title: Does intraarticular inflammation predict biomechanical cartilage properties?
abstract: BACKGROUND
  Intact cartilage in the lateral compartment is an important requirement for medial unicompartmental knee arthroplasty (UKA). Progression of cartilage degeneration in the lateral compartment is a common failure mode of medial UKA. Little is known about factors that influence the mechanical properties of lateral compartment cartilage.
  
  
  OBJECTIVE
  The purposes of this study were to answer the following questions: (1) Does the synovial fluid white blood cell count predict the biomechanical properties of macroscopically intact cartilage of the distal lateral femur? (2) Is there a correlation between MRI grading of synovitis and the biomechanical properties of macroscopically intact cartilage? (3) Is there a correlation between the histopathologic assessment of the synovium and the biomechanical properties of macroscopically intact cartilage?
  
  
  METHODS
  The study included 84 patients (100 knees) undergoing primary TKA for varus osteoarthritis between May 2010 and January 2012. All patients underwent preoperative MRI to assess the degree of synovitis. During surgery, the cartilage of the distal lateral femur was assessed macroscopically using the Outerbridge grading scale. In knees with an Outerbridge grade of 0 or 1, osteochondral plugs were harvested from the distal lateral femur for biomechanical and histologic assessment. The synovial fluid was collected to determine the white blood cell count. Synovial tissue was taken for histologic evaluation of the degree of synovitis.
  
  
  RESULTS
  The mean aggregate modulus and the mean dynamic modulus were significantly greater in knees with 150 or less white blood cells/mL synovial fluid compared with knees with greater than 150 white blood cells/mL synovial fluid. There was no correlation among MRI synovitis grades, histopathologic synovitis grades, and biomechanical cartilage properties.
  
  
  CONCLUSIONS
  The study suggests that lateral compartment cartilage in patients with elevated synovial fluid white blood cell counts has a reduced ability to withstand compressive loads.
  
  
  METHODS
  Level III, diagnostic study. See the Instructions for Authors for a complete description of levels of evidence.
authors.affiliation: Adult Reconstruction & Joint Replacement Division, Hospital for Special Surgery, 535 East 70th Street, New York, NY, 10021, USA.
authors.forename: Wenzel
authors.initials: W
authors.lastname: Waldstein
authors.forename: Giorgio
authors.initials: G
authors.lastname: Perino
authors.forename: Shari T
authors.initials: ST
authors.lastname: Jawetz
authors.forename: Susannah L
authors.initials: SL
authors.lastname: Gilbert
authors.forename: Friedrich
authors.initials: F
authors.lastname: Boettner
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee; D001696:Biomechanical Phenomena; D002358:Cartilage, Articular / Q000473:pathology / Q000503:physiopathology* / Q000601:surgery; D019245:Compressive Strength; D055119:Elastic Modulus; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000276:immunology* / Q000473:pathology / Q000503:physiopathology / Q000601:surgery; D007958:Leukocyte Count; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000276:immunology* / Q000473:pathology / Q000503:physiopathology / Q000601:surgery; D011237:Predictive Value of Tests; D011446:Prospective Studies; D013314:Stress, Mechanical; D013582:Synovial Fluid / Q000276:immunology*; D013585:Synovitis / Q000276:immunology* / Q000473:pathology / Q000503:physiopathology / Q000601:surgery