This study reports the mid-term results of a large bearing hybrid metal on metal total hip replacement (MOMHTHR) in 199 hips (185 patients) with mean follow up of 62 months. Clinical, radiological outcome, metal ion levels and retrieval analysis were performed.

Seventeen patients (8.6%) had undergone revision, and a further fourteen are awaiting surgery (defined in combination as failures). Twenty one (68%) failures were females. All revisions and ten (71%) of those awaiting revision were symptomatic. Twenty four failures (86%) showed progressive radiological changes.

Fourteen revision cases showed evidence of adverse reactions to metal debris (ARMD). The failure cohort had significantly higher whole blood cobalt ion levels (p=0.001), but no significant difference in cup size (p=0.77), inclination (p=0.38) or cup version (p=0.12) in comparison to the non revised cohort. Female gender was associated with an increased risk of failure (chi squared p=0.04). Multifactorial analysis demonstrated isolated raised Co levels in the absence of either symptoms or XR changes was not predictive of failure (p=0.675). However both the presence of pain (p<0.001) and XR changes (p<0.001) in isolation were both significant predictors of failure. Wear analysis (n=5) demonstrated increased wear at the trunnion/head interface (mean out of roundness measurements of 34.5 microns +/−13.3 (+/−2SD, normal range 8-10 microns) with normal levels of wear at the articulating surfaces. There was evidence of corrosion at the proximal and distal stem surfaces. The cumulative survival rate, with revision for any reason was 92.4% (95%CI: 87.4-95.4) at 5 years. Including those awaiting surgery, the revision rate would be 15.1% with cumulative survival at 5 years of 89.6% (95% CI: 83.9-93.4).

This MOMHTHR series has demonstrated unacceptable high failure rates with evidence of high wear at the head/trunnion interface and passive corrosion to the stem surface. This raises concern with the use of large heads on conventional 12/14 tapers. Female gender was an independent risk factor of failure. Metal ion levels remain a useful aspect of the investigation work up but in isolation are not predictive of failure.

The aim of this study is to investigate whether MoM implants result in more chromosome aberrations and increased blood metal ions postoperatively whe compared to MoP implants.

MoM arthroplasties are being inserted in increasing numbers of younger patients due to the increased durability and reduced requirements for revision in these implants. Recent studies have raised many concerns over possible genotoxicity of MoM implants.

This is a prospective study of patients who have undergone elective total hip replacement, they were selected and then randomised into two groups. Group A received a MoP implant and group B received a MoM implant. Patients are reviewed pre-operatively (control group), at 3 months, 6 months, 1 year and 2 years post-operatively. On each occasion blood tests are taken to quantify metal ion levels (chromium, cobalt, titanium, nickel and vanadium) using HR-ICPMS method and chromosome aberrations in T lymphocytes using 24 colour fluorescent in situ hydridisation (FISH).

51 patients have been recruited to date, 23 of whom had MoP prosthesis and 28 a MoM. 47 of these had their 1 year follow-up with blood analysis and 38 have had 2 year follow up. There appeared to be a bedding period for both MoM and MoP groups, with an increase in metal ion release. The blood concentration of chromium, cobalt and titanium rise significantly in the MoM group at the 2 year stage. Chromosome aberrations occurred in both groups. Both the MoM and MoP groups showed increase frequency of aneuploidy aberrations and structural damage. The greatest increase in metal ion levels occurred at the 1 to 2 year interval corresponding to significant rise in chromosome aberrations.

Preliminary results of this study show that the levels of chromium, cobalt and titanium are significantly higher in the MoM group compared to the MoP group. This corresponds to increases in chromosome aberrations in the groups with increases in structural chromosome damage after two years.

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

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

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

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

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

Porous collagen-glycosaminoglycan (Col/GAG) scaffolds have previously been used clinically as regeneration templates for peripheral nerves and skin^[1]. For defects involving even minimal load-bearing applications however, these scaffolds do not possess the required stiffness. Calcium phosphates (CaPs) are often used as bone-graft substitutes due to their biocompatibility and direct bone-bonding ability. While CaPs have sufficient stiffness for bone-defect applications, unlike Col/GAG they lack elasticity and are very brittle. Combining these two materials produces a composite with enhanced material properties and chemical similarity to natural bone. The addition of CaP nanocrystallites into the Col/GAG matrix produces a 3-dimensional structure that maintains its structural integrity even when wet. In this study, the in vivo performance of mineralised Col/GAG composites was evaluated by implantation into a six-week ovine bone-defect model.

Four different materials were implanted; Col/GAG alone, Col/GAG with octacalcium phosphate, Col/GAG with hydroxyapatite and Col/GAG with brushite. Implants with a diameter of 9mm and length of 9mm, were placed bilaterally into the distal femoral condyle of the hind legs of thirteen sheep. This site was selected due to the large volume of load-bearing cancellous bone. Cancellous autograft was harvested from the tibial tuberosity and placed in the defect sites of two sheep as a positive control.

All animals were sacrificed after 6 weeks and tissue containing the implants was prepared for histological evaluation. Image analysis of Von Kossa stained sections showed that all mineralised Col/GAG implants had significantly more bone in the implant site than unmineralised Col/GAG but were not significantly different between CaPs. Interestingly, new bone formation often followed the structure of the porous material struts which acted as a template. The defect containing the autograft contained the greatest amount of new bone.

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.

Articular cartilage implantation (ACI) and associated procedures (MACI = Matrix-assisted cartilage implantation) are now established treatments for osteochondral defects in the knee. The quality of repair in terms of histological appearance is frequently not known, whilst the correlation of histology results with functional outcomes remains undefined. Histological data of the quality of the repair tissue is sparse and a precise classification proved difficult.

This was a single-centre, prospective study. Over 12 years (1998-2010) 406 patients that underwent articular cartilage implantation procedures at our institution (ACI = 170, MACI = 205) had biopsies taken at the 1-2 year interval, in order to assess whether these contained ‘hyaline-like’ cartilage, ‘mixed hyaline-like with fibrocartilage’, fibrocartilage or fibrous tissue alone.

Histological sections of the biopsies were prepared and stained with haematoxylin, eosin and proteoglycan stains and viewed under polarised light. All biopsies were studied by a single histopathologist in a specialist, dedicated musculoskeletal laboratory.

All patients were assessed by the Cincinnati, Bentley and Visual Analogue scores both pre-operatively and at the time of the review.

The findings revealed that 56 patients healed with ‘hyaline-like’ cartilage (14.9%), 103 with ‘mixed’ (27.5%), 179 with fibrocartilage (47.7%) and 37 with fibrous tissue (9.9%).

These findings showed that 42.4% of defects were filled with ‘hyaline-like’ or ‘mixed’ cartilage, with 70% of these achieving a ‘fair’ to ‘excellent’ functional outcome. This was also observed in the fibrocartilage group, where 72% achieved similar results. Predictably 89% of the patients that healed by fibrous tissue had a poor functional outcome.

This study shows that 71% of patients whose osteochondral defects healed by either ‘hyaline-like’, ‘mixed’ or fibrocartilage experienced an improvement in the function. In contrast, only 11% of the patients whose defects filled with fibrous tissue, showed some functional improvement. Additionally, this data indicates the advantage of biopsies in assessing the overall results of cartilage implantation procedures.

We used an atomic layer deposition (ALD) approach to create titanium oxide nanolayers on ultra high molecular weight polyethylene (UHMWPE) surfaces. These materials were then characterised in terms of rat osteoblast adhesion, morphology and differentiation.

UHMWPE discs produced from a machined cylinder or impact moulded discs were coated with titanium oxide by ALD. Light, atomic force microscopy and scanning electron microscopy with EDX were used to characterise the coated surfaces. These approaches showed 1-1.5 micron tooling grooves with a periodicity of 40 microns on the machined discs whilst the moulded discs exhibited nanotopographical features. The titanium oxide coating was successfully deposited on discs from both sources but was not uniform across the surfaces, with vein-like ‘creases’ clearly visible. We believe that these features are due to the thermal expansion of the UHMWPE discs during the ALD process and their subsequent cooling.

Coated and uncoated discs were seeded with osteoblasts for 24 hours, then fixed. Immunofluorescence microscopy and computer-based image processing enabled determination of osteoblast numbers, size and shape. A trend of larger average cell area was associated with the coated discs and P<0.01 for an H0 of no difference in cell area between coated and uncoated grooved discs.

Osteoblasts were also cultured on the discs in osteogenic medium to promote bone nodule formation. After a few weeks, von Kossa staining and computer-based image processing allowed calculation of surface area covered with bone nodules for each of the discs. Based on results from three of each type of disc, a significantly greater proportion of the surface area of coated discs was covered with calcified deposits compared to uncoated discs (P<0.025 for grooved discs and P<0.005 for smooth discs). On average, the coated discs had bone nodules on 1.4 times the surface area as compared to their uncoated counterparts.

The hypothesis for our study was that TiO2 coating of a polymer might better promote osteoblast interaction with the biomaterial surface leading to enhanced osteogenesis. Our preliminary data support this view and suggest that this approach could likely be exploited in the fabrication of implant materials with tailored biological activity.

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.

Bone marrow lesions (BMLs) have been extensively linked to the osteoarthritis (OA) disease pathway in the knee. Semi-quantitative evaluation has been unable to effectively study the spatial and temporal distribution of BMLs and consequently little is understood about their natural history. This study used a novel statistical model to precisely locate the BMLs within the subchondral bone and compare BML distribution with the distribution of denuded cartilage.

MR images from individuals (n=88) with radiographic evidence of OA were selected from the Osteoarthritis Initiative. Slice-by-slice, subvoxel delineation of the lesions was performed across the paired images using the criteria laid out by Roemer (2009). A statistical bone model was fitted to each image across the cohort, creating a dense set of anatomically corresponded points which allowed BML depth, position and volume to be calculated. The association between BML and denudation was also measured semi-quantitatively by visually scoring the lesions as either overlapping or adjacent to denuded AC, or not.

At baseline 75 subjects had BMLs present in at least one compartment. Of the 188 compartments with BMLs 46% demonstrated change greater than 727mm cubed, the calculated smallest detectable difference. The majority of lesions were found in medial compartments compared to lateral compartments and the patella (Figure 1A). Furthermore, in the baseline images 76.9% of all BMLs either overlapped or were adjacent to denuded bone. The closeness of this relationship in four individuals is shown in Figure 1B.

The distribution of lesions follows a clear trend with the majority found in the patellofemoral joint, medial femoro-tibial joint and medial tibial compartment. Moreover the novel method of measurement and display of BMLs demonstrates that there is a striking similarity between the spatial distribution of BMLs and denuded cartilage in subjects with OA. This co-location infers the lesions have a mechanical origin much like the lesions that occur in healthy patients as a direct result of trauma. It is therefore suggested that OA associated BMLs are in fact no different from the BMLs caused by mechanical damage, but occur as a result of localised disruption to the joint mechanics, a common feature of OA.

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

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

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

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

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

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

Bioreactors used in tissue engineering are mostly batch-fed with media added and removed periodically. Continuous flow bioreactors help increase ECM accumulation and cell proliferation, due to continuous flow of fresh media, thus, maintaining a steady extracellular nutrient environment. In previous work, we found chondrocytes cultured in continuous flow bioreactors with 20mM HEPES, accumulated considerably more matrix than static cultures. Hence, the objective of this study is to determine if NaHCO3 helps maintain a more physiological extracellular pH in the bioreactor, thus, enhancing ECM accumulation.

Cartilaginous tissue constructs were generated from isolated chondrocytes harvested from the metacarpal joints of 12-18 month old calves. Cells were seeded in high-density 3D cultures (2 million cells/construct). Constructs were cultivated in a continuous flow bioreactor, with and without 14 mM NaHCO3 supplemented media, for 5 weeks, at 37 degrees Celsius, 95% relative humidity and 5% CO2. After 5 weeks of culture the tissue weight, thickness, pH and ECM deposition were determined.

From the results obtained (Table 1), it is evident that chondrocytes cultured in the continuous flow bioreactor with 14mM NaHCO3 and 20mM HEPES, proliferated more extensively and produced more ECM than chondrocytes cultured in only 20mM HEPES. Additionally, the NaHCO3 constructs accumulated ECM in both the vertical (thickness) and horizontal (outgrowth) planes. The question then arises, are the effects mediated by improved buffering, or by addition of NaHCO3 itself. There was a significant difference between the pH of media with (pH 7.41) and without NaHCO3 (pH 6.95) supplementation, with no exposure to cells or tissue; when allowed to equilibrate with 5% CO2 at 37 degrees Celsius. However, there was little difference between the media after exposure to cells; after five weeks of culture in the bioreactor (Table 1). Thus, in the bioreactor with bicarbonate present, because of increased cell number and activity, the pH fell 0.54 pH units during the 7 hour residence time in comparison to the bioreactor with no bicarbonate supplementation. With no NaHCO3 supplementation, the extracellular pH of the medium fed to the cells was never above pH 7.0 (Table 1); low pH could account, at least in part, for lower ECM and cell numbers.

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

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

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

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

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

Saline (0.9%) is typically used to rinse joints during osteo-articular surgery. It is not unusual for cartilage to then be exposed to the air of the operating theatre for 1-2hrs, which can lead to chondrocyte death. We have compared the survival of in situ chondrocytes within bovine cartilage which has been rinsed in various solutions or simply drained of synovial fluid (SF) and then allowed to dry, to identify approaches that could reduce chondrocyte death arising from cartilage drying.

Metacarpophalangeal joints from 3yr-old cows were opened under aseptic conditions. The joints were then (a) rinsed with saline (Baxter's Healthcare, Newbury), (b) rinsed with saline+glucose (20mM; both 300mOsm) or (c) drained of SF, and allowed to dry at room temperature. Full depth cartilage explants were taken after 2hrs, placed into Dulbecco's modified Eagle's medium and incubated with CMFDA (5-chloromethyl-fluorescein diacetate; 10microM) and propidium iodide (10microM) for the identification/quantification of living and dead cells respectively by confocal scanning laser microscopy and image analysis.

After 2hrs, the appearance and properties of the cartilage of the drying joints were clearly different. Saline-rinsed cartilage was dark purple and appeared dull with the cartilage difficult to sample. However when the rinsing solution was saline+glucose, or when joints were drained of SF, the cartilage was almost identical to the freshly-opened joint with a pearly-blue, shiny appearance, and cartilage sampling was easy.

Chondrocyte death was markedly increased in saline rinsed/dried joints after 2hrs (21±9% cell death). In contrast, there was no significant (P>0.05) death in saline+glucose rinsed/dried (2±1%) or SF-drained joints (3±2%;means±s.e.m.;n=5). The loss of cartilage wet weight over 2hrs (time=0 taken as 100%) was almost identical between cartilage rinsed in saline (73.6±1.6%), saline + glucose (78.6±1.1%) or SF (75.0±0.2%; data means±s.d.;n=2).

These results suggest that it was not the loss of water per se during cartilage drying that was the key determinant of chondrocyte viability. As chondrocytes are normally anaerobic, the rise in cartilage pO2 which occurs during exposure to air could have a deleterious effect on cell viability however the presence of glucose or SF protects through an anti-oxidant effect.

In vitro the introduction of microseparation and edge loading to hip simulator gait cycle has replicated clinically relevant wear rates and wear mechanisms in ceramic-on-ceramic bearings^[1], and elevated the wear rates of MoM surface replacements (SR) to levels similar to those observed in retrievals^[2]. The aim was to assess the wear of two different sized MoM total hip replacement bearings under steep cup inclination angles and adverse microseparation and edge loading conditions.

Two tests were performed on the Leeds II hip joint simulator using two different size bearings (28mm and 36mm). Cups were mounted to provide inclination angles of 45 degrees (n=3) and 65 degrees (n=3). The first three million cycles were under standard gait conditions. Microseparation and edge loading conditions as described by Nevelos et al^[1] were introduced to the gait cycle for the subsequent three million cycles. The lubricant was 25% new born calf serum. The mean wear rates and 95% confidence limits were determined and statistical analysis was performed using One Way ANOVA.

Under standard gait conditions, when the cup inclination angle increased from 45 degrees to 65 degrees, the wear of size 28mm bearing significantly (p=0.004) increased by 2.7-fold, however, the larger bearings did not show any increase in wear (p=0.9). The introduction of microseparation conditions resulted in a significant (p=0.0001) increase in wear rates for both bearing sizes under both cup inclination angle conditions. Under microseparation conditions, the increase in cup inclination angle had no influence on the wear rate for both bearing sizes (Figure 1).

With larger bearings, head-rim contact occurs at a steeper cup inclination angle providing an advantage over smaller bearings. The introduction of edge loading and microseparation conditions resulted in a significant increase in wear rates for both bearing sizes. The wear rates obtained in this study under combined increased cup inclination angle and microseparation were half of those obtained when SR MoM bearings were tested under similar adverse conditions^[2]. This study shows the importance of prosthesis design and accurate surgical positioning of the head and acetabular cup in MoM THRs.

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.

Metal and their alloys have been widely used as implantable materials and prostheses in orthopaedic surgery. However, concerns exist as the metal nanoparticles released from wear of the prostheses cause clinical complications and in some cases result in catastrophic host tissue responses. The mechanism of nanotoxicity and cellular responses to wear metal nanoparticles are largely unknown. The aim of this study was to characterise macrophage phagocytosed cobalt/chromium metal nanoparticles both in vitro and in vivo, and investigate the consequent cytotoxicity. Two types of macrophage cell lines, murine RAW246.7 and human THP-1s were used for in vitro study, and tissues retrieved from pseudotumour patients caused by metal-on-metal hip resurfacing (MoMHR) were used for ex vivo observation. Transmission electron microscopy (TEM), scanning electron microscopy (SEM) in combination with backscatter, energy-disperse X-ray spectrometer (EDS), focused ion beam (FIB) were employed to characterise phagocytosed metal nanoparticles. Alamar blue assay, cell viability assays in addition to confocal microscopy in combination with imaging analysis were employed to study the cytotoxiticy in vitro. The results showed that macrophages phagocytosed cobalt and chromium nanoparticles in vitro and the phagocytosed metal particles were confirmed by backscatter SEM+EDS and FIB+EDS. these particles were toxic to macrophages at a dose dependent manner. The analysis of retrieved tissue from revision of MoMHR showed that cobalt/chromium metal nanoparticles were observed exclusively in living macrophages and fragments of dead macrophages, but they were not seen within either live or dead fibroblasts. Dead fibroblasts were associated with dead and disintegrated macrophages and were not directly in contact with metal particles; chromium but not cobalt was the predominant component remaining in tissue. We conclude that as an important type of innate immune cells and phagocytes, macrophages play a key role in metal nanoparticles related cytotoxicity. Metal nanoparticles are taken up mainly by macrophages. They corrode in an acidic environment of the phagosomes. Cobalt that is more soluble than chromium may release inside macrophages to cause death of individual nanoparticle-overloaded macrophages. It is then released into the local environment and results in death of fibroblasts and is subsequently leached from the tissue.

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

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

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

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

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

Autologous chondrocyte implantation (ACI) has been used for many years for the treatment of symptomatic defects in articular joints, predominantly the knee. Traditionally, cells were implanted behind a periosteal membrane, but in more recent times Chondrogide, a membrane consisting of porcine collagens I and III, has been used. There have been trials comparing the clinical outcome of these two groups of patients; in this study we compare the histological outcome using the two different patch types.

In a study of 100 patients having received ACI treatment of cartilage defects in the knee, 41 received Chondrogide (ACI-C) and 59 received periosteum (ACI-P). All of these patients had a post-operative biopsy taken at a mean of 16.9±9.2 months and 20.8±23.2 months for ACI-C and ACI-P respectively for histology using the ICRS II scoring system. Lysholm scores, a measure of knee function, were obtained pre- and post-operatively at the time of biopsy and statistical differences tested for via a Mann-Whitney U-test.

The mean age of the two groups at treatment was 37±8 and 35±10 years, the size of defect treated was 6.1±5.4 and 4.4±2.7 cm2 and the biopsy follow-up time was 50.6±22.2 and 81.2±34.8 months for ACI-C and ACI-P patients respectively. Both groups exhibited a significant improvement in Lysholm score from pre-operative to the time of biopsy (14.3±25.7; n=100), although there was no significant difference in improvement in Lysholm score between the two patch types. There was no significant difference between the histology score of the two groups, nor was the score found to correlate with the Lysholm score at that time. The individual components of the ICRS II score did not differ significantly with patch type (even for the surface architecture) apart from cellular morphology which was 6.5±3 and 8.2±1.6 for ACI-C and ACI-P respectively.

The histological quality of repair tissue formed with ACI-C differed little from that seen with ACI-P, despite the former group being biopsied ∼4 months sooner after treatment and being used to treat defects which were 39% larger. Hence Chondrogide appears just as suitable as periosteum for use as a patch in the procedure of ACI.

Wear debris induced osteolysis is a recognized complication in conventional metal-on-polyethylene hip arthroplasty. One method of achieving wear reduction is through the use of metal-on-metal articulations. One of the latest manifestations of this biomaterial combination is in designs of hip resurfacing which are aimed at younger, more active patients. But, do these metal-on-metal hip resurfacings show low wear when implanted into patients?

Using a Mitutoyo Legex 322 co-ordinate measuring machine (scanning accuracy less than 1 micron) and a bespoke computer program, volumetric wear measurements for retrieved Articular Surface Replacements (ASR, DePuy) metal-on-metal hip resurfacings were undertaken. Measurements were validated against gravimetric calculations for volumetric wear using a sample femoral head that was artificially worn in vitro. At 5mm3, 10mm3, and 15mm3 of material removal, the method was shown to be accurate to within 0.5mm3.

Thirty-two femoral heads and twenty-two acetabular cups were measured. Acetabular cups exhibited mean volumetric wear of 29.00mm3 (range 1.35 - 109.72mm3) and a wear rate of 11.02mm3/year (range 0.30 - 63.59mm3/year). Femoral heads exhibited mean wear of 22.41mm3 (range 0.72 - 134.22mm3) and a wear rate of 8.72mm3/year (range 0.21 - 31.91mm3/year). In the 22 cases where both head and cup from the same prosthesis were available, mean total wear rates of 21.66mm3/year (range 0.51 - 95.50mm3/year) were observed.

Revision was necessitated by one of five effects; early femoral neck fracture (4 heads), avascular necrosis (AVN) (2 heads, 1 cup), infection (1 head, 1 cup), adverse reaction to metal debris (ARMD) (19 heads, 18 cups) or ARMD fracture (6 heads, 2 cups). Mean paired wear rates for the AVN and infection retrievals were 0.51mm3/year and 3.98mm3/year respectively. In vitro tests typically offer wear rates for metal-on-metal devices in the region of 2-4mm3.

Mean paired wear rates for ARMD and ARMD fracture were 17.64mm3/year and 68.5mm3/year respectively, significantly greater than those expected from in vitro tests. In the 4 cases of early fracture, only the heads were revised so a combined wear rate calculation was not possible. The heads exhibited mean wear rate of 8.26mm3/year. These high wear rates are of concern.

Allogeneic blood transfusion is associated with many complications and significant cost. The RD&E has looked at the use of autologous drains after our study of 100 cases showed an improved post-operative haemoglobin and reduced length of stay. There is a need to identify those patients of increased need for an autologous drain, in order to decrease the frequency of allogeneic transfusion. In 2007 a protocol was drawn up using information from our study of 191 cases which showed an average haemoglobin drop post-operatively of 3.05g/dl and average intra-operative blood loss of 285 ml. This protocol gives the surgeon triggers for autologous drain use; preoperative haemoglobin of <13g/dl, intra-operative blood loss of >400ml, tourniquet use, patient weight <50kg and patients refusing donated blood.

In 2007-08, 65% of a further 275 cases analysed met the triggers for use of an autologous system. The remaining patients received low vacuum drains. Of the 275 patients, only 2 (<1%) of those who did not fulfil the criteria for an autologous drain required allogeneic blood, compared with 43 patients (24%) of those deemed high risk of transfusion, and assigned autologous drains. The protocol was therefore deemed to be successful in identifying those patients who required additional support and expenditure to minimise allogeneic blood transfusion.

Analysis of this data led to recommended changes to the protocol in order to maximise the efficiency of the autologous drain use. In 2010 a further patient cohort studied showed a reduction in allogeneic blood transfusion to <10% of those receiving autologous drains, and an increase to 5% of those with low vacuum drains.

Due to the increased cost of autologous drains (£68) compared with the low vacuum systems (£32), and the cost of allogeneic units at £141, the expenditure per patient was calculated and shown to fall from £92 in 2007 to £78 in the 2010.

In conclusion, this protocol allows the clinician to appropriately target the use of the more expensive autologous drains to those of increased risk of transfusion. This protocol helps to minimise unnecessary allogeneic blood transfusion risks, and this has been shown to be more cost effective.

The reinfusion of perioperative cell salvage is one method employed to reduce exposure to donor blood. Data on the safety of this process, however, are scant. Notably, the effect of intraoperative, washed cell salvage reinfusion on prothrombotic markers has not been demonstrated. The risk of postoperative venous thromboembolism following major orthopaedic operations is not insignificant. The study objective was to assess the effect of cell salvage reinfusion on coagulation and platelet activation.

Twenty-one patients undergoing elective primary hip operations were recruited. Nine patients received washed cell salvage intraoperatively, and were compared with 12 patients undergoing similar surgery that did not. Two patients in the cell salvage group also received postoperative, unwashed cell salvage. Blood samples were collected pre-operatively, immediately post-operatively, and one day post-operatively for assays of platelet activation markers, P-selectin expression and fibrinogen binding by flow cytometry in diluted whole blood; coagulation activation marker, thrombin-antithrombin complex (TAT); D-dimer by ELISA, thrombin generation by chromogenic assay, and full blood count. Samples of cell salvage material were also analysed for prothrombotic markers.

There were no significant differences between the groups preoperatively. Postoperatively haemoglobin levels did not differ significantly between the cell salvage group and controls. Postoperative TAT and D-dimer were significantly higher in the cell salvage group compared with controls (p<0.05). One day postoperatively, there were significantly higher platelet P-selectin expression (p=0.006) and platelet fibrinogen binding (p=0.004) in the cell salvage group compared with controls. The white cell count (WCC) was also significantly higher (p=0.04). In the intraoperative washed cell salvage material, and in postoperative cell salvage, the platelet count was low, but significant proportions of platelets were activated, and levels of D-dimer were elevated compared with venous blood. The postoperative salvage material also contained high levels of TAT.

The results from this pilot study show the induction of a prothrombotic state following reinfusion of intraoperative, washed cell salvage in recipients undergoing primary elective hip operations. An inflammatory response to reinfusion is also indicated by the raised WCC. Further investigation into the safety of cell salvage is indicated.

Angiogenesis and the ability to provide appropriate vascular supply are crucial for skeletal tissue engineering. The aim of this study was to investigate the angiogenic potential of human dental pulp stromal cells (HDPSCs) and stro-1 positive populations as well as their role in tissue regeneration (the clinical reality).

HDPSC were isolated from the pulp tissues of human permanent teeth by collagenase digestion. STRO-1 positive cells were enriched using monoclonal anti- STRO-1 and anti- CD45 PE conjugated antibodies together with and fluorescence activated cell sorting (FACS). Cells isolated by FACS were grown to passage4 and cultured as monolayers or on 3D Matrigel scaffold in endothelial cell growth medium-2 (EGM-2) with/without 50ng/mL of vascular endothelial growth factor (VEGF). Cells cultured in alpha MEM supplemented with 10% FCS were used as controls. After 24, 48 and 72 hours angiogenic marker expression (CD31, CD34, vWF and VEGFR-2) was determined by qRT-PCR and immuno-histochemistry.

Using three different donors, 0.5-1.5% of total HDPSCs population was characterized as STRO-1+/CD45- cells At each time point cells cultured as monolayer in EGM-2 with VEGF showed up regulation of CD31 and VEGFR-2 expression compared to the control group while expression of CD34 and vWF remained unaffected. However on Matrigel, all four genes were up regulated to different extents. CD31 and VEGFR-2 were up regulated to a greater degree compared to CD34 and vWF. Changes in gene expression in both cell types were time dependent. Immuno-histochemical staining confirmed that the HDPSCs cultured in the test group showed positive staining for the four angiogenic markers (CD31, CD34 vWF and VEGFR-2) when grown in both monolayer and 3D Matrigel culture compared to control cultures. When cultured on Matrigel (but not Monolayer) for 7 days, HDPSC formed tube-like structures in the VEGF treated group.

This indicates the potential of use HDPSCs and their STRO-1 positive population for angiogenesis to enhance skeletal tissue repair and/or regeneration toward translational research for clinical benefit.

Growth rods are currently used in young children to hold a scoliosis until the spine has reached a mature length. Only partial deformity correction is achieved upon implantation, and secondary surgeries are required at 6-12 month intervals to lengthen the holding rod as the child grows. This process contains, rather than corrects, the deformity and spinal fusion is required at maturity. This treatment has a significant negative impact on the bio-psychosocial development of the child.

Vertebroplasty is a minimal invasive surgical procedure for treatment of vertebral compressive fractures, whereby cement is injected percutaneously into a vertebral body. Cement viscosity is believed to influence injectability, cement wash-out and leakage. Altering the liquid to powder ratio can affect the viscosity, level of cohesion and extent cement fill within the vertebral body and the ultimately strength and stiffness of the cement-vertebra composite. The association of these combined factors remains unclear. The aim of this study was to determine the relationship between cement viscosity and the potential augmentation of strength and stiffness in a model simulating in-vitro prophylactic vertebroplasty of osteoporotic vertebral bodies.

Samples of synthetic bone (Sawbone) representing osteoporotic bone were manually injected with 1mL of calcium phosphate cement using a 11G cannulated needle. Calcium phosphate cement was produced by mixing alpha-tricalcium phosphate, calcium carbonate and hydroxyapatite with an aqueous solution of 5 wt% disodium hydrogen phosphate. Three liquid to powder ratio (LPR) representing different viscosity levels were used; i.e. 0.5mL/g (low viscosity), 0.45mL/g (medium viscosity) and 0.35mL/g (high viscosity). Cement filled samples were then placed in an oven (37oC) for 20 min and then immersed in Ringer's solution (37oC) for 3 days. Samples of synthetic bone without cement injection were used as controls.

Potential for leakage and wash-out was determined using gravimetric analysis. Extent of cement fill was determined using computer tomography (CT).

Samples were tested under axial compression at a rate of 1 mm/min and the strength and stiffness determined. Statistical significance against controls was determined using a one-way analysis of variance (p<0.05).

Low viscosity cement showed more cement leakage (p=0.512) and increased cement wash-out after 3 days in Ringer's solution (p=0.476). Qualitative assessment of cement fill within the vertebral body using CT imaging supported the wash-out results. The strength (p<0.05-0.01) and stiffness (p<0.01) of samples significantly increased by cement injection in comparison to control, the extent of this increase was greater with increasing cement viscosity.

Linear correlation analysis showed a definite association between the mechanical properties and viscosity of injected cement and was dependent on the amount of cement retained within the synthetic bone post-setting.

Tribology and wear of articular cartilage is associated with the mechanical properties, which are governed by the extracellular matrix (ECM). The ECM adapts to resist the loads and motions applied to the tissue. Most investigations take cartilage samples from quadrupeds, where the loading and motions are different to human. However, very few studies have investigated the differences between human and animal femoral head geometry and the mechanical properties of cartilage.

This study assessed the differences between human, porcine, ovine and bovine cartilage from the femoral head; in terms of anatomical geometry, thickness, equilibrium elastic modulus and permeability.

Diameter of porcine (3-6 months old), bovine (18-24 months old), ovine (4 years old) and human femoral heads were measured (n=6). Plugs taken out of the superior region of each femoral head and creep indentation was performed. The human femoral heads were obtained from surgery due to femoral neck fracture. Cartilage thickness was measured by monitoring the resistive force change as a needle traversed the cartilage and bone at a constant feed rate using a mechanical testing machine. The percentage deformation over time was determined by dividing deformation by thickness. A biphasic finite element model was used to obtain the intrinsic material properties of each plug. Data is presented as the mean ± 95% confidence limits. One-way ANOVA was used to test for significant differences (p < or = 0.05).

Significant differences in average femoral head diameter were observed between all animals, where bovine showed the largest femoral head. Human cartilage was found to be significantly thicker than cartilage from all quadrupedal hips. Human cartilage had a significantly larger equilibrium elastic modulus compared to porcine and bovine cartilage. Porcine articular cartilage was measured to be the most permeable which was significantly larger than all the other species. No significant difference in permeability was observed between human and the other two animals: bovine and ovine (Table 1).

The current study has shown that articular cartilage mechanical properties, thickness and geometry of the femoral heads differ significantly between different species. Therefore, it is necessary to consider these variations when choosing animal tissue to represent human.

In pre-operative planning for total hip arthroplasty (THA), femoral offset (FO) is frequently underestimated on AP pelvis radiographs as a result of inaccurate patient positioning, imprecise magnification, and radiographic beam divergence. The aim of the present study was to evaluate the reliability and accuracy of predicting three-dimensional (3-D) FO as measured on computed tomography (CT) from measurements performed on standardised AP pelvis radiographs.

In a retrospective cohort study, pre-operative AP pelvis radiographs and corresponding CT scans of a consecutive series of 345 patients (345 hips, 146 males, 199 females, mean age 60 (range: 40-79) years, mean body-mass-index 27 (range: 29-57) kg/m2) with primary end-stage hip osteoarthritis were reviewed. Patients were positioned according to a standardised protocol and all images were calibrated. Using validated custom programmes, FO was measured on corresponding AP pelvis radiographs and CT scans. Inter- and intra-observer reliability of the measurement methods were evaluated using intra-class correlation coefficients (ICC). To predict 3-D FO from AP pelvis measurements, the entire cohort was randomly split in two groups and gender specific linear regression equations were derived from a subgroup of 250 patients (group A). The accuracy of the derived prediction equations was subsequently assessed in a second subgroup of 100 patients (group B).

In the entire cohort, mean FO was 39.2mm (95%CI: 38.5-40.0mm) on AP pelvis radiographs and 44.6mm (95%CI: 44.0-45.2mm) on CT scans. FO was underestimated by 14% on AP pelvis radiographs compared to CT (5.4mm, 95%CI: 4.8-6.0mm, p<0.001) and both parameters demonstrated a linear correlation (r=0.642, p<0.001). In group B, we observed no significant difference between gender specific predicted FO (males: 48.0mm, 95%CI: 47.1-48.8mm; females: 42.0mm, 95%CI: 41.1-42.8mm) and FO as measured on CT (males: 47.7mm, 95%CI: 46.1-49.4mm, p=0.689; females: 41.6mm, 95%CI: 40.3-43.0mm, p=0.607).

The results of the present study suggest that femoral offset can be accurately and reliably predicted from AP pelvis radiographs in patients with primary end-stage hip osteoarthritis. Our findings support the surgeon in pre-operative templating and may improve offset and limb length restoration in THA without the routine performance of CT.

Study of failed Oxford medial unicompartmental knee replacements at the Royal Cornwall Hospital.

Although bovine serum is the lubricant recommended by several international standards for the wear testing of orthopedic biomaterials there are issues over its use. The inherent batch variation in protein content means that two bovine serum lubricants can give different wear rates. Due to degradation, the lubricant needs to be changed regularly, so that any third body wear particles are removed, thus potentially influencing wear regimes. There are also cost and safety issues with the use of bovine serum. For these reasons, alternative lubricants were investigated.

A 50-station wear test rig was used, which applied multi-directional motion to each ultra-high molecular weight polyethylene (UHMWPE) test pin. Each pin articulated against a cobalt chrome plate polished to better than 0.05 microns Ra. The following lubricants were used: 50% dilute bovine serum; soy protein; olive oil; wheatgerm oil; soya oil; albumin and globulin (AG) mix; albumin, globulin and chondroitin sulphate (AGC) mix; whole milk; Channel Island milk; 11 mg/ml protein egg white; 20 mg/ml egg white; and 40 mg/ml egg white. A minimum of 6 UHMWPE pins per lubricant were wear tested and the tests ran to 2.5 million cycles. Gravimetric measurements were taken throughout the test to determine the volume of wear and at the end of the test the samples were examined using a SEM.

The lubricants giving the closest results to bovine serum were 20 and 40 mg/ml egg white, with mean UHMWPE total wear volumes of 17.4 mm3 and 17.8 mm3 compared to bovine serum which gave 20.7 mm3. Surface topographies showed similar features too. The 11 mg/ml egg white lubricant and the AG and AGC lubricants were next closest in terms of wear. An UV absorbance assay found that all the protein based lubricants suffered from a high degradation rate, and the rate increased with increasing protein content.

Egg white may offer a less expensive alternative to dilute bovine serum as a test lubricant although it is likely that it too would need to be changed as regularly as bovine serum.

The fixation of comminuted femoral fractures with intramedullary nails is commonplace but there remains little work on the mechanical ability of the different diameters of nail available to resist bending. What previous work there is has produced conflicting conclusions. The bending stiffness against the intramedullary nail diameter and the extent of the comminuted fracture is clinically important due to the impact on fracture healing and implant failure.

Intramedullary nails of differing diameters (10 mm, 11 mm and 13 mm) were loaded axially in fourth generation composite femurs with increasing mid shaft bone defects, namely 3cm, 5cm, 8cm and 10cm bones. The loading versus the displacement was recorded for each nail.

A one-way ANOVA analysis demonstrated a significant difference between intramedullary nail diameters and the bending stiffness, with p values of less than 0.012; 3cm mean 12.26 (CI 9.06-15.46) mm, p=0.012; 5 cm mean 10.63 (CI 8.35-12.92) mm, p=<0.001; 8 cm mean 11.04 (CI 8.35-13.74) mm, p=<0.001; 10 cm mean 11.68 (CI 7.86-15.50) mm, p=<0.001. For the 11 mm diameter intramedullary nail, failure occurred at around two times the body weight of an average individual or 1400 to 1800 N. A repeated measure ANOVA analysis of the effect of the increasing bone defect showed a mixed picture, with a significant difference between the 5 cm and 8 cm gap and only a trend towards significance between 5 cm and 10 cm.

Caution should be advised when considering using a cannulated femoral intramedullary nail in a patient with a fracture gap of greater than 5 cm. Further, the mechanical effect of comminuted fractures treated with nails suggests reduced stiffness with increasing length of fracture gap although the picture is complex and explains the divergence of research conclusions.

The calcar femorale or ‘true neck’ of the femur has a role in transmitting load from the cantilevered neck to the femoral shaft (Zhang 2009). It can appear as a distinct condensation in clinical CT images because its structure is very similar to compact bone (Aspden 1998). Harty (1957) proposed that the calcar acts as a ‘spike’ in certain fall situations, contributing to splitting of the trochanter. We hypothesised that among elderly fallers, the size of the calcar would influence whether fractures occurred in the trochanteric (TR) or femoral neck (FN) site. We also asked whether patients who sustained a fracture had more or less calcar bone than frailty-matched controls that fell but didn't fracture.

The FEMCO study is designed to investigate male (M) and female (F) patients with acute hip fracture with multi-detector CT, before they undergo surgery. It includes an age, sex and frailty-matched control group (who have sustained at least one injurious fall without hip fracture). The fractured hip is reconstructed in 3D for classification of fracture type (FN or TR). For the present pilot study, there were 14 cases (5TR, 9FN mean 80+/−8.5yrs. 7M, 7F) and 11 controls (83+/−7.0yrs. 3M, 8F). Axial CT slices where a calcar was visible were opened in Stradwin 4.1 software (Treece 2011). The calcar femorale was semi-automatically selected with the flood fill tool. Each axial image that contained a visible calcar was included in the analysis, so that for each femur a single calcar volume was generated. Results were examined using ANOVA.

Combining male and female results, there was a non-significant trend towards a higher calcar volume in patients sustaining trochanteric rather than femoral neck fractures (0.73cm3 +/− 0.26 vs 0.61cm3 +/−0.14, p=0.27) but no difference between cases and controls. Males had a significantly higher calcar volume than females (mean 0.82cm3 +/− 0.24 vs 0.59cm3 +/− 0.13, p=0.005). Further studies are now planned in larger samples of each sex, to examine the role of the calcar in fracture mechanics. Three-dimensional visualisations provide a novel insight into the damage patterns and resultant fragment locations.

Myostatin (GDF-8) is known to play an important role in muscle regeneration, and myostatin is also expressed during the early phases of fracture healing. In this study we used fluorescent immunohistochemistry to define the temporal and spatial localization of myostatin during muscle and bone repair following deep penetrant injury in a mouse model. We then used hydrogel delivery of exogenous myostatin in the same injury model to determine the effects of myostatin exposure on muscle and bone healing. Results show that while myostatin was constitutively expressed in the cytoplasm of intact skeletal muscle fibers, a pool of intense myostatin staining was observed amongst injured skeletal muscle fibers 12-24 hours post-surgery. Myostatin was also expressed in the soft callus chondrocytes 4 days following osteotomy. Hydrogel delivery of 10 or 100 ug/ml recombinant myostatin decreased fracture callus cartilage area relative to total callus area in a dose-dependent manner by 41% and 80% (p<0.05), respectively, compared to vehicle treatment. Myostatin treatment also dose-dependently decreased fracture callus total bone volume by 23% and 47% (p<0.05), with the higher dose of recombinant myostatin yielding the greatest decrease in callus bone volume. Finally, exogenous myostatin treatment caused a significant, dose-dependent increase in fibrous tissue formation in skeletal muscle. Together, these findings suggest that myostatin may inhibit bone repair after traumatic musculoskeletal injury through both autocrine (soft-callus chondrocytes) and paracrine (surrounding injured muscle fibers) mechanisms. Thus, early pharmacological inhibition of myostatin is likely to improve the regenerative potential of both muscle and bone following deep penetrant musculoskeletal injury.

Evidence suggests that anterior cruciate ligament (ACL) injured individuals do not use the same movement strategies as healthy individuals. It is unknown how this may affect them in more challenging activities of daily living and sport. The aim of this study is to evaluate how ACL injured patients perform a single leg squat (SLS) compared to healthy controls. SLS was evaluated as it is more challenging than gait and therefore more relevant to clinical decision making about progressing to sporting maneuvers.

To date, 6 ACL deficient (ACLD) (5 males, 1 female; mass=88±22 kg; height=1.78±0.11 m; age=35±11 years), 5 ACL reconstructed (ACLR) (5 males; mass= 83±12 kg; height=1.74±0.07 m; age=29±10 years) and 5 controls (3 males, 2 females; mass= 72±13 kg; height=1.70±0.09 m; age=30±3 years) performed a SLS on the injured leg for the ACL injured participants and the dominant leg for the control group. Motion analysis was performed using a Vicon Nexus system and a Kistler force platform. Knee extension moments and angles were calculated using Vicon Nexus software.

