BackgroundThe median nerve and flexor tendons are known to translate transversely in the carpal tunnel. The purpose of this study was to investigate these motions in differential finger motion using ultrasound, and to compare them in healthy people and carpal tunnel syndrome patients.MethodsTransverse ultrasounds clips were taken during fist, index finger, middle finger and thumb flexion in 29 healthy normal subjects and 29 CTS patients. Displacement in palmar-dorsal and radial-ulnar direction was calculated using Analyze software. Additionally, the distance between the median nerve and the tendons was calculated.ResultsWe found a changed motion pattern of the median nerve in middle finger, index finger and thumb motion between normal subjects and CTS patients (p<0.05). Also, we found a changed motion direction in CTS patients of the FDS III tendon in fist and middle finger motion, and of the FDS II and flexor pollicis longus tendon in index finger and thumb motion, respectively (p<0.05). The distance between the median nerve and the FDS II or FPL tendon is significantly greater in patients than in healthy volunteers for index finger and thumb motion, respectively (p<0.05).ConclusionOur results suggest a changed motion pattern of the median nerve and several tendons in carpal tunnel syndrome patients compared to normal subjects. Such motion patterns may be useful in distinguishing affected from unaffected individuals, and in studies of the pathomechanics of carpal tunnel syndrome.

The purpose of this study was to investigate the deformation and displacement of the normal median nerve in the carpal tunnel during index finger and thumb motion, using ultrasound. Thirty wrists from 15 asymptomatic volunteers were evaluated. Cross-sectional images during motion from full extension to flexion of the index finger and thumb were recorded. On the initial and final frames, the median nerve, flexor pollicis longus (FPL), and index finger flexor digitorum superficialis (FDS) tendons were outlined. Coordinate data were recorded and median nerve cross-sectional area, perimeter, aspect ratio of the minimal-enclosing rectangle, and circularity in extension and flexion positions were calculated. During index finger flexion, the tendon moves volarly while the nerve moves radially. With thumb flexion, the tendon moves volarly, but the median nerve moves toward the ulnar side. In both motions, the area and perimeter of the median nerve in flexion were smaller than in extension. Thus, during index finger or thumb flexion, the median nerve in a healthy human subject shifts away from the index finger FDS and FPL tendons while being compressed between the tendons and the flexor retinaculum in the carpal tunnel. We are planning to compare these data with measurements in patients with carpal tunnel syndrome (CTS) and believe that these parameters may be useful tools for the assessment of CTS and carpal tunnel mechanics with ultrasound in the future. The carpal tunnel contains nine flexor tendons and the median nerve. These structures are surrounded by the subsynovial connective tissue (SSCT), which functions as a sliding interface among these structures. 1 The major pathological finding in carpal tunnel syndrome (CTS) is fibrosis of the SSCT, which changes the motion characteristics of the SSCT, tendon excursion, and median nerve, as noted during intraoperative inspection in cases of carpal tunnel release. 1-4 These changes may also cause elevated strain and pressure in the carpal tunnel, which ultimately can lead to CTS. 2,5 We hypothesize that due to fibrosis of the SSCT, the kinematics of the nerve and tendons in the carpal tunnel change in patients with CTS. We further hypothesize that these changes are associated with the evolution of CTS and that these changes can be monitored noninvasively by ultrasound. A first step in testing our hypotheses is to identify the normal motion pattern of the tendons and the median nerve in the carpal tunnel. These data can then be used as a baseline against which to compare CTS patients' data. If, as we hypothesize, detectable differences exist in the SSCT and tendon and nerve kinematics in patients with CTS, then these differences could be sought in individuals at risk for CTS. If our hypotheses are supported, then ultrasound could be a useful noninvasive tool to study the genesis of CTS and to monitor at risk individuals.Ultrasonography is a good imaging technique for the structures in the carpal tunnel. Several parameters within the carpal tunnel have been assess...

PURPOSE We investigated the median nerve deformation in the carpal tunnel in patients with carpal tunnel syndrome and controls during thumb, index finger, middle finger and a four finger motion, using ultrasound. METHODS Both wrists of 29 asymptomatic volunteers and 29 patients with idiopathic carpal tunnel syndrome were evaluated by ultrasound. Cross-sectional images during motion from full extension to flexion were recorded. Median nerve cross-sectional area, perimeter, aspect ratio of the minimal enclosing rectangle, and circularity in extension and flexion positions were calculated. Additionally, a deformation index was calculated. We also calculated the intra-rater reliability. RESULTS In both controls and patients, the median nerve cross sectional area became significantly smaller from extension to flexion in all finger motions (p<0.05). In flexion and extension, regardless of the specific finger motion, the median nerve deformation, circularity and the change in perimeter were all significantly greater in CTS patients than in controls (p<0.05). We found excellent intra-rater reliability for all measurements (ICC>0.84). CONCLUSIONS With this study we have shown that it is possible to assess the deformation of the median nerve in carpal tunnel syndrome with ultrasonography and that there is more deformation of the median nerve in carpal tunnel syndrome patients during active finger motion. These parameters might be useful in the evaluation of kinematics within the carpal tunnel, and in furthering our understanding of the biomechanics of carpal tunnel syndrome in the future.