title: Response of knee cartilage T1rho and T2 relaxation times to in vivo mechanical loading in individuals with and without knee osteoarthritis.
abstract: OBJECTIVE
  The objective of this study was to evaluate the effects of mechanical loading on knee articular cartilage T1ρ and T2 relaxation times in patients with and without osteoarthritis (OA).
  
  
  METHODS
  Magnetic resonance (MR) images were acquired from 137 subjects with and without knee OA under two conditions: unloaded and loaded at 50% body weight. Three sequences were acquired: a high-resolution 3D-CUBE, a T1ρ relaxation time, and a T2 relaxation time sequences. Cartilage regions of interest included: medial and lateral femur (MF, LF); medial and lateral tibia (MT, LT), laminar analysis (superficial and deep layers), and subcompartments. Changes in relaxation times in response to loading were evaluated.
  
  
  RESULTS
  In response to loading, we observed significant reductions in T1ρ relaxation times in the MT and LT. In both the MF and LF, loading resulted in significant decreases in the superficial layer and significant increases in the deep layer of the cartilage for T1ρ and T2. All subcompartments of the MT and LT showed significant reduction in T1ρ relaxation times. Reductions were larger for subjects with OA (range: 13-19% change) when compared to healthy controls (range: 3-13% change).
  
  
  CONCLUSIONS
  Loading of the cartilage resulted in significant changes in relaxation times in the femur and tibia, with novel findings regarding laminar and subcompartmental variations. In general, changes in relaxation times with loading were larger in the OA group suggesting that the collagen-proteoglycan matrix of subjects with OA is less capable of retaining water, and may reflect a reduced ability to dissipate loads.
authors.affiliation: Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA, United States; Department of Physical Therapy and Rehabilitation Science, University of California, San Francisco, San Francisco, CA, United States. Electronic address: richard.souza@ucsf.edu.
authors.forename: R B
authors.initials: RB
authors.lastname: Souza
authors.affiliation: Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA, United States.
authors.forename: D
authors.initials: D
authors.lastname: Kumar
authors.affiliation: Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA, United States.
authors.forename: N
authors.initials: N
authors.lastname: Calixto
authors.affiliation: Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA, United States.
authors.forename: J
authors.initials: J
authors.lastname: Singh
authors.affiliation: Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA, United States.
authors.forename: J
authors.initials: J
authors.lastname: Schooler
authors.affiliation: Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA, United States.
authors.forename: K
authors.initials: K
authors.lastname: Subburaj
authors.affiliation: Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA, United States.
authors.forename: X
authors.initials: X
authors.lastname: Li
authors.affiliation: Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA, United States.
authors.forename: T M
authors.initials: TM
authors.lastname: Link
authors.affiliation: Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA, United States.
authors.forename: S
authors.initials: S
authors.lastname: Majumdar
mesh_terms: D002358:Cartilage, Articular / Q000473:pathology / Q000502:physiology / Q000503:physiopathology*; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007719:Knee Joint / Q000473:pathology / Q000502:physiology / Q000503:physiopathology*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000473:pathology / Q000503:physiopathology*; D016474:Weight-Bearing
keywords: Acute loading; Cartilage; Magnetic resonance imaging; Osteoarthritis