Radial nerve palsy (radial neuropathy) occurs when the radial nerve in the arm is damaged, disrupting nerve signaling. This damage results in a loss of motor function, such as the ability to move the wrist and fingers, and a loss of sensation in specific areas of the hand and forearm. The condition can significantly impair a person’s ability to perform everyday tasks.
The Role of the Radial Nerve and Definition of Palsy
The radial nerve originates from the brachial plexus near the shoulder and travels down the arm, wrapping around the humerus bone. It is responsible for both motor control and sensory perception in the upper limb. Its primary function is to stimulate the muscles that allow for the extension of the elbow, wrist, fingers, and thumb, controlling movements on the back of the arm and forearm.
The nerve also provides sensory input to the skin on the back of the forearm and the back of the hand, particularly over the thumb, index finger, middle finger, and half of the ring finger. The term “palsy” refers to nerve damage or injury that leads to temporary or permanent weakness or paralysis of the controlled muscles, or a loss of sensation. Symptom severity depends directly on where the injury occurs along the nerve’s path.
Common Causes and Mechanisms of Injury
The radial nerve is susceptible to damage at various points along its length, with causes generally categorized into compression, trauma, and repetitive strain. Compressive neuropathy occurs when prolonged, external pressure is applied to the nerve, often while the individual is deeply asleep or unconscious, such as in cases of “Saturday Night Palsy” or “Honeymoon Palsy.” This pressure typically occurs in the upper arm, where the nerve spirals around the humerus bone, and can temporarily restrict blood flow or damage the nerve’s protective coating.
Trauma is a frequent cause of radial nerve injury, especially fractures of the humerus. The nerve is particularly vulnerable to injury from a mid-shaft fracture due to its close anatomical proximity to the bone’s spiral groove. Direct trauma, like deep cuts or penetrating wounds, can also partially or completely sever the nerve, which is a severe injury requiring surgical repair.
Repetitive strain or overuse can lead to nerve entrapment, often occurring near the elbow where the nerve separates into the posterior interosseous nerve (PIN). Activities involving repetitive forearm rotation can cause the nerve to become compressed by surrounding structures, such as muscle tissue or fibrous bands. In all these mechanisms, the resulting nerve damage disrupts the electrical signals traveling to the muscles, causing weakness.
Clinical Presentation
The most recognizable symptom of radial nerve palsy is “wrist drop,” which is the inability to actively lift or extend the wrist and fingers. When the wrist cannot be extended, the hand hangs limply, making it difficult to perform activities that require a stable, elevated wrist, such as grasping objects or typing.
The loss of motor control also affects the ability to straighten the fingers and thumb, impairing fine motor skills and grip strength. The sensory component manifests as altered sensation, which may include numbness, tingling, or burning pain, along the back of the forearm and the top of the hand. This sensory loss is typically focused on the web space between the thumb and index finger. The location and extent of the weakness help determine the exact site of the nerve damage.
Diagnostic Procedures and Recovery Pathways
Diagnostic Procedures
The evaluation of radial nerve palsy begins with a physical examination to assess the pattern of muscle weakness and sensory loss. To confirm the diagnosis and determine the severity and location of the injury, electrophysiological studies are commonly used.
Nerve Conduction Studies (NCS) measure the speed and strength of electrical signals along the nerve, identifying slowdowns that indicate damage or compression. Electromyography (EMG) involves inserting a needle electrode into affected muscles to record electrical activity, helping differentiate between a nerve injury and a muscular problem. Imaging studies, such as X-rays or Magnetic Resonance Imaging (MRI), may also be ordered to check for underlying causes like bone fractures, soft tissue masses, or structural compression.
Recovery Pathways
The majority of radial nerve palsies caused by acute compression, such as “Saturday Night Palsy,” resolve spontaneously within a few weeks to three months with conservative management. Conservative treatment focuses on supporting the affected limb and preventing muscle contractures while the nerve heals. This often involves wearing a dynamic splint or brace that holds the wrist and fingers in an extended position, allowing the patient to use their hand for gripping tasks.
Physical therapy is used for maintaining a passive range of motion in the joints and strengthening unaffected muscles. If the nerve damage is more severe, such as a complete severance from trauma, or if there is no sign of recovery after three to six months, surgical intervention may be necessary.
Surgical options include nerve decompression to relieve pressure, direct nerve repair using grafts, or nerve transfers, which reroute a functioning nerve to restore movement to the paralyzed muscles. Recovery following surgical repair is a slow process due to the natural rate of nerve regeneration, which is approximately one millimeter per day.