title: The importance of the valgus stress test in the diagnosis of posterolateral instability of the knee.
abstract: BACKGROUND
  The diagnosis of posterolateral instability of the knee is often based on a typical indirect mechanism of injury, a history of "giving way" and a positive dial test. Our search of the English literature revealed no mention of including the valgus stress test in the diagnostic protocol for posterolateral instability.
  
  
  OBJECTIVE
  Based on our experience, we hypothesised that a medial collateral ligament (MCL) tear will also produce a positive dial test and that a valgus stress test would provide differential diagnostic information.
  
  
  METHODS
  The MCL's of 14 fresh cadaveric knees (7 cadavers) were cut to simulate a grade 3 tear, taking care not to damage the medial retinaculum or the posteromedial stabilisers of the knee. The amount of tibial external rotation (the dial test) was measured for each knee before and after transection of the MCL.
  
  
  RESULTS
  The results of the dial test after transection of the MCL were similar to those stemming from a solitary injury to the posterolateral corner. There was a significant increase in external rotation of the knee in 30 degrees and 90 degrees of flexion. More over, external rotation in 30 degrees was significantly greater than external rotation in 90 degrees of knee flexion.
  
  
  CONCLUSIONS
  Whenever suspecting a posterolateral complex injury, one has to carefully perform a valgus stress test in 0 degrees and 30 degrees. Although the support of a clinical study is needed in order to make a definite conclusion, the dial test is probably not reliable in the presence of medial instability, and alternative diagnostic measures should be used.
authors.affiliation: Department of Orthopaedic Surgery B', Tel Aviv Sourasky Medical Center, Tel Aviv, Israel. Pritsch@zahav.net.il
authors.forename: Tamir
authors.initials: T
authors.lastname: Pritsch
authors.forename: Nehemia
authors.initials: N
authors.lastname: Blumberg
authors.forename: Amir
authors.initials: A
authors.lastname: Haim
authors.forename: Shmuel
authors.initials: S
authors.lastname: Dekel
authors.forename: Ron
authors.initials: R
authors.lastname: Arbel
mesh_terms: D002102:Cadaver; D006801:Humans; D007593:Joint Instability / Q000175:diagnosis* / Q000503:physiopathology; D007718:Knee Injuries / Q000175:diagnosis*; D007719:Knee Joint / Q000503:physiopathology*; D017888:Medial Collateral Ligament, Knee / Q000293:injuries; D012399:Rotation; D013314:Stress, Mechanical