title: Subchondral cysts create increased intra-osseous stress in early knee OA: A finite element analysis using simulated lesions.
abstract: OBJECTIVE
  To investigate the role of intra-osseous lesions in advancing the pathogenesis of Osteoarthritis (OA) of the knee, using Finite Element Modeling (FEM) in conjunction with high-resolution imaging techniques.
  
  
  METHODS
  Twenty early stage OA patients (≤ Grade 2 radiographic score) were scanned with a prototype, cone-beam CT system. Scans encompassed the mid-shaft of the femur to the diaphysis of the proximal tibia. Individual bones were segmented to create 3D geometric models that were transferred to FE software for loading experiments. Patient-specific, inhomogeneous material properties were derived from the CT images and mapped directly to the FE models. Duplicate models were also created, with a 3D sphere (range 3-12 mm) introduced into a weight-bearing region of the joint, mimicking the size, location, and composition of a subchondral bone cyst (SBC). A spherical shell extending 1mm radially around the SBC served as the sample volume for measurements of von Mises equivalent stress. Both models were vertically loaded with 750 N, or approximately 1 body weight during a single-leg stance.
  
  
  RESULTS
  All FE models exhibited a physiologically realistic weight-bearing distribution of stress, which initiated at the joint surface and extended to the cortical bone. Models that contained the SBC experienced a nearly two-fold increase in stress (0.934 ± 0.073 and 1.69 ± 0.159 MPa, for the non-SBC and SBC models, respectively) within the bone adjacent to the SBC. In addition, there was a positive correlation found between the diameter of the SBC and the resultant intra-osseous stress under load (p = 0.004).
  
  
  CONCLUSIONS
  Our results provide insights into the mechanism by which SBC may accelerate OA, leading to greater pain and disability. Based on these findings, we feel that patient-derived FE models of the OA knee - utilizing in vivo imaging data - present a tremendous potential for monitoring joint mechanics under physiological loads.
authors.affiliation: Imaging Laboratories, Robarts Research Institute,Schulich School of Medicine and Dentistry, The University of Western Ontario, London, Ontario, Canada. david.holdsworth@imaging.robarts.ca
authors.forename: David D
authors.initials: DD
authors.lastname: McErlain
authors.forename: Jaques S
authors.initials: JS
authors.lastname: Milner
authors.forename: Todor G
authors.initials: TG
authors.lastname: Ivanov
authors.forename: Lubica
authors.initials: L
authors.lastname: Jencikova-Celerin
authors.forename: Steven I
authors.initials: SI
authors.lastname: Pollmann
authors.forename: David W
authors.initials: DW
authors.lastname: Holdsworth
mesh_terms: D001845:Bone Cysts / Q000150:complications* / Q000473:pathology* / Q000503:physiopathology; D001842:Bone and Bones / Q000473:pathology* / Q000503:physiopathology; D005269:Femur / Q000473:pathology / Q000503:physiopathology; D020342:Finite Element Analysis; D006801:Humans; D016014:Linear Models; D008954:Models, Biological; D020370:Osteoarthritis, Knee / Q000150:complications* / Q000473:pathology* / Q000503:physiopathology; D013312:Stress, Physiological; D013977:Tibia / Q000473:pathology / Q000503:physiopathology; D016474:Weight-Bearing / Q000502:physiology