ALTERED LOADING PATTERNS AND FEMORAL BONE-MINERAL DENSITY IN CHILDRENWITH UNILATERAL LEGG-CALVE-PERTHES-DISEASE

Maximization of bone accrual during the growing years is thought to be an important factor in minimizing fracture risk in old age. Mechanica l loading through physical activity has been recommended as a modality for the conservation of bone mineral in adults; however, few studies have evaluated the impact of different loading regimes in growing chil dren. The purpose of this study was to compare bone mineral density (B MD) in weight-bearing and non-weight-bearing limbs in 17 children with unilateral Legg Calve Perthes Disease (LCPD). Children with this cond ition have an altered weight-bearing pattern whereby there is increase d mechanical loading on the noninvolved normal hip and reduced loading on the involved painful hip. Thus, these children provide a unique op portunity to study the impact of differential mechanical loading on BM D during the growing years while controlling for genetic disposition. BMD at four regions of the proximal femur (trochanter, intertrochanter , femoral neck, total of the regions) was measured using dual energy x -ray absorptiometry (DXA), and the values were compared between the in volved and noninvolved sides of the children with LCPD. The BMD of bot h sides also were compared with normative values based on both chronol ogical and skeletal age data. A significantly higher BMD was found on the noninvolved side over the involved side for all regions (P <0.01 a nd percentage differences of 12-15%) except at the femoral neck (perce ntage difference of 3.9%). The BMD (at all regions) of the noninvolved side also was significantly greater (P<0.01) than either the chronolo gical or skeletal age based norms for all sites except the trochanter. The results support the concept that mechanical loading of the skelet on during the growing years is an important factor in BMD accrual.