Radial Nerve: A Quick Guide

Introduction:

In this comprehensive blog, we will delve into the intricate details of radial nerve injuries, covering the relevant anatomy, different grades of injuries, mechanisms of injury, and management strategies based on recent scientific journals.

Anatomy and Function of the Radial Nerve:

The radial nerve, a branch of the brachial plexus, plays a crucial role in the innervation of the upper limb, providing motor and sensory functions. Originating from the posterior cord of the brachial plexus (C5-T1), it descends the humerus in the radial groove, supplying the triceps brachii. Accompanied by the deep brachial artery, it travels anteriorly to the lateral epicondyle, entering the forearm. The nerve bifurcates (splits in 2) into a deep branch (motor) for the posterior forearm (extensor) muscles and a superficial branch (sensory) contributing to back of the hand and finger innervation.

Motor Function:

The radial nerve innervates key extensor muscles, including the triceps brachii, anconeus, and the Majority of the forearm and hand extensor muscles. This motor control is vital for executing precise and powerful movements required in sports such as tennis, weightlifting, and martial arts to name a few.

Sensory Function:

The radial nerve has four cutaneous branches providing innervation to the upper limb. Three branches originate in the upper arm:

• Lower lateral cutaneous nerve of the arm – Innervates the lateral arm below the deltoid insertion.
• Posterior cutaneous nerve of the arm – Innervates the posterior arm.
• Posterior cutaneous nerve of the forearm – Innervates the middle strip of skin on the posterior forearm.
• The fourth branch, the superficial branch, is a terminal division of the radial nerve. It innervates the dorsal surface of the lateral 3.5 digits and the corresponding area on the dorsum of the hand.

Grades of Radial Nerve Injury:

Radial nerve injuries are typically classified into three grades, ranging from mild to severe:

Neurapraxia (Grade I):

Mildest form of injury involving a temporary loss of nerve function without structural damage.

Usually associated with excessive compression or stretching of the nerve, often due to direct impact or improper technique during athletic activities. This is usually dealt with by resting from aggravating factors, activity modification, and physiotherapy to educate and prescribe exercises that stimulate the nerve.

Axonotmesis (Grade II):

Axonotmesis involves damage to the nerve fibres, but the nerve's connective tissue (neurolemma) remains intact. This can be a result of prolonged compression or significant stretching leading to axonal damage. Physiotherapy should include targeted exercises and neuromuscular re-education, to facilitate nerve excitation.

Neurotmesis (Grade III):

This is anything including complete disruption of the nerve, including the neurolemma. Usually occurring after severe trauma, such as fractures or penetrating injuries. Surgical intervention may be required, followed by an extensive rehabilitation program involving both surgical and conservative approaches.

Mechanisms of Radial Nerve Injury:

Direct Trauma:

Impact or blunt force trauma to the posterior lateral aspect of the arm upper arm or posterior aspect of the forearm, leading to compression of the radial nerve. For example 11.8% of humeral fractures end up with some form of radial nerve disruption according to shao et al., 2005. 

Overuse or Repetitive Stress:

Repeated and forceful wrist extension or excessive weight-bearing activities can contribute to overuse injuries of the radial nerve. Athletes engaging in sports that involve repetitive wrist and finger extension must ensure proper technique and structured progressive overload to avoid these kinds of injuries.

Management:

Exercises that use the muscles the radial nerve facilitates should be selected, neural adaptation and tissue regeneration happens from a steady structured progressive overloading plan. Tailored rehabilitation programs focusing on range of motion, strength training, and neuromuscular re-education, may include additional activities such as nerve gliding exercises to facilitate the movement of the nerve through its anatomical path.

Surgical Intervention:

In cases of severe cases surgical interventions may be used to try and correct, or facilitate minimal loss of function. Removing the compression on the nerve, repairing the nerve, or grafting nerve tissue to help facilitate function. It should go without saying that when these options are required the injury is relatively severe and functional outcome can be expected to be altered.

Conclusion:

Radial nerve injuries can pose significant challenges to the athlete or non athlete alike, impacting their performance and career longevity. Understanding the complex anatomy, grades of injuries, mechanisms, and advanced management strategies is crucial for designing effective rehabilitation programs tailored to the unique demands of the athlete or person.

References:

El Madhoun, T., & Midha, R. (2016). Radial nerve. Journal of Neurosurgery, 124(1), 175-178. doi: 10.3171/2015.1.JNS142802.

Gragossian A, Varacallo M. (2023, August 14). Radial Nerve Injury. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK537304/ [Accessed 5 January 2024]

Physio-pedia. (2023, October 26). Radial nerve. https://www.physio-pedia.com/Radial_Nerve

Shao, Y. C., Harwood, P., Grotz, M. R. W., Limb, D., & Giannoudis, P. V. (2005). Radial nerve palsy associated with fractures of the shaft of the humerus: a systematic review. The Journal of Bone and Joint Surgery. British Volume, 87(12), 1647-1652. doi: 10.1302/0301-620X.87B12.16132.