Figved W, Dahl J, Snorrason F, Frihagen F, Röhrl S, Madsen JE, Nordsletten L. Radiostereometric analysis of hemiarthroplasties of the hip - a highly precise method for measurements of cartilage wear. Osteoarthritis Cartilage. 2012 Jan;20(1):36-42

A phantom model study was conducted to show that radiostereometric analyses (RSA) is suitable to calculate an accurate three-dimensional computer model of a bipolar prosthetic head, and is able to measure the acetabular wear in patients with hemiarthroplasties. 22 patients with femoral neck fractures were randomised to treatment with either a cemented hemiarthroplasty or an uncemented hydroxyapatite-coated hemiarthroplasty. Eight to ten 1 mm diameter tantalum markers were inserted in the pelvis around the acetabulum for conducting radiostereometric analyses (RSA) of acetabular wear. A mean migration of the prosthetic head into the acetabulum of 0.62 mm was found at three months, and a further migration of -0.07 mm at 12 months. There were no differences between the two groups in prosthetic head migration or functional outcome. We concluded that RSA may be used for the measurement of cartilage wear in hemiarthroplasties of the hip, and that after three months there was no detectable cartilage degradation during the first postoperative year.