The ACLD group had reduced peak flexion angles compared to ACLR and control groups (65±5, 77±7 and 82±9 degrees respectively). Peak extension moments were similar across all groups (ACLD= 0.94±0.26 Nm/kg, ACLR=1.06±0.37 Nm/kg, control=1.04±0.36 Nm/kg). Peak knee moments occurred just after peak flexion and therefore at a smaller flexion angle for the ACLD group compared to the ACLR and control group (59±13, 75±7 and 80±6 degrees). Extension moments were similar when evaluated at a consistent angle of 50 degrees (ACLD=0.70±0.30Nm/kg, ACLR=0.63±0.34Nm/kg control=0.61±0.32Nm/kg).

In this sample, the controls squatted deepest followed by the ACLR group, with the ACLD group squatting least deep. This did not translate to an identical pattern for the knee extensor moments. Performance of ACL injured individuals needs to be evaluated on more challenging tasks to fully assess recovery. Further research, with more subjects, will clarify if ACLD individuals are using a strategy to protect their knee or if others factors are preventing them from squatting deeper. This would suggest that these individuals may not have fully recovered and will not be able to perform more challenging activities

ACL injured patients show variability in the ability to perform functional activities (Button et al., 2006). It is unknown whether this is due to differences in physical capability or whether fear of re-injury plays a role. Fear of re-injury is not commonly addressed in rehabilitation. This study aimed to investigate whether fear of re-injury impacts rehabilitation of ACL injured patients.

An initial group of five ACL reconstructed participants (ACLR, age: 30±11 years, weight: 815±115 N, height: 1.74±0.07 m, all male), five ACL deficient participants (ACLD, age: 31±12 years, weight: 833±227 N, height: 1.80±0.11 m, four male and one female), and five healthy controls (age: 30±3 years, weight: 704±126 N, height: 1.70±0.09 m, three male and two female) were compared. Fear of re-injury was assessed using the Tampa Scale for Kinesiophobia (Kvist, 2004). Quadriceps strength was measured on a Biodex dynamometer. Functional activity was assessed by a single legged maximum distance hop (on the injured leg for ACL patients). Motion analysis was performed with a VICON system, and a Kistler force plate. Hop distance was calculated using the ankle position. The peak knee extension moment during landing, and the knee angle at this peak moment were calculated in VICON Nexus.

The ACLD group scored worse on the Tampa scale for Kinesiophobia than the ACLR group (32±4 and 26±4). The ACLD patients did not hop as far as the ACLR and control groups (1.0±0.3, 1.3±0.1 and 1.4±0.3 m). The peak knee extension moments during landing were lowest in the ACLD group (263±159 Nm), slightly higher in the control group (354±122 Nm) and highest in the ACLR group (490±222 Nm), while knee flexion angles at these moments were similar (ACLD: 28±11, ACLR: 33±7 and control: 36±13 degrees). The ACLD group had weaker quadriceps than the control group, while the ACLR group was stronger (143±44 Nm, 152±42, and 167±50 Nm respectively).

Fear of re-injury and decreased quadriceps strength potentially both impact on the functional performance of ACL injured patients. Rehabilitation of ACL injured patients could therefore be improved by addressing strength and fear of re-injury. Future research with more participants will further clarify this.

Bone related adverse events including failure of implant osseo-integration, periprosthetic fracture, femoral neck narrowing, and unexplained pain occur more frequently following metal-on-metal hip resurfacing (MoMHR) versus total hip arthroplasty (THA). The exact mechanism for the adverse effects is still unclear and may be due to the direct effect on bone cells of metal ions released from the prostheses.

The aim of the present study was to determine the effect of clinically relevant combinations of metal ions on osteoblast cell survival and function. To assess cell proliferation and alkaline phosphatase (ALP) activity of osteoblasts, human osteoblast cells (SaOS-2), were cultured in 96-well plates for 24-hours and then treated with metal ions. Cell proliferation was measured at day 3 and day 7 using MTS assay, whilst ALP activity was assessed at day 3 by measuring pNPP substrate hydrolysis by the cell lysate. Mineralisation ability of the cells was assessed in 24-well plates cultured until day 21 and staining the calcium deposits using Alizarin red. All cultures were treated with the IC50 concentration of Co(II) (135μM) and an equivalent Cr(III) concentration (1Co(II):1Cr(III)).

After 3 days, Co(II) at an IC50 concentration decreased osteoblast proliferation as expected, but no further decrease in proliferation was observed with the 1Co(II):1Cr(III) combination treatment. However, after 7 days, a further significant decrease (P<0.05) in proliferation was observed with the combination treatment compared to Co(II) IC50. A similar significant decrease (P<0.01) was observed for ALP activity at day 3 with 1Co(II):1Cr(III) compared to Co(II) alone. For mineralization, a significant reduction (P<0.0001) was observed for Co(II) IC50 concentration, however no further reduction was seen with the 1Co(II):1Cr(III) combination treatment.

The observed decrease in cell proliferation and ALP activity with combination treatments suggest an additive detrimental effect compared to single ions alone. The mineralisation ability did not show any additive effect due to cell toxicity of chronic exposure to IC50 concentrations calculated from 3 day proliferation cultures. The results suggest that presence of both cobalt and chromium ions in the periprosthetic environment have more severe detrimental effect on osteoblasts than single ions alone and extend our understanding of the periprosthetic bone health.

Finger arthroplasty lacks the success seen with hip and knee joint replacements. The Van Straten Leuwen Poeschmann Metal (LPM) prosthesis was intended for the proximal interphalangeal (PIP) joints. However revision rates of 30% after 19 months were reported alongside massive osteolysis. Three failed LPM titanium niobium (TiNb) coated cobalt chrome (CoCr) components were obtained- two distal and one proximal.

All three components were analysed using an environmental scanning electron microscope (ESEM). This gave the chemical composition of the surface to determine if the TiNb surface coating was still intact. The distal components were analysed using a ZYGO non-contact profilometer (1nm resolution) with the proximal component unable to be analysed due to its shape. ZYGO analysis gave the roughness average (Ra) of the surface and determined the presence of scratches, pitting and other damage.

Images obtained from both the ZYGO and the ESEM indicated that the surfaces of all components were heavily worn. On the articulating surfaces of both distal components unidirectional scratching was dominant, while the non-articulating surface showed multidirectional scratching. The presence of unidirectional scratching suggested two-body wear, whilst the multidirectional scratching on the non-articulating surface of the distal component suggested that trapped debris may have caused three-body wear.

The ESEM chemical analysis showed that in some regions on the distal component the TiNb coating had been removed completely and in other areas it had been scratched or penetrated. On the proximal component the TiNb coating had been almost completely removed from the articulating surfaces and was only present in small amounts on the non-articulating surfaces. There was little evidence of bone attachment to the titanium coating which was intended to help provide fixation.

ESEM images showed the coating had been removed in some sections where there was minimal scratching, suggesting this scratching did not impact significantly in the coating removal. Therefore here the main cause of coating removal may have been corrosion, although scratching may have also have played a part.

The osteolysis reported clinically may have been linked to the wear debris from the failed coating.

The annulus fibrosus (AF) of the intervertebral disc (IVD) has a unique, complex structure. If engineered tissues for the IVD are to be successfully developed, it is essential that the constituent level mechanics of the tissues in their natural form are fully understood (Nerurkar, J. Biomech. 2010).

Published finite element (FE) models of the IVD do not represent lamellae behaviour and are validated using bulk mechanics of the intervertebral joint. This study aims to develop models of the IVD that include representation of the lamellae structure of the AF and the behaviour of this tissue within the disc.

Knee injuries in cyclists are often thought to result from an imbalance of load during the cycling motion as a consequence of inappropriate bike set-up. Recently, it has been postulated that incorrect foot positioning may be a significant factor in lower limb injury and poor cycling performance. The purpose of this study is to assess the effect of changing the foot position at the shoe-pedal interface on Vastus Medialis (VM) and Vastus Lateralis (VL) activity (mean and mean peak), knee angle and knee displacement.

Maximum power tests were completed on a first visit, with data collection on a second visit recorded at 60% of the subjects maximum. Video footage and surface electromyography (SEMG) from VM and VL muscles was obtained. Data was recorded over 10 crank cycles in 3 experimental conditions; neutral, 10 degrees inversion and 10 degrees eversion using Ethylene Vinyl Acetate (EVA) wedges fitted between the cyclists shoe and the shoe cleat. Raw data (mean SEMG, mean peak SEMG) was obtained using Noraxon and SiliconCOACH measured knee angle and knee displacement. Data was analyzed using Friedmans test with appropriate post hoc tests.

12 male subjects (range 26-45, mean 35.9 years) completed the study. Mean and mean peak SEMG data showed no significant differences between the 3 experimental conditions for VM and VL. VM:VL ratios from raw mean SEMG data demonstrated a decrease in synchronicity in inversion and eversion compared to neutral. Pronators demonstrated most synchronicity in inversion and least synchronicity in eversion. There were statistically significant differences in knee angle and knee displacement between neutral, inversion and eversion (p<0.05). Inversion promoted smaller knee valgus angles and greater knee displacement from the bike. Eversion promoted larger knee valgus angles and a smaller displacement from the bike.

By altering the foot position to either 10 degrees inversion or 10 degrees eversion, knee angle and knee displacement can be significantly influenced. Clinically, subjects who foot type is classified as pronating may benefit from some degree of forefoot inversion posting. Further research on subjects with knee pain needs to be undertaken.

Assessing the efficacy of cervical orthoses in restricting spinal motion has historically proved challenging due to a poor understanding of spinal kinematics and the difficulty in accurately measuring spinal motion. This study is the first to use an 8 camera optoelectronic, passive marker, motion analysis system with a novel marker protocol to compare the effectiveness of the Aspen, Aspen Vista, Philadelphia, Miami-J and Miami-J Advanced collars. Restriction of cervical spine motion was assessed for physiological and functional range of motion (ROM).

Nineteen healthy volunteers (12 female, 7 male) were fitted with collars by an approved physiotherapist. ProReflex (Qualisys, Sweden) infra-red cameras were used to track the movement of retro-reflective marker clusters attached to the head and trunk. 3-D kinematic data was collected from uncollared and collared subjects during forward flexion, extension, lateral bending and axial rotation for physiological ROM and during five activities of daily living (ADLs). ROM in the three clinical planes was analysed using the Qualisys Track Manager (Qualisys, Sweden) 6 Degree of Freedom calculation to determine head orientation relative to the trunk.

For physiological ROM, the Aspen and Philadelphia were more effective at restricting flexion/extension than the Vista (p<0.001), Miami-J (p<0.001 and p<0.01) and Miami-J Advanced (p<0.01 and p<0.05). The Aspen was more effective at restricting rotation compared to the Vista (p<0.001) and Miami-J (p<0.05). The Vista was least effective at restricting lateral bending (p<0.001). Through functional ROM, the Vista was less effective than the Aspen (p<0.001) and other collars (p<0.01) at restricting flexion/extension. The Aspen and Miami-J Advanced were more effective at restricting rotation than the Vista (p<0.01 and p<0.05) and Miami-J (p<0.05). All the collars were comparable when restricting lateral bending.

The Aspen is superior to, and the Aspen Vista inferior to, the other collars at restricting cervical spine motion through physiological ROM. Functional ROM observed during ADLs are less than those observed through physiological ROM. The Aspen Vista is inferior to the other collars at restricting motion through functional ROM. The Aspen collar again performs well, particularly at restricting rotation, but is otherwise comparable to the other collars at restricting motion through functional ranges.

We report an unusual case of knee disease where calcific tendonitis occurring in both quadriceps and patellar tendon simultaneously in the same knee. A 47 year old female presented to orthopaedics outpatient clinic with acute onset of swelling and knee pain with no history of trauma. She was found to have a moderate effusion of the knee joint with mild tenderness over the mid quadriceps tendon. Active flexion of the knee joint was painful with a range of motion between 0-90 degrees. She is otherwise healthy with no past medical history. Plain radiographs and Magnetic Resonance Imaging (MRI) Scan revealed calcification of both tendons.

Calcific tendonitis is classically found in the supraspinatus tendon of the shoulder. In addition, it has been described in other areas of the body such as the wrist, thigh, hip, knee and ankle. This condition usually occurs in the quadriceps or patellar tendons separately and rarely affecting both tendons in the same knee simultaneously. The patients condition improved significantly with physiotherapy, anti-inflammatory medications and ultrasound therapy.

Calcific tendinitis of both quadriceps and patellar tendon is a very rare cause of knee pain. Most of the time it is treated conservatively with non-steroidal anti-inflammatory drugs and ultrasound therapy and some times steroid injection. However; patient may require surgical intervention especially in refractory cases to resolve the condition.

Several authors have used 3D motion analysis to measure upper limb kinematics, but none have focused solely on wrist movements, in six degrees of freedom, during activities of daily living (ADL). This study aimed to determine the role of the different planar wrist movements during three standardised tasks, which may be affected by surgical procedures.

Nine volunteers (age range 22-45) were recruited and each participant performed three simulated ADLs: using a door lever, a door knob and opening/closing a jam jar. The ADLs were simulated using a work-sim kit on an isokinetic dynamometer. Motion analysis was performed by a 10-camera Oqus system (Qualisys Medical AB, Gothenburg, Sweden). All raw kinematic data were exported to Visual3D (C-Motion Inc.), where the biomechanical model was defined and joint kinematics calculated.

Table 1 shows a similar range of radial-ulnar deviation and flexion-extension as previous studies. However a substantial amount of wrist rotation also occurred in all tasks. This was significantly greater when using the door lever compared with the door knob and jam jar tasks.

Previous studies have stated that a negligible degree of rotation occurs at the wrist. This study found a maximum mean of 31.7 degrees of wrist rotation. This indicates that considerable rotational movement occurs at the wrist during certain functional tasks. Surgical approaches and clinical pathology may disrupt structures responsible for rotational stability. Further investigation of this rotational component of carpal movement during additional ADLs is proposed in both normal and clinical subjects, to explore the potential relationship between carpal surgery and rotational laxity.

End-stage osteoarthritis is characterised by pain and reduced physical function, for which total knee arthroplasty (TKA) is recognised to be a highly effective treatment. Most implants are multi radius in design, though modern kinematic theory suggests a single flexion/extension axis is located in the femur. A recently launched TKA implant (Triathlon, Stryker US), is based on this theory, adopting a single radius of curvature femoral component. It is hypothesised that this design allows better function, and specifically, that it results in enhanced efficiency of the quadriceps group through a longer patello-femoral moment arm.

