title: Improving the detection of radiographically occult ankle fractures: positive predictive value of an ankle joint effusion.
abstract: OBJECTIVE
  To assess the value of an ankle effusion on plain radiographs as a predictor of radiographically occult fracture after acute ankle trauma.
  
  
  METHODS
  Consecutive patients with acute ankle trauma and radiographic evidence of an ankle joint effusion. Patients were excluded if ankle trauma was sustained more than 48 h previously or if a fracture was visible on initial photographs.
  
  
  METHODS
  All subjects (n = 26) underwent computed tomography (CT) of the ankle in sagittal and coronal planes. Ankle effusion size was measured from initial lateral ankle radiographs.
  
  
  RESULTS
  Twelve patients (46%) had radiographically occult fractures identified with CT. Fracture sites included: posterior or lateral malleoli (n = 4), calcaneus (n = 1), or talus (n = 7). Ankle effusion size was 11.2 mm in the group without fracture and 17.1 mm in the group with fracture (P < 0.0001). The positive predictive value of an effusion 15 mm or greater was 83%. CT detected significant soft-tissue injuries in four (15%) patients including peroneal retinaculum tear (n = 1), anterior talofibular ligament avulsion (n = 1), and tears of the peroneus longus (n = 1) and tibialis posterior (n = 1) tendons.
  
  
  CONCLUSIONS
  The presence of a large ankle effusion of radiographs after acute ankle trauma suggests an underlying fracture. An ankle effusion of > or = 15 mm is a reasonable threshold to prompt additional imaging. Computed tomography provides good visualization of subtle bone injuries and may detect clinically imported soft-tissue injuries.
authors.affiliation: Department of Radiology, Vancouver Hospital and Health Sciences Centre, University of British Columbia, Canada.
authors.forename: T W
authors.initials: TW
authors.lastname: Clark
authors.forename: D L
authors.initials: DL
authors.lastname: Janzen
authors.forename: P M
authors.initials: PM
authors.lastname: Logan
authors.forename: K
authors.initials: K
authors.lastname: Ho
authors.forename: D G
authors.initials: DG
authors.lastname: Connell
mesh_terms: D000328:Adult; D000368:Aged; D016512:Ankle Injuries / Q000000981:diagnostic imaging*; D005122:Exudates and Transudates / Q000000981:diagnostic imaging*; D050723:Fractures, Bone / Q000000981:diagnostic imaging*; D006801:Humans; D008875:Middle Aged; D011237:Predictive Value of Tests; D012680:Sensitivity and Specificity; D017695:Soft Tissue Injuries / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed