Introduction: Pelvic fixation (PF) has traditionally been utilized in long-construct deformity surgery to achieve greater control over sagittal and coronal imbalance and construct stability and to improve solid arthrodesis rates^1,2. As the incidences of both operative degenerative lumbar disease requiring short-to-medium length fusions as well as osteoporosis have increased with an aging patient population, the role of adjunct PF has become increasingly relevant. However, outcomes associated with adjunct PF in the degenerative population has not been studied sufficiently. This is the first large-scale database study to compare 30-day readmission, reoperation, and morbidity following short-to-medium length multilevel lumbar fusion with and without adjunct PF for the treatment of degenerative lumbar disease.

Methods: This is a retrospective database study using the 2005-2018 NSQIP datasets. Adults who underwent multilevel degenerative lumbar fusion were identified using CPT codes 22612, 22630, 22633, and 22558 with ≥1 entry of a corresponding additional level CPT code (22614, 22632, 22634, 22585). Short-to-medium length fusion was specifically isolated by excluding patients with >4 additional level codes. Patients were classified into groups with and without PF using CPT code 22848. Patients were excluded if they underwent single level, traumatic, deformity, non-elective, tumor, or revision surgery; had evidence of prior infection; or underwent additional procedures including osteotomy, arthroplasty, or cervical or thoracic procedures. Univariate and multivariate regression analyses were used to compare readmission, reoperation, morbidity, and specific complications between patients with and without PF, and to control and evaluate for significant predictors and baseline differences between patients.

Results: We identified 38,413 patients (818 with PF). PF independently predicted readmission (p=0.001, OR=1.546) and morbidity (p<0.001, OR=2.740). PF had greater reoperation rates in univariate analysis (p<0.001), but not in multivariate analysis (p=0.119, OR=1.298). Multivariate analyses of readmission, reoperation, and morbidity are provided in Tables 1-3. PF had greater rates of wound complication (p=0.015, OR=1.533), transfusion (p<0.001, OR=3.299), DVT (p=0.002, OR=2.054), and sepsis (p=0.038, OR=1.713). Length of stay was longer in the PF group (8 vs 4 days, p<0.001).

Obesity (OR=1.210), chronic steroids (OR=1.631), and ASA-class ≥3 (OR=1.297) predicted readmission (p<0.001). Obesity (p=0.021, OR=1.164), steroids (p=0.024, OR=1.324), and preoperative transfusion (p=0.037, OR=1.829) predicted reoperation. Male gender (p=0.027, OR=0.861) and inclusion of ALIF within the fusion construct (p<0.001, OR=0.759) were protective against reoperation. African American race (OR=1.212), decreased hematocrit (OR=0.938), and bleeding disorder (OR=1.516) predicted morbidity (p<0.001). Inclusion of ALIF within the fusion construct (p<0.001, OR=0.644) and navigated surgery (p=0.010, OR=0.855) were protective against morbidity.

Conclusion: PF was associated with a 1.5-times increased-odds of readmission and a 2.7-times increased-odds of morbidity, with significantly greater rates of transfusion, DVT, sepsis, and wound-related complications, despite controlling for patient and procedural-related factors. There were no differences in 30-day reoperation. Thus, these findings suggest that PF may achieve greater construct stability in the degenerative spine population, but at a significantly elevated risk of medical and surgical morbidity. The benefits of navigated surgery and anterior column support manifested as protective against poor outcomes. Increased age, ASA-class ≥3, obesity, and other demographic factors and medical comorbidities predicted poorer 30-day outcomes.