Skier’s thumb is a sprain or tear of the ligament on the inner side of your thumb, at the large knuckle where the thumb meets the hand. It happens when the thumb is forced sharply outward, most classically when a skier falls while gripping a pole. The injury ranges from a mild stretch to a complete rupture, and how it’s treated depends entirely on how much damage the ligament sustained.
The Ligament Involved
The injured structure is the ulnar collateral ligament (UCL), a short, thick band roughly 12 to 14 mm long that runs along the inner edge of your thumb’s main knuckle joint. It connects the base of the first thumb bone to the knuckle above it, and its job is to keep the thumb stable when you grip, pinch, or push against something. Without a functioning UCL, simple tasks like turning a key, opening a jar, or gripping a pen become difficult or painful because the thumb buckles sideways under any lateral force.
How the Injury Happens
The classic scenario involves a skier catching a fall with an outstretched hand while still holding a ski pole. The pole, or the strap wrapped around the wrist, levers the thumb outward with enough force to stretch or tear the UCL. But you don’t need to be on a mountain for this to happen. Any forceful bending of the thumb away from the hand can cause the same injury: catching a ball awkwardly, breaking a fall on flat ground, or even twisting the thumb during a car accident. The name “skier’s thumb” stuck because the sport accounts for a disproportionate number of cases.
Grades of Injury
Doctors classify the injury into three grades based on how much of the ligament is torn and how unstable the joint becomes:
- Grade I: An incomplete tear with no looseness in the joint. The ligament is stretched or partially damaged but still holds the thumb stable.
- Grade II: A larger but still incomplete tear. The joint shows some asymmetric looseness compared to the other thumb.
- Grade III: A complete rupture. The ligament is fully torn, and the thumb joint opens significantly when stressed. An angulation greater than 35 degrees, or a difference of more than 15 degrees compared to the uninjured thumb, points to a complete tear.
Why Complete Tears Are Different
A partial tear can heal on its own with proper immobilization. A complete tear often cannot, and the reason comes down to anatomy. In 64% to 87% of complete UCL ruptures, the torn end of the ligament flips over a nearby sheet of muscle tissue and gets trapped on the wrong side of it. This is called a Stener lesion. The muscle tissue acts as a physical barrier between the two torn ends, preventing them from ever reconnecting. No amount of rest or splinting will fix this because the ligament simply cannot reach itself to heal. Surgery is the only option when a Stener lesion is present.
How It’s Diagnosed
After examining the thumb for swelling, bruising, and tenderness along the inner edge of the knuckle, a doctor will perform a stress test. This involves stabilizing the hand and gently pushing the thumb outward to see how far the joint opens. If the joint angles more than 30 degrees, or if there’s a difference greater than 15 degrees compared to the other thumb, a complete tear is likely and surgery is typically recommended.
An X-ray is often taken first to check for a fracture. Sometimes the ligament tears away with a small chip of bone still attached, and displacement of that bone fragment can confirm that the tear is complete. If the stress test and X-ray leave any ambiguity, an MRI or ultrasound can reveal exactly where the tear is and whether a Stener lesion has formed.
Treatment Without Surgery
Grade I and most grade II injuries are treated with immobilization. You’ll wear a thumb spica splint or cast that locks the thumb in place while allowing the rest of your fingers to move. This period of protection typically lasts about four weeks, during which the ligament repairs itself. After the splint comes off, you’ll start gentle range-of-motion exercises to regain flexibility and strength. Most people with partial tears recover full function, though some stiffness or mild discomfort during heavy gripping can linger for a few months.
When Surgery Is Needed
Complete tears, displaced bone fragments, and confirmed Stener lesions all require surgical repair. The procedure involves stitching the torn ligament back to bone, sometimes using a small anchor to secure it. In cases where the ligament tissue is too damaged to repair directly, a reconstruction using tendon tissue may be necessary.
Recovery after surgery follows a more structured timeline. Early controlled motion is now favored over prolonged immobilization, as studies show better outcomes when gentle movement begins sooner. Some patients return to light activity within 5 to 8 weeks. Full return to sport or heavy hand use typically takes around 10 to 14 weeks, though your thumb will need protection with a brace or tape during physical activity for some time after that.
What Happens if You Ignore It
Skier’s thumb is easy to dismiss as a “jammed thumb,” and many people try to push through it. An untreated complete tear leads to chronic instability. The thumb wobbles under stress, pinch strength drops significantly, and over time the joint surfaces wear unevenly. This accelerates arthritis in the thumb knuckle, which can become painful enough to require a more complex reconstructive surgery years later. The earlier a complete tear is repaired, the better the long-term outcome.
Prevention on the Slopes
The traditional way of threading your hand through the pole strap and gripping over it is exactly what creates the lever that forces the thumb outward in a fall. Dropping the poles during a fall would prevent most of these injuries, but reflexes make that difficult. Some newer ski pole designs feature breakaway straps or grips that release under sudden force. If you use conventional poles, learning to let go during a fall, rather than bracing against the pole, is the simplest way to protect your thumbs.