Impact of sagittal imbalance correction on clinical outcomes in patients undergoing MIS-TLIF for LSS.

Objective: In the present study, we aimed to evaluate the effect of sagittal imbalance correction on clinical outcomes in patients undergoing single-segment minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) for lumbar spinal stenosis (LSS). Patients and

Methods: A total of 114 LSS patients with a minimum 2-year follow-up were included. Preoperative and final follow-up sagittal parameters were determined. Sagittal imbalance was defined as a sagittal vertical axis (SVA) ≥40 mm. Patients were divided into balanced group (group A: preoperative SVA <40 mm) and imbalanced group (group B: preoperative SVA ≥40 mm), and group B was further divided into recovered group (postoperative SVA <40 mm) and unrecovered group (postoperative SVA ≥40 mm). Visual analog scale (VAS) score, Japanese Orthopaedic Association (JOA) score and Oswestry Disability Index (ODI) were used to assess clinical outcomes.

Results: The incidence of preoperative sagittal imbalance in LSS patients was 36.0% (41/114). A large mismatch between pelvic incidence and lumbar lordosis (PI-LL) was a risk factor for sagittal imbalance. After 2-year follow-up, sagittal imbalance was normalized in 65.9% of patients. Single- segment MIS-TLIF led to a significant decrease in SVA, pelvic tilt (PT) and PI-LL, as well as a significant increase in LL, thoracic kyphosis (TK) and sacral slope (SS) in both group A and group B. Preoperatively, the VAS, JOA and ODI scores were significantly poorer in patients with sagittal imbalance compared with those without sagittal imbalance. After MIS-TLIF, all clinical outcomes improved significantly. However, there was no significant difference in postoperative VAS, JOA and ODI scores between the group A and group B. In addition, there was no significant difference in postoperative VAS, JOA, and ODI scores between the recovered group and unrecovered group.

Conclusions: A significant proportion of LSS patients with preoperative sagittal malalignment had a compensatory mechanism rather than a structural malalignment, while single-segment MIS-TLIF could effectively improve sagittal imbalance at 2-year follow-up. However, we found no correlation between the improvements of sagittal imbalance and 2- year clinical outcomes. Reconstruction of sagittal balance might not be the main goal of single-segment MIS-TLIF for LSS, and did not affect its clinical results at two-year follow-up.