generative joints. BMLs in OA are understood as non-cystic subchondral areas of ill-defined hyperintensity on T2w images and of hypointensity on T1w MR images. BMLs are observed regularly in conjunction with adjacent cartilage alterations. As the disease progresses, an increase in BML volume is seen in the same region subchondrally in many patients, which is positively correlated with an increase in cartilage loss and radiographic joint space narrowing. Subchondral cysts are strongly associated with BMLs in the same subregion and develop within non-cystic BMLs. BMLs fluctuate in size and the majority of subchondral BMLs may regress or resolve completely. Fluctuation of joint pain is positively correlated with fluctuation of BMLs in the same direction. Several validated semiquantitative and quantitative methods exist to assess BMLs in a research setting. Histologic correlation studies showed that the lesions consisted of a mixture of different tissue patterns with only little oedema. Specific changes in bone mineralisation and remodelling in areas of BMLs have further been reported. Differential diagnoses of OA-related BMLs include traumatic bone contusions and fractures with or without disruption of the articular surface. Osteonecrosis, inflammation, idiopathic BMLs, red marrow and post-surgical alterations should also be considered.