Radiostereometric analysis of hemiarthroplasties of the hip – a highly precise method for measurements of cartilage wear

SummaryObjectiveCartilage wear is a feature of osteoarthritis and rheumatoid arthritis. Precise measurements of wear have been difficult. Cartilage wear caused by an artificial articulating joint surface is a well-known feature of hemiarthroplasties. The aim of this study was to demonstrate that radiostereometric analysis (RSA) may be used for three-dimensional measurements of cartilage wear in hemiarthroplasties of the hip.MethodWe performed a phantom model study to assess the feasibility of a subsequent clinical trial. We showed that the motion of the prosthetic head relative to the pelvis was not influenced by the orientation of the prosthetic head. Twenty-two patients were randomised to treatment with a cemented or an uncemented hemiarthroplasty for an acute femoral neck fracture. Migration of the prosthetic head into the acetabulum was measured using RSA.ResultsA mean migration of the prosthetic head into the acetabulum of 0.62 mm was found at 3 months [95% confidence interval (CI): 0.27–0.97] and a further migration of −0.07 mm at 12 months (95% CI: −0.16–0.32). There were no differences between the groups in prosthetic migration or functional outcome. Between three and 12 months, there was no detectable cartilage wear during the first postoperative year.ConclusionWhether the migration during the first 3 months represents a period of bedding in due to a harder opposite surface remains to be shown. RSA may be used for measurement of cartilage wear in hemiarthroplasties of the hip. This study demonstrates a highly precise method for measurements of cartilage wear