Skier's Thumb: The Injury Everyone Calls "Just a Sprain" | Form & Function MD
ORTHO / UPPER EXTREMITY

Skier's Thumb: The Injury Everyone Calls “Just a Sprain”

Form & Function MD · Dr. Ben, MD

Dr. Ben, MD · Orthopaedic Hand & Upper Extremity Surgeon

Every winter — and honestly, every boating season here on the Cape Fear coast — I see a version of the same injury: someone falls, catches themselves badly, and the base of the thumb takes the force. Most walk away thinking they've sprained it. A meaningful number of them have torn the ulnar collateral ligament, and that distinction changes everything about how the injury should be treated.

Why the mechanism matters

The name comes from the classic ski injury — a pole strap catches around the thumb during a fall, forcing it backward and outward (radial deviation with hyperextension) while the rest of the hand goes a different direction. But I see the identical injury from a fall onto an outstretched hand, a tackle in football, a dog leash yanked hard, or a hand slipping off a dock rail during a fall. The mechanism, not the sport, is what matters.

The ulnar collateral ligament (UCL) sits on the inside of the thumb's base joint (the MCP joint) and is what allows you to pinch with any real force — turning a key, gripping a jar lid, holding a fishing rod under tension. Tear it, and pinch strength drops immediately and noticeably.

A sprain stretches. A tear doesn't heal itself back into position — and in this joint, that distinction is easy to miss on exam.

The exam that actually separates a sprain from a tear

Swelling and pain look identical in the first 48 hours whether the ligament is partially or completely torn. What separates them is a stress test — gently applying a valgus (outward) force to the thumb's base joint at both 0 and 30 degrees of flexion, and comparing the amount of laxity to the uninjured thumb. A meaningful side-to-side difference, especially with a soft or absent endpoint, points toward a complete tear.

When imaging changes management
  • X-ray first, to rule out an avulsion fracture at the ligament's attachment point
  • MRI or ultrasound if a Stener lesion is suspected — where the torn ligament flips out from under the adductor aponeurosis and cannot re-approximate on its own
  • A confirmed Stener lesion does not heal with immobilization alone, regardless of how long you wait

Treatment: why timing matters more here than in most hand injuries

A partial tear with a stable joint on exam does well in a thumb spica splint for 4–6 weeks, followed by progressive strengthening. A complete tear with a Stener lesion is a different conversation — surgical repair within roughly the first 3–4 weeks reliably restores stability and function. Waited-out beyond that window, the ligament can retract and scar in a shortened position, and reconstruction becomes more involved than a straightforward repair.

The bottom line for patients
Any thumb injury with instability on pinch, marked swelling at the base of the thumb, or bruising along the inner edge deserves an exam within the first one to two weeks — not because every case needs surgery, but because the cases that do need it have a real window to get the best outcome.
  • Rhee PC, et al. Management of thumb ulnar collateral ligament injuries. J Am Acad Orthop Surg. 2012.
  • Ritting AW, et al. Ulnar collateral ligament injury of the thumb metacarpophalangeal joint. Clin Sports Med. 2010.