Skier’s Thumb: UCL Injury at the Base of the Thumb
Skier's Thumb: UCL Injury at the Base of the Thumb
A thumb bent sideways in a fall or by a ski pole commonly tears the UCL — the ligament that makes pinching possible. Whether it needs surgery or a cast depends on one critical distinction. Here is how to tell, and what happens if it is missed.
Skier’s Thumb — The Ligament at the Base of the Thumb
The ulnar collateral ligament (UCL) of the thumb MCP joint is the ligament on the inner (pinch) side of the base of the thumb. It is what allows you to pinch against resistance — holding a key, turning a screwdriver, or grasping a pen. When it tears, the thumb becomes unstable and weak at the base, making precise pinch and grip painful and unreliable.
The classic mechanism: a ski pole forced into the thumb during a fall, bending the thumb radially and rupturing the UCL. But the same injury occurs in football, basketball, handball, and any fall on an outstretched hand where the thumb is caught in radial deviation.
Partial vs. Complete Tear — The Critical Distinction
The management of thumb UCL injury is entirely determined by whether the tear is partial or complete — and specifically whether a Stener lesion is present.
Partial Tear
The ligament is stretched or partially divided but maintains some continuity and provides some stability on testing. The thumb does not open grossly abnormally on valgus stress compared to the other side.
Treatment: Thumb spica cast or brace for 4–6 weeks. Gradual return to activity after confirmed clinical healing. No surgery required in the majority of partial tears.
Complete Tear
The UCL is fully divided. The thumb opens abnormally on valgus stress (typically >30 degrees of opening, or >15 degrees more than the contralateral thumb). In approximately 80% of complete tears, a Stener lesion is present.
Treatment: Surgical repair is required for complete tears with a Stener lesion. Without surgery, the ligament cannot heal in its correct position and the thumb remains permanently unstable.
When the UCL tears completely, its distal end can retract and flip superficial to the adductor pollicis aponeurosis — a fibrous layer that normally overlies the ligament. This interposes the aponeurosis between the torn ligament ends, physically blocking healing even with cast immobilisation. MRI confirms whether a Stener lesion is present — which is why every significant thumb UCL injury should be assessed by a hand surgeon before deciding on cast vs. surgery.
Surgical Repair
UCL repair is performed under local or regional anaesthesia as an outpatient procedure. The Stener lesion is reduced, the adductor aponeurosis is reflected, and the torn UCL is reattached to the base of the proximal phalanx with a suture anchor. The repair is protected in a thumb spica splint or cast for 4–6 weeks post-operatively, followed by therapy.
Recovery: Cast 4–6 weeks → hand therapy 4–6 weeks → return to full grip and pinch: 3 months → return to skiing or contact sport: 3–4 months. Success rate of acute repair: 90%+. See Thumb Ligament Injury →
X-Ray First — Then MRI
X-ray should be performed immediately after a significant thumb injury to exclude an avulsion fracture at the UCL insertion (where the ligament pulls off a fragment of bone). A large avulsion fracture (>30% of the joint surface or displaced) is also a surgical indication. MRI is then used to confirm UCL tear severity and detect Stener lesion. Do not delay evaluation — acute repair within 3 weeks produces better outcomes than chronic reconstruction. See Thumb Ligament Injuries →
Frequently Asked Questions
Skier’s thumb (gamekeeper’s thumb) is a sprain or rupture of the ulnar collateral ligament (UCL) of the thumb MCP joint — the ligament on the inner side of the base of the thumb. It is the most common skiing injury to the upper extremity, caused by forced radial deviation of the thumb when a ski pole impacts the ground during a fall. The UCL resists sideways stress at the base of the thumb — when torn, pinch and grip are significantly weakened.
A partial UCL tear presents with pain and tenderness at the inner thumb base but relative stability on valgus stress testing — the thumb does not open more than 30 degrees or does not open more than 15 degrees greater than the other side. A complete tear presents with the same tenderness plus gross instability on valgus stress — the thumb opens significantly further than normal. X-ray should be performed first to exclude an avulsion fracture. Complete tears almost always require surgical repair; partial tears are managed in a thumb spica cast for 4–6 weeks.
A Stener lesion occurs when the completely torn UCL retracts and becomes displaced outside (superficial to) the adductor pollicis aponeurosis — a fibrous layer that normally lies over the ligament. The interposed aponeurosis physically prevents the ligament from healing in its correct position even with cast immobilisation. A Stener lesion is present in approximately 80% of complete UCL tears and is the primary reason complete tears require surgery: without removing the interposed tissue and reattaching the ligament to bone, the thumb will remain permanently unstable. MRI confirms Stener lesion presence before surgery.
Partial UCL tears treated in a cast: return to sport in the cast is possible for activities that do not require thumb loading (running, stationary cycling). Return to skiing or contact sport: after cast removal and confirmation of healing at 4–6 weeks, typically 6–8 weeks total. Complete tears requiring surgery: return to skiing or contact sport at 3–4 months post-operatively once the repair has healed and grip and pinch strength are restored.
An untreated complete UCL tear — particularly one with a Stener lesion — results in chronic thumb MCP instability. The thumb gives way with pinching and gripping, causing pain and significant functional limitation. Over time, chronic instability leads to post-traumatic arthritis at the MCP joint. Chronic reconstruction (with a tendon graft) is possible but produces less reliable outcomes than acute repair. Early treatment gives the best results.
Skier's Thumb? Get Assessed Before It Becomes Chronic.
Acute UCL repair succeeds in 90%+ of cases. Delayed repair is more complex. No referral needed.
Stephen Chambers, M.D.
Dual Board-Certified Hand & Upper Extremity Surgeon · Raleigh Orthopaedic
