The functional significance of the long extensors and juncturae tendinum in finger extension.

To determine the role of the long extensors and soft tissues in the extension and interaction of the fingers, we applied traction to the extensors and measured the angles of the finger joints. The tendons, juncturae tendinum and intertendinous fascia, and the web between the fingers were sequentially sectioned, and the effects on the joints were again determined with tendon traction. Traction produced hyperextension of the metacarpophalangeal joints and some extension of the interphalangeal joints, although the latter remained partially flexed, producing a clawhand. Cutting the long extensor tendons had no effect on the interaction between adjacent fingers. Traction on the extensor digitorum communis to the index and the extensor indicis proprius produced the same extension of index finger joints and adjacent digits. Traction on the extensor digitorum communis to the index produced 32% of the maximal extension of the long finger MP joint. We reduced this to 22% by cutting the juncturae and intertendinous fascia and to 5% by cutting the web. The interaction between fingers was greater on the ulnar half of the hand because of the juncturae but was similarly reduced by ablative cuts of these structures.