Biomechanical analysis of elbow medial ulnar collateral ligament tear location and its effect on rotational stability

Background: Recent anatomic and clinical studies have shown that the location of the injury to the elbow ulnar collateral ligament (UCL) is an important variable in deciding on surgical intervention; however, no studies have evaluated these findings biomechanically. Methods: This study tested 16 intact elbow specimens. Valgus torques of 2.5 and 5 Nm were applied to the elbow at various flexion angles, and the resulting valgus angles were measured. The valgus angles were applied to the elbows in their intact states and again after partial and complete cuts were made on the proximal and distal insertions of the UCL. Resulting valgus torques were measured, and stiffness was calculated for each elbow flexion angle. Unpaired t tests were used to evaluate the effects of cut location and flexion angle on joint rotational stability and stiffness. Results: The posterior-distal insertion contributed the most to stability. At valgus angles generated from 2.5 Nm intact torques, the posterior-distal insertions contributed to 51% +/- 26% (P < .03) intact rotational stability, and at valgus angles generated from 5 Nm intact torques, the posterior-distal insertions contributed to 41% +/- 17% (P < .02) intact rotational stability. For overall stiffness, the posterior-distal insertions contributed to 31% +/- 12% (P < .045) intact stiffness. Conclusion: Overall, the posterior distal insertion of the UCL contributed most to rotational stability and stiffness of the medial elbow when subjected to valgus stress at 90 degrees and 120 degrees of elbow flexion. At higher elbow flexion angles, the posterior insertions contributed more to stability, whereas the anterior insertions had a greater effect at lower flexion angles. (C) 2018 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved.