title: MRI of the thumb: anatomy and spectrum of findings in asymptomatic volunteers.
abstract: OBJECTIVE.:The purpose of this article is to analyze the MR anatomy and variable imaging characteristics of the thumb in asymptomatic volunteers.
  
  
  METHODS
  MRI of the thumb was obtained in 34 asymptomatic volunteers (mean age, 33.9 ± 9.2 years). Two radiologists independently assessed visibility and signal intensity (SI) and thickness of the following structures of the metacarpophalangeal and interphalangeal joints: proper and accessory radial and ulnar collateral ligaments, volar and dorsal plates, adductor pollicis aponeurosis, and annular pulleys. The presence and size of a synovial recess at the base of all plates was assessed.
  
  
  RESULTS
  On intermediate-weighted fat-saturated images, the ulnar collateral ligament of the metacarpophalangeal joint (reader 1, 79%; reader 2, 62%) and the adductor pollicis aponeurosis (reader 1, 50%; reader 2, 82%) commonly had a striated appearance. The radial collateral ligament of both joints was mainly of low SI (metacarpophalangeal joint, 53% for reader 1 and 85% for reader 2; interphalangeal joint, 59% for reader 1 and 82% for reader 2). All four pulleys were visible in each volunteer. An intermediate SI was observed in almost all pulleys, whereas the variable annular pulley had predominantly a low SI (reader 1, 50%; reader 2, 74%). The ulnar collateral ligament of the metacarpophalangeal joint is typically less than 3 mm thick, and the radial collateral ligament is less than 2 mm thick. A full-thickness synovial recess at the base of the dorsal plate of the metacarpophalangeal joint was seen in almost all volunteers (reader 1, 97%; reader 2, 100%).
  
  
  CONCLUSIONS
  The ligaments and pulleys of the thumb show considerable variability on MRI in healthy volunteers. The ulnar collateral ligament of the metacarpophalangeal joint is typically striated and less than 3 mm thick. A full-thickness synovial recess at the base of the dorsal plate of the metacarpophalangeal joint is a normal finding and should not be misdiagnosed as a tear.
authors.affiliation: 1 Department of Radiology, Orthopedic University Hospital Balgrist, University of Zurich, Forchstrasse 340, 8008 Zurich, Switzerland.
authors.forename: Anna
authors.initials: A
authors.lastname: Hirschmann
authors.forename: Reto
authors.initials: R
authors.lastname: Sutter
authors.forename: Andreas
authors.initials: A
authors.lastname: Schweizer
authors.forename: Christian W A
authors.initials: CW
authors.lastname: Pfirrmann
mesh_terms: D000328:Adult; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D013933:Thumb / Q000033:anatomy & histology*