Autologous stem cell implantation with core decompression for avascular necrosis of the femoral head using a new device.

INTRODUCTION: Autologous stem cell progenitor implantation into necrotic lesions of the femoral head has previously been described as a potential treatment for avascular necrosis (AVN), on the basis that there is a reduced number of functioning stem cells in the marrow within the necrotic segment. We present a case series of patients with AVN that underwent core decompression with autologous stem cell implantation using a new device. METHODS: The records and imaging of patients with AVN of the femoral head treated by a single surgeon were retrospectively reviewed. All patients were treated with core decompression and stem cell progenitor implantation, using the PerFuse system. Preoperatively, demographic information, AVN staging (as per Ficat and Arlet classification) and visual analogue pain scores (VAS) of the hips were recorded. These results were compared with postoperative VAS and imaging, with further review on the progression of AVN. RESULTS: We treated 14 hips in 13 patients with an average follow up of 12 months. Patients with Ficat I-II were selected for the procedure. The average preoperative VAS was 3.9. Postoperatively, this dropped to 2.6, with over half of patients reporting at least a two-point decrease in pain. Eight of the 14 treated hips showed no radiological progression of the disease, while six showed femoral head collapse requiring total hip arthroplasty (THA) at an average of ten months after treatment. CONCLUSION: Our early findings indicate that hip decompression with stem cell progenitor implantation for AVN of the femoral head provides symptomatic relief and may be beneficial in arresting progression of disease using this simple new device.

The inferomedial femoral neck is compromised by age but not disease: Fracture toughness and the multifactorial mechanisms comprising reference point microindentation.

The influence of ageing on the fracture mechanics of cortical bone tissue is well documented, though little is known about if and how related material properties are further affected in two of the most prominent musculoskeletal diseases, osteoporosis and osteoarthritis (OA). The femoral neck, in close proximity to the most pertinent osteoporotic fracture site and near the hip joint affected by osteoarthritis, is a site of particular interest for investigation. We have recently shown that Reference Point micro-Indentation (RPI) detects differences between cortical bone from the femoral neck of healthy, osteoporotic fractured and osteoarthritic hip replacement patients. RPI is a new technique with potential for in vivo bone quality assessment. However, interpretation of RPI results is limited because the specific changes in bone properties with pathology are not well understood and, further, because it is not conclusive what properties are being assessed by RPI. Here, we investigate whether the differences previously detected between healthy and diseased cortical bone from the femoral neck might reflect changes in fracture toughness. Together with this, we investigate which additional properties are reflected in RPI measures. RPI (using the Biodent device) and fracture toughness tests were conducted on samples from the inferomedial neck of bone resected from donors with: OA (41 samples from 15 donors), osteoporosis (48 samples from 14 donors) and non age-matched cadaveric controls (37 samples from 10 donoros) with no history of bone disease. Further, a subset of indented samples were imaged using micro-computed tomography (3 osteoporotic and 4 control samples each from different donors) as well as fluorescence microscopy in combination with serial sectioning after basic fuchsin staining (7 osteoporotic and 5 control samples from 5 osteoporotic and 5 control donors). In this study, the bulk indentation and fracture resistance properties of the inferomedial femoral neck in osteoporotic fracture, severe OA and control bone were comparable (p > 0.05 for fracture properties and <10% difference for indentation) but fracture toughness reduced with advancing age (7.0% per decade, r = -0.36, p = 0.029). Further, RPI properties (in particular, the indentation distance increase, IDI) showed partial correlation with fracture toughness (r = -0.40, p = 0.023) or derived elastic modulus (r = -0.40, p = 0.023). Multimodal indent imaging revealed evidence of toughening mechanisms (i.e. crack deflection, bridging and microcracking), elastoplastic response (in terms of the non-conical imprint shape and presence of pile-up) and correlation of RPI with damage extent (up to r = 0.79, p = 0.034) and indent size (up to r = 0.82, p < 0.001). Therefore, crack resistance, deformation resistance and, additionally, micro-structure (porosity: r = 0.93, p = 0.002 as well as pore proximity: r = -0.55, p = 0.027 for correlation with IDI) are all contributory to RPI. Consequently, it becomes clear that RPI measures represent a multitude of properties, various aspects of bone quality, but are not necessarily strongly correlated to a single mechanical property. In addition, osteoporosis or osteoarthritis do not seem to further influence fracture toughness of the inferomedial femoral neck beyond natural ageing. Since bone is highly heterogeneous, whether this finding can be extended to the whole femoral neck or whether it also holds true for other femoral neck quadrants or other material properties remains to be shown.

