THE SUPERFICIAL BRANCH OF THE RADIAL NERVE: A MORPHOLOGIC STUDY

The Branching and Innervation Pattern of the Radial Nerve in the Forearm: Clarifying the Literature and Understanding Variations and Their Clinical Implications

BACKGROUND

This study attempted to clarify the innervation pattern of the muscles of the distal arm and posterior forearm through cadaveric dissection.

METHODS

Thirty-five cadavers were dissected to expose the radial nerve in the forearm. Each muscular branch of the nerve was identified and their length and distance along the nerve were recorded. These values were used to determine the typical branching and motor entry orders.

RESULTS

The typical branching order was brachialis, brachioradialis, extensor carpi radialis longus, extensor carpi radialis brevis, supinator, extensor digitorum, extensor carpi ulnaris, abductor pollicis longus, extensor digiti minimi, extensor pollicis brevis, extensor pollicis longus and extensor indicis. Notably, the radial nerve often innervated brachialis (60%), and its superficial branch often innervated extensor carpi radialis brevis (25.7%).

CONCLUSIONS

The radial nerve exhibits significant variability in the posterior forearm. However, there is enough consistency to identify an archetypal pattern and order of innervation. These findings may also need to be considered when planning surgical approaches to the distal arm, elbow and proximal forearm to prevent an undue loss of motor function. The review of the literature yielded multiple studies employing inconsistent metrics and terminology to define order or innervation.

Sensory deficits after a radial nerve injury

BACKGROUND

The aim of our study was to objectively test sensibility on the dorsal side of the hand in patients with radial nerve injury, to document deficits and to detect if surgery for sensory reconstruction is needed.

METHODS

Nineteen patients of mean age 31 ± 10 years were examined at a mean of 26.4 ± 27.8 months post radial nerve injury. Sensory mechanical thresholds on the dorsal surface of the hand were evaluated using Semmes-Weinstein monofilaments. Sensation was considered significantly impaired when there was no perception of a 2.0 gr. Semmes-Weinstein filament. Nociception was evaluated using Adson forceps.

RESULTS

Five patients had normal 2.0 monofilament perception. Two of these five also had normal perception of the lighter 0.05 monofilament. In nine patients, zones of impaired sensibility were restricted to the first web space. In combined radial and musculocutaneous nerve lesions, the zone of impaired sensibility extended to the dorsum of the third metacarpus and occasionally to the dorsal aspect of the thumb. This zone averaged being five times the size as in isolated radial nerve injuries. On average, the zone of decreased 0.05 monofilament perception was six times the size detected for the 2.0 monofilament. No patient had complete anesthesia over the dorsum of the hand. No patient complained about pain or numbness. Only one patient among four with a combined radial and musculocutaneous nerve injury required sensory reconstruction.

CONCLUSIONS

Minimal sensory abnormalities should be expected after a radial nerve injury. Patients likely neither warrant nor request sensory reconstruction.

An Anatomical Study to Demonstrate the Proximity of Kirschner Wires to Structures at Risk in Percutaneous Pinning of Distal Radius Fractures

Distal radius fractures are often treated using percutaneous Kirschner wires (K-wires). The sensory nerves in this area, extensor tendons, radial artery and cephalic vein are at risk of injury in this procedure. We undertook a cadaveric investigation to identify probability of damage to these 'at risk' structures by measuring their distances in relation to standard K-wire sites. Nine upper limbs from six formalin-preserved cadavers were studied. Four K-wires were placed percutaneously simulating fixation of a distal radius fracture. Careful dissection was done preserving the original position of neurovascular and tendinous structures. Distances to relevant soft-tissue structures from each K-wire were measured using an electronic digital caliper. Distance of superficial nerves from radial styloid and Lister's tubercle was measured to determine their 'safe distance' from these fixed landmarks. None of the superficial nerves were injured by a K-wire. Cephalic vein had been pierced on 4 occasions (4/18) and extensor tendons on 3 occasions (3/18). Wilcoxon signed-rank test was used to compare distance of the superficial nerves from radial styloid and Lister tubercle, and the latter was found to be the safer option. This study highlights the inherent danger in percutaneous K-wire fixation of wrist fractures. Limited size of the area, where K-wires can be positioned, and anatomic variations of neurovascular structures pose obstacles in developing guidelines for reducing risk of injury. We advocate use of mini-open approach and guiding devices to avert complications of inadvertent impalement and damage to these structures.