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R. Loch Macdonald

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Anshit Goyal, Che Ngufor, Panagiotis Kerezoudis, Brandon McCutcheon, Curtis Storlie and Mohamad Bydon

OBJECTIVE

Nonhome discharge and unplanned readmissions represent important cost drivers following spinal fusion. The authors sought to utilize different machine learning algorithms to predict discharge to rehabilitation and unplanned readmissions in patients receiving spinal fusion.

METHODS

The authors queried the 2012–2013 American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) for patients undergoing cervical or lumbar spinal fusion. Outcomes assessed included discharge to nonhome facility and unplanned readmissions within 30 days after surgery. A total of 7 machine learning algorithms were evaluated. Predictive hierarchical clustering of procedure codes was used to increase model performance. Model performance was evaluated using overall accuracy and area under the receiver operating characteristic curve (AUC), as well as sensitivity, specificity, and positive and negative predictive values. These performance metrics were computed for both the imputed and unimputed (missing values dropped) datasets.

RESULTS

A total of 59,145 spinal fusion cases were analyzed. The incidence rates of discharge to nonhome facility and 30-day unplanned readmission were 12.6% and 4.5%, respectively. All classification algorithms showed excellent discrimination (AUC > 0.80, range 0.85–0.87) for predicting nonhome discharge. The generalized linear model showed comparable performance to other machine learning algorithms. By comparison, all models showed poorer predictive performance for unplanned readmission, with AUC ranging between 0.63 and 0.66. Better predictive performance was noted with models using imputed data.

CONCLUSIONS

In an analysis of patients undergoing spinal fusion, multiple machine learning algorithms were found to reliably predict nonhome discharge with modest performance noted for unplanned readmissions. These results provide early evidence regarding the feasibility of modern machine learning classifiers in predicting these outcomes and serve as possible clinical decision support tools to facilitate shared decision making.

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Lorenzo Rinaldo, Brandon A. McCutcheon, Meghan E. Murphy, Daniel L. Shepherd, Patrick R. Maloney, Panagiotis Kerezoudis, Mohamad Bydon and Giuseppe Lanzino

OBJECTIVE

The mechanism by which greater institutional case volume translates into improved outcomes after surgical clipping of unruptured intracranial aneurysms (UIAs) is not well established. The authors thus aimed to assess the effect of case volume on the rate of various types of complications after clipping of UIAs.

METHODS

Using information on the outcomes of inpatient admissions for surgical clipping of UIAs collected within a national database, the relationship of institutional case volume to the incidence of different types of complications after clipping was investigated. Complications were subdivided into different categories, which included all complications, ischemic stroke, intracerebral hemorrhage, medical complications, infectious complications, complications related to anesthesia, and wound complications. The relationship of case volume to different types of complications was assessed using linear regression analysis. The relationships between case volume and overall complication and stroke rates were fit with both linear and quadratic equations. The numerical cutoff for institutional case volume above and below which the authors found the greatest differences in mean overall complication and stroke rate was determined using classification and regression tree (CART) analysis.

RESULTS

Between October 2012 and September 2015, 125 health care institutions reported patient outcomes from a total of 6040 cases of clipping of UIAs. On linear regression analysis, increasing case volume was negatively correlated to both overall complications (r2 = 0.046, p = 0.0234) and stroke (r2 = 0.029, p = 0.0557) rate, although the relationship of case volume to the complication (r2 = 0.092) and stroke (r2 = 0.067) rate was better fit with a quadratic equation. On CART analysis, the cutoff for the case number that yielded the greatest difference in overall complications and stroke rate between higher- or lower-volume centers was 6 cases/year and 3 cases/year, respectively.

CONCLUSIONS

Although the authors confirm that increasing case volume is associated with reduced complications after clipping of UIAs, their results suggest that the relationship between case volume and complications is not necessarily linear. Moreover, these results indicate that the effect of case volume on outcome is most evident between very-low-volume centers relative to centers with a medium-to-high volume.

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Lorenzo Rinaldo, Brandon A. McCutcheon, Meghan E. Murphy, Mohamad Bydon, Alejandro A. Rabinstein and Giuseppe Lanzino

OBJECTIVE

Hypoplasia of the A1 segment of the anterior cerebral artery is frequently observed in patients with anterior communicating artery (ACoA) aneurysms. The effect of this anatomical variant on ACoA aneurysm morphology is not well understood.

