title: Structure-function relationships in osteoarthritic human hip joint articular cartilage.
abstract: OBJECTIVE
  It is currently poorly known how different structural and compositional components in human articular cartilage are related to their specific functional properties at different stages of osteoarthritis (OA). The objective of this study was to characterize the structure-function relationships of articular cartilage obtained from osteoarthritic human hip joints.
  
  
  METHODS
  Articular cartilage samples with their subchondral bone (n = 15) were harvested during hip replacement surgeries from human femoral necks. Stress-relaxation tests, Mankin scoring, spectroscopic and microscopic methods were used to determine the biomechanical properties, OA grade, and the composition and structure of the samples. In order to obtain the mechanical material parameters for the samples, a fibril-reinforced poroviscoelastic model was fitted to the experimental data obtained from the stress-relaxation experiments.
  
  
  RESULTS
  The strain-dependent collagen network modulus (E(f)(ε)) and the collagen orientation angle exhibited a negative linear correlation (r = -0.65, P < 0.01), while the permeability strain-dependency factor (M) and the collagen content exhibited a positive linear correlation (r = 0.56, P < 0.05). The nonfibrillar matrix modulus (E(nf)) also exhibited a positive linear correlation with the proteoglycan content (r = 0.54, P < 0.05).
  
  
  CONCLUSIONS
  The study suggests that increased collagen orientation angle during OA primarily impairs the collagen network and the tensile stiffness of cartilage in a strain-dependent manner, while the decreased collagen content in OA facilitates fluid flow out of the tissue especially at high compressive strains. Thus, the results provide interesting and important information of the structure-function relationships of human hip joint cartilage and mechanisms during the progression of OA.
authors.affiliation: Department of Applied Physics, University of Eastern Finland, POB 1627, FI-70211 Kuopio, Finland. Janne.Makela@uef.fi
authors.forename: J T A
authors.initials: JT
authors.lastname: Mäkelä
authors.forename: M R J
authors.initials: MR
authors.lastname: Huttu
authors.forename: R K
authors.initials: RK
authors.lastname: Korhonen
mesh_terms: D001696:Biomechanical Phenomena; D002358:Cartilage, Articular / Q000378:metabolism / Q000473:pathology* / Q000503:physiopathology; D003094:Collagen / Q000378:metabolism; D004548:Elasticity; D005272:Femur Neck / Q000473:pathology; D020342:Finite Element Analysis; D006621:Hip Joint / Q000473:pathology* / Q000503:physiopathology; D006801:Humans; D008859:Microscopy, Polarization; D015207:Osteoarthritis, Hip / Q000378:metabolism / Q000473:pathology* / Q000503:physiopathology; D011509:Proteoglycans / Q000378:metabolism; D016059:Range of Motion, Articular; D012720:Severity of Illness Index; D013314:Stress, Mechanical; D013718:Tensile Strength
chemical_list: D011509:Proteoglycans; D003094:Collagen