Local anaesthetic infiltration increases the accuracy of assessment of ulnar collateral ligament injuries.

Objective: To assess the effectiveness of a systematic examination of the ulnar collateral ligament (UCL) of the thumb metacarpophalangeal joint (MCPJ) prior to and post infiltration of local anaesthetic.
Methods: During the study period from 24 October 2001 to 22 February 2002, 51 patients with clinical signs suggestive of UCL injuries were identified prospectively from initial ED attendances and attendances at a subsequent review clinic. Patients were formally assessed a mean of 6.6 days post injury. A single ED Senior House Officer carried out examination before and after direct infiltration of local anaesthetic around the site of injury. Stress radiography was also performed as the 'gold standard' diagnostic test of UCL instability.
Results: Forty-seven patients were enrolled in the study. When reviewed by the single observer, examination prior to and post local anaesthetic infiltration revealed a degree of joint stability in 28% (95% CI 16-43%) and 98% (95% CI 88-100%) cases, respectively, compared to the gold standard. Post infiltration, this technique had a specificity of 100% (95% CI 94-100%) and a sensitivity of 87.5% (95% CI 74-95%) (P < 0.001). Stress radiography offered additional information in one patient. A total of eight patients previously underdiagnosed in the ED were found to have unstable thumb MCPJs.
Conclusion: This simple technique improves assessment of suspected UCL injuries approximately 1 week post injury. Further studies are indicated to determine its effectiveness in the ED immediately post injury.