title: A new methodology for the planning of single-cut corrective osteotomies of mal-aligned long bones.
abstract: BACKGROUND
  Corrections of combined torsional and angular deformities of long bones may be performed creating a single osteotomy which is oriented so that rotating the two fragments on the created osteotomy plane allows to correct all deformities in one step. A practical geometrical tool is presented to facilitate the difficult preoperative planning of such osteotomies.
  
  
  METHODS
  The geometrical tool consists of two limbs connected by a mobile disk representing the osteotomy plane. This allows the two limbs to be deliberately bent and rotated against each other. Thereby, the mobile disk will change orientation in such a way that it will indicate the osteotomy plane needed in order to anatomically align the two limbs. The geometrical principle of the tool has been confirmed mathematically and compared with data from the literature. Five deformed test bones have been used to test the effectiveness of the tool.
  
  
  RESULTS
  . The geometrical principle of the tool is equivalent with the mathematical data from the literature. The maximal osteotomy angle which can be indicated by the tool is 65 degrees , with an error of +/-3 degrees compared to mathematically calculated values. The five test bones were all aligned anatomically with appropriate accuracy.
  
  
  CONCLUSIONS
  The presented tool can be easily used and facilitates largely the preoperative planning of a single cut osteotomy for complex deformities of long bones. It allows to avoid sophisticated mathematical calculations and helps to avoid the risk for errors in planning and performing correctional osteotomies.
authors.affiliation: Department of Orthopaedics, University of Zürich, Balgrist, Forchstr. 340, 8008 Zürich, Switzerland.
authors.forename: D C
authors.initials: DC
authors.lastname: Meyer
authors.forename: K A
authors.initials: KA
authors.lastname: Siebenrock
authors.forename: B
authors.initials: B
authors.lastname: Schiele
authors.forename: C
authors.initials: C
authors.lastname: Gerber
mesh_terms: D017760:Bone Malalignment / Q000175:diagnosis* / Q000601:surgery*; D003198:Computer Simulation; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005269:Femur / Q000601:surgery*; D006801:Humans; D008954:Models, Biological; D010027:Osteotomy / Q000295:instrumentation* / Q000379:methods; D010808:Physical Examination / Q000295:instrumentation* / Q000379:methods; D011300:Preoperative Care / Q000295:instrumentation* / Q000379:methods; D025321:Surgery, Computer-Assisted / Q000295:instrumentation / Q000379:methods