It has been speculated that high wear at the head-stem taper may contribute to the high failure rates reported for stemmed large head metal-on-metal (LH-MOM) hips. In this study of 53 retrieved LH-MOM hip replacements, we sought to determine the relative contributions of the bearing and taper surfaces to the total wear volume. Prior to revision, we recorded the relevant clinical variables, including whole blood cobalt and chromium levels. Volumetric wear of the bearing surfaces was measured using a coordinate measuring machine and of the taper surfaces using a roundness measuring machine. The mean taper wear volume was lower than the combined bearing surface wear volume (p = 0.015). On average the taper contributed 32.9% of the total wear volume, and in only 28% cases was the taper wear volume greater than the bearing surface wear volume. Despite contributing less to the total material loss than the bearing surfaces, the head-stem taper junction remains an important source of implant-derived wear debris. Furthermore, material loss at the taper is likely to involve corrosion and it is possible that the material released may be more biologically active than that from the bearing surface.

Repair of tendon injuries aims to restore length, mechanical strength and function. We hypothesise that Demineralised Cortical Bone (DCB) present in biological tendon environment will result in remodelling of the DCB into ligament tissue. A cadaveric study was carried out to optimize the technique. The distal 1cm of the patellar tendon was excised and DCB was used to bridge the defect. 4 models were examined, Model-1: one anchor, Model-2: 2 anchors, Model-3: 2 anchors with double looped off-loading thread, Model-4: 2 anchors with 3 threads off-loading loop. 6 mature sheep undergone surgical resection of the distal 1cm of the right patellar tendon. Repair was done using DCB with 2 anchors. Immediate mobilisation was allowed, animals were sacrificed at 12 weeks. Force plate assessments were done at weeks 3, 6, 9 and 12. Radiographs were taken and pQCT scan was done prior to histological analysis. In the cadaveric study, the median failure force for the 4 models; 250N, 290N, 767N and 934N respectively. In the animal study, none of the specimens showed evidence of ossification of the DCB. One animal failed to show satisfactory progress, X-rays showed patella alta, on specimen retrieval there was no damage to the DCB and sutures and no evidence of anchor pullout. Functional weight bearing was 79% at week12. Histological analysis proved remodelling of the collagen leading to ligamentisation of the DCB. Results prove that DCB can be used as biological tendon substitute, combined with the use of suture bone anchor early mobilisation can be achieved.

Treatment of tendon and ligament injuries remains challenging; the aim is to find a biocompatible substance with mechanical and structural properties that replicate those of normal tendon and ligament. We examined the mechanical properties of Demineralised Cortical Bone (DCB) after gamma irradiation (GI) and freeze drying (FD). We also used different techniques for repairing bone-tendon-bone with DCB in order to measure the mechanical performance of the construct. DCB specimens were allocated into 4 groups; FD, GI, combination of both or none. The maximum tensile forces and stresses were measured. 4 cadaveric models of repair of 1cm patellar tendon defect using DCB were designed; model-1 using one bone anchor, Model-2 using 2 bone anchors, Model-3 off-loading by continuous thread looped twice through bony tunnels, Model-4 off-loading with 3 hand braided threads. Force to failure and mode were recorded for each sample. FD groups results were statistically higher (p=<0.05) compared to non-FD groups, while there was no statistical difference between GI and non-GI groups. The median failure force for model-1: 250N, model-2: 290N, model-3: 767N and model-4: 934N. There was no statistical significance between model-1 and model-2 (p=0.249), however statistical significance was found between other models (p=<0.006). GI has no significant effect on mechanical strength of the CDB while FD may have positive effect on its mechanical strength. Our study shows that a tendon rupture can be successfully augmented with CDB giving initial appropriate mechanical strength suitable for in vivo use providing the biological reactions to the graft are favourable.

Introduction

Tendon injuries remain challenging, secondary healing and prolonged immobilisation result in suboptimal outcome. Previous study by our group showed that demineralised bone matrix (DBM) can result in faster healing of a tendon enthesis. The aim of this study is to test different ways augmenting tendon with DBM to enhance tendon repair and regeneration.

Introduction

Demineralised Bone Matrix (DBM) is widely used in Orthopaedics and dentistry as a bone graft substitute and may be used to augment bone formation in load bearing applications.

In this study we examine the effect of gamma irradiation and freeze drying on the tensile strength of Demineralised Cortical Bone (DCB).

