Quantitative Anatomic Analysis of the Medial Ulnar Collateral Ligament Complex of the Elbow

Abstract

Background: A more detailed assessment of the anatomy of the entire medial ulnar collateral ligament complex (MUCLC) is desired as the rate of medial elbow reconstruction surgery continues to rise.

Purpose: To quantify the anatomy of the MUCLC, including the anterior bundle (AB), posterior bundle (PB), and transverse ligament (TL).

Study design: Descriptive laboratory study.

Methods: Ten unpaired, fresh-frozen cadaveric elbows underwent 3-dimensional (3D) digitization and computed tomography with 3D reconstruction. Ligament footprint areas and geometries, distances to key bony landmarks, and isometry were determined. A surgeon digitized the visual center of each footprint, and this location was compared with the geometric centroid calculated from the outline of the digitized footprint.

Results: The mean surface area of the AB was 324.2 mm², with an origin footprint of 32.3 mm² and an elongated insertional footprint of 187.6 mm² (length, 29.7 mm). The mean area of the PB was 116.6 mm² (origin, 25.9 mm²; insertion, 15.8 mm²), and the mean surface area of the TL was 134.5 mm² (origin, 21.2 mm²; insertion, 16.7 mm²). The geometric centroids of all footprints could be predicted within 0.8 to 1.3 mm, with the exception of the AB insertion centroid, which was 7.6 mm distal to the perceived center at the apex of the sublime tubercle. While the PB remained relatively isometric from 0° to 90° of flexion (P = .606), the AB lengthened by 2.2 mm (P < .001).

Conclusion: Contrary to several historical reports, the insertional footprint of the AB was larger, elongated, and tapered. The TL demonstrated a previously unrecognized expansive soft tissue insertion directly onto the AB, and additional analysis of the biomechanical contribution of this structure is needed.

Clinical relevance: These findings may serve as a foundation for future study of the MUCLC and help refine current surgical reconstruction techniques.

Keywords: anterior bundle; elbow; medial ulnar collateral ligament; posterior bundle; transverse ligament.

Figure 1.

Fully dissected specimens revealing the (A) tendons of the biceps, brachialis, and triceps; (B) medial ulnar collateral ligament complex; and (C) origins and insertions of the anterior bundle (AB), posterior bundle (PB), and transverse ligament (TL).

Figure 2.

Orientations and areas of the (A) entire ligaments and (B) their origins and insertions for the medial side of the elbow. AB, anterior bundle; PB, posterior bundle; TL, transverse ligament.

Figure 3.

Distances between ligament centers and key bony landmarks when viewing from (A) medial and (B) anterior. The solid circle represents the apex of the sublime tubercle and the apparent center of the footprint, while the solid triangle represents the geometric centroid. AB, anterior bundle.

Figure A1.

Image of the fully dissected specimen showing the posterior aspect of the humerus with glass spheres mounted on top of plastic hex-socket cap screws, which were screwed into the bone in step 1. Six spheres were fixed to the humerus (shown) and 6 to the ulna (not shown).

Figure A2.

Three-dimensional geometries of bones and spheres were reconstructed from computed tomography (CT) scans. The centroid of each sphere geometry was identified in the CT reference frame. The center of a uniformly distributed 6.35 mm-diameter sphere was created on each of the centroids.

Figure A3.

The specimen was locked at each flexion angle using a custom fixture, and the center of each sphere was identified using the digitizer with a ball probe affixed to its end.

Figure A4.

A point probe was affixed to the end of the digitizer and was used to identify the soft tissue and bony landmarks with the specimen fixed at 90° of flexion.

Figure A5.

A screw was placed across the ulnohumeral (asterisk) and radiocapitellar (arrow) joints to stabilize the elbow at 90° of flexion before digitizing the anatomic features of the elbow.

Figure A6.

Sphere geometries obtained from computed tomography in step 3 were matched to the sphere geometries obtained from digitization in step 4 at each flexion angle that the elbow was fixed using the iterative closest point best-fit algorithm (90° of flexion, 60° of flexion, 30° of flexion, and full extension [Ext]).

Figure A7.

Anatomic landmarks (outlined in gray) were identified on the bones at 90° of flexion. Then, they were registered to the surfaces of the 3-dimensional reconstructed bone geometries.