title: Cell deformation behavior in mechanically loaded rabbit articular cartilage 4 weeks after anterior cruciate ligament transection.
abstract: OBJECTIVE
  Chondrocyte stresses and strains in articular cartilage are known to modulate tissue mechanobiology. Cell deformation behavior in cartilage under mechanical loading is not known at the earliest stages of osteoarthritis. Thus, the aim of this study was to investigate the effect of mechanical loading on volume and morphology of chondrocytes in the superficial tissue of osteoarthritic cartilage obtained from anterior cruciate ligament transected (ACLT) rabbit knee joints, 4 weeks after intervention.
  
  
  METHODS
  A unique custom-made microscopy indentation system with dual-photon microscope was used to apply controlled 2 MPa force-relaxation loading on patellar cartilage surfaces. Volume and morphology of chondrocytes were analyzed before and after loading. Also global and local tissue strains were calculated. Collagen content, collagen orientation and proteoglycan content were quantified with Fourier transform infrared microspectroscopy, polarized light microscopy and digital densitometry, respectively.
  
  
  RESULTS
  Following the mechanical loading, the volume of chondrocytes in the superficial tissue increased significantly in ACLT cartilage by 24% (95% confidence interval (CI) 17.2-31.5, P < 0.001), while it reduced significantly in contralateral group tissue by -5.3% (95% CI -8.1 to -2.5, P = 0.003). Collagen content in ACLT and contralateral cartilage were similar. PG content was reduced and collagen orientation angle was increased in the superficial tissue of ACLT cartilage compared to the contralateral cartilage.
  
  
  CONCLUSIONS
  We found the novel result that chondrocyte deformation behavior in the superficial tissue of rabbit articular cartilage is altered already at 4 weeks after ACLT, likely because of changes in collagen fibril orientation and a reduction in PG content.
authors.affiliation: Department of Applied Physics, University of Eastern Finland, POB 1627, FI-70211 Kuopio, Finland. siru.turunen@uef.fi
authors.forename: S M
authors.initials: SM
authors.lastname: Turunen
authors.forename: S-K
authors.initials: SK
authors.lastname: Han
authors.forename: W
authors.initials: W
authors.lastname: Herzog
authors.forename: R K
authors.initials: RK
authors.lastname: Korhonen
mesh_terms: D000818:Animals; D016118:Anterior Cruciate Ligament / Q000378:metabolism; D000070598:Anterior Cruciate Ligament Injuries; D001169:Arthritis, Experimental; D002358:Cartilage, Articular / Q000378:metabolism / Q000473:pathology*; D019902:Chondrocytes / Q000378:metabolism / Q000473:pathology*; D003094:Collagen / Q000378:metabolism; D003720:Densitometry / Q000379:methods; D005260:Female; D008859:Microscopy, Polarization; D020370:Osteoarthritis, Knee / Q000378:metabolism / Q000473:pathology*; D011509:Proteoglycans / Q000378:metabolism; D011817:Rabbits; D017550:Spectroscopy, Fourier Transform Infrared; D013264:Stifle; D013314:Stress, Mechanical
chemical_list: D011509:Proteoglycans; D003094:Collagen