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Unstable thumb metacarpophalangeal joint ulnar collateral ligament injury — MSRA MCQ

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HardSoft Tissue InjuryUnstable thumb metacarpophalangeal joint ulnar collateral ligament injuryMSRA

A 33-year-old right-hand-dominant secondary-school teacher presents to a GP-led urgent treatment centre 4 hours after falling while holding a ski pole. Her left thumb was forced into abduction and extension at the metacarpophalangeal (MCP) joint. She has swelling and maximal tenderness over the ulnar aspect of the thumb MCP joint. Plain radiographs show no fracture or dislocation. With the thumb MCP joint supported, valgus stress testing demonstrates substantially greater opening than on the unaffected side, both in 30 degrees of flexion and in full extension; there is no firm end point. She reports weak key pinch. Capillary refill, sensation and flexor and extensor tendon function are normal. What is the most appropriate management now?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: C — Immobilise the thumb in a thumb-spica splint and arrange urgent hand-trauma or fracture-clinic assessment

Explanation lettering: E = shown as A · D = shown as B · A = shown as C · B = shown as D · C = shown as E

This is a clinically unstable thumb MCP ulnar collateral ligament (UCL) injury. The abducting and extending mechanism, focal ulnar MCP tenderness and marked valgus laxity without a firm end point indicate a likely complete UCL rupture. Laxity in both flexion and extension supports significant ligamentous disruption rather than pain-limited examination alone. A normal radiograph excludes neither a UCL rupture nor soft-tissue displacement that may prevent healing. Immediate thumb-spica immobilisation protects pinch stability, and urgent hand-trauma or fracture-clinic assessment is required because unstable injuries may need operative management. B is inappropriate because delayed reassessment risks deferring specialist assessment of an unstable ligament injury. C would be appropriate for a stable minor thumb sprain, not objective MCP instability. D is attractive because MRI can characterise ligament injury, but imaging should not delay referral when examination already identifies an unstable UCL injury; the receiving hand service can determine the required imaging. E addresses an occult bony injury but does not adequately manage the decisive finding here: clinically significant MCP ligament instability.

Reference: Hand Injuries (Published 26 November 2025) — https://www.rightdecisions.scot.nhs.uk/media/jujp5l25/hand-injuries-dec-24.pdf