Paper 36: Change in Humeral Anchor Position Significantly Affects Isometry in UCL Repair: A 3-Dimensional Computer Modeling Study

Objectives: Medial ulnar collateral ligament (UCL) repair utilization is increasing in recent years, bolstered by shorter rehabilitation and satisfactory clinical outcomes. While previous literature has illustrated the importance of tunnel position on restoring graft isometry in UCL reconstruction, there remains a paucity of literature guiding anchor placement in UCL repair. Herein, we describe a 3-dimensional (3D) elbow model to measure and optimize anchor location during UCL repair. Methods: A 3D computer model of a human elbow joint was created using CT and MRI images from a single patient. The humeral and ulnar attachments of the UCL were plotted using three distinct methodologies: 1) geometric cloud mapping; 2) quantitative measurements as described by the anatomical studies by Camp et al1; and 3) Frangiamore et al2. A 3.5mm-diameter clockface was placed on each attachment site which allowed for simulation of 12 distinct, 1.75mm deviations in anchor position. The three elbow models were then ranged through 0-120 degrees of flexion at 10-degree increments, and the 3D distances were measured between the two ligament centroids. The humeral and ulnar anchors were sequentially repositioned around the clockfaces, and ligament lengths were again measured to evaluate changes in isometry. An independent t-test was performed to determine if there was a significant difference in isometry between the humeral or ulnar anchor deviations. Results: Using method 1, the UCL length at 90 degrees of elbow flexion was 26.8mm. This ligament underwent 13.6mm of total excursion for a 46.4% change in length throughout arc of motion. Method 2 produced a 19.3mm ligament that underwent 0.8mm of excursion for a 3.9% length change throughout the arc. Method 3 produced a 24.5mm ligament that underwent 2.3mm of excursion for a 9.4% length change throughout arc. Identifying ligament footprints using the quantitative anatomical measurements as described by Camp et al1 and Frangiamore et al2 produced better ligament isometry through 120 degrees of flexion (ligament length changes of 3.9% and 9.4%, respectively) when compared to using the geometric cloud technique (46.4% length change). Humeral anchor deviations produced a statistically significant increase in ligament excursion when compared to ulnar anchor deviations (p < 0.001). Conclusions: When performing UCL repair, small deviations in humeral anchor position may significantly influence graft and ligament isometry. Anchor position was most isometric while using the quantitative measurements as described in Camp et al1. Particularly when addressing detachments of the humeral footprint, surgeons should be critical of the humeral anchor position in order to restore native anatomy and optimal biomechanics.