Abstract
Lumbar lordosis (LL) is more prominent in women than in men, but the mechanisms responsible for this discrepancy are poorly defined. A recent study indicates that newborn girls have smaller vertebral cross-sectional area (CSA) when compared to boys—a difference that persists throughout life and is independent of body size. We determined the relations between vertebral cross-sectional area (CSA) and LL angle and whether sex differences in lumbar lordosis are related to sex differences in vertebral CSA. Using multi-planar magnetic resonance imaging (MRI), we measured vertebral cross-sectional area (CSA) and vertebral height of the spine of 40 healthy boys and 40 girls, ages 9–13 years. Measures of the CSA of the lumbar vertebrae significantly differed between sexes (9.38 ± 1.46 vs. 7.93 ± 0.69 in boys and girls, respectively; P < 0.0001), while the degree of LL was significantly greater in girls than in boys (23.7 ± 6.1 vs. 27.6 ± 8.0 in boys and girls, respectively; P = 0.02). When all subjects were analyzed together, values for LL angle were negatively correlated to vertebral CSA (r = -0.47; P < 0.0001); this was also true when boys and girls were analyzed separately. Multivariate regression analysis indicated that vertebral CSA was independently associated with LL, even after accounting for sex, age, height or vertebral height, and weight. Similar negative relations were present when thoracic vertebrae were analyzed (Model P < 0.0001, R2 = 0.37, thoracic vertebral CSA slope P < 0.0001), suggesting that deficient vertebral cross-sectional dimensions are not merely the consequence of the anterior lumbar curvature. We conclude that vertebral CSA is negatively associated with LL, and that the greater degree of LL in females could, at least in part, be due to smaller vertebral cross-sectional dimensions. Studies are needed to examine the potential relations between vertebral CSA and spinal conditions known to be associated with increased LL, such as spondylolysis and spondylolisthesis.
Highlights
Lumbar lordosis (LL) refers to the anterior curvature of the lumbar spine, expressed in humans as a response to upright posture and bipedalism
We examined the degree of LL and vertebral cross-sectional dimensions in 40 boys and 40 girls, ages 9–13 years, and hypothesized that 1) adolescent girls have a greater degree of lumbar lordosis than boys, 2) the degree of lumbar lordosis is predicted by vertebral cross-sectional area (CSA), and 3) differences in lumbar lordosis between boys and girls are related to sex differences in vertebral CSA
Measures of the CSA of the lumbar vertebrae significantly differed between sexes (Table 1); on average, vertebral CSA was 15.5% smaller in girls
Summary
Lumbar lordosis (LL) refers to the anterior curvature of the lumbar spine, expressed in humans as a response to upright posture and bipedalism. Pregnant women habitually extend their lumbar spine to counteract the shift in the center of mass associated with increases in abdominal size and weight by as much as 30% (~7 kg) [7,8,9,10]. The degree of lumbar lordosis in women is significantly associated with the number of pregnancies [8]. Since the smaller female vertebra is associated with greater range of spinal motion [17], it could facilitate the lordosis needed to maintain upright posture during pregnancy [12]
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