The mechanical role of the digital fibrous sheath: application to reconstructive surgery of the flexor tendons.

The movements of flexion of the digital articular chain are dependent upon a vast functional complex comprising the long flexor tendons, their antagonist long extensor tendons, and the coupled action of the interosseous and lumbricales muscles. Based on theoretical biomechanical data backed up by experimental investigation, the authors emphasize the important role of the digital fibrous sheath in the mechanism of action of the long flexor tendon. Any proximal resection (even of minor degree) of the proximal pulley of the digit induces severe mechanical disturbances by enhancing flexion of the metacarpophalangeal joint to the detriment of the proximal interphalangeal joint. Conversely, distal resection of the pulley enhances flexion of the interphalangeal joint to the detriment of the metacarpophalangeal articulation, although the resulting abnormalities are less pronounced than those due to proximal resection. The fibrous pulley plays a role in tendinous orientation in the frontal plane and in digital orientation of the index finger where the angulation between the pulley and flexor tendon is most pronounced. In this latter case ulnar deviation of the second finger occurs on flexion. Reconstructive surgery of the long flexor tendons requires that the digital fibrous sheath, especially its proximal segment, be preserved. The metacarpophalangeal joint seems to be the most vulnerable to morphological modifications of the pulley, as stressed from the anatomical standpoint by the absence of insertion of the long flexor tendons on the proximal phalanx.