What is the factor for segmental lordosis angle after transforaminal interbody fusion at L4-L5?

<p>Introduction: Segmental lordosis is an important radiographic parameter as sagittal alignment has been correlated to clinical outcomes. However, there are few reports on the relationship between segmental lordosis angle (SLA) and global spinal alignment (GSA) after short segment lumbar fusion. This study retrospectively examined the relationship between SLA and GSA after L4/5 transforaminal lumbar interbody fusion (TLIF).</p><p>Methods: The subjects were 91 patients who underwent consecutive mini-open L4/5 TLIF at our hospital between 2014 and 2020 with a minimum one-year follow-up. Subjects consisted of 48 men and 43 women with a mean age of 69.4±9.8 years. Patient factors (age, sex, BMI), cage factors (position, cage subsidence), radiographic parameters (LL, PI-LL, PT, SVA, and TPA), and SLA of L4/5 were investigated. In addition, the SLA change was compared between two groups. The group with increased SLA at 1 year postoperatively was defined as the SLA (+) group and the group with decreased SLA postoperatively as the SLA (−) group., The independent factor of SLA (+) was identified by logistic regression analysis.</p><p>Results: The SLA increased significantly from 14.6 degrees before surgery to 16.9 degrees after surgery (P<0.001). SLA, LL, PI-LL, PT, SVA, and TPA also improved significantly after TLIF. There were 73 patients in the SLA (+) group and 18 patients in the SLA (−) group. There were no significant differences in SLA between the two groups with regard to patient background factors. However, there were significant differences in preoperative LL and SLA. Patients in the SLA (+) group had significantly lower preoperative SLA (13.7° vs. 18.4°, P=0.001) than the SLA (−) group, and there was a negative correlation between SLA change and preoperative SLA (r=−0.439). The cage subsidence was significantly lower (72% vs. 38%, P=0.010), and the cage was placed significantly more anteriorly in the SLA (+) group. However, there was no significant difference in the cage lordosis angle. There was no significant difference in GSA at 1 year postoperatively between the two groups, but there were significantly more cases of PI-LL mismatch in the SLA (−) group (50% vs. 24%, P=0.030). Logistic regression analysis showed that preoperative SLA (odds ratio 1.15, 95% confidence interval 0.02-0.19, P=0.024) and cage subsidence (odds ratio 6.69, 95% confidence interval −1.72-−0.18, P=0.009) were independent factors for SLA (+). The cutoff value via ROC analysis for preoperative SLA was 15.3°.</p><p>Conclusions: Postoperative SLA increased in patients with low preoperative LL and SLA. Preoperative SLA and cage subsidence were independent factors for increased SLA. SLA change had no effect on GSA at 1 year postoperatively, however, there was less PI-LL mismatch in the SLA (+) group. Preoperative SLA and cage subsidence of L4/5 should be kept in mind for long-term outcomes.</p>