Comprehensive ultrasound assessment of thumb metacarpophalangeal collateral ligament injuries reveals frequent concomitant abnormalities

INTRODUCTION: Ulnar collateral ligament (UCL) tears of the thumb are well-recognized injuries, while radial collateral ligament (RCL) and dorsal extensor-related abnormalities are less frequently studied. The pattern of concomitant ultrasound abnormalities in patients after thumb trauma is not well documented. The aim of this study was to characterize concomitant UCL, RCL, and dorsal extensor-related abnormalities within a selected cohort referred to thumb ultrasound after trauma, and to explore associations with injury mechanism. MATERIALS AND METHODS: A retrospective review was performed of 42 consecutive adult patients who underwent high-resolution ultrasound of the thumb metacarpophalangeal joint between April 2014 and February 2025 for suspected ligamentous injury after acute trauma. Patients were included if ultrasound demonstrated pathologic findings in at least one stabilizing structure, UCL or RCL, and the extensor mechanism was systematically assessed. Collateral ligament injuries were graded using standard sonographic criteria, while dorsal extensor-related findings were recorded descriptively. Associations between injury severity and mechanism of injury were tested using chi-square or Fisher's exact analysis, as appropriate. RESULTS: UCL pathology was present in 35/42 (83.3%) patients, RCL pathology in 23/42 (54.8%), and dorsal extensor-related abnormalities in 17/42 (40.5%). The severity distribution of UCL injuries was grade I in 15 patients, grade II in 8, grade III in 9, and grade IV in 3; RCL injuries were grade I in 18 patients, grade II in 4, and grade III in 1. Nearly half of patients with UCL injury also demonstrated RCL involvement, and dorsal extensor-related abnormalities accompanied 75% of combined UCL and RCL injuries. No significant associations were observed between trauma mechanism and injury presence or severity (all p > 0.22). CONCLUSIONS: In this selected cohort, combined ultrasound abnormalities involving the thumb MCP collateral ligaments and dorsal extensor structures were frequently observed. In suspected thumb MCP injury, assessment of adjacent stabilizing structures may improve diagnostic completeness and patient counseling and follow-up.