Characterizing Bone Tunnel Placement in Medial Ulnar Collateral Ligament Reconstruction Using Patient-Specific 3-Dimensional Computed Tomography Modeling

Abstract

Background: Medial ulnar collateral ligament (MUCL) reconstruction is successful in restoring valgus elbow stability, but variability in bone tunnel characteristics exists among surgical techniques. Hypothesis: Tunnel parameters such as diameter, drill angle, and starting location in MUCL reconstruction affect tunnel length and bone bridge size between tunnels. Study Design: Descriptive laboratory study. Methods: Three-dimensional models were created from elbow computed tomography scans of 10 throwing athletes and analyzed using Mimics (Materialise) software. The MUCL reconstructions were simulated on each elbow with 3 techniques: Jobe, humeral docking, and DANE TJ. Humeral central tunnels were modified by diameter, medial-lateral epicondylar starting point, and angle with respect to the humeral axis. Ulnar tunnels were varied by diameter and angle with respect to the ulnar axis. Humeral tunnel length, humeral and ulnar bone bridge sizes, and ulnar tunnel aperture and distance from the articular surface of the olecranon were measured. Comparisons were made using 1- and 2-way analysis of variance and Student-Newman-Keuls multiple comparison tests. Results: Mean central humeral tunnel length varied significantly by starting point and angulation of the tunnel both in sagittal and coronal planes, ranging from 14.2 ± 2.3 mm to 25.5 ± 4.3 mm ( P < .05). Mean bone bridge size between humeral exit tunnels ranged from 9.0 ± 2.5 mm to 15.1 ± 3.1 mm, varying by central humeral tunnel orientation and exit tunnel diameter ( P < .05). Bone bridge size between ulnar tunnels with the Jobe and docking techniques averaged 6.7 ± 0.9 mm (3.2-mm tunnels) and 6.4 ± 0.8 mm (3.5-mm tunnels), respectively. Angle of ulnar tunnels affected distance from the articular surface with the Jobe and docking techniques ( P < .0001) and affected tunnel aperture size with the interference screw technique ( P < .0001). Conclusion: Humeral and ulnar tunnel angles, starting points, and diameters affect tunnel length, distance from the articular surface, and bone bridge size in MUCL reconstructions. Maximal humeral tunnel length is achieved by starting central or lateral to the midpoint of the epicondyle, angulated 30° to the humeral axis in the sagittal plane and 15° in the coronal plane. A reasonable goal tunnel depth should range from 15 to 20 mm. Ulnar tunnels should be placed on the anterior and posterior aspects of the sublime tubercle, directed away from the joint to minimize the likelihood of breaching the articular cartilage. A bone bridge of 6 to 8 mm between these tunnels can be reasonably achieved. Tunnels with the ulnar interference screw fixation technique should also be directed away from the joint but at an angle more perpendicular than 45° to minimize tunnel aperture size. Regardless of angle of the tunnel drilled for the ulnar interference screw employed in the DANE TJ technique, the tunnel length is sufficient to fully contain a 15-mm screw. Clinical Relevance: Computer models can guide MUCL reconstruction technique by indicating tunnel placement for maximizing the bone bridge and tunnel length.