;ry " he tO Copyright1981 by The Journalof Boneand Joint Surgery, Incorporated hy ar- The Pronator Teres Syndrome: ior tal Compressive Neuropathy of the Median Nerve* .~nt dl, BY CHARLES R. HARTZ, M.D.’~, RONALD L. LINSCHEID, M.D.’~, R. REED GRAMSE, M.D.’~, AND JASPER R. DAUBE, M.D.J’, ROCHESTER, MINNESOTA ior in From the Departments of Orthopedics, Physical Medicine and Rehabilitation, and Neurology, MayoClinic and MayoFoundation, Rochester at- ~re ABSTRACT:Thirty-nine patients with a clinical gically g, an anomalous fibrous band that compressed the the diagnosis of the pronator teres syndrome were seen median nerve was identified and cut. Since then, the syn- during a seven-year period. They typically complained drome has been recognized with increasing frequen- FIS, of aching discomfort in the forearm, weakness in the cy2,’,’,9,1e, ¯ it hand, and numbness in the thumb and index finger. We are reporting a study of thirty-nine patients in as Cyclic stress usually brought on the symptoms. The whomwe diagnosed the pronator teres syndrome and at- the distinctive physical finding was tenderness overthe tempted to identify the factors by which one can differ- ’ tO proximal part of the pronator teres, which was aggra- entiate this disorder from other lesions. SO vated by resisted pronation of the forearm, flexion of To the elbow, and occasionally by resisted contraction of Clinical Material ~al- the flexor superficialis of the long finger..Elec- From 1972 to 1979, thirty-nine patients seen at the der trophysiological testing of the median nerve showed Mayo Clinic were diagnosed as having the pronator teres caft abnormalities in a few patients, but localization of the syndrome. Preoperatively and postoperatively, all of the der abnormality was possible only rarely. Intraoperative patients were examined by one or two of us (C. R. H. and recordings showed some improvement shortly after R. L. L.). Twenty-nine patients were female and ten were release of the median nerve in six of the ten forearms male; their ages ranged from fourteen to seventy-eight that were tested. Surgical exploration of thirty-six years. The criteria for diagnosis were symptoms and signs forearms in thirty-two patients showed intramuscular of a median neuropathy localized to the forearm and hand: tendinous bands in the pronator, indentation of the aching discomfort and easy fatigability of the muscles muscle belly of the pronator teres by the lacertus fi- of tile forearm brought on by cyclic stress, and indentation brosus, or a taut tendinous origin of the flexor super- and tenderness of the pronator teres muscle. With repeti- ficialis in most forearms. Vascular and muscular tive pronation the patients also had numbness in the dis- abnormalities were seen occasionally. Of the thirty-six tribution of the median nerve in the hand; the nu__mbness operations, twenty-eight gave good or excellent results; seldom was well localized, although it tended to involve five, fair; "and in three patients the symptoms were un- the index finger and thumb and first was noticed after the changed. The cause of failure was either inadequate discomfort became evident. Nocturnal awakening because decompression or misdiagnosis. ~3f pain as well as numbness in the hand in the morning, commonly associated with the carpal tunnel syndrome, Compressive neuropathy of the median nerve in the typically was absent. The duration of symptoms averaged arm and forearm Can be a difficult diagnostic and thera- twenty-three months (range, one to 120 months). The peutic challengeZ’V’a’12~ It must be distinguished from cer- symptoms usually began insidiously, but occasionally vical radiculitis, the thoracic outlet syndrome, brachial after a specific muscle sprain or episode of activity their plexus neuritis, overuse of the muscles of the forearm, and onset was rapid and dramatic. The symptoms frequently carpal tunnel syndrome. In 1951, Seyffarth described a began during activities that required repetitive grasping or group of seventeen patients with symptoms that he con- pronation, or both (for example, prolonged hammering, sidered to be caused by compression of the median nerve scraping dishes, ladling food, or practicing tennis serves). in its course through the pronator teres muscle. In the first One of our patients had a rather sudden onset of symptoms patients with pronator teres syndrome to be treated sur- of the pronator teres syndrome in a forearm affected by spastic hemiparesis. Previously he had had a tendon trans- * Read at the Annual Meeting of The American Orthopaedic As- fer from the flexor digkorum superficia~is to the pr~3fundus sociation, San Juan, Puerto Rico, June !8, 1979, and a ieng~hening of the flexor carpi radia!is. It ’,~..’as be- ~" Mayo Clinic. 