Clinical aspect of dorsum of hand

Extensor apparatus

This is called dorsal digital expansion or gextensor expansion and it covers the dorsum of the proximal phalanx and then wraps around the dorsal and collateral aspects of the metacarpophalangeal joints. The base of the expansion is connected to the extensor digitorum tendon. It then forms a hood called extensor hood which is moveable. This hood is connected to the tendons of lumbricals and the palmar interossei distally and also to the dorsal interossei proximally. Because of the connections to the lumbricals and interossei, the apparatus is capable of extending the interphalangeal joints, while flexing the metacarpophalangeal joints. This is the writing position.

1 collateral slip 2 middle slip 3 lumbrical 4 palmar interossei 5 dorsal interossei  6 extensor digitorum tendon

When the ulnar nerve that supplies the lumbricals and interossei muscles, is damage, then the hand is placed in the position opposite to the writing position. The interphalangeal joints are flexed while the metacarpophalangeal joints are extended. The way to correct this effect is tendon transplant in which the tendons of the flexor digitorum superficialis (supplied wholly by median nerve) are split and connected in each finger to the extensor expansion. This then replaces the action of the lumbricals and interossei and allows the writing position to be maintained once more.


Imaging anatomy
Surgical anatomy
Anesthetic anatomy
Endoscopic anatomy



Dorsum of hand

Lymphatic drainage
Clinical anatomy


Injuries to carpus
See body map


Electronic School of Medicine
Creator: Oluwole Ogunranti