Spinal Alignment in Asymptomatic Adults With Negative Sagittal Balance

Cross-sectional radiologic study.

We aimed to examine spinal alignment in asymptomatic adults with negative sagittal balance and determine the limit of negative physiological balance.

Although many studies have examined positive sagittal imbalance over the physiological cone, little is known about negative sagittal imbalance in the backward direction.

A total of 106 young asymptomatic adults with a sagittal vertical axis (SVA) of ≤-3 cm were obtained from our database. Global sagittal parameters, including SVA, T1 pelvic angle (T1PA), global tilt (GT), odontoid-hip axis (OD-HA) angle, and center of acoustic meatus-hip axis (CAM-HA) distance, were measured. The sacral segment where each SVA was dropped was examined as S1, S2, S3, S4, or outside the sacrum. Spinal alignment in negative balance was analyzed using the Roussouly type and pelvic incidence (PI) values.

The study participants comprised 51 males and 55 females, with a mean age of 33.0±9.9 years. The mean SVA was -4.3±1.1 cm, T1PA was 2.8±5.1 degrees, GT was 4.2±6.7 degrees, OD-HA was -5.8±1.6 degrees, CAM-HA was -8.0±2.2 cm, PI was 44.9±8.1 degrees, and pelvic tilt was 10.4±5.3 degrees. The sacral segment level where the SVA landed was S2 in 57 participants (53.8%), S3 in 34 (32.1%), and S4 in 13 (12.3%). No predominant pattern was observed in terms of Roussouly types or PI values.

A negative balance is not uncommon in young asymptomatic adult populations. Anterior pelvic rotation may occur to compensate for negative balance. The physiological limit of a posteriorly displaced C7 SVA does not extend beyond the sacrum.