Deficits in the Functional Muscle-Bone Unit in Youths with Fontan Physiology

Objective To determine whether dual energy X-ray absorptiometry (DXA), a clinically available tool, mirrors the magnitude of deficits in trabecular and cortical bone mineral density (BMD) demonstrated on peripheral quantitative computed tomography in youth with Fontan physiology. Study design We aimed to describe DXA-derived BMD at multiple sites and to investigate the relationship between BMD and leg lean mass, a surrogate for skeletal muscle loading. Subjects with Fontan (n = 46; aged 520 years) underwent DXA in a cross-sectional study of growth and bone and muscle health as described previously. Data from the Bone Mineral Density in Childhood Study were used to calculate age-, sex-, and race-specific BMD z-scores of the whole body, lumbar spine, hip, femoral neck, distal one-third radius, ultradistal radius, and leg lean mass z-score (LLMZ). Results Fontan BMD z-scores were significantly lower than reference at all sites-whole body, -0.34 +/- 0.85 (P =.01); spine, -0.41 +/- 0.96 (P =.008); hip, -0.75 +/- 1.1 (P <.001); femoral neck, -0.73 +/- 1.0 (P <.001); distal one-third radius, -0.87 +/- 1.1 (P <.001); and ultradistal radius. -0.92 +/- 1.03 (P <.001)-as was LLMZ (-0.93 +/- 1.1; P <.001). Lower LLMZ was associated with lower BMD of the whole body (R-2 = 0.40; P <.001), lumbar spine (R-2 = 0.16; P =.005), total hip (R-2 = 0.32; P <.001), femoral neck (R-2 = 0.47; P <.001), and ultradistal radius (R-2 = 0.35; P <.001). Conclusions Patients with Fontan have marked deficits in both cortical (hip, distal one-third radius) and trabecular (lumbar spine, femoral neck, ultradistal radius) BMD. Lower LLMZ is associated with lower BMD and may reflect inadequate skeletal muscle loading. Interventions to increase muscle mass may improve bone accrual.

Automated summary

Patients with Fontan physiology exhibit significant deficits in both cortical (hip, distal one-third radius) and trabecular (lumbar spine, femoral neck, ultradistal radius) bone mineral density (BMD). Lower leg lean mass is associated with lower BMD and may indicate inadequate skeletal muscle loading. Interventions to increase muscle mass may improve bone accrual.