Risk factors for insufficient segmental lordosis at the fused level following posterior lumbar interbody fusion: Effect of change in segmental lordosis in the intraoperative prone position.

Background A decrease in segmental lordosis (SL) at the fused level (ΔSL < 0) following posterior lumbar interbody fusion (PLIF) has been identified as a contributing factor to early-onset adjacent segment disease. However, achieving sufficient SL can be challenging despite technical strategies such as optimized cage placement. This study aimed to identify risk factors for ΔSL < 0 following PLIF, with a particular focus on intraoperative prone SL.

Methods A total of 105 patients who underwent primary single-level PLIF at L4-5 for degenerative lumbar spondylolisthesis between 2017 and 2022 were included. Radiological evaluations included measurements of preoperative, intraoperative (prone position), and 1-week postoperative radiographs, as well as preoperative CT images. ΔSL-P was defined as the change in SL between preoperative standing and intraoperative prone positions. Patients were categorized into the ΔSL ≥ 0 and the ΔSL < 0 group. Patient demographics, preoperative radiological parameters, intraoperative SL, ΔSL-P, cage configuration, and the cage height-disc height ratio were compared between the 2 groups.

Results The ΔSL ≥ 0 group comprised 48 patients, while the ΔSL < 0 group included 57. Multivariate analysis identified preoperative standing SL (OR 1.15, 95% CI 1.01-1.31, p = .033) and ΔSL-P (OR 0.66, 95% CI 0.53-0.82, p < .001) as significant risk factors for ΔSL < 0. Preoperative standing SL showed a significant negative correlation with ΔSL (r = -0.591, p < .001), while ΔSL-P demonstrated a significant positive correlation with ΔSL (r = 0.661, p < .001). Receiver operating characteristic curve analysis identified a ΔSL-P cutoff value of -1° for predicting ΔSL < 0 (AUC 0.84), sensitivity of 91% and specificity of 58%.

Conclusions ΔSL-P was identified as the most significant risk factor for ΔSL < 0. A decrease in prone SL relative to the preoperative standing value may warrant careful attention.