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 backwards, 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 unopposed 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 invasion 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 intoxicated 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.

Klumpke Palsy

Fig. 144 Deformities of the hand. (a) Radial palsy —wrist drop. (b) Ulnar nerve palsy—'main en griffe' or claw hand.

(d) Volkmann's contracture—another claw hand deformity. The pale blue areas represent the usual distribution of anaesthesia.

Fig. 144 Deformities of the hand. (a) Radial palsy —wrist drop. (b) Ulnar nerve palsy—'main en griffe' or claw 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.

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 inspecting the dorsum of the hand. Sensory loss over the ulnar 1-2 fingers is 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 abduction 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 disability because of the loss of sensation over the thumb, adjacent 22 fingers and 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 accompanied 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.

2 The long extensors of the fingers are inserted into the proximal phalanges; their contracture extends the m/p joints.

3 The long flexors are inserted into the distal and middle phalanges and therefore flex the i/p joints.

There is, therefore, flexion at the wrist, extension at the m/p and flexion at the i/p joints.

If the wrist is passively further flexed by the examiner, the tight flexor tendons are somewhat relaxed and therefore the fingers become a little less clawed.

Dupuytren's contracture results from a fibrous contraction of the palmar aponeurosis, particularly of the 4th and 5th fingers.

The palmar aponeurosis is merely part of the deep fascial sheath of the upper limb; it passes from the palm along either side of each finger, blends with the fibrous flexor sheath of the fingers and is attached to the sides of the proximal and middle phalanges. Contracture of this fascia results in a longitudinal thickening in the palm together with flexion of the m/p and proximal i/p joints. However, the distal i/p joints are not involved and, in fact, in an advanced case, are actually extended by the distal phalanx being pushed backwards against the palm of the hand.

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    What is claw deformity in anatomy?
    12 months ago

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