title: Predictors of hip internal rotation during running: an evaluation of hip strength and femoral structure in women with and without patellofemoral pain.
abstract: BACKGROUND
  Recent studies have suggested that excessive hip internal rotation during dynamic tasks may be associated with patellofemoral pain. Although diminished hip-muscle strength and altered femoral morphologic characteristics have been implicated in abnormal hip rotation in persons with patellofemoral pain, no study has confirmed this hypothesis.
  
  
  OBJECTIVE
  Women with patellofemoral pain would demonstrate increased average hip internal rotation, decreased hip-muscle performance, and abnormal femoral shape compared with controls. Furthermore, measures of hip strength and femoral shape are predictive of average hip internal rotation during running.
  
  
  METHODS
  Cross-sectional study; Level of evidence, 3.
  
  
  METHODS
  Nineteen women with patellofemoral pain and 19 pain-free controls participated. Lower extremity kinematics during running, hip-muscle performance, and femoral morphologic characteristics on magnetic resonance imaging were quantified. Independent t tests were used to assess group differences. Stepwise linear regression was used to determine whether measures of strength and/or structure were predictive of average hip internal rotation during running.
  
  
  RESULTS
  Participants with patellofemoral pain demonstrated significantly greater average hip internal rotation (8.2 degrees +/- 6.6 degrees vs 0.3 degrees +/- 3.6 degrees ; P < .001), reduced hip-muscle strength in 8 of 10 hip strength measurements, and greater femoral inclination (132.8 degrees +/- 5.2 degrees vs 128.4 degrees +/- 5.0 degrees ; P = .011) compared with controls. Stepwise regression revealed that isotonic hip extension endurance was the only predictor of average hip internal rotation (r = -.451; P = .004).
  
  
  CONCLUSIONS
  Abnormal hip kinematics in women with patellofemoral pain appears to be the result of diminished hip-muscle performance as opposed to altered femoral structure. The results suggest that assessment of hip-muscle performance should be considered in the evaluation and treatment of patellofemoral joint dysfunction.
authors.affiliation: Musculoskeletal and Quantitative Imaging Research Laboratory, Department of Radiology and Biomedical Engineering, University of California, San Francisco, California, USA.
authors.forename: Richard B
authors.initials: RB
authors.lastname: Souza
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Powers
mesh_terms: D000328:Adult; D003430:Cross-Sectional Studies; D005260:Female; D005269:Femur / Q000503:physiopathology*; D006621:Hip Joint / Q000503:physiopathology*; D006801:Humans; D016014:Linear Models; D008279:Magnetic Resonance Imaging; D053580:Muscle Strength / Q000502:physiology*; D046788:Patellofemoral Pain Syndrome / Q000503:physiopathology*; D012399:Rotation; D012420:Running / Q000502:physiology*