Review Question - QID 211963

Thumb Collateral Ligament Injury Etiology Pathophysiology QID: 211963 (SBQ17SE.78)

QID 211963 (Type "211963" in App Search)

A 27-year-old competitive skier fell one week ago onto his right hand. He has had persistent thumb pain with gripping since the fall. He is evaluated in your orthopedic hand clinic and found to have disrupted a ligament in his thumb with the decision for operative intervention. During the surgery, which of the following structures may block your reduction?

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53/1922

61/1922

12%

225/1922

13%

243/1922

69%

1325/1922

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The reduction of a ruptured ulnar collateral ligament (UCL) can be blocked by the adductor pollicis tendon aponeurosis, indicated by the letter "E" in the figure.

Ulnar collateral ligament rupture occurs with a hyperabduction force that goes through the MCPJ of the thumb. Patients present with ulnar sided thumb pain and on exam have valgus laxity at the MCPJ. It is associated with skiers who fall while holding their ski pole. Most often the ligament avulses off of the proximal phalanx. Treatment options include immobilization for partial tears, acute repair, or reconstruction in chronic injuries. Sometimes the UCL avulses off a piece of bone, which is identifiable on xray. At times the adductor pollicis aponeurosis becomes interposed between the torn ligament and its insertion and this requires surgical repair as the ligament is unable to scar back into its appropriate location. This phenomenon is called a Stener lesion.

Carlson et al. performed an anatomic study to accurately define the origin and insertion of the UCL and RCL of the thumb. Using 18 cadaveric thumbs they found that the UCL origin is 4.2mm from the dorsal surface and 5.3mm from the articular surface. Insertion on the proximal phalanx was measured at 2.8mm from the volar surface and 3.4mm from the articular surface.

Bean performed a biomechanical study evaluating UCL position on metacarpophalangeal joint range of motion. They found that palmar placement of the UCL origin increased radial deviation amount, while proximal movement decreased radial deviation. Dorsal displacement of the attachment on the proximal phalanx increased radial deviation, while distal placement decreased it. Distal and palmar placement of the insertion decreased flexion range of motion as well.

Figure A is a hand diagram with muscles and tendons indicated. The letters correspond as such: A - Opponens pollicis, B - Abductor pollicis brevis, C - Flexor pollicis brevis, D - Flexor pollicis longus, E - Adductor pollicis.

Incorrect Answers:
Answer 1-4 are different muscles or tendons of the hand that is not associated with interposition after the avulsion of the UCL from its insertion.