title: Day-to-day variability of median nerve location within the carpal tunnel.
abstract: BACKGROUND
  Carpal tunnel syndrome is a commonly encountered entrapment disorder resulting from mechanical insult to the median nerve. Magnetic resonance imaging (MRI)-based investigations have documented typical locations of the median nerve within the carpal tunnel; however, it is unclear whether those locations are consistent within an individual on different days.
  
  
  METHODS
  To determine the day-to-day variability of nerve location, 3.0T MRI scans were acquired from six normal volunteers over multiple sessions on three different days. Half of the scans were acquired with the wrist in neutral flexion and the fingers extended, and the other half were acquired with the wrist in 35 degrees of flexion and the fingers flexed. Prior to half of the scans (in both poses), subjects performed a preconditioning routine consisting of specified hand activities and several repetitions of wrist flexion/extension. The shape, orientation, location, and location radius of variability of the median nerve and three selected flexor tendons were determined for each subject and compared between days.
  
  
  RESULTS
  Two of the six subjects had substantial variability in nerve location when the wrist was in neutral, and four of the subjects had high variability in nerve position when the wrist was flexed. Nerve variability was typically larger than tendon variability. The preconditioning routine did not decrease nerve or tendon location variability in either the neutral or the flexed wrist positions.
  
  
  CONCLUSIONS
  The high mobility and potential for large variability in median nerve location within the carpal tunnel needs to be borne in mind when interpreting MR images of nerve location.
authors.affiliation: Department of Orthopaedics & Rehabilitation, Orthopedic Biomechanics Lab, University of Iowa, Iowa City, IA 52242, USA. jessica-goetz@uiowa.edu
authors.forename: Jessica E
authors.initials: JE
authors.lastname: Goetz
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Thedens
authors.forename: Nicole M
authors.initials: NM
authors.lastname: Kunze
authors.forename: Ericka A
authors.initials: EA
authors.lastname: Lawler
authors.forename: Thomas D
authors.initials: TD
authors.lastname: Brown
mesh_terms: D000328:Adult; D002348:Carpal Bones / Q000033:anatomy & histology*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008475:Median Nerve / Q000033:anatomy & histology*; D008953:Models, Anatomic; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D055815:Young Adult