Low-Profile Radial Nerve Palsy Orthosis

The radial nerve is the terminal continuation of the posterior cord of the brachial plexus. It contains fibers from nerve roots C5 – T1.  From the axilla region, the radial nerve travels down the arm and innervates the triceps muscle.  The radial nerve then descends down the arm, travelling in a shallow depression within the surface of the humerus, known as the radial groove.

The radial nerve wraps around the humerus laterally and enters the forearm anterior to the lateral epicondyle of the humerus, through the cubital fossa. The nerve then terminates by dividing into two branches:

Deep branch (motor) – innervates the muscles in the posterior compartment of the forearm.
Superficial branch (sensory) – contributes to the cutaneous innervation of the dorsal hand and fingers.

The loss of radial nerve function typically has a significant negative motor impact on an individual.

Neuropraxia is a temporary interruption of conduction without loss of axonal continuity.

In neurapraxia, there is a physiologic block of nerve conduction in the affected axons.

Other characteristics:

• It is the mildest type of peripheral nerve injury.
• There are sensory-motor problems distal to the site of injury.
• Everything is still intact.

Neurotmesis is a total severance or disruption of the entire nerve fiber. A peripheral nerve fiber contains an axon (Or long dendrite), myelin sheath (if existence), their Schwann cells, and the endoneurium. Neurotmesis may be partial or complete.

• Sensory-motor problems and autonomic function defects are severe.

The radial nerve can be damaged in the axilla region by a dislocation at the shoulder joint, or a fracture of the proximal humerus. Occasionally, it is injured via excessive pressure on the nerve within the axilla (use of crutches) or falling asleep with the arm draped over a sofa.

• Motor functions – the triceps brachii and muscles in posterior compartment are affected. The patient is unable to extend at the elbow, wrist, and fingers. Unopposed flexion of wrist occurs, known as wrist-drop.
• Sensory functions – all four cutaneous branches of the radial nerve are affected. There will be a loss of sensation over the lateral and posterior arm, posterior forearm, and dorsal surface of the lateral three and a half

The radial nerve can be damaged in the mid -shaft of the humerus, commonly during a fall and subsequent humeral fracture.

• Motor functions – The radial nerve is most likely to be damaged in humerus fractures that have a lateral displacement of the distal fracture segment, as the nerve is tethered to the bone and cannot withstand the forces applied to it as a result of the displacement. On physical exam, patients with a radial nerve injury may have wrist drop (loss or weakness of wrist extensors), loss or weakness of finger extension.
• Up to 90% of patients with a closed humeral fracture with radial nerve injury will have a resolution of neuropraxia within three to four months following the injury.
• Sensory decreased or absent sensation to the posterior forearm, digits 1 to 3, and the radial half of the fourth digit.

There are many different styles and designs of orthoses for radial nerve palsy. The goals are always the same:

1. Provide wrist support or assisted wrist extension
2. Provide assisted Metacarpal-phalangeal (MCP) joint extension while allowing full finger flexion.

We have created a low-profile radial nerve palsy orthosis! The beauty of this design is that it does not include high outriggers but maintains the MCP joints in extension with waistband elastic. It allows for full finger flexion and can accommodate the MCP joints in flexion with an opening. The wrist is maintained in extension, but a simple modification allows for assisted wrist extension with adjustable tension.