LONG-TERM RSA RESULTS OF 18 SOUTER-STRATHCLYDE ELBOW PROSTHESESMOST HUMERAL COMPONENTS MIGRATE, BUT THERE IS LIMITED CLINICAL IMPACT

Abstract

Background and purpose: The Souter-Strathclyde total elbow prosthesis is a well-studied replacement therapy for the destructed rheumatoid elbow joint. In the short-term results of a RSA-study we concluded that 8 out of 18 humeral components were at risk for loosening at two years of follow-up. Now we present the long-term results of this study to evaluate these predictions.

Patients and Methods: Twenty-one elbows (18 patients) were included in the RSA-study. At risk for loosening was defined as increase of translation of more than 0.4 mm or increase of rotation of more than one degree during the second postoperative year. The average follow-up was 98 months (range: 12–134 months). RSA-measurements were performed post-operatively, at 3 months, 6 months, 12 months and at yearly intervals thereafter. Prosthetic position and radiolucent lines (RLLs) were examined on conventional radiographs.

Results: Almost all humeral components, including the ones that were defined to be ‘at risk’ for loosening in our short-term study, showed increased and irregular migration in this long-term follow-up study. In contrast to this, the ulnar components were stable. Translations were most prominent in the posterior-anterior direction, the most prominent rotations took place about the transverse axis. No obvious influences of prosthetic alignment on micromotions were found. Four humeral components were clinically loose – three of them could be revised -, but only one of them was defined to be at risk for loosening in the short term study.

Radiological assessment based on conventional radiographs showed that a prediction of humeral loosening can be made within four years after surgery.

Interpretation: The RSA results clearly show that almost all humeral components migrate up to several millimeters and several degrees in an irregular manner, but often without clinical consequences.