To compare values for Kellgren-Lawrence (K-L) grade, joint space narrowing (JSN), and osteophytes (OST) in anteroposterior (AP) extended and fixed-flexion posteroanterior (PA-FF) radiographs obtained during a single clinic visit (the first follow-up of the Johnston County Osteoarthritis Project (JoCo OA)).
All films (n=1664 bilateral knees) were read by an experienced musculoskeletal radiologist (JBR). For each subject, AP and PA-FF films were read in one sitting. K-L grades (from 0–4), JSN and OST (from 0–3) were assessed using standard atlases. Descriptive statistics were calculated for demographic and clinical variables. AP and PA-FF results were compared by contingency table methods to obtain frequencies for K-L, JSN, and OST grades, using percentage agreement and kappa coefficients (κ). Results from the right and left knees were similar; data for the right knee are presented.
There was substantial agreement between AP and PA-FF reads for radiographic OA (rOA), defined as K-L grade ≥2 (89% agreement; κ=0.73 with 95% CI 0.69–0.76). Substantial agreement was also seen for tibial OST and medial JSN; slightly lower κ was observed for femoral OST and lateral JSN.
The requirements of large observational cohort studies are different than those of clinical trials, and sensitivity is less of an issue because of longer follow up times. In cohort studies such as the JoCo OA, there is substantial agreement by K-L grade for AP and PA-FF radiographs, allowing incorporation of older films in longitudinal analyses.