2!30 First Street S.W., Rochester. Mklnesota 55~05. P!~ase addv~Ss r~r.ri~:t requests ’:o Dr. Hartz, c/o Secti:~ ~f Pub- !ieved ~hat the dorsiflexion of th,~ wris~ ai]o,ve~ by the VOL. 63-A, NO. 6, JULY1981 885 886 C.R. HARTZ, R. L. LINSCHEID, R. R. GRAMSE, AND J. R. DAUBE der the taut origin of the flexor digitorumsuperficialis. We nerve at the level of the pronator terns, and electromyo- had no patients with po~t-traumatic syndromes in our graphic abnormalities limited to muscles innervated by the series. The lack of specificity of the symptomsand the median nerve, were considered definitive electrophysi- subtlety of the physical findings in-several patients led to ological findings for the pronator terns syndrome. In- suspicion of either functional neurosis or conversion hys- traoperative recordings from the median nerve were made teria. Sevenpatients had had misdiagnoses that had led to in ten forearmsin eight patients in an attempt to identify a carpal tunnel release, and one of them had had an ulnar more localized abnormality than could be detected witti transposition operation without relief of symptoms. The routine recordings, and to record any electrophysiological previous operations were done between three and twenty- changes in the nerve after decompression. Direct in- eight monthsbefore our initial examination. traoperative measurementsof mixed nerve-action poten- The physical findings in the seven patients whowere tials were madefrom the exposed nerve both proximal and not operated on and in the thirty-two whowere operated on distal to the pronator terns before and after surgical release differed only in degree. The outstanding positive finding of compression on the median nerve. Nerve-action poten- was tenderness in the proximal part of the pronator teres tials were stimulated and recorded using hand-held muscle, which was noted in thirty-seven patients. In the silver-hook pairs of electrodes with the nerve elevated other two patients, this symptommay have been present away from surrounding tissue. Stimulation was applied but it was not noted. Wefound tenderness in the median distally in the forearm while recording was done proximal nerve in the antecubital space in thirty-one patients, while to the pronator teres muscle. Recordings were made be- tenderness was noted distally less frequently. Thirty pa- fore, immediatelyafter, and fifteen to twentyminutes after tients experienced paresthesias in the distribution of the surgical decompressionof the nerve. Distances along the median nerve and the hand when the forearm was pronated nerve betweenthe stimulating and the recording electrodes forcibly against resistance. A positive Tinel sign at the were measuredwith a millimeter ruler to allow calculation proximal edge of the pronator teres was elicited in twenty of velocities fromthe latencies of the initial-positive peak. patients. Fourteen patients suffered exacerbation of the Amplitudes were measured from peak to peak. paresthesias whenthe flexors of the long finger were con- tracted against resistance. In seventeen patients, the pro- Treatment nator muscle was observed to be unusually firm compared Seven patients considered that their symptomswere with the contralateral muscle. A depression in the contour not severe enough to justify an operation. Anexplanation of the forearm superficial to the lacertus fibrosus was obvi- of the probable cause for the symptomsand steps that ous in three patients. Mild thenar atrophy was present in could be taken to minimize them, including job only three patients, and the Tinel test was rarely positive at modifications, were given. Surgical exploration was per- the wrist, although nineteen patients had a positive Phalen formedin thirty-two patients (thirty-six forearms). In all sign at the wrist. Hypohidrosis in the distribution of the thirty-two patients, cutaneous sensory nerves of the arm median nerve, which is commonin the carpal tunnel syn- and forearm were identified and protected. Weinspected drome, was not found in any of our patients. the lacertus fibrosus, assessed its thickness, and deter- mined whether it indented the antebrachial fascia-over the Electrical Studies pronator, especially during passive pronation and exten- El.ectromyography was done on forty forearms in sion. Then the course of the median nerve was noted, and thirty-eight patients. One patient had had an electromyo- it wasfreed along the radial border. The relationship of the graphic study at another institution six months before an nerve to the pronator teres was assessed. Intramuscular unsuccessful carpal-tunnel release, and the test was not re- tendinous bands within or under the pronator and fascial peated. All patients had bilateral measurements in the constricting bands betweenthe superficial and deep