Temperature Enhanced Extremity Lengthening Is Growth Rate Dependent

Limb length inequality is a potentially disabling condition with few noninvasive treatment options. Our lab has previously shown that unilateral heat increases bone elongation rate, suggesting that temperature therapy could be a non-surgical way to promote limb length equalization. Treatment age is important because we have shown that temperature effects occur primarily when growth is most rapid. We compared heat effects on limb lengthening during early (3-5 weeks age) and late (5-7 weeks age) phases of post-weaning growth in mice (N=24). We tested the hypothesis that heat-induced limb elongation varies with postnatal growth rate. Female mice (N=6 per age) were treated with 40C unilateral heat for 40 minutes per day for 14 days. Controls (N=6 per age) were not treated. Tibial elongation rate, measured by fluorochrome labeling, was over two-fold greater during the early phase. Bone elongation rate reflected overall body growth rate, with lower absolute heat-induced differences during the later phase. Relat...