The radial nerve is a peripheral nerve that provides motor and sensory function to the arm. The motor function innervates the posterior compartment of the arm including the medial and lateral heads of the triceps brachii muscles in addition to all 12 muscles in the posterior forearm compartment, as well as, the extrinsic extensor muscles found in the wrist and fingers. The sensory function provides cutaneous innervation to a portion of the anterolateral arm, distal posterior arm, posterior forearm, posterior aspects of the thumb, index finger, middle finger, and the lateral half of the ring finger. The radial nerve originates from the ventral roots of the spinal nerves C5-T1 of brachial plexus which eventually forms the posterior cord. Disruption of the radial nerve can have motor consequences such as an inability to extend the arm, wrist, and fingers and paresthesias about its sensory distribution.
The radial nerve is formed as a continuation of the posterior cord of the brachial plexus and arises from the C5-T1 nerve fibers. It courses from the axilla to the posterior compartment of the arm, then into the anterior compartment of the arm, and continues into the posterior compartment of the forearm.
The radial nerve derives from the posterior cord of the brachial plexus and exits the axilla posteriorly the brachial artery. It passes with the deep brachial artery and gives two motor branches and one sensory branch before traversing the triangular interval. These motor branches innervate the medial and long heads of the triceps. This sensory branch is called the posterior cutaneous nerve of the arm which supplies cutaneous sensory innervation to a portion of the distal posterior arm. After passing through the triangular interval, radial nerve descends the radial groove before laterally wrapping around the humerus. At this point, the radial nerve gives a motor branch to the lateral head of the triceps brachii followed by two sensory branches: the inferior lateral cutaneous nerve of the arm which perforates through the lateral head of the triceps and the posterior cutaneous nerve of the forearm.
The posterior cutaneous nerve of the antebrachium also perforates through the lateral head of the triceps but continues to innervate a posterior strip of the forearm. After giving these two sensory branches, the radial artery passes through the lateral intermuscular septum to infiltrate the anterior compartment of the forearm between the brachialis and brachioradialis muscles. The radial nerve then passes over the lateral epicondyle into the cubital fossa and forearm. Here, the radial nerve separates into the deep and superficial branches. The deep branch is a motor branch which passes between the heads of the supinator muscle and becomes the posterior interosseous nerve to innervate the muscles of the posterior compartment of the forearm. The superficial branch follows the radial artery inferiorly to the anterolateral portion of the radius, deep to the brachioradialis muscle. The superficial branch then courses dorsally over the distal radius over the anatomical snuffbox to innervate the posterior lateral three and a half digits (the thumb, index, middle, and lateral half of the ring fingers) and the associated hand area.
The following is a list of the motor and cutaneous sensory functions of the radial nerve.
The Radial Nerve branches off to the Deep Branch after it passes through the cubital fossa and then continues as the Posterior Interosseous Nerve after it passes between the supinator muscle heads.
Deep Branch of the Radial Nerve:
Posterior interosseous nerve:
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 exits the axilla with the axillary artery and follows it posteriorly with the brachial artery. It then continues with the deep brachial artery into the posterior compartment via the triangular interval. The radial nerve follows the radial collateral artery until it wraps anteriorly over the cubital fossa. At this point the radial nerve branches into the superficial branch of the radial nerve which passes with the radial artery, the deep branch of the radial artery, and the posterior interosseous artery.
The radial nerve forms as a continuation of the posterior cord of the brachial plexus with nerve fibers from the C5-T1 nerve roots.
The Radial Nerve branches:
The radial nerve and its branches provide innervation the following muscles (See Structure and Function for specific nerve branch innervations and muscle actions):
The deep branch of the radial nerve normally passes between the heads of the supinator muscle as it becomes the posterior interosseous nerve to innervate the muscles of the posterior compartment of the forearm. A variant can occur where the deep branch of the radial nerve passes through the Arcade of Frohse (Supinator Arch) which can increase the likelihood of impingement.
Any surgery near the radial nerve holds a potential risk for an injury which will cause adverse downstream effects.
The brachial plexus injury with radial nerve involvement can occur with use of sternal retraction after sternotomy, particularly with internal mammary dissection during cardiac surgery.
Damage to the superficial radial nerve is a potential complication to surgery for de Quervain tendinopathy.
There is a theoretical risk of radial nerve injury with hyperextension of the elbow and forearm should be placed in a slightly flexed position during anesthesia.
Radial Tunnel Syndrome
Radial Tunnel Syndrome presents with symptoms including fatigue or dull, aching pain at the proximal portion of the forearm during use. Less commonly these symptoms can occur at the dorsal aspect of the wrist or hand. Radial Tunnel Syndrome typically occurs secondary to overuse or repetitive movements from pushing, pulling, gripping, pinching, or bending at the wrist typically from a job or playing sports. Muscle overuse may cause compression of the radial nerve anywhere along its path, but most commonly occurs over the elbow as it passes through the radial tunnel. Treatment for radial tunnel syndrome can be conservative or surgical if non-operative therapy fails.
Radial Nerve Palsy
Radial neuropathies occur from injury to the radial nerve due to compression, ischemia, fractures to the arm, or penetrating wounds. Wrist drop is the most common presentation. The severity of the neuropathy depends on the level of the injury. Surgical procedures such as stabilization of an acute humeral fracture with humeral nailing can also cause radial neuropathies. Palsy of the radial nerve is also known as crutch palsy, Saturday night palsy, and honeymooner’s palsy, conditions which may occur after placing one’s arm over a chair (or crutches) for an extended period causing a pressure injury to the radial nerve.
Radial Nerve Entrapment
Radial nerve injury or compression can occur anywhere along the nerves path which can cause extensor or supinator muscle denervation. This can result in pain, weakness, dysfunction, or paresthesias and numbness along the sensory distribution of the radial nerve. The proximal forearm is the most common area of compression where the posterior interosseous branch of the radial nerve passes between the supinator heads. Other, less common, sites of compression can occur due to fractures of the humerus about the middle and proximal thirds of the shaft. The radial aspect of the wrist is another site of possible compression of the radial nerve. Treatment for radial nerve entrapment depends on the pathology and may be treated conservatively or surgically if conservative measures fail.
Cheiralgia Paresthetica (Wartenberg's syndrome)
Cheiralgia paresthetica is a hand neuropathy commonly caused by trauma or compression of the superficial branch of the radial nerve. The dorsum of the hand near the base of the thumb (in the vicinity of the anatomical snuffbox) is typically affected; however, it may affect the dorsum of the thumb, index finger, and hand. Symptoms include pain, numbness, tingling, or a burning sensation. There is no motor involvement since the superficial branch is purely sensory. Its etiology is thought to be caused by a constriction of the wrist as with a watch band or bracelet. It is associated with handcuff use and is also commonly referred to as handcuff neuropathy.