Loss of hyaline articular cartilage is a central pathologic event in osteoarthritis, but the pathogenesis of cartilage loss is poorly understood. Bone marrow lesion (BML) is indicated by focally increased signal in the marrow on fat-suppressed T2-weighted images.

To correlate histopathology of a bone marrow lesion (BML) pattern with severity and structural damage in osteoarthritic knees.

Twenty consecutive patients (age range, 59–66 years; mean, 65 years) referred for total knee replacements were examined with sagittal short inversion time inversion-recovery (STIR) and T1- and T2-weighted MRI one week prior to surgery before surgery. Different structural abnormalities on MRI were compared with those on histologic maps.

The histopathology of BML in cases of OA revealed that 6 biopsies of cases showing bone marrow fibrosis (30%), 4 of them grade 1 (20%) and 2 of them grade 2 (10%). Eighteen biopsies showing cyst (90%), 9 biopsies showing abnormal trabeculae (45%), 2 of them with grade 1 (10%), 4 of them grade 2 (20%) and 3 of them grade 3 (15%). Five biopsies showing lymphocyte (25%), 40% of them had++CD3, while 60% of them had ++ CD20.

Five biopsies showing fatty marrow (25%), 9 biopsies showing haemosidrotic marrow (45%), 6 biopsies showing blood vessels (30%), 5 of them with grade 2 (25%) and 1 with grade 3 (5%). The MRI findings of OA patients had been revealed that there was 6 patients with BML of grade 1 (30%), 10 patients of grade 2 (50%) and 4 patients of grade 3 (20%).

BML has a strong correlation with radiographic severity measurements of osteoarthritis of the knee and pain. In patients with knee osteoarthritis, BML in bone underneath cartilage markedly increase risk for structural progression in the knee. Hyperemia and hematopoietic marrow were possible reasons for appearance of BML as high signal intensity on STIR images. BMLs are a cornerstone in progression of osteoarthritis.