Study design:

Retrospective study.

Objective:

To elucidate factors that determine segmental lordosis after lateral retroperitoneal lumbar interbody fusion (LLIF) with percutaneous pedicle screw fixation.

Summary of background data:

LLIF has been widely used in degenerative lumbar spine surgery. However, the detailed mechanisms that determine segmental lordosis are still unknown.

Methods:

A total of 69 patients who underwent LLIF with posterior pedicle screw fixation without posterior osteotomy were analyzed. Computed tomography was performed before and within 2 weeks after surgery, and segmental lordotic angle (SLA) after surgery (Post-SLA) was predicted using multiple regression analysis. Explanatory factors considered in this study included SLA before surgery (Pre-SLA), disc height before surgery (DiscH), cage position (CageP; distance between the center of the cage and the center of the disc, where a positive value indicates an anterior cage position), cage angle (CageA), cage height (CageH), CageH-DiscH (amount of lift up), previous decompression surgery, and level fused.

Results:

A total of 102 levels were analyzed. Multiple regression analysis revealed that the Post-SLA can be predicted with three independent variables, CageP, Pre-SLA, and CageH-DiscH and the adjusted R was 0.70. In cases when the cage was located anteriorly (CageP > 3 mm), Post-SLA was greater with larger CageH, larger CageA, and larger Pre-SLA. When the cage was located in the middle (3 mm ≤CageP ≤-1 mm), Post-SLA was greater with larger CageP, larger Pre-SLA, and without previous decompression surgery. If the cage was located posteriorly (CageP < -1 mm), Post-SLA was greater with smaller CageH-DiscH and greater Pre-SLA.

Conclusion:

To gain maximum segmental lordosis in LLIF, the cage should be located anteriorly. Furthermore, if the cage can be located anteriorly, a thicker cage with proper angle cage will gain segmental lordosis. If the cage is located posteriorly, a thin cage should be selected.

Level of evidence:

3.