Variation in lumbar regional kyphosis between supine and standing positions. Implications for spinal fracture management.

Purpose: The variation of lumbar lordosis between standing and supine position is poorly explored in literature. This study sought to analyze variation of lumbar regional angulations (RA) in healthy volunteers between standing and supine positions, according to pelvic incidence (PI).

Methods: This study included 171 patients who had an abdominal CT-scan in supine position and 879 healthy volunteers with full-body stereoradiographs. The two populations were matched using a propensity score including age, PI, and sex. PI and RAs for all vertebrae from T12 to L5 (measured between the overlying vertebra's upper endplate of and the underlying vertebra's lower endplate) were assessed. Studied parameters were compared between Supine and Standing groups in the whole cohort and in every PI group. Multivariate analysis was performed to ascertain the effect of position change.

Results: The analysis was performed on 314 subjects (157 matched in each group). In the overall cohort, all RAs from L1 to L4 were more lordotic in the Standing group, ranging from 3 to 8° difference (all p < 0.001), while T12 and L5 RAs were comparable in both groups (p = 0.55 and 0.49, respectively). Multivariate analysis confirmed the significant associations between subject's position and all RAs except for L5 and T12. RA variation between positions occurred at more vertebral levels and tended to be greater in higher PI groups.

Conclusion: RA values in the lumbar spine are more lordotic in standing position than supine, except for T12 and L5. These results help estimate RA in Standing position in patients with lumbar fractures.

Level of evidence: IV.