Corpus: Extensor expansion of fingers

The robust and flexible extensor expansion consist of longitudinally, transversely, and vertically interwoven fibrous tissues. They serve as the insertion points for several hand extensors, whose muscle bellies are located in the forearm. In turn, they insert via the tracts onto the phalanges of the fingers. The following distinctions are made:

Intermedius Tract

The intermedius tract, or middle tract, extends dorsally on the fingers distally and reaches up to the middle phalanx. It primarily receives fibers from the terminal tendons of the long extensors originating in the forearm. It is further divided into a medial part (Pars medialis) and a lateral part (Pars lateralis).

Lateral Tract

The lateral tract extends on both sides of each finger distally and reaches the end phalanx. It receives the terminal tendons of the lumbrical muscles of the hand, and to a lesser extent, those of the interosseous muscles.

The following muscles insert via extensor expansion on the respective fingers:

• extensor indicis muscle: Extensor expansion of d2
• extensor digiti minimi muscle: Extensor expansion of d5
• abductor digiti minimi muscle: Extensor expansion of d5 on the ulnar side
• extensor digitorum muscle: Extensor expansion from d2 to d5
• lumbrical muscles of the hand: Extensor expansion from d2 to d5 on the radial side
• interossei palmares muscles: Extensor expansion of d2, d4, or d5
• dorsal interossei muscles: Extensor expansion from d2 to d5