Wrist drop is the inability to actively lift or extend the wrist and fingers, leaving the hand to hang limply in a flexed position. This condition is not a disease but a manifestation of underlying dysfunction, often termed radial nerve palsy. The weakness and loss of muscle control associated with the drop hinder daily activities requiring strong grip or wrist movement.
How Radial Nerve Damage Leads to Wrist Drop
The inability to extend the wrist is directly linked to an issue with the radial nerve, which originates from the brachial plexus. This nerve travels down the arm and provides the necessary signals to the extensor muscles located in the back of the forearm. These extensor muscles are responsible for straightening the wrist, fingers, and thumb. When the radial nerve is compressed or damaged, the electrical signals meant for these muscles are interrupted, leading to their paralysis. The opposing flexor muscles, which are still functional, pull the hand into the characteristic position of flexion, resulting in the “drop.” Damage to the radial nerve can also result in sensory deficits, such as numbness or tingling along the back of the hand near the thumb and index finger.
Traumatic and Non-Traumatic Causes
The causes of radial nerve damage can be broadly categorized into traumatic injuries and non-traumatic conditions. Traumatic causes include direct physical impact that disrupts the nerve’s structure. A common instance is a fracture of the humerus, the upper arm bone, where the radial nerve wraps closely around the shaft, making it vulnerable to injury during the break. Deep cuts or stab wounds in the upper arm or axilla can also sever the nerve fibers, leading to an immediate loss of function.
Non-traumatic causes often involve chronic compression, where sustained pressure on the nerve interferes with its blood supply and signaling. “Saturday Night Palsy” is a classic example, occurring when a person falls asleep with their arm draped over a hard object, compressing the nerve against the bone. Similarly, “Crutch Palsy” results from the improper use of crutches, placing pressure directly on the nerve in the armpit. Systemic issues like lead poisoning, diabetes, or severe nutritional deficiencies can also cause a generalized neuropathy that affects the radial nerve.
Confirming the Diagnosis and Treatment
A diagnosis of wrist drop typically begins with a physical examination, where a physician will test the patient’s ability to extend the wrist, fingers, and thumb, and assess sensation along the nerve’s distribution. To confirm the extent and location of the nerve damage, electrodiagnostic studies are often utilized. These tests, which include electromyography (EMG) and nerve conduction studies, measure the electrical activity of the muscles and the speed at which the nerve transmits signals.
Treatment for wrist drop often begins with conservative, non-surgical approaches, as approximately 70% of radial nerve palsy cases resolve with this type of care. A static or dynamic splint or brace is commonly used to support the wrist in a functional, extended position, preventing muscle contractures and protecting the nerve while it heals. Physical therapy is instituted to maintain the range of motion and strengthen the muscles as the nerve recovers. For cases where the nerve is severed or fails to recover after several months, surgical options may be explored, including nerve repair or tendon transfer procedures to restore function.