Summary

Our study shows that a tendon rupture can be successfully augmented with Demineralised Cortical Bone (DCB) giving initial appropriate mechanical strength suitable for in vivo use providing the biological reactions to the graft are favourable.

Summary

Osseointegrated Amputation Prostheses can be functionalised by both biological augmentation and structural augmentation. These augmentation techniques may aid the formation of a stable skin-implant interface.

Introduction

Bone-anchored devices have been used as skin-crossing conduits to record neuromuscular signals in sedated animals. Long-term recordings from cognisant subjects must be assessed. Hypothesis A bone-anchored device is suitable as a conduit for epimysial EMG (Electromyogram) recordings and is reliable in the long-term.

Material loss at the head-stem taper junction may contribute to the high early failure rates of stemmed large head metal-on-metal (LH-MOM) hip replacements. We sought to quantify both wear and corrosion and by doing so determine the main mechanism of material loss at the taper. This was a retrospective study of 78 patients having undergone revision of a LH-MOM hip replacement. All relevant clinical data was recorded. Corrosion was assessed using light microscopy and scanning electron microscopy, and graded according to a well-published classification system. We then measured the volumetric wear of the bearing and taper surfaces. Evidence of at least mild taper corrosion was seen in 90% cases, with 46% severely corroded. SEM confirmed the presence of corrosion debris, pits and fretting damage. However, volumetric wear of the taper surfaces was significantly lower than that of the bearing surfaces (p = 0.015). Our study supports corrosion as the predominant mechanism of material loss at the taper junction of LH-MOM hip replacements. Although the volume of material loss is low, the ionic products may be more biologically active compared to the particulate debris arising from the bearing surfaces.

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

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

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

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

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

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

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

Introduction

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

Introduction

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

Introduction

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

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

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

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

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

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

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

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

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

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

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

An experimental sheep model was used for impaction allografting of 12 hemiarthroplasty femoral components placed into two equal-sized groups. In group 1, a 50:50 mixture of ApaPore hydroxyapatite bone-graft substitute and allograft was used. In group 2, ApaPore and allograft were mixed in a 90:10 ratio. Both groups were killed at six months. Ground reaction force results demonstrated no significant differences (p > 0.05) between the two groups at 8, 16 and 24 weeks post-operatively, and all animals remained active. The mean bone turnover rates were significantly greater in group 1, at 0.00206 mm/day, compared to group 2 at 0.0013 mm/day (p < 0.05). The results for the area of new bone formation demonstrated no significant differences (p > 0.05) between the two groups. No significant differences were found between the two groups in thickness of the cement mantle (p > 0.05) and percentage ApaPore-bone contact (p > 0.05).

The results of this animal study demonstrated that a mixture of ApaPore allograft in a 90:10 ratio was comparable to using a 50:50 mixture.

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

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

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

Impacted morsellised allografts have been used successfully to address the problem of poor bone stock in revision surgery. However, there are concerns about the transmission of pathogens, the high cost and the shortage of supply of donor bone. Bone-graft extenders, such as tricalcium phosphate (TCP) and hydroxyapatite (HA), have been developed to minimise the use of donor bone. In a human cadaver model we have evaluated the surgical and mechanical feasibility of a TCP/HA bone-graft extender during impaction grafting revision surgery.

A TCP/HA allograft mix increased the risk of producing a fissure in the femur during the impaction procedure, but provided a higher initial mechanical stability when compared with bone graft alone. The implications of the use of this type of graft extender in impaction grafting revision surgery are discussed.