title: Trajectories of functional decline in knee osteoarthritis: the Osteoarthritis Initiative.
abstract: OBJECTIVE
  To describe trajectories of functional decline over 84 months and study associated risk factors among adults initially without limitation who had or were at risk of knee OA.
  
  
  METHODS
  We used annual measures of WOMAC physical function over 84 months from the OA Initiative. We included knees with no functional limitation (i.e. WOMAC = 0) at baseline. Knee-based trajectories of functional decline from WOMAC were identified from a group-based trajectory model (PROC TRAJ).
  
  
  RESULTS
  We identified five trajectories from 2110 knees (1055 participants, age 61.0 ± 9.3, BMI 27.1 ± 4.4, 52% women). Half of the knees (54%) remained free of limitation over 84 months, 26% slowly declined to a WOMAC of 1.5, 9% were limitation free for the first 36 months and declined to a WOMAC of 11.3, 6% rapidly declined over the first 12 months and gradually recovered to a WOMAC of 3.3 and 5% steadily declined to a WOMAC of 13.2. Baseline radiographic disease, knee pain, obesity and depressive symptoms at baseline were associated with trajectories of worse functional decline.
  
  
  CONCLUSIONS
  Five per cent of our sample initially without limitation was on a trajectory of progressive functional decline over 84 months later. We found worse disease and health status at baseline to be associated with faster decline over time.
authors.affiliation: Department of Physical Therapy, University of Delaware, Newark, DE, Department of Physical Therapy and Athletic Training, College of Health and Rehabilitation Sciences, Boston University, dkw@udel.edu.
authors.forename: Daniel K
authors.initials: DK
authors.lastname: White
authors.affiliation: Clinical Epidemiology Research and Training Unit, Boston University School of Medicine, Boston and.
authors.forename: Tuhina
authors.initials: T
authors.lastname: Neogi
authors.affiliation: Orthopedics and Physical Rehabilitation, University of Massachusetts Medical School, Worcester, MA, USA.
authors.forename: Uyen-Sa D T
authors.initials: US
authors.lastname: Nguyen
authors.affiliation: Clinical Epidemiology Research and Training Unit, Boston University School of Medicine, Boston and.
authors.forename: Jingbo
authors.initials: J
authors.lastname: Niu
authors.affiliation: Clinical Epidemiology Research and Training Unit, Boston University School of Medicine, Boston and.
authors.forename: Yuqing
authors.initials: Y
authors.lastname: Zhang
mesh_terms: D000368:Aged; D003863:Depression / Q000150:complications; D018450:Disease Progression; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000000981:diagnostic imaging / Q000209:etiology / Q000503:physiopathology*; D050177:Overweight / Q000150:complications; D010146:Pain / Q000209:etiology; D010147:Pain Measurement / Q000379:methods; D011859:Radiography; D012307:Risk Factors; D012720:Severity of Illness Index
keywords: knee osteoarthritis; physical function; trajectory