The "functional muscle-bone unit": a two-step diagnostic algorithm in pediatric bone disease

Bone densitometric data often are difficult to interpret in children and adolescents because of large inter- and intraindividual variations in bone size. Here we propose a functional approach to bone densitometry that addresses two questions. Is bone strength normally adapted to the largest physiological loads, i.e., muscle force? Is muscle force adequate for body size? Previously published reference data were used to evaluate results from children with preterminal chronic renal failure (n=11) and renal transplant recipients (n=15). In both groups mean height, muscle cross sectional area (MCSA), and bone mineral content (BMC) were low for age, but muscle MCSA was normal for height. In the renal transplant recipients the BMC/muscle MCSA ratio was decreased (P < 0.05), suggesting that bone cortical strength was not adapted adequately to muscle force. In contrast, chronic renal failure patients had a normal cortical BMC/muscle MCSA ratio, suggesting that their musculoskeletal system was adapted normally to their (decreased) body size.