title: Indentation stiffness does not discriminate between normal and degraded articular cartilage.
abstract: BACKGROUND
  Relative indentation characteristics are commonly used for distinguishing between normal healthy and degraded cartilage. The application of this parameter in surgical decision making and an appreciation of articular cartilage biomechanics has prompted us to hypothesise that it is difficult to define a reference stiffness to characterise normal articular cartilage.
  
  
  METHODS
  This hypothesis is tested for validity by carrying out biomechanical indentation of articular cartilage samples that are characterised as visually normal and degraded relative to proteoglycan depletion and collagen disruption. Compressive loading was applied at known strain rates to visually normal, artificially degraded and naturally osteoarthritic articular cartilage and observing the trends of their stress-strain and stiffness characteristics.
  
  
  RESULTS
  While our results demonstrated a 25% depreciation in the stiffness of individual samples after proteoglycan depletion, they also showed that when compared to the stiffness of normal samples only 17% lie outside the range of the stress-strain behaviour of normal samples.
  
  
  CONCLUSIONS
  We conclude that the extent of the variability in the properties of normal samples, and the degree of overlap (81%) of the biomechanical properties of normal and degraded matrices demonstrate that indentation data cannot form an accurate basis for distinguishing normal from abnormal articular cartilage samples with consequences for the application of this mechanical process in the clinical environment.
authors.affiliation: Institute of Health and Biomedical Innovation, Faculty of Built Environment and Engineering, Queensland University of Technology, 2 George St., Brisbane Q 4001, Australia.
authors.forename: Cameron P
authors.initials: CP
authors.lastname: Brown
authors.forename: Ross W
authors.initials: RW
authors.lastname: Crawford
authors.forename: Adekunle
authors.initials: A
authors.lastname: Oloyede
mesh_terms: D000818:Animals; D002357:Cartilage Diseases / Q000175:diagnosis* / Q000503:physiopathology*; D002358:Cartilage, Articular / Q000503:physiopathology*; D002417:Cattle; D004548:Elasticity; D006245:Hardness Tests / Q000379:methods*; D066298:In Vitro Techniques; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013314:Stress, Mechanical