Change in power output was compared between single and multi radius implants as part of a larger ongoing randomised controlled trial to benchmark the new implant. Power output was assessed using a Leg Extensor Power Rig, well validated for use with this population, pre-operatively and at 6, 26 and 52 weeks post-operatively in 101 Triathlon and 82 Kinemax implants. All patients were diagnosed with osteoarthritis, and drawn from a single centre. Output was reported as maximal wattage (W) generated in a single leg extension, and expressed as a proportion of the contralateral limb power output to act as an internal control.

The results are shown in the table below. Two-way repeated measures ANOVA demonstrated a significant effect of TKA on the quadriceps power output, F = 249.09, p = <0.001 and also a significant interaction of the implant group on the output F = 11.33, p = 0.001. Independent samples t-tests of between group differences at the four assessment periods highlighted greater improvement in the single radius TKA group at all post-operative assessments (p <0.03), see table.

The theoretical enhanced quadriceps efficiency conferred by single radius design was found in this study. Power output was significantly greater at all post-operative assessments in the single radius compared to the multi radius group. This difference was particularly relevant at early 6 week and 1 year assessment. Lower limb power output is known to link positively to functional ability. The results support the hypothesis that TKAs with a single radius design have enhanced recovery and better function.

Great interest in unicompartmental knee arthroplasty (UKA) for medial osteoarthritis has rapidly increased following the introduction of minimally invasive UKA (MI-UKA). This approach preserves the normal anatomy of knee, causes less damage to extensor mechanism and results in a more rapid post-operative recovery. However, experience with this approach is limited in China. The aim of this report was to determine the short-term clinical and radiographic outcomes of MI-UKA in the Chinese, and to identify any features that are unique to this population. Fifty two knees, in forty-eight patients, with medial compartmental osteoarthritis treated by MI-UKA via C-arm intensifier guide (CAIG) from May 2005 to January 2009 were reviewed. Pain and range of motion (ROM) was assessed using the HSS scoring system before and after surgery. Pre- and postoperative alignment of the lower limbs was measured and compared. The mean follow up time was 24 months (12-42 months). In all cases the pain over medial compartment of the knees was relieved or subsided. The post-operative ROM was 0-136 degree (mean 122degree), and the mean alignment was 2degree varus (0- 7degree varus). The HSS score increased from 72(61-82) to 92(72-95). 93% of the postoperative scores were good or excellent. Interestingly, the distribution of femoral component sizes of these patients was XS 2%, Small 83%, Medium 15%, Large 0%, XL 0%; whereas tibial component size was AA 27%, A 55%, B 15%, C 3%, D 0%, E 0%, and F 0%. The optimal fitted match between tibial and femoral size was: tibia AA and A with XS and small femur, tibia B and C with medium femur. The estimated match was: tibia D and E with large femur, tibia F with XL femur. In contrast to the Oxford report, the sizes of these components are smaller and not in correlation with the height, weight and BMI of the patients. We conclude that MI-UKA is an effective method for treating medial compartmental osteoarthritis of the knee in the Chinese population. CAIG is a feasibly intraoperative measure to predict femoral component sizes. However, component sizes and combinations are different from the Oxford guideline.

The aim of this study was to determine whether the clinical outcome of autologous chondrocyte transplantation was dependent on the timing of a high tibial osteotomy in tibio-femoral mal-aligned knees. Between 2000 and 2005, forty-eight patients underwent autologous chondrocyte implantation with HTO performed at varying times relative to the second stage autologous chondrocyte implantation procedure. 24 patients had HTO performed simultaneously with their second stage cartilage transplantation, (the HTO Simultaneous Group). 5 patients had HTO prior to their cartilage procedure, (the HTO pre-ACI Group) and 19 had HTO performed between 1 to 4 years after their second stage cartilage implantation, (the HTO post-ACI Group). There were 29 men and 19 women with a mean age of 37 years (Range 28 to 50) at the time of their second stage procedure.

With average follow-up of 72 months we have demonstrated a significant functional benefit in performing the HTO either prior to or simultaneously with the ACI procedure in the mal-aligned knee. The failure rate in the Post-ACI group was 45% compared to the Pre-ACI and Simultaneous group, with failure rates of 20% and 25%, respectively.

An HTO performed prior to or simultaneously with an autologous chondrocyte implantation procedure in the mal-aligned knee, provides a significant protective effect by reducing the failure rate by approximately 50%.

Mesenchymal stem cells (MSCs) have potential for therapeutic repair of cartilage and bone but still require optimization in terms of their capacity to deposit an appropriate extracellular matrix (ECM). Adult human cartilage has a limited capacity for repair and is unusual in that it is one of the few tissues where injury is not followed by an influx of monocytes. We are studying the effects of co-culturing primary monocytes with MSCs differentiating along chondrogenic lineage but in addition we needed to investigate the effects of the monocytes on the mature chondrocytes that will result from the MSCs and will also be present in the host tissue.

Human articular cartilage chondrocytes were isolated from human donors undergoing knee replacement surgery for osteoarthritis (OA) with full ethical consent. Cultures were expanded and cells used below passage five for co-culture experiments. Monocytes were prepared from fresh heparinized human blood samples by Ficoll gradient. Co-cultures consisted of either chondrocyte micromasses overlaid with monocytes, or chondrocytes and monocytes seeded together within a collagen/glycosaminoglycan scaffold (Chondromimetic, Tigenix UK). Media, cell pellets and scaffolds were analysed for extracellular matrix (ECM) proteins and proteases by dot blot, western blot, zymography and immunohistochemistry.

Human chondrocytes maintained stable micromasses and laid down an ECM for at least 40 days. Human monocytes eventually formed a proliferating cell population with a rounded morphology on top of the chondrocyte micromasses. These cells established an adherent population with a fibroblastic morphology when replated on plastic. Analysis of chondrocyte ECM proteins indicated that monocytes affected deposition of types I and II collagen, decorin and fibronectin and the overall amounts of gelatinases released. RTPCR demonstrated a decrease in type I collagen expression and a concomitant increase in MMP13 expression.

The precise interaction between monocytes and and chondrocytes has yet to be established but is thought to involve a mixture of contact and paracrine factors. In this study co-culture of monocytes with chondrocytes resulted in phenotypic changes to the chondrocytes which may warrant the inclusion of monocytes in cartilage/bone repair and also provide information as to the responses of OA chondrocytes to external stimuli.

One reason why NICE (National Institute for Clinical Excellence) does not support operations by the NHS to heal hyaline cartilage lesions using a patients own cells is because there is no clear evidence to show that these operations are beneficial and cost-effective in the long term. Specifically, NICE identified a deficiency of high quality cartilage being produced in repaired joints. The presence of high quality cartilage is linked to long-lasting and functional repair of cartilage. The benchmark for quality, NICE stipulate, is repair cartilage that is stiff and strong and looks similar to the normal tissue surrounding it, i.e. mature hyaline articular cartilage.

Biopsy material from autologous cartilage implantation surgical procedures has the appearance of immature articular cartilage and is frequently a mixture of hyaline and fibrocartilage. Osteoarthritic cartilage, in its early stages, also exhibits characteristics of immature articular cartilage in that it expresses proteins found in embryonic and foetal developmental stages, and is highly cellular as evidenced through the presence of chondrocyte clusters. Therefore, an ability to modulate the phenotype and the structure of the extracellular matrix of articular cartilage could positively affect the course of repair and regeneration of articular cartilage lesions. In order to do this, the biochemical stimuli that induce the transition of an essentially unstructured amorphous cartilage mass (immature articular cartilage) to one that is highly structured and ordered, and biomechanically adapted to its particular function (mature articular cartilage) has to be identified.

We show for the first time, that fibroblast growth factor-2 and transforming growth factor beta-1 induce precocious maturation of immature articular cartilage. Our data demonstrates that it is possible to significantly enhance maturation of cartilage tissue using growth factor stimulation; consequently this may have applications in transplantation therapy, or through phenotypic modulation of osteoarthritic chondrocytes in diseased cartilage in order to stimulate growth and maturation of repair tissue.

Periprosthetic femoral fractures can occur as a complication of total hip arthroplasty and are often challenging to treat as the mechanical scenario is influenced by the presence of the metal prosthesis within the bone. This research focuses on finding the optimum fixation for transverse, Vancouver type B1 periprosthetic fractures, stabilised using locking plates and secured using screws. The aim of this study was to experimentally validate a computer model of a human femur, develop that model to represent a periprosthetic femoral fracture fixation and show how the model could be used to indicate differences between plating techniques.

In the first development stage, both a laboratory model and a finite element model were developed to evaluate the mechanical behaviour of an intact composite femur under axial loading. Axial strains were recorded along the medial length of the femur in both cases and compared to provide validation for the computational model predications. The computational intact femur model was then modified to include a cemented total hip replacement, and further adapted to include a periprosthetic fracture stabilised using a locking plate, with unicortical screws above, and bicortical screws below the transverse fracture.

For the intact femur case, the experimental and computational strain patterns correlated well with an average difference of 16%. Following the inclusion of the stem, there was a reduction in the strain in the region of the prosthesis reducing by an average of 45%. There was also a large increase in bulk stiffness with the introduction of the prosthesis. When the fracture and plate fixation were included, there was little difference in the proximal strain where the stem dominated, and the strains in the distal region were found to be highly sensitive to the distribution of the screws.

The results of this study indicate that screw configuration is an important factor in periprosthetic fracture fixation. A laboratory model of the periprosthetic facture case is now under development to further validate the computational models and the two approaches will then be used to determine optimum fixation methods for a range of clinical scenarios.

Staphylococcus aureus is the most common bacterial isolate in septic arthritis. From studies on isolated cartilage cells, the ‘pore-forming’ alpha and gamma toxins are considered the most virulent factors. However, understanding the response of in situ chondrocytes is important in order to identify new treatments to reduce the extent of cartilage damage during, and following, episodes of septic arthritis. Animal models can give useful information; however the interpretation of data can be complex because of the strong immune response. Thus, to clarify the role of S. aureus toxins on in situ chondrocytes we have developed a bovine cartilage explant model.

Metacarpophalangeal joints, from 3-year-old cows, were opened under sterile conditions within 6hrs of slaughter and cartilage explants harvested. Explants were placed into flasks containing Dulbecco's Modified Eagle Medium (DMEM). Aspirates from a patient with septic arthritis of the hip, containing S. aureus, were compared to negative aspirates (no bacterial growth) from a patient with an inflamed knee joint (controls).

The explants were incubated at 37 degrees Celsius and stained after 18, 24 and 40hrs with the fluorescent probes chloromethylfluorescein di-acetate and propidium iodide (10 micromolar each) to label living chondrocytes green and dead cells red respectively. Following imaging of cartilage by confocal laser scanning microscopy, the percentage cell death at each time point was obtained using Volocity 4 software.

There was no detectable change in chondrocyte viability (<1% cell death) over 40hrs incubation with the negative aspirate. However, for the aspirate from a patient positive for S. aureus, there was a rapid increase in cell death between 18 and 24hrs (0.2 +/− 0.3% to 23 +/− 5% cell death respectively) and almost complete cell death at 40hrs (80 +/− 12%; data are means +/− s.d; n=4).

These results show that a strain of S. aureus capable of manifesting clinical disease exerts a potent effect on in situ chondrocytes. In the absence of an immune response, chondrocyte death was purely the result of the bacteria and their products. This bovine cartilage explant model could therefore be useful for studying the effects of S. aureus on chondrocyte behaviour and, ultimately, cartilage integrity.

Intramedullary (IM) femoral alignment guide for unicondylar knee arthroplasty (UKA) is a classic and generally accepted technique to treat unicompartmental knee osteoarthritis. However, IM system has a risk of excessive blood loss, fat embolism and activation of coagulation.Moreover, the implant placement and limb alignment may be less accurate in IM for UKA than total knee arthroplasty. So we try to use extramedullary (EM) femoral alignment for UKA to avoid above disadvantages. To our knowledge, few current studies have been reported by now. We reported a series of cases treated through a newly developed EM technique and evaluated the accuracy of femoral component alignment and preliminary clinical results. Between January 2009 and January 2010, 11 consecutive patients(15 knees)consisting of 8 males and 3 females were enrolled. There were 7 cases in unilateral knee and 4 cases in bilateral knees. The mean age was 65.2 years (range 60∼72 years). Incision, surgical time, blood loss and complications were measured. The pre- and post operative function of the knees were evaluated by HSS score system. The pre- and postoperative femoral component alignment was measured and compared. All cases were followed up for average 15 months (10-22 months). The mean length of incision was 7.2cm (range 6 to 8cm), the mean surgical time was 115.0min(range 90 to 125min),the mean blood loss was 50.8ml (range 50 to 80ml). The mean preoperative HSS score increased from 75 (range 63 to 83) to 95 (range 88 to 97) postoperatively (p<0.05). All femoral components were within the recommended range for varus/valgus (±10 degree) and lexion/extension (±5 degree) angle. None had complications associated with reamed canal injury. By using our EM technique, we could achieve an accurate femoral component alignment and satisfactory clinical effect. However, strict comparison between EM and cconventional IM technique and large amount of cases are essential. Further mid- and long-term studies are required.

Metal-on-metal hip resurfacing prostheses are a relatively recent intervention for relieving the symptoms of common musculoskeletal diseases such as osteoarthritis. While some short term clinical studies have offered positive results, in a minority of cases there is a recognised issue of femoral fracture, which commonly occurs in the first few months following the operation. This problem has been explained by a surgeon's learning curve and notching of the femur but, to date, studies of explanted early fracture components have been limited.

Tribological analysis was carried out on fourteen retrieved femoral components of which twelve were revised after femoral fracture and two for avascular necrosis (AVN). Eight samples were Durom (Zimmer, Indiana, USA) devices and six were Articular Surface Replacements (ASR, DePuy, Leeds, United Kingdom). One AVN retrieval was a Durom, the other an ASR. The mean time to fracture was 3.4 months. The AVNs were retrieved after 16 months (Durom) and 38 months (ASR).

Volumetric wear rates were determined using a Mitutoyo Legex 322 co-ordinate measuring machine (scanning accuracy within 1 micron) and a bespoke computer program. The method was validated against gravimetric calculations for volumetric wear using a sample femoral head that was artificially worn in vitro. At 5mm3, 10mm3, and 15mm3 of material removal, the method was accurate to within 0.5mm3. Surface roughness data was collected using a Zygo NewView500 interferometer (resolution 1nm).

Mean wear rates of 17.74mm3/year were measured from the fracture components. Wear rates for the AVN retrievals were 0.43mm3/year and 3.45mm3/year. Mean roughness values of the fracture retrievals (PV = 0.754nm, RMS = 0.027nm) were similar to the AVNs (PV = 0.621nm, RMS = 0.030nm), though the AVNs had been in vivo for significantly longer.