Introduction

Following amputation, residual stumps used to attach the external prostheses can be associated with sores, infection and skin necrosis. These problems could be overcome by off loading the soft tissues. Intraosseous transcutaneous amputation prostheses (ITAP) attach external implants directly to residual bone reducing these complications. However, a tight seal at the skin implant interface is crucial in preventing epithelial down-growth and infection. Fibronectin (Fn) and laminin 332 (Ln), enhance early cell growth and adhesion of keratinocytes. Silanization to titanium alloy (Ti) allows these proteins to bond to the metal directly. We hypothesize that silanized dual coatings of fibronectin and laminin (SiFnLn) will be more durable than absorbed proteins and that keratinocyte adhesion will be increased compared with Ti controls and single silanized proteins.

Introduction

Intraosseous transcutaneous amputation prostheses (ITAP) provide an alternative means of attaching artificial limbs for amputees. Conventional stump-socket devices are associated with soft tissue complications including; pressure sores and tissue necrosis. ITAP resolves these problems by attaching the exo-prosthesis transcutaneously to the skeleton. The aim of this study is to increase the attachment of dermal fibroblasts to titanium alloy in vitro. Fibronectin (Fn) and laminin 332 (Ln) enhance early cell growth and adhesion. We hypothesize that silanized dual coatings of fibronectin and laminin (SiFnLn) will be more durable when compared with adsorbed dual coating (AdFnLn), and will enhance early fibroblast growth and adhesion compared to single coatings.

INTRODUCTION

Autologous bone grafts are considered gold standard in the repair of bone defects. However they are limited in supply and are associated with donor site morbidity. This has led to the development of synthetic bone graft substitute (BGS) materials, many of which have been reported as being osteoinductive. The structure of the BGS is important and bone formation has been observed in scaffolds with a macroporous morphology. Smaller pores termed ‘strut porosity’ may also be important for osteoinduction. The aim of this study was to compare the osteoinductive ability of one silicate-substituted calcium phosphate (SiCaP) with differing strut porosities in an ectopic ovine model. Our hypothesis was that SiCaP with greater strut porosity would be more osteoinductive.

Background

Extendable proximal femoral replacements(PFR) are used in children with bone tumours in proximity to the proximal femoral physis, previously treated by hip disarticulation. Long-axis growth is preserved, allowing limb salvage. Since 1986, survival outcomes after limb salvage and amputation have been known to be equal.

Background

Extendable partial femoral replacements (EPFR) permit limb salvage in children with bone tumours in proximity to the physis. Older designs were extended through large incisions or minimally invasive surgery. Modern EPFR are lengthened non-invasively. Lengthening improves functional score (Futani, 2006) but has been associated with complications including infection (Jeys, 2005). This study is the first to look specifically at the relationship between EPFR lengthening and complications.

Background/Aims

The development of extendable prostheses has permitted limb salvage surgery in paediatric patients with bone tumours in proximity to the physis. Prostheses are extended to offset limb length discrepancy as the child grows. Aseptic loosening (AL) is a recognised complication. The implant stem must fit the narrow paediatric medullary canal and remain fixed while withstanding growth and increasing physical demands. Novel designs incorporate a hydroxyapatite (HA) coated collar that manufacturers claim improves bony ongrowth and stability, providing even stress distribution in stem and shoulder regions and providing a bone-implant seal, resulting in decreased AL and prolonged survival. This study aims to assess whether there is a relationship between bony ongrowth onto a HA collar and AL. Hypothesis: Bone ongrowth onto the HA collar of extendable prostheses is associated with more stable fixation and less AL despite patient growth.

Introduction

A new conservative hip stem has been designed to address the complex problem of total hip arthroplasty in the younger population.

Synthetic bone grafts are used in several major dental and orthopaedic procedures. Strontium, in the form of strontium ranelate, has been shown to reduce fracture risk when used to treat osteoporosis. The aim of the study was to compare bone repair in femoral condyle defects filled with either a 10% strontium substituted bioactive glass (StronBoneTM) or a TCP-CaSO4 graft. We hypothesise that strontium substituted bioactive glass increases the rate of bone ingrowth into a bone defect when compared to a TCP-CaSO4 ceramic graft.