Long term results of impaction Bone grafting using a synthetic graft (Apapore) in revision hip surgery.

INTRODUCTION: Impaction Bone grafting (IBG) in Revision THR is challenging and places demands on allograft stores. Identifying a potential synthetic replacement that works in the longer term was the aim of this study. METHODS: We retrospectively reviewed 21 sequential patients who had undergone revision THR using IBG. They were randomised to receive either combined allograft and synthetic graft or Allograft alone. Among the surviving 15 patients, there were total of 25 procedures were carried out. 15 hips underwent IBG in the acetabulum and 10 hips underwent femoral IBG. Eight patients received a 50/50 mixture of allograft and synthetic Bone graft (Apapore) and seven allograft alone. Bone loss was classified using Paprosky classification. The average follow up was 10 years. RESULTS: Of the 21 patients, 6 had died of unrelated causes and were excluded. There were 3 re-operations but no revision of the original components. There was no significant implant migration detected. 3 acetabular components had confluent lucent lines in zone-1 which remained stable on long term follow up. 2 patients sustained femoral peri-prosthetic fractures after a simple fall and one patient who developed deep infection treated by DAIR. The modified oxford hip score post-operatively was 18 in allograft group and 22 in Apapore group. CONCLUSION: Long-term results indicate that the combined use of synthetic graft in Impaction Bone grafting is an effective substitute.

Variability in reference point microindentation and recommendations for testing cortical bone: location, thickness and orientation heterogeneity.

Reference Point Indentation (RPI) has been proposed as a new clinical tool to aid the diagnosis of Osteoporosis. This study has examined the performance of the tool within entire femurs to improve the understanding of the mechanical properties of bone and also to guide future RPI testing to optimize repeatability of results obtained using the technique. Human, bovine, porcine and rat femurs were indented along three longitudinal axes: anterior and posterior: medial and lateral as well as around the circumference of the femoral head and neck. Cortical and subchondral bone thickness was measured using CT and radiography. The study shows that in some samples, bone is too thin to support the high loads applied with the technique and in these cases, RPI values are highly influenced by thickness. The technique will be useful in the mid-shaft region where cortical thickness is greatest, providing previously established guidelines are followed to optimize measurement repeatability, including performing multiple measurements per sample and investigating multiple samples. The study has also provided evidence that RPI values vary significantly with test site, hence mechanical properties should not be inferred from RPI findings alone away from the test site, even within the same bone. In conclusion, RPI appears to be a useful tool for scientific investigation; however further work is required to examine the feasibility of using RPI for assessing differences between healthy and diseased bone in a clinical setting.

Variability in reference point microindentation and recommendations for testing cortical bone: maximum load, sample orientation, mode of use, sample preparation and measurement spacing.

