Knee MRI patterns of bone marrow reconversion and relationship to anemia

Bone marrow changes are commonly encountered on knee magnetic resonance imaging (MRI). The clinical relevance of these changes, especially as they relate to anemia, has not been studied in a large patient series.

To determine if the extent of bone marrow reconversion (BMR) can assist the radiologist in making recommendations for further evaluation for underlying anemia.

This study included 457 patients who had knee MRI over a 2-year period. Bone marrow patterns in the distal femur, proximal tibia, and fibula were graded as follows: 1, homogeneous fatty marrow; 2, patchy red marrow in the distal femur; 3, patchy red marrow in the distal femur and tibia and/or fibula; and 4, complete BMR in the femoral, tibial, and/or fibular metaphyses.

There was a statistically significant difference (P < 0.001) between the hemoglobin concentration and BMR grades. In women, anemia (Hb ≤12.0 g/dL) was found in 31 of 127 (24%) patients with grade 1, 31 of 83 (37%) with grade 2, 24 of 64 (37%) with grade 3, and 12 of 24 (50%) with grade 4. In men, anemia (Hb ≤13.0 g/dL) was found in 33 of 125 (26%) patients with grade 1, 12 of 19 (63%) with grade 2, five of 14 (36%) with grade 3, but not in the one patient with grade 4.

Women demonstrating marrow changes of a grade 4 BMR pattern should get a laboratory assessment for anemia.