title: Wear-lines and split-lines of human patellar cartilage: relation to tensile biomechanical properties.
abstract: BACKGROUND
  Articular cartilage undergoes age-associated degeneration, resulting in both structural and functional biomechanical changes. At early stages of degeneration, wear-lines develop in the general direction of joint movement. With aging, cartilage exhibits a decrease in tensile modulus. The tensile modulus of cartilage has also been related to the orientation of the collagen network, as revealed by split-lines.
  
  
  OBJECTIVE
  To determine the relative contribution of wear-line and split-line orientation on the tensile biomechanical properties of human patellar cartilage from different depths.
  
  
  METHODS
  In human patellar cartilage, wear- and split-lines are aligned parallel to each other at the proximal facet, and perpendicular to each other at the medial facet. Using superficial, middle, and deep cartilage sections from these two sites, tensile samples were prepared in two orthogonal orientations. Thus, for each depth, there were four groups of samples, with their long axes were aligned either parallel or perpendicular to wear-line direction and also aligned parallel or perpendicular to split-line direction. Uniaxial tensile tests were performed to assess equilibrium and ramp moduli.
  
  
  RESULTS
  Tensile equilibrium moduli varied with wear-line orientation (P<0.05) and depth (P<0.001), in an interactive manner (P<0.05), and tended to vary with split-line orientation (P=0.16). In the superficial layer, equilibrium and ramp modulus were higher when the samples were loaded parallel to wear-lines (P<0.05).
  
  
  CONCLUSIONS
  These results indicate that mild wear (i.e., wear-line formation) at the articular surface has deleterious functional effects on articular cartilage and represent an early aging-associated degenerative change. The identification and recognition of functional biomechanical consequences of wear-lines are useful for planning and interpreting tensile biomechanical tests in human articular cartilage.
authors.affiliation: Department of Bioengineering, University of California-San Diego, La Jolla, CA 92093-0412, United States.
authors.forename: W C
authors.initials: WC
authors.lastname: Bae
authors.forename: V W
authors.initials: VW
authors.lastname: Wong
authors.forename: J
authors.initials: J
authors.lastname: Hwang
authors.forename: J M
authors.initials: JM
authors.lastname: Antonacci
authors.forename: G E
authors.initials: GE
authors.lastname: Nugent-Derfus
authors.forename: M E
authors.initials: ME
authors.lastname: Blewis
authors.forename: M M
authors.initials: MM
authors.lastname: Temple-Wong
authors.forename: R L
authors.initials: RL
authors.lastname: Sah
mesh_terms: D000328:Adult; D000375:Aging / Q000473:pathology / Q000502:physiology; D001696:Biomechanical Phenomena; D002244:Carbon; D002358:Cartilage, Articular / Q000033:anatomy & histology / Q000502:physiology*; D006801:Humans; D010329:Patella / Q000033:anatomy & histology / Q000502:physiology*; D013194:Staining and Labeling / Q000379:methods; D013718:Tensile Strength
chemical_list: C028433:chinese ink; D002244:Carbon