title: Contrasting alterations of apposed and unapposed articular cartilage during joint contracture formation.
abstract: OBJECTIVE
  To quantify histologic articular cartilage alterations after immobilization, distinguishing between apposed and unapposed sites in an animal model of joint contracture.
  
  
  METHODS
  Experimental controlled trial.
  
  
  METHODS
  Laboratory, in vivo study.
  
  
  METHODS
  Adult male Sprague-Dawley rats (N=128).
  
  
  METHODS
  One hundred seventeen animals had 1 knee internally immobilized or sham-operated for 2, 4, 8, 16, or 32 weeks. One knee in 11 nonoperated animals served as controls. Main outcome measures On standardized sections, we identified femur and tibia cartilage sites that were apposed or that were unapposed. We quantified 4 characteristics: number of chondrocytes in the superficial and deep cartilage; matrix staining intensity to toluidine blue; surface irregularity of articular cartilage; and thickness of cartilage.
  
  
  RESULTS
  Immobilized knees harbored fewer chondrocytes in the superficial cartilage at apposed sites and in the deep cartilage at unapposed sites. Matrix staining decreased only at unapposed sites. Cartilage surface became significantly more irregular at both sites but cartilage thickness remained unchanged. Noncartilaginous tissues appeared only at unapposed sites in the superficial and deep cartilage.
  
  
  CONCLUSIONS
  Immobilization led to contrasting patterns of cartilage degeneration at apposed sites compared with unapposed sites. These results suggest distinct pathogenetic pathways for cartilage alterations, possibly through absence of mechanical forces (negative mechanotransduction) at unapposed sites and cyclic pressure at apposed sites. Considering the limited potential for cartilage self-repair, these results support the need for early diagnosis and aggressive mobilization of joints that are developing contractures.
authors.affiliation: Bone and Joint Research Laboratory, University of Ottawa, Ottawa, ON, Canada. gtrudel@ottawahospital.on.ca
authors.forename: Guy
authors.initials: G
authors.lastname: Trudel
authors.forename: Ko
authors.initials: K
authors.lastname: Himori
authors.forename: Hans K
authors.initials: HK
authors.lastname: Uhthoff
mesh_terms: D000818:Animals; D002358:Cartilage, Articular / Q000473:pathology*; D002452:Cell Count; D019902:Chondrocytes / Q000502:physiology; D003286:Contracture / Q000209:etiology* / Q000473:pathology; D004195:Disease Models, Animal; D007103:Immobilization / Q000009:adverse effects*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D013264:Stifle / Q000473:pathology; D013499:Surface Properties