Characteristics of ulnohumeral joint alignment in distal ulnar collateral ligament tears compared to proximal tears in baseball and softball players.

Abstract

Dysfunctional features of distal ulnar collateral ligament (UCL) tears remain unclear. We aimed to clarify the characteristics of valgus and rotational alignment of the ulnohumeral joint at rest in distal UCL tears compared with those in proximal tears. The participants were baseball and softball players diagnosed with UCL tears, classified as proximal, middle, or distal. Valgus and rotation alignment of ulnohumeral joint were measured using computed tomography-like images and a 3-dimensional image analysis system. For valgus alignment, the medial joint space was measured as the distance between the medial epicondyle and the ulnar coronoid processes. For rotational alignment, the medial distance (MD) and lateral distance (LD) of the ulnohumeral joint were measured in the reconstructed axial views at the medial epicondyle and trochlear levels. MD was measured as the distance between the medial edges of the olecranon fossa and trochlear notch, whereas LD was measured as the distance between the lateral edges of the olecranon fossa and trochlear notch. Of the 20 included cases, 6 (30%) were distal and 14 (70%) were proximal UCL tears. The medial joint space results showed no significant difference between the 2 groups. The MD was significantly higher in the distal tear than the proximal tear only at the trochlea level. The LD showed no significant difference at either level. Distal tears did not show hypervalgus malalignment compared to proximal tears using conventional measurements. In contrast, distal tears showed hyperinternal rotation malalignment of the ulnohumeral joint only at the distal side of the joint compared to proximal tears.