Structural knee MRI findings are already frequent in a general population-based birth cohort at 33 years of age.

OBJECTIVE To evaluate the incidence and severity of knee magnetic resonance imaging (MRI) findings and their associated lifestyle and health factors in a relatively healthy subset of a general population-based birth cohort. DESIGN The study population (n = 288, 61.1% females, mean age 33.7 years) is a subpopulation of the Northern Finland Birth Cohort 1986 (NFBC1986) on whom a thorough clinical evaluation, laboratory analyses and knee MRI were conducted at 33 years of age. Knee MRI data was graded using the MRI Osteoarthritis Knee Score (MOAKS) system. Descriptive statistics and multivariable regression models were used for data analysis. RESULTS Subjects were mostly asymptomatic. Detected articular cartilage lesions were mostly small and identified in 56.2 % (n = 162) of patellofemoral and 25.3 % (n = 63) of tibiofemoral joints. Full thickness cartilage lesions and bone marrow lesions were mostly located in the patellofemoral joint. Osteophytes, mostly small or doubtful, were detected in 51.7 % (n = 146) of patellofemoral and 17.4 % (n = 41) of tibiofemoral joints. In finding-specific regression analyses, higher body mass index (BMI) was most frequently associated with knee MRI findings. CONCLUSIONS In this relatively young and asymptomatic population, subtle knee MRI findings were already frequent, especially in the patellofemoral joint. Of analyzed background and clinical parameters, higher BMI was most frequently associated with MRI findings. Based on these results, longitudinal studies are warranted to further identify risk factors and proportions of progressing MRI findings.