title: Predicting Kyphosis Correction During Posterior-Only Vertebral Column Resection by the Amount of Spinal Column Shortening.
abstract: METHODS
  Retrospective.
  
  
  OBJECTIVE
  To investigate the relationship between the amount of correction achieved (K°) and extent of vertebral column shortening (mm) with posterior vertebral column resection (PVCR).
  
  
  BACKGROUND
  There is no scientific reference to the correlation between K° and column shortening (mm) with PVCR.
  
  
  METHODS
  Based on simple geometry, we tested the hypothesis that we could predict the amount of actual kyphosis correction (K°) by calculation on 26 kyphotic PVCR patients. Using multiple linear measurements (mm), two angular approximations (°) were calculated: the geometric approximation (G°) using the geometric calculation (G-cal), and the rough approximation (R°) by more simplistic calculation (R-cal). Both G° and R° were compared against K° as measured on the pre- and postoperative radiographs. If calculated G° and R° is close to measured K°, we can use the calculations (G-cal and R-cal) in the clinical situation.
  
  
  RESULTS
  The mean correction of K° was 38°. K°-G° and K°-R° were not significantly greater than 3° and 6°, respectively. As K° was very close to G° and R°, K° can replace G° and R°. Therefore, we can use G-cal and R-cal in the clinical setting and we can determine how much posterior shortening and what cage size is required to obtain a certain amount of K°.
  
  
  CONCLUSIONS
  With two calculations (G-cal & R-cal), we can determine how much vertebral column shortening (mm) we need during PVCR to obtain the amount of kyphosis correction desired (K°). In order to obtain K°, using the formula deduced from G-cal and R-cal, we can determine the shortening between the upper and lower pedicle screws and cage size.
authors.affiliation: Department of Orthopaedic Surgery, Albert Einstein College of Medicine, New York, NY; Department of Orthopaedic Surgery, Washington University School of Medicine, St. Louis, MO.
authors.forename: Woojin
authors.initials: W
authors.lastname: Cho
authors.affiliation: Department of Orthopaedic Surgery, Washington University School of Medicine, St. Louis, MO. Electronic address: lenkel@wudosis.wustl.edu.
authors.forename: Lawrence G
authors.initials: LG
authors.lastname: Lenke
authors.affiliation: Department of Orthopaedic Surgery, Washington University School of Medicine, St. Louis, MO.
authors.forename: Kathy M
authors.initials: KM
authors.lastname: Blanke
authors.affiliation: Department of Orthopaedic Surgery, Washington University School of Medicine, St. Louis, MO; Howell Allen Clinic, Nashville, TN.
authors.forename: Brian A
authors.initials: BA
authors.lastname: O'Shaughnessy
authors.affiliation: Department of Orthopaedic Surgery, Washington University School of Medicine, St. Louis, MO; Department of Neurosurgery, Washington University School of Medicine, St. Louis, MO.
authors.forename: Ian G
authors.initials: IG
authors.lastname: Dorward
authors.affiliation: Department of Orthopaedic Surgery, Washington University School of Medicine, St. Louis, MO.
authors.forename: Linda A
authors.initials: LA
authors.lastname: Koester
authors.affiliation: Department of Orthopaedic Surgery, Washington University School of Medicine, St. Louis, MO.
authors.forename: Brenda A
authors.initials: BA
authors.lastname: Sides
authors.affiliation: Department of Orthopaedic Surgery, Washington University School of Medicine, St. Louis, MO.
authors.forename: Christine R
authors.initials: CR
authors.lastname: Baldus
keywords: Correlation formula; Kyphosis correction; Posterior vertebral column resection; Vertebral column shortening