Ulnar Collateral Ligament Injury — Skier’s Thumb

The ulnar collateral ligament (UCL) of the thumb metacarpophalangeal (MCP) joint is the primary restraint to radial deviation (valgus stress) at the thumb MCP joint. Its acute disruption — most commonly from a forced radial deviation injury — produces the condition variably termed skier`s thumb (acute injury) or gamekeeper`s thumb (chronic attenuation). The critical surgical consideration in acute UCL tears is whether a Stener lesion is present, which prevents healing with conservative management and mandates surgical repair.

• Mechanism: forced radial deviation (abduction) of the thumb at the MCP joint — typically a fall onto an outstretched hand holding a ski pole (skier`s thumb), or a fall with the thumb trapped in a position of radial deviation; the thumb is forced radially as the MCP joint is stressed into valgus
• UCL anatomy: the UCL consists of the proper collateral ligament (taut in flexion — the primary stabiliser) and the accessory collateral ligament (taut in extension, restrains volar plate); the adductor aponeurosis of the adductor pollicis overlies the UCL superficially; in a complete UCL tear, the torn proximal end of the UCL may displace superficial to the adductor aponeurosis — this is the Stener lesion; the aponeurosis prevents the torn ligament from returning to its anatomical position, preventing healing
• Gamekeeper`s thumb: a chronic insufficiency of the UCL from repetitive forced abduction (originally described in Scottish gamekeepers who killed rabbits by forcible neck-twisting); presents with chronic thumb MCP instability rather than acute pain; may have a chronic Stener lesion or just attritional UCL stretching

• Stener lesion: when the UCL tears from its distal (phalangeal) attachment and the thumb is radially deviated, the torn proximal end of the ligament is displaced superficial to the adductor aponeurosis; the ligament end is therefore interposed outside the aponeurosis and cannot reach its anatomical footprint on the proximal phalanx for healing; the Stener lesion is present in approximately 50–80% of complete UCL tears; it can sometimes be palpated as a nodule on the ulnar side of the MCP joint (the `Stener bump`); its presence is an absolute indication for surgical repair — conservative management will result in permanent instability
• MRI is the investigation of choice to confirm a Stener lesion pre-operatively — shows the displaced ligament end lying superficial and proximal to the adductor aponeurosis; USS (dynamic) can also identify it in experienced hands; the Stener lesion on MRI appears as a `yo-yo` sign — the torn ligament end folded back on itself, lying proximal and superficial to the normal UCL footprint

• History: acute injury — fall onto a ski pole or outstretched hand; immediate pain and swelling at the ulnar aspect of the thumb MCP joint; difficulty pinching and gripping; may hear or feel a `pop` at the time of injury
• Examination: tenderness at the ulnar MCP joint (UCL footprint — distal phalanx base); ecchymosis; swelling; the Stener bump (a palpable firm nodule at the ulnar MCP joint); assess stability with valgus stress testing
• Valgus stress testing: apply radial deviation force to the thumb MCP joint — (1) in full extension (tests accessory UCL and volar plate); (2) in 30° MCP flexion (isolates the proper UCL); compare with the contralateral thumb; instability >30–35° of radial deviation in flexion OR >15° compared to the contralateral side = complete UCL tear; instability only in extension with stability in flexion = partial or accessory ligament tear; test with and without anaesthetic block — pain may mask true instability; IMPORTANT: avoid performing valgus stress if a Stener lesion is suspected and MRI has not been obtained — aggressive stressing of a Stener lesion may further displace the ligament
• Grading of UCL injury: partial tear (Grade I/II) — some intact fibres; pain and tenderness but no instability on stress testing; complete tear (Grade III) — no intact fibres; instability on stress testing; Stener lesion may be present

• Plain radiographs: AP, lateral, and oblique views of the thumb; assess for avulsion fracture at the proximal phalanx base (the UCL avulses a bony fragment in approximately 30% of cases — `gamekeeper`s fracture`); a large avulsion fragment involving >20–25% of the articular surface with displacement requires ORIF; small non-displaced avulsion fragments can be treated non-operatively with immobilisation
• MRI: investigation of choice for complete UCL tears to confirm or exclude a Stener lesion; MRI is not required for all UCL injuries — if clinically clearly a partial tear (no instability on stress testing), conservative management is appropriate without imaging; MRI should be obtained for complete tears (instability on stress testing) to guide surgical vs conservative management; sensitivity and specificity for detecting Stener lesions on MRI approximately 90–96%
• USS: dynamic assessment by an experienced radiologist can identify the Stener lesion; useful and accessible; operator-dependent; lower sensitivity than MRI for distinguishing partial from complete tears

• Acute vs chronic repair outcomes: acute UCL repair (within 3–4 weeks of injury) achieves excellent results in >90% of cases — good stability, minimal morbidity; delayed repair (3 weeks to 3 months) is more technically challenging but still achievable; chronic UCL insufficiency (>3–6 months) requires reconstruction (tendon graft) as primary repair tissue quality is poor; the distinction between acute, subacute, and chronic guides surgical planning — early referral for suspected complete UCL tears is therefore important
• Radial collateral ligament (RCL) injury of the thumb MCP: the radial collateral ligament injury (forced ulnar deviation) is much less common than UCL injury; the RCL does not have an equivalent of the Stener lesion (the adductor aponeurosis is only on the ulnar side); most RCL injuries heal with conservative treatment; the RCL is involved in less pinch-critical stability than the UCL, so functional deficit from RCL tears is generally less significant than UCL tears
• UCL of the finger MCP joints: the UCL of the index through little finger MCP joints can also be injured, particularly the index finger radial collateral ligament (forced ulnar deviation of the index) and the little finger ulnar collateral ligament; the same principles of assessment (stress testing, Stener equivalent in fingers — less common than in the thumb) apply; most finger MCP collateral ligament injuries heal conservatively with neighbour strapping and early mobilisation

• Skier`s thumb: acute UCL injury from forced radial deviation (valgus stress); Stener lesion present in ~50–80% of complete tears; Stener = absolute surgical indication
• Stener lesion: torn UCL end lies superficial to the adductor aponeurosis; cannot heal spontaneously; MRI is the investigation of choice to confirm; `yo-yo sign` on MRI; palpable `Stener bump`
• Valgus stress test: instability >30–35° in 30° MCP flexion OR >15° vs contralateral = complete tear; test in flexion to isolate proper UCL; avoid aggressive stressing before MRI if Stener suspected
• Partial tear (no instability): thumb spica splint 4–6 weeks; conservative; no surgery
• Complete tear + Stener lesion: surgical repair; retrieve UCL from beneath aponeurosis; suture anchor to proximal phalanx; K-wire for 4 weeks; best results within 3–4 weeks of injury
• Bony avulsion >20–25% articular surface + displaced: ORIF; <20% non-displaced: conservative
• Chronic insufficiency (gamekeeper`s thumb): reconstruction with tendon graft (palmaris longus / FCR strip); or MCP arthrodesis for arthritic low-demand patients
• UCL anatomy: proper UCL = taut in flexion (primary stabiliser); accessory UCL = taut in extension; adductor aponeurosis overlies UCL superficially — creates Stener lesion when UCL tears
• RCL injury: less common than UCL; no Stener equivalent; generally conservative treatment; less functional impairment than UCL tears
• Acute repair: >90% excellent results; delayed repair (3 weeks–3 months): more difficult but achievable; chronic (>3–6 months): requires reconstruction — primary repair not possible