title: Morphological and postural sexual dimorphism of the lumbar spine facilitates greater lordosis in females.
abstract: Previous work suggests females are evolutionarily adapted to have greater lumbar lordosis than males to aid in pregnancy load-bearing, but no consensus exists. To explore further sex-differences in the lumbar spine, and to understand contradictions in the literature, we conducted a cross-sectional retrospective study of sex-differences in lumbar spine morphology and sacral orientation. In addition, our sample includes data for separate standing and supine samples of males and females to examine potential sex-differences in postural loading on lumbosacral morphology. We measured sagittal lumbosacral morphology on 200 radiographs. Measurements include: lumbar angle (L1-S1), lumbar vertebral body and disc wedging angles, sacral slope and pelvic incidence. Lumbar angle, representative of lordotic curvature between L1 and S1, was 7.3° greater in females than males, when standing. There were no significant sex-differences in lumbar angle when supine. This difference in standing lumbar angle can be explained by greater lordotic wedging of the lumbar vertebrae (L1-L5) in females. Additionally, sacral slope was greater in females than males, when standing. There were no significant sex-differences in pelvic incidence. Our results support that females have greater lumbar lordosis than males when standing, but not when supine - suggesting a potentially greater range of motion in the female spine. Furthermore, sex-differences in the lumbar spine appear to be supported by postural differences in sacral-orientation and morphological differences in the vertebral body wedging. A better understanding of sex-differences in lumbosacral morphology may explain sex-differences in spinal conditions, as well as promote necessary sex-specific treatments.
authors.affiliation: Anthropology and Orthopaedics & Sports Medicine, University of Washington, Seattle, WA, USA.|Orthopaedic Surgery, University of California, San Francisco, CA, USA.
authors.forename: Jeannie F
authors.initials: JF
authors.lastname: Bailey
authors.affiliation: Mechatronic Systems Engineering, Simon Fraser University, Surrey, British Columbia, Canada.
authors.forename: Carolyn J
authors.initials: CJ
authors.lastname: Sparrey
authors.affiliation: Anatomy & Anthropology, Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel.|Physical Therapy, Faculty of Health Professions, Ono Academic College, Kiryat Ono, Israel.
authors.forename: Ella
authors.initials: E
authors.lastname: Been
authors.affiliation: Anthropology and Orthopaedics & Sports Medicine, University of Washington, Seattle, WA, USA.
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Kramer
mesh_terms: D000293:Adolescent; D000328:Adult; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000033:anatomy & histology*; D008297:Male; D008875:Middle Aged; D004856:Postural Balance; D012189:Retrospective Studies; D012727:Sex Characteristics; D055815:Young Adult
keywords: lumbar lordosis; lumbosacral spine; sacral orientation; sex-differences; spinal curvature