Patterns of red marrow in the adult femur.

Purpose: Conversion of red marrow (RM) to fatty marrow in the skeleton of the lower extremities begins at the distal end, ie, feet, and progresses proximally with distal bone marrow (ie, tibia) being converted more rapidly than proximal bone marrow (ie, femur). However, in an individual long bone, conversion begins in the diaphysis and progresses both distally and proximally (more rapidly toward the distal side). In a normal adult's femur, RM is present in the proximal one third or less. Reconversion of fatty marrow to RM is reported to occur in the reverse order of conversion. We assessed the frequency of various patterns of RM in the adult femur on In-111 leukocyte scans for a better understanding of the bone marrow regeneration process in individual long bones. Methods: The patterns of marrow activity in the femur shown on In-111 leukocyte scans performed in 354 adults were divided into a) RM limited to the proximal one third or less, b) to the proximal two thirds, c) to the proximal one third and distal one third with no activity in the middle shaft, and d) in the entire femur. Results: There were 207 patients with pattern A, 91 pattern B, 14 pattern C, and 42 pattern D. Conclusions: A considerably higher number of adults showed pattern B than pattern C. This suggests that regeneration of diaphyseal marrow precedes that of the distal marrow in an individual long bone or possibly that conversion of the latter precedes the former, which is different from that proposed in the literature.