Page 213 - Clinical Anatomy

ECA3 7/18/06 6:45 PM Page 198

198 The upper limb

Fig. 144◊Deformities of
the hand. (a) Radial palsy
—wrist drop. (b) Ulnar
nerve palsy—‘main en
griffe’ or claw hand.
(c) Median nerve palsy—
‘monkey’s hand’.
(d) Volkmann’s
contracture—another
claw hand deformity. The
pale blue areas represent
the usual distribution of
anaesthesia.

Damage to the main trunk of the radial nerve results in a wrist drop due
to paralysis of all the wrist extensors (Fig. 144). Damage to the posterior
interosseous nerve, however, leaves extensor carpi radialis longus intact, as
it is supplied from the radial nerve above its division; this muscle alone is
sufficiently powerful to maintain extension of the wrist.
The disability produced by a wrist drop is inability to grip firmly, since,
unless the flexor muscles are stretched by extending the wrist, they act at a
mechanical disadvantage. Try yourself to grip strongly with the wrist
flexed and realize how, by operative fusion of the wrist joint in extension,
the weakness produced by a radial nerve paralysis would be overcome.
Nerve overlap means that division of the radial nerve produces only a
small area of anaesthesia of the dorsum of the hand between the 1st and
2nd metacarpals.