title: Sonographic Visualization of Thenar Motor Branch of the Median Nerve: A Cadaveric Validation Study.
abstract: The thenar motor branch (TMB) of the median nerve may be affected in carpal tunnel syndrome and can be injured during carpal tunnel surgery. Although ultrasound has been used to identify small nerves throughout the body, the sonographic evaluation of the TMB has not been investigated formally.
  
  
  
  To document the ability of ultrasound to visualize the TMB of the median nerve in an unembalmed cadaveric model.
  
  
  
  Prospective laboratory investigation.
  
  
  
  Procedural skills laboratory at a tertiary medical center.
  
  
  
  On the basis of anatomical descriptions, dissection and clinical experience, a technique was developed to sonographically identify the presumed TMB of the median nerve at the distal carpal tunnel. A single, experienced examiner then identified the presumed TMB in 10 unembalmed, cadaveric upper limb specimens (4 right, 6 left) obtained from 9 donors (4 male, 5 female) ages 76-85 years with body mass indices of 18.2-29.5 kg/m2with both 12-3 MHZ and 16-7 MHz linear array transducers. The same examiner then injected 0.2-0.3 mL of diluted colored latex into and around the presumed TMB using direct ultrasound guidance. At a minimum of 24 hours postinjection, specimens were dissected under loupe magnification to determine the location of the latex injectate.
  
  
  
  The location of latex injectate relative to the anatomically identified TMB.
  
  
  
  A vertical, linear, hypoechogenic region was sonographically identified arising from the median nerve at the distal carpal tunnel in all 10 specimens and was hypothesized to represent the vertical segment of the TMB. Both transducers allowed identification of the TMB, although localization was subjectively facilitated by the higher frequency transducer. All 10 sonographically guided injections placed latex into and around the TMB of the median nerve, confirming that ultrasound had accurately identified the TMB.
  
  
  
  Sonographic evaluation of the TMB of the median nerve is technically feasible and should be considered when clinically indicated. Further research and clinical experience is necessary to define the role of sonographic TMB imaging in the evaluation and management of patients with carpal tunnel syndrome.
  
  
  
  IV.
authors.affiliation: Departments of Physical Medicine & Rehabilitation, Radiology, and Anatomy, Mayo Clinic Sports Medicine Center, Mayo Clinic, W14, Mayo Building, 200 1st St, SW, Rochester, MN 55905(∗). Electronic address: Smith.jay@mayo.edu.
authors.forename: Jay
authors.initials: J
authors.lastname: Smith
authors.affiliation: Department of Orthopedics and Sports Medicine, Mayo Clinic Health System, Austin, MN(†).
authors.forename: Darryl E
authors.initials: DE
authors.lastname: Barnes
authors.affiliation: University of Minnesota Rochester, Rochester, MN(‡).
authors.forename: Kailee J
authors.initials: KJ
authors.lastname: Barnes
authors.affiliation: Department of Physical Medicine and Rehabilitation, The Ohio State University, Columbus, OH(§).
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Strakowski
authors.affiliation: Departments of Anatomy and Plastic Surgery, Mayo Clinic, Rochester, MN(¶).
authors.forename: Nirusha
authors.initials: N
authors.lastname: Lachman
authors.affiliation: Department of Orthopedic Surgery, Mayo Clinic, Rochester, MN(#).
authors.forename: Sanjeev
authors.initials: S
authors.lastname: Kakar
authors.affiliation: Cattedra "R" di Radiologia-DIMI, Universita' di Genova, Genoa, Italy(∗∗).
authors.forename: Carlo
authors.initials: C
authors.lastname: Martinoli
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002102:Cadaver; D002349:Carpal Tunnel Syndrome / Q000000981:diagnostic imaging; D005260:Female; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000000981:diagnostic imaging*; D014463:Ultrasonography / Q000379:methods*