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

extensor tendons In anatomy, extension is a movement of a joint that increases the angle between two bones or body surfaces at a joint. Extension usually results in straightening of the bones or body surfaces involved. For example, extension is produced by extendin ...

insert into the

phalanges The phalanges (singular: ''phalanx'' ) are digital bones in the hands and feet of most vertebrates. In primates, the thumbs and big toes have two phalanges while the other digits have three phalanges. The phalanges are classed as long bones. ...

. These flattened tendons (

aponeurosis An aponeurosis (; plural: ''aponeuroses'') is a type or a variant of the deep fascia, in the form of a sheet of pearly-white fibrous tissue that attaches sheet-like muscles needing a wide area of attachment. Their primary function is to join musc ...

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

metacarpal In human anatomy, the metacarpal bones or metacarpus form the intermediate part of the skeletal hand located between the phalanges of the fingers and the carpal bones of the wrist, which forms the connection to the forearm. The metacarpal bones ...

, 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 ( grc, φάλαγξ; plural phalanxes or phalanges, , ) was a rectangular mass military formation, usually composed entirely of heavy infantry armed with spears, pikes, sarissas, or similar pole weapons. The term is particularly use ...

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 flex the metacarpophalangeal joints, and extend the interphalangeal joints. p. 97 The lumbrical muscles of the foot also have a similar action, though they are of less clinical concern. S ...

extensor indicis muscle In human anatomy, the extensor indicis roprius'' is a narrow, elongated skeletal muscle in the deep layer of the dorsal forearm, placed medial to, and parallel with, the extensor pollicis longus. Its tendon goes to the index finger, which it exte ...

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 hand's midline (ray of middle finger) and assist in flexion at the metacarpophalangea ...

, and

palmar interossei In human anatomy, the palmar or volar interossei (interossei volares in older literature) are three small, unipennate muscles in the hand that lie between the metacarpal bones and are attached to the index, ring, and little fingers. They are small ...

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