title: False negative rate of syndesmotic injury in pronation-external rotation stage IV ankle fractures.
abstract: BACKGROUND
  To investigate false negative rate in the diagnosis of diastasis on initial static anteroposterior radiograph and reliability of intraoperative external rotational stress test for detection of concealed disruption of syndesmosis in pronation external rotation (PER) stage IV (Lauge-Hansen) ankle fractures.
  
  
  METHODS
  We prospectively studied 34 PER stage IV ankle fractures between September 2001 and September 2008. Twenty (59%) patients show syndesmotic injury on initial anteroposterior radiographs. We performed an intraoperative external rotation stress test in other 14 patients with suspicious PER stage IV ankle fractures, which showed no defined syndesmotic injury on anteroposterior radiographs inspite of a medial malleolar fracture, an oblique fibular fracture above the syndesmosis and fracture of the posterior tubercle of the tibia.
  
  
  RESULTS
  All 14 fractures showed different degrees of tibiofibular clear space (TFCS) and tibiofibular overlapping (TFO) on the external rotation stress test radiograph compared to the initial plain anteroposterior radiograph. It is important to understand the fracture pattern characterstic of PER stage IV ankle fractures even though it appears normal on anteroposterior radiographs, it is to be confirmed for the concealed syndesmotic injury through a routine intraoperative external rotational stress radiograph.
authors.affiliation: Department of Orthopedic Surgery, Keimyung University, Daegu, Korea.
authors.forename: Kwang-Soon
authors.initials: KS
authors.lastname: Song
authors.forename: Sin-Gi
authors.initials: SG
authors.lastname: Kim
authors.forename: Young-Jae
authors.initials: YJ
authors.lastname: Lim
authors.forename: Jong-Hyuk
authors.initials: JH
authors.lastname: Jeon
authors.forename: Kyunng-Keun
authors.initials: KK
authors.lastname: Min
keywords: Ankle fracture; external rotation stress test; false negative; syndesmotic injury