title: Assessment of midcarpal deformity of the wrist using the triangulation method.
abstract: OBJECTIVE
  The purpose of this study is to present an alternative method for static radiologic assessment of the wrist for midcarpal instability (ie, palmar intercalated segmental instability [PISI] and dorsal intercalated segmental instability [DISI]). The triangulation method uses 3 anatomic landmarks observed on the standard lateral x-ray of the wrist.
  
  
  METHODS
  A total of 125 normal lateral radiographs were measured to determine the normal range for the dorsal limb (DL) to palmar limb (PL) ratio. A 2-step process of performing triangulation is described. The first step is nonspecific screening of the radiograph and defines values greater than 1.0 as having a DISI deformity and values less than 0.5 as having a PISI deformity. The second step is used only for borderline values, which takes the position of the wrist into consideration and uses a normagram (reference chart) to match the DL:PL ratio with the radiometacarpal (RM) angle.
  
  
  RESULTS
  The average lateral wrist position was 8.4 degrees of extension (-8.4). The average DL:PL ratio was 0.75 +/- 0.09 (range, 0.93-0.57).
  
  
  CONCLUSIONS
  Based on these data we defined DISI deformity of the wrist as DL:PL ratios greater than 1.0, and ratios less than 0.5 representing PISI deformities. The triangulation method of assessing midcarpal alignment of the carpus is a practical and simple alternative to the traditional static radiologic method of assessing midcarpal instability of the wrist.
authors.affiliation: Department of Orthopaedic Surgery and Department of Radiology, Texas Tech University Health Sciences Center, El Paso, TX, USA.
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Pirela-Cruz
authors.forename: Mark F
authors.initials: MF
authors.lastname: Hansen
mesh_terms: D000328:Adult; D000368:Aged; D002348:Carpal Bones; D005260:Female; D006801:Humans; D016916:Joint Deformities, Acquired / Q000175:diagnosis*; D008297:Male; D008875:Middle Aged; D014955:Wrist Joint