Bone Abstracts

Muscle size and function are closely correlated with skeletal development. Examining the relationship between muscle and bone is thus of central interest in clinical bone research. Surprisingly, however, there is little information on how to evaluate the functional muscle-bone relationship in clinical studies. Many past studies on muscle–bone interaction seem to have analyzed muscle and bone measures that were convenient to collect but did not evaluate a specific model of the muscle-bone relationship. Recently, Anliker et al. (Med Sci Sports Exerc 2011 43 2102–2109) have proposed a an approach to examine the relationship between bone and muscle function that is based on the mechanostat model. According to this model, bone strength adapts to the largest physiological forces to which it is exposed. The proposed approach relates tibia characteristics, as assessed by peripheral quantitative computed tomography to results of muscle performance tests on a force plate (‘mechanography’). Bone mineral content at the 14% site of the tibia (measured from the distal articular surface) is used as a surrogate parameter of bone strength, as this is the cross-sectional location where bone mineral content is at its minimum. As the largest physiological forces on bones result from eccentric muscle contraction, the approach uses peak force during forefoot hopping as a measure of muscle function (‘functional muscle-relationship’). In a study on 30 individuals with X-linked hypophosphatemic rickets (XLH), we found that muscle force was significantly lower in XLH patients than in age- and sex-matched controls. The XLH cohort had statistically significant higher bone mineral content, due to a larger bone cross-sectional area. Thus, patients with XLH had increased bone mass and size at the distal tibia despite muscle function deficits. Viewed from the perspective of the mechanostat model, these results suggest that the bones of individuals with XLH are more sensitive to mechanical forces than those of healthy controls.

Funding: Research was funded by Novartis and Alexion.