Reference Point Indentation (RPI) is a novel microindentation tool that has emerging clinical potential for the assessment of fracture risk as well as use as a laboratory tool for straight-forward mechanical characterisation of bone. Despite increasing use of the tool, little research is available to advise the set-up of testing protocols or optimisation of testing parameters. Here we consider five such parameters: maximum load, sample orientation, mode of use, sample preparation and measurement spacing, to investigate how they affect the Indentation Distance Increase (IDI), the most published measurement parameter associated with the RPI device. The RPI tool was applied to bovine bone; indenting in the proximal midshaft of five femora and human bone; indenting five femoral heads and five femoral neck samples. Based on the findings of these studies we recommend the following as the best practice. (1) Repeat measurements should be utilised to reduce the coefficient of variation (e.g. 8-15 repeats to achieve a 5-10% error, however the 3-5 measurements used here gives a 15-20% error). (2) IDI is dependent on maximum load (r=0.45 on the periosteal surface and r=0.94 on the machined surface, p<0.05), mode of use (i.e. comparing the device held freehand compared to fixed in its stand, p=0.04) and surface preparation (p=0.004) so these should be kept consistent throughout testing. Though sample orientation appears to have minimal influence on IDI (p>0.05), care should also be taken in combining measurements from different orientations. (3) The coefficient of variation is higher (p=0.04) when holding the device freehand, so it should ideally be kept supported in its stand. (4) Removing the periosteum (p=0.04) and machining the surface of the bone (p=0.08) reduces the coefficient of variation, so should be performed where practical. (5) There is a hyperbolic relationship between thickness and IDI (p<0.001) with a sample thickness 10 fold greater than the maximum indentation depth recommended, to ensure a representative measurement. (6) Measurement spacing does not appear to influence the IDI (p>0.05), so it can be as low as 500 µm. By following these recommendations, RPI users can minimise the potential confounding effects associated with the variables investigated here and reduce the coefficient of variation, hence achieving more consistent testing. This optimisation of the technique enhances both the clinical and laboratory potential of the tool.

A comparison of polymer and polymer-hydroxyapatite composite tissue engineered scaffolds for use in bone regeneration. An in vitro and in vivo study.

Previous in vitro work demonstrated porous PLA and PLGA both had the mechanical strength and sustained the excellent skeletal stem cell (SSC) growth required of an osteogenic bonegraft substitute, for use in impaction bone grafting. The purpose of this investigation was to assess the effects of the addition of hydroxyapatite (HA) to the scaffolds before clinical translation. PLA, PLA+10% HA, PLGA, and PLGA+10% HA were milled and impacted into discs before undergoing a standardized shear test. Cellular compatibility analysis followed 14 days incubation with human skeletal stems cells (SSC). The best two performing polymers were taken forward for in vivo analysis. SSC seeded polymer discs were implanted subcutaneously in mice. All polymers had superior mechanical shear strength compared with allograft (p < 0.01). Excellent SSC survival was demonstrated on all polymers, but the PLA polymers showed enhanced osteoblastic activity (ALP assay p < 0.01) and collagen-1 formation. In vivo analysis was performed on PLA and PLA+10% HA. MicroCT analysis revealed increased bone formation on the PLA HA (p < 0.01), and excellent neo-vessel formation in both samples. Histology confirmed evidence of de novo bone formation. PLA HA showed both enhanced osteoinductive and osteogenic capacity. This polymer composite has been selected for scaled-up experimentation before clinical translation.

From bench to clinic and back: skeletal stem cells and impaction bone grafting for regeneration of bone defects.

Tissue engineering offers enormous potential for bone regeneration. Despite extensive in vitro and in vivo work, few strategies translate into clinical practice. This paper describes the combination of skeletal stem cells (SSCs) and impaction bone grafting (IBG) for the treatment of patients with bone defects associated with avascular necrosis of the femoral head. SSCs and milled allograft were impacted into necrotic bone in the femoral heads of four patients. Three patients remained asymptomatic at 22-44 month follow-up, but one patient has required total hip replacement (both hips). This has allowed retrieval of the femoral heads, which were analysed structurally and functionally by µCT, histology and mechanical testing. A central channel of impacted bone was found in the femoral heads, which displayed a mature trabecular micro-architecture. The impacted bone was denser than the surrounding trabecular bone, as strong in compression and with histological micro-architecture comparable to that of trabecular bone. Analysis of the retrieved femoral head samples has demonstrated that this tissue-engineering strategy regenerates bone that is both structurally and functionally analogous to normal trabecular bone. SSCs, together with IBG, have proved an effective treatment for avascular necrosis of the femoral head and offer significant potential for the broader spectrum of bone defects.

