The nerve that is involved in pronator teres syndrome is the
median nerve. Pronator Teres Syndrome is caused by a compression of the median
nerve at the level of the elbow which occurs more in women. In the forearm, the
median nerve runs between the two heads of the pronator teres muscle and then
it lies between the flexor digitorum superficialis and flexor digitorum
profundus muscles. This syndrome may be associated with medial epicondylitis.
The principle symptoms of numbness in the radial 3 ½ fingers as well as thenar
weakness which may be mistakenly attributed to carpal tunnel syndrome.
The most common cause of entrapment is due to compression of
the median nerve between the two heads of the pronator teres muscle. This
commonly occurs in people who perform repetitive forceful pronation of the
forearm. Compression may be due to the thickening of the bicipital aponeurosis.
The aponeurosis crosses from lateral to medial over the antecubital fossa and
may irritate the median nerve. Compression of the nerve may also occur due to
the fibrous arch of the origin of the flexor digitorum superficialis (FDS). 
The median nerve runs down the medial side of the arm and
passes 2 ½ to 4 cm 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 and the median nerve can become compressed by the supracondylar spur. 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 the
compression of the ulnar nerve around the elbow.
Paresthesia in these lateral 3 ½ fingers may occur with the compression
of the median nerve at the elbow region or at the carpal tunnel region. These 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 nighttime symptoms. The pain is usually worsened by
repetitive or forceful pronation. Tenderness of palpation to the pronator teres
muscle will be detected. 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 disturbances in
this area indicates median nerve problems proximal to the carpal tunnel. This differentiates
between carpal tunnel syndrome and pronator teres syndrome.
There are specific provocative tests that produce the pain
and distal paresthesia that are used to localize the site of compression. The
Tinel’s sign at the wrist and the Phalen’s test will be negative. The 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 be abnormal
sensation in the “palmar triangle”. When compression of the nerve involves the
supracondylar process, the test is considered positive if symptoms of tingling
worsen while tapping on the spur.
Occassionally, the spur can be felt. The
pronator teres muscle can be assessed as the cause of the median nerve
compression in different ways. Resisted forearm pronation with elbow flexion
will test for compression at the two heads of the pronator teres muscle. During
this test, 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 may also be tested by: resisted elbow flexion
with forearm supination (compression at the bicipital aponeurosis) and resisted
contraction of the FDS to the middle finger (compression at the FDS arch).
Differential Diagnosis
C6/C7 Radiculopathy occurs due to involvement of the nerves
at these levels which 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.
X-rays, imaging and nerve conduction studies may be helpful
in the diagnosis.
Treatment typically consists of rest, splints, and NSAIDs.
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 as only
about 80% of patients improve from surgery. The skin incision may leave an
unsatisfactory scar.
