The radial nerve is the terminal continuation of the posterior cord of the brachial plexus. It therefore contains fibres from nerve roots C5 – T1.
The radial nerve helps you move your elbow, wrist, hand and fingers. It runs down the back of the arm from the armpit to the hand. The radial nerve is part of the peripheral nervous system. The peripheral nervous system sends signals from your brain to your arms and fingers, lower limbs, skin and internal organs.
The radial nerve is a peripheral nerve that arises from the bilaterally paired neural crest, which are strips of cells arising from the ectoderm at the margins of the neural tube during embryonic development. The migration of the neural crest cells eventually forms what becomes the radial nerve in a fully developed body.
The radial nerve lies posterior to the third part of the axillary artery and anterior to the muscles forming the posterior wall of the axilla. Here it gives off the following three branches: 1. Posterior cutaneous nerve of arm, 2. Nerve to the long head of triceps and 3. Nerve to the medial head of triceps.
Radial nerve enters the arm at the lower border of the teres major. It passes between the long and medial heads of triceps to enter the lower triangular space, through which it reaches the spiral groove along with profunda brachii artery.
The radial nerve in the spiral groove lies in direct contact with the humerus. At the lower 3rd of the humerus, it pierces the lateral intermuscular septum to enter the anterior part of the arm again where it lies deeply in the interval between the brachialis & the brachioradialis. Then between brachialis and extensor carpi radialis longus before entering the cubital fossa.
To enter the forearm, the radial nerve travels 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.
Radial nerve injuries are associated with the path it travels close to the humerus. Mechanisms of injury can be humerus fracture, a direct blow or sustained pressure. Motor functions of the triceps are usually preserved as they are innervated superiorly whereas wrist and digit extensors are often paralysed leading to the dropped wrist deformity.
A loss of synergic action between wrist flexors and extensors causes excessive and unwanted wrist flexion. This can be observed in a simple gripping task or asking the individual to make a fist. Both tasks will be difficult to complete as movement will be ineffective. Interphalangeal joints can be extended by the lumbricals and interossei due to their attachments at the dorsal digital expansion.
Radial tunnel syndrome: The radial tunnel (created by normal muscles and ligaments in the elbow and forearm area) can press on the radial nerve. Radial tunnel syndrome is also called radial nerve entrapment.
Radial nerve palsy: Palsy is weakness, or paralysis of several forearm muscles that are responsible for wrist, hand and finger upward motion.
Wartenberg syndrome: A type of mononeuropathy that affects the radial nerve. It occurs when muscles trap or compress the nerve’s superficial sensory branch in the wrist.