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A new method of investigating the mechanisms of strain-induced bone remodeling has been developed. Bone cells were subjected to cyclical strains in vitro by computer-controlled stretching of the plastic substrate on which they were cultured, enabling both physiological and pathological strains to be investigated. Physiological strains have not previously been investigated in vitro. The prostaglandin E2 (PGE2) released by the cells was found to depend on the strain magnitude. It was independent of cycle time, and 5 hours after straining had ceased, it had returned to control levels. These results are similar to the in vivo findings that bone remodeling is dependent on strain magnitude and not strain frequency, indicating that PGE2 may play an important role in strain-induced bone remodeling. The relationship between PGE2 release and strain magnitude was biphasic, with particularly high levels being released at strains that would be associated with either abnormally strenuous activity or microstructural bone damage. It is therefore possible that PGE2 stimulates the osteogenesis caused by increased functional demands, and initiates the remodeling caused by bone damage. This new method of investigating strain-induced remodeling is useful, as any cell type, any mediator, and any strain pattern or parameter can be individually studied.

The upper portions of three cadaveric femora were examined by high-resolution computed tomography. Analysis of the resulting images provided both quantitative and spatial distributions of bone density within the femoral head and neck. The information obtained provides new insights into aspects of proximal femoral architecture for both normal and osteoporotic bone. The study also points the way towards a clinical technique for measuring the material properties of proximal femoral bone.

Carbon fibre reinforced high density polyethylene (CFRHDP) Meuller acetabular cups are available for total hip replacement. Despite the improved mechanical properties of CFRHDP over high density polyethylene (HDP) the wear characteristics of CFRHDP are a contentious issue. The biocompatibility of CFRHDP wear debris was investigated by intra-articular injection into mice and compared with that induced by HDP and carbon fibres. The response to CFRHDP was identical to that seen with HDP: the carbon fibre component did not appear to modify the response. From the biological point of view, therefore, the wear properties of CFRHDP must be better than those of HDP to offer a significant advantage.

A survey of revision hip arthroplasties was performed, using a retrospective review of the patients' case notes and radiographs, and an assessment of the patients, at least 1 year after the revision. The patients were divided into three categories: a) First revision hip arthroplasty (41 patients); b) Second revision hip arthroplasty (8 patients); c) Revision of femoral hemi-arthroplasty (14 patients). The reasons for revision, the type of revision and the final outcome have been identified in each group. This is the first study which allows direct comparison of the final outcome, as assessed by accurate objective criteria, between patients having revision hip arthroplasty for different reasons. Radiographs of the hip arthroplasty after the original operation and after revision have been analysed. The final outcome of first revision hip arthroplasty and revision of hemi-arthroplasty to total hip replacement was generally good. The outcome of second revision hip arthroplasty was generally poor.

The purpose of this research was to establish the possible role of starch glove powder in complications following orthopaedic surgery using in vivo and in vitro techniques. Exposure of primary mouse peritoneal macrophages to starch glove powder caused 10% release of prostaglandin E2 (0.1 mg/ml, 16 h) but no increased release of lactate dehydrogenase, demonstrating that cell integrity had not been compromised. Long-term tissue reaction to starch glove powder was investigated in vivo by injection into mouse knee joints. Over a period of 52 weeks no inflammatory response was elicited, no starch was observed in the regional lymph nodes and none was found in joints after the 8th week. Starch glove powder appeared to be innocuous in the joint and although prostaglandin E2 release was stimulated in vitro, this had no apparent effect on joints in vivo.