The Effect of Spinopelvic Parameters on Anterior Bone Graft Subsidence in Surgical Treatment of Pyogenic Lumbar Spondylodiscitis

Objective: To evaluate the effect of spinopelvic parameters on anterior bone graft subsidence and functional outcomes after anterior interbody fusion (AIF) and posterior instrumented fusion (PIF) in pyogenic spondylodiscitis (PS). Methods: Sixty-five patients who had received AIF+PIF for PS from July 2003 to December 2015 were enrolled. Based on the degree of bone graft subsidence, the patients were divided into groups A (minimal subsidence), B (moderate subsidence), and C (severe subsidence). Comparative analysis was performed evaluating patient demographics, spinopelvic parameters (kyphosis angle, involved segment's intervertebral height, pelvic incidence [PI], pelvic tilt, sacral slope, lumbar lordosis [LL], thoracolumbar kyphosis, and PI minus LL [PI−LL]), and clinical evaluation including Oswestry Disability Index score and visual analog scale (VAS) scores. The data were collected in a patient registry at perioperative, postoperative 3-month, and 2-year to assess clinical and radiological outcomes. Receiver operating characteristic analysis was applied for identification of cutoff points of LL and PI−LL in suggestion of clinical practice. Results: The 65 included patients had a mean follow-up period of 35.09 ± 38.30 months. Generalized estimating equation analysis showed that LL and PI−LL changes in group A were significantly different from those in group C but not in group B, revealing that preoperative LL and postoperative PI−LL are bone graft subsidence type indicators. By contrast, preoperative Oswestry Disability Index, postoperative 3-month VAS-back, preoperative VAS-leg, and postoperative 2-year VAS-leg scores were associated with bone graft subsidence type. Receiver operating characteristic analysis identified preoperative LL < 40.79° and postoperative PI−LL > 15° as significant predictive markers for severe bone graft subsidence, providing valuable thresholds for surgical risk evaluation. Conclusions: Among spinopelvic parameters, preoperative LL and postoperative PI−LL are important parameters associated with bone graft subsidence severity in patients who had received AIF+PIF for PS.