Background context: Risk factors associated with rod fracture (RF) following adult spinal deformity (ASD) surgery fused to the sacrum remain debatable, and the impact of RF on patient-reported outcomes (PROs) after ASD surgery has not been investigated.
Purpose: We aimed to evaluate the prevalence of and risk factors for RF and determine PROs changes associated with RF after ASD surgery fused to the sacrum.
Study design/setting: A retrospective single-center cohort study was performed.
Patient sample: Patients undergoing long-construct posterior spinal fusions to the sacrum performed at a single institution by two senior spine surgeons from 2004 to 2014 were included.
Outcome measures: Patient demographics, radiographic parameters, and surgical factors were assessed for risk factors associated with RF. Oswestry Disability Index (ODI) and Scoliosis Research Society-30 (SRS-30) scores were assessed at baseline, 1 year postoperatively, and latest follow-up.
Methods: Inclusion criteria were ASD patients age >18 who had ≥5 vertebrae instrumented and fused posteriorly to the sacrum and either development of RF or no development of RF with minimum 2-year follow-up. Patient characteristics, operative data, radiographic parameters, and PROs were analyzed at baseline and follow-up. Separate Cox proportional hazard models based on rod material and diameter were used to determine factors associated with RF.
Results: Five hundred twenty-six patients (80%) were available for analysis. RF occurred in 97 (18.4%) patients (unilateral RF n=61 [63%]; bilateral RF n=36 [37%]). Risk factors for fracture of 5.5 mm cobalt chromium (CC) instrumentation (CC 5.5 model) included preoperative sagittal vertical axis (hazard ratio [HR] 1.07, 95% confidence interval [95% CI] 1.02-1.14 per 1-cm increase), preoperative thoracolumbar kyphosis (HR 1.02, 95% CI 1.01-1.04 per 1-degree increase), and number of levels fused for patients who received rhBMP-2 <12 mg per level fused (HR 1.48, 95% CI 1.20-1.82 per 1-level increase). Implants that were 5.5-mm CC constructs were at a higher risk for fracture than 6.35-mm stainless steel (SS) constructs (HR 8.49, 95% CI 4.26-16.89). The RF group had less overall improvement in SRS Satisfaction (0.93 vs. 1.32; p=.007) and SRS Self-image domain scores (0.72 vs. 1.02; p=.01). The bilateral RF group had less overall improvement in ODI (8.1 vs. 15.8; p=.02), SRS Subscore (0.51 vs. 0.85; p=.03), and SRS Pain domain scores (0.48 vs. 0.95; p=.02) compared with the non-RF group at final follow-up.
Conclusions: The prevalence of all RF after index procedures was 18.4%, 37% for bilateral RF. Greater preoperative sagittal vertical axis, greater preoperative thoracolumbar kyphosis, increased number of vertebrae fused for patients who received rhBMP-2 <12 mg per level fused, and CC 5.5-mm rod were associated with RF. Less improvement in patient satisfaction and self-image was noted in the RF group. Furthermore, bilateral RF significantly affected PROs as measured by ODI and SRS Subscore at final follow-up.
Keywords: Adult spinal deformity; Patient-reported outcomes; Prevalence; Risk factors; Rod fracture; Surgical complications.
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