A critical size defect was created in the medial femoral condyle of 24 sheep; half were treated with a Sr-bioactive glass (StronBoneTM), and in the other animals defects were filled TCP-CaSO4. Two time points of 90 and 180 days were selected. The samples were examined with regard to: bone mineral density (BMD) from peripheral quantitative CT (pQCT), mechanical properties through indentation testing, and bony ingrowth and graft resorption through histomorphometry.

The radiological density of Sr-bioactive glass in the defect is significantly higher than that of the TCP-CaSO4-filled defect at 90 and 180 days, (p=0.035 and p=0.000). At 90 days, the stiffness of the defect containing Sr-bioactive glass and is higher than that of the TCP-CaSO4 filled defect, (p=0.023). At 6 months there is no significant difference between the two materials. Histomorphometry showed no significant difference in bone ingrowth at any time point, however significantly more of the graft is retained for the StronBoneTM treatment group than the TCP-CaSO4 group at both 0 days (p=0.004) and 180 days (p=0.000). The amount of soft tissue within the defect was significantly less in the StronBoneTM group than for the TCP-CaSO4 group at 90 days (p=0.006) and 180 days (p=0.000)

The data shows the mechanical stability of the defect site is regained at a faster rate with the strontium substituted bioglass than the TCP-CaSO4 alternative. Histomorphmetry shows this is not due to increased bone ingrowth but may be due to the incorporation of stiff graft particles into the trabeculae. Sr-bioactive glass produces a stronger repair of a femoral condyle defect at 3 months compared with TCP-CaSO4.

Introduction

The National Joint Registry has recently identified failure of large head metal on metal hip replacements. This failure is associated with the high torque at the interface of standard modular taper junction leading to fretting and corrosion. A number of manufacturers produce mini spigots, which in theory, provide a greater range of motion as the neck head junction is reduced. However, the relative torque to interface ratio at this junction is also increased. In this study we investigated hypothesis that the use of small spigots (minispigots) will increase wear and corrosion on modular tapers.

Introduction

A modified anodisation technique where a titanium surface releases bactericidal concentrations of silver was developed and called Agluna. Our hypothesis was that silver incorporation was bactericidal and had no effects on the viability of fibroblasts and osteoblasts, would have no negative effect on interfacial shear strength and bone contact in an in vivo trans-cortical implant ovine model.

Introduction

This study investigated the binding agent Calcium/Sodium Alginate fibre gel and the addition of autogenic bone marrow aspirate (BMA) on bone growth into a porous HA scaffold implanted in an ovine femoral condyle critical-sized defect. Our hypothesis was that Alginate fibre gel would have no negative effect on bone formation and osteoconduction within the scaffold and that BMA would augment the incorporation of the graft with the surrounding bone at 6 and 12 weeks post implantation.

Impaction allograft using cement is commonly used in revision surgery for filling bone defects and provides a load bearing interface. However, the variable regeneration of new bone within the defect makes clinical results inconsistent. Previous studies showed that addition of mesenchymal stem cells (MSCs) seeded on allograft can enhance bone formation in the defect site. The purpose of this study is to test the hypothesis that heat generated during cement polymerization will not affect viability of the human MSCs.

The temperatures and durations were taken from previous studies that recorded the maximum temperature generated at the bone-cement interface. Temperatures of below 30 degrees Celsius to over 70 degrees Celsius have been detected and the duration of elevated temperature varies from 30 seconds to 5 minutes. In this study the viability of MSCs cultured at different temperatures was assessed. Ten groups were studied with three repeats (Table 1). A control group in which cells were cultures normally was used.

Culture medium was heated to the required temperature and added to the cells for the required duration. The metabolism of MSCs was measured using the alamar Blue assay, cell viability was analysed using Trypan Blue and cell apoptosis and necrosis were tested using Annexin V and Propidium Iodide staining.

Results showed that cell metabolism was not affected with temperatures up to 48 degrees Celsius for periods of 150s, while cells in the 58 degrees Celsius group eventually died (Fig. 1). Similar results were shown in Trypan Blue analysis (Fig. 2). When comparing the group of cells heated to 48 degrees Celsius for 150s with the control group for apoptosis and necrosis, no significant difference was observed.

The study suggests that human MSCs seeded to allograft can be exposed to temperatures up to 48 degrees Celsius for 150s, which covers many of the situations when cement is used. This indicates that the addition of mesenchymal stem cells to cemented impaction grafting can be carried out without detrimental effects on the cells and that this may increase osteointegration.

