title: Best performing definition of accelerated knee osteoarthritis: data from the Osteoarthritis Initiative.
abstract: BACKGROUND
  We evaluated agreement among several definitions of accelerated knee osteoarthritis (AKOA) and construct validity by comparing their individual associations with injury, age, obesity, and knee pain.
  
  
  METHODS
  We selected knees from the Osteoarthritis Initiative that had no radiographic knee osteoarthritis [Kellgren-Lawrence (KL) 0 or 1] at baseline and had high-quality quantitative medial joint space width (JSW) measures on two or more consecutive visits (n= 1655 knees, 1143 participants). Quantitative medial JSW was based on a semi-automated method and was location specific (x= 0.25). We compared six definitions of AKOA: stringent JSW (averaged): average JSW loss greater than 1.05 mm/year over 4 years; stringent JSW (consistent): JSW loss greater than 1.05 mm/year for at least 2 years; lenient JSW (averaged): average JSW loss greater than 0.25 mm/year over 4 years; lenient JSW (consistent): JSW loss greater than 0.25 mm/year for at least 2 years; comprehensive KL based: progression from no radiographic osteoarthritis to advance-stage osteoarthritis (KL 3 or 4; development of definite osteophyte and joint space narrowing) within 4 years; and lenient KL based: an increase of at least two KL grades within 4 years.
  
  
  RESULTS
  Over 4 years the incidence rate of AKOA was 0.4%, 0.8%, 15.5%, 22.1%, 12.4%, and 7.2% based on the stringent JSW (averaged and consistent), lenient JSW (averaged and consistent), lenient KL-based definition, and comprehensive KL-based definition. All but one knee that met the stringent JSW definition also met the comprehensive KL-based definition. There was fair substantial agreement between the lenient JSW (averaged), lenient KL-based, and comprehensive KL-based definitions. A comprehensive KL-based definition led to larger effect sizes for injury, age, body mass index, and average pain over 4 years.
  
  
  CONCLUSIONS
  A comprehensive KL-based definition of AKOA may be ideal because it represents a broader definition of joint deterioration compared with those focused on just joint space or osteophytes alone.
authors.affiliation: Division of Rheumatology, Tufts Medical Center, 800 Washington Street, Box 406, Boston, MA 02111, USA.
authors.forename: Jeffrey B
authors.initials: JB
authors.lastname: Driban
authors.affiliation: Division of Rheumatology, Tufts Medical Center, Boston, MA, USA.
authors.forename: Alina C
authors.initials: AC
authors.lastname: Stout
authors.affiliation: Medical Care Line and Research Care Line, Houston Health Services Research and Development (HSR&D) Center of Excellence Michael E. DeBakey VAMC, Houston, TX, USA.
authors.forename: Grace H
authors.initials: GH
authors.lastname: Lo
authors.affiliation: Center for Primary Care and Prevention, Alpert Medical School of Brown University, Pawtucket, RI, USA.
authors.forename: Charles B
authors.initials: CB
authors.lastname: Eaton
authors.affiliation: The Institute for Clinical Research and Health Policy Studies, Tufts Medical Center, Boston, MA, USA.
authors.forename: Lori Lyn
authors.initials: LL
authors.lastname: Price
authors.affiliation: Brigham & Women's Hospital and Harvard Medical School, Boston, MA, USA.
authors.forename: Bing
authors.initials: B
authors.lastname: Lu
authors.affiliation: Department of Anatomy and Cell Biology, Temple University School of Medicine, Philadelphia, PA, USA.
authors.forename: Mary F
authors.initials: MF
authors.lastname: Barbe
authors.affiliation: Division of Rheumatology, Tufts Medical Center, Boston, MA, USA.
authors.forename: Timothy E
authors.initials: TE
authors.lastname: McAlindon
keywords: classification; knee; osteoarthritis; phenotype; radiography