DXA evaluating different modifications of the femoral neck related to age: densitometric, geometric and redistribution of bone mass

Abstract

Thickness of the femoral neck (FN) in adult women is not even all around its perimeter. The upper thickness is smaller than the lower one. Some studies have shown that such difference is already seen in young adults and increases with aging. The purpose of this study was to evaluate the capacity of DXA in capturing some of these modifications of the FN shown by sophisticated 3D methodologies. Methods: we designed an observational and transversal study including 224 women (34-88 years). Bone mineral density (BMD), bone mineral content (BMC), femoral neck area (A) and BMC of upper (BMCu) and lower neck (BMCl ) were assessed by Dual X-ray Absorptiometry (DXA, Lunar Prodigy) in every women. The relation upper/lower BMC was expressed as an index BMCu/l. Results: BMCu/l was <1 in all patients. BMC of femoral neck was reduced asymmetrically along life. BMCu was 17% smaller in the group belonging to the oldest quartile of age comparing to the youngest, meanwhile such difference was only 8% in the BMCl. Consequently the BMCu/l was reduced with aging. Weight correlated positively with BMC of the lower and upper neck but with different slopes (regression coefficient 0.015 and 0.006, respectively), showing an inverse correlation between weight and BMCu/l index. Weight and A and consequently FN width correlated positively, and so did A, with BMCl and BMCu individually, but similarly to weight with different slopes (0.48 and 0.21, respectively), also showing an inverse correlation between A and BMCu/l index. Age, BMC, area and weight resulted independent predictors of BMCu/l in multivariate analysis: R2 adjusted = 0.35; p<0.001. Conclusions: BMC of femoral neck is reduced during aging, bone loss being higher in the upper portion of the FN. Weight mitigates bone loss of the femoral neck probably by an anticatabolic effect, and stimulating subperiostic apposition. This effect is more pronounced in the lower femoral neck. These findings, evaluated by DXA, are similar to those using other sophisticated methodologies.