Radial nerve dysfunction is a form of peripheral neuropathy. It occurs when there is damage to the radial nerve, which travels down the arm and supplies movement to the triceps muscle at the back of the upper arm. It also provides extension to the wrist and helps in movement and sensation of the wrist and hand.

Dysfunction of a single nerve group (such as the radial nerve) is classed as mononeuropathy. Mononeuropathy implies a local cause of the nerve damage, although systemic disorders may occasionally cause isolated nerve damage (such as that which occurs with mononeuritis multiplex).

The usual causes are direct trauma, prolonged pressure on the nerve, or compression of the nerve caused by swelling or injury of nearby body structures. Entrapment involves pressure on the nerve where it passes through a narrow structure.

The radial nerve may be injured at the axilla (underarm) by direct pressure, such as "crutch palsy," caused by improper use of crutches, or pressure caused by hanging the arm over the back of a chair.

A more common cause of radial nerve dysfunction is trauma that occurs in the upper arm, such as a fracture of the humerus (upper arm bone) or pressure to the upper arm from arm positions during sleep or coma.

"Saturday-night palsy" is a term for an injury that occurs to the radial nerve during deep sleep, such as that which may occur when a person is intoxicated. Prolonged or repeated constriction of the wrist (caused by wearing a tight watch strap, for example) can also cause an injury to terminal portions of the radial nerve.

In some cases, no detectable cause can be identified. These mechanical factors may be complicated by ischemia (lack of oxygen from decreased blood flow) in the area.