The development of bone mineral lateralization in the arms

Summary Bone mineral content (BMC) is known to be greater in the dominant arm after the age of 8 years. We studied a group of children and found that BMC sidedness gradually increased up to the age of 6 years and then remained stable into late adolescence. Introduction Bone mineral content (BMC) exhibits sided- ness in the arms after the age of 8 years, but it is not known whether BMC is greater in the dominant arm from birth or whether lateralization develops in early childhood. To ad- dress this, we examined bone mineral status in relation to handedness and age. Methods Subjects (N0158) were children recently initiating glucocorticoids for underlying disease (leukemia 43 %, rheumatic conditions 39 %, nephrotic syndrome 18 %). Handedness was determined by questionnaire and BMC by dual-energy X-ray absorptiometry. Results Median age was 7.2 years (range, 1.5 to 17.0 years), 49 % was male, and the spine BMD Z-score was −0.9 (SD, 1.3). By linear regression, BMC sidedness in the arms was significantly related to age (r00.294, p00.0005). Break- point analysis revealed two lines with a knot at 6.0 years (95 % CI, 4.5-7.5 years). The formula for the first line was: dominant:nondominant arm BMC ratio00.029×age (in years)+0.850 (r00.323, p00.017). The slope of the second line was not different from 0 (p00.332), while the slopes for the two lines were significantly different (p00.027). Conclusions These results show that arm BMC sidedness in this patient group develops up to age 6 years and then remains stable into late adolescence. This temporal profile is consistent with mechanical stimulation of the skeleton in response to asymmetrical muscle use as handedness becomes manifest.