title: Shear strain and motion of the subsynovial connective tissue and median nerve during single-digit motion.
abstract: OBJECTIVE
  The objective of this study was to measure the relative motion of the middle finger flexor digitorum superficialis (FDS) tendon, its adjacent subsynovial connective tissue (SSCT), and the median nerve during single-digit motion within the carpal tunnel in human cadaver specimens and to estimate the relative motions of these structures in different wrist positions.
  
  
  METHODS
  Using fluoroscopy during simulated single-digit flexion, we measured the relative motion of the middle finger FDS tendon, SSCT, and median nerve within the carpal tunnel in 12 human cadavers. Measurements were obtained for 3 wrist positions: neutral, 60 degrees flexion, and 60 degrees extension. After testing with an intact carpal tunnel was completed, the flexor retinaculum was cut with a scalpel, and the same testing procedure was repeated for each wrist position. The relative motions of the tendon, SSCT, and median nerve were compared using a shear index, defined as the ratio of the difference in motion along the direction of tendon excursion between 2 tissues divided by tendon excursion, expressed as a percentage.
  
  
  RESULTS
  Both tendon-SSCT and tendon-nerve shear index were significantly higher in the 60 degrees of wrist flexion and extension positions than in the neutral position. After division of the flexor retinaculum, the shear index in the 60 degrees wrist extension position remained significantly different from that of the neutral position.
  
  
  CONCLUSIONS
  We have found that the relative motion between a tendon and SSCT in the carpal tunnel is maximal at extremes of wrist motion. These positions may predispose the SSCT to shear injury.
authors.affiliation: Orthopedic Biomechanics Laboratory, Division of Orthopedic Research, Mayo Clinic, Rochester, MN 55905, USA.
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Yoshii
authors.forename: Chunfeng
authors.initials: C
authors.lastname: Zhao
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Henderson
authors.forename: Kristin D
authors.initials: KD
authors.lastname: Zhao
authors.forename: Kai-Nan
authors.initials: KN
authors.lastname: An
authors.forename: Peter C
authors.initials: PC
authors.lastname: Amadio
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002102:Cadaver; D003238:Connective Tissue / Q000502:physiology*; D005260:Female; D005385:Fingers / Q000502:physiology*; D005471:Fluoroscopy; D006801:Humans; D008023:Ligaments, Articular / Q000293:injuries; D008297:Male; D008475:Median Nerve / Q000502:physiology*; D008875:Middle Aged; D009068:Movement / Q000502:physiology*; D013314:Stress, Mechanical; D013710:Tendons / Q000502:physiology; D014953:Wrist / Q000502:physiology*