliac crest of six goats, and BMSCs isolated and expanded in vitro. 10 x 10e6 BMSCs were suspended in reconstituted thrombin pre-operatively. A standard posterior approach was used. The acetabular shell was then coated with 2 ml of fibrin glue, with (n=6) or without 10 x 10e6 autologous BMSCs (n=6), and the acetabular component impacted into position. Antibiotic and analgesic prophylaxes were carried out. All animals were weight bearing within 48 hours post-operatively. Walking and ground reaction forces were assessed pre-operatively, as well as 6 and 12 weeks post-operatively. Results were expressed as a percentage of force transmitted through the right leg versus the left leg. After 12 weeks, the acetabulae were retrieved, and processed for histology. The percentage of new bone around the cups was measured within 5 radial zones, using image analysis. Bone-implant contact was also analysed between the new bone and implant surface. Mann Whitney U test was used to show statistical significance.

Results: New bone formation in Zone 5 showed a significant increase in the BMSC group (71.97±10.91%), when compared to the controls (23.85±15.13%, p=0.028). The other zones did not show a significant difference. Overall new bone growth in the BMSC group was 30% greater than the control group (71.42±8.97% and 54.22±16.56%, respectively, p=0.58). Bone-implant contact was significantly improved in the BMSC group (20.03±4.64%), in contrast to the control group (13.71±8.32%, p=0.027). With regards to the force plate analysis, there was no significant difference in loading between groups at both 6 weeks (Controls-79.74±3.63%, BMSCs-59.39±9.33%, p=0.086) and 12 weeks (Controls-86.0%±2.85%, BMSCs-62.33±5.12%, p=0.055).

Discussion and Conclusions: In this study, overall bone growth was greater when cups were treated with BMSCs. Bone-implant contact was significantly improved as well. This study has clinical applications, as using MSCs in fibrin glue promotes a bony seal in contact with the implant which may prevent the migration of particles, or joint fluid, decreasing the likelihood of aseptic loosening of THAs, and improving their longevity. Also, this technique may improve fixation in situations where bone stock is reduced.

Introduction: Finite element (FE) simulation of damage accumulation in the femoral cement mantle is widely used to predict failure of hip prostheses. It is often assumed that the stem-cement interface remains bonded, although debonding is thought to affect cement stress and damage. Rough stems may reduce subsidence, but have been reported to have a detrimental effect on implant survival. Other factors thought to influence cement damage include stem design and orientation and cement thickness. This study investigates the effect of cement mantle thickness and stem malpositioning on cement damage around a smooth, collared implant, and the extent to which this is affected by debonding of the stem-cement interface.

Method: Three FE meshes were built to represent proximal femora with Stanmore Hip prostheses implanted into a thick (2.5 mm) and a thin (1.0 mm) cement mantle, and another thin (1.0 mm) mantle with the implant tilted in varus to achieve a minimal thickness of 0.1 mm laterally. Each model consisted of 4304 eight-noded brick elements with frictional contact at the stem-cement interface. Two analyses were run for each model, in which the stem-cement interface was (a) fully bonded, and (b) fully debonded, with Coulomb frictional contact using a friction coefficient of 0.5. Standardised femur geometry and elastic properties were used. Creep and non-linear damage accumulation in the cement mantle under cyclic loading was modelled using subroutines developed by Stolk et al. (2003). Boundary conditions were applied representing a peak stair-climbing load.

Results: Bonded cases showed extensive cracking around the tip in all cases. Debonded cases had 4–8 times less cracking, which was much more focused at the tip; only the poorly-centralised mantle showed extensive damage elsewhere, in the very thin lateral region. When bonded, the thick mantle had least cracks and the poorly-centralised mantle had most; in the debonded cases, there was no major difference between thick, thin, and poorly-centralised mantles. For each cement mantle geometry, peak maximum principal cement stress was consistently lower in the debonded case than in the bonded case.

