Importance of the superficial tissue layer for the indentation stiffness of articular cartilage

• Published in: Medical engineering & physics Vol. 24; no. 2; pp. 99 - 108
• Main Authors: Korhonen, R.K, Wong, M, Arokoski, J, Lindgren, R, Helminen, H.J, Hunziker, E.B, Jurvelin, J.S
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01-03-2002; Elsevier Science
• Subjects: Animals; Articular cartilage; Biological and medical sciences; Cartilage mechanics; Cartilage, Articular - physiology; Cartilage, Articular - ultrastructure; Collagen; Computer Simulation; Dogs; Elastic moduli; Elasticity; Femur - physiology; Finite Element Analysis; Finite element method; Finite element model; Humerus - physiology; In Vitro Techniques; Indentation; Investigative techniques, diagnostic techniques (general aspects); Light polarization; Mathematical models; Medical sciences; Microscopy, Polarization; Models, Biological; Nondestructive examination; Optical microscopy; Orthopedic surgery; Osteoarticular system. Muscles; Pathology. Cytology. Biochemistry. Spectrometry. Miscellaneous investigative techniques; Polarized light microscopy; Stiffness; Stress, Mechanical; Surgery (general aspects). Transplantations, organ and tissue grafts. Graft diseases; Tibia - physiology; Time Factors; Finite element model; Cartilage mechanics; Articular cartilage; Polarized light microscopy; Indentation; Fissipedia; Animal model; Carnivora; Experimental study; Screening test; Modeling; Finite element method; Pathology; Heterogeneity; Vertebrata; Optical microscopy; Mammalia; Anisotropy; Animal; Mechanical characteristic; Stiffness; Dog; Quantitative analysis
• ISSN: 1350-4533; 1873-4030
• DOI: 10.1016/S1350-4533(01)00123-0

Indentation testing is a widely used technique for nondestructive mechanical analysis of articular cartilage. Although cartilage shows an inhomogeneous, layered structure with anisotropic mechanical properties, most theoretical indentation models assume material homogeneity and isotropy. In the present study, quantitative polarized light microscopy (PLM) measurements from canine cartilage were utilized to characterize thickness and structure of the superficial, collageneous tissue layer as well as to reveal its relation to experimental indentation measurements. In addition to experimental analyses, a layered, transversely isotropic finite element (FE) model was developed and the effect of superficial (tangential) tissue layer with high elastic modulus in the direction parallel to articular surface on the indentation response was studied. The experimental indentation stiffness was positively correlated with the relative thickness of the superficial cartilage layer. Also the optical retardation, which reflects the degree of parallel organization of collagen fibrils as well as collagen content, was related to indentation stiffness. FE results indicated effective stiffening of articular cartilage under indentation due to high transverse modulus of the superficial layer. The present results suggest that indentation testing is an efficient technique for the characterization of the superficial degeneration of articular cartilage.