Bone marrow lesions and subchondral bone pathology of the knee

Bone marrow lesions (BMLs) around the knee are a common magnetic resonance imaging (MRI) finding. However, despite the growing interest on BMLs in multiple pathological conditions, they remain controversial not only for the still unknown role in the etiopathological processes, but also in terms of clinical impact and treatment. The differential diagnosis includes a wide range of conditions: traumatic contusion and fractures, cyst formation and erosions, hematopoietic and infiltrated marrow, developmental chondroses, disuse and overuse, transient bone marrow oedema syndrome and, lastly, subchondral insufficiency fractures and true osteonecrosis. Regardless the heterogeneous spectrum of these pathologies, a key factor for patient management is the distinction between reversible and irreversible conditions. To this regard, MRI plays a major role, leading to the correct diagnosis based on recognizable typical patterns that have to be considered together with coexistent abnormalities, age, and clinical history. Several treatment options have been proposed, from conservative to surgical approaches. In this manuscript the main lesion patterns and their management have been analysed to provide the most updated evidence for the differential diagnosis and the most effective treatment. Level of evidence IV.