METHODS

Digital subtraction angiography images were reviewed for 204 patients presenting to the authors' institution with either a ruptured or an unruptured ACoA aneurysm. The ratio of the width of the larger A1 segment to the smaller A1 segment was calculated. Patients with an A1 ratio greater than 2 were categorized as having A1 segment hypoplasia. The relationship of A1 segment hypoplasia to both patient and aneurysm characteristics was then assessed.

RESULTS

Of 204 patients that presented with an ACoA aneurysm, 34 (16.7%) were found to have a hypoplastic A1. Patients with A1 segment hypoplasia were less likely to have a history of smoking (44.1% vs 62.9%, p = 0.0410). ACoA aneurysms occurring in the setting of a hypoplastic A1 were also found to have a larger maximum diameter (mean 7.7 vs 6.0 mm, p = 0.0084). When considered as a continuous variable, increasing A1 ratio was associated with decreasing aneurysm dome-to-neck ratio (p = 0.0289). There was no significant difference in the prevalence of A1 segment hypoplasia between ruptured and unruptured aneurysms (18.9% vs 10.7%; p = 0.1605).

CONCLUSIONS

Our results suggest that a hypoplastic A1 may affect the morphology of ACoA aneurysms. In addition, the relative lack of traditional risk factors for aneurysm formation in patients with A1 segment hypoplasia argues for the importance of hemodynamic factors in the formation of ACoA aneurysms in this anatomical setting.

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Brandon A. McCutcheon, Brian R. Hirshman, Brandon C. Gabel, Michael W. Heffner, Logan P. Marcus, Tyler S. Cole, Clark C. Chen, David C. Chang and Bob S. Carter

OBJECTIVE

The subspecialization of neurosurgical practice is an ongoing trend in modern neurosurgery. However, it remains unclear whether the degree of surgeon specialization is associated with improved patient outcomes. The authors hypothesized that a trend toward increased neurosurgeon specialization was associated with improved patient morbidity and mortality rates.

METHODS

The Nationwide Inpatient Sample (NIS) was used (1998–2009). Patients were included in a spinal analysis cohort for instrumented spine surgery involving the cervical spine (International Classification of Diseases, Ninth Revision, Clinical Modification [ICD-9-CM] codes 81.31–81.33, 81.01–81.03, 84.61–84.62, and 84.66) or lumbar spine (codes 81.04–81.08, 81.34–81.38, 84.64–84.65, and 84.68). A cranial analysis cohort consisted of patients receiving a parenchymal excision or lobectomy operation (codes 01.53 and 01.59). Surgeon specialization was measured using unique surgeon identifiers in the NIS and defined as the proportion of a surgeon’s total practice dedicated to cranial or spinal cases.

RESULTS

A total of 46,029 and 231,875 patients were identified in the cranial and spinal analysis cohorts, respectively. On multivariate analysis in the cranial analysis cohort (after controlling for overall surgeon volume, patient demographic data/comorbidities, hospital characteristics, and admitting source), each percentage-point increase in a surgeon’s cranial specialization (that is, the proportion of cranial cases) was associated with a 0.0060 reduction in the log odds of patient mortality (95% CI 0.0034–0.0086) and a 0.0042 reduction in the log odds of morbidity (95% CI 0.0032–0.0052). This resulted in a 15% difference in the predicted probability of mortality for neurosurgeons at the 75th versus the 25th percentile of cranial specialization. In the spinal analysis cohort, each percentage-point increase in a surgeon’s spinal specialization was associated with a 0.0122 reduction in the log odds of mortality (95% CI 0.0074–0.0170) and a 0.0058 reduction in the log odds of morbidity (95% CI 0.0049–0.0067). This resulted in a 26.8% difference in the predicted probability of mortality for neurosurgeons at the 75th versus the 25th percentile of spinal specialization.

CONCLUSIONS

For both spinal and cranial surgery patient cohorts derived from the NIS database, increased surgeon specialization was significantly and independently associated with improved mortality and morbidity rates, even after controlling for overall case volume.

