Introduction: We established the Obuse Study, involving a cohort of local residents, to clarify the degree and frequency of age-related changes in the musculoskeletal system. The objective of this study was to investigate the sagittal alignment of the spinal column to clarify: 1) the characteristics of spinal column alignment by sex and age group; 2) the relationship between sagittal alignment and motor function; and 3) the frequency of low back pain and factors related to low back pain.

Methods: Invitations for examinations were sent to 1,297 randomly selected residents of Obuse, Nagano Prefecture, who were randomly selected from 5,352 residents aged 50-89 years listed in the resident registry. A total of 413 people (approximately 50 men and 50 women per age group) underwent examinations of motor function and standing full-spine lateral radiographs. Spinal sagittal parameters were measured. Their characteristics were analyzed by age and sex, and the relationship between spinal sagittal alignment and motor function (knee extension-flexion muscle strength, time to stand on one leg, grip strength, and locomotion test) and their relationships with low back pain were examined.

Results: Changes in spinal sagittal alignment were more pronounced in men, with an anterior shift of the cervical spine occurring at age 60 years and older. In women, decreased lumbar lordosis and pelvic retroversion occurred at younger ages than in men. The worse the sagittal alignment of the spine, the lower the performance in grip strength, stand-up, and two-step tests. Low back pain was present in 12.9% of the participants, and pelvic incidence-lumbar lordosis (PI-LL) mismatch (>10 degrees) was an independent and significant factor associated with low back pain.

Conclusions: A cross-sectional study of sagittal spinal alignment in a community-dwelling population showed that changes in sagittal spinal alignment tended to differ between men and women. There was a clear association between sagittal spinal alignment and physical function. The approach to sagittal spinal alignment may be an important disease control measure not only for low back pain in elderly persons, but also for motor function decline.