Assessing Radial Nerve Function in Humeral Fractures
Test wrist extension, thumb extension, and finger extension at the metacarpophalangeal (MCP) joints, and assess sensation over the first dorsal web space—these are the critical motor and sensory components of radial nerve function that must be documented immediately in any humeral fracture.
Motor Examination
The radial nerve provides motor innervation to the wrist and finger extensors, and testing these functions is essential:
Wrist extension: Ask the patient to extend the wrist against resistance. Loss of this function produces the classic "wrist drop" deformity 1, 2.
Thumb extension: Test extension of the thumb at the interphalangeal joint and metacarpophalangeal joint. The extensor pollicis longus and brevis are radial nerve-innervated 1.
Finger extension at MCP joints: Have the patient extend all fingers at the metacarpophalangeal joints. The extensor digitorum communis is radial nerve-dependent 1, 2.
Brachioradialis function: Test forearm supination with the elbow flexed, though this may be difficult to isolate in the setting of acute trauma 1.
Sensory Examination
First dorsal web space: Test light touch and pinprick sensation in the area between the thumb and index finger on the dorsal hand. This is the autonomous zone of the radial nerve and the most reliable sensory indicator 1, 2.
Dorsal forearm and hand: Assess sensation over the posterior forearm and dorsal hand, though overlap with other nerves makes this less specific 1.
Critical Clinical Context
Radial nerve injury occurs in 2-18% of humeral shaft fractures, making it the most common peripheral nerve injury associated with this fracture pattern 1, 3. The nerve is particularly vulnerable where it courses in the spiral groove of the humerus 4.
Timing and Documentation
Perform the examination immediately upon patient presentation, before any manipulation or reduction attempts 2.
Document whether the deficit is present before or after any fracture manipulation, as this critically affects management decisions 1, 5, 2.
Distinguish between complete (both motor and sensory loss) versus incomplete nerve deficits, as this influences prognosis 2.
Important Pitfalls to Avoid
Multiple concomitant injuries to the same extremity can make clinical evaluation of the radial nerve impossible 6. If the patient has:
- Digital amputations
- Flexor tendon injuries requiring immediate surgery
- Severe pain limiting cooperation
- Other fractures preventing positioning for examination
In these scenarios, document that radial nerve assessment is limited by associated injuries and plan for reassessment when feasible 6.
Closed vs. Open Fractures
Closed fractures with radial nerve palsy: Nearly always recover spontaneously (9 of 10 cases), with initial signs of recovery averaging 7 weeks (range 1-25 weeks) and full recovery at 6 months (range 1-21 months) 2.
Open fractures with radial nerve palsy: Have a 64% incidence of nerve laceration or entrapment between fracture fragments, requiring surgical exploration 5, 2.
High-energy injuries with complete sensory and motor deficit: If part of a complex upper-extremity injury (multiple ipsilateral fractures or near-amputation), nerve transection is more likely 2.
When Examination is Impossible
If clinical evaluation cannot be performed due to multiple trauma, consider ultrasound to detect nerve entrapment within the fracture gap, though surgical exploration remains the definitive diagnostic method 3.