Anatomy, Shoulder and Upper Limb, Hand Flexor Digitorum Profundus Muscle

The flexor digitorum profundus (FDP) is an extrinsic hand muscle that flexes the metacarpophalangeal (MCP) and distal interphalangeal (DIP) joints of the medial 4 fingers. This muscle originates from the upper three-fourths of the volar and medial surfaces of the ulna, interosseous membrane, and deep forearm fascia. The FDP lies in the deep volar forearm compartment (see . Deep External Hand Flexors). The FDP tendons insert on the bases of the medial 4 distal phalanges, deep to the flexor digitorum superficialis (FDS) tendons. The medial 3 FDP tendons are partially attached as they pass through the carpal tunnel. The FDP tendon of the index finger separates from its medial 3 counterparts proximal to the flexor retinaculum. Since the FDP tendons arise at or distal to the wrist joint, muscle contraction produces mass action movement in all 4 tendons and allows for a power grip.