Wrist drop is a medical condition characterized by the inability to actively extend the wrist and fingers. It results in the hand hanging limply, making it difficult to perform everyday tasks. This article explores the specific nerve responsible for this condition, its common causes, and how medical professionals approach its management.
The Radial Nerve and Its Role
The radial nerve is the primary nerve controlling muscles for wrist and finger extension. It originates from a network of nerves in the neck and shoulder called the brachial plexus, then travels down the back of the arm. As it descends, it wraps around the humerus bone. The radial nerve supplies motor function to various muscles in the forearm and hand, enabling movements like straightening the elbow, wrist, and fingers. It also provides sensory input to a portion of the back of the hand and parts of the thumb and first two fingers.
Understanding Wrist Drop
Wrist drop manifests as a characteristic drooping of the hand, where the wrist and fingers are unable to lift upwards against gravity. Individuals often experience difficulty straightening their wrist, extending their fingers, or moving their thumb away from the palm. This impairment can affect fine motor skills and the ability to grasp objects. Accompanying symptoms might include numbness, tingling, or a burning sensation along the back of the hand and fingers, as well as weakness in the affected muscles. These symptoms occur because the muscles no longer receive proper electrical signals from the injured radial nerve, leading to their dysfunction.
Common Causes of Radial Nerve Injury
Injury to the radial nerve can occur through various mechanisms, leading to wrist drop. A common cause is direct trauma, such as fractures of the humerus. The radial nerve’s close proximity to the humerus shaft makes it vulnerable to damage from these bone breaks, with radial nerve injury occurring in up to 18% of humeral shaft fractures. Nerve damage can result directly from the fracture or from pressure applied by a healing bone callus.
Compression injuries are another frequent cause of radial nerve dysfunction. “Saturday night palsy” is a well-known example, occurring when prolonged pressure is applied to the radial nerve, often by falling asleep with the arm draped over a hard surface. This compression restricts blood flow to the nerve, leading to temporary dysfunction. Similarly, “crutch palsy” can occur when crutches are used improperly, causing sustained pressure on the radial nerve in the armpit.
Repetitive strain or overuse can also contribute to radial nerve damage. Activities involving repeated grasping and swinging motions, such as hammering, may lead to nerve compression over time. Certain medical conditions like diabetes, kidney disease, or lead poisoning can also affect the radial nerve by causing inflammation or fluid retention that leads to nerve compression.
Diagnosis and Management
Diagnosis of wrist drop typically begins with a physical examination, where a doctor assesses the patient’s ability to move their wrist and fingers, looking for weakness or loss of sensation. To confirm radial nerve injury and pinpoint its location and severity, specialized tests are employed. Nerve conduction studies (NCS) measure how quickly electrical signals travel through the nerve, while electromyography (EMG) assesses the electrical activity of muscles. These tests can differentiate between nerve and muscle problems and determine if the nerve damage is due to demyelination or axonal loss. Imaging techniques like X-rays, MRI, or ultrasound may also be used to identify underlying causes such as fractures, tumors, or other structural issues compressing the nerve.
Management of wrist drop varies depending on the cause and extent of the radial nerve injury. Conservative approaches are often the first line of treatment, especially for compression-related injuries, with many cases resolving on their own. Initial steps include supporting the wrist with a splint or brace to maintain proper positioning and prevent contractures. Physical therapy is crucial, involving exercises to maintain range of motion, strengthen weakened muscles as the nerve recovers, and promote nerve gliding. Medications, such as anti-inflammatory drugs, may be prescribed to manage pain and reduce swelling.
If conservative treatments do not lead to recovery, or if the nerve is severely damaged, surgical intervention might be necessary. Surgical options include nerve decompression to relieve pressure on the nerve, nerve repair (suturing the ends of a cut nerve), or nerve grafting, where a segment of nerve from another part of the body is used to bridge a gap in the injured nerve. In cases where nerve recovery is unlikely, tendon transfer surgery may be performed, rerouting healthy tendons to take over the function of the paralyzed muscles, restoring some wrist and hand function. The timing of surgical exploration for radial nerve injuries, particularly those associated with humeral fractures, can vary, with some surgeons preferring to wait a few months to observe for spontaneous recovery.