In the proximal forearm it gives rise to the anterior interosseous nerve 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. 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. It innervates most of the flexor muscles in the forearm and hand. It then runs between flexor digitorum superficialis and flexor digitorum profundus muscles and enters the hand through the carpal tunnel. The median nerve passes through the cubital fossa and passes between the two heads of pronator teres muscle into the forearm. Other causes are compression of the nerve from the fibrous arch of the flexor superficialis, or the thickening of the bicipital aponeurosis. The most common cause is entrapment of the median nerve between the two heads of the pronator teres muscle. 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). 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. For instance, "child-proof" prescription pill bottles may be difficult to open. Pinching with the wrist flexed magnifies the expression of this weakness, by reducing resting tension on the muscles of pinch. The weakness of the FPL and FDP IF is painless, but causes people to "drop things" and have a sense of loss of dexterity. 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). It is rare compared to compression at the wrist ( carpal tunnel syndrome) or isolated injury of the anterior interosseous branch of the median nerve ( anterior interosseous syndrome).Ĭompression 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 ("FPL"), the flexor digitorum profundus of the index finger ("FDP IF"), and the pronator quadratus ("PQ"). Pronator teres syndrome is a compression neuropathy of the median nerve at the elbow. Medical condition Pronator teres syndrome
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