The effects of body mass index and age on cross‐sectional properties of the femoral neck

Abstract

Research on the relationship between body mass index (BMI) and cross-sectional geometry of long bone diaphyses demonstrates that strength properties are significantly greater in obese versus normal BMI individuals. However, articular dimensions do not differ appreciably. If femoral head size remains constant, we hypothesize that the femoral neck remodels to accommodate greater loads associated with increased BMI. High-resolution CT scans (n = 170 males) were divided into three BMI groups (normal, overweight, and obese) and two age groups (21-50 and >50). OsiriX software was used to obtain a cross-sectional slice at the waist of the femoral neck. Cortical area (CA), total cross-sectional area (TA), percent cortical area (%CA), circularity index (Imax /Imin ), section modulus (Zpol ), and second moment of area (J) were measured with ImageJ software. The effects of age and BMI were evaluated statistically. Pairwise comparisons in the younger group only detected significant differences between normal and obese males in the circularity index (P = 0.022). The older cohort showed significant differences in CA (P < 0.001), %CA (P = 0.004), Zpol (P = 0.007), and J (P < 0.001) between normal and obese groups. This study shows that the effects of obesity on the cross-sectional geometry of the femoral neck are more pronounced in older males relative to younger males. Older males with increased BMI have greater cortical area and bone strength in the femoral neck relative to younger males, thus making the femoral neck less susceptible to fractures in obese individuals.

Radiographic anatomy of the proximal femur: femoral neck fracture vs. transtrochanteric fracture

“…Wheeler et al, 8 in their study of the cross-sectional geometry of long bone diaphyses that correlated BMD, BMI, and age, demonstrated that bone strength is significantly higher in obese individuals when compared with those with normal BMI. However, the joint dimensions do not differ appreciably; older individuals with a higher BMI are less likely to develop a fracture than younger individuals with normal BMI.…”

“…The specialized literature emphasizes that bone mineral density (BMD), an age-related predictor of fracture, is not always consistent: individuals with very low femoral neck BMD may not present fracture, while those with normal BMD might. 8 There may be other relevant variables that determine fractures and especially their types, such as bone anatomy. 8 , 9 …”

“… 8 There may be other relevant variables that determine fractures and especially their types, such as bone anatomy. 8 , 9 …”

Influence of varying stem and metaphyseal sleeve size on the primary stability of cementless revision tibial trays used to reconstruct AORI IIA defects. A simulation study

“…However this study did not consider the effect of obese BMI on bone cross sectional area (CSA), geometry, and material properties. Recent studies have shown that BMI and age can have a direct effect on bone CSA, geometry, and material properties …”

Do people with overweight have bigger bones? Body mass index (BMI) and the size of the femoral head

“…On the one hand, obese people have chronic inflammation that predisposes bone osteolysis, which leads to the development of osteoporosis [10]. On the other hand, increased body mass, and hence greater load on the hip joint may have a positive effect on the femoral neck [12]. Our study did not check the effect of body mass on bone density and structure, only on its thickness.…”