title: Decreasing pelvic incidence is associated with greater risk of cam morphology.
abstract: OBJECTIVE
  The spinopelvic relationship (including pelvic incidence) has been shown to influence pelvic orientation, but its potential association with femoroacetabular impingement has not been thoroughly explored. The purpose of this study was to prove the hypothesis that decreasing pelvic incidence is associated with increased risk of cam morphology.
  
  
  METHODS
  Two matching cohorts were created from a collection of cadaveric specimens with known pelvic incidences: 50 subjects with the highest pelvic incidence (all subjects > 60°) and 50 subjects with the lowest pelvic incidence (all subjects < 35°). Femoral version, acetabular version, and alpha angles were directly measured from each specimen bilaterally. Cam morphology was defined as alpha angle > 55°. Differences between the two cohorts were analysed with a Student's t-test and the difference in incidence of cam morphology was assessed using a chi-squared test. The significance level for all tests was set at p < 0.05.
  
  
  RESULTS
  Cam morphology was identified in 47/100 (47%) femurs in the cohort with pelvic incidence < 35° and in only 25/100 (25%) femurs in the cohort with pelvic incidence > 60° (p = 0.002). The mean alpha angle was also greater in the cohort with pelvic incidence < 35° (mean 53.7°, sd 10.7° versus mean 49.7°, sd 10.6°; p = 0.008).
  
  
  CONCLUSIONS
  Decreased pelvic incidence is associated with development of cam morphology. We propose a novel theory wherein subjects with decreased pelvic incidence compensate during gait (to maintain optimal sagittal balance) through anterior pelvic tilt, creating artificial anterior acetabular overcoverage and recurrent impingement that increases risk for cam morphology.Cite this article: W. Z. Morris, C. A. Fowers, R. T. Yuh, J. J. Gebhart, M. J. Salata, R. W. Liu. Decreasing pelvic incidence is associated with greater risk of cam morphology. Bone Joint Res 2016;5:387-392. DOI: 10.1302/2046-3758.59.BJR-2016-0028.R1.
authors.affiliation: Case Western Reserve University, 11100 Euclid Ave, HAN 504, Cleveland, OH 44106, USA William.Morris2@UHHospitals.org.
authors.forename: W Z
authors.initials: WZ
authors.lastname: Morris
authors.affiliation: Case Western Reserve University, 11100 Euclid Ave, HAN 504, Cleveland, OH 44106, USA.
authors.forename: C A
authors.initials: CA
authors.lastname: Fowers
authors.affiliation: St. Luke's Hospital & Health Network, 801 Ostrum St, Bethlehem, PA, 18015, USA.
authors.forename: R T
authors.initials: RT
authors.lastname: Yuh
authors.affiliation: Case Western Reserve University, 11100 Euclid Ave, HAN 504, Cleveland, OH 44106, USA.
authors.forename: J J
authors.initials: JJ
authors.lastname: Gebhart
authors.affiliation: Case Western Reserve University, 11100 Euclid Ave, HAN 504, Cleveland, OH 44106, USA.
authors.forename: M J
authors.initials: MJ
authors.lastname: Salata
authors.affiliation: Case Western Reserve University, 11100 Euclid Ave, HAN 504, Cleveland, OH 44106, USA.
authors.forename: R W
authors.initials: RW
authors.lastname: Liu
keywords: Cam morphology; Femoroacetabular impingement; Pelvic incidence