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MECHANISM OF LOOSENING OF THE SOUTER-STRATHCLYDE TOTAL ELBOW REPLACEMENT – EVIDENCE FROM REVISION SURGERY.

The Queen Elizabeth Hospital, Sheriff Hill, Gateshead, UK

Purpose of the study: to demonstrate a mechanism of loosening of the Souter-Strathclyde Total Elbow Replacement (TER) using evidence from revision surgery.

Methods: nine Souter-Strathclyde humeral and ulnar components retrieved from revision surgery for aseptic loosening were examined macroscopically and then microscopically under low power magnification. The wear patterns were compared and photographed.

Results and conclusion: inspection of the retrieved cobalt chrome steel humeral components revealed no evidence of surface wear. However on examination of the polyethylene ulnar components six of the nine exhibited macroscopic wear taking the form of deep linear grooves on either the medial or lateral articulating surface. Microscopic examination revealed wear exhibited as complete disruption of the polyethylene machining lines on the medial and lateral articular surfaces, but almost complete preservation on the central gliding ridge. The findings are best explained in the context of normal elbow kinematics and congruence of the Souter-Strathclyde components. The normal elbow joint is not a simple hinge joint. In addition to flexion/extension, axial rotation and abduction/adduction motion patterns occur. However articulating surfaces of the Souter-Strathclyde components are highly congruent and thus resist the elbow’s normal translational and rotational movements. Our wear patterns are the result of humeral component rocking during flexion and extension as a result of this resistance. The central gliding ridge is preserved because the humeral component is not always in contact with it as it rocks out of its articulation in the coronal plane. Furthermore as the humeral component rocks, the sharp edge of its articulating surface makes contact with the articulating surface of the ulna causing abrasion and in the extreme circumstance the deep linear grooves observed. The biomechanics eventually lead to component loosening.

The abstracts were prepared by Cormac Kelly. Correspondence should be addressed to The Secretary, British Elbow and Shoulder Society, Royal College of Surgeons, 35–43 Lincoln’s Inn Fields, London WC2A 3PE