Infection is the primary failure modality for transcutaneous implants because the skin breach provides a route for pathogens to enter the body. Intraosseous transcutaneous amputation prostheses (ITAP) are being developed to overcome this problem by creating a seal at the skin-implant interface to prevent bacterial invasion. Oral gingival epithelial cell adhesion creates an infection free seal around dental implants; however this has yet to be demonstrated outside the oral environment. All epithelial cells attach via hemidesmosomes (HD) and focal adhesions (FA) and their expression is an indicator of adhesion efficiency. The aim of this study was to compare epidermal keratinocyte with oral gingival epithelial cell adhesion on titanium alloy in vitro to determine whether these two cell types differ in their speed and strength of adhesion. It was hypothesised that oral gingival epithelial cells attach to titanium alloy earlier than epidermal keratinocytes; with greater expression of hemidesmosomes and focal adhesions.

Human oral gingival epithelial cell (HGEP) and primary human epidermal keratinocyte (HPEK) adhesion to titanium alloy, was assessed at 4, 24, 48 and 72 hrs. Adhesion was measured by the number of FAs per unit cell area and expression of HDs using a semi-quantitative scale.

At 4 and 24hrs, there was a significant increase in vinculin marker expression per unit cell area of 4.3 and 4.7 times in HGEP compared with HPEK (p=0.000). At 48 and 72hrs there were no significant differences.

HD expression was significantly greater in HGEP at 4 and 24hrs (p=0.002) compared with HPEK. Up-regulation of HD expression in HPEK lagged that of HGEP until 48hrs, after which no significant differences were observed.

This study has demonstrated that oral gingival cells up-regulate both focal adhesion and hemidesmosome expression at earlier time points compared with epidermal keratinocytes. Expression of hemidesmosomes lags that of focal adhesions, suggesting that focal adhesion formation is a prerequisite for hemidesmosome assembly. We postulate that early attachment of oral gingival epithelial cells to dental implant biomaterials may be responsible for the formation of an infection-free seal.

Introduction

Following bone tumour resection, lower limb reconstruction results in leg-length discrepancy in skeletally immature patients. Previously, minimally invasive endoprostheses have been associated with a high risk of complications including joint stiffness, nerve injury, aseptic loosening and infection. The purpose of this study was to examine the outcome of the Stanmore non-invasive extendible endoprostheses used in our institution between 2002 and 2009 and compare them with implants used in the past.

Introduction

Primary bone tumours of the distal radius are rare, while it remains the third commonest site for primary lesions and recurrences of Giant Cell Tumours (GCT). The functional demands on the hand make reconstruction of the wrist joint following the excision of distal radius, particularly challenging.

Non-invasive expandable prostheses for limb salvage tumour surgery were first used in 2002. These implants allow ongoing lengthening of the operated limb to maintain limb-length equality and function while avoiding unnecessary repeat surgeries and the phenomenon of anniversary operations.

A large series of skeletally immature patients have been treated with these implants at the two leading orthopaedic oncology centres in England (Royal National Orthopaedic Hospital, Stanmore, and Royal Orthopaedic Hospital, Birmingham).

An up to date review of these patients has been made, documenting the relevant diagnoses, sites of tumour and types of implant used. 87 patients were assessed, with an age range of 5 to 17 years and follow up range of up to 88 months.

Primary diagnosis was osteosarcoma, followed by Ewing's sarcoma. We implanted distal femoral, proximal femoral, total femoral and proximal tibial prostheses. All implants involving the knee joint used a rotating hinge knee. 6 implants reached maximum length and were revised. 8 implants had issues with lengthening but only 4 of these were identified as being due to failure of the lengthening mechanism and were revised successfully. Deep infection was limited to 5% of patients.

Overall satisfaction was high with the patients avoiding operative lengthening and tolerating the non-invasive lengthenings well. Combined with satisfactory survivorship and functional outcome, we commend its use in the immature population of long bone tumour cases.

Infected mega-endoprostheses are difficult to treat with systemic antibiotics due to encapsulation of the implant by fibrous tissue, formation of biofilms and antibiotic resistant bacteria. Modifying the implant surface by incorporating a bactericidal agent may reduce infection. Infection rates are typically in the range of 8% to 30%. This study describes a novel process method of “stitching-in” ionic silver into the implant surface, in vitro testing and its early clinical usage.

