MICROMOVEMENT OF HUMERAL AND ULNAR COMPONENTS OF THE ACCLAIM ELBOW REPLACEMENT USING RSA

Abstract

To measure any observed migration and rotation of humeral and ulnar components using radiostereometric analysis. From 2002–2004 in a prospective ongoing study, twelve elbows in patients treated with either a linked or unlinked Acclaim total elbow prosthesis were included in a radiostereometry study. Six tantalum markers were introduced into the humerus another three markers were located on a humeral component. Four markers were placed in to ulna and three markers located on the ulnar component. RSA radiographs were taken postoperatively, six, twelve and twenty-four months. The radiographs were digitised and analysed using UmRSA software. The relative movement of the humeral and ulnar implants with respect to the bone was measured. At twelve months, the largest segment translation of the humeral component was in the anterior/posterior direction with a mean of 0.44mm followed by medial/lateral translation of 0.39 mm; there was minimal proximal/ distal translation or with a mean of 0.16mm. Paired t-tests between twelve and 24 months segment translation data showed the mean differences to be no more than 0.056mm. The largest rotation at twelve months was anteversion/retroversion with a mean of 2.40deg, anterior tilt had a mean of 1.20deg and varus/valgus tilt was minimal mean 0.60deg. Mean difference between twelve and 24 months segment rotation was no more than 0.30deg. In contrast, humeral tip motion produced a mean of 1.1mm at 12 months dominated by movement in the plane horizontal plane with a mean difference at 24 months of 0.06mm. No patients could be measured for segment micromotion of the ulnar component due to technical difficulty in visualising tantalum markers in the ulna. Early micromotion of the Acclaim humeral implant occurs mostly by rotation about the vertical axis accompanied by anterior tilt. This motion reaches a plateau at 12 months after operation.