An extensor expansion (extensor hood, dorsal expansion, dorsal hood, dorsal aponeurosis) is the special connective attachments by which the extensor tendons insert into the

phalanges The phalanges (: phalanx ) are digit (anatomy), digital bones in the hands and foot, feet of most vertebrates. In primates, the Thumb, thumbs and Hallux, big toes have two phalanges while the other Digit (anatomy), digits have three phalanges. ...

. These flattened tendons (

aponeurosis An aponeurosis (; : aponeuroses) is a flattened tendon by which muscle attaches to bone or fascia. Aponeuroses exhibit an ordered arrangement of collagen fibres, thus attaining high tensile strength in a particular direction while being vulnerable ...

) of extensor muscles span the proximal and middle phalanges. At the distal end of the

metacarpal In human anatomy, the metacarpal bones or metacarpus, also known as the "palm bones", are the appendicular bones that form the intermediate part of the hand between the phalanges (fingers) and the carpal bones ( wrist bones), which articulate ...

, 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 The phalanx (: phalanxes or phalanges) was a rectangular mass military formation, usually composed entirely of heavy infantry armed with spears, pikes, sarissas, or similar polearms tightly packed together. The term is particularly used t ...

Bands

The expansion soon divides into three bands: * 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 lumbricals are intrinsic muscles of the hand that flexion, flex the metacarpophalangeal joints, and extension (kinesiology), extend the Interphalangeal articulations of hand, interphalangeal joints. p. 97 The lumbrical muscle of the foot, lu ...

, extensor indicis muscle,

dorsal interossei of the hand In human anatomy, the dorsal interossei (DI) are four muscles in the back of the hand that act to abduct (spread) the index, middle, and ring fingers away from the hand's midline (ray of middle finger) and assist in flexion at the metacarpophal ...

, and

palmar interossei In human anatomy, the palmar or volar interossei (interossei volares in older literature) are four muscles, one on the thumb that is occasionally missing, and three small, unipennate, central muscles in the hand that lie between the metacarpal bo ...

insert on these bands. *A single median band passes down the middle of the finger along the back of the proximal phalanx, inserting into 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.

Function

The extensor expansion allows for contractile forces from the extensor compartment muscles to be transferred to the phalanges. It also balances the forces across the phalanges.

References

External links

* * Muscular system Tendons {{musculoskeletal-stub