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Panagiotis Kerezoudis, Brandon McCutcheon, Meghan E. Murphy, Kenan R. Rajjoub, Daniel Ubl, Elizabeth B. Habermann, Gregory Worrell, Mohamad Bydon and Jamie J. Van Gompel

OBJECTIVE

Temporal lobectomy is a well-established treatment modality for the management of medically refractory epilepsy in appropriately selected patients. The aim of this study was to assess 30-day morbidity and mortality after temporal lobectomy in cases registered in a national database.

METHODS

A retrospective cohort analysis was conducted using a multiinstitutional surgical registry compiled between 2006 and 2014. The authors identified patients who underwent anterior temporal lobectomy and/or amygdalohippocampectomy for a primary diagnosis of intractable epilepsy. Univariate and multivariable analyses with regard to patient demographics, comorbidities, operative characteristics, and 30-day outcomes were applied.

RESULTS

A total of 216 patients were included in the study. The median age was 38 years and 46% of patients were male. The median length of stay was 3 days and the 30-day mortality rate was 1.4%. Fourteen patients (6.5%) developed at least one major complication. Return to the operating room was observed in 7 patients (3.2%). Readmission within 30 days and discharge to a location other than home were available for 2011–2014 (n = 155) and occurred in 11% and 10.3% of patients, respectively. Multivariable regression analysis revealed that increasing age was an independent predictor of discharge disposition other than home and that male sex was a significant risk factor for the development of a major complication. Interestingly, the presence of the attending neurosurgeon and a resident during the procedure was significantly associated with decreased odds of prolonged length of stay (i.e., > 75th percentile [5 days]) and discharge to a location other than home.

CONCLUSIONS

Using a multiinstitutional surgical registry, 30-day outcome data after temporal lobectomy for medically intractable epilepsy demonstrates a mortality rate of 1.4%, a major complication rate of 6.5%, and a readmission rate of 11%. Temporal lobectomy is an extremely effective therapy for seizures originating there—however, surgical intervention must be weighed against its morbidity and mortality outcomes.

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Mohamed Macki, Rafael De la Garza-Ramos, Ashley A. Murgatroyd, Kenneth P. Mullinix, Xiaolei Sun, Bryan W. Cunningham, Brandon A. McCutcheon, Mohamad Bydon and Ziya L. Gokaslan

OBJECTIVE

Aggressive sacral tumors often require en bloc resection and lumbopelvic reconstruction. Instrumentation failure and pseudarthrosis remain a clinical concern to be addressed. The objective in this study was to compare the biomechanical stability of 3 distinct techniques for sacral reconstruction in vitro.

METHODS

In a human cadaveric model study, 8 intact human lumbopelvic specimens (L2–pelvis) were tested for flexion-extension range of motion (ROM), lateral bending, and axial rotation with a custom-designed 6-df spine simulator as well as axial compression stiffness with the MTS 858 Bionix Test System. Biomechanical testing followed this sequence: 1) intact spine; 2) sacrectomy (no testing); 3) Model 1 (L3–5 transpedicular instrumentation plus spinal rods anchored to iliac screws); 4) Model 2 (addition of transiliac rod); and 5) Model 3 (removal of transiliac rod; addition of 2 spinal rods and 2 S-2 screws). Range of motion was measured at L4–5, L5–S1/cross-link, L5–right ilium, and L5–left ilium.

RESULTS

Flexion-extension ROM of the intact specimen at L4–5 (6.34° ± 2.57°) was significantly greater than in Model 1 (1.54° ± 0.94°), Model 2 (1.51° ± 1.01°), and Model 3 (0.72° ± 0.62°) (p < 0.001). Flexion-extension at both the L5–right ilium (2.95° ± 1.27°) and the L5–left ilium (2.87° ± 1.40°) for Model 3 was significantly less than the other 3 cohorts at the same level (p = 0.005 and p = 0.012, respectively). Compared with the intact condition, all 3 reconstruction groups statistically significantly decreased lateral bending ROM at all measured points. Axial rotation ROM at L4–5 for Model 1 (2.01° ± 1.39°), Model 2 (2.00° ± 1.52°), and Model 3 (1.15° ± 0.80°) was significantly lower than the intact condition (5.02° ± 2.90°) (p < 0.001). Moreover, axial rotation for the intact condition and Model 3 at L5–right ilium (2.64° ± 1.36° and 2.93° ± 1.68°, respectively) and L5–left ilium (2.58° ± 1.43° and 2.93° ± 1.71°, respectively) was significantly lower than for Model 1 and Model 2 at L5–right ilium (5.14° ± 2.48° and 4.95° ± 2.45°, respectively) (p = 0.036) and L5–left ilium (5.19° ± 2.34° and 4.99° ± 2.31°) (p = 0.022). Last, results of the axial compression testing at all measured points were not statistically different among reconstructions.

