Anatomical Relationships between Muscles Overlying Distal Transverse Carpal Ligament and Thenar Motor Branch of the Median Nerve

BACKGROUND: The purpose of the current study is to investigate anatomical relationships between the muscle overlying the distal transverse carpal ligament (TCL) and the thenar motor branch of the median nerve. METHODS: Of the 192 wrists that underwent open carpal tunnel release, a muscle belly overlying the TCL was observed on the distal margin of TCL in 25 wrists and ligament exposure could not be achieved without transection of it. We recorded surgical findings of these 25 wrists. The origin of the recurrent motor branch arising from the major median nerve was marked on the axial and coronal section diagrams of the wrist. RESULTS: The presence of muscle overlying the TCL was seen in 25 wrists (21 patients, 13%). The locations of origin were distributed not only on the radial side but anterior or ulnar side of the major median nerve. Abnormal branches originated from the unusual side in 14 cases (56% of those with a muscle overlying the TCL): central-anterior side in eight cases, ulnar-anterior side in five cases, and ulnar side in one case. These anomalous branches were frequently associated with the muscle belly overlying the TCL in our study regardless of the origin site. The branches were prone to cut if careless midline incision along the third web space was performed. Unusual origin and aberrant pathway of the recurrent thenar motor branch were associated with the presence of a muscle overlying the TCL. CONCLUSIONS: A thorough knowledge of the standard and variant anatomy of the muscle belly and recurrent motor branch in the carpal tunnel is fundamental to prevention of complications such as muscle wasting or atrophy by iatrogenic motor branch injury during carpal tunnel release.

Early Surgical Treatment of Pronator Teres Syndrome

We report a rare case of pronator teres syndrome in a young female patient. She reported that her right hand grip had weakened and development of tingling sensation in the first-third fingers two months previous. Thenar muscle atrophy was prominent, and hypoesthesia was also examined on median nerve territory. The pronation test and Tinel sign on the proximal forearm were positive. Severe pinch grip power weakness and production of a weak "OK" sign were also noted. Routine electromyography and nerve conduction velocity showed incomplete median neuropathy above the elbow level with severe axonal loss. Surgical treatment was performed because spontaneous recovery was not seen one month later.

Sonographic Appearance of Idiopathic Hypertrophy of the First Dorsal Interosseous Muscle of the Hand

We present a rare case of a 28-year-old man with a non-tender soft tissue enlargement on the dorsal side of the first web space of the right hand. Sonographic evaluation showed thickening of the dorsal thenar muscle (dorsal interosseous muscle) without a mass-like or cystic lesion, as compared with the left dorsal thenar muscle. On grasping position, this finding was more prominent and no significantly increased vascular flow was observed in this muscle. We were able to diagnose idiopathic hypertrophy of the first dorsal interosseous muscle solely by sonography. Ultrasonographic evaluation is a noninvasive and accessible tool for diagnosis of pseudotumors, such as idiopathic thenar muscle hypertrophy.

Motor Unit Number Estimation in Thenar Muscles of the Hemiplegic Patients

Motor unit number estimation(MUNE) was performed in the thenar muscles of 22 hemiplegic patients without a peripheral nerve lesion using the statistical method. The studies were done bilaterally in the affected and unaffected sides. The distal latency and conduction velocity of median nerve in the affected side were not different from those in the unaffected side. But the amplitude and area of the compound muscle action potential in the affected side were smaller than those in the unaffected side. Motor unit numbers in the affected side decreased than those of the unaffected side, especially in the first 6 months after the onset of hemiplegia. And the motor unit numbers in the affected side decreased as the muscle strength decreased. Single motor unit potential(SMUP) area in the affected side increased after 1 year from the onset of hemiplegia. The estimation of the number of motor units in the thenar muscles of hemiplegic patients could be an indicator for predicting recovery of the muscle power in hemiplegia.