Double-level degenerative spondylolisthesis: what is different in the sagittal plane?

Degenerative spondylolisthesis (DS) is a common disease. The importance of sagittal malalignment in the DS population has been widely described. However, there is no study reporting sagittal alignment analysis in double-level DS. This study aims to analyze patients with double-level DS and compare them with single-level DS patients in terms of demographic and radiographic data.

Retrospective multicenter (n = 13) study. Adult patients with one (uni_DS) or two-level DS (multi_DS) were included. Sagittal radiographic parameters were measured by an experienced observer: pelvic, spinal and global parameters with C7 sagittal tilt (C7 tilt, angle between the center of C7 vertebral body and the middle of the sacral endplate with the vertical reference line). After a descriptive analysis, radiographic and demographic data were compared between single and multi_DS.

78 patients were included in multi_DS group and 576 in uni_DS group. Multi_DS were older than uni_DS (70.2 ± 9.4 vs 66.9 ± 10.6 years, p = 0.009). C7tilt was greater in multi_DS (6.2° ± 5.3 vs. 4.8° ± 3.8, p = 0.003). Multi_DS had a greater pelvic incidence (62.4° ± 11.3 vs. 58.3° ± 11.1, p = 0.002). Pelvic tilt was larger in multi-DS (26.0° ± 7.5 vs. 22.6° ± 8.1, p = 0.001). L4S1 lordosis represented 40.4 % of the LLmax in multi_DS and 45.8 % in uni_DS group (p = 0.013).

Multi_DS have different sagittal alignment than single DS with greater PI. In multi_DS, malalignment is more important with larger anterior tilt, loss of lumbosacral lordosis and more compensatory mechanisms such as pelvic retroversion. These findings highlight the need for an adapted surgical correction in these older patients with greater sagittal malalignment.