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Sprained Thumb

Rounding a corner on the South Mountain race loop, your tires begin to dig into the soft shoulder. For a second, you think you're going to pull it out. But then the bike flips sideways, and you're flying off the trail. As you catch yourself, your thumb hangs up in the soft dirt and bends down towards your wrist.

A sprain is a stretching of ligaments -- the tissues that hold two bones together. In the thumb, you have these ligaments on the inner and outer sides of each joint, and on the underside of each joint. When an accident bends the joint in a direction it's not supposed to go (most commonly, bending backwards), it injures the ligament. Ligament injuries come in three degrees of seriousness: 1st degree = stretching, 2nd degree = partial tear, and 3rd degree = complete rupture.

If the spraining force bends the thumb straight back (in the direction of the thumbnail), the sprain usually won't be serious. But it forces the thumb laterally downward (force on the side of the thumb that faces the index finger, pulling it down towards the wrist), it can rupture the ulnar collateral ligament, making the thumb unstable.

A rupture of the ulnar collateral ligament (located on the side of the thumb right where it meets the skin fold coming over from the index finger) is serious. Of course, the same forces that sprain a thumb can also cause dislocation, tendon rupture, fracture, or volar plate injury. So you should assess careful for the signs of serious injury. Only if the injury seems trivial should you self-diagnose a sprain.

See the doctor for an injured finger if:
    there's significant swelling or deformity
    there's pain when the thumb is resting (after the first hour)
    you can't move the joint fully
    there's severe pain with motion of the thumb
    there's numbness or weakness
    there's weakness at the base of the thumb with pinching motion
    the thumb can be bent outward at either knuckle

Immediate care:
Rest, Ice, Compress, and Elevate. Immediately elevate the injured part and apply an ice bag. If the distant knuckle is injured, splint it. If the pain is at the first knuckle, you'll probably need to see the doctor for adequate splinting. (And maybe an x-ray.)

To assess the ulnar collateral ligament (UCL), have the injured thumb straight and out away from the hand. Put your index finger pad on the side of the thumb that faces the hand, right at the end. Put the tip of your good thumb right up against the other side of the thumb metacarpophalangeal joint (first knuckle or MCPJ).

Location of tenderness and swelling in ulnar collateral ligament injury.

bf-ucl2.jpg (7274 bytes)

bf-ucl.jpg (7740 bytes) While bracing the MCPJ of the injured thumb with your thumbtip, pull down with your index finger. If the thumb can be bent downward more than about a half-inch, the UCL is probably ruptured. See the doc.

Stress test for ruptured ulnar collateral ligament: pulling downward on the side of the thumb while bracing the MCPJ with the thumbtip. Compare to the normal side. The thumb can bent outward if the ligament is ruptured.


Ongoing care:
For the first 48 hours, repeat ice and elevation 1/4 of the time (for example, 30 minutes of ice every two hours). Continue splinting for a few days. As the pain subsides, return to activities. Often you can protect the injured finger by "buddy taping," taping it to an adjacent bigger stronger finger. It will take about three weeks for the sprain to heal. As you resume sports, remember the rule: "If it hurts, don't do it." If the finger becomes increasingly swollen, or remains weak or painful in routine use, go to the doctor.

Finger rehab:
After the first few days of splinting, start range of motion exercises.
Range of motion: Warm the finger for 10 minutes (heating pad or sink of warm water). Gently bend the finger until it begins to feel uncomfortable, then hold the stretch for 30 seconds. Rest for a minute, then do it again. Repeat 10 times. Now straighten the finger and hold for 30 seconds, rest a minute, and repeat 10 times. If the finger has increased discomfort after the exercises, ice the wrist for 20 minutes after the exercises. Do the exercises twice a day.

Watch for:
If the injured area doesn't improve promptly, see the doctor.

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