Differences in lumbar segment angle among Roussouly types of global sagittal alignment in asymptomatic adult subjects

Abstract

STUDY DESIGN: A radiological study. OBJECTIVES: To examine lumbar segment angle according to the Roussouly type of global sagittal alignment and to determine the reference disc angles in minimally invasive surgery (MIS) for adult spinal deformity. Optimal restoration of lumbar lordosis (LL) in adult spinal deformity surgery includes achieving the ideal shape of LL as well as the amount of LL. However, the distribution of lumbar segment angles by the Roussouly type has yet to be elucidated. METHODS: Forty sets of whole spine lateral radiographs covering the four Roussouly types (N = 160) were obtained from a database of asymptomatic adult subjects. Global and spinopelvic parameters were measured. Disc and vertebral angles at each lumbar level were compared among the Roussouly types. RESULTS: There were 75 (46.9%) men with a mean age of 32.8 +/- 8.9 years among the total of 160 study subjects. A significant difference was found in spino-sacral angle, sacral slope, pelvic incidence, LL, and lower arc of LL (L4S1) among the Roussouly types (all P < 0.001). The ratio of the lower arc of LL (L4S1) to LL was 83.4% in Roussouly type 1, 65.2% in type 2, 64.7% in type 3, and 61.5% in type 4. The disc angles at the L1-2 and L2-3 levels in Roussouly type 1 were significantly smaller than in the other types. The disc angle at the L5-S1 level in Roussouly type 1 was significantly larger than that in type 2. Roussouly type 4 had a larger disc angle at the L2-3 and L4-5 levels than types 1 and 2. CONCLUSIONS: The results of this study showed that the disc angle distribution differs among Roussouly types. The configuration of LL as well as the amount of LL should be considered in adult spinal deformity surgery. LEVEL OF EVIDENCE: Level IV.