title: The lambda sign: a new radiographic indicator of latent syndesmosis instability.
abstract: BACKGROUND
  Latent syndesmotic instability is a common cause of chronic ankle pain. The diagnosis is not readily apparent on static imaging as the fibula remains reduced. The hypothesis of this study was that a previously undescribed novel finding on coronal MRI (lambda sign) is an independent indicator of latent syndesmosis instability. We also report on the utility of classic radiographic and physical exam findings.
  
  
  METHODS
  A total of 23 patients with latent syndesmotic instability diagnosed via arthroscopy (group I) were compared to a cohort of 40 patients who were found to have a stable syndesmosis during arthroscopy for unrelated conditions (group II). A retrospective chart review was performed evaluating their clinical history, preoperative physical examination, and radiologic findings. The lambda sign is a high intensity signal seen on coronal MR imaging that resembles the Greek letter lambda.
  
  
  RESULTS
  All of the physical exam findings tested were statistically significant. Pain at the syndesmosis had the highest sensitivity (83%), while pain reproduced with the proximal squeeze test resulted in the highest specificity (89%). The external rotation stress test had the highest positive predictive value (75%). Of the radiographic examinations performed, only the lambda sign was found to have statistical significance with a sensitivity of 75% and a specificity of 63%. The presence of a lambda sign on the MRI of patients with physical exam findings suggestive of syndesmotic pain was highly sensitive (75%) and specific (85%).
  
  
  CONCLUSIONS
  The lambda sign noted on the coronal MRI was both sensitive and specific for injuries involving greater than 2 mm of diastasis on arthroscopic stress examination of the syndesmosis. While neither the lambda sign nor any other finding on physical or radiographic examination represented an independent predictor of syndesmotic instability, the presence of a lambda sign in concert with positive physical exam findings might help health care providers determine which patients might benefit from operative intervention or referral.
  
  
  METHODS
  Level III, case control study.
authors.affiliation: Tripler Army Medical Center, Honolulu, HI, USA paulryan1@hotmail.com.
authors.forename: Ltc Paul
authors.initials: LP
authors.lastname: Ryan
authors.affiliation: Orthopaedic Surgeon, 121st CSH/BAACH, US Army, Korea.
authors.forename: Maj Chad
authors.initials: MC
authors.lastname: Hills
authors.affiliation: Madigan Army Medical Center, Tacoma, WA, USA.
authors.forename: James
authors.initials: J
authors.lastname: Chang
authors.affiliation: Madigan Army Medical Center, Tacoma, WA, USA.
authors.forename: Cpt David
authors.initials: CD
authors.lastname: Wilson
mesh_terms: D000293:Adolescent; D000328:Adult; D000843:Ankle Joint / Q000473:pathology* / Q000503:physiopathology / Q000601:surgery; D018771:Arthralgia / Q000209:etiology / Q000503:physiopathology; D001182:Arthroscopy; D016022:Case-Control Studies; D015331:Cohort Studies; D005260:Female; D005360:Fibula / Q000473:pathology; D006801:Humans; D007593:Joint Instability / Q000175:diagnosis* / Q000503:physiopathology / Q000601:surgery; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D010808:Physical Examination; D011237:Predictive Value of Tests; D012189:Retrospective Studies; D012399:Rotation; D012680:Sensitivity and Specificity; D055815:Young Adult
keywords: external rotation stress test; instability; lambda sign; proximal squeeze test; syndesmosis; tibiofibular clear space; tibiofibular overlap