An Overview
The median nerve is involved in pronator teres syndrome. Pronator teres syndrome is a compression of the median nerve at the level of the elbow. This syndrome occurs more in females.
In the forearm, the median nerve runs between the two heads of the pronator teres muscle and then lies between the flexor digitorum superficialis and flexor digitorum profundus muscles. In this way, pronator teres syndrome may be associated with medial epicondylitis.
Potential sites for entrapment of the median nerve include compression of the nerve between the two heads of the pronator teres muscle, seen in people who perform repetitive forceful pronation of the forearm; compression due to thickening of the bicipital aponeurosis, which crosses from lateral to medial over the antecubital fossa, which may irritate the nerve; and compression of the nerve from the fibrous arch of the origin of the flexor digitorum superficialis.
The median nerve runs down the medial side of the arm and passes 2.5 to 4 cm below the level of the medial epicondyle before it enters between the two heads of the pronator teres. About 1% of patient have a medial supracondylar humeral spur about 5 cm proximal to the medial epicondyle. The ligament of Struthers is attached to this bony projection which connects the process of the medial epicondyle. This 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.
The principle symptoms of numbness in the radial 3 ½ fingers as well as thenar weakness may often be mistakenly attributed to carpal tunnel syndrome, but this is not the case
Clinical Presentation
Paresthesia in the lateral 3 ½ fingers may occur with compression of the median nerve at the elbow region or at the carpal tunnel region. Symptoms of pronator teres syndrome are similar to carpal tunnel syndrome, but the symptoms with pronator teres syndrome are worse with rotation of the forearm.
Patients will complain of a dull aching pain over the proximal forearm with no night symptoms. The pain is usually worsened by repetitive or forceful pronation. There may also be tenderness of palpation to the pronator teres muscle.
The median nerve gives off a palmar cutaneous branch before entering the carpal tunnel. So, sensory disturbances over the palm of the hand occur due to involvement of the palmar cutaneous branch of the median nerve. This occurs proximal to the carpal tunnel. Sensory disturbance in this area indicates median nerve problems proximal to the carpal tunnel, and this differentiates between carpal tunnel syndrome and pronator teres syndrome.
Examination & Tests
There are no specific provocative tests used to localize the site of the compression that produce the pain and distal paresthesia. In pronator teres syndrome, Tinel’s sign at the wrist will be negative and Phalen’s test will be negative. Therefore, 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. To do so, resisted forearm pronation with the elbow extension will test for compression at the two heads of the pronator teres muscle. The patient’s forearm should be 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 in two other ways. The first is resisted elbow flexion with forearm supination, which indicates compression of the median nerve at the bicipital aponeurosis. The other way of testing compression of the median nerve is by resisted contraction of the flexor digitorum superficialis to the middle finger, and this indicates compression at the flexor digitorum superficialis arch.
Differential Diagnosis
C6 and C7 radiculopathy will have involvement of the nerves at these levels that will cause numbness of the thumb, index, and long fingers. It will also cause weakness of the muscles of the forearm that are innervated by the median nerve. However, the radial nerve part of C6-C7 will show normal function of the wrist extensors and the triceps.
Carpal tunnel syndrome will also need to be differentiated. X-rays, imaging, and nerve conduction studies will be useful in diagnosis of carpal tunnel syndrome, in addition to careful clinical examination.
Treatment
Treatment for pronator teres syndrome include rest, non-steroidal anti-inflammatory medication, and splints. Surgical decompression of the median nerve through all 4 or 5 possible sites of compression is also an option for treatment of pronator teres syndrome. However, this is only done when non-operative management fails after 3-6 months. The results of surgery are variable, and full recovery is not always seen in all patient. About 80% of the patients improve with surgery. In addition, the skin incision may leave an unsatisfactory scar.
