title: Biomechanics of cartilage articulation: effects of lubrication and degeneration on shear deformation.
abstract: OBJECTIVE
  To characterize cartilage shear strain during articulation, and the effects of lubrication and degeneration.
  
  
  METHODS
  Human osteochondral cores from lateral femoral condyles, characterized as normal or mildly degenerated based on surface structure, were selected. Under video microscopy, pairs of osteochondral blocks from each core were apposed, compressed 15%, and subjected to relative lateral motion with synovial fluid (SF) or phosphate buffered saline (PBS) as lubricant. When cartilage surfaces began to slide steadily, shear strain (Exz) and modulus (G) overall in the full tissue thickness and also as a function of depth from the surface were determined.
  
  
  RESULTS
  In normal tissue with SF as lubricant, Exz was highest (0.056) near the articular surface and diminished monotonically with depth, with an overall average Exz of 0.028. In degenerated cartilage with SF as lubricant, Exz near the surface (0.28) was 5-fold that of normal cartilage and localized there, with an overall E(xz) of 0.041. With PBS as lubricant, Exz values near the articular surface were approximately 50% higher than those observed with SF, and overall Exz was 0.045 and 0.062 in normal and degenerated tissue, respectively. Near the articular surface, G was lower with degeneration (0.06 MPa, versus 0.18 MPa in normal cartilage). In both normal and degenerated cartilage, G increased with tissue depth to 3-4 MPa, with an overall G of 0.26-0.32 MPa.
  
  
  CONCLUSIONS
  During articulation, peak cartilage shear is highest near the articular surface and decreases markedly with depth. With degeneration and diminished lubrication, the markedly increased cartilage shear near the articular surface may contribute to progressive cartilage deterioration and osteoarthritis.
authors.affiliation: University of California, San Diego, La Jolla, California 92093-0412, USA.
authors.forename: Benjamin L
authors.initials: BL
authors.lastname: Wong
authors.forename: Won C
authors.initials: WC
authors.lastname: Bae
authors.forename: June
authors.initials: J
authors.lastname: Chun
authors.forename: Kenneth R
authors.initials: KR
authors.lastname: Gratz
authors.forename: Martin
authors.initials: M
authors.lastname: Lotz
authors.forename: Robert L
authors.initials: RL
authors.lastname: Sah
mesh_terms: D001696:Biomechanical Phenomena; D002358:Cartilage, Articular / Q000502:physiology* / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D033081:Shear Strength; D013582:Synovial Fluid / Q000502:physiology*