Tantalum trabecular metal - addition of human skeletal cells to enhance bone implant interface strength and clinical application.

The osteo-regenerative properties of allograft have recently been enhanced by addition of autogenous human bone marrow stromal cells (HBMSCs). Limitations in the use of allograft have prompted the investigation of tantalum trabecular metal (TTM) as a potential alternative. TTM is already in widespread orthopaedic use, although in applications where there is poor initial stability, or when TTM is used in conjunction with bone grafting, initial implant loading may need to be limited. The aim of this study was to evaluate the osteo-regenerative potential of TTM with HBMSCs, in direct comparison to human allograft and autograft. HBMSCs were cultured on blocks of TTM, allograft or autograft in basal and osteogenic media. Molecular profiling, confocal and scanning electron microscopy (SEM) and biochemical assays were used to characterize cell adherence, proliferation and phenotype. Mechanical testing was used to define the tensile characteristics of the constructs. HBMSCs displayed adherence and proliferation throughout TTM, evidenced by immunocytochemistry and SEM, with significant cellular ingrowth and matrix production through TTM. In contrast to cells cultured with allograft, cell proliferation assays showed significantly higher activity with TTM (p < 0.001), although molecular profiling confirmed no significant difference in expression of osteogenic genes. In contrast to acellular constructs, mechanical testing of cell-TTM constructs showed enhanced tensile characteristics, which compared favourably to cell-allograft constructs. These studies demonstrated the ability of TTM to support HBMSC growth and osteogenic differentiation comparable to allograft. Thus, TTM represents an alternative to allograft for osteo-regenerative strategies, extending its clinical applications as a substitute for allograft.

A tissue engineering strategy for the treatment of avascular necrosis of the femoral head.

BACKGROUND & PURPOSE: Skeletal stem cells (SSCs) and impaction bone grafting (IBG) can be combined to produce a mechanically stable living bone composite. This novel strategy has been translated to the treatment of avascular necrosis of the femoral head. Surgical technique, clinical follow-up and retrieval analysis data of this translational case series is presented. METHODS: SSCs and milled allograft were impacted into necrotic bone in five femoral heads of four patients. Cell viability was confirmed by parallel in vitro culture of the cell-graft constructs. Patient follow-up was by serial clinical and radiological examination. Tissue engineered bone was retrieved from two retrieved femoral heads and was analysed by histology, microcomputed tomography (µCT) and mechanical testing. RESULTS: Three patients remain asymptomatic at 22- to 44-month follow-up. One patient (both hips) required total hip replacement due to widespread residual necrosis. Retrieved tissue engineered bone demonstrated a mature trabecular micro-architecture histologically and on µCT. Bone density and axial compression strength were comparable to trabecular bone. CONCLUSIONS: Clinical follow-up shows this to be an effective new treatment for focal early stage avascular necrosis of the femoral head. Unique retrieval analysis of clinically translated tissue engineered bone has demonstrated regeneration of tissue that is both structurally and functionally analogous to normal trabecular bone.

Translational hurdles for tissue engineering: an in vitro analysis of commonly used local anaesthetics on skeletal stem cell survival.

