The radial nerve is one of the three major peripheral nerves traveling down the arm, supplying a vast network of muscles and skin. It originates from the brachial plexus near the shoulder and extends all the way to the wrist and hand. This nerve controls many movements and sensations in the arm and hand. When the radial nerve is compromised, the body’s ability to interact with the world through grasping and lifting is significantly affected. The nerve is responsible for nearly all movements that involve straightening the elbow, wrist, and fingers.
The Role of the Radial Nerve
The primary function of the radial nerve is to provide motor control to the extensor muscles, which are responsible for straightening the joints. It innervates the triceps brachii muscle, allowing for the extension of the elbow joint. Moving further down the arm, the nerve controls all 12 muscles in the posterior compartment of the forearm. These muscles are responsible for extending the wrist and straightening the fingers and thumb, giving the hand its ability to release objects.
On the sensory side, the radial nerve provides feeling to the skin over the back of the arm, the forearm, and a specific area of the hand. The superficial branch of the nerve supplies sensation to the dorsal surface of the hand, particularly on the thumb side. This includes the back of the thumb, index finger, middle finger, and half of the ring finger.
Common Causes of Impairment
Impairment of the radial nerve, known as radial neuropathy or palsy, typically results from direct pressure or trauma along its path. A frequent cause is compression of the nerve as it wraps around the humerus in the upper arm, often referred to as “Saturday night palsy.” This condition occurs when prolonged, awkward positioning, such as falling asleep with the arm draped over a chair, compresses the nerve against the bone. Improper use of crutches can also cause a compression injury higher up in the armpit region.
Traumatic injuries are another significant source of damage, particularly fractures of the humerus, the long bone of the upper arm. The nerve runs close to this bone, making it vulnerable to injury during a break. When the nerve is impaired, the muscles it supplies become weak or paralyzed, which commonly manifests as “wrist drop,” an inability to lift the wrist and hand back. Sensory symptoms, such as numbness, tingling, or a burning sensation, are felt on the back of the hand near the thumb.
Simple Tests for Motor and Sensory Function
Self-assessment for radial nerve function involves simple, observable movements and sensation checks that require no special equipment. For motor function, a simple test is to assess the wrist’s ability to extend against gravity. With the forearm resting on a table or thigh, try to lift the wrist upward toward the ceiling. Weakness or an inability to perform this action suggests a possible deficit.
Another important motor test involves the ability to straighten the fingers at the knuckles. Place the hand palm-down on a flat surface and try to lift the fingers off the surface without lifting the wrist. Failure to fully extend the index finger and middle finger is a strong indication of radial nerve involvement. The thumb’s ability to lift straight up, moving away from the palm, should be tested similarly.
To test the sensory function, focus on the dorsal web space, the skin area on the back of the hand between the thumb and the index finger. Gently touch or lightly scratch this area on the potentially affected hand. Compare the sensation to the exact same spot on the unaffected hand, noting any differences in feeling, such as numbness or a duller sensation. This specific area is considered the most reliable spot for testing the superficial radial sensory nerve.
When to Seek Professional Medical Care
While these simple at-home tests can suggest an issue, they are not a substitute for a professional medical diagnosis. If there is a sudden, acute loss of function, such as an immediate inability to move the wrist or fingers following an injury or trauma, immediate medical attention is necessary. Any open wound near the nerve’s path, particularly in the arm or elbow area, also warrants urgent evaluation.
For less acute symptoms, such as persistent numbness, tingling, or weakness that does not improve within a few days, a healthcare provider should be consulted. A medical professional can confirm a suspected radial neuropathy through specialized diagnostic procedures. These often include nerve conduction velocity (NCV) studies and electromyography (EMG), which measure how quickly electrical signals travel along the nerve and assess the health of the muscles it controls.
Treatment plans vary based on the cause and severity of the damage. For compression injuries, the initial approach is often conservative, involving splinting to support the wrist and prevent “wrist drop,” alongside physical therapy to maintain muscle strength. If the nerve is severed or if symptoms fail to improve after a period of watchful waiting, a surgical intervention may be required to repair the nerve or relieve pressure.