A novel process has been developed to “stitch in” ionic silver into the upper surface of titanium alloy (Ti6Al4V). The process produces a modification by anodisation of the titanium alloy in dilute phosphoric acid, followed by absorption of silver from an aqueous solution. The engineered surface modification is therefore integral with the substrate and loaded with silver by an ion exchange reaction. Using this technique the maximum inventory of silver for typical a mega-prosthesis is 6mg and this is greater than 300 times lower than the No Observable Adverse Affects Level (NOAEL). Scanning electron microscopy revealed that the silver was concentrated in pits and forming reservoirs of ionic silver exposed to the body tissues.

Laboratory-based studies focusing on the safety and efficacy of silver as a bactericidal agent have included investigation into cytotoxicity using fibroblast and osteoblast cell lines, the impact of silver in reducing corrosion and laboratory testing to establish if the modified surface has an effect on the wear and mechanical characteristics. A range of fatigue, static, tensile pull off tests were performed. The silver elution profiles for both silver loaded and HA coated over a silver loaded surface have been examined. Histological studies were also performed to examine the impact of the silver on osseointegration.

The in vitro results confirm that silver is an effective antimicrobial agent. The mechanical characterization studies have identified that the surface treatment has no or minimal impact on the implant surface. Early results of the elution studies are encouraging showing that the HA coating of a silver loaded surface does not “seal” in the silver.

To date (May 10) 147 silver treated mega-prostheses have been implanted since March 2006. The majority of implants were distal femoral (29%), proximal tibial (23%) or hemiplevic (10%). The most common indication was revision of a failed limb salvage reconstruction (58%), with the dominant cause of failure being infection. The next most common indication was bone tumour (31%) and the large majority were used in the high risk skeletal locations of the tibia (44%) and the pelvis (27%). Early clinical results are encouraging indicating a significant reduction in the incidence of infection.

Three implants have been retrieved. An analysis of a proximal humeral replacement that had been in situ for 6 mths identified that there was 10-20% remaining on the implant surface.

This novel process of “stitching-in” silver appears to be a safe and effective surface treatment in helping to control infections of mega-prostheses. This technology has the potential to be transferred to other arthroplasty joints.

Polymethyl methacrylate spacers are commonly used during staged revision knee arthroplasty for infection. In cases with extensive bone loss and ligament instability, such spacers may not preserve limb length, joint stability and motion.

We report a retrospective case series of 19 consecutive patients using a custom-made cobalt chrome hinged spacer with antibiotic-loaded cement. The “SMILES spacer” was used at first-stage revision knee arthroplasty for chronic infection associated with a significant bone loss due to failed revision total knee replacement in 11 patients (58%), tumour endoprosthesis in four patients (21%), primary knee replacement in two patients (11%) and infected metalwork following fracture or osteotomy in a further two patients (11%). Mean follow-up was 38 months (range 24–70). In 12 (63%) patients, infection was eradicated, three patients (16%) had persistent infection and four (21%) developed further infection after initially successful second-stage surgery. Above knee amputation for persistent infection was performed in two patients.

In this particularly difficult to treat population, the SMILES spacer two-stage technique has demonstrated encouraging results and presents an attractive alternative to arthrodesis or amputation.

Medial Displacement Osteotomy (MDO) of the os calcis is used to correct the hind foot valgus in a flat foot deformity. Screw fixation is commonly used although contemporary locking plate systems are now available. This study tested the hypothesis that a 10mm MDO would support a higher load to failure with a locked step plate than with a single cannulated screw.

We performed a retrospective review of 98 patients with malignant tumours of the periacetabular region, treated by resection and endoprosthetic reconstruction between 1971 and 2005 at the Royal National Orthopaedic Hospital, Stanmore and The Royal Orthopaedic Hospital, Birmingham.

The mean age of the patients was 43.6 years (10 to 76). 53 patients (54%) were male. The age distribution demonstrated peaks in the 2nd and 6th decades. The mean follow up was 65 months (2 to 405. The overall 10-year survival rate was 56% (determined by the Kaplan-Meier method).

54 patients (58.1%) had one or more complications. Infection was the most common (30%) with the majority occurring in the first 2 years. Dislocation occurred in 19 (20%) of our patients all in the first year following surgery. All were recurrent with a mean of 2.9 (2 to 6) episodes. Operations performed before 1994 were associated with a dislocation rate of 40.5% and after 1996 the rate was only 3.9% (p < 0.001).