Theoretical lubrication calculations were carried out which found that in both AVN retrievals and in seven of the twelve cases of femoral fracture the roughening was sufficient to change the lubrication regime from fluid film to mixed. Three of these surfaces were bordering on the boundary lubrication regime. The results show that even before the femoral fracture, wear rates and roughness values were high and the implants were performing poorly.

In uncemented total hip arthroplasty (THA), the optimal femoral component should allow both maximum cortical contact with proximal load transfer and accurate restoration of individual joint biomechanics. This is often compromised due to a high variability in proximal femoral anatomy. The aim of this on-going study is to assess the variation in proximal femoral canal shape and its association with geometric and anthropometric parameters in primary hip OA.

In a retrospective cohort study, AP-pelvis radiographs of 98 consecutive patients (42 males, 56 females, mean age 61 (range:45-74) years, BMI 27.4 (range:20.3-44.6) kg/m2) who underwent THA for primary hip OA were reviewed. All radiographs were calibrated and femoral offset (FO) and neck-shaft-angle (NSA) were measured using a validated custom programme. Point-based active shape modelling (ASM) was performed to assess the shape of the inner cortex of the proximal femoral meta- and diaphysis. Independent shape modes were identified using principal component analysis (PCA). Hierarchical cluster analysis of the shape modes was performed to identify natural groupings of patients. Differences in geometric measures of the proximal femur (FO, NSA) and demographic parameters (age, height, weight, BMI) between the clusters were evaluated using Kruskal-Wallis one-way-ANOVA or Chi-square tests, as appropriate.

In the entire cohort, mean FO was 39.0 mm, mean NSA was 131 degrees. PCA identified 10 independent shape modes accounting for over 90% of variation in proximal femoral canal shape within the dataset. Cluster Analysis revealed 6 shape clusters for which all 10 shape modes demonstrated a significantly different distribution (p-range:0.000-0.015). We observed significant differences in age (p=0.032), FO (p<0.001) and NSA (p<0.001) between the clusters. No significant differences with regard to gender or BMI were seen.

Our preliminary analysis has identified 6 different patterns of proximal femoral canal shape which are associated with significant differences in femoral offset, neck-shaft-angle and age at time of surgery. We are currently evaluating the entire dataset of 345 patients which will allow a comprehensive classification of variation in proximal femoral shape and joint geometry. The present data may optimise preoperative planning and improve future implant design in THA.

Intra-articular screw fixation is indicated for internal fixation of large osteochondral fragments secondary to trauma or osteochondritis dissecans. During surgery, orthopaedic drills are used to prepare a hole through which the screw can pass. Previous work has shown that mechanical injury to articular cartilage results in a zone of cell death adjacent to the traumatised articular cartilage (1). Here, we characterise and quantify the margin of in situ chondrocyte death surrounding drill holes and screws (standard cortical and headless compression designs) placed in mature bovine articular cartilage to model the orthopaedic procedure.

Drill holes (1mm) were made through the articular cartilage and bone of intact bovine metacarpophalangeal joints obtained from 3-yr old cows within 12hrs of slaughter. Osteochondral explants (∼1cm square and 2-3mm thick) encompassing the drilled holes in articular cartilage and subchondral bone were harvested using a chisel. Explants were then incubated in Dulbecco's modified Eagle's medium for 45mins with CMFDA (5-chloromethylfluorescein diacetate) and PI (propidium iodide; both at 10micromolar) to identify/quantify living and dead in situ chondrocytes respectively in a consecutive series of axial optical sections using confocal scanning laser microscopy (CLSM).

The drill holes through cartilage appeared to have clearly defined edges with no macroscopic evidence of cartilage splitting. However visualisation of fluorescently-labelled in situ chondrocytes by CLSM demonstrated clear cell death around the periphery of the drilled hole which was 166±19 micrometers in width. This increased with a larger diameter (1.5mm) drill to 450±151 micrometers (all data are means±s.e.m.; n=3). Preliminary experiments indicated that the margin of chondrocyte death around a 1.5mm hole was dramatically increased further by the insertion of screws into pre-drilled holes.

These results suggest that the mechanical trauma associated with cartilage drilling and the insertion of intra-articular screws occurs with marked death of in situ chondrocytes extending into normal cartilage beyond the area occupied by the screw. As chondrocytes are not replaced in mature cartilage, their loss around the hole/screw will mean that the extracellular matrix is not maintained, inevitably leading to cartilage failure.

Meniscal cartilage provides joint stabilisation, load distribution, impact absorption and decreased friction in joints that have a complex movement such as the knee. If the meniscal cartilage degrades or is surgically removed, there is a strong probability, over time, of damage to the articular surface. The ability to regenerate damaged meniscal cartilage with an implanted device that replaces the biological equivalent would allow for joint stabilisation, robust movement and reduce the risk of damage to the articular cartilage. An implant with many of the characteristics of meniscus and with the ability to integrate correctly and firmly with the surrounding tissue, would be advantageous.

Inclusion of Platelet Rich Plasma (PRP) into the scaffolds to provide a concentrated source of matrix proteins and autologous growth factors may further enhance the regenerative repair process. To investigate the suitability of the collagen scaffolds, addition of meniscal chondrocytes and or PRP was examined in vitro.

Human meniscal chondrocyte cells were isolated, via collagenase digestion, from meniscal cartilage recovered from total knee replacement surgery. Meniscal chondrocytes were cultured in vitro to expand cell numbers. PRP was produced from volunteer's blood using a centrifuge and density based platelet recovery system. Release of Platelet Derived Growth Factor type AB (PDGF-AB) was measured by ELISA as an indicator of the behaviour of the peptide growth factor component. Combinations of scaffold, meniscal chondrocytes and PRP were tested for interaction, suitability and viability.

Experiments so far have shown good biocompatibility, in vitro, as meniscal chondrocytes were able to grow within the range of scaffolds produced. Cell retention could be enhanced by addition of PRP to the scaffolds. PDGF-AB was released over 5 days from the scaffold and PRP combination.

Further studies are in progress to derive relevant scaffold modifications and combinations for practical, robust, treatment strategies.

Weight-bearing is a known stimulus for bone remodelling and a reduction in weight-bearing is associated with reduced bone mineral density (BMD) in affected limbs post lower limb fracture. This study investigated short and long-term precision of a method for measuring relative left/right weight-bearing using two sets of identical calibrated scales. The effect of imbalance on BMD at the hip and on lower limb lean tissue mass (LLTM) was also assessed.

46 postmenopausal women, with no history of leg or ankle fracture, were measured three times whilst standing astride two scales (Seca, Germany). 34 of the participants were re-measured after 6 months by the same method. Bilateral hip and total body dual x-ray absorptiometry measurements were performed using a GE Lunar Prodigy (Bedford, MA). Precision errors in weight-bearing measures were calculated using the root mean square coefficient of variation (RMSCV%). The correlations at the first visit between left/right differences in weight-bearing and differences in BMD and LLTM were calculated.

The short-term RMSCV% for left and right weights were 4.20% and 4.25% respectively and the long-term RMSCV% were 6.91% and 6.90%. Differences in left/right weight-bearing ranged from 0 to 24% (SD 8.63%) at visit 1 and 0 to 30% (SD 10.71%) at visit 2. Using data from visit 1, the relationship between hip BMD differences and left/right weight-bearing differences were investigated, with no significant correlations found. However, a weak, but statistically significant correlation of r=0.35 (p=0.02) was found for differences in LLTM and left/right weight-bearing differences.

In conclusion, left/right weight-bearing measured using two scales is a precise method for evaluating differences in weight-bearing in the short and long-term. Differences in left/right weight-bearing in this population varied by up to 30%. Participants showed a high degree of consistency in their long-term balance in a natural standing posture. Inequalities in left/right weight-bearing did not correlate significantly with BMD at the hip, but demonstrated a weak but statistically significant correlation with lean tissue mass.

Finite element models of the musculoskeletal system have the possibility of describing the in vivo situation to a greater extent than a single in vitro experimental study ever could. However these models and the assumptions made must be validated before they can be considered truly useful. The object of this study was to validate, using digital image correlation (DIC) and strain gauging, a novel free boundary condition finite element model of the femur.

The femur was treated as a complete musculoskeletal construct without specific fixed restraint acting on the bone. Spring elements with defined force-displacement relationships were used to characterize all muscles and ligaments crossing the hip and knee joints. This model was subjected to a loading condition representing single leg stance. From the developed model muscle, ligament and joint reaction forces were extracted as well as displacement and strain plots. The muscles with the most influence were selected to be represented in the simplified experimental setup.

To validate the finite element model a balanced in vitro experimental set up was designed. The femur was loaded proximally through a construct representative of the pelvis and balanced distally on a construct representing the tibio-femoral joint. Muscles were represented using a cabling system with glued attachments. Strains were recorded using DIC and strain gauging. DIC is an image analysis technique that enables non-contact measurement of strains across surfaces. The resulting strain distributions were compared to the finite element model.

The finite element model produced hip and knee joint reaction forces comparable to in vivo data from instrumented implants. The experimental models produced strain data from both DIC and strain gauging; these were in good agreement with the finite element models. The DIC process was also shown to be a viable method for measuring strain on the surface of the specimen.

In conclusion a novel approach to finite element modeling of the femur was validated, allowing greater confidence for the model to be further developed and used in clinical settings.

Finite element (FE) modelling has been widely used to create and assess musculoskeletal models. However to achieve a high degree of resolution in describing the structure, significant computational power and time are required. The objective of this study was to introduce a complimentary approach to FE modelling using structural beam theory. This requires far less computational power and models can be analyzed in a fraction of a second, offering quick, intuitive results for engineers and surgeons.

Beam theory was first introduced as a method for analyzing the stresses in long bones in 1917. It was used as the de facto method for several decades. The introduction of FE modelling offered great advances; beam theory calculations were considered laborious and less accurate. However with the advances in computational power so too comes the ability to create modern automated beam theory models.

A study was conducted using the commercially available general structural analysis software Oasys GSA. A synthetic biomechanical femur was CT scanned and the solid model constructed. This model was sectioned into approximately seventy sections in the regions of the shaft and condyles, thirty in the neck and thirty in the head. Line plots of the shape of each of the sections, for both cortical and trabecular parts, were then imported into Oasys GSA. The centroid, area, second moments of area and torsion constant were calculated for each section. The sections were plotted at the position of the cortical centroid and parallel axis theorem was used to plot the trabecular section in the same position. A force representing the hip joint reaction force was applied to a node corresponding to the centre of the femoral head. Muscular forces were applied to stiff radial elements according to those active at the point of peak joint contact force during gait.

Oasys GSA produced instant results showing moment and deflection characteristics of the femur. This data was then used to predict strain plots, which were directly compared to FE results. Initial results compare favourably.

This study has demonstrated an updated fast, efficient and intuitive alternative to finite element modelling.

Finite element modelling is being extensively used to evaluate the biomechanical behaviour of fractured bone treated with fixation devices. Appropriate modelling of the bone-implant interface is key to quality biomechanical prediction.

The present study considers this interface modelling in the context of locking plates. A majority of previous studies assume the interface to be represented by a tied constraint or a fully bonded interface. Many other studies incorporate a frictional interface but ignore screw threads. This study compares the various interface modelling strategies. An interface with screw threads explicitly included is also considered.

The study finds that interface modelling has significant impact on both the global and local behaviour. Globally, the load-deflection behaviour shows considerable difference depending on the interface model. Locally, the stress-strain environment within the bone close to the screws is significantly altered.

The results show that the widely used tie constraint can overestimate stiffness of a construct which must be correctly predicted to avoid non-union or periprosthetic re-fracture, especially in osteoporotic bone. In addition, the predictions of screw loosening, bone damage and stress shielding are very different when screw threads are included in the model.

Long term, secondary implant fixation of Total Disc Replacements (TDR) can be enhanced by hydroxyapatite or similar osseo-conductive coatings. These coatings are routinely applied to metal substrates. The objective of this in vivo study was to investigate the early stability and subsequent bone response adjacent to an all polymer TDR implant over a period of six months in an animal model.

Six skeletally mature male baboons (Papio annubis) were followed for a period of 6 months. Using a transperitoneal exposure, a custom-sized Cadisc L device was implanted into the disc space one level above the lumbo-sacral junction in all subjects. Radiographs of the lumbar spine were acquired prior to surgery, and post-operatively at intervals up to 6 months to assess implant stability. Flourochrome markers (which contain molecules that bind to mineralization fronts) were injected at specified intervals in order to investigate bone remodeling with time.

Animals were humanely euthanized six months after index surgery. Test and control specimens were retrieved, fixed and subjected to histological processing to assess the bone-implant-bone interface. Fluorescence microscopy and confocal scanning laser microscopy were utilized with BioQuant image analysis to determine the bone mineral apposition rates and gross morphology.

Radiographic evaluation revealed no loss of disc height at the operative level or adjacent levels. No evidence of subsidence or significant migration of the implant up to 6 months. Heterotopic ossification was observed to varying degrees at the operated level.

Histology revealed the implant primary fixation features embedded within the adjacent vertebral endplates. Flourochrome distribution revealed active bone remodeling occurring adjacent to the polymeric end-plate with no evidence of adverse biological responses. Mineral apposition rates of between 0.7 and 1.7 microns / day are in keeping with literature values for hydroxyapatite coated implants in cancellous sites of various species.

Radiographic assessment demonstrates that the Cadisc L implant remains stable in vivo with no evidence of subsidence or significant migration. Histological analysis suggests the primary fixation features are engaged, and in close apposition with the adjacent vertebral bone. Flourochrome markers provide evidence of a positive bone remodelling response in the presence of the implant.

Recently finite element studies have incorporated bone remodelling algorithms in an attempt to simulate bone's mechano-adaptation to loading conditions. In order to simplify these analyses, bone is usually considered to be isotropic, which does not explain the directionality of its internal structures; neither the orthotropic properties measured at the continuum level. Furthermore, simplified loading is usually applied to the bone models, which can result in an unrealistic remodelling stimulus. However, free boundary condition modelling of the femoral and pelvic constructs has been shown to produce more physiological stress and strain distributions.

This paper describes the application of a 3D remodelling algorithm (with bone modelled as a strain-adaptive continuum with local orthotropic material properties) to a free boundary model of the femoral construct, where the hip and knee joints, as well as muscles and ligaments crossing the joints were included explicitly. Two load cases were analysed: single leg stance and standing up.

