The abductor pollicus longus is a muscle which begins at the top of the radius (forearm bone) and runs across the carpus (wrist), ending on the first metacarpal bone just below the carpus (wrist). It acts to extend and allow some abduction (movement away from the midline) of the first digit, our equivalent is the thumb. A tendon is the tough, fibrous part of a muscle which attaches the muscle to bone.
Chronic strain of the tendon leads to a fibrosis (thickening), or occasionally ossification (bone formation) within the tendon. This restricts movement of the tendon in its sheath (protective covering layer) causing pain and lameness.
Affected dogs are generally large breeds that present with mild to moderate forelimb lameness. There may be palpable swelling or thickening of the inside of the carpus (wrist joint) with pain on flexion of the joint.
Diagnosis is usually confirmed through radiographs showing signs of soft tissue swelling along with bony proliferation at the medial (inside) aspect of the bottom of the radius (long bone of the forearm). The condition can be bilateral (affecting both forelimbs).
Conservative treatment with anti-inflammatory drugs is rarely effective so other treatments may be required.
In mild to moderate cases, injections of long-acting corticosteroids may be tried initially and can be very helpful. With doses depending on the size of the patient, a steroid drug can be injected into the area of the tendon sheath (the tendon’s protective covering) on the inner surface of the lower radius in the area of the inflammation. The treatment can be repeated in 2 to 3 weeks.
In chronic cases or if the lameness persists, surgical removal of the proliferative soft tissue and bone can be undertaken to free the tendon. This is accomplished through an incision over the inner aspect of the bottom of the carpus (wrist) allowing identification of the tendon and its sheath. Fibrous or bony attachments are released until the tendon is seen to freely move.
Tenotomy is a surgical procedure whereby the tendon itself is cut or ‘released’. This procedure has been associated with relief of clinical signs but also appears to lead to the development of significant carpal osteoarthritis (arthritis of the wrist). This may result from the fact that the abductor pollicus longus tendon helps provide stability to the carpal (wrist) joint. Consequently, tenotomy is not recommended as a primary form of surgical therapy.
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