Variation in Lumbar Shape and Lordosis in a Large Asymptomatic Population

Abstract

Study Design. Prospective, cross-sectional cohort study. Objective. To determine the relationship between lumbar shape and sagittal parameters. Summary of Background Data. Understanding the lumbar shape is vital for deformity surgery. Normative sagittal parameters and spine shape remain unstudied in large, multiethnic, asymptomatic cohorts. Materials and Methods. A prospective, cross-sectional cohort of 468 asymptomatic volunteers between 18 and 80 years was enrolled across 5 countries. Demographic data and radiographic parameters such as pelvic incidence (PI) were collected. Pearson correlation test and linear regression were used to find the relationship between lumbar lordosis (LL) and other parameters. One-way analysis of variance and Welch 2-sample t test were performed to compare lumbar shape across such categories as PI and lumbar apex followed by post hoc Bonferroni correction if needed. Results. PI was moderately correlated with proximal lumbar lordosis (pLL) (r = −0.54) and weakly correlated with distal lumbar lordosis (dLL) (r = −0.16). Thoracic kyphosis (T1–T12) was moderately correlated with pLL (r = −0.35) and dLL (r = −0.29). dLL was moderately correlated with LL (r = 0.64). 2.6% (12/468) of subjects had lumbar apex at L2, 40.2% (188/468) at L3, 56.6% at L4 (265/468), and 0.6% (3/468) at other levels. Mean PI was different between volunteers with the apex at L3 and L4. A lower mean PI was associated with the apex at L4 (49.0°), whereas a higher mean PI was associated with the apex at L3 (55.8°). The mean PI−LL mismatch for volunteers was −5.4° with a range from −35° to 39.7°. PI−LL mismatch increased from a mean of −10.1° in volunteers with low PI to a mean of 2.2° in volunteers with high PI. Age was not correlated with LL (P = 0.84). Conclusions. In asymptomatic adult volunteers, pLL showed a moderate correlation with PI and increased with PI, whereas dLL showed a weak correlation. The lumbar apex migrated proximally with increasing PI. Segmental lordosis and apex position instead of solely global lordosis should be emphasized. Level of Evidence. Level III.