When transferring tissue regenerative strategies involving skeletal stem cells to human application, consideration needs to be given to factors that may affect the function of the cells that are transferred. Local anaesthetics are frequently used during surgical procedures, either administered directly into the operative site or infiltrated subcutaneously around the wound. The aim of this study was to investigate the effects of commonly used local anaesthetics on the morphology, function and survival of human adult skeletal stem cells. Cells from three patients who were undergoing elective hip replacement were harvested and incubated for two hours with 1% lidocaine, 0.5% levobupivacaine or 0.5% bupivacaine hydrochloride solutions. Viability was quantified using WST-1 and DNA assays. Viability and morphology were further characterised using CellTracker Green/Ethidium Homodimer-1 immunocytochemistry and function was assessed by an alkaline phosphatase assay. An additional group was cultured for a further seven days to allow potential recovery of the cells after removal of the local anaesthetic. A statistically significant and dose dependent reduction in cell viability and number was observed in the cell cultures exposed to all three local anaesthetics at concentrations of 25% and 50%, and this was maintained even following culture for a further seven days. This study indicates that certain local anaesthetic agents in widespread clinical use are deleterious to skeletal progenitor cells when studied in vitro; this might have relevance in clinical applications.

Supercritical CO2 fluid-foaming of polymers to increase porosity: a method to improve the mechanical and biocompatibility characteristics for use as a potential alternative to allografts in impaction bone grafting?

Disease transmission, availability and cost of allografts have resulted in significant efforts to find an alternative for use in impaction bone grafting (IBG). Recent studies identified two polymers with both structural strength and biocompatibility characteristics as potential replacements. The aim of this study was to assess whether increasing the polymer porosity further enhanced the mechanical and cellular compatibility characteristics for use as an osteogenic biomaterial alternative to allografts in IBG. Solid and porous poly(DL-lactide) (P(DL)LA) and poly(DL-lactide-co-glycolide) (P(DL)LGA) scaffolds were produced via melt processing and supercritical CO(2) foaming, and the differences characterized using scanning electron microscopy (SEM). Mechanical testing included milling and impaction, with comparisons made using a shear testing rig as well as a novel agitation test for 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 skeletal stem cells. SEM showed excellent porosity throughout both of the supercritical-foam-produced polymer scaffolds, with pores between 50 and 200 µm. Shear testing showed that the porous polymers exceeded the shear strength of allograft controls (P<0.001). Agitation testing showed greater cohesion between the particles of the porous polymers (P<0.05). Cellular studies showed increased cell number, viability, and osteogenic differentiation on the porous polymers compared to solid block polymers (P<0.05). The use of supercritical CO(2) to generate porous polymeric biodegradable scaffolds significantly improves the cellular compatibility and cohesion observed compared to non-porous counterparts, without substantial loss of mechanical shear strength. These improved characteristics are critical for clinical translation as a potential osteogenic composite for use in IBG.

The effect of hip and knee arthroplasty on oral anti-inflammatory use and the relationship to body mass index: results from the UK general practice research database.

OBJECTIVE: To determine the use of oral anti-inflammatory drugs in the year before and the 2 years after primary total hip (THR) or knee (TKR) replacement, and whether this varies according to Body mass Index (BMI). DESIGN: 28,068 THR's and 24,364 TKR's, with five matched controls per case were identified from the General Practitioner Research Database. Anti-inflammatory usage was categorized into "zero coverage" - no prescribed anti-inflammatory medication and ">80% coverage" - prescribed anti-inflammatory medication for greater than 80% of the days in the year. Secondary subset analysis was performed according to BMI. RESULTS: 1 year post-surgery the proportion of cases on >80% coverage reduced from 21% (95%confidence interval (CI): 20-22%) to 8% (95%CI: 7-10%) for THR and 21% (95%CI: 20-22%) to 13% (95%CI: 11-14%) for TKR, with no ongoing reduction at 2 years. Zero coverage increased at one and both time points. The proportion of THR's on >80% coverage increased with BMI pre-op. The magnitude in reduction post-op was similar across all BMI groups. The proportion of TKR's on >80% coverage pre-op was greatest in extreme BMI categories. The magnitude in reduction post-op was similar across all BMI groups. CONCLUSION: THR/TKR's reduce the need for anti-inflammatory medication with most benefit observed in the first post-operative year. Increasing BMI affects anti-inflammatory use both in the general population and those undergoing THR/TKR surgery but without strong evidence of a detrimental effect on the benefits of pain relief.