Function was assessed according the Toronto Extremity Salvage Sore (TESS). The overall TESS was 59.4. In patients that had a major complication the TESS was 37.1 but in the group that did not the TESS was 70.3 (p < 0.001).

Men experienced higher rates of death, infection and revision than women (p < 0.05). The local recurrence rate was 31% with high grade tumours associated with higher recurrence rates (p < 0.05). Tumour resection in the ilium is associated with higher rates of infection than tumours located in the periacetabular region alone (p < 0.05).

This method of reconstruction is still associated with high complication rates. Function is good if a major complication can be avoided. The lower dislocation rate more recently is probably the result of improved surgical technique and the use of larger femoral heads.

Chondrosarcoma is a malignant tumour and accounts for approximately 20% of bone sarcomas. The pelvis is one of the commonest sites. Chondrosarcoma of the pelvis lends itself to surgical excision and is relatively resistant to irradiation and chemotherapy. A long term survival analysis of this challenging condition is rarely reported in literature. We review and evaluate the oncological and functional results of all the patients operated at our centre and we analyse the survival analysis of these patients with special focus on the prognostic factors.

Fifty-four consecutive patients with chondrosarcoma of the pelvis who were treated at the Royal National Orthopaedic Hospital, Stanmore, UK between 1987 and 2001 were included in the study. Demographic data, case notes, histopathological results and follow-up data were obtained and statistically analysed.

There were 38 males and 16 females with a mean age of 48.4 years [18-77]. The chondrosarcomas were primary [n=38], secondary [n-7] or recurrences [n=9]. The anatomical sites in the pelvis were in the epicentre I [n=24], II [n=20] and III [n=10]. The surgical procedures performed were local resection [n=28], local resection and hip arthroplasty [n=6], hemipelvectomy (+endoprothesis) [n=16], hemipelvectomy [+fibular strut graf] [n=2] and hinquarter amputation [n=2]. The histological grade was Gr [n=27], Gr 2[n=20] and Gr 3 [n=7]. The complication rate was 24%:wound revision [9%], dislocation [8%] and infection [7%]. There was a 5, 10 and 15 year cumulative survival rate of 74%, 65% and 40%. The overall recurrence rate was 24%.

The factors associated with a worse prognosis were high histologic tumour grade, increasing patient age, anatomical location in site I and III, primary surgery outside of tumour centre, inadequate surgical margins, and those treated by local extension. Aggressive surgical approach significantly improves the prognosis of the patients with chondrosarcoma of the pelvis.

When performing limb salvage operations for malignant bone tumours in skeletally immature patients, it is desirable to reconstruct the limb with a prosthesis that can be lengthened without surgery at appropriate intervals to keep pace with growth of the contra-lateral side. We have developed a prosthesis that can be lengthened non-invasively. The lengthening is achieved on the principle of electromagnetic induction.

The purpose of this study was to look at our early experience with the use of the Non Invasive Distal Femoral Expandable Endoprosthesis. A prospective study of 17 skeletally immature patients with osteosarcoma of the distal femur, implanted with the prosthesis, was performed at the Royal National Orthopaedic Hospital, Stanmore. The patients were aged between 9 and 15 years (mean 12.1 years) at the time of surgery. Patients were lengthened at appropriate intervals in outpatient clinics. Patients were functionally evaluated using the Musculoskeletal Tumour Society (MSTS) Scoring System and the Toronto Extremity Severity Score (TESS). Average time from the implantation to the last follow-up was 18.2 months (range 14-30 months). The patients have been lengthened by an average of 25mm (4.25-55mm). The mean amount of knee flexion is 125 degrees. The mean MSTS score is 77% (23/30; range 11-29) and the mean TESS score is 72%. There have been two complications: one patient developed a flexion deformity of 25 degrees at the knee joint and one patient died of disseminated metastatic malignancy.

The early results from patients treated using this device have been encouraging. Using this implant avoids multiple surgical procedures and general anaesthesia. This results in low morbidity, cost savings and reduced psychological trauma. We do need additional data regarding the long-term structural integrity of the prosthesis.

