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.
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.
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 R2 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.
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