Skeletal stem cells and bone regeneration: translational strategies from bench to clinic.

Clinical imperatives for new bone to replace or restore the function of traumatized or bone lost as a consequence of age or disease has led to the need for therapies or procedures to generate bone for skeletal applications. Tissue regeneration promises to deliver specifiable replacement tissues and the prospect of efficacious alternative therapies for orthopaedic applications such as non-union fractures, healing of critical sized segmental defects and regeneration of articular cartilage in degenerative joint diseases. In this paper we review the current understanding of the continuum of cell development from skeletal stem cells, osteoprogenitors through to mature osteoblasts and the role of the matrix microenvironment, vasculature and factors that control their fate and plasticity in skeletal regeneration. Critically, this review addresses in vitro and in vivo models to investigate laboratory and clinical based strategies for the development of new technologies for skeletal repair and the key translational points to clinical success. The application of developmental paradigms of musculoskeletal tissue formation specifically, understanding developmental biology of bone formation particularly in the adult context of injury and disease will, we propose, offer new insights into skeletal cell biology and tissue regeneration allowing for the critical integration of stem cell science, tissue engineering and clinical applications. Such interdisciplinary, iterative approaches will be critical in taking patient aspirations to clinical reality.

Removal of the well-fixed hip resurfacing acetabular component: a simple, bone preserving technique.

Removal of the acetabular component of a hip resurfacing prosthesis is occasionally necessary for infection, malposition, metal sensitivity, wear, or as a necessary part of a femoral revision. Extraction of a well-fixed acetabular component can be technically demanding as it is often extremely well integrated into host bone and can result in catastrophic bone loss or fracture. We present an undescribed, simple technique that enables use of the Explant system (Zimmer, Warsaw, Ind) to remove the component with minimal bone loss and reduce fracture risk. Bone stock is therefore preserved for subsequent cup reimplantation.

Development of in vivo muCT evaluation of neovascularisation in tissue engineered bone constructs.

Due to an increasing aging population the need for innovative approaches to aid skeletal repair and reconstruction is a significant socio-economic increasing problem. The emerging discipline of tissue engineering has sort to augment the growth and repair of bone loss particularly in areas of trauma, degeneration and revision surgery. However, the initiation and development of a fully functional vascular network are critical for bioengineered bone to repair large osseous defects, whether the material is osteosynthetic (poly (d,l)-lactic acid, PLA) or natural bone allograft. Quantification and three-dimensional visualization of new vessel networks remain a problem in bone tissue engineering constructs. A novel technique utilising a radio-opaque dye and micro-computed tomography (muCT) has been developed and applied to study angiogenesis in an impaction bone graft model. Tissue-engineered constructs combining human bone marrow stromal cells (HBMSC) with natural allograft and synthetic grafts (PLA) were impacted and implanted into the subcutis of MF-1 nu/nu mice for a period of 28 days. Microfil consisting of radio-opaque polymer was perfused through the mice and scanned using a Bench Top CT system for micro-computed tomography. Analysis of three-dimensional muCT reconstructions demonstrated an increase in vessel volume and vessel number in the impacted scaffolds/HBMC compared to scaffolds alone. Vessel volume: allograft/HBMSC=0.57 mm(3)+/-0.19; allograft=0.04 mm(3)+/-0.04; PLA/HBMSC=1.19 mm(3)+/-0.31; and PLA=0.12 mm(3)+/-0.01. Penetrating vessel number: allograft/HBMSC=22.33+/-3.21; allograft=3.67+/-1.153; PLA/HBMSC=32.67+/-8.33; and PLA=7.67+/-3.06. Type 1 collagen and von Willebrand factor immunohistochemistry in scaffold/HBMSC constructs indicated the osteogenic cell phenotype, and new blood vessel formation respectively. Contrast-enhanced 3D reconstructions facilitated the visualization and quantification of neovascularisation. This novel technique has been used to demonstrate neovascularisation in impacted tissue engineered constructs providing a facile approach with wide experimental application.

