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Year |
2001 |
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Question Number |
169. |
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Category |
Select |
Question
Thumb adduction in low ulnar nerve palsy is provided by the:
1- extensor pollicis longus
2- extensor pollicis brevis
3- flexor pollicis brevis
4- first dorsal interosseous
5- accessory head of the flexor pollicis longus (Gantzer’s muscle).
Figures
Answer (click for answer)
Preferred response: 1
The power grip of the thumb is usually adducted and in neutral rotation. In this position it is best able to balance the force of all four fingers against the object that is to be grasped. The muscles that are most effective in holding the thumb tightly against an object with power grip are the adductor pollicis and the radial head of the first dorsal interosseous. These muscles are almost always supplied by the ulnar nerve.
After ulnar nerve injury, the thumb can be fully adducted through contraction of the extensor pollicis longus. However, thumb adduction by the EPL is extremely weak since the EPL has barely one half the adduction force of the radial head of the first dorsal interosseous and less than one fourth that of the adductor pollicis. The flexor pollicis longus also contributes to power grip but its important function is not as an adductor but as a thumb flexor.
Reference: Smith RJ: Tendon Transfers of the Hand and Forearm. Boston, MA, Little Brown, 1987, pp 85-102.