Discussion: Our results show greater, more widely distributed cracking in bonded than debonded cement mantles, in contrast with previous studies involving collarless implants. For a collared stem, calcar contact prevents subsidence, allowing cement stress relaxation. A possible explanation for our result is that debonding enhances the stress relaxation process, reducing and redistributing interfacial and shear stresses; thus reducing damage rates. In contrast, a debonded collarless stem subsides continuously, sustaining high cement stress levels and damage rates. These results may explain the disappointing clinical performance of some rough-surfaced prostheses. Our results suggest that bonding might increase both cement damage and its sensitivity to cement thickness. Similar results for all debonded cement mantles indicate that cement thickness may be less critical than previously thought for smooth, collared prostheses. Bonding should not be assumed in FE studies of smooth stems which clinically are likely to debond; cement damage simulation should be extended to incorporate the debonding process.

Introduction: Incorporation of Silicon into the HA structure enhances the bioactivity of Hydroxyapatite (HA). Silicon substituted calcium phosphate (SiCaP/SiHA) has been introduced as an osteoconductive material for bone formation. However, the osseoinductive capacity of this biomaterial has not been assessed. A previous study by Hing et al shows that bioactivity of stoichiometric hydroxyapatite bone substitute materials is enhanced by increasing the level of porosity within the implant struts [1].

The aim of this study was to test the hypothesis that SiCaP bone graft results in superior osseoinduction compared to stoichiometric HA and osseoinduction enhancement using high microporosity materials.

Methods: Implantation of 32 bone graft plugs (16 granular and 16 blocks) with 3 different strut porosities: 20% SiHA, 35% SiHA, 10% SiHA and 20% HA, all with matched 80% total porosity supplied by ApaTech Ltd into the paraspinalis muscle of 4 sheep for 12 weeks. HA and %SiHA locations were randomized at implant sites.

Following euthanasia at 12 weeks histomorphometry was carried out to calculate Percentage of bone, soft tissue and implant area and Percentage of the amount of bone in contact with the calcium phosphate surface (% Bone attachment). Further evaluation of Calcium, Phosphate and Silicon levels within the implants and surrounding bone was carried out by Scanning Electron Microscopy (SEM) and EDAX.

Results: Bone formation was observed within the pores of both granules and blocks of SiCaP and HA implants. Greater bone formation and attachment was detected in scaffolds with higher strut porosity (SiHA35) compared to implants of the same chemical composition but lower strut porosity (SiHA10, SiHA20. More bone formation and contact was observed in SiHA implants (SiHA20) compared to matched porosity HA implants where the amount of bone formed was minimal. Uniform distribution of Silicon (Si) was visible within the SiHA scaffold struts according to EDAX results. Greater quantities of Si existed in newly formed bone as compared to soft tissue adjacent to the SiHA implants. Silicon was not detected in either soft or hard tissues adjacent to HA implants.

Conclusion: Both microporous HA and SiCaP promote bone ingrowth, as ectopic bone formation was observed in all four groups of synthetic materials. Matched porosity SiCaP is more osseoinductive than HA. Increasing strut porosity results in promotion of osseoinductivity. High strut porosity (> 10%) block environment contributes to greater osseoinductive behaviour. In conclusion we report that presence of silicon and the strut porosity influence the osseoinductive capacity of calcium phosphate bone substitute biomaterials.

Introduction There are 1 million cases of major skeletal defects :that occur worldwide each year that lead to significant morbidity and disability and currently require bone grafting as the main mode of treatment. Limitations of bone-grafting include donor site morbidity, reduced osseoinductivity and risk of pathogen transmission to the host. There is considerable interest in finding ways of differentiating mesenchymal stem cells down the osteoblastic lineage to form bone tissue. We hypothesized that there is an optimum strain that promotes differentiation of mesenchymal stem cells into osteoblasts.

Methods: A bioreactor was developed that was capable of applying tensional forces across a culture strip in a graduated manner within a range of 1-4373me. Mesenchymal stem cells were grown on these strips and subjected to cyclical tensile strain at 1Hz. Cell morphology using Scanning Electron Microscopy, mineralization using specialized stains and expression of core binding factor1 (Cbfa1) was studied at various strain levels.

Results: Scanning Electron Microscopy revealed classic osteoblastic cells in the regions subjected to tensile force, especially in the region where average strain was 1312me. X-ray microanalysis revealed calcium deposits on the strip, indicating osteoblastic differentiation. Cbfa1 expression was greatest in the region with an average strain 1312 me followed by a region on the strip subjected to just fluid shear without any tension. Cbfa1 expression was significantly greater in cells subjected to tensile forces than unstrained controls at all levels of strain tested (p< 0.05). Cbfa1 expression was further enhanced significantly by the addition of osteogenic factors (p< 0.05). Significantly greater mineralization (p< 0.05) occurred in the regions subject to tension with the greatest being in the region with an average strain of 1312 me.

