Total elbow prosthesis loosening caused by ulnar component pistoning.

BACKGROUND Linked semiconstrained total elbow prostheses have been used successfully but may be at higher risk for implant loosening than unlinked implants are. The purpose of the present report was to describe a previously unreported and potentially preventable cause of mechanical loosening of the ulnar component of a linked total elbow prosthesis. METHODS A series of ten patients who had painful pistoning of the polymethylmethacrylate-coated ulnar component of a Coonrad-Morrey linked total elbow prosthesis were evaluated clinically and radiographically. RESULTS All ten patients complained of elbow pain, and eight had a distinct sensation of the ulnar component moving within the ulna. Six patients either complained of squeaking within the elbow or could demonstrate squeaking on examination. Four patients had a complete radiolucent line around the ulnar component or the cement mantle, and six had an incomplete line around the ulnar component. Six patients had a radiolucent gap between the cement and the tip of the ulnar prosthesis. Two patients had proximal migration of the ulnar component within the cement mantle on lateral flexion radiographs. Three patients had anterior impingement, such as between the anterior flange of the humeral implant and a prominent coronoid process, on lateral flexion radiographs. At the time of revision arthroplasty, all ten patients were found to have a loose ulnar component, which was successfully revised with or without impaction grafting. At the time of the most recent follow-up, nine of the ten ulnar components were intact and stable. Three patients required an additional reoperation: one required triceps repair, one required revision of a loose humeral component, and one required a revision total elbow arthroplasty. CONCLUSIONS Pistoning of the ulnar component in the cement mantle leading to failure by means of a pullout mechanism can occur in association with the Coonrad-Morrey total elbow prosthesis with a polymethylmethacrylate-precoated ulnar component. To prevent this problem following any total elbow arthroplasty, the surgeon should check for anterior impingement intraoperatively by ensuring that there is no contact between the anterior flange and a prominent coronoid process or the cement and that no distraction of the trial ulnar component from the ulna occurs with passive elbow flexion. This condition also can be avoided by ensuring that the ulnar component is not inserted too far distally. This mechanism of failure should be considered when future total elbow arthroplasty implants are designed. LEVEL OF EVIDENCE Therapeutic Level IV.