Bone marrow lesions: two pillars concept

A common magnetic resonance imaging pattern of bone marrow lesion has been described in numerous pathological entities. However, despite intensive research, its etiopathological pathways and repercussions on disease progression remain controversial. From our current knowledge, subchondral bone represents an active site of remodelling fulfilling both mechanical and biological joint requirements. Alteration of bone remodelling activity, as one of the major characteristics of bone marrow lesions, can potentially lead to biological and structural impairment of the affected tissue and consequently the entire joint. The discovered close connection between subchondral bone biology and its structural changes together with parallel changes in overlying cartilage is setting the scene for a potentially new concept. In this "Two Pillar" concept both structure and biology of subchondral bone (and its biomechanical and biochemical interference with the layer above) represent the foundations of the structure and function of articular cartilage. In light of the proposed concept, we will review current knowledge on aetiology, pathogenesis, and clinical presentation of BML and correlate it to existing and emerging treatment options.