Rod fracture in adult spinal deformity surgery fused to the sacrum: prevalence, risk factors and impact on health related quality of life in 526 patients

Publication date: Available online 28 February 2018
Source:The Spine Journal
Author(s): Thamrong Lertudomphonwanit, Michael P. Kelly, Keith H. Bridwell, Lawrence G. Lenke, Steven J. McAnany, Prachya Punyarat, Timothy P. Bryan, Jacob M. Buchowski, Lukas P. Zebala, Brenda A. Sides, Karen Steger-May, Munish C. Gupta
Background contextRisk 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.PurposeTo evaluate the prevalence of and risk factors for RF and determine PROs change associated with RF after ASD surgery fused to the sacrum.Study Design/SettingRetrospective single-center cohort.Patient SamplePatients 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 MeasuresPatient 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.MethodsInclusion 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.ResultsFive 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 5.5mm 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 to 1.14] per 1-cm increase), preoperative thoracolumbar kyphosis (HR 1.02 [95%CI 1.01 to 1.04] per 1-degree increase) and number of levels fused for patients that received rhBMP-2 <12 mg per level fused (HR, 1.48 [95%CI 1.20 to 1.82] per 1-level increase). 5.5mm CC implants were at a higher risk for fracture than 6.35mm stainless steel (SS) constructs (HR, 8.49 [95%CI 4.26 to 16.89]). The RF group had less overall improvement in SRS Satisfaction (0.93 vs 1.32; p=0.007) and SRS Self-image domain scores (0.72 vs 1.02; p=0.01). The bilateral RF group had less overall improvement in ODI (8.1 vs 15.8; p=0.02), SRS Subscore (0.51 vs 0.85; p=0.03) and SRS Pain domain scores (0.48 vs 0.95; p=0.02) compared to the non-RF group at final follow-up.ConclusionsThe 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 that 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.



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