Background

Endoprosthetic reconstruction is an established method of treatment for primary bone tumours in children. Traditionally these were implanted with cemented intramedullary fixation. Hydroxyapatite collars at the shoulder of the implant are now standard on all extremity endoprostheses, but older cases were implanted without collars. Uncemented intramedullary fixation with hydroxyapatite collars has also been used in an attempt to reduce the incidence of problems such as aseptic loosening. Currently there are various indications that dictate which method is used.

Non-invasive expandable prostheses for limb salvage tumour surgery were first used in 2002. These implants allow ongoing lengthening of the operated limb to maintain limb-length equality and function while avoiding unnecessary repeat surgeries and the phenomenon of anniversary operations.

A large series of skeletally immature patients have been treated with these implants at the two leading orthopaedic oncology centres in England (Royal National Orthopaedic Hospital, Stanmore, and Royal Orthopaedic Hospital, Birmingham).

An up to date review of these patients has been made, documenting the relevant diagnoses, sites of tumour and types of implant used. 74 patients were assessed, with an age range of 7 – 16 years and follow up range of 4 – 88 months.

We identified five problems with lengthening. One was due to soft tissue restriction which resolved following excision of the hindering tissue. Another was due to autoclaving of the prosthesis prior to insertion and this patient, along with two others, all had successful further surgery to replace the gearbox. Another six patients required mechanism revision when the prosthesis had reached its maximal length. Complications included one fracture of the prosthesis that was revised successfully and six cases of metalwork infection (two of which were present prior to insertion of the implant and three of which were treated successfully with silver-coated implants). There were no cases of aseptic loosening.

Overall satisfaction was high with the patients avoiding operative lengthening and tolerating the non-invasive lengthenings well. Combined with satisfactory survivorship and functional outcome, we commend its use in the immature population of long bone tumour cases.

Introduction: Hydrogenated (acetylene:C2H2) and silanized (tetra methyl silane:TMS) diamond-like-carbon coatings (DLC) are applied to titanium alloy to reduce surface energy, cell adhesion and hydrophilicity. The incorporation of silicon into DLC reduces its surface energy. It was hypothesized that surfaces that have high surface energy and high hydrophilicity favoured the adhesion and maturation of fibroblasts when compared with C2H2 and TMS coated substrates in vitro. This would help in achieving a seal at the prosthesis – soft tissue interface, thereby helping in reducing infection.

Methods: and Materials: Fibroblasts were cultured on 10 mm diameter titanium alloy, C2H2 and TMS coated titanium alloy discs for 4 hours and 24 hours (2500 cells per disc). Cell area, adhesion plaque numbers, number of plaques per unit area (plaque density) and the total area of adhesion plaques per cell were analysed. The results were compared between experimental groups and controls at 4 and 24 hours. In order to measure the strength of adhesion of cells fibroblasts were cultured on discs (30 mm diameter)[machine finished and polished(Ra = 0.031)](density-300,000 cells per disc) for 4 and 24 hours with similar coatings and exposed to radial shear by flow (100 mls/min) of culture media over their surface. These discs were then stained and analysed using Photoshop (ver.5.5) and SPSS (ver.16). Mann-Whitney tests were used to calculate significance (p< 0.05).

Results: At 4 and 24 hours, the number of adhesion plaques was significantly greater on control and C2H2 compared with TMS. At 4 hours, cell area on control discs was significantly greater than C2H2 and TMS. At 24 hours, cell area on control and C2H2 was significantly greater than TMS. Between 4 and 24 hours, the number of adhesion plaques increased significantly on all the surfaces. Cell area increased significantly on C2H2 and TMS between 4 and 24 hours. At 4 hours, shear stress needed to dislodge the cells was highest for polished C2H2 and least for titanium unpolished surface. Cells on polished surfaces in corresponding groups required higher shear stress to remove the cells than cells on unpolished surfaces. At 24 hours, cells on polished C2H2 required significantly higher shear stresses to detach them than cells on unpolished C2H2 and TMS (polished and unpolished). Cells on unpolished Ti required higher stress to dislodge than cells on unpolished TMS. From 4 to 24 hours, a significant increase in shear stress to remove the cells was required on all unpolished surfaces and polished C2H2. A significant correlation was seen between adhesion plaque density at 4 hours and shear stress.

Discussion: This work supports the hypothesis that surfaces with high surface energy and high hydrophilicity lead to increased cell attachment and cell area. It also shows the correlation between adhesion plaque density and the shear stress needed to dislodge fibroblasts from bioactive surfaces.

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.