Radial Nerve Palsy

Radial nerve palsy is loss of function of the radial nerve, causing wrist drop (inability to extend the wrist) and finger drop (inability to extend the metacarpophalangeal joints), with sensory loss over the dorsum of the hand in a classic lesion.

• The level of the lesion determines the pattern:
  • Axilla (crutch palsy, shoulder dislocation): triceps, wrist extensors, finger extensors and brachioradialis weak, with loss of the triceps reflex.
  • Spiral groove of the humerus (humeral shaft fracture, compression during sleep, tourniquet, injection injury): triceps spared, wrist and finger extensors weak.
  • Posterior interosseous nerve (supinator tunnel, Monteggia fracture, lipoma, ganglion, radial head dislocation): finger drop with preserved wrist extension (the wrist deviates radially because extensor carpi radialis longus is spared) and no sensory loss.
  • Superficial radial sensory branch (tight handcuffs or watch straps, cheiralgia paraesthetica): numbness over the dorsum of the thumb and first web space only, without weakness.
• Humeral shaft fractures cause radial palsy in about 8 to 12 percent; most are neurapraxia and recover.
• Other causes: lead poisoning, alcohol, diabetes, vasculitis, hereditary neuropathy with pressure palsies, neuralgic amyotrophy, and prolonged sedation with arm hanging.

• Wrist drop with a flexed wrist and fingers, weak grip (because wrist extension is needed to stabilise the fingers), weak thumb extension and abduction, difficulty releasing objects.
• Sensory loss on the dorsum of the hand over the first web space, thumb and radial two and a half fingers (variable because of overlap).
• Brachioradialis weakness (elbow flexion in mid-pronation) and loss of the brachioradialis reflex; triceps weakness only for lesions at the axilla.
• Tests: ask the patient to extend the wrist and fingers with the forearm pronated; grip is tested with the wrist passively supported.
• Posterior interosseous palsy: finger drop, radial deviation on wrist extension, no sensory loss, sometimes pain over the supinator region.
• Check for fracture, deformity, wounds, vascular injury, and brachial plexus involvement (shoulder and elbow function).

• Clinical localisation; document power in the triceps, brachioradialis, wrist and finger extensors and thumb extensors, plus sensation, before and after any manipulation of a fracture.
• X-ray of the humerus, elbow and forearm after trauma.
• Nerve conduction studies and EMG at 3 weeks or later to define level, axonal loss and prognosis; repeat at 3 months if there is no recovery.
• Ultrasound or MRI for suspected mass, entrapment (supinator, Frohse arcade) or after penetrating injury.
• Blood tests when no mechanical cause: glucose and HbA1c, FBC, ESR, CRP, renal function, vitamin B12, blood lead level, toxicology, autoantibodies.
• Differentials: C7 radiculopathy, stroke, extensor tendon rupture (rheumatoid arthritis, with intact passive tenodesis effect), cervical cord lesion, lateral epicondylitis, de Quervain tenosynovitis.

Immediate

• Remove the cause of compression: avoid crutch pressure in the axilla, release tight bands, review the position of the arm.
• Humeral shaft fracture with palsy present at the time of injury: immobilise the fracture and observe the nerve, since most closed injuries recover. Urgent exploration is needed for an open fracture, a palsy that appears after manipulation or surgery, vascular compromise, penetrating injury, or high energy injury with suspected transection.

Protect function (during recovery)

• Wrist extension splint (cock up splint) with finger extension outrigger, worn during the day to hold the wrist at about 20 to 30 degrees extension and prevent overstretch of the extensors and flexor contracture; remove for exercises.
• Hand therapy: passive range of motion of the wrist, fingers and thumb several times a day, then active assisted strengthening as the muscles recover; electrical stimulation in selected cases.
• Protect numb skin from burns and injury.

Medicines

• Neuropathic pain, if present: amitriptyline 10 mg at night increasing to 50 mg; gabapentin 300 mg at night increasing to 300 to 600 mg three times daily; pregabalin 75 mg twice daily (reduce doses in renal impairment).
• Short oral prednisolone is not routinely used; may be considered by a specialist in idiopathic or inflammatory cases.

Prognosis and timing

• Neurapraxia recovers over days to 12 weeks; axonal injury recovers at about 1 mm/day, so recovery starts proximally (brachioradialis, extensor carpi radialis longus) and reaches the finger extensors last, over 4 to 12 months.
• About 70 to 90 percent of palsies from closed humeral fractures recover without surgery.

Surgery

• Nerve exploration, neurolysis, repair, graft or nerve transfer when there is no clinical or electrical recovery by 3 to 4 months, or immediately for transection.
• Tendon transfers for permanent palsy (typically after 12 months): pronator teres to extensor carpi radialis brevis, flexor carpi radialis or flexor carpi ulnaris to extensor digitorum communis, palmaris longus to extensor pollicis longus.
• Posterior interosseous nerve compression: decompression at the arcade of Frohse if no recovery after 3 months, or sooner if a mass is present.

Follow up

• Review at 2 to 4 weeks, 3 months, and 6 months; examine for contractures; refer to hand or peripheral nerve surgery at 3 months if no recovery.