title: Effect of the variation of loading frequency on surface failure of bovine articular cartilage.
abstract: BACKGROUND
  Mechanical loading of synovial joints can damage the articular cartilage surface and may lead to osteoarthritis. It is unknown if, independent of load, frequency alone can cause failure in cartilage. This study investigated the variation of articular cartilage surface damage under frequencies associated with normal, above normal and traumatic loading frequencies.
  
  
  METHODS
  Cartilage on bone, obtained from bovine shoulder joints, was tested. Damage was created on the cartilage surface through an indenter being sinusoidally loaded against it at loading frequencies of 1, 10 and 100 Hz (i.e., relevant to normal, above normal and up to rapid heel-strike rise times, respectively). The frequencies were applied with a maximum load in the range 60-160 N. Surface cracks were marked with India ink, photographed and their length measured using image analysis software.
  
  
  RESULTS
  Surface damage increased significantly (P < 0.0001) with frequency throughout all load ranges investigated. The dependence of crack length, c, on frequency, f, could be represented by, c=A(log10(f))2+B(log10(f))+Dc=A(log10(f))2+B(log10(f))+D where A = 0.006 ± 0.23, B = 0.62 ± 0.23 and D = 0.38 ± 0.51 mm (mean ± standard deviation).
  
  
  CONCLUSIONS
  The increase in crack length with loading frequency indicated that, increased loading frequency can result in cartilage becoming damaged. The results of this study have implications in the early stages of osteoarthritis.
authors.affiliation: School of Mechanical Engineering, University of Birmingham, B15 2TT, UK.
authors.forename: H
authors.initials: H
authors.lastname: Sadeghi
authors.affiliation: School of Mechanical Engineering, University of Birmingham, B15 2TT, UK. Electronic address: d.e.shepherd@bham.ac.uk.
authors.forename: D E T
authors.initials: DET
authors.lastname: Shepherd
authors.affiliation: School of Mechanical Engineering, University of Birmingham, B15 2TT, UK.
authors.forename: D M
authors.initials: DM
authors.lastname: Espino
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D002358:Cartilage, Articular / Q000293:injuries / Q000502:physiology / Q000503:physiopathology*; D002417:Cattle; D004548:Elasticity; D010003:Osteoarthritis / Q000503:physiopathology*; D012785:Shoulder Joint / Q000502:physiology / Q000503:physiopathology; D013314:Stress, Mechanical; D016474:Weight-Bearing / Q000502:physiology*
keywords: Articular cartilage; Crack; Failure; Frequency; Mechanical loading; Osteoarthritis