Shaft Humerus — Radial Nerve Palsy

Fractures of the humeral shaft are relatively common injuries and represent approximately 3–5% of all fractures. These fractures are clinically important because of their close anatomical relationship with the radial nerve. Radial nerve palsy is the most common nerve injury associated with humeral shaft fractures and may present either at the time of injury or following fracture manipulation or surgical treatment.

Most radial nerve palsies associated with humeral shaft fractures are neuropraxias and recover spontaneously. Therefore, understanding the mechanism of injury, fracture pattern, and natural history of radial nerve injury is essential to guide treatment decisions and avoid unnecessary surgical exploration.

The radial nerve arises from the posterior cord of the brachial plexus (C5–T1). It travels posterior to the humerus in the spiral groove, making it particularly vulnerable to injury in fractures of the middle third of the humeral shaft.

• Origin: Posterior cord of brachial plexus
• Course: Posterior arm within spiral groove
• Innervation: Extensor muscles of wrist and fingers
• Sensory supply: Dorsal hand and posterior forearm

The radial nerve crosses the humerus approximately at the junction of the middle and distal thirds, where it is particularly susceptible to injury during fractures.

• Radial nerve palsy occurs in 10–18% of humeral shaft fractures
• Most common nerve injury associated with long bone fractures
• Frequently associated with spiral and oblique fractures

• Direct trauma to the arm
• Road traffic accidents
• Sports injuries
• Fall on outstretched hand
• Twisting injuries causing spiral fractures

Radial nerve palsy typically presents with characteristic motor and sensory deficits.

• Wrist drop due to loss of wrist extension
• Loss of finger extension
• Weak thumb extension
• Sensory loss over dorsum of hand

Patients often demonstrate an inability to extend the wrist and fingers, producing the classical wrist drop deformity.

• X-ray of humerus (AP and lateral views)
• CT scan in complex fractures
• Nerve conduction studies if palsy persists
• Electromyography after 3–4 weeks

Electrodiagnostic studies help determine the severity and prognosis of radial nerve injury.

Most humeral shaft fractures can be treated conservatively using functional bracing.

• Functional humeral brace
• Hanging cast
• Sarmiento brace
• Early mobilization

The majority of radial nerve palsies recover spontaneously within several months.

• Open fracture with radial nerve injury
• Associated vascular injury
• Entrapment of nerve in fracture site
• Lack of recovery after several months
• Secondary palsy following surgical fixation

• Persistent radial nerve palsy
• Malunion
• Nonunion
• Joint stiffness
• Complex regional pain syndrome

• Radial nerve injury is the most common nerve injury in humeral shaft fractures
• Most cases recover spontaneously
• Middle third humerus fractures carry the highest risk
• Wrist drop is the hallmark clinical sign