Motion and laxity of the capitellocondylar total elbow prosthesis

The motion and laxity of the capitellocondylar unconstrained total elbow prosthesis were assessed, with use of an electromagnetic tracking device and simulated muscle-loading, after implantation in seventeen cadaveric elbows. The axis of motion of the elbows with the capitellocondylar implants averaged 2.1 ± 2.3 degrees more varus angulation than that of the intact elbows. This difference may be attributed to the design of the implant, as the 5-degree- valgus humeral component used in this study has a smaller valgus inclination than the articular surface of the distal aspect of the humerus. Although the maximum valgus-varus laxity of the capitellocondylar elbow prostheses was, on the average, 4.3 ± 2.4 degrees greater than normal (with simulated muscle- loading), the data must be interpreted in light of the fact that this in vitro study did not allow for soft-tissue healing. The prosthetic components tracked well, and there were no dislocations or malarticulations provided that appropriate soft-tissue tensioning and positioning of the components had been achieved at the time of implantation. Sectioning of either the medial or the lateral collateral ligament resulted in gross instability of the joint after capitellocondylar arthroplasty. The 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 stability to the elbow if there is adequate positioning of the components and appropriate soft-tissue balance. Both collateral ligaments were shown to be essential stabilizers of this implant, and their integrity is a prerequisite for stable function. The ulnar insertion of the anterior bundle of the medial collateral ligament is vulnerable to damage during placement of the relatively broad ulnar component, and such an injury may be one reason for instability of the joint after replacement of the elbow with this device. The use of this implant in patients who have small-caliber bones must be undertaken with caution, as inadvertent injury to the medial collateral ligament is difficult to avoid.