title: Longitudinal sensitivity to change of MRI-based muscle cross-sectional area versus isometric strength analysis in osteoarthritic knees with and without structural progression: pilot data from the Osteoarthritis Initiative.
abstract: OBJECTIVE
  Biomechanical measurement of muscle strength represents established technology in evaluating limb function. Yet, analysis of longitudinal change suffers from relatively large between-measurement variability. Here, we determine the sensitivity to change of magnetic resonance imaging (MRI)-based measurement of thigh muscle anatomical cross sectional areas (ACSAs) versus isometric strength in limbs with and without structural progressive knee osteoarthritis (KOA), with focus on the quadriceps.
  
  
  METHODS
  Of 625 "Osteoarthritis Initiative" participants with radiographic KOA, 20 had MRI cartilage and radiographic joint space width loss in the right knee isometric muscle strength measurement and axial T1-weighted spin-echo acquisitions of the thigh. Muscle ACSAs were determined from manual segmentation at 33% femoral length (distal to proximal).
  
  
  RESULTS
  In progressor knees, the reduction in quadriceps ACSA between baseline and 2-year follow-up was -2.8 ± 7.9 % (standardized response mean [SRM] = -0.35), and it was -1.8 ± 6.8% (SRM = -0.26) in matched, non-progressive KOA controls. The decline in extensor strength was more variable than that in ACSAs, both in progressors (-3.9 ± 20%; SRM = -0.20) and in non-progressive controls (-4.5 ± 28%; SRM = -0.16).
  
  
  CONCLUSIONS
  MRI-based analysis of quadriceps muscles ACSAs appears to be more sensitive to longitudinal change than isometric extensor strength and is suggestive of greater loss in limbs with structurally progressive KOA than in non-progressive controls.
authors.affiliation: Institute of Anatomy and Musculoskeletal Research, Paracelsus Medical University, Strubergasse 21, 5020, Salzburg, Austria, torben.dannhauer@pmu.ac.at.
authors.forename: Torben
authors.initials: T
authors.lastname: Dannhauer
authors.forename: Martina
authors.initials: M
authors.lastname: Sattler
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Wirth
authors.forename: David J
authors.initials: DJ
authors.lastname: Hunter
authors.forename: C Kent
authors.initials: CK
authors.lastname: Kwoh
authors.forename: Felix
authors.initials: F
authors.lastname: Eckstein
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D002356:Cartilage / Q000473:pathology; D018450:Disease Progression; D005260:Female; D006801:Humans; D007537:Isometric Contraction; D007719:Knee Joint / Q000473:pathology; D008137:Longitudinal Studies; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D053580:Muscle Strength; D018482:Muscle, Skeletal / Q000473:pathology; D020370:Osteoarthritis, Knee / Q000473:pathology*; D010865:Pilot Projects; D011446:Prospective Studies; D015203:Reproducibility of Results