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

Abstract

ObjectiveIn 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 methodsA 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. ResultsThe 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. ConclusionsA 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.