Prognostic power of criteria for symptomatic early knee osteoarthritis from a 2-year longitudinal observation of the Iwaki cohort study

This study aimed to investigate whether symptomatic early knee osteoarthritis (EKOA) effectively predicts the incidence of definitive knee osteoarthritis (DKOA) in the general Japanese population. A total of 133 women from the Japanese Iwaki cohort study were enrolled and followed-up over 2 years in order to calculate the rate of progression of EKOA to DKOA. Weight-bearing anteroposterior bilateral knee radiographs and magnetic resonance imaging (MRI) were conducted at baseline and follow-up. Radiographs were classified according to the Kellgren–Lawrence grade. The presence of cartilage lesion, bone marrow lesions, attrition, cysts, osteophytes, and meniscal lesions was evaluated according to the Whole-Organ Magnetic Resonance Imaging Score (WORMS). Logistic regression analyses were performed to determine the predictive power of EKOA. Of 25 women with EKOA, 15 (60%) progressed to DKOA over 2 years, showing a relative risk (RR) of 1.44 compared with the non-osteoarthritis (non-OA) group (P ​= ​0.120). Logistic regression analysis showed associations of EKOA (P ​= ​0.048) and high body mass index (P ​< ​0.001) with progression to DKOA. Combined EKOA and meniscal lesions increased the RR for osteoarthritis incidence to 2.32 (P ​= ​0.004) compared with the non-OA group. Also, meniscus and bone marrow lesion scores on MRI of the EKOA group maintained high scores over 2 years. The prognostic power of EKOA criteria was confirmed with a RR of 1.44. The combination of symptomatic EKOA criteria and MRI-detected meniscal lesions was a valuable predictor of progression to DKOA over 2 years in women without radiographic abnormalities.