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

Objective: Cartilage 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. Method: We 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. Results: A mean migration of the prosthetic head into the acetabulum of 0.62 mm was found at 3 months [95% confidence interval (Cl): -0.27-0.971 and a further migration of -0.07 mm at 12 months (95% Cl: -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. Conclusion: Whether 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. (C) 2011 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.