Osteoarthritis (OA), or the degeneration of a joint, commonly occurs at the base of the thumb. OA at this joint is diagnosed with conventional radiographs (x-rays), but often can be recognized based on symptoms. Symptoms occur predominantly with pain at the base of the thumb, especially when performing tasks that require a pinch (i.e. pulling on socks). This disease progression can occur with a thumb deformity, but may be symptomatic without an obvious change in the thumbs appearance.
Wear and tear of the bones, and of the ligaments and muscles that surround the base joint (TMC, also called the CMC) of the thumb occurs commonly during tasks that require a resisted pinch or grip. Ligaments that normally provide joint support can become weak and lax and less able to absorb forces thereby contributing to degeneration at this joint.
Several deformities are possible with OA at the base of the thumb, but one particular deformity pattern (the Zig Zag deformity) is most common. With weakening of the stabilizing ligaments, the joint has a tendency to become flexed and adducted meaning the thumb moves closer into the palm of the hand. Over time, the small thumb muscles can tighten causing closure of the first web space making it difficult to move the thumb away from the palm. As this posture becomes fixed, the metacarpal phalangeal (MP) joint of the thumb compensates by overstretching into hyperextension. Eventually the interphalangeal (IP) joint may move into a flexed posture related to the change in pull of the soft tissue and tendons.
The key factors to consider when assessing orthotic intervention for a zigzag deformity are, how to counteract the deforming forces and how to position the thumb for function.
There a variety of options to assist with providing comfort and increased function for individuals with OA at the base of the thumb including the 3pp ThumSling, the Fix Comfort Thumb Brace, and CMCcare Thumb Brace.
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3pp ThumSling | Fix Comfort Thumb Brace | CMCcare Thumb Brace |
There doesn't have to be deformity for an orthosis to be beneficial. Symptoms will dictate the appropriateness of orthotic intervention. In advanced arthritis with fixed deformities, orthotic intervention may not be the appropriate choice and the patient should be referred to a hand surgeon for further evaluation.
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