The Effect of Humeral and Ulnar Tunnel Placement on Achieving UCL Graft Isometry

OBJECTIVES: The elbow medial ulnar collateral ligament (UCL) is frequently injured in throwing athletes, most commonly baseball pitchers. When conservative management fails, surgical intervention can allow the athlete to return to sport. While extensive research has been devoted to UCL graft incorporation and outcomes based on varying surgical techniques, there is a paucity of literature available addressing optimal bone tunnel placement in achieving medial UCL graft isometry. The purpose of this study is to assess the effect of humeral and ulnar bone tunnel placement on achieving UCL graft isometry through elbow range-of-motion. METHODS: Ten fresh-frozen cadaveric upper extremities were dissected to expose the native UCL in its entirety. Three equidistant humeral and ulnar tunnels were created at each UCL footprint. Suture was passed between nine possible tunnel combinations for each elbow affixed to an isometry guage. Each elbow was moved through a 120-degree arc of motion for each tunnel combination at 0, 30, 60, 90, and 120 degrees. Measured changes in isometry gauge tension were recorded and analyzed using one-way analysis of variance (ANOVA) with Tukey’s HSD for pairwise comparisons. A p-value of 0.05 was used to determine significance for all tests. RESULTS: There was an overall significant effect (p < 0.0001) of tunnel placement at all degrees of flexion measured. Pairwise comparisons revealed increases in displacement between the central and posterior tunnel positions of the medial epicondyle, with significant differences (p=0.0009) occurring when paired with both the central and posterior aspect of the sublime tubercle. Profound differences (p < 0.0001) were noted between the anterior and posterior humeral tunnel positions. No significant differences noted between ulnar tunnel locations at any humeral location. Figure 1: Tunnel placement in the central part of the medial epicondyle (Central(epi)) was generally the most isometric grouping, with Central(epi -) Anterior(tub) being the most isometric combination of all. Data are represented as mean +/- SEM. CONCLUSION: Isometric graft placement of the medial elbow UCL is undoubtedly dependent upon optimal tunnel placement and even slight deviations from the native centroid at either the medial epicondyle or sublime tubercle can possibly lead to early graft failure or abnormal joint kinematics. This information can aid surgeons in performing isometric single bone tunnel UCL reconstruction or repair procedures in the future.