The Middle and Distal Aspects of the Ulnar Footprint of the Medial Ulnar Collateral Ligament of the Elbow Do Not Provide Significant Resistance to Valgus Stress: A Biomechanical Study

Abstract

Background:The medial ulnar collateral ligament (UCL) insertion of the elbow has been shown to extend distally beyond the sublime tubercle. The contribution to valgus stability of the distal aspect of the footprint is unknown.Purpose/Hypothesis:The purpose of this study was to determine the contribution of each part of the UCL footprint to the elbow valgus stability provided by the UCL. It was hypothesized that the distal two-thirds of the ulnar UCL footprint would not contribute significantly to valgus stability provided by the UCL.Study Design:Descriptive laboratory study.Methods:Fifteen cadaveric arms were dissected to the capsuloligamentous elbow structures and potted. A servohydraulic load frame was used to place 5 N·m of valgus stress on the intact elbow at 30°, 60°, 90°, and 120° of flexion. The UCL insertional footprint was measured and divided into thirds (proximal, middle, and distal). One-third of the UCL footprint was elevated off the bone (leaving the ligament in continuity), and the elbow was retested at the same degrees of flexion. This was repeated until the entire UCL footprint on the ulna was sectioned. Each elbow was randomized for how the UCL would be sectioned (sectioning the proximal, then middle, and then distal third or sectioning the distal, then middle, and then proximal third). Ulnohumeral joint gapping (millimeters) was recorded with a 3-dimensional motion capture system using physical and virtual markers. Two-group comparisons were made between each sectioned status versus the intact condition for each flexion angle.Results:When the UCL was sectioned from distal to proximal, none of the ligaments failed prior to complete sectioning. When the UCL was sectioned from proximal to distal, 3 of the 6 ligaments failed after sectioning of the proximal third, while 2 more failed after the proximal and middle thirds were sectioned. Of the specimens with the distal third of the ligament sectioned first, no significant differences were found between intact, distal third cut, and distal plus middle thirds cut at all flexion angles.Conclusion:The middle and distal thirds of the insertional footprint of the UCL on the ulna did not significantly contribute to gap resistance at 5 N·m of valgus load. The proximal third of the footprint is the primary resistor of valgus load.Clinical Relevance:This cadaveric biomechanical study demonstrated that the middle and distal thirds of the native UCL insertion onto the ulna did not significantly contribute to valgus resistance at the elbow. When a UCL reconstruction is performed, the proximal third of the UCL insertion may be the most clinically important portion of the ligament to reconstruct.

Anatomic and Biomechanical Evaluation of Ulnar Tunnel Position in Medial Ulnar Collateral Ligament Reconstruction

“…1,16,19,26,27,30,35 Reconstruction with ulnar tunnels at all 3 tunnel locations (5, 10, and 15 mm from the ulnohumeral joint line) successfully restored medial elbow stability across all angles of flexion, and there were no significant differences in torque to failure among the 3 tunnel locations. Erickson et al 12 recently published biomechanical data demonstrating the relative contribution of the proximal, middle, and distal thirds of the mUCL ulnar footprint and found that only release of the proximal third resulted in increased valgus rotation. While the proximal third of the ligament plays a key role in stability in a native ligament, as Erickson et al 12 recently quantified, the results of our study demonstrate that reconstruction that places the distal fixation within up to 15 mm of the ulnotrochlear joint line can restore valgus stability.…”

“…Erickson et al 12 recently published biomechanical data demonstrating the relative contribution of the proximal, middle, and distal thirds of the mUCL ulnar footprint and found that only release of the proximal third resulted in increased valgus rotation. While the proximal third of the ligament plays a key role in stability in a native ligament, as Erickson et al 12 recently quantified, the results of our study demonstrate that reconstruction that places the distal fixation within up to 15 mm of the ulnotrochlear joint line can restore valgus stability.…”

“…However, more recent studies have clarified that while the proximal ulnar footprint does in fact insert on the sublime tubercle, a significant portion of the ulnar collateral ligament (UCL) insertion continues more distally along the median ulnar ridge. 5,12,15 While increased understanding of the insertional anatomy of stabilizing structures—such as the anterior cruciate ligament, posterior cruciate ligament, posterolateral corner, lateral collateral ligament of the elbow, and rotator cuff—have helped guide advancements in surgical technique, there has been a paucity of literature regarding adjustment of the tunnel location in UCL reconstruction. Despite studies demonstrating that the ulnar insertion of the mUCL extends more distally on the ulna, 15,20 as well as literature assessing the role that the proximal, middle, and distal thirds of the ligament play in valgus stability, 12 there have been no biomechanical studies to date assessing the effect of more distal placement of ulnar fixation during mUCL reconstruction.…”

Ulnar Collateral Ligament Tear Location May Affect Return-to-Sports Rate but Not Performance Upon Return to Sports After Ulnar Collateral Ligament Reconstruction Surgery in Professional Baseball Players

“…3,13 Furthermore, only the proximal-most portion of the UCL insertion onto the sublime tubercle of the ulna contributes significantly to valgus stability of the elbow, indicating that there is a large amount of stress seen by a small area of the distal UCL insertion. 10 This is in contrast to the proximal insertion where the load is dispersed throughout the entire footprint. 13 However, during UCLR a distal tunnel and proximal socket are created and a graft is used to reconstruct the UCL.…”

Elbow ulnar collateral ligament reconstruction using suture tape augmentation

“…Cadaveric studies have described the origin of this ligament to have a mean footprint of 45.5 mm 2 on a flat portion of the humerus, 13.4 mm anteroinferior to the most prominent portion of the medial epicondyle. 11,13 The ligament spans an average length of 53.9 mm distally and has a central insertion onto the sublime…”