Pronator Teres Syndrome

Pronator teres syndrome is a compression of the median nerve at the level of the elbow which occurs more in females. In the forearm, the median nerve runs between the two heads of the pronator teres muscle, and it lies between the flexor digitorum superficialis and flexor digitorum profundus muscles. Pronator teres syndrome could be associated with medial epicondylitis. The principle symptoms of numbness in the radial 3 ½ fingers as well as thenar weakness may be mistakenly attributed to carpal tunnel syndrome. Potential sites for entrapment of the nerve include the median nerve. Compression of the median nerve between the two heads of the pronator teres muscle (most common cause). It occurs in people who perform repetitive forceful pronation of the forearm. Entrapment can also occur due to compression due to thickening of the bicipital aponeurosis. The aponeurosis crosses from lateral to medial over the antecubital fossa, and it may irritate the median nerve. Compression of the nerve from the fibrous arch of the origin of the flexor digitorum superficialis (FDS) can be a potential site for entrapment. The median nerve runs down the medial side of the arm and passes 2 ½ to 4cm below the level of the medial epicondyle before it enters between the two heads of the pronator teres. About 1% of patients have a medial supracondylar humeral spur about 5cm proximally to the medial epicondyle. The ligament of Struthers is attached to this bony projection which connects the process to the medial epicondyle. The bony process points towards the elbow joint. The median nerve can become compressed or entrapped by the supracondylar spur and by the ligament of Struthers. The median nerve can also become trapped by the ligament of Struthers that extends from the supracondylar process to the medial epicondyle. The ligament of Struthers is different from the arcade of Struthers, which deals with compression of the ulnar nerve around the elbow.

Paresthesia in these lateral 3 ½ fingers may occur with compression of the median nerve at the elbow region or at the carpal tunnel region. Symptoms are similar to carpal tunnel syndrome but the symptoms are worse with rotation of the forearm. The patient will complain of dull aching pain over the proximal forearm with no night symptoms. The pain is usually worsened by repetitive or forceful pronation. Tenderness of palpation to the pronator teres muscle. The median nerve gives off a palmar cutaneous branch before entering the carpal tunnel. Sensory disturbances over the palm of the hand occur due to involvement of the palmar cutaneous branch of the medial nerve, and this occurs proximal to the carpal tunnel. Sensory disturbance in this area indicates median nerve problems proximal to the carpal tunnel. This differentiates between carpal tunnel syndrome and pronator teres syndrome. There are no specific provocative tests used to localize the site of compression that produce the pain and distal paresthesia. Tinel’s sign at the wrist will be negative. Phalen’s test will be negative. Median nerve compression tests are negative at the carpal tunnel; however, there will be a positive Tinel’s sign at the proximal forearm. There will also be abnormal sensation in the palm of the hand. When compression of the nerve involves the supracondylar process, the test is considered positive if symptoms of tingling worsen while tapping on the spur. The pronator teres muscle can be assessed as the cause of the median nerve compression. Resisted forearm pronation with elbow extension will test for compression at the two heads of the pronator teres muscle. The patient’s forearm is held in resisted pronation and flexion. While remaining in a pronated position, the forearm is gradually extended. Compression of the median nerve can also be tested by resisted elbow flexion with forearm supination (indicates compression of the median nerve at the bicipital aponeurosis) or resisted contraction of the FDS to the middle finger (compression at the FDS arch). C6/C7 radiculopathy can be a differential diagnosis. Involvement of the nerves at these levels will cause numbness of the thumb, index and long fingers, as well as weakness of the muscles of the forearm that are innervated by the median nerve. The radial nerve part of C6/C7 will show normal function of the wrist extensors and the triceps. Carpal tunnel syndrome is also a differential diagnosis. X-rays, imaging, and nerve conduction studies may be helpful in diagnosis as well as careful clinical examination. To treat pronator teres syndrome, rest, use splints, and prescribe NSAIDs. Do surgical decompression of the median nerve through all 4 or 5 possible sites of compression when non-operative management fails for 3-6 months. The results of surgery are variable. Full recovery is not always seen in all patients. About 80% of the patients improve with surgery. The skin incision may leave an unsatisfactory scar.

Nabil Ebraheim, MD

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