MOTION AND LAXITY OF THE CAPITELLOCONDYLAR TOTAL ELBOW PROSTHESIS

The motion and laxity of the capitellocondylar unconstrained total elb ow prosthesis were assessed, with use of an electromagnetic tracking d evice and simulated muscle-loading, after implantation in seventeen ca daveric elbows. The axis of motion of the elbows with the capitellocon dylar implants averaged 2.1 +/- 2.3 degrees more varus angulation than that of the intact elbows. This difference may be attributed to the d esign of the implant, as the 5-degree-valgus humeral component used in this study has a smaller valgus inclination than the articular surfac e of the distal aspect of the humerus. Although the maximum valgus-var us laxity of the capitellocondylar elbow prostheses was, on the averag e, 4.3 +/- 2.4 degrees greater than normal (with simulated muscle-load ing), the data must be interpreted in light of the fact that this in v itro study did not allow for soft-tissue healing. The prosthetic compo nents tracked well, and there were no dislocations or malarticulations provided that appropriate soft-tissue tensioning and positioning of t he components had been achieved at the time of implantation. Sectionin g of either the medial or the lateral collateral ligament resulted in gross instability of the joint after capitellocondylar arthroplasty. T he ulnar attachment of the medial collateral ligament was found to be vulnerable to injury during the positioning of the ulnar component of this implant. CLINICAL RELEVANCE: The capitellocondylar unconstrained total elbow prosthesis can restore acceptable patterns of motion and s tability to the elbow if there is adequate positioning of the componen ts and appropriate soft-tissue balance. Both collateral ligaments were shown to be essential stabilizers of this implant, and their integrit y is a prerequisite for stable function. The ulnar insertion of the an terior bundle of the medial collateral ligament is vulnerable to damag e during placement of the relatively broad ulnar component, and such a n injury may be one reason for instability of the joint after replacem ent of the elbow with this device. The use of this implant in patients who have small-caliber bones must be undertaken with caution, as inad vertent injury to the medial collateral ligament is difficult to avoid .