The Longterm Outcome of Osteoarthritis: Rates and Predictors of Joint Space Narrowing in Symptomatic Patients with Knee Osteoarthritis

Objective: To determine the rate of progression of radiographic joint space narrowing (JSN) and the factors that predict it in symptomatic clinic patients with knee osteoarthritis (OA).

Methods: In total 1,507 patients with knee OA were studied with extended weight-bearing anterior-posterior views of the knee as part of a longitudinal study of longterm outcomes of osteoarthritis (OA). Baseline demographic and severity measurements included body mass index (BMI), pain, global severity, Health Assessment Questionnaire disability, and erythrocyte sedimentation rate. Rates and predictors of progression were obtained by Kaplan-Meier survival analyses and Cox regressions using a JSN score of 3 as "failure."

Results: For the 1,232 patients who had not reached the endpoint narrowing score of 3 when first evaluated, the 75th and 50th survival times (time to JSN = 3) were 11.27 and 17.84 years for those with JSN = 0 at onset, 7.41 and 12.03 years for those with JSN = 1 at onset, and 4.49 and 7.44 years for those with JSN = 2 at onset. The corresponding yearly incidence rates for the 3 initial groups were 0.017, 0.032, and 0.077. In multivariate Cox models, initial JSN, BMI, symptom duration, and global severity were predictors of progression, but only JSN was a strong predictor. BMI predicted JSN in those with JSN = 0 at onset, but not in patients with more severe disease. Although contralateral JSN predicted progression, it was only of value with initial homolateral JSN scores of 0. Assessment of homolateral osteophytes aided prediction in patients with initial JSN = 0, but was of much less help when JSN had a higher severity score.

Conclusion: The risk of progression in clinical OA patients with radiographic abnormalities is substantial. Nonradiographic predictors of OA progression (e.g., BMI) are weak predictors of radiographic progression compared to current radiographic status. Rates of progression are greatest in those with established radiographic abnormalities. Osteophytes are of limited additional values once JSN = 2 is present. Contralateral radiographic abnormalities are useful predictors only in those with JSN = 0. Intervention studies to prevent radiographic progression probably should utilize joints where evidence of abnormality already exists. At a clinical level, current radiographic status predicts future status, with 50% of patients with JSN = 1 and 50% of patients with JSN = 2 progressing to complete joint space loss in 12.03 and 7.44 years, respectively.