title: Biomechanical characterization of passive laxity of the hip joint in dogs.
abstract: OBJECTIVE
  To investigate the in vitro load/displacement characteristics of the hip joints in dogs as a function of joint position.
  
  
  METHODS
  10 hip joints from 5 healthy dogs.
  
  
  METHODS
  A material test system was used to generate load/displacement curves for each joint. Joints were mounted in a custom-designed jig that held the joint in fixed anatomic orientations while plotting displacement and corresponding applied loads. All hips were cycled between 40 N of compression and 80 N of distraction. Each hip was tested at 10 degrees increments from 30 degrees flexion to 70 degrees extension.
  
  
  RESULTS
  When the hips were in a neutral orientation (approximately a standing position), load/displacement curves were characteristically sigmoidal (tri-phasic), indicating that, in this position, displacement was not highly dependent on load. The curves had a central low-stiffness region in which most of the lateral displacement took place. In contrast, when hips were positioned at the extremes of flexion and extension, this central, low-stiffness region was less distinct, and load/displacement curves were more linear, indicating a proportional relation between load and displacement. The load/displacement curve of 1 hip joint in the study deviated markedly from the others in a pattern consistent with cavitation of the synovial fluid.
  
  
  CONCLUSIONS
  When the hip joint is positioned in a neutral position, load-displacement behavior is sigmoidal, whereas when the hip joint is in an extended position, load/displacement behavior is more linear.
  
  
  CONCLUSIONS
  Establishing load/displacement behavior of the hip joints in dogs was an important exercise in establishing the position for and estimating the repeatability of a clinical stress-radiographic method for quantitating joint laxity in dogs.
authors.affiliation: Department of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, Philadelphia 19104, USA.
authors.forename: G K
authors.initials: GK
authors.lastname: Smith
authors.forename: E
authors.initials: E
authors.lastname: LaFond
authors.forename: S J
authors.initials: SJ
authors.lastname: Heyman
authors.forename: M A
authors.initials: MA
authors.lastname: Cofone
authors.forename: T P
authors.initials: TP
authors.lastname: Gregor
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D004283:Dog Diseases / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology*; D004285:Dogs; D006621:Hip Joint / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology*; D007593:Joint Instability / Q000473:pathology / Q000503:physiopathology / Q000662:veterinary*; D008954:Models, Biological; D011859:Radiography; D015203:Reproducibility of Results; D016474:Weight-Bearing / Q000502:physiology