The role of the lateral part of the distal triceps and the anconeus in varus stability of the elbow: A biomechanical study: The role of the lateral triceps tendon and anconeus under gravity varus.

Abstract

The role of the lateral part of the distal triceps as a stabilizer in the lateral collateral ligament (LCL) deficient elbow and whether its effect in improving the stability is independent of that of the anconeus is unclear. Seven cadaveric elbows were tested under gravity varus stress using a custom-made machine designed to simulate muscle loads while allowing passive flexion of the elbow. An injury model was created by sectioning the LCL and sparing the common extensor origin. The lateral part of the distal triceps tendon was loaded sequentially with 0 N, 10 N, 25 N and 40 N. Each stage of the lateral part of the distal triceps loading was tested with the anconeus unloaded (inactive) or with a 25 N load applied (active). Articular contact pressure on the coronoid, the medial facet, and the lateral facet were collected and processed using TekScan sensors and software. A significant decrease in the mean coronoid contact pressure was seen with sequential loading of the lateral part of the distal triceps (p < 0.001). The ratio of medial to lateral facet contact pressures (M/L ratio) significantly decreased with sequential loading of the lateral part of the distal triceps (p < 0.001), indicating a better distribution of the contact pressure between the medial and lateral facets as the lateral part of the distal triceps was loaded. These effects were statistically significant, both with and without anconeus loading. There was no significant modification of the effect of the lateral part of the distal triceps loading on the contact pressure by the anconeus loading (p = 0.47). However, with active anconeus loading, the contact pressure and the M/L ratio were significantly lower for any stage of lateral triceps loading (p < 0.001), indicating a synergistic effect of the anconeus. In an LCL-deficient elbow, the lateral part of the distal triceps loading prevents the increased contact pressure on the coronoid under varus stress and improves the distribution of contact pressures on the coronoid. Anconeus loading further decreases and improves the distribution of the contact pressures; however, its effect is independent of that of the lateral part of the distal triceps. These results substantiate a role of the lateral part of the distal triceps as a dynamic constraint against elbow varus and have clinical implications for prevention and rehabilitation of elbow instability.