Deficits in the Functional Muscle-Bone Unit in Youth With Fontan Physiology.

Abstract

OBJECTIVE\nTo 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. We aimed to describe DXA-derived BMD at multiple sites and investigate the relationship between BMD and leg lean mass, a surrogate for skeletal muscle loading.\n\n\nSTUDY DESIGN\nFontan participants (n= 46; 5-20y) underwent DXA in a cross-sectional study of growth, bone and muscle health as previously described. 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 1/3 radius, ultradistal radius and leg lean mass Z-scores (LLMZ).\n\n\nRESULTS\nFontan BMD Z-scores were significantly lower than reference at all sites: whole body: -0.34±0.85, p=0.01, spine: -0.41±0.96, p=0.008, hip: -0.75±1.1, p<0.001, femoral neck: -0.73±1.0, P < .001, distal 1/3 radius: -0.87±1.1, p<0.001, ultradistal radius: -0.92±1.03, p<0.001, as was LLMZ: -0.93 ± 1.1, p<0.001. Lower LLMZ was associated with lower BMD of the whole body (R2 = 0.40, p<0.001), lumbar spine (R2 = 0.16, p=0.005), total hip (R2 = 0.32, p<0.001), femoral neck (R2 = 0.47, p<0.001), and ultradistal radius (R2 = 0.35, p <0.001).\n\n\nCONCLUSIONS\nFontan patients have marked deficits in both cortical (hip, distal 1/3 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.