Aging and increasing obesity are contributing to the increase in the number of people with knee disease. Osteoarthritis is the most common form of arthritis requiring treatment, affecting 3,522 of every 100,000 people in the United States. The diagnosis of osteoarthritis relies primarily on x-rays combined with clinical examination. Population-based longitudinal studies in the United States have shown that osteoarthritis of the knee has a lifelong risk of becoming a lifelong disease with advancing age. Although structural damage of knee osteoarthritis is detected by x-ray, studies have also shown that structural damage is present in knees with no arthritic features on x-ray. Researchers in the Department of Radiology at Boston University School of Medicine conducted a population-based community cohort study based on the Framingham Study, designed to look at the prevalence of structural damage associated with arthritis by MRI in osteoarthritis without X-ray evidence to confirm the diagnosis. The study involved 710 participants aged >50 years with no radiographic evidence of knee osteoarthritis (K-L grade of 0), who were examined by researchers for MRI of the knee. All participants had MRI examinations suggestive of knee osteoarthritis (osteoarthrosis, cartilage damage, bone marrow damage, subchondral cysts, meniscal damage, synovitis, wear and tear, and ligament damage). The researchers also stratified the analysis by age, gender, body mass index and presence of knee pain. The study found that of the 710 participants, 393 (55%) were female, 660 (93%) were Caucasian, and 206 (29%) had experienced knee pain in the past month. The mean age of the participants was 62.3 years and the mean body mass index was 27.9. The prevalence of any abnormality was 89% (631/710). Among all participants, bone redundancy was the most common abnormality with a prevalence of 74% (524/710), followed by cartilage damage with a prevalence of 69% (492/710) and bone marrow damage with a prevalence of 52% (371/710). The prevalence of all types of abnormalities was found to increase with age by MRI. There was no significant difference in the prevalence of any of the features among the different body mass index groups. The prevalence of at least one pathology type was higher in both painful and pain-free knee patients, ranging from 90 to 97% and 86 to 88%, respectively. This study demonstrates that in most middle-aged and older adults, MRI reveals damage to the tibial joint with or without pain, even when there are no features of osteoarthritis on x-ray.