39. Optimizing safety in robotic lumbar instrumented fusions: a risk factor analysis of robotic failures

BACKGROUND CONTEXT Robot-guided lumbar instrumented fusion (RGLF) has the potential to improve safety and accuracy of pedicle screw placement. However, there are pitfalls in adopting this new technology and, as in adopting any new OR technology, there may be early complications. Optimizing workflow by avoiding interbody placement prior to pedicle screws placement (interbody-first workflow, IFW) and using caution in patients with poor bone quality (L1 Hounsfield units [HU] under 148) may improve outcomes. PURPOSE To determine risk factors for robot-related complications and suggest optimal OR workflow. STUDY DESIGN/SETTING Single-center retrospective study. PATIENT SAMPLE A total of 344 RGLF cases from 2018 to 2021. OUTCOME MEASURES L1 and UIV HU, levels fused, L5-S1 inclusion, interbody placed first workflow (IFW), hyperlordotic interbody, robot registration method, robot registration failure, intraoperative robot mechanical failures and pedicle screw malpositioning. METHODS Retrospective analysis of RGLFs at a single institution. Univariate analysis with t-tests, Mann-Whitney U tests, or chi-squared analysis assessed demographics, L1 and UIV HU, levels fused, L5-S1 inclusion, IFW, hyperlordotic cage, and robot registration method as risk factors for robot registration failure, intraoperative robot mechanical failures, and pedicle screw malpositioning. Multivariate logistic regression of risk factors approaching or achieving significance was conducted. A receiver operating characteristic (ROC) curve was created to determine a threshold for independent risk factors. RESULTS A total of 344 RGLFs were included. In registered vs registration failure cases, smoking (12.73% vs 28.57%; p=0.041), L1HU (139.81±46.86 vs 177.16±55.74; p=0.009), L5-S1 inclusion (50.00% vs 80.95%; p=0.006), and IFW (58.07% vs 85.71%; p=0.014) were significant risk factors on univariate analysis. On multivariate analysis, smoking (p=0.003), L1HU (p=0.006), and L5-S1 inclusion (p=0.022) were independent risk factors and IFW approached significance (p=0.099) for risk of registration failure. In successful vs all robot failures cases, age (55.72±13.38 vs 59.92±11.38 years; p=0.046), female gender (48.70% vs 69.44%; p=0.018), levels fused (1.37±0.63 vs 1.67±0.76; p=0.010), L5-S1 inclusion (50.00% vs 69.44%; p=0.027), and IFW (57.47% vs 77.78%; p=0.012) were significant risk factors on univariate analysis. On multivariate analysis, female gender (p=0.047) and L5-S1 inclusion (p=0.049) were independent risk factors and IFW approached significance (p=0.055) for risk of mechanical failure. In successful vs pedicle screw malpositioned cases, IFW was a significant independent risk factor for pedicle screw malpositioning on multivariate analysis (p=0.038). On subanalysis of 124 robot-guided anterior-posterior lumbar fusion (RG APLF), L1 HU was an independent risk factors for registration failure (p=0.007) and approached significance for mechanical failures (p=0.051). ROC analysis revealed a cutoff of L1 HU of 148.55 for mechanical failures (area under the curve = 0.778). Levels fused (1.41±0.69 vs 2.00±0.54; p=0.018) was a significant risk factor for pedicle screw malpositioning on univariate analysis. CONCLUSIONS In all RGLFs, IFW was a risk factor for robot-related complications. In RG APLF, low L1 HU was a risk factor. Robot-related complications may be avoided by placing pedicle screws prior to interbody and by using caution in patients with poor bone quality. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.