The aim of this study was to fabricate porous implant materials with graded pore structures similar to the bimodal structure of cortical and cancellous bone. Porous hydroxyapatite/tricalcium phosphate (HA/TCP) bioceramics with interconnected porosity and controlled pore sizes required to simulate natural bone tissue morphology were fabricated by a novel technique of vacuum impregnation of reticulated polymeric foams with ceramic slip. Functionally gradient materials (FGMs) with porosity gradients were made by joining different pore per inch (ppi) foams together by either stitching or pressfitting to form templates. Post production, no defects could be seen at the interface between the two different porosity sections. The macropore sizes of the HA/TCP bioceramics were larger than 100 mum which is appropriate for bone ingrowth. A sample with a graded porous structure which is close to the human bone morphology was also developed. The two component structures were conspicuously different but joined together firmly. Four point bend testing of FGM samples showed them to have similar mechanical properties to homogeneous ceramics based on foam templates with uniform pore sizes, with no evidence of interfacial weakness. Many potential biomedical applications could be developed utilising graded porous structures. The ease of processing will make it possible to fabricate a range of complex shapes for different applications.

In comparison with monofilament wire, multifilament cable was found to be a more suitable material for fixation of the greater trochanter. It is versatile, easy to work with and has superior mechanical properties. The "trochanter cable-grip system" was developed to exploit the use of multifilament cable as a means of reattaching the greater trochanter and experimental studies have yielded excellent results. This system was subjected to clinical trials for over four years in 321 hips and, at its present state of development, the incidence of detachment has been reduced to 1.5 per cent and that of cable breakage to 3.1 per cent.

The incidence of revision total hip arthroplasty is increasing dramatically and the associated demand for allograft bone is likely to exceed the available supply. In addition, allograft presents potential problems with regard to infection, antigenicity, availability, reproducibility and cost. It is therefore desirable to develop an alternative to allograft. This study investigated BoneSave, a porous tricalcium phosphate-hydroxyapatite ceramic for use in impaction grafting of the femur at revision total hip arthroplasty. The findings of an in vitro mechanical study comparing the initial stability of pure allograft, a volume mixture of 50 per cent allograft and 50 per cent BoneSave, and a volume mixture of 10 per cent allograft and 90 per cent BoneSave are reported. The BoneSave-allograft mixtures exhibit both much greater mechanical stability and reproducibility than the pure allograft (p < 0.05) at all tested loads (200-800 N). At high peak loads the high volume (90%, v/v) BoneSave mix also provided higher mechanical stability than the medium volume (50 per cent BoneSave-50 per cent allograft) mix (p < 0.05). These results demonstrate thatfrom a mechanical standpoint the tested ceramic provides adequate initial stability to be used as a bone graft extender with allograft in impaction grafting of the femur.

No abstract

We report the results of a 4-to 17-year clinical and radiological follow-up of 264 Charnley first-generation stems in comparison with those of 402 second-and subsequent-generation stems. The incidence offracture was 4.1% in first-generation stems and 0.5% in second-and subsequent-generation stems. The incidence of stem loosening requiring or likely to require revision was 3.1% in first-generation and 11.4% in second-generation stems. We believe that the increased loosening rate in second-and subsequent-generation stems is due to their larger crosssectional area, which produces an increase in flexural stiffness.