Vibration-assisted bone-graft compaction in impaction bone grafting of the femur.

The complications of impaction bone grafting in revision hip replacement includes fracture of the femur and subsidence of the prosthesis. In this in vitro study we aimed to investigate whether the use of vibration, combined with a perforated tamp during the compaction of morsellised allograft would reduce peak loads and hoop strains in the femur as a surrogate marker of the risk of fracture and whether it would also improve graft compaction and prosthetic stability. We found that the peak loads and hoop strains transmitted to the femoral cortex during graft compaction and subsidence of the stem in subsequent mechanical testing were reduced. This innovative technique has the potential to reduce the risk of intra-operative fracture and to improve graft compaction and therefore prosthetic stability.

A new method to determine graft angles after knee ligament reconstruction.

In posterior cruciate ligament (PCL) reconstruction, the acute angle of the graft at the tibial tunnel ('the killer curve') has been implicated as a cause of graft failure. Similar acute angles also occur at the entrance to the femoral tunnel. We describe a method to determine the true graft angle, based on measurements taken from two orthogonal radiographs in a cadaveric model, analysed using three-dimensional geometry. The true angles for the tibial and femoral tunnels are presented for a variety of tunnel positions. The effect on these angles of knee flexion and extension is analysed. Resultant graft-tunnel forces at a constant ligament tension are described. Based on these results, drilling the femoral tunnel from outside-in and lateral placement of the tibial tunnel are theoretically advantageous.

Acute compartment syndrome: diagnosis and immediate care.

Acute compartment syndrome is an uncommon but potentially limb-threatening condition whose early recognition and treatment can prevent or reduce serious complications. Identifying at-risk patients and appropriate investigation is the key.

Impaction grafting with morsellised allograft and tricalcium phosphate-hydroxyapatite: incorporation within ovine metaphyseal bone defects.

An ovine model was used to investigate the in vivo properties of impacted tricalcium phosphate-hydroxyapatite (TCP-HA) aggregates, varying in chemical composition (ratio of TCP to HA) and particle size distribution (8 versus 3 particle size ranges). All pellets were impacted to a standard compactive effort. Eight sheep underwent implantation of pellets in 4 metaphyseal defects in both rear limbs. Treatment groups consisted of: (1) allograft (clinical control). (2) 50/50 allograft/80% HA/20% TCP in 8 particle size ranges, (3) 50/50 allograft/80% TCP/20% HA in 8 sizes and (4) 50/50 allograft/80% HA/20% TCP in only 3 sizes of particles. Healing of defects was evaluated at 14 weeks with computed tomography, histology and histomorphometry. The computer tomography (CT) density measured in all defects containing synthetic agents was higher than in defects filled with allograft alone (p<0.01). Defects containing 8 sizes of 80% HA/ 20% TCP granules (group 2) achieved lower histological scores and contained less bone than the clinical control (p<0.05), whereas groups 3 and 4 did not differ from the control. Although all synthetic agents were osteoconductive, our results suggest that increasing the ratio of TCP over HA and limiting the number of particle size ranges to 3 instead of 8 improve the performance of impacted aggregates as graft expanders. Evaluation under loading conditions of morsellised allograft expanded with 80% TCP/20% HA (BoneSave) in 3 particle size ranges is warranted.

Cup removal in revision hip arthroplasty.

When revision hip surgery is undertaken to remove a cemented cup from the pelvis the preservation of bone stock and structural integrity of the acetabulum is a major concern. We describe a safe technique for cup removal, which helps avoid a rim fracture occurring during this procedure. This should ensure the defect remains a cavitatory defect and does not become a segmental one with a more uncertain prognosis.