SN3 SHORT NOTE 5M

Define Median Nerve Palsy. Describe its clinical features and management.

General Surgery · Final Professional

Definition & Cause

Median nerve palsy affects the muscles and sensation of the radial (thumb) side of the hand. The nerve may be injured at the wrist (lacerations, carpal tunnel), the elbow/forearm, or by supracondylar humeral fractures in children. It is often called the ‘labourer’s / eye of the hand’ because of its importance to grip and sensation.

Clinical Features

A low (wrist) lesion paralyses the thenar muscles — causing thenar wasting and loss of thumb abduction and opposition (the ‘ape hand’) — with sensory loss over the radial three-and-a-half digits. A high (elbow) lesion additionally affects the long flexors, so on trying to make a fist the index (and middle) finger cannot flex — the ‘pointing / benediction hand’. Ochsner’s clasping test demonstrates the retained index extension.

CLINICAL PEARL

Two eponyms: a low median lesion gives the ape hand (loss of thumb opposition, thenar wasting); a high lesion gives the pointing/benediction hand when attempting to clench, because the index/middle flexors are also lost.

Management

As for other nerve injuries: observe a likely neurapraxia (e.g. After reduction of a supracondylar fracture), repair or graft a divided nerve, and use splintage and hand therapy to maintain function and prevent contracture. Late loss of opposition is corrected by an opponensplasty (tendon transfer).

Complications & Note on the Anterior Interosseous Nerve

A purely motor branch of the median nerve, the anterior interosseous nerve, may be affected in isolation, causing weakness of the long flexors to the thumb and index finger so that the patient cannot make a normal ‘OK’ sign (an abnormal pinch attitude) but has no sensory loss. As with other nerve injuries, an untreated median lesion leads to fixed loss of thumb opposition and a functionally poor hand, which is why opposition is restored by opponensplasty when spontaneous recovery fails.

CLINICAL PEARL

The median nerve is the ‘eye of the hand’: its loss robs the hand of thumb opposition and radial-side sensation, so restoring opposition (by opponensplasty when recovery fails) is the priority for function.

Loss of thumb opposition is the functional hallmark.

KEY POINT

Key points TO remember

Median nerve palsy: thenar wasting, loss of thumb abduction/opposition; radial-side sensory loss.
Low lesion → ‘ape hand’; high lesion → ‘pointing/benediction hand’ on clenching.
Causes: wrist lacerations/carpal tunnel, forearm/elbow injury, supracondylar fracture (children).
Observe neurapraxia; repair division; opponensplasty for lost opposition.

EXAM TIP

Sources: Maheshwari's Essential Orthopaedics; Apley & Solomon's System of Orthopaedics and Trauma; AO Principles of Fracture Management.

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