Muscle cross-sectional area is associated with specific site of bone in prepubertal girls: A quantitative magnetic resonance imaging study

It is well established that forces applied to bone are the result of muscle contraction. However, data regarding the contribution of muscle cross-sect ional area (because muscle area is proportional to muscle strength) to cort ical bone area before puberty are controversial. We tested the hypothesis t hat muscle cross-sectional area is associated with total cortical bone area , and whether there is a region-specific relationship between these paramet ers in prepubertal and early pubertal girls. Seventeen healthy (9-11 years, Tanner stages I-II) white girls participated in the study. We measured bon e loading characteristics (maximal ground reaction forces; GRFs) for a drop jump (50 cm) and side-to-side jump (over a 20-cm-high fence) on a multicom ponent force platform. Muscle cross-sectional area and bone cortical area ( square centimeters) of the proximal third of the left and right lower leg w as measured with a 1.5 T magnetic resonance system using a quadrature head coil. The sequence was T, weighted, with spin-echo in transverse (tibial) p lanes and 3 mm sections with no gap (ten slices). The tibial cross-sectiona l areas were subdivided into three anatomical sectors (SI-SIII), with the t ibial centroid as origin. SI extended from the medial tibial border to the most anterior edge, SII extended from the anterior edge laterally to the in terosseous border, and SIII extended posteromedially from the interosseous border to the medial tibial border. The nonparametric bone and muscle volum e correlations demonstrated that the total muscle cross-sectional area corr elated significantly with the total cortical area in both legs (left leg: r (s) = 0.59, p = 0.020;, right leg: r(s) = 0.57, p = 0.016). Significant cor relations were also found between left and right muscle area and cortical a rea in SII (r(s) = 0.68, p = 0.003, 0.67, and 0.003, respectively). There w as no significant association between the muscle area and cortical area in SI or SIII In addition, there was a significant correlation between GRFs of the side-to-side jump and total cortical area (left leg: r = 0.75, p < 0.0 1; right leg: r = 0.78, p < 0.01). Thus, we found that muscle area was most highly associated with bone cortical area in SII, the anterolateral sector of the tibia, which emphasizes the specific interplay of muscles and bone in the lower limb. This relationship was present in a regional, site-specif ic fashion. (Bone 29:388-392;2001) (C) 2001 by Elsevier Science Inc. All ri ghts reserved.