title: Trajectories and risk profiles of pain in persons with radiographic, symptomatic knee osteoarthritis: data from the osteoarthritis initiative.
abstract: BACKGROUND
  Little is known about the temporal evolution of pain severity in persons with knee osteoarthritis (OA). We sought to describe the pain trajectory over 6 years in a cohort of subjects with radiographic, symptomatic knee OA.
  
  
  METHODS
  We used data from the Osteoarthritis Initiative (OAI), a multi-center, longitudinal study of subjects with diagnosed radiographic evidence of knee OA. Pain was assessed at baseline and annually for 6 years. Our analysis cohort included subjects with symptomatic knee OA at baseline, defined as baseline Kellgren-Lawrence (KL) score ≥2 with Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain score >0. We used group-based trajectory modeling to identify distinct patterns of pain progression over a 6-year follow-up. Factors examined included sex, race, education, comorbidities, age, body mass index (BMI), alignment, KL grade, and depression.
  
  
  RESULTS
  We used data from 1753 OAI participants with symptomatic knee OA. Mean baseline WOMAC pain score was 26.5 (0-100, 100=worst) with standard deviation (SD) 19. Group-based trajectory modeling identified five distinct pain trajectories; baseline pain scores for each ranged from 15 to 62. None of the trajectories exhibited substantial worsening. One fifth of subjects in the two trajectories with the greatest pain underwent total knee replacement (TKR) over follow-up. Higher KL grade, obesity, depression, medical comorbidities, female sex, non-white race, lower education, and younger age were associated with trajectories characterized by greater pain.
  
  
  CONCLUSIONS
  We found that knee pain changes little, on average, over 6 years in most subjects. These observations suggest knee OA is characterized by persistent rather than inexorably worsening symptoms.
authors.affiliation: Orthopaedic and Arthritis Center for Outcomes Research, Department of Orthopedic Surgery, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA; Department of Biostatistics, Boston University School of Public Health, Boston, MA, USA. Electronic address: JCOLLINS13@PARTNERS.ORG.
authors.forename: J E
authors.initials: JE
authors.lastname: Collins
authors.affiliation: Orthopaedic and Arthritis Center for Outcomes Research, Department of Orthopedic Surgery, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA; Division of Rheumatology, Immunology and Allergy, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA.
authors.forename: J N
authors.initials: JN
authors.lastname: Katz
authors.affiliation: Orthopaedic and Arthritis Center for Outcomes Research, Department of Orthopedic Surgery, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA.
authors.forename: E E
authors.initials: EE
authors.lastname: Dervan
authors.affiliation: Orthopaedic and Arthritis Center for Outcomes Research, Department of Orthopedic Surgery, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA; Department of Biostatistics, Boston University School of Public Health, Boston, MA, USA.
authors.forename: E
authors.initials: E
authors.lastname: Losina
mesh_terms: D000368:Aged; D015992:Body Mass Index; D015897:Comorbidity; D018450:Disease Progression; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000150:complications* / Q000000981:diagnostic imaging / Q000453:epidemiology; D010146:Pain / Q000000981:diagnostic imaging / Q000453:epidemiology / Q000209:etiology*; D010147:Pain Measurement / Q000379:methods; D011859:Radiography; D012307:Risk Factors; D012720:Severity of Illness Index; D014481:United States / Q000453:epidemiology
keywords: Cohort study; Group-based trajectory modeling; Osteoarthritis; Pain; Trajectories