title: Longitudinal (4 year) change of thigh muscle and adipose tissue distribution in chronically painful vs painless knees--data from the Osteoarthritis Initiative.
abstract: OBJECTIVE
  To evaluate 4-year longitudinal change in thigh muscle and adipose tissue content in chronically painful vs painless knees.
  
  
  METHODS
  Knees from Osteoarthritis Initiative (OAI) participants with non-acceptable symptom status (numerical rating scale (NRS) ≥4) and frequent pain (≥6 months at baseline, year 2 and year 4 follow-up) were studied. These were matched with painless controls (bilateral NRS pain intensity ≤1 and ≤infrequent pain at all 3 timepoints). 4-year longitudinal changes in thigh muscle anatomical cross-sectional areas (CSAs), isometric muscle strength, and in subcutaneous (SCF) and intermuscular fat (IMF) CSAs were obtained from magnetic resonance images (MRI) and were compared between groups (paired t-tests).
  
  
  RESULTS
  43 participants fulfilled the inclusion criteria of chronic pain, had complete thigh muscle MRI acquisitions and strength measurements, and a matched control. Quadriceps CSAs, but not extensor strength, showed a significant longitudinal decrease in chronically painful knees (-3.9%; 95% confidence interval [95 CI] -6.3%, -1.5%) and in painless controls (-2.4%; 95% CI -4.1%, -0.7%); the difference in change was not statistically significant (P = 0.33). There was a significant 4-year gain in SCF in painful knees (8.1%; 95% CI 3.1%, 13%) but not in controls (0.0%; 95% CI -4.4%, +4.4%) with the difference in change being significant (P = 0.03). The gain in IMF (∼5.2%) was similar between painful and painless knees.
  
  
  CONCLUSIONS
  This is the first paper to show a significant impact of (chronic) knee pain on longitudinal change in local subcutaneous adipose tissue. The effect of pain on subcutaneous fat appeared stronger than that on intermuscular adipose tissue and on muscle status.
authors.affiliation: Institute of Anatomy, Paracelsus Medical University Salzburg and Nuremberg, Salzburg, Austria. Electronic address: anja.ruhdorfer@pmu.ac.at.
authors.forename: A
authors.initials: A
authors.lastname: Ruhdorfer
authors.affiliation: Institute of Anatomy, Paracelsus Medical University Salzburg and Nuremberg, Salzburg, Austria.
authors.forename: W
authors.initials: W
authors.lastname: Wirth
authors.affiliation: Institute of Anatomy, Paracelsus Medical University Salzburg and Nuremberg, Salzburg, Austria.
authors.forename: T
authors.initials: T
authors.lastname: Dannhauer
authors.affiliation: Institute of Anatomy, Paracelsus Medical University Salzburg and Nuremberg, Salzburg, Austria.
authors.forename: F
authors.initials: F
authors.lastname: Eckstein
mesh_terms: D000273:Adipose Tissue / Q000473:pathology*; D016022:Case-Control Studies; D059350:Chronic Pain / Q000473:pathology; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D008137:Longitudinal Studies; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D053580:Muscle Strength; D018482:Muscle, Skeletal / Q000473:pathology*; D020370:Osteoarthritis, Knee / Q000473:pathology*; D050151:Subcutaneous Fat / Q000473:pathology*
keywords: Intermuscular fat; Knee pain; Magnetic resonance imaging; Subcutaneous fat; Thigh muscle cross-sectional areas