The incidence of fibrous arch overlying the motor branch of the ulnar nerve as it passes beneath the origin of the hypothenar muscles in Guyon's canal was investigated in dissections of 50 hands. Forty percent of the hands had a fibrous edge to the flexor digiti minimi muscle. The fibrous edge was a mean of 2 mm in width (range, 1-6 mm). Awareness of this fibrous arch will facilitate appropriate surgical management of ulnar-innervated intrinsic muscle weakness or wasting associated with ulnar compression at the wrist.
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