Abstract
Total hip arthroplasty (THA) using modular components offers many advantages such as a reduction in the implant inventory required and increased intra-operative flexibility with component sizing and selection. However, it also comes at the price of the additional complication of component dissociation, in particular at the non-fixed interface between the polyethylene cup and the acetabular metal backing.
A review of 110 patients requiring revision THA from June 1993 to December 2000 performed by the senior authors revealed seven patients presenting with the triad of signs suggestive of this complication – a previously successful, painless THA that had become acutely painful and with radiographic evidence of femoral head asymmetry in the acetabular cup. Each of these patients had Harris - Galante II porous acetabular cups. At the time of the revision, these patients were found to have dissociated polyethylene cup liners and several with broken locking mechanisms warranting replacement of the acetabular cups, the liners and the worn femoral heads.
This is an uncommon complication of THA, with characteristic presenting symptoms and signs. The importance of comparison of previous radiographs with those at presentation and the postulated mechanisms for dissociation is stressed. Certain precautions are imperative when using modular implants and the pitfalls of the Harris - Galante II porous acetabular component locking mechanism should be acknowledged.
The abstracts were prepared by Professor A. J. Thurston. Correspondence should be addressed to him at the Department of Surgery, Wellington School of Medicine, PO Box 7343, Wellington South, New Zealand
