Pronator teres syndrome is a compression neuropathy of the

median nerve The median nerve is a nerve in humans and other animals in the upper limb. It is one of the five main nerves originating from the brachial plexus. The median nerve originates from the lateral and medial cords of the brachial plexus, and has contr ...

at the elbow. It is rare compared to compression at the wrist (

carpal tunnel syndrome Carpal tunnel syndrome (CTS) is the collection of symptoms and signs associated with median neuropathy at the carpal tunnel. Most CTS is related to idiopathic compression of the median nerve as it travels through the wrist at the carpal tunn ...

) or isolated injury of the anterior interosseous branch of the median nerve (

anterior interosseous syndrome Anterior interosseous syndrome is a medical condition in which damage to the anterior interosseous nerve (AIN), a distal motor and sensory branch of the median nerve, classically with severe weakness of the pincer movement of the thumb and index f ...

Symptoms

Compression of the median nerve in the region of the elbow or proximal part of the forearm can cause pain and/or numbness in the distribution of the distal median nerve, and weakness of the muscles innervated by the anterior interosseous nerve: the

flexor pollicis longus The flexor pollicis longus (; FPL, Latin ''flexor'', bender; ''pollicis'', of the thumb; ''longus'', long) is a muscle in the forearm and hand that flexes the thumb. It lies in the same plane as the flexor digitorum profundus. This muscle is uniqu ...

("FPL"), the

flexor digitorum profundus The flexor digitorum profundus is a muscle in the forearm of humans that flexes the fingers (also known as digits). It is considered an extrinsic hand muscle because it acts on the hand while its muscle belly is located in the forearm. Together t ...

of the index finger ("FDP IF"), and the

pronator quadratus Pronator quadratus is a square-shaped muscle on the distal forearm that acts to pronate (turn so the palm faces downwards) the hand. Structure Its fibres run perpendicular to the direction of the arm, running from the most distal quarter of the ...

("PQ"). The pain tends to be at the wrist joint, in the distribution of the terminal branch of the anterior interosseous nerve, and is exacerbated by sustained pronation (i.e., wrist down). The weakness of the FPL and FDP IF is painless, but causes people to "drop things" and have a sense of loss of dexterity. Pinching with the wrist flexed magnifies the expression of this weakness, by reducing resting tension on the muscles of pinch. For instance, "child-proof" prescription pill bottles may be difficult to open. People easily adapt to this weakness without conscious effort or self-awareness, by using 1) the next muscles down, which are innervated by a different nerve, or 2) using ligaments to give resistance, pinching laterally against the index finger or against the side of the end of the thumb, or 3) by what is called "tenodesis," which in this case is extension of the wrist joint, which tightens the muscles on the palm side of the hand. These adaptations on a moment-to-moment basis do not cause problems, but over time in loose-jointed patients, such as many women and people with collagen disorders such as Ehlers Danlos Syndrome, the adaptations can cause soft tissue failures that can become painful, particularly at the base of the thumb and in the proximal forearm (i.e., "Tennis Elbow" in a non-tennis player).

Causes

The most common cause is entrapment of the median nerve between the two heads of the pronator teres muscle. Other causes are compression of the nerve from the fibrous arch of the flexor superficialis, or the thickening of the

bicipital aponeurosis The bicipital aponeurosis (also known as lacertus fibrosus) is a broad aponeurosis of the biceps brachii, which is located in the cubital fossa of the elbow. It separates superficial from deep structures in much of the fossa. Structure The bicip ...

