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Purpose: Radial collateral ligament (RCL) injuries to the thumb metacarpophalangeal joint have been reported to occur at a variable incidence compared with ulnar collateral ligament (UCL) injuries. The reasons for the discrepancy of incidence rates are unclear. Delay in diagnosis of the injury leads to greater patient disability time. The purpose of this study is to define the demographics and presentation of patients with RCL injuries in a military health care system.

Methods: We performed a retrospective review of electronic medical records over a five-year period to determine the incidence and epidemiology related to patients with instability of thumb metacarpophalangeal joint due to injury of the radial or ulnar collateral ligaments.

Results: 56 patients presented with thumb MCPJ instability. Eighteen (32 percent) had an RCL injury. Patients with an RCL injury were, on average, younger than those with UCL injuries. RCL patients were more likely than UCL patients to require surgery (67 versus 40 percent). With regard to time to presentation, most UCL patients presented 2-10 weeks after injury, while nearly all RCL patients presented greater than 10 weeks post injury. RCL injuries were more likely than UCL injuries to be due to an axial load (56 versus 16 percent), while UCL injuries were more likely to be due to an abduction/adduction moment (50 versus 22 percent).

Discussion: In this series, patients sustaining injuries to the RCL were younger, presented later and were more likely to undergo surgery than their counterparts with UCL instability. Maintaining a high index of suspicion of RCL instability in younger patients with axial loading injury mechanisms may allow earlier diagnosis and appropriate treatment of this injury.