Extensor mechanism

The extensor mechanism is the integrated tendinous network on the dorsum of each digit. The extensor digitorum communis tendon broadens over the proximal phalanx into a fibrous hood that receives contributions from the lumbrical and interosseous muscles. Over the proximal interphalangeal joint the mechanism divides into a central slip — inserting on the dorsal base of the middle phalanx — and two lateral bands that course along the sides of the middle phalanx and reunite distally to form the terminal tendon that inserts on the dorsal base of the distal phalanx. This arrangement allows the long extensor and the intrinsic muscles to coordinate extension across all three finger joints.