Page 212 - Clinical Anatomy

ECA3 7/18/06 6:45 PM Page 197

Course and distribution of nerves 197

Note that there is considerable variation in the exact cutaneous distribu-
tion of the nerves in the hand; for example, the ulnar nerve may encroach
on median territory and supply the whole of the 4th and 5th digits
(Fig. 143).

The anatomy of
upper limb deformities

Many deformities of the upper limb, particularly those resulting from
nerve injuries, are readily interpreted anatomically.
Brachial plexus injuries may occur from traction on the arm during birth.
The force of downward traction falls upon roots C5 and 6, resulting in
paralysis of the deltoid and short muscles of the shoulder, and of brachialis
and biceps which flex and supinate at the elbow. The arm, therefore, hangs
limply by the side with the forearm pronated and the palm facing back-
wards, like a porter hinting for a tip (Erb–Duchenne paralysis). In adults this
lesion is seen in violent falls on the side of the head and shoulder forcing
the two apart and thus putting a tearing strain on the upper roots of the
plexus.
Upward traction on the arm (e.g. in a forcible breech delivery) may tear
the lowest root, T1, which is the segmental supply of the intrinsic hand
muscles. The hand assumes a clawed appearance because of the unop-
posed action of the long flexors and extensors of the fingers; the extensors,
inserting into the bases of the proximal phalanges, extend the m/p joints
while the flexor profundus and sublimis, inserting into the distal and
middle phalanges, flex the i/p joints (Klumpke’s paralysis). There is often an
associated Horner’s syndrome (ptosis and constriction of the pupil), due to
traction on the cervical sympathetic chain.
A mass of malignant supraclavicular lymph nodes or the direct inva-
sion of a pulmonary carcinoma (Pancoast’s syndrome) may produce a similar
neurological picture by involvement of the lowest root of the plexus.
Not infrequently, the lower trunk of the plexus (C8, T1) is pressed upon
by a cervical rib, or by the fibrous strand running from the extremity of such
a rib, resulting in paraesthesiae along the ulnar border of the arm and
weakness and wasting of the small muscles of the hand.
The radial nerve may be injured in the axilla by the pressure of a crutch
(‘crutch palsy’) or may be compressed when a drunkard falls into an intoxi-
cated sleep with the arm hanging over the back of a chair (‘Saturday night
palsy’). Fractures of the humeral shaft may damage the main radial nerve,
whereas its posterior interosseous branch, to the extensor muscles of the
forearm, may be injured in fractures or dislocations of the radial head. An
ill-placed incision to expose the head of the radius taken more than three
fingers’ breadth below the head will divide the nerve as it lies in the supina-
tor muscle.