The Association of Metacarpal Head Morphology with Risk of Ulnar Collateral Ligament Rupture.

Abstract

Purpose: A flat metacarpal head of the thumb is thought to predispose to ulnar collateral ligament ruptures because of limited range of motion. In this study, we quantitatively compared the roundness of the thumb metacarpal head in individuals with an ulnar collateral ligament rupture to the roundness in patients without any thumb pathology using conventional thumb metacarpophalangeal joint anteroposterior radiographs.

Methods: Patient data were extracted from a single institutional system, including six urban hospitals in the United States. Eighty-two patients with a thumb ulnar collateral ligament rupture between January 2004 and December 2021 were identified and compared with 97 patients without any thumb pathology. The roundness of the thumb metacarpal head was calculated by dividing the length of the articular surface by the radius of the best-fit circle through the metacarpal head (a higher ratio corresponds to a rounder head).

Results: The roundness ratios ranged between 0.47 and 1.95 across all 179 patients in the data set. The mean roundness ratio for uninjured patients was 1.12 (standard deviation [SD] 0.25) and did not differ significantly from that of the patients with ulnar collateral ligament rupture (1.16 [SD 0.26]).

Conclusions: We found no difference in metacarpal head roundness between patients with a thumb ulnar collateral ligament rupture and healthy patients. This may suggest that a flat thumb metacarpal head is not associated with a traumatic thumb ulnar collateral ligament tear.

Type of study/level of evidence: Diagnostic IV.