Median Nerve · What Is It, Location, Innervation, Damage, and More

The median nerve is a sensory and motor nerve of the arm (or upper limb). It arises from the lateral and medial cords of the brachial plexus, originating in the spinal cord, and runs through the anterior portion of the arm and forearm before finishing its path at the hand and digits (fingers). 

The median nerve innervates some of the major muscles of the forearm and hand, which allows for a two-way communication between the brain and spinal cord, and the muscles and overlying skin. The brain and spinal cord can send signals through the medial nerve, to the muscles that it innervates, with instructions on when to contract and complete specific actions. Similarly, the muscles and overlying skin can transmit sensations and sensory information, such as heat and pain, through the median nerve, and back to the brain and spinal cord for processing.

The median nerve innervates many muscles of the anterior forearm and hand, providing signals to and from the brain and spinal cord. The flexor digitorum superficialis and pronator quadratus are among the muscles of the anterior forearm that are solely innervated by the median nerve. They are involved in flexing and pronating the forearm and wrist. 

The median nerve is usually damaged at either the elbow, due to a fracture of the humerus bone of the upper arm, or the wrist, due to either carpal tunnel syndrome or a wrist laceration or gashing. If the median nerve is damaged at the elbow region, it is known as a proximal injury to the median nerve. Proximal injury to the median nerve often presents with the hand of benediction, a sign that occurs when an individual is unable to make a complete fist. This occurs because flexion of the finger joints, specifically the first and third finger joints (the metacarpophalangeal and distal interphalangeal joints, respectively) of the 1^st and 2^nd fingers, are lost with median nerve damage. Consequently, when an individual with such nerve damage attempts to make a fist, the thumb and first two fingers remain partially distended, resembling the hand gesture of a Pope as he gives blessings, hence, the name “hand of benediction”.

If the median nerve is damaged at the wrist, this injury is called a distal injury to the median nerve. The most common cause of medial nerve injury at the wrist is carpal tunnel syndrome (CTS), although a wrist laceration may also cause injury to the median nerve. 

Clinical presentation of symptoms and physical examination are used to diagnose median nerve compression. For instance, a physical exam may confirm diagnosis through the help of the Tinel sign and Phalen maneuver. The Tinel sign is positive if tingling is experienced when pressure is applied to the wrist. The Phalen maneuver is positive if tingling is experienced when the wrist is placed at a 90° angle. With median nerve injury, specifically due to CTS, both the Tinel sign and Phalen maneuver will likely be positive. 

When treating median nerve compression, splinting is considered a first-line treatment. Other conservative, or traditional, treatments can include physical therapy, yoga and therapeutic ultrasound. Therapeutic ultrasound uses ultrasound technology to speed up the rate of healing and enhance the quality of repair. In some cases, oral steroids or the injection of steroids may also be considered for severe pain relief. Individuals with CTS may also be advised to make ergonomic adjustments to their workspace and computer space, such as wrist and elbow supports to help relieve pain. 

Patients with severe pain of more than four to six months and no relief from conservative treatments may be offered surgical decompression.