Relatively high rates of fracture of the femoral stem of total hip replacements were seen with early designs manufactured with stainless steel. Improvements in metallurgy, alloy chemistry, materials and stem design have led to a reduction in the incidence of this complication and the occurrence of fracture with modern femoral stems is a now a rare event. However, the implantation of modern stems into heavy patients and the use of higher offset stems leads to considerable testing of the mechanical capabilities of some stem designs.

We present ten cases of fracture of modern stainless steel polished tapered stems. The fractures occur either in the neck, or in the distal half of the stem. Our clinical data suggests that heavy patients with small stems and high offsets are at risk of breaking their implants. Varus positioning of the stem in a number of cases further increases the bending moment of the stems, and the sacrifice of cement mantle thickness for implant size within narrow medullary canals may lead to the loss of proximal support. Failure analysis of the retrieved high nitrogen stainless stems also suggests there may be metallurgical factors that contribute to their failure.

On the basis of our findings, careful consideration is required when using high offset stainless steel stems in large patients.

The concept of two-stage revision of infected total hip arthroplasties is well established in the literature. What has been lacking has been a user friendly, simple, safe, cost-effective interim prosthesis which can achieve hip stability, maintain ambulatory status and still deliver antibiotics at high local concentrations. Other commercially available products are expensive, difficult to implant and prone to dislocation. We have developed a modular, antibiotic-laden spacer hemiarthroplasty of the hip which has been fully bench tested. The prosthesis consists of a head/neck module utilising antibiotic impregnated bone cement (PMMA) as the bearing surface and a stainless steel neck. This can be assembled onto a polyacetal (Delrin) stem of varying lengths and diameters. Bone defects are accommodated with hand moulded PMMA at the time of implantation.

We have inserted 47 of these implants in the period 9/97 to 5/2000. 28 of these have been retrieved and submitted for biomechanical analysis at the Royal Perth Hospital Implant Retrieval Laboratory.

This paper presents the concept of the implant, the clinical results, the results of retrieval analysis and elutional studies on antibiotic release from the implant.

We have analysed the retrieved implants and there have been no implant failures. Two implants have been fractured during extraction and one has dislocated secondary to subsidence. Wear analysis has shown polishing of the PMMA in the weightbearing area of the head.

Elution studies are ongoing but suggest that antibiotic release is continuing for up to 8 weeks post implantation providing ambulation is encouraged. Clinical results indicate success rates comparable to other published reports of infected total hip arthroplasties.

This implant in the hands of a variety of orthopaedic surgeons has proven itself simple to use and to maintain ambulatory status to patients whilst maximising antibiotic delivery to the infected hip.