.⁠

Anatomy

The median nerve passes through the

cubital fossa The cubital fossa, chelidon, or elbow pit, is the triangular area on the anterior side of the upper limb between the arm and forearm of a human or other hominid animals. It lies anteriorly to the elbow (Latin ) when in standard anatomical position ...

and passes between the two heads of

pronator teres The pronator teres is a muscle (located mainly in the forearm) that, along with the pronator quadratus, serves to pronate the forearm (turning it so that the palm faces posteriorly when from the anatomical position). It has two attachments, to t ...

muscle into the forearm. It then runs between

flexor digitorum superficialis Flexor digitorum superficialis (''flexor digitorum sublimis'') is an extrinsic flexor muscle of the fingers at the proximal interphalangeal joints. It is in the anterior compartment of the forearm. It is sometimes considered to be the deepest pa ...

and

muscles and enters the hand through the

carpal tunnel In the human body, the carpal tunnel or carpal canal is the passageway on the palmar side of the wrist that connects the forearm to the hand. The tunnel is bounded by the bones of the wrist and flexor retinaculum from connective tissue. Normall ...

. It innervates most of the flexor muscles in the forearm and hand. Its sensory component supplies the skin of the palm, thumb, index and middle finger as well as half the ring finger, and, importantly and often forgotten, the bones of the wrist. In the proximal forearm it gives rise to the

anterior interosseous nerve The anterior interosseous nerve (volar interosseous nerve) is a branch of the median nerve that supplies the deep muscles on the anterior of the forearm, except the ulnar (medial) half of the flexor digitorum profundus. Its nerve roots come from C8 ...

which innervates the flexor of the thumb (FPL), the flexor digitorum profundus of the index finger (FDP IF), and the pronator quadratus, and terminates in a sensory branch to the bones of the wrist, i.e., the carpal tunnel. Compression of the proximal median nerve results in weakness of these three muscles, and can cause aching pain in the wrist on the basis of the sensory nerve to the carpal bones.

Diagnosis

The most common chief complaint is intermittent pain in the wrist, associated with sustained pronation, frequently misinterpreted by patients and providers as "tendonitis." This is usually accompanied by the perception of "hand weakness," and "dropping things." The characteristic physical finding is tenderness over the proximal median nerve, with ensuing numbness in the hand in less than a minute, and/or numbness in the hand with resisted pronation of the forearm in less than a minute. The flexor pollicis longus and FDP of the index finger are weak, leading to impairment of pinching firmly. This reflects involvement of the

. Sensory changes may be found in the first three fingers as well as in the palm, indicating impairment of the median nerve proximal to the flexor retinaculum, but tend to involve the sensation of the entire hand going numb at night, with any pressure on the median nerve on the areas at the inside of the elbow. The clinical and electrophysiological features of pronator teres syndrome are quite different from patients with

or pure

, and are typically normal. Proper localisation is crucial to treatment options.

Conduction velocity In neuroscience, nerve conduction velocity (CV) is an important aspect of nerve conduction studies. It is the speed at which an electrochemical impulse propagates down a neural pathway. Conduction velocities are affected by a wide array of factors ...

of the median nerve in the proximal forearm may be slow but the distal latency and sensory nerve action potential at the wrist are normal. Although

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

may show denervation atrophy of the affected muscles, its role in the evaluation of pronator teres syndrome is unclear.⁠ If the EMG or the MRI are abnormal for the pronator teres muscle and the flexor carpi radialis, this implies that the problem is at or proximal to the elbow, as the takeoff of the nerves to these muscles occurs proximal to the elbow.

Treatment

Injection of

corticosteroids Corticosteroids are a class of steroid hormones that are produced in the adrenal cortex of vertebrates, as well as the synthetic analogues of these hormones. Two main classes of corticosteroids, glucocorticoids and mineralocorticoids, are involve ...

into the pronator teres muscle may produce relief of symptoms. Massage therapy can also provide relief for individuals experiencing this condition. Surgical decompression can provide benefit in selected cases.Kalliainen LK, Ericson WB. "Management of Compressive Neuropathies of the Upper Extremity," Chapter 70, Grabb and Smith's Plastic Surgery, 8th Edition, Chung K et al, Editors. Lippincott Williams & Wilkins, 2018

References

External links

{{PNS diseases of the nervous system Peripheral nervous system disorders Syndromes