Radial Nerve Palsy in Humeral Shaft Fractures: Dynamic Extension Splinting and Axonal Recovery
In short
Mid-shaft humeral fractures commonly trap the radial nerve in the spiral groove; dynamic extension splints restore functional grip while waiting for axonal regeneration.
In this guide (4 sections)
The Anatomy of the Radial Nerve in the Humeral Spiral Groove
The radial nerve arises from the posterior cord of the brachial plexus (C5 through T1). As it traverses the arm, it wraps tightly around the mid-posterior cortex of the humerus within the spiral groove (radial sulcus), directly sandwiched between the lateral and medial heads of the triceps brachii muscle before piercing the lateral intermuscular septum.
Due to this intimate periosteal contact, closed fractures of the mid-to-distal third junction of the humeral shaft (specifically spiral fractures of the Holstein-Lewis type) carry a 12% to 18% incidence of primary radial nerve palsy. Fortunately, over 70% to 85% of closed fracture palsies represent neurapraxia or axonotmesis, resolving spontaneously over 3 to 6 months as axons regenerate distally at a rate of 1 mm per day.
Axonal Recovery Staging and Motor Re-innervation Sequence
| Re-innervation Order | Muscle Group & Peripheral Branch | Clinical Motor Action Restored | Targeted Physiotherapy & Splinting Directive | |
|---|---|---|---|---|
| 1. Proximal Forearm (Month 2 to 3) | Brachioradialis (BR) & Extensor Carpi Radialis Longus (ECRL) | Forearm flexion in neutral; radial wrist extension without finger ext | Observe for visible muscle twitching during resisted elbow flexion | |
| 2. Mid Forearm (Month 3 to 4) | Extensor Carpi Radialis Brevis (ECRB) & Supinator | Balanced, central wrist extension without radial deviation drift | Begin weaning from daytime wrist cock-up splinting | |
| 3. Distal Extensors (Month 4 to 6) | Extensor Digitorum Communis (EDC), EDM, Extensor Carpi Ulnaris | Active extension of all four fingers at the metacarpophalangeal (MCP) joints | Transition from dynamic finger splint to light active opening exercises | |
| 4. Thumb Outcroppers (Month 6 to 8) | Abductor Pollicis Longus (APL), EPB, Extensor Pollicis Longus (EPL) | Active thumb extension and retropulsion off tabletop | Full functional release of splints; fine motor coordination drills |
Standardized Clinical Rehabilitation Protocols and Dynamic Splinting
- Low-Profile Dynamic Radial Nerve Splint Fabrication: Fabricate a custom thermoplastic forearm splint with an outrigger or elastic slings that passively support the wrist in 30 degrees of extension and the MCP joints in neutral extension; dynamic recoil allows the patient to actively flex their fingers to grasp objects, which spring back into extension upon muscle relaxation.
- Passive Range of Motion and Flexion Contracture Prevention: Perform passive joint range of motion into full composite wrist and finger flexion multiple times daily; dynamic extension splints must not be allowed to cause tight, stiff extensor hood contractures.
- Neuromuscular Electrical Stimulation (NMES) to Paralyzed Extensors: Apply biphasic electrical muscle stimulation over the motor points of the ECRL, ECRB, and EDC to maintain muscle fiber bulk, prevent fibrotic fatty degeneration, and facilitate cortical re-innervation awareness.
Frequently Asked Questions
Why did my hand suddenly 'drop' and become paralyzed after breaking my upper arm?
The main nerve that straightens your wrist and fingers (the radial nerve) wraps tightly around the bone of your upper arm. When the bone breaks, the nerve gets bruised or stretched. In most cases, the nerve is not torn, but is 'stunned' (neurapraxia) and takes several months to wake up.
How does a dynamic spring splint help me use my hand while my nerve heals?
Without a splint, your wrist hangs limp, making it impossible to grip anything. A dynamic splint uses gentle elastic bands to hold your wrist and knuckles up. When you want to grab a cup, you can easily squeeze your fingers, and when you let go, the springs lift your fingers back up for you.
What if my nerve does not wake up after 6 to 9 months?
If electrodiagnostic tests (EMG) show no signs of nerve regrowth after 6 to 9 months, an orthopaedic hand surgeon can perform a 'tendon transfer'. Working muscles from the front of your forearm are rerouted to the back of your wrist, permanently restoring your ability to lift your wrist and fingers.
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