To examine the usefulness of the second lumbrical-interosseous (2L-INT) distal motor latency (DML) comparison test in localizing median neuropathy to the wrist in patients with absent median sensory and motor response in routine nerve conduction studies.
Electrodiagnostic results from 1,705 hands of patients with carpal tunnel syndrome (CTS) symptoms were reviewed retrospectively. All subjects were evaluated using routine nerve conduction studies: median sensory conduction recorded from digits 1 to 4, motor conduction from the abductor pollicis brevis muscle, and the 2L-INT DML comparison test.
Four hundred and one hands from a total of 1,705 were classified as having severe CTS. Among the severe CTS group, 56 hands (14.0%) showed absent median sensory and motor response in a routine nerve conduction study, and, of those hands, 42 (75.0%) showed an abnormal 2L-INT response.
The 2L-INT DML comparison test proved to be a valuable electrodiagnostic technique in localizing median mononeuropathy at the wrist, even in the most severe CTS patients.
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Objective: The purpose of this study was to find out diagnostic clue for the carpal tunnel syndrome. So we investigated the postional relationships between the structures, the degree of entrance of the muscle bellies in the carpal tunnel, the location of flexor retinaculum (FR) and the cross sectional area to the tunnel of the tendons, the median nerve and the soft tissues occupied with the wrist.
Method: Seventy-seven wrists of Korean adults's cadavers were dissected. Fifty-three wrists were examined by posteroanterior view of X-ray. The area of each structure was measured by image analyzer (Optimas Co. WA). The upper and lower borders the FR were confirmed at the sagittal plane after sagittal section.
Results: Frequency of the bellies of FDS, FDP and lumbricalis observed in each finger, the length of these bellies entering into the carpal tunnel were obtained. The cases that the third and fourth FDS were located side by side, the second FDS tendon under the third FDS tendon and the fifth tendon under the fourth FDS tendon were most common. The cases that the median nerve was bordered on the third FDS and the second FDS deep inside of the median nerve were most common. Mean length of the FR was 32.1 mm. The cases that the location of the upper margin of the FR was 10 mm and 15 mm from the end of radius were most common (44%). The cases that the margin of FR was 5 mm and 10 mm from the base of the 3rd metacarpal bone were most common (52%). The cross sectional area ratios to the carpal tunnel of the tendon, median nerve and connective tissues were 30%, 4%, 66% at the level of the pisiform bone, 36%, 4%, 60% at the level of the hook of hamate and 28%, 3%, 67% at the level of the lower margin of the FR, respectively.
Conclusion: These results could help to understand the etiology of the carpal tunnel syndrome and would be a helpful information to the diagnostic imaging of the carpal tunnel.
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