Title: Individuals with accelerated knee osteoarthritis have greater pain and functional impairments than individuals with common knee osteoarthritis: Data from the osteoarthritis
Abstract: Purpose: Knee osteoarthritis (KOA) is typically a slowly progressive disorder; however, a subset of knees progress with dramatic rapidity (e.g. from normal appearance to end-stage disease within 4 years). It is unclear if knee pain, other patient-reported outcomes, and physical performance measures differ between individuals who develop accelerated KOA (AKOA) verus those with a more gradual progression. Therefore, we aimed to evaluate whether AKOA was associated with greater pain and other outcomes and if outcomes varied over time differently among those with AKOA or gradual disease progression. Methods: We conducted longitudinal analyses among participants in the Osteoarthritis Initiative who had no radiographic KOA at baseline (Kellgren-Lawrence [KL]<2). Participants were divided into two groups: 1) AKOA: at least one knee progressed to end-stage KOA within 48 months and 2)common KOA: at least one knee increased in radiographic scoring within 48 months (excluding those with accelerated KOA). For individuals with AKOA the study outcome visit was when they first had a KL grade > 3. For individuals with common KOA the study outcome visit was when they first had an increase in KL grade. We evaluated the 3 years before and after the study outcome visit. Every participant contributed at least two time points. Our primary outcome was WOMAC pain score, which we converted to an ordinal scale: no pain (pain score = 0 or 1), mild pain (pain score = 2 or 3), and moderate-severe pain (pain score > 3). We explored 11 other secondary outcome measures (see table). For knee pain and other ordinal outcome measures we performed an ordinal logistic regression with generalized estimating equations (GEE) to account for within-participant correlations over time. Similarly, for continuous outcomes we developed a linear model using GEE. The predictors in all models were group (AKOA or common KOA), time (7 visits), and a group by time interaction. Since all knees with common KOA progressed to the study outcome in 1 year we conducted a secondary analysis among 34 knees with AKOA that progressed from no KOA to end-stage in OA during a 1 year period. Results: We previously described the baseline characteristics of OAI participants with common KOA (n=187, 65% female, mean age of 58.0 [8.3] years) and AKOA (n=54, 63% female, mean age of 61.8 [8.6] years). Among those with AKOA, most knees progressed from no radiographic KOA to end-stage KOA in less than 12 month (63%); 17% progressed over 2 years, 13% progressed over 3 years, 2% progressed over 4 years, and 6% had a missing x-ray the precluded us from determining their rate of progression. Overall, individuals with AKOA had greater pain, less physical activity, slower chair-stand pace, and weaker maximum isometric knee flexion force compared with those with common KOA (see Table and Figures). There was no significant interaction between group and time for knee pain; however, there was for chair-stand pace and global rating scale (see Table and Figures 2 and 3). Our secondary analyses had similar results to the primary analyses but with attenuated estimates and no significant results. Conclusions: Individuals with AKOA had greater pain and functional limitations compared with individuals with common KOA, regardless of time before or after the study outcome. Individuals with AKOA tend to report being more affected by their knee pain (global rating scale) and have diminished performance on the chair stand test years before developing end-stage KOA – a similar trend although not significant was also detected for knee pain. We propose a conceptual model in which AKOA may initially be characterized by subtle changes related to knee pain, which are not visible on radiographs. Based on our prior work, these changes may be related to aging and being overweight and the increased knee pain may increase the risk of a new knee injury, which could represent a final catalyst leading to AKOA. Therefore, AKOA may be a painful and disabling phenotype that warrants more attention by clinicians and researchers.View Large Image Figure ViewerDownload Hi-res image Download (PPT)View Large Image Figure ViewerDownload Hi-res image Download (PPT)View Large Image Figure ViewerDownload Hi-res image Download (PPT)