Material properties and directionality distributions were produced for the whole femur, showing good agreement with observed structures from clinical studies. This indicates that the loading conditions modelled correspond to those experienced in vivo. In addition, the impact of the different load cases in bone structure modelling could be compared. Observations of the material properties distribution and orientation for standing up indicate that it promotes changes in bone stiffness in the anterior regions of the femoral neck and cortical shaft and the posterior side of the condyles.

Development of this approach to modelling and bone structure prediction can lead to a better understanding of bone's mechanical behaviour and to the development and public release of orthotropic heterogeneous models for different constructs. These can be applied in many areas of interest in orthopaedic biomechanics, such as the study of bone-implant interfaces, improvement of the currently used surgical tools and techniques and the influence of certain activities in affecting local bone strength and mineralisation.

Hyaline cartilage defects are a significant clinical problem for which a plethora of cartilage repair techniques are used. One such technique is cartilage replacement therapy using autologous chondrocyte or mesenchymal stem cell (MSC) implantation (ACI). Mesenchymal stem cells are increasingly being used for these types of repair technique because they are relatively easy to obtain and can be expanded to generate millions of cells. However, implanted MSCs can terminally differentiate and produce osteogenic tissue which is highly undesirable, also, MSCs generally only produce fibrocartilage which does not make biomechanically resilient repair tissue, an attribute that is crucial in high weight-bearing areas. Tissue-specific adult stem cells would be ideal candidates to fill the void, and as we have shown previously in animal model systems [Dowthwaite et al, 2004, J Cell Sci 117;889], they can be expanded to generate hundreds of millions of cells, produce hyaline cartilage and they have a restricted differential potential. Articular chondroprogenitors do not readily terminally differentiate down the osteogenic lineage.

At present, research focused on isolating tissue-specific stem cells from articular cartilage has met with modest success. Our results demonstrate that using differential adhesion it is possible to easily isolate articular cartilage progenitor populations from human hyaline cartilage and that these cells can be subsequently expanded in vitro to a high population doubling whilst maintaining a normal karyotype. Articular cartilage progenitors maintain telomerase activity and telomere length that are a characteristic of progenitor/stem cells and differentiate to produce hyaline cartilage.

In conclusion, we propose the identification and characterisation of a novel articular cartilage progenitor population, resident in human cartilage, which will greatly benefit future cell-based cartilage repair therapies.

Metal on metal press-fit acetabular cups are the worst performing acetabular cup type with severe failure consequences compared to cups made from more inert materials such as polyethylene or ceramic. The cause of failure of these cup types is widely acknowledged to be multi-factorial, therefore creating a complex scenario for analysis through clinical studies. A factorial analysis has been carried out using an experimentally validated finite element analysis to investigate the relative influence of four input factors associated with acetabular cup implantation on output parameters indicating potential failure of the implantation. These input factors were: cup material stiffness; cup inclination; cup version; cup seating; and level of press-fit. The output parameter failure indicators were: wear; tensile strains in the underlying bone; bone remodelling; and cup-bone micromotions.

The factorial analysis concluded that the most significant influence was that of cup inclination on wear, and the second most significant was the influence of the level of press-fit on bone remodelling at the acetabular rim. Significant influence was also observed between version angle and wear, and cup-seating and micro-motion.

The results demonstrated the clear multi-factorial nature of implant failure and highlighted the importance of correct implant positioning and fit.

Osteoarthritis (OA) is the most common form of joint disease leading to disability and dependence. In severe cases of knee OA, the joint is deemed irrecoverable and total knee replacements are indicated. Tissue engineering is a possible solution for this pathology and previous work from our laboratory has demonstrated that it is possible to isolate and expand chondroprogenitor cells in vitro from healthy knee-joint articular cartilage. Work presented here describes the detection and isolation of chondroprogenitor cells derived from osteoarthritic cartilage following total knee replacement in patients with severe OA, suggesting a pool of viable cells from this degenerate region which has been previously deemed non-recoverable.

Human articular cartilage was excised from tibial plateaux (TP's) obtained from total knee replacements following the diagnoses of severe OA. Cells were isolated by a sequential pronase and collagenase digestion and subject to a fibronectin adhesion assay. Cells were expanded in monolayer in supplemented growth medium. Clonal 3D pellet cultures were established in chondrogenic and osteogenic differentiation media. Adipogenic cultures were also established in monolayer cultures. Histological procedures, immunohistochemistry and molecular biology were undertaken in order to determine the extent of differentiation. In addition, osteochondral plugs were excised from the TP's and wax embedded for further histological and immunohistochemical analysis.

Clonal cell lines obtained from osteoarthritic knee-joint cartilage using the fibronectin adhesion assay were isolated and successfully cultured to a maximum of 60 population doublings whilst still demonstrating a chondrogenic capacity. Three-D pellet cultures after 21 days of chondrogenic induction produced smooth and iridescent pellets which stained positively for toluidine blue and safranin O. Positive labelling for collagen type II and aggrecan were also observed. Following osteogenic induction; evidence of mineralisation was indicated by the von Kossa stain. Adipogenic induction revealed a positive result. Osteochondral plugs demonstrated sporadic positive labelling in the surface region for putative stem cell marker Stro-1.

Chondroprogenitor cells isolated from osteoarthritic display a strong chondrogenic phenotype, and have the ability to be induced into different lineages. These findings suggest the presence of a pool of viable chondroprogenitors from osteoarthritic tissue which was otherwise deemed irrecoverable.

A novel scoring system for the grading of osteoarthritis has been developed.

Scoring systems for the measurement of Osteoarthritis (OA) are essential for the understanding of the osteoarthritic process. OA is a mutifactorial degenerative joint disease affecting not only hyaline cartilage but also the surrounding tissues and particularly the subchondral bone. It as questionable as to why the articular cartilage remains the sole component used for histopathological assessment. The intimate relationship between the subchondral bone and overlying cartilage provide major difficulty in their independent measurement.

A new scoring system has been developed to incorporate the subchondral bone into the assessment process and relating it to the structure of the overlying hyaline cartilage, which together permit a more accurate description of the degree of degenerate change.

The new scoring system was developed from the analysis of 26 operative specimens from tibial plateau (TP) from patients who underwent total knee replacement (TKR). Multiple osteochondral plugs were taken from weight-bearing regions of the whole TP. The specimens were fixed and decalcified before being sectioned and stained with Masson's trichrome.

Using a standard imaging system (Photoshop) the areas of bone and hyaline cartilage were identified and measured. Further parameters 1) cartilage thickness 2) tidemark integrity, 3) surface integrity 4) cartilage morphology were measured using a numeric measurement scale.

The scoring system indicated a relationship between the area of subchondral bone and the hyaline cartilage degeneration. The overall sum of scores was also successful in distinguishing between the milder and more severe samples of OA. More comprehensive inter and intra observer variability needs to be tested in order validate the system. Quantifying changes to the subchondral bone may also serve beneficial to clinicians, as it is possible that monitoring these changes clinically could lead to early identification of OA.

Unique progenitor cells have been identified recently and successfully cultured in vitro from human articular cartilage. These cells are able to maintain chondrogenic potential upon extensive expansion. In this study, we have developed a sheep, ex-vivo model of cartilage damage and repair, using these progenitor cells. This study addresses the question can such a model be used to determine factors required for progenitor cell proliferation, differentiation and integration of matrix onto bone. The hypothesis was that sheep allogenic cartilage derived progenitor cells could regenerate artificially damaged sheep articular cartilage in an osteochondral culture model. Progenitor cells were derived from ovine articular cartilage using a differential adhesion assay to fibronectin and expanded clonally. These clonal cells were marked with lentiviral vectors derived from the Human Immunodeficiency Virus-1. When a self-inactivating lentiviral vector encoding a ubiquitous phosphoglycerate kinase promoter, driving a Green Fluorescent Protein (GFP) reporter gene, was used to transduce these cells, up to 80% of these progenitor cells expressed GFP. Normal sheep medial femoral condyles containing about 2mm thick sub-condral bone were obtained and 4mm circular defects created on the cartilage surface using a biopsy punch. Condyles were cultured for two weeks in vitro with GFP labelled progenitor cells within a fibrin glue scaffold (Tisseel Lyo) and matrix production (collagen) as determined by spatially offset Raman spectroscopy and immunohistochemistry was demonstrated. Progenitor cells were able to proliferate and differentiate into collagen producing cells. Such an ex-vivo model system is an effective tool for the analysis of cartilage repair from various sources of stem cells. These ex-vivo experiments and variations on defect type, size, titration of scaffold and progenitor cell numbers requirements can further be used as a basis for screening prior to in vivo experiments.

Osteoporosis (OP) results in a reduction in the mechanical competence of the bone tissue of the sufferers. In skeletal sites such as the proximal femur and the vertebrae, OP manifests itself in low trauma fragility fractures which are debilitating for the patient. The relationships between the compressive strength of cancellous tissue and its apparent density are well established in studies of the past. Recently the authors have presented a method able to assess the fracture toughness properties of cancellous bone (1), a challenging cellular material which can exhibit large elasto-plastic deformations. The in-vitro measurement of fracture toughness alongside the customary compressive strength can provide a comprehensive assessment of the mechanical capacity of cancellous bone, which will reflect closer its ability to resist crack initiation. The aims of the present study were: (1) to examine whether the observed fracture toughness deterioration can also be detected by non-invasive quantitative ultrasound (QUS); and (2) to provide rational evidence for the well proven ability of QUS to predict directly ‘risk of fracture’. 20 femoral heads were obtained from donors undergoing emergency surgery for a fractured neck of femur. QUS investigations of the calcaneus, proximal phalanx and distal radius were undertaken within 72 hours of surgery. 128 fracture toughness samples and 20 compression cores were manufactured and tested. Two clinical QUS systems were used to obtain in-vivo scan data and then directly compared those to the density, porosity and the fracture mechanics of tissue extracted from the same individuals. The results demonstrated not only that there was a significant link between in-vivo determined QUS values for the calcaneus and finger to the density of the density of the femoral head; but that there was also a significant link between the QUS results from the calcaneus and the fracture toughness of the cancellous bone from the femoral head. These results point towards a systemic effect of osteoporosis which affects similarly different parts of the skeleton and supports the use of clinical QUS systems as a diagnostic tool for the prediction of fracture risk.

Early diagnosis of delayed- and non-union tibial fractures is difficult, but treatment options are available if timely data are available. Direct correlation between implant forces and healing status is difficult during stance phase loading due to soft tissue forces. This ongoing study seeks to find a minimal set of strain gauge sites needed to determine healing at any of several fracture sites, using isometric loading suitable for routine clinical usage. A series of instrumented tibial nails are being used to help determine whether an alternative technology can replace or augment existing routine methods for assessment of fracture healing.

In a prior study, a single strain gauge positioned close to the fracture site had produced mixed results. In the current study, a TRIGEN META NAIL, 10mm OD x 380mm long, was instrumented with 8 gauged sites spiraled down the nail at 34mm axial and 120deg angular separation (Gen1), and loaded in a Sawbone model in offset axial compression, 3 point bending and torque.

In order to gain early clinical results, and in a design informed by the Gen1 data, a set of instrumented nails have been made for an ovine wireless telemetry study (Gen3a), shortly to commence, in which the tibial nail has been over-gauged enabling multiple d.o.f. measurements to be made during gait, torque, axial compression and 3 point bending; the latter protocols offering more controlled patient postures. This study is to be followed by a similar human study (Gen3) involving five subjects (12 gauges per nail). Meanwhile, a parallel biomechanical study involving six nails with 20 gauges each is also planned.

In the Gen1 study, the strains diminished with distance from the fracture site and with out-of-plane sites during bending. During torque, however, the response was much more uniform for all strain sites. Significant increases in strains due to both loading regimes were seen in the fractured case vs. an intact bone.

Preliminary conclusions are that strains measured due to applied torque may offer a more sensitive and fracture site-independent means of assessing healing than induced bending. We now aim to confirm these observations in animal and human studies.

Spinal total disc replacement (TDR) designs rely heavily on total hip replacement (THR) technology and it is therefore prudent to check that typical TDR devices have acceptable friction and torque behaviour. For spherical devices friction factor (f) is used in place of friction coefficient (mju). The range of loading for the lumbar spinal discs is estimated at perhaps 3 times body weight (BW) for normal activity rising to up to 6 times BW for strenuous activity^[1]. For walking this equates to around 2000 N, which is the maximum load required by the ISO standard for TDR wear testing^[2].

Three Prodisc-L TDR devices (Synthes Spine) were tested in a single station friction simulator. Bovine serum diluted to 25% was used as a lubricating medium. Flexion-extension was ±5 deg for all experiments with constant axial loading of 500, 2000 and 3000 N. The cycle run length was limited to 100 and the f and torque (T) values recorded around the maximum velocity of the cycle point and averaged over multiple cycles.

Preliminary results shows that the 500 N loading produced the largest f of 0.05 ± 0.004. The 2000 N load, which approximates daily activity, gave f = 0.036 ± 0.05 and the 3000 N load gave f = 0.013 ± 0.003. The trend was for lower f with increasing loads.

A lumbar TDR friction factor of 0.036 for a 2000N load and the reduction in f for increasing loads is comparable to the lower end of the range of values reported for THR in similar simulator studies using metal-on-polyethylene bearing materials^[3]. The 3000 N result showing that increasing the load above that expected in daily activity does not raise the f could be important when considering rotational stability and anchorage in a TDR device because frictional torque at the bearing surfaces is proportional to the product of load, device radius and f.

Maintaining femoral neck cortical thickness may help prevent hip fracture. Fracture initiation probably starts superiorly at flaws, ie where the cortex is thinnest. Whole body computed tomography (QCT) is now being used to study cortical thickness but limited resolution (> 300 micrometers) makes in vivo estimates imprecise, whereas microscopy s resolution approaches 1 micrometer. We have therefore extended our microscopic studies on femoral neck biopsies to include men (14 cases, 26 controls) and women (50 cases, 23 controls), and here provide data on true cortical thickness in subjects with and without hip fracture.

Whole femoral neck cross-sections obtained at hemiarthroplasty (or at post-mortem in controls) were embedded in methacrylate, cut, stained and imaged at medium power. Image-J was used to define cortical boundaries and to measure cortical thicknesses at 5 degree intervals of arc from the cross-sections centre of area.

