Are There Age- and Sex-related Differences in Spinal Sagittal Alignment and Balance Among Taiwanese Asymptomatic Adults?

BACKGROUND: Sagittal spinopelvic balance and proper sagittal alignment are important when planning corrective or reconstructive spinal surgery. Prior research suggests that people from different races and countries have moderate divergence; to the best of our knowledge, the population of Taiwan has not been studied with respect to this parameter. QUESTIONS/PURPOSES: To investigate normal age- and sex-related differences in whole-spine sagittal alignment and balance of asymptomatic adults without spinal disorders. METHODS: In this prospective study, we used convenience sampling to recruit asymptomatic volunteers who accompanied patients in the outpatient orthopaedic department. One hundred forty males with a mean age of 48 ± 19 years and 252 females with a mean age of 53 ± 17 years underwent standing lateral radiographs of the whole spine. For analysis, participants were divided in three groups by age (20 to 40 years, 41 to 60 years, and 61 to 80 years) and analyzed by sex (male and female). The following eight radiologic parameters were measured: sacral slope, pelvic tilt, pelvic incidence, thoracic kyphosis, lumbar lordosis, cervical lordosis, C2-C7 sagittal vertical axis, and C7-S1 sagittal vertical axis. Three observers performed estimations of the sagittal parameters twice, and the intraclass correlation coefficients for inter- and intraobserver variability were 0.81 and 0.83. RESULTS: The mean pelvic incidence was 49° ± 12°; lumbar lordosis was smaller in the group that was 61 to 80 years old than in the groups that were 20 to 40 years and 41 to 60 years (95% CI of the difference, 4.50–13.64 and 1.00– 9.60; p < 0.001), while cervical lordosis was greater in the 61 to 80 years age group than the other two groups (95% CI of the difference, -14.64 to -6.57 and -11.57 to -3.45; p < 0.001). The mean C7-S1 sagittal vertical axis was 30 ± 29 mm, and there was no difference among the three groups and between males and females. Pelvic tilt was greater in the group 61 to 80 years old than the 20 to 40 years and 41 to 60 years age groups (95% CI of the difference, -10.81 to -5.42 and -7.15 to -2.08; p < 0.001), while sacral slope was larger in 61 to 80 years age group than in the 41 to 60 years group (95% CI of the difference, 0.79–6.25; p = 0.006). C7 slope was greater in 61 to 80 years age group than in the 20 to 40 years group (95% CI of the difference, -7.49 to -1.26; p = 0.002) and larger in 41 to 60 years age group than in 20 to 40 years group (95% CI of the difference, -6.31 to -0.05; p = 0.045). C2-C7 sagittal vertical axis was greater in males than in females (95% CI of the difference, 2.84–7.74; p < 0.001). C7 slope was negatively correlated with thoracic kyphosis (95% CI of the difference, -0.619 to 0.468; p < 0.001) and lumbar lordosis (95% CI of the difference, -0.356 to -0.223; p < 0.001), and positively correlated with pelvic incidence (95% CI of the difference, 0.058– 0.215; p < 0.001) and cervical lordosis (95% CI of the difference, 0.228 – 0.334; p < 0.001). CONCLUSIONS: Normal values of the spinopelvic sagittal parameters vary by age and sex in Taiwanese individuals. CLINICAL RELEVANCE: Pelvic incidence and sacral slope observed in this population seemed smaller than those reported in other studies of white populations; this seems important when considering spine surgery in Taiwanese patients. Future studies should include collection of whole body sagittal parameters of larger and more-diverse populations, and assessments of patients with symptomatic spinal disorders.