MICROMOTION OF THE ACCLAIM TOTAL ELBOW ARTHROPLASTY USING RADIOSTEREOMETRY

Abstract

Purpose: To measure any observed migration and rotation of humeral and ulnar components using radiostereometric analysis.

Methods: From 2002–2004 in a prospective study, twelve elbows in patients treated with either a linked(3) or unlinked(9) Acclaim total elbow prosthesis were included in a radiostereometry study. Six tantalum markers were introduced into the humerus another 3 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.

Results: At twelve months, the largest rotation of the humeral component was anteversion/retroversion with a mean of 20, anterior tilt had a mean of 1.10 and varus/valgus tilt was minimal mean 0.60. Mean difference between twelve and 24 months segment rotation was no more than 0.50. Rotation in unlinked humeral implants reached a plateau at 12 months this did not occur in linked implants. Paired t-tests between twelve and 24 months segment translation data showed the mean differences to be no more than 0.04mm. In contrast, humeral tip motion produced a mean of 1.3mm at 12 months dominated by movement in the horizontal plane with a mean difference at 24 months of 0.2mm. Mean micro-motion of the ulna implant tip was 0.32mm at 12 months with a mean difference at 24 months of 0.1mm.

Conclusions: Early micromotion of the Acclaim humeral implant occurs mostly by rotation about the vertical axis accompanied by anterior tilt. In unlinked implants this motion reaches a plateau at 12 months after operation but does occur in linked implants.