Conclusions: Mechanical tensile forces especially in the range of up to 2173me promote differentiation of Mesenchymal Stem Cells into osteoblasts and encourage expression of the Cbfa1 gene. Tensile strain also promotes mineralization. Chemical factors in form of osteogenic media accelerate the differentiation of MSCs and encourages earlier production of osteoblast specific markers. Fluid shear appears to have a beneficial effect in stimulating differentiation into the osteoblast phenotype and, combined with tensile strain, may offer an even greater osteogenic stimulus.

Introduction & Aims: A new femoral component for hip arthroplasty has been designed for a younger patient population. The design makes use of a higher femoral cut, which conserves bone stock, increasing options for future revision surgery. It uses the existing load bearing properties of the proximal femur, and therefore distributes load more evenly. The stem is longer than that of a resurfacing, so will be easier to insert at the correct orientation, minimising failure rates in inexperienced hands. The cross-sectional dimensions have been designed to produce torsional stability. The collar maximises the loading of the calcar, reducing stress resorption. The surface is hydroxyapatite coated and porous, which will produce a long-term biological fixation.

This project assessed the long-term stability of this design at different orientations, by measuring the change in surface strain distribution following its insertion.

Methods: Ten composite bones were coated in a Photoelastic material, positioned at a simplified single leg stance, and loaded at 2.3 KN. The surface strain was measured at one-centimetre intervals down the medial cortex. Then the prostheses were inserted into the bone at 135°, 145° and 125° to the femoral shaft, and the surface strains reread.

Results: The results were compared with an FEA model, and analysed statistically using the Wilcox signed rank test. The prosthesis inserted at 135° produced no significant difference in surface strain distribution compared with the intact bone.

Conclusions: This study suggests this stem design will be stable in the long term following insertion, and there were no areas of excessively high or low strain.

We previously demonstrated that cartilaginous tissue was induced on a reamed acetabular articulation in an ovine hemiarthroplasty model with three different femoral head sizes. At maximum loading during stance phase, the acetabular peak stresses immediately after reaming could reach approximately 80 MPa under direct implant-bone contact with in-vitro measurements.

We aimed to establish finite element (FE) models of the ovine hip hemiarthroplasty which examine stress distribution on the reamed acetabula by three head sizes. We hypothesized that the stress distribution did not differ between different sizes when the joint is congruent and that the peak stresses in the acetabulum immediately after reaming occurred in the dorsal acetabulum.

Three two-dimensional FE models of ovine hip hemi-arthroplasty were built; each comprised a head component, 25, 28, and 32 mm in diameter, and an acetabular component. The acetabular geometry was acquired from an ovine acetabular histological section. The head was moved to partly intersect with the acetabulum representing the reaming procedure and a congruent contact was confirmed. Cortical bone and cancellous bone were modelled as linear elastic, with moduli of 20 and 1.2 GPa, respectively. Variable moduli were also assessed. The finest mesh for each model consisted of over 100,000 four-node quadrilateral elements. Loading conditions were chosen to represent peak hip joint force developed during the stance phase. Stress distribution in the acetabular area in contact with the head was plotted against the articulating arc length.

The results confirmed that the stress distribution between different prosthetic head sizes in a reamed hemiarthroplasty model did not change when the joint was congruent. The peak compressive stresses occurred in the dorsal acetabulum with the 32 mm model being the highest at approximately 69 MPa, the 28 mm model at 63 MPa, and the 25 mm model at 54 MPa. An increase in the cancellous modulus and a decrease in the cortical modulus increased the peak stresses in the dorsal acetabulum.

This presents an indicative study into the effect of prosthetic femoral head sizes on the stress distribution in the acetabulum. The idealized 2-D models showed reasonable agreement when compared quantitatively with the in vitro study.

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 mini compression screws on cortical and cancellous bone models.

Material and Methods: The screws that were tested are listed in the table below. 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.

Results: The Headed AO 3.5 mm cortical screw gave the best compression force 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 talonavicular arthrodeses, Headed AO 3.5 mm or 2.7 mm cortical or 4 mm cancellous screws, which give better compression, should be used.