Ulnar Neuropathy After Surgery

Ulnar neuropathy after surgery is injury to the ulnar nerve, most often at the elbow (cubital tunnel), from compression or stretch in the perioperative period. It is the commonest perioperative upper limb nerve injury.

Epidemiology. It accounts for about one third of anaesthesia related nerve injury claims. Incidence is about 0.04% to 0.5% after surgery. Men are affected 3 to 4 times as often as women, and obese patients, thin patients and the bedridden are at greater risk. Symptoms may start 1 to 7 days after surgery and half of cases do not show an obvious intraoperative cause.

Risk factors. Male sex, obesity (body mass index over 38 kg/m2) or very thin habitus, prolonged hospital stay and bed rest, diabetes, alcohol use, pre-existing neuropathy, elbow flexion over 90 degrees, pronated forearm, surgery over 2 to 3 hours, cardiac surgery with retractors, and prone or lateral position.

Pathophysiology.

The ulnar nerve is superficial at the cubital tunnel and the epicondylar groove. Direct pressure, stretching with elbow flexion and ischaemia cause demyelination (neuropraxia). Postoperative bed rest and repetitive pressure add to injury.

Numbness and tingling in the ring and little fingers, hand weakness (grip), clumsiness, claw hand deformity in severe cases, weak finger abduction and adduction, positive Froment sign, Tinel sign at the elbow and wasting of hand muscles late.

Red flags.

• Rapid progression.
• Complete motor loss.
• Bilateral symptoms (consider other causes).
• Neck pain and arm weakness (cervical cord or root disease).

Clinical examination (sensory map and motor power). Nerve conduction studies and electromyography at 2 to 3 weeks locate the lesion (slowing across the elbow) and grade severity. Ultrasound or MRI of the elbow for entrapment or mass. Exclude cervical radiculopathy, brachial plexopathy and C8 to T1 root disease.

Differential diagnosis.

• Cervical radiculopathy.
• Brachial plexus injury.
• Thoracic outlet syndrome.
• Median or radial nerve injury.
• Diabetic neuropathy.
• Wrist entrapment (Guyon canal).

Most recover (about 80% over 6 to 12 months in sensory cases). Early care: avoid elbow pressure and flexion over 90 degrees, use an elbow pad and night splint in extension, and physiotherapy.

• Paracetamol: 1 g orally every 6 hours; maximum 4 g daily; reduce in hepatic impairment or under 50 kg.
• Gabapentin: 300 mg orally, titrated to 900 to 1,800 mg daily in three divided doses; maximum 3.6 g daily; monitor sedation and renal function; reduce in creatinine clearance under 60 mL/min.
• Surgical decompression or transposition is considered for persisting motor deficit, progression, or no recovery by 3 to 6 months (earlier with severe axonal loss).

Prevention. Pad the elbow, keep the forearm supinated or neutral, and the elbow extended (under 90 degrees of flexion) with arms at the side. Avoid placing the arm over a hard edge, check positions regularly, and re-position patients in bed.

Monitoring. Neurological examination at 1 week, 6 weeks and 3 months, with repeat electrophysiology when no progress.

Referral and escalation. Neurology, hand surgery or peripheral nerve surgery. Disclosure and reporting.