CONCLUSIONS

The addition of a transverse bar in Model 2 offered no biomechanical advantage. Although the implementation of 4 iliac screws and 4 rods conferred a definitive kinematic advantage in Model 3, that model was associated with significantly restricted lumbopelvic ROM.

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Brandon A. McCutcheon, David C. Chang, Logan Marcus, David D. Gonda, Abraham Noorbakhsh, Clark C. Chen, Mark A. Talamini and Bob S. Carter

OBJECT

This study was designed to assess the relationship between insurance status and likelihood of receiving a neurosurgical procedure following admission for either extraaxial intracranial hemorrhage or spinal vertebral fracture.

METHODS

A retrospective analysis of the Nationwide Inpatient Sample (NIS; 1998–2009) was performed. Cases of traumatic extraaxial intracranial hematoma and spinal vertebral fracture were identified using International Classification of Diseases, Ninth Revision (ICD-9) diagnosis codes. Within this cohort, those patients receiving a craniotomy or spinal fusion and/or decompression in the context of an admission for traumatic brain or spine injury, respectively, were identified using the appropriate ICD-9 procedure codes.

RESULTS

A total of 190,412 patients with extraaxial intracranial hematoma were identified between 1998 and 2009. Within this cohort, 37,434 patients (19.7%) received a craniotomy. A total of 477,110 patients with spinal vertebral fracture were identified. Of these, 37,302 (7.8%) received a spinal decompression and/or fusion. On multivariate analysis controlling for patient demographics, severity of injuries, comorbidities, hospital volume, and hospital characteristics, uninsured patients had a reduced likelihood of receiving a craniotomy (odds ratio [OR] 0.76, 95% confidence interval [CI] 0.71–0.82) and spinal fusion (OR 0.67, 95% CI 0.64–0.71) relative to insured patients. This statistically significant trend persisted when uninsured and insured patients were matched on the basis of mortality propensity score. Uninsured patients demonstrated an elevated risk-adjusted mortality rate relative to insured patients in cases of extraaxial intracranial hematoma. Among patients with spinal injury, mortality rates were similar between patients with and without insurance.

CONCLUSIONS

In this study, uninsured patients were consistently less likely to receive a craniotomy or spinal fusion for traumatic intracranial extraaxial hemorrhage and spinal vertebral fracture, respectively. This difference persisted after accounting for overall injury severity and patient access to high- or low-volume treatment centers, and potentially reflects a resource allocation bias against uninsured patients within the hospital setting. This information adds to the growing literature detailing the benefits of health reform initiatives seeking to expand access for the uninsured.

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Anthony L. Asher, Clinton J. Devin, Brandon McCutcheon, Silky Chotai, Kristin R. Archer, Hui Nian, Frank E. Harrell Jr., Matthew McGirt, Praveen V. Mummaneni, Christopher I. Shaffrey, Kevin Foley, Steven D. Glassman and Mohamad Bydon

OBJECTIVE

In this analysis the authors compare the characteristics of smokers to nonsmokers using demographic, socioeconomic, and comorbidity variables. They also investigate which of these characteristics are most strongly associated with smoking status. Finally, the authors investigate whether the association between known patient risk factors and disability outcome is differentially modified by patient smoking status for those who have undergone surgery for lumbar degeneration.

METHODS

A total of 7547 patients undergoing degenerative lumbar surgery were entered into a prospective multicenter registry (Quality Outcomes Database [QOD]). A retrospective analysis of the prospectively collected data was conducted. Patients were dichotomized as smokers (current smokers) and nonsmokers. Multivariable logistic regression analysis fitted for patient smoking status and subsequent measurement of variable importance was performed to identify the strongest patient characteristics associated with smoking status. Multivariable linear regression models fitted for 12-month Oswestry Disability Index (ODI) scores in subsets of smokers and nonsmokers was performed to investigate whether differential effects of risk factors by smoking status might be present.

