title: Redefining the technique for the radiologic measurement of slip in spondylolisthesis.
abstract: METHODS
  Comparison of 2 radiographic measurement techniques of slip severity in spondylolisthesis.
  
  
  OBJECTIVE
  To analyze the differences between 2 radiologic measurement techniques of slip severity in L5-S1 developmental spondylolisthesis.
  
  
  BACKGROUND
  Different techniques for the assessment of slip in spondylolisthesis have been described in the literature, resulting in 2 different methods to report the position of the L5 vertebra on the S1 superior endplate. The clinical impact of these differences in slip measurement is unknown.
  
  
  METHODS
  Radiographs of 130 subjects with developmental spondylolisthesis were reviewed. Two different techniques were used to assess the grade and percentage of slip. The technique 1 uses a line drawn from the L5 vertebra postero-inferior corner that is perpendicular to the S1 vertebra endplate. The technique 2 uses a line tangential to the L5 vertebra posterior wall that intersects the S1 vertebra endplate. The lumbosacral angle (LSA) was also measured to assess the orientation of L5 over S1. The slip percentage and grade obtained from the 2 techniques were compared. The influence of the LSA on the measurement of slip severity was also assessed.
  
  
  RESULTS
  A significant difference (P < 10(-5)) was found between technique 1 (mean = 34.2% +/- 32.6%) and technique 2 (mean = 42.5% +/- 25.8%) with respect to the slip percentage. Eight subjects were found to switch classification from a low to a high-grade slip (or inversely) depending on the technique used. There was a significant relationship between the LSA and the difference in the measurement of slip percentage using either technique 1 or technique 2.
  
  
  CONCLUSIONS
  The 2 measurement techniques can have a significant impact on the interpretation of slip severity in spondylolisthesis. The differences between the measurement techniques are influenced by the orientation of L5 over S1 and could potentially affect the clinical decision making. It is important to standardize and specify the technique used to plan and assess interventions in L5-S1 developmental spondylolisthesis.
authors.affiliation: Division of Orthopedic Surgery, CHU Sainte-Justine, Montreal, Quebec, Canada.
authors.forename: Etienne
authors.initials: E
authors.lastname: Bourassa-Moreau
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Mac-Thiong
authors.forename: Hubert
authors.initials: H
authors.lastname: Labelle
mesh_terms: D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging*; D008297:Male; D011859:Radiography / Q000379:methods / Q000592:standards*; D015203:Reproducibility of Results; D012447:Sacrum / Q000000981:diagnostic imaging*; D013168:Spondylolisthesis / Q000175:diagnosis*; D055815:Young Adult