Abstract
The results of wear testing using hip simulators have suggested that highly cross-linked polyethylene (PE) is more resistant to abrasive wear than “conventional” polyethylene that has been sterilized by 2.5 – 4 Mrad of radiation. Optimum methods for testing other mechanical properties of PE are controversial, but some studies have suggested that highly cross-linked polyethylenes have reduced impact strength when compared to either “conventional” PE or PE that has never been cross-linked. T he principle mechanism of loosening of most total hip prostheses is bone loss induced by debris particles that have been generated by abrasive wear, hence the rationale for using highly cross-linked PE for total hip arthroplasty. The principle mechanism of failure of bipolar hips, however, is less clear. If abrasive wear is important in bipolars, then the use of highly cross-linked PE is reasonable, but if impingement is an important complication of bipolar arthroplasty, then the use of highly cross-linked polyethylene might We revewied the implant registry of the Cleveland Clinic and identified 62 retrieved bipolar implants. The peripheral rim of each was evaluated, and a previously published scoring system used to grade the extent of rim damage due to impingement. A subset of implants were disassembled, and the shadowgraph method was used to measure the extent and rate of polyethylene abrasive wear. Adequate clinical information and radiographs were available in relatively few cases, but when available, the results of implant evaluation were correlated with clinical and radiographic findings.
The results suggest that both abrasive wear and rim damage due to impingement are common findings in retrieved bipolar devices. Further studies with better clinical and radiographic correlation are needed to clarify the most significant factors with respect to osteolysis and implant failure, but our results suggest caution in implementing highly cross-linked polyethylene for bipolar devices.
The abstracts were prepared by Nico Verdonschot. Correspondence should be addressed to him at Orthopaedic Research Laboratory, University Medical Centre, PO Box 9101, 6500 HB Nijmegen, The Netherlands.