We confirmed that the mid-femoral neck (or narrow neck) site, defined as where the ratio of maximum to minimum neck diameter (max:min) is 1.4, shows great asymmetry, with the thick inferior cortical octant averaging over 3mm thickness (mean age 79 years inter-quartile range 74-85). In the superior 3 octants cortical thickness averaged 26% of that seen inferiorly. To assess statistical determinants of cortical thickness, the data were modelled with linear regression in octants after adjusting for subjects age, sex, max:min, and hip fracture status. To achieve normality of residuals the cortical thickness data were log-transformed. 95% of measured cortical thicknesses fell between 45% and 220% of the mean for octant. In the thinner, superior three octants, minimum thicknesses were just under 0.3 mm in the fracture cases ie close to 35% of the subjects mean for octant. Cases had about 17% thinner cortical thicknesses in all octants than controls, while female controls had cortical thicknesses that uniformly averaged 90% of male. In conclusion, compared to gender and age-matched controls, intra-capsular hip facture cases had generalized cortical thinning in all mid-neck octants. This disease effect contrasts markedly with the effect of normal ageing, which thins preferentially the mechanically under-loaded superior cortex and spares the infero-anterior cortex.

Prosthesis migration and acetabular cup wear are useful short term measurement which may predict later implant outcome. However, the significance of the magnitude and pattern of the migration is very much dependent on the specific design studied. This study aimed to characterise patterns of migration by following four cemented femoral stem designs using Radiostereometry (RSA) within a prospective randomised longitudinal trial.

164 patients undergoing cemented femoral hip replacement for osteoarthritis were randomised to receive either an Exeter (Howmedica Stryker), Ultima Tapered Polished Stem (TPS) (Depuy), Ultima Straight Stem (USS) (Johnson and Johnson) or Elite Plus (Depuy) stem. Each subject received the OGEE PE cemented acetabular component (Depuy). RSA examinations were performed at 1 week and 6, 12, 18, 24 and 60 months post surgery. They were analysed using the UMRSA system (RSA Biomedical AB, Umea, Sweden), and our local geometric stem measurement software. 149 patients had RSA measurements available to 2 years, and 96 patients to 5 years. Differences were analysed using mixed linear modelling (SPSS).

Median linear proximal cup wear rate reduced to a minimum of 0.02-0.06mm/year in year two. Between 2 and 5 years the wear rate increased, being significantly higher for the Elite.

Cup migration was small but continuous. At 2 years it was median 0.3mm proximally, increasing to 0.5 mm at 5 years. Median rotations were less than 0.3 degrees.

Proximal migration was positive and increasing at all time points for all stems. For the tapered polished designs, while the overall magnitude was significantly higher, the rate of migration significantly decreased, whereas for the other stem designs it did not.

The TPS stem showed a tendency for posterior tilt which was significant compared to the other stems at 5 years.

All stems tended to retroversion, with the USS significantly less than the others and the Elite showing and relative increase at 5 years.

In summary migration patterns are characterised by the stem design, including where there were only small changes between designs. We are now testing measured migrations as predictors of outcome, and will continue to follow this group of patients to 10 years.

The Adora RSA (NRT, Denmark) is a new stereo X-ray system custom built for Radeostereometry. Images are acquired using CXDI50C digital detectors (Canon, Netherlands). Analysis software was written locally to detect both Tantalum markers and the spherical head of the hip implant, and for RSA reconstruction and kinematic analysis.

To assess geometric reproducibility, a planar grid phantom was constructed with 1400 2mm markers in a grid pattern over a 350 by 430 mm glass plate. Additionally 25 tantalum markers of each diameter 1.0, 0.8 and 0.5 mm were added within a 120mm square of the grid. The phantom was imaged repeatedly with translation and rotation over the detector. For small phantom movements of up to 10mm over the detector, very small measurement errors were observed of median 2 microns, maximum 6 microns. For larger movements, the errors increased to median 5 microns and maximum 50 microns. Errors also increased with decreasing exposure.

For RSA validation, an acetabular PE cup was cemented to a Sawbone pelvis. Tantalum markers were inserted into the pelvis (10), cement (4), and cup (10). A 28mm metal head was fixed to the cup. The phantom was imaged repeatedly without movement, then moved in translation (up to 100 mm) and rotation (all axes, up to 45 degrees), and with full X-ray repositioning. Precision errors were calculated on the assumption of no relative movement between components.

Results are given for repositioning movement categorised as none, small (less than 25mm or 15 degrees), medium (less than 50mm or 30 degrees), and large. For the head, the mean total point motion error was 4, 10, 14 and 24 micrometers. Mean error of segment fitting was less than 60 microns with no markers rejected from the composite segment of 24 markers. Cup migration total translation error was 10, 16, 24, and 35 micrometers with rotation errors less than 0.05 degrees.

Observed RSA errors were small, increasing with phantom movement. This is consistent with the geometric uniformity tests. X-ray exposure and tissue thickness were also identified as factors in precision. We conclude this system has excellent precision for Radiostereometry.

There is an established link between bone quality and fracture risk. It has been suggested that reduced bone quality will also reduce the toughening mechanisms displayed during loading at a high strain rate. We hypothesised that partially decalcified bone will not demonstrate an increase in force required to cause failure when comparing low and high strain rate loading.

Mechanical properties were defined by the maximum force at failure. Bone quality was defined by the mineral content. This was altered by subjecting the bones to ultrasonically assisted decalcification in 10M EDTA to achieve an average 18% mineral reduction (A 70 yr old woman has approx 18% of her peak bone mass). 20 pairs of sheep femurs were harvested and split into four equal groups: normal bone quality, fast strain rate (NF); normal bone quality, slow strain rate (NS); low bone quality, fast strain rate (LF) and low bone quality, slow strain rate (LS). All mechanical testing was carried out by means of 3-point bending. Load representing the slow strain rate was applied by a mechanical testing machine (Zwick) at a rate resulting in a deflection of 1mm/s. The dynamic loading was applied by a custom designed pneumatic ram at a mean rate of deflection between the specimens of 2983 mm/s (±SD 1155), this equates to strain rates experienced in a road traffic accident.

The following results for force at failure were found (mean ± SD). NF: Force 5503N (± 1012); NS: Force 3969N (± 572); LF: Force 3485N (± 772); LS: Force 3165N (± 605). Groups were compared using a Mann-Whitney U test. Significant results were found between the following groups: Normal bone quality, strain rate compared (NF-NS) p<0.002; Fast strain rate, bone quality compared (NF-LF) p=0.008; Slow strain rate, bone quality compared (NS-LS) p=0.02. No statistical significance was found when comparing low bone quality, strain rate compared (LF-LS) p=0.47.

These results show that normal healthy bone has an ability to withstand higher strain rates which protects it against fracture. This ability to withstand high strain rates is lost in decalcified bone making it more susceptible to fracture. The results of this study indicate the importance of strain rate reduction as well as energy absorption in the design of hip protectors and in environmental modifications.

Despite the development of skeletal or mesenchymal stem cell (MSC) constructs aimed at creating viable cartilage and bone, few studies have examined the effects of cytokines present in rheumatoid arthritis (RA) and osteoarthritis (OA) synovial tissues, or inhibition of these, on such constructs. This work addresses these issues using both in vitro and in vivo approaches and examines potential ways of overcoming the effects of cytokines on the integrity of cartilage and bone constructs.

Synovial samples were obtained from RA or OA (n=10) patients undergoing elective hip or knee arthroplasty at Southampton General Hospital. Full ethical approval was obtained. Control bone marrow-derived stromal cells were obtained from patients undergoing emergency fractured neck of femur repair, cultured in basal, osteogenic (ascorbate and dexamethasone) and chondrogenic (transforming growth factor beta (TGFbeta3)) conditions. Differentiation towards bone and cartilage was assessed using alkaline phosphatase (ALP) staining, ALP and DNA biochemical assays and analysis of osteogenic/chondrogenic gene expression using real time polymerase chain reaction (rt-PCR). Exogenous interleukin-1 (IL-1) (10ng/mL), tumour necrosis factor alpha (TNFalpha) (10ng/mL) or interleukin-6 (IL-6) (100ng/mL) was added and effects on differentiation noted. RA and OA synovial samples were digested, cultured for 48 hours then centrifuged to produce supernatants. Cytokine profiles were determined using ELISA. These supernatants were then added to MSCs and their effects on differentiation assessed.

Mesenchymal cultures in osteogenic media with IL-1 showed an additive osteogenic effect on biochemical assays. TNF exerted a less marked and IL-6 no apparent effect on osteogenic differentiation. ALP expression by rt-PCR correlated with these findings. Addition of supernatants to mesenchymal cultures produced a marked osteogenic profile that was IL-1 and TNFalpha concentration dependent, correlating with lower supernatant dilutions on initial ELISA analysis.

Preliminary studies indicate that exogenous IL-1 and TNFalpha modulate the osteogenic phenotype in MSCs in vitro. OA and RA synovial supernatants affect skeletal cell differentiation. Variations in cytokine profiles between supernatants require analysis for potential confounders. A larger study is underway to investigate these effects, the effects of cytokines on skeletal cell differentiation on commercially available scaffolds both in vitro and in an in vivo murine model of bone formation.

It is known that excessive varus alignment of the femoral stem in total hip replacement (THR) creates a sub-optimal biomechanical environment which is associated with increased rates of revision surgery and component wear. Little is known regarding the effect of femoral stem alignment on patient functional outcome.

Medical and allied health staff are beginning to incorporate the Nintendo Wii-Fit into musculoskeletal rehabilitation protocols. One potential application is the assessment of standing balance following Orthopaedic lower limb surgery. The Wii Balance Board (WBB) has been shown to be a valid equivalent to a laboratory grade force platform for the assessment of standing balance. Our objective was to investigate the validity and reliability of the balance tests included with the Wii-Fit software.

Initially, a single subject performed multiple repeats of a standing balance test. The data was collected simultaneously from a commercial force platform using its integrated software that measured centre of pressure and from the WBB using the Wii-Fit software that generated a percentage score. The data from each was compared and analyzed, applying the equations of known, validated standing balance measurements.

Then, thirty subjects free of lower limb pathology performed a series of standing balance tests combining single leg and double leg stance with their eyes open and then closed. Data was collected from one set of trials on the WBB using the Wii-Fit software and another using bespoke centre of pressure software on a laptop computer. The tests were then repeated on a second occasion within 2 weeks.

The algorithm used by the Wii-Fit software to generate the ‘Stillness’ standing balance score was calculated with a predictive value (R squared) of 0.94. This correlated well to a known, valid measure of standing balance.

Test-retest reliability was examined for the data from both pieces of software. Both demonstrated good-to-excellent test-retest reliability within ‘software’. The laptop data was transformed using the algorithm and the between ‘software’ reliability was calculated as good-to-excellent.

The Wii-Fit software collects standing balance data from the WBB at a fraction of the cost of laboratory grade systems. The score generated by the Wii-Fit software is reliable and valid as an overall assessment of standing balance. Although its application would be limited for detailed assessment of balance disorders, it could still provide surgeons with an affordable, clinic based balance-screening tool. This could form part of an assessment protocol following lower limb surgery.

The aseptic loss of bone after hip replacement is a serious problem leading to implant instability. Hydroxyapatite coating of joint replacement components produces a bond with bone and helps to reduce loosening. However, over time bone remodeling at the implant interface leads to loss of hydroxyapatite. One possible solution would be to develop a coating that reduces hydroxyapatite and bone loss. Hydroxyapatite can be chemically modified through the substitution of ions to alter the biological response. Zinc is an essential trace element that has been found to inhibit osteoclast-like cell formation and decrease bone resorption. It was hoped that by substituting zinc into the hydroxyapatite lattice, the resultant zinc-substituted hydroxyapatite (ZnHA) would inhibit ceramic resorption and the resorption of bone. The aim of this work was to investigate the effect of ZnHA on the number and activity of osteoclasts.

Discs of phase pure hydroxyapatite (PPHA), 0.37wt% ZnHA and 0.58wt% ZnHA were produced, sintered at 1100 degrees Celsius and ground with 1200 grit silicon carbide paper. They were cultured in medium containing macrophage colony stimulating factor and receptor activator of nuclear factor kappa B ligand (RANKL) for 11 and 21 days. A control disc of PPHA cultured in medium containing no RANKL was also used. On the required dates the discs were removed and the cells stained for actin with phalloidin-TRITC and the cell nuclei with 4',6-Diamidino-2-phenylindole dihydrochloride. Cells with 3 or more nuclei were classed as osteoclasts and counted using ImageJ. On day 21 after the cells had been counted, the cells were removed and the discs coated in platinum before viewing with a scanning electron microscope. Resorption areas were then measured using ImageJ.

The addition of zinc was observed to significantly decrease the number of differentiated osteoclasts after 21 days (p<0.005 for 0.58wt% ZnHA compared to PPHA and p<0.01 for 0.37wt% ZnHA compared to PPHA). The area of resorption was also significantly decreased with the addition of zinc (p<0.005 for the comparison of 0.58wt% ZnHA with PPHA)

The work found that zinc substituted hydroxyapatite reduced the number and subsequent activity of osteoclasts.

Long bone fractures are a commonly presented paediatric injury. Whilst the possibility of either accidental or non-accidental aetiology ensures significant forensic relevance, there remain few clinical approaches that assist with this differential diagnosis. The aim of this current study was to generate a reproducible model of spiral fracture in immature bone, allowing investigation of the potential relationship between the rotational speed and the angle of the subsequent spiral fracture.

Seventy bovine metacarpal bones were harvested from 7 day old calves. Sharp dissection ensured removal of the soft tissue, whilst preserving the periosteum. The bones were then distributed evenly before eleven groups, before being aligned along their central axis within a torsional testing machine. Each group of bones were then tested to failure at a different rotational speed (0.5, 1, 15, 20, 30, 40, 45, 60, 75, 80 and 90 degrees s-1). The angle of spiral fracture, relative to the long axis, was then measured, whilst the fracture location, the extent of comminution and periosteal disruption, were all recorded.

Sixty-two out of 70 specimens failed in spiral fracture, with the remaining tests failing at the anchorage site. All bone fractures centred on the narrowest waist diameter, with 5 specimens (all tested at 90 degrees s-1) demonstrating comminution and periosteal disruption. The recorded spiral fracture angles ranged from 30 - 45 degrees, and were dependant on the rotational speed.

This study has established a relationship between the speed of rotation and the angle of spiral fracture in immature bovine bone. It is anticipated that further study will enable investigation of this trend in paediatric bone, ultimately providing an additional diagnostic tool for clinicians trying to verify the proposed mechanism of injury.