Pronator Syndrome

Background

Carpal tunnel syndrome is one of the most common compression neuropathies and represents a compression of the median nerve at the wrist. Occasionally, the median nerve is compressed higher up along the forearm, close to the elbow and it's possible to miss this less common site of compression. This condition is called pronator syndrome.

Causes

In this form of median nerve compression, the nerve is compressed at the proximal to mid-forearm by several structures, most often the pronator teres, but there can also be other compression sites such as the superficial flexor tendon origin called sublimis arch, and aberrant fascial bands or vascular leashes.

Symptoms

In contrast to carpal tunnel syndrome, more advanced cases of median nerve compression at the forearm can present with numbness and tingling in the distribution of the palmar cutaneous nerve. This is the classic differentiation of carpal tunnel syndrome from the less common median nerve compression at the forearm. The patient may also have pronounced pain in the forearm along the course of the median nerve. A tinel sign can be present.

Diagnosis & Treatment

The patient's history is critical in making the diagnosis, followed by a physical exam that includes a number of so-called provocative maneuvers such as the Tinel, Phalen, and carpal compression test, resisted forearm pronation and passive forearm supination. Sensory examination in the distribution of the palmar cutaneous nerve is critical. Electromyography (EMG, also called “nerve test”) aids in further confirming and locating the site of nerve compression. In terms of imaging studies, both MRI and ultrasound are helpful modalities, in particular the ultrasound since this can delineate any component of dynamic compression.

Treatment

Depending on the severity of symptoms and the results of electrophysiologic studies, a customized treatment is often required which can range from physical or occupational therapy to surgical decompression.

Patient that underwent an endoscopic carpal tunnel release with persistence of symptoms. We performed an open release (patient incidentally had a bifid median nerve at the carpal tunnel). The blue marking on the forearm outlines the planned incision to access the median nerve at the pronator tunnel. The incision we made ended up being shorter than the initial marking.