Radial palsy, often recognized by the descriptive term “wrist drop,” is a neurological condition resulting from damage to the radial nerve. This major pathway transmits signals from the brain and spinal cord to the muscles of the arm, forearm, and hand. When this communication is interrupted, the muscles responsible for extending the wrist, fingers, and thumb become weak or paralyzed.
Understanding the Radial Nerve and Its Function
The radial nerve is a continuation of the posterior cord of the brachial plexus, a network of nerves originating from the spinal roots C5 through T1 in the neck. From the axilla, the nerve travels down the arm, wrapping around the back of the humerus in a shallow depression known as the radial groove. This anatomical position makes it susceptible to injury along the upper arm.
For movement, the radial nerve primarily supplies the muscles that extend the elbow, wrist, fingers, and thumb. These include the triceps brachii in the arm and the numerous extensor muscles in the posterior compartment of the forearm.
The radial nerve provides sensation to the back of the forearm, the lateral side of the back of the hand, and the dorsal surface of the thumb, index, and middle fingers.
Recognizing the Symptoms of Radial Palsy
The most noticeable symptom of radial palsy is the characteristic “wrist drop.” This occurs when the paralyzed extensor muscles cannot lift or hold the wrist up, causing the hand to hang limply. The inability to extend the wrist severely compromises the ability to perform a functional grip, as the fingers cannot effectively curl into a fist without a stable, extended wrist.
Along with the wrist, the patient typically experiences a significant difficulty or inability to straighten the fingers and the thumb. This is often described as “finger drop” and makes tasks requiring fine motor control, such as pinching or grasping small objects, nearly impossible. If the injury occurs high up in the arm, weakness in the triceps muscle, which extends the elbow, may also be present.
Sensory changes are also a common presentation, depending on the location of the nerve injury. Patients may report feelings of numbness, tingling, or a burning sensation along the radial nerve’s cutaneous distribution. This sensory loss is usually found on the back of the hand, particularly over the web space between the thumb and index finger.
Common Causes and Mechanisms of Injury
Radial nerve palsy frequently results from direct compression or trauma to the nerve along its path. A common mechanism is prolonged, unrelieved pressure on the nerve against the humerus, leading to conditions like “Saturday night palsy” or “Honeymoon palsy.” These names refer to scenarios where the arm is compressed for an extended period, often while intoxicated or sleeping deeply.
Traumatic injuries are another major cause, with fractures of the humerus being particularly implicated. Radial nerve injury is associated with a significant percentage of humeral shaft fractures, especially those involving the middle or distal third of the bone. The nerve can be directly lacerated, bruised, or entrapped between the broken bone fragments.
Other mechanisms involve external pressure or entrapment as the nerve passes through tight anatomical spaces. The improper use of crutches, where the pressure is placed in the armpit (axilla), can compress the nerve and cause a condition sometimes called “crutch palsy.” Less frequently, repetitive motions or chronic inflammation can lead to radial tunnel syndrome, which causes pain and weakness due to nerve compression near the elbow.
Treatment and Recovery Pathways
Diagnosis of radial palsy begins with a thorough physical examination to assess the specific pattern of muscle weakness and sensory loss. Physicians will confirm the diagnosis and determine the extent and location of the nerve damage using specialized tests. Electromyography (EMG) and Nerve Conduction Studies (NCS) are often utilized to measure the electrical activity of the muscles and the speed of nerve signal transmission.
For mild compression injuries, initial management is often conservative, including a period of observation. The nerve has a capacity to heal itself, with regeneration occurring at an approximate rate of one to three millimeters per day. Splinting or bracing the wrist, typically with a dynamic extension splint, is a standard non-surgical intervention that supports the wrist and fingers in a functional position while the nerve recovers.
Physical and occupational therapy are integral to the recovery process. Therapists guide patients through range-of-motion exercises to prevent contractures and initiate strengthening exercises as nerve function returns. Non-steroidal anti-inflammatory drugs (NSAIDs) may be used to manage any associated pain or discomfort.
Surgical intervention is considered for severe injuries, such as a nerve laceration from an open fracture, or if there is no sign of nerve recovery after several months of conservative treatment. Options include direct nerve repair, using a nerve graft to bridge a gap, or neurolysis, which involves freeing the nerve from scar tissue or compression. If nerve function does not return, a final reconstructive option is a tendon transfer, where a working muscle’s tendon is rerouted to take over the function of the paralyzed extensors. Recovery is a slow process that can take weeks, months, or even a year or more, depending on the severity of the initial nerve damage.