title: Effects of unloading on knee articular cartilage T1rho and T2 magnetic resonance imaging relaxation times: a case series.
abstract: METHODS
  Case series.
  
  
  BACKGROUND
  It has been shown in rodent and canine models that cartilage composition is significantly altered in response to long-term unloading. To date, however, no in vivo human studies have investigated this topic. The objective of this case series was to determine the influence of unloading and reloading on T1rho and T2 relaxation times of articular cartilage in healthy young joints.
  
  
  METHODS
  Ten patients who required 6 to 8 weeks of non-weight bearing (NWB) for injuries affecting the distal lower extremity participated in the study. Quantitative T1rho and T2 imaging of the ipsilateral knee joint was performed at 3 time points: (1) prior to surgery (baseline), (2) immediately after a period of NWB (post-NWB), and (3) after 4 weeks of full weight bearing (post-FWB). Cartilage regions of interest were segmented and overlaid on T1rho and T2 relaxation time maps for quantification. Descriptive statistics are provided for all changes.
  
  
  RESULTS
  Increases of 5% to 10% in T1rho times of all femoral and tibial compartments were noted post-NWB. All values returned to near-baseline levels post-FWB. Increases in medial tibia T2 times were noted post-NWB and remained elevated post-FWB. The load-bearing regions showed the most significant changes in response to unloading, with increases of up to 12%.
  
  
  CONCLUSIONS
  The observation of a transient shift in relaxation times confirms that cartilage composition is subject to alterations based on loading conditions. These changes appear to be mostly related to proteoglycan content and more localized to the load-bearing regions. However, following 4 weeks of full weight bearing, relaxation times of nearly all regions had returned to baseline levels, demonstrating reversibility in compositional fluctuations.
  
  
  METHODS
  Therapy, level 4.
authors.affiliation: Department of Physical Therapy and Rehabilitation Science, University of California, San Francisco, San Francisco, CA, USA. richard.souza@ucsf.edu
authors.forename: Richard B
authors.initials: RB
authors.lastname: Souza
authors.forename: Thomas
authors.initials: T
authors.lastname: Baum
authors.forename: Samuel
authors.initials: S
authors.lastname: Wu
authors.forename: Brian T
authors.initials: BT
authors.lastname: Feeley
authors.forename: Nancy
authors.initials: N
authors.lastname: Kadel
authors.forename: Xiaojuan
authors.initials: X
authors.lastname: Li
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Link
authors.forename: Sharmila
authors.initials: S
authors.lastname: Majumdar
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D002358:Cartilage, Articular / Q000502:physiology*; D003094:Collagen; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000502:physiology*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D008297:Male; D055595:Mechanical Phenomena; D008875:Middle Aged; D010329:Patella; D011509:Proteoglycans; D016059:Range of Motion, Articular; D016474:Weight-Bearing / Q000502:physiology; D055815:Young Adult
chemical_list: D011509:Proteoglycans; D003094:Collagen