Lordosis distribution index in an asymptomatic elderly population: the role of lower and upper lumbar lordosis according to individual pelvic incidence and Roussouly type

OBJECTIVE The roles of upper and lower lumbar lordosis (ULL and LLL) in relation to individual pelvic incidence (PI) and Roussouly type have yet to be established. This study aimed to determine the optimal ULL and LLL based on individual pelvic and spinal morphology within a normal asymptomatic elderly population. METHODS Whole spine standing radiographs were obtained from asymptomatic elderly volunteers who had not undergone previous spinal surgery. The following parameters were measured: lumbar lordosis (LL) from the T12 lower endplate (LEP) to the S1 upper endplate (UEP), ULL from the T12 LEP to the L4 UEP, and LLL from the L4 UEP to the S1 UEP. PI and the lordosis distribution index for the upper and lower lumbar spine (ULDI and LDI, respectively) were calculated. Pearson correlation and linear regression analyses were performed, and the mean value for each parameter was obtained according to PI subgroup (PI < 40°, 40° ≤ PI < 50°, 50° ≤ PI < 60°, and 60° ≤ PI) and “theoretical” Roussouly type. RESULTS Overall, 150 male volunteers were enrolled in the study, with an average age of 64.1 ± 6.4 years. The mean height was 167.0 ± 5.5 cm, weight was 67.3 ± 9.8 kg, and body mass index was 24.1 ± 3.1 kg/m ² . The average LL was −57.5° ± 9.0°, LLL was −39.7° ± 6.8°, and PI was 48.6° ± 8.6°. PT tended to increase with ULL, PI-LL, PI-ULL, PI-LLL, and ULDI and decrease with LLL and LDI. However, PT was not significantly related to LL. The mean ULDI and LDI were 30.4% ± 11.7% and 69.7% ± 11.7%, respectively. The differences between PI and LL (PI-LL) and between PI and LLL (PI-LLL) were −8.9° ± 8.0° and 9.0° ± 9.3°, respectively. As PI increased from low (<40°) to high (≥60°), ULDI increased significantly from _{25.9% to 38.9%, while LDI decreased from 74.1% to 61.1%. Additionally, LDI varied by Roussouly type, ranging from 62.6% to 81.0%. The LDIs of Roussouly types 1 and 4 were significantly higher and lower, respectively, than those of types 2 and 3 (p < 0.001). CONCLUSIONS As PI and Roussouly type increase, the contribution of ULL to overall LL rises, reaching up to 38.9%. Conversely, LLL substantially impacts LL in patients with a low PI and those classified as Roussouly type 1. PT is significantly related to LLL instead of LL according to PI. When planning surgical correction, the optimal ULL and LLL should be tailored to the patient’s PI and Roussouly type.}