【Introduction】Degenerative changes in the lumbar spine increase with aging. To date, many radiological parameters have been published that indicate the progression of adult spinal deformity. However, the relationship between radiological parameters and symptoms has yet been unclear. The purpose of this study is to investigate the relationship between L1 axis sacral distance (LASD) and sacral slope angle (SS), which are indices on lumbar spine X-ray lateral views, and low back pain (LBP).

 【Methods】This was a cross-sectional study, using a database of community health check-ups conducted in rural areas of Fukushima Prefecture in 2004 (Minami-Aizu Study). The participants were 514 residents (170 males and 344 females, mean age were 65.1 years) who were evaluated for the presence of LBP and underwent X-ray photography of the lumbar spine on the standing lateral view. We defined LBP as "LBP lasting more than 24 hours" and included acute and chronic pain. Patients after lumbar fusion surgery were excluded. LASD (horizontal distance between the vertical line from the center of the L1 vertebra and the superior posterior angle of the sacrum) and SS were measured from the radiographs, and each index was categorized into three groups: low, middle, and high. Several candidate cutoff values were created for each group, and the set that maximized the F value by one-way analysis of variance with the presence of LBP as a factor was adopted. In addition, logistic regression analysis was conducted to analyze the relationship with LBP. The presence of LBP was the dependent variable; gender, age, and BMI were adjusted variables; and LASD and SS were independent variables. A p-value of less than 5% was used as statistical significance in this study.

 【Results】One-way analysis of variance showed that LASD had the largest F values at cutoffs of less than 20 mm, 20-30 mm, and greater than 30 mm, and SS had the largest F values at cutoffs of less than 30°, 30-40°, and greater than 40°. Logistic regression analysis showed that the odds ratio of having LBP was significantly higher in the low and high groups compared to the LASD middle group (low group: odds ratio 3.71, 95% CI 1.11-12.4, p=0.033; high group: odds ratio 8.12, 95% CI 2.01-33.2, p=0.003). In SS, the odds ratio of having LBP was significantly higher in the low group than in the high group; no significant difference was observed in the middle group (low group: odds ratio 4.68, 95% CI 1.46-15.0, p=0.009; middle group: odds ratio 2.69, 95% CI 0.87-8.30, p=0.085).

 【Discussion】This study revealed that LASD and SS were associated with LBP, and the odds ratio for the presence of LBP was lowest when LASD was 20-30 mm, and SS was greater than 40°. Numerous reports have shown that sagittal imbalance of the spine is involved in LBP, and LASD also could be one of the indices in radiographic lumbar lateral views.