title: Elbow effusions: distribution of joint fluid with flexion and extension and imaging implications.
abstract: OBJECTIVE
  The authors study the distribution of elbow joint fluid with flexion and extension of the joint and evaluate the imaging implications of such distribution.
  
  
  METHODS
  Three cadaveric elbows were studied with radiography, ultrasonography, and magnetic resonance imaging after the incremental injections of 1 to 15 mL of saline solution into the elbow joint. Imaging was obtained with full flexion and extension of the joint. Anatomic sections were obtained for correlation.
  
  
  RESULTS
  In flexion fluid initially collected posteriorly and, with larger quantities, anteriorly. In extension the anterior fat pad was pressed into its fossa and the posterior fat pad was displaced superiorly by the olecranon process. On lateral radiographs in elbow flexion a positive fat pad sign was seen with 5 to 10 mL of fluid in the joint. Sonography allowed identification of 1 to 3 mL of fluid posteriorly with the elbow flexed. Magnetic resonance imaging allowed identification of 1 mL of fluid, regardless of joint position and location.
  
  
  CONCLUSIONS
  The distribution of joint fluid in the elbow is influenced by flexion and extension of the joint. Radiography is best performed in flexion. Sonography is more sensitive than radiography in diagnosing effusions, but should be performed along the olecranon fossa with the elbow flexed. Magnetic resonance imaging is most sensitive in identifying effusions, regardless of joint position or location.
authors.affiliation: Department of Radiology, Veterans Administration Medical Center, San Diego, California 92161, USA.
authors.forename: M
authors.initials: M
authors.lastname: De Maeseneer
authors.forename: J A
authors.initials: JA
authors.lastname: Jacobson
authors.forename: S
authors.initials: S
authors.lastname: Jaovisidha
authors.forename: L
authors.initials: L
authors.lastname: Lenchik
authors.forename: K N
authors.initials: KN
authors.lastname: Ryu
authors.forename: D R
authors.initials: DR
authors.lastname: Trudell
authors.forename: D
authors.initials: D
authors.lastname: Resnick
mesh_terms: D001826:Body Fluids / Q000502:physiology*; D002102:Cadaver; D004487:Edema / Q000175:diagnosis* / Q000503:physiopathology; D004551:Elbow Joint / Q000000981:diagnostic imaging / Q000473:pathology; D006801:Humans; D008279:Magnetic Resonance Imaging; D016059:Range of Motion, Articular; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed; D014463:Ultrasonography