The ulnar collateral ligament connects the base of the thumb's proximal phalanx to the thumb's metacarpal bone on the ulnar aspect of the joint. The usual injury mechanism is radial deviation of the thumb, commonly caused by falling on the hand while holding a ski pole.
Sometimes when the ligament tears, it avulses part of the proximal phalanx at the ligament attachment.
Initially, patients have pain and point tenderness on the ulnar aspect of the thumb metacarpal joint. Long-term complications can include weakness and instability of the joint.
Diagnosis
Stress testing is done to check for radial deviation of the thumb; before testing, some patients require anesthesia (infiltration of a local anesthetic). The examiner stabilizes the radial side of the metacarpophalangeal joint of the thumb and pulls on the distal thumb in a radial direction. Both thumbs are tested, and the degree of laxity is compared.
Anteroposterior and lateral x-rays are taken to check for an avulsion fracture of the proximal phalanx. Sometimes stress x-rays are taken.
Treatment
Initial treatment is immobilization with a thumb spica splint (see figure Thumb spica splint) for several weeks. After a few weeks of wearing the splint, patients are instructed to take the splint off and do strengthening exercises, then put the splint back on. Patients should continue this regimen for 2 to 3 weeks.
Surgical repair is sometimes necessary (eg, if instability persists). After surgery, a thumb spica cast is worn for 6 to 8 weeks.
