Spinal degeneration and deformity present an enormous healthcare burden, with spine surgery among the main treatment modalities. Unfortunately, spine surgery (e.g., lumbar fusion) exhibits broad variability in the quality of outcome, with ~20-40% of patients gaining no benefit in pain or function (“failed back surgery”) and earning criticism that is difficult to reconcile versus rapid growth in frequency and cost over the last decade. Vital to advancing the quality of care in spine surgery are improved clinical decision support (CDS) tools that are accurate, explainable, and actionable: accurate in prediction of outcomes; explainable in terms of the physical / physiological factors underlying the prediction; and actionable within the shared decision process between a surgeon and patient in identifying steps that could improve outcome. This technical note presents an overview of a novel outcome prediction framework for spine surgery (dubbed SpineCloud) that leverages innovative image analytics in combination with explainable prediction models to achieve accurate outcome prediction. Key to the SpineCloud framework are image analysis methods for extraction of high-level quantitative features from multi-modality peri-operative images (CT, MR, and radiography) related to spinal morphology (including bone and soft-tissue features), the surgical construct (including deviation from an ideal reference), and longitudinal change in such features. The inclusion of such image-based features is hypothesized to boost the predictive power of models that conventionally rely on demographic / clinical data alone (e.g., age, gender, BMI, etc.). Preliminary results using gradient boosted decision trees demonstrate that such prediction models are explainable (i.e., why a particular prediction is made), actionable (identifying features that may be addressed by the surgeon and/or patient), and boost predictive accuracy compared to analysis based on demographics alone (e.g., AUC improved by ~25% in preliminary studies). Incorporation of such CDS tools in spine surgery could fundamentally alter and improve the shared decisionmaking process between surgeons and patients by highlighting actionable features to improve selection of therapeutic and rehabilitative pathways.
Purpose: Data-intensive modeling could provide insight on the broad variability in outcomes in spine surgery. Previous studies were limited to analysis of demographic and clinical characteristics. We report an analytic framework called “SpineCloud” that incorporates quantitative features extracted from perioperative images to predict spine surgery outcome.
Approach: A retrospective study was conducted in which patient demographics, imaging, and outcome data were collected. Image features were automatically computed from perioperative CT. Postoperative 3- and 12-month functional and pain outcomes were analyzed in terms of improvement relative to the preoperative state. A boosted decision tree classifier was trained to predict outcome using demographic and image features as predictor variables. Predictions were computed based on SpineCloud and conventional demographic models, and features associated with poor outcome were identified from weighting terms evident in the boosted tree.
Results: Neither approach was predictive of 3- or 12-month outcomes based on preoperative data alone in the current, preliminary study. However, SpineCloud predictions incorporating image features obtained during and immediately following surgery (i.e., intraoperative and immediate postoperative images) exhibited significant improvement in area under the receiver operating characteristic (AUC): AUC = 0.72 (CI95 = 0.59 to 0.83) at 3 months and AUC = 0.69 (CI95 = 0.55 to 0.82) at 12 months.
Conclusions: Predictive modeling of lumbar spine surgery outcomes was improved by incorporation of image-based features compared to analysis based on conventional demographic data. The SpineCloud framework could improve understanding of factors underlying outcome variability and warrants further investigation and validation in a larger patient cohort.
Purpose. We report the initial implementation of an algorithm that automatically plans screw trajectories for spinal
pedicle screw placement procedures to improve the workflow, accuracy, and reproducibility of screw placement in freehand
navigated and robot-assisted spinal pedicle screw surgery. In this work, we evaluate the sensitivity of the algorithm
to the settings of key parameters in simulation studies.
Methods. Statistical shape models (SSMs) of the lumbar spine were constructed with segmentations of L1-L5 and
bilateral screw trajectories of N=40 patients. Active-shape model (ASM) registration was devised to map the SSMs to
the patient CT, initialized simply by alignment of (automatically annotated) single-point vertebral centroids. The atlas
was augmented by definition of “ideal / reference” trajectories for each spinal pedicle, and the trajectories are
deformably mapped to the patient CT. A parameter sensitivity analysis for the ASM method was performed on 3
parameters to determine robust operating points for ASM registration. The ASM method was evaluated by calculating
the root-mean-square-error between the registered SSM and the ground-truth segmentation for the L1 vertebra, and the
trajectory planning method was evaluated by performing a leave-one-out analysis and determining the entry point, end
point, and angular differences between the automatically planned trajectories and the neurosurgeon-defined reference
trajectories.
Results. The parameter sensitivity analysis showed that the ASM registration algorithm was relatively insensitive to
initial profile length (PLinitial) less than ~4 mm, above which runtime and registration error increased. Similarly stable
performance was observed for a maximum number of principal components (PCmax) of at least 8. Registration error ~2
mm was evident with diminishing return beyond a number of iterations, Niter, ~2000. With these parameter settings,
ASM registration of L1 achieved (2.0 ± 0.5) mm RMSE. Transpedicle trajectories for L1 agreed with reference
definition by (2.6 ± 1.3) mm at the entry point, by (3.4 ± 1.8) mm at the end point, and within (4.9° ±2.8°) in angle.
Conclusions. Initial results suggest that the algorithm yields accurate definition of pedicle trajectories in unsegmented
CT images of the spine. The studies identified stable operating points for key algorithm parameters and support ongoing
development and translation to clinical studies in free-hand navigated and robot-assisted spine surgery, where fast,
accurate trajectory definition is essential to workflow.
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