A prospective radiostereometric analysis (RSA) study of 18 patients with cemented revision hip surgery and impaction grafting with an Exeter stem was done with a follow-up of 2 years for all patients. All factors that could influence migration (ie, micromotion) of the stem were analyzed with a repeated measurements analysis of variance. Two groups could be identified: a stable group and a continuous migrating group. Two factors significantly influenced micromotion during the fol-low- up measurements. The first factor was the Paprosky classification (the bigger the defect, the higher the micromotion). The second factor was cement mantle defects in >=1 Gruen zones. The migrating hip stems had more Gruen zones with cement mantle defects (45%) compared with the stable prostheses (21%). The effect of the first factor on micromotion was limited and probably clinically less relevant. Because the cement mantle defects found in this study were caused by poor instrumentation, the second factor stresses the importance of good instrumentation, which is essential to make this technically demanding technique effective in creating a stable stem¿ allograft construct in the defective femoral canal. Key words: migration, cemented hip revision, tapered polished stems, bone impaction grafting.@en

21 elbows in 18 patients with rheumatoid arthritis were treated with a Souter-Strathclyde total elbow prosthesis. 18 elbows were included in a radiostereometry (RSA) study. The aim of this clinical RSA study was to assess the three-dimensional micromotion pattern of the Souter-Strathclyde prosthesis, and thereby gain insight in the aseptic loosening process of this prosthesis. Implants were defined as at risk of aseptic loosening when the translation rate during the second postoperative year was more than 0.4 mm along one or more coordinate axes and/or the rate of rotation was more than 1° about one or more coordinate axes. Clinical examination revealed an increase in the range of motion and a marked reduction in pain. The RSA showed that 8 of 18 humeral components were at risk of aseptic loosening, although no signs of such loosening - defined as a complete radiolucent line of 2 mm or more - were found on the plain radiographs. In 7 humeral components, an anterior tilt about the transverse axis was seen that resulted in an anterior translation of the proximal tip and a posterior translation of the component's trochlea. Long-term studies of the Souter- Strathclyde prosthesis, have shown that this rotation is a specific pattern of failure in some implants. None of the ulnar components was at risk for aseptic loosening. Improvements in fixation of the Souter-Strathclyde total elbow arthroplasty should focus on the humeral component. At present, the lateral flange of the implant is enlarged to improve rotational stability about the transverse and longitudinal axes. The effect of this change in design on micromotion of the Souter-Strathclyde total elbow prosthesis will be studied in a randomized RSA study comparing the new design to the existing one.@en