An anatomical study of the mechanical interactions of flexor digitorum superficialis and profundus and the flexor tendon sheath in zone 2

Abstract

The mechanical interactions of tendon loading and motion between FDS and FDP tendons and the distal edge of the A2-pulley (DEA2) were investigated in cadaveric hands. The FDP tendon showed a two-stranded contrarotational spiral of tendon fibres, their course parallel to the FDS fibres. On loading, the FDP tendon changed cross-sectional shape and the two slips of FDS moved closer together, applying lateral force on the FDP tendon. The formula DEA2-MCP/proximal phalanx length was calculated as 0.64 +/- 0.052 mm/mm. Excursions of bifurca and chiasma were measured relative to the DEA2. In full extension the bifurca was well proximal to the DEA2, the chiasma always distal. In flexion, the chiasma approximated to DEA2 level. Therefore, an additional anteroposterior force should exist at DEA2 level between FDS and the DEA2 on the FDP-tendon. The changes in tendon shape and the lateral- and anteroposterior forces produce a "compressional" mechanism on FDP by FDS which may alter frictional resistance. This mechanism is compared with the Chiropteran tendon locking mechanism.