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

Abstract

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.