Radial nerve dysfunction is a problem associated with the

radial nerve The radial nerve is a nerve in the human body that supplies the posterior portion of the upper limb. It innervates the medial and lateral heads of the triceps brachii muscle of the arm, as well as all 12 muscles in the Posterior compartment of the ...

resulting from injury consisting of acute trauma to the

. The damage has sensory consequences, as it interferes with the

innervation A nerve is an enclosed, cable-like bundle of nerve fibers (called axons). Nerves have historically been considered the basic units of the peripheral nervous system. A nerve provides a common pathway for the electrochemical nerve impulses called ...

of the skin of the posterior forearm, lateral three digits, and the

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage The fus ...

surface of the

lateral Lateral is a geometric term of location which may also refer to: Biology and healthcare * Lateral (anatomy), a term of location meaning "towards the side" * Lateral cricoarytenoid muscle, an intrinsic muscle of the larynx * Lateral release ( ...

side of the palm. The damage also has motor consequences, as it interferes with the

of the muscles associated with the extension at the elbow, wrist, and fingers, as well the

supination Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relativ ...

of the forearm. This type of injury can be difficult to localize, but relatively common, as many ordinary occurrences can lead to the injury and resulting mononeuropathy. One out of every ten patients with

dysfunction do so because of a fractured

humerus The humerus (; : humeri) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius (bone), radius and ulna, and consists of three sections. The humeral upper extrem ...

Signs and symptoms

People experiencing radial nerve dysfunction may also experience any of the following symptoms: * Lost ability or discomfort in extending the elbow * Lost ability or discomfort bending hand back at the wrist * Numbness * Abnormal sensations near the thumb, index and middle fingers * Sharp or burning pain * Weakness in grip * Drooping of the hand, also called wrist drop

Cause

There are many ways to acquire radial nerve palsy. The term ''Saturday Night Palsy'' refers to an injury to the radial nerve in the spiral groove of the humerus caused while sleeping in a position that would under normal circumstances cause discomfort. It can occur when a person falls asleep while heavily medicated and/or under the influence of alcohol with the underside of the arm compressed by a bar edge, bench, chair back, or like object. Sleeping with the head resting on the arm can also cause radial nerve palsy. Breaking the

and deep puncture wounds can also cause the condition. Posterior interosseus palsy is distinguished from radial nerve palsy by the preservation of elbow extension. Symptoms vary depending on the severity and location of the trauma; however, common symptoms include wrist drop (the inability to extend the wrist upward when the hand is palm down);

numbness Hypoesthesia or numbness is a common side effect of various medical conditions that manifests as a reduced sense of touch or sensation, or a partial loss of sensitivity to Sensory receptor, sensory stimuli. In everyday speech this is generally r ...

of the back of the hand and wrist, specifically over the first web space which is innervated by the radial nerve; and inability to voluntarily straighten the fingers or extend the thumb, which is performed by muscles of the extensor group, all of which are primarily innervated by the radial nerve. Loss of wrist extension is due to paralysis of the posterior compartment of forearm muscles; although the elbow extensors are also innervated by the radial nerve, their innervation is usually spared because the compression occurs below, distal, to the level of the axillary nerve, which innervates the long head of the triceps, and the upper branches of the radial nerve that innervate the remainder of the Triceps. Saturnine neuropathy can also be a cause of radial neuropathy ( radial palsy).

Mechanism

The

, like any other in the nervous system, is vulnerable to damage. This damage can originate when the

nerve fiber An axon (from Greek ἄξων ''áxōn'', axis) or nerve fiber (or nerve fibre: see spelling differences) is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action pot ...

s experience pressure, stretching, or cutting. All of the tissues can prevent

action potentials An action potential (also known as a nerve impulse or "spike" when in a neuron) is a series of quick changes in voltage across a cell membrane. An action potential occurs when the membrane potential of a specific cell rapidly rises and falls. ...

from continuing up or down

axons An axon (from Greek ἄξων ''áxōn'', axis) or nerve fiber (or nerve fibre: see spelling differences) is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action pot ...

within the nerve, which would interrupt

signal transduction Signal transduction is the process by which a chemical or physical signal is transmitted through a cell as a biochemical cascade, series of molecular events. Proteins responsible for detecting stimuli are generally termed receptor (biology), rece ...

to and from the brain. As a result of the interrupted signal, the patient may experience loss of feeling and/or

motor control Motor control is the regulation of movements in organisms that possess a nervous system. Motor control includes conscious voluntary movements, subconscious muscle memory and involuntary reflexes, as well as instinctual taxes. To control ...

Diagnosis

In order to diagnose radial nerve dysfunction, a doctor will conduct a physical examination. During the exam of the arm, wrist, and hand, the doctor will look for: difficulty straightening the arm at the elbow; trouble turning the arm outward; difficulty lifting the wrist; muscle loss or

atrophy Atrophy is the partial or complete wasting away of a part of the body. Causes of atrophy include mutations (which can destroy the gene to build up the organ), malnutrition, poor nourishment, poor circulatory system, circulation, loss of hormone, ...

in the forearm; weakness of the wrist and/or fingers. In addition, tests may need to be conducted to confirm the doctors findings. These tests include: blood tests;

MRI Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to generate pictures of the anatomy and the physiological processes inside the body. MRI scanners use strong magnetic fields, magnetic field gradients, and rad ...

of the neck and shoulders to screen for other problems; nerve

biopsy A biopsy is a medical test commonly performed by a surgeon, interventional radiologist, an interventional radiologist, or an interventional cardiology, interventional cardiologist. The process involves the extraction of sampling (medicine), sample ...

; nerve conduction tests;

ultrasound Ultrasound is sound with frequency, frequencies greater than 20 Hertz, kilohertz. This frequency is the approximate upper audible hearing range, limit of human hearing in healthy young adults. The physical principles of acoustic waves apply ...

of the elbow.

Prognosis

Radial neuropathy is not necessarily permanent. The majority of radial neuropathies due to an acute compressive event (Saturday night palsy) do recover without intervention. If the injury is demyelinating (meaning only the myelin sheath surrounding the nerve is damaged), then full recovery typically occurs within 2–4 weeks. If the injury is axonal (meaning the underlying nerve fiber itself is damaged) then full recovery may take months or years, or may never occur. EMG and nerve conduction studies are typically performed to diagnose the extent and distribution of the damage, and to help with prognosis for recovery.

Society and culture

There are a number of colloquial terms used to describe radial nerve injuries, which are usually dependent on the causation factor: *Saturday night palsy from falling asleep with one's arm hanging over the arm rest of a chair, compressing the radial nerve at the spiral groove. *Honeymoon palsy from another individual sleeping on and compressing one's arm overnight. This can also refer to anterior interosseous nerve palsy from compression on the forearm resulting in an inability to flex the index and thumb tips. In this interpretation, it is a branch of the median nerve and not the radial nerve which is affected. *Handcuff neuropathy from tight-fitting handcuffs compressing the superficial branch of the distal radial nerve; this is also referred to as cheiralgia paresthetica. * Crutch palsy from poorly fitted axillary crutches.

References

{{PNS diseases of the nervous system Nerves of the upper limb Neurological disorders Peripheral nervous system disorders Symptoms and signs: Nervous system Mononeuropathies of upper limb