Femoral Bone Marrow Adiposity in Men with Motor Complete Spinal Cord Injury

Abstract

Obesity and osteoporosis are hallmark adaptations following spinal cord injury (SCI). Bone marrow (BM) mesenchymal cells can be differentiated to become osteoblasts or adipocytes. The major objective of the work is to quantify yellow marrow and cortical bone cross‐sectional areas (CSA) of the femur in individuals with SCI compared to healthy able‐bodied (AB) controls. Eight individuals with motor complete SCI as well as 6 age matched healthy AB controls underwent MRI of both thighs to measure BM adiposity (BMA) and cortical geometry. Cortical bone CSA adjusted to total sub‐perisoteal bone CSA was 1.5–2 × lower in men with SCI compared to AB‐controls across the femoral length (P =0.003). Yellow BMA CSA was 2–3 × greater in men with SCI compared to AB‐controls (P < 0.0001). BMA CSA was twice greater in the distal 1/3 compared to the proximal 2/3 in both groups. Negative association was noted between the yellow BMA CSA and cortical bone CSAs in men with SCI and positive association in AB‐controls. Yellow BMA was negatively associated with skeletal muscle CSA (P < 0.05) in men with SCI. After SCI, cortical bone CSA becomes thinner and associated with greater accumulation of yellow marrow as measured by BMA. BMA is linked to several of the adaptations that men with SCI encounter, including changes in bone geometry as well as increased fat mass. Loading may reciprocally influence the relationships between BMA and cortical bone CSA.