Objective Prognostic estimates for knee osteoarthritis worsening over the full disease spectrum have not been reported. Osteoarthritis Initiative data were used to determine the association between knee radiographic osteoarthritis worsening and future knee pain and function. Methods Yearly data over a 5-year period were analyzed. Outcome measures were the Western Ontario and McMaster Universities Osteoarthritis Index and the Knee Injury and Osteoarthritis Outcome Score pain and symptoms scales. Knees were grouped based on whether yearly Kellgren/Lawrence (K/L) grades worsened. Associations of yearly K/L worsening with knee pain, symptoms, or function scores at the end of the year and with lagged outcomes observed at least 1 year after worsening were assessed using linear models with generalized estimating equations. Results A total of 25,932 knee-years of observations were examined in the primary analysis. For knees with yearly K/L worsening, all outcome scores were significantly worse (P values from 0.02 to <0.001) at the end of the index year, as compared to unchanged knees. All outcomes for knees with worsened versus unchanged K/L scores exceeded the minimal clinically important difference (MCID). For lagged effects, outcomes at 1 year following the index K/L year exceeded the MCID and were statistically significant (P ≤ 0.001) for knees with baseline K/L grades of 2 or 3. Conclusion K/L worsening over a 1-year period is prognostically important over the short term for all baseline K/L grades, and for knees with baseline K/L grades of 2 or 3 worsening continues over the following year.
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