title: Calculation of the opening wedge for a low tibial osteotomy.
abstract: BACKGROUND
  Medial opening wedge distal tibial osteotomy, a relatively new technique for treatment of intermediate ankle joint arthritis, is a technically demanding procedure that requires preoperative planning to determine the size of the wedge that will restore anatomic alignment of the joint surface. The purpose of this study was to facilitate the preoperative planning process for distal tibial osteotomy by determining angular correction obtained with various wedge heights.
  
  
  METHODS
  Measurements of the distal tibia were taken from cadaver specimens to develop a database of average distal tibial widths. A distal tibial osteotomy was then done on the cadaver specimens with the placement of wooden block wedges of various heights at the osteotomy site. Preoperative and postoperative radiographic measurements of the joint surface angle were obtained on all specimens. The measured amount of angular change was compared to the mathematically predicted angular change using the formula tan theta = H/W.
  
  
  RESULTS
  The mathematical model accurately predicted the amount of measured angular correction of the distal tibial articular surface. There was an approximate 2-degree angular change of the articular surface per millimeter of wedge height. As the tibial width increased, a smaller amount of angular correction per millimeter of wedge height was noted, and as wedge height increased with the same tibial width, less angular correction was obtained per millimeter of wedge height.
  
  
  CONCLUSIONS
  With appropriate preoperative planning, an accurate prediction can be made as to the amount of ankle joint correction that should be obtained with surgery. The size of the wedge that will provide the desired amount of correction can be accurately determined preoperatively.
authors.affiliation: The Department of Orthopaedic Surgery, The University of Texas Medical School at Houston, USA.
authors.forename: Kenneth Mathew
authors.initials: KM
authors.lastname: Warnock
authors.forename: Brian Douglas
authors.initials: BD
authors.lastname: Johnson
authors.forename: John Braxton
authors.initials: JB
authors.lastname: Wright
authors.forename: Catherine Glauber
authors.initials: CG
authors.lastname: Ambrose
authors.forename: Thomas Oscar
authors.initials: TO
authors.lastname: Clanton
authors.forename: William Christopher
authors.initials: WC
authors.lastname: McGarvey
mesh_terms: D000368:Aged; D000843:Ankle Joint / Q000601:surgery*; D001168:Arthritis / Q000601:surgery*; D002102:Cadaver; D019992:Databases as Topic; D005260:Female; D006801:Humans; D008297:Male; D010027:Osteotomy / Q000379:methods*; D013977:Tibia / Q000601:surgery*