Factors influencing segmental lumbar lordosis after lateral transpsoas interbody fusion

Although contributions to sagittal alignment have been characterized for anterior, posterior and transforaminal lumbar interbody fusion, sagittal alignment after lateral transpsoas interbody fusion (LTIF) has not yet been characterized. This study examined the ability of LTIF to restore lumbar lordosis and identified factors associated with change in sagittal alignment.

Twenty-nine patients and 67 levels were studied. Segmental lordosis, anterior-posterior cage position, and cage obliquity were measured on preoperative and postoperative radiographs and CT scans. Change in sagittal alignment was analyzed with respect to demographic information and measures of cage position and obliquity to identify factors associated with segmental alignment change.

Mean lordosis increased 3.7° at instrumented segments, increasing from 4.1° preoperatively to 7.8° postoperatively. Although increases at each level were significant, there were no significant differences between levels. Lordosis increase was inversely-associated with preoperative lordosis; levels with the least preoperative lordosis gained the most lordosis. Cage obliquity and height were not significantly associated with lordosis change. Anterior cage placement resulted in the largest lordosis gain (+7.4°/level) while posterior placement was prokyphotic (-1.2°/level). There were no significant associations with age, sex or body mass index.

Anteroposterior cage placement is an important intraoperative determinant of postoperative alignment; anterior placement results in greater lordosis while middle/posterior placement has a minimal effect on sagittal alignment.