title: Cyclical articular joint loading leads to cartilage thinning and osteopontin production in a novel in vivo rabbit model of repetitive finger flexion.
abstract: OBJECTIVE
  An in vivo rabbit model of repetitive joint flexion and loading was used to characterize the morphological effects of cyclical loading on articular cartilage.
  
  
  METHODS
  The forepaw digits of eight anesthetized New Zealand White adult female rabbits were repetitively flexed at 1 Hz with a mean peak digit load of 0.42 N for 2 h per day for 60 cumulative hours. Metacarpophalangeal joints were collected from loaded and contra-lateral control limbs, fixed, decalcified, embedded, and thin-sectioned. Serial sections were stained for histology or for immunohistochemistry. Morphometric data including the mean thicknesses of the uncalcified cartilage and of the calcified cartilage were collected from digital photomicrographs of safranin O-stained sections. The number of cells stained with anti-osteopontin antibody was counted.
  
  
  RESULTS
  We observed a decrease in uncalcified cartilage mean thickness with no significant change in calcified cartilage thickness. We also observed a significant increase in the number of cells positive for osteopontin (OPN) in the uncalcified cartilage. These changes occurred without overt cartilage surface degeneration.
  
  
  CONCLUSIONS
  Cyclical loading leads to changes at the tissue and cellular levels in articular cartilage. These changes are suggestive of tidemark advancement and may indicate a reactivation of cartilage mineralization steps analogous to endochondral ossification. This novel in vivo rabbit model of repetitive flexion and loading can be used to investigate the effects of cyclical loading on articular joints.
authors.affiliation: Department of Medicine, University of California, San Francisco, CA, USA. kbking@itsa.ucsf.edu
authors.forename: K B
authors.initials: KB
authors.lastname: King
authors.forename: C F
authors.initials: CF
authors.lastname: Opel
authors.forename: D M
authors.initials: DM
authors.lastname: Rempel
mesh_terms: D000818:Animals; D002114:Calcinosis / Q000473:pathology / Q000503:physiopathology; D002358:Cartilage, Articular / Q000033:anatomy & histology* / Q000502:physiology; D004558:Electric Stimulation / Q000379:methods; D005260:Female; D005552:Forelimb; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D007596:Joints / Q000033:anatomy & histology / Q000502:physiology*; D023421:Models, Animal; D009068:Movement / Q000502:physiology; D053495:Osteopontin; D011817:Rabbits; D012795:Sialoglycoproteins / Q000032:analysis; D013314:Stress, Mechanical
chemical_list: D012795:Sialoglycoproteins; D053495:Osteopontin