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Encyclopedia > Extensor expansion

An extensor expansion (dorsal expansion, dorsal hood) is an anatomical term that refers to the flattened tendons (aponeurosis) of extensor muscles that run into the back of the hand. At the distal end of the metacarpal, the extensor tendon will expand to form a hood, which covers the back and sides of the head of the metacarpal and the proximal phalanx. Aponeurosis is the singular of Aponeuroses Grays Anatomy states that Aponeuroses are flattened or ribbon-shaped tendons, of a pearly white color, iridescent, glistening, and similar in structure to the tendons. ... The metacarpus is the intermediate part of the hand skeleton that is located between the fingers distally and the carpus which forms the connection to the forearm. ... The phalanges in a human hand Bones of the human hand. ...


The expansion soon divides into three bands:

  • Two lateral bands pass on either side of the proximal phalanx and stretch all the way to the distal phalanx. The lumbricals of the hand, the dorsal interossei of the hand, and the palmar interossei insert on these bands.
  • A single median band passes down the middle of the finger along the back of the proximal phalanx, ending at the base of the middle phalanx.

A band known as the retinacular ligament runs obliquely along the middle phalanx, and connects the fibrous digital sheath on the anterior side of the phalanges to the extensor expansion. The lumbrical muscles are intrinsic muscles in the fingers that allow flexion at the metacarpophalangeal joints, while maintaining extension at the interphalangeal joints. ... The dorsal interossei of the hand are muscles that occupy the space between the metacarpals. ... The palmar interossei (interossei volares) are small muscles in the hand that lie on the anterior aspect of the metacarpals. ...


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