Clinical and experimental studies on wear and osteolysis in total joint replacement

Sammanfattning: Total hip arthroplasty is a very successful procedure. Despite this fact, however, a certain portion of patients has to be revised. One major reason for revision is the wear of the polyethylene leading to loosening and osteolysis. The overall aim of this thesis was to evaluate linear wear and migration of cemented, all - polyethylene sockets and polyethylene liners in total hip arthroplasty. The aim was also to identify patients for whom increased wear was a risk and who therefore were likely to require a revision, and further to evaluate different methods for measuring wear and their accuracy Material and results Study I: 154 hips had received an uncemented Omnifit total hip. 66 cups were revised and in these cases mean annual wear was 0.32 mm compared to 0.12 mm in hips not revised. Osteolytic processes were present in 51 patients at revision but these could be observed in only 35 hips on radiographs. Micromotion evaluated by RSA, weight, age, side, size of cup, screw fixation, polyethylene thickness or shelf - life of the polyethylene did not correlate to wear, whereas male gender did. Study II: Cross - linked N-telopeptide of type I Collagen (NTx), a marker of osteoclast - mediated bone resorption, has been proposed for the evaluation of the often non-symptomatic peri-prosthetic osteolysis. NTx in urine was analysed in 160 patients with and without osteolysis. The group of patients with osteolysis had significantly higher mean NTx levels (p=0.03) and an increased annual wear of the polyethylene. Study III: 120 patients were randomised to have a primary total hip replacement with one out of four possible articulations. The femoral heads were of conventional steel or of a new ceramic, zirconium oxide. The cup was either made of conventional polyethylene or of polyethylene that had been reheated under pressure, Hylamer. All combinations that included Hylamer or Zirconium oxide had increased polyethylene wear as compared to the standard steel / polyethylene combination (p<0.008). 12 patients have been revised to date- none had a stainless steel / polyethylene articulation. Study IV: Polyethylene penetration (wear) was measured by RSA in 111 patients by radiostereometric analysis (RSA) in the supine and weight-bearing position. There was a small (0.02mm) systematic difference. The degree of penetration of the head into the polyethylene or the time for the first examination did not alter this result. Study V: We analysed the accuracy of 2 radiostereometric (RSA) techniques for wear measurement and 3 standard radiographic techniques using a phantom with different prosthetic components. The mean differences between phantom and measurement were, for digital RSA examinations 0.010 mm (accuracy 0.42, n=175). The corresponding error values for the three radiographic techniques were 0.19 (accuracy 1.3, n=180) for Charnley Duo, 0.13 (accuracy 1.3, n=180) for Imagika corrected, and 1.021 (accuracy 2.99, n=180) for Imagika. Measurement error decreased from 0.011 mm with ordinary RSA to 0.004 with RSA digital measurement. Head size, direction of wear in relation to the cup or type of prosthetic component did not influence the measurement error.