The development of bone mineral lateralization in the arms

Abstract

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 sidedness 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 address this, we examined bone mineral status in relation to handedness and age.

Methods: Subjects (N = 158) 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 (r = 0.294, p = 0.0005). Breakpoint 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 ratio = 0.029 × age [in years] + 0.850 (r = 0.323, p = 0.017). The slope of the second line was not different from 0 (p = 0.332), while the slopes for the two lines were significantly different (p = 0.027).

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.

Fig. 1

Ratios of dominant to nondominant limb mineral for subjects with left or right hand dominance. (A) Arm BMC ratio. (B) Arm BMD ratio. (C) Leg BMC ratio. (D) Leg BMD ratio. The slopes were significant for arm BMC (r = 0.294; p = 0.0005) and leg BMD (r = 0.193; p = 0.024)

Fig. 2

Residual graphs for dominant to nondominant arm BMC ratios for subjects with left or right hand dominance. (A) Unstandardized residuals vs. age. (B) Studentized residuals vs. age. Plots show funnel patterns with more spread at lower ages

Fig. 3

Knot (breakpoint) analysis of dominant to nondominant arm BMC ratios revealed two lines with a knot at 6.0 years (95% CI, 4.5–7.5 years). The slope for the first line was 0.029/year (95% CI, 0.005 to 0.052; r = 0.323; p = 0.017). The slope for the second line was not different from 0 (95% CI, −0.002 to 0.007; r = 0.108; p = 0.332). The slopes for the two lines were significantly different (p = 0.027). Solid circles are children with leukemia, open circles are children with rheumatic conditions, and solid triangles are children with nephrotic syndrome

Fig. 4

Right to left arm BMC ratios for left-handed (n = 9), mixed-handed (n = 11), and right-handed (n = 74) children over age 6.0 years of age. The ratio for left handers differed from that of right handers (p = 0.036) while the ratios for mixed-handers did not differ from left-handers (p = 0.152) or right-handers (p = 0.565) a p = 0.036 compared to right handed subjects