title: Hip abductor function in individuals with medial knee osteoarthritis: Implications for medial compartment loading during gait.
abstract: BACKGROUND
  Hip abductor muscles generate moments of force that control lower extremity frontal plane motion. Strengthening these muscles has been a recent trend in therapeutic intervention studies for knee osteoarthritis. The current study investigated the relationship between hip abductor muscle function (strength and activation) and the net external knee adduction moment during gait in those with medial compartment knee osteoarthritis.
  
  
  METHODS
  54 individuals with moderate knee osteoarthritis walked at their self-selected velocity while gluteus medius electromyograms, segment motions and ground reaction forces were recorded. Net external knee adduction moment (KAM) and linear enveloped electromyographic profiles were calculated. Peak KAM was determined and then principal component analyses (PCA) were applied to KAM and electromyographic profiles. Isometric hip abductor strength, anthropometrics and gait velocity were measured. Multiple regression models evaluated the relationship between walking velocity, hip abductor strength, electromyographic variables recorded during gait and KAM waveform characteristics.
  
  
  RESULTS
  Minimal peak KAM variance was explained by abductor strength (R(2)=9%, P=0.027). PCA-based KAM waveform characteristics were not explained by abductor strength. Overall gluteus medius amplitude (PP1-scores) was related to a reduction in the bi-modal KAM (PP3-scores) pattern (R(2)=16%, P=0.003).
  
  
  CONCLUSIONS
  There was no clear relationship between hip abductor muscle strength and specific amplitude and temporal KAM characteristics. Higher overall gluteus medius activation amplitude was related to a sustained KAM during mid-stance. 84 to 90% of the variance in KAM waveform characteristics was not explained by hip abductor muscle function showing hip abductor muscle function has minimal association to KAM characteristics.
authors.affiliation: School of Physiotherapy, Dalhousie University, 4th Floor Forrest Building, 5869 University Avenue, Halifax, NS, Canada, B3H 3J5. Electronic address: djr@dal.ca.
authors.forename: Derek James
authors.initials: DJ
authors.lastname: Rutherford
authors.affiliation: School of Physiotherapy, Dalhousie University, 4th Floor Forrest Building, 5869 University Avenue, Halifax, NS, Canada, B3H 3J5. Electronic address: clk@dal.ca.
authors.forename: Cheryl
authors.initials: C
authors.lastname: Hubley-Kozey
authors.affiliation: Department of Surgery, Division of Orthopaedics, Dalhousie University, Halifax, NS, Canada. Electronic address: wstanish@ns.sympatico.ca.
authors.forename: William
authors.initials: W
authors.lastname: Stanish
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena / Q000502:physiology; D002081:Buttocks; D004576:Electromyography; D005260:Female; D005684:Gait / Q000502:physiology*; D006621:Hip Joint / Q000503:physiopathology; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D053580:Muscle Strength / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D020370:Osteoarthritis, Knee / Q000503:physiopathology*; D025341:Principal Component Analysis / Q000379:methods; D016138:Walking / Q000502:physiology
keywords: Electromyography; Gait Analysis; Gluteus Medius; Hip abduction strength; Knee adduction moment; Knee osteoarthritis