RESULTS

In total, 18% (n = 1365) of patients were smokers and 82% (n = 6182) were nonsmokers. In a multivariable logistic regression analysis, the factors significantly associated with patients’ smoking status were sex (p < 0.0001), age (p < 0.0001), body mass index (p < 0.0001), educational status (p < 0.0001), insurance status (p < 0.001), and employment/occupation (p = 0.0024). Patients with diabetes had lowers odds of being a smoker (p = 0.0008), while patients with coronary artery disease had greater odds of being a smoker (p = 0.044). Patients’ propensity for smoking was also significantly associated with higher American Society of Anesthesiologists (ASA) class (p < 0.0001), anterior-alone surgical approach (p = 0.018), greater number of levels (p = 0.0246), decompression only (p = 0.0001), and higher baseline ODI score (p < 0.0001). In a multivariable proportional odds logistic regression model, the adjusted odds ratio of risk factors and direction of improvement in 12-month ODI scores remained similar between the subsets of smokers and nonsmokers.

CONCLUSIONS

Using a large, national, multiinstitutional registry, the authors described the profile of patients who undergo lumbar spine surgery and its association with their smoking status. Compared with nonsmokers, smokers were younger, male, nondiabetic, nonobese patients presenting with leg pain more so than back pain, with higher ASA classes, higher disability, less education, more likely to be unemployed, and with Medicaid/uninsured insurance status. Smoking status did not affect the association between these risk factors and 12-month ODI outcome, suggesting that interventions for modifiable risk factors are equally efficacious between smokers and nonsmokers.

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David D. Gonda, Alexander A. Khalessi, Brandon A. McCutcheon, Logan P. Marcus, Abraham Noorbakhsh, Clark C. Chen, David C. Chang and Bob S. Carter

Object

Using a database that enabled longitudinal follow-up, the authors assessed the long-term outcomes of unruptured cerebral aneurysms repaired by clipping or coiling.

Methods

An observational analysis of the California Office of Statewide Health Planning and Development (OSHPD) database, which follows patients longitudinally in time and through multiple hospitalizations, was performed for all patients initially treated for an unruptured cerebral aneurysm in the period from 1998 to 2005 and with follow-up data through 2009.

Results

Nine hundred forty-four cases (36.5%) were treated with endovascular coiling, 1565 cases (60.5%) were surgically clipped, and 76 cases were treated with both coiling and clipping. There was no significant difference in any demographic variable between the two treatment groups except for age (median: 55 years for the clipped group, 58 years for the coiled group, p < 0.001). Perioperative (30-day) mortality was 1.1% in patients with coiled aneurysms compared with 2.3% in those with clipped aneurysms (p = 0.048). The median follow-up was 7 years (range 4–12 years). At the last follow-up, 153 patients (16.2%) in the coiled group had died compared with 244 (15.6%) in the clipped group (p = 0.693). The adjusted hazard ratio for death at the long-term follow-up was 1.14 (95% CI 0.9–1.4, p = 0.282) for patients with endovascularly treated aneurysms. The incidence of intracranial hemorrhage was similar in the two treatment groups (5.9% clipped vs 4.8% coiled, p = 0.276). One hundred ninety-three patients (20.4%) with coiled aneurysms underwent additional hospitalizations for aneurysm repair procedures compared with only 136 patients (8.7%) with clipped aneurysms (p < 0.001). Cumulative hospital costs per patient for admissions involving aneurysm repair procedures were greater in the clipped group (median cost $98,260 vs $81,620, p < 0.001) through the follow-up.

Conclusions

For unruptured cerebral aneurysms, an observed perioperative survival advantage for endovascular coiling relative to that for surgical clipping was lost on long-term follow-up, according to data from an administrative database of patients who were not randomly allocated to treatment type. A cost advantage of endovascular treatment was maintained even though endovascularly treated patients were more likely to undergo subsequent hospitalizations for additional aneurysm repair procedures. Rates of aneurysm rupture following treatment were similar in the two groups.