Page 214 - Clinical Anatomy

ECA3 7/18/06 6:45 PM Page 199

The anatomy of upper limb deformities 199

The ulnar nerve, in its vulnerable position behind the medial epicondyle
of the humerus, may be damaged in fractures or dislocations of the elbow; it
is also frequently divided in lacerations of the wrist. In the latter case, all the
intrinsic muscles of the fingers (apart from the radial two lumbricals) are
paralysed so that the hand assumes the clawed position already described
under Klumpke’s palsy (Fig. 144). The clawing is slightly less intense in the
2nd and 3rd digits because of their intact lumbricals, supplied by the
median nerve. In late cases, wasting of the interossei is readily seen on
1
inspecting the dorsum of the hand. Sensory loss over the ulnar 1– fingers is
2
present.
If the nerve is injured at the elbow, the flexor digitorum profundus to
the 4th and 5th fingers is paralysed so that the clawing of these two fingers
is less intense than in division at the wrist. Paralysis of the flexor carpi
ulnaris results in a tendency to radial deviation of the wrist.
Division of the ulnar nerve leaves a surprisingly efficient hand. The
long flexors enable a good grip to be taken; the thumb, apart from loss of
adductor pollicis, is intact and sensation over the palm of the hand is
largely maintained. Indeed, it may be difficult to determine clinically
with certainty that the nerve is injured; a reliable test is loss of ability to
adduct and abduct the fingers with the hand laid flat, palm downwards
on the table; this eliminates ‘trick’ movements of adduction and abduc-
tion of the fingers brought about as part of their flexion and extension
respectively.
The median nerve is occasionally damaged in supracondylar fractures
but it is in greatest danger in lacerations of the wrist.
If divided at the wrist, only the thenar muscles (excluding adductor pol-
licis) and the radial two lumbricals are paralysed and wasting of the thenar
muscles occurs. The best clinical test for this is to ask the patient, with his
hand resting palm upwards on the table, to touch a pencil held above the
thumb. Failure to be able to do this, (abduction), is diagnostic of paralysis of
abductor pollicis brevis. It might be thought that such a lesion is relatively
trivial since the only motor defect is loss of accurate opposition movement
of the thumb to other fingers. In point of fact this injury is a serious disabil-
1
ity because of the loss of sensation over the thumb, adjacent 2– fingers and
2
the radial two-thirds of the palm of the hand, which prevents the accurate
and delicate adjustments the hand makes in response to tactile stimuli
(Fig. 144).
If the median nerve is divided at the elbow, there is serious muscle
impairment. Pronation of the forearm is lost and is replaced by a trick
movement of rotation of the upper arm. Wrist flexion is weak and accompa-
nied by ulnar deviation, since this now depends on the flexor carpi ulnaris
and the ulnar half of flexor digitorum profundus.
Volkmann’s contracture of the hand follows ischaemia and subsequent
fibrosis and contraction of the long flexor and extensor muscles of the
forearm (Fig. 144).
The deformities are readily explained as follows:
1◊◊Since the flexors of the wrist are bulkier than the extensors, their fibrous
contraction is greater and the wrist is therefore flexed.