CHANGES IN THE CARPAL-TUNNEL DUE TO ACTION OF THE FLEXOR TENDONS - VISUALIZATION WITH MAGNETIC-RESONANCE-IMAGING

Successive cross-sectional areas (CSA) of the carpal tunnel were measu red with the fingers in both extension and full flexion in 12 healthy volunteers using magnetic resonance imaging. During flexion, lumbrical muscles could be observed to move into the carpal tunnel up to differ ent revels in all volunteers. For each of the volunteers, the level of the hook of hamate was used as the reference level. The mean CSA meas ured at this level was considerably larger in flexion than in extensio n: 191 mm(2) (SD, +/-26) and 169 mm(2) (SD, +/-15), respectively (p = .004). In three volunteers, no difference in CSA between extension and flexion was measured at the hamate level, despite the presence of lum brical muscles, whereas in these same volunteers at levels more distal , the CSA clearly increased during flexion. The mean CSA for extension and flexion distal and just proximal to the smallest level differed s ignificantly, but the absence of expansion was noticed only at the sma llest level. Other changes that were frequently observed during flexio n were fat compression, flattening and displacement of the median nerv e, and pressure on the superficial and deep flexor tendons.