Impact of neurosurgeon specialization on patient outcomes for intracranial and spinal surgery: a retrospective analysis of the Nationwide Inpatient Sample 1998–2009

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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.

ABBREVIATIONS ICD-9-CM = International Classification of Diseases, Ninth Revision, Clinical Modification; IQR = interquartile range; NIS = Nationwide Inpatient Sample.

Article Information

Correspondence Bob S. Carter, Massachusetts General Hospital, 55 Fruit St., Boston, MA 02114. email: bcarter@mgh.harvard.edu.

INCLUDE WHEN CITING Published online August 4, 2017; DOI: 10.3171/2016.4.JNS152332.

Drs. McCutcheon and Hirshman contributed equally to this work.

Disclosures The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

© AANS, except where prohibited by US copyright law.

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Figures

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    Histograms showing the number of neurosurgeons (A) as a function of neurosurgeon specialization (x axis), indicating that most neurosurgeons are specialized in spinal surgery. B–D: Histograms showing the number of cranial surgery patients (B) and deaths (C), and the mortality rate per surgeon (D). E–G: Histograms showing the number of spinal surgery patients (E) and deaths (F), and the mortality rate per surgeon (G), respectively. In panels D and G, colors represent mortality rate ranges from lower (green) to higher (red).

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    A and B: Mortality rate and adverse discharge disposition for cranial surgeries (y axis) shown for 4 groups of surgeons categorized by total surgical volume (1st quartile < 92 cases per year, 2nd quartile 92–127 cases per year, 3rd quartile 128–176 cases per year, 4th quartile > 176 cases per year). The x axis shows neurosurgeon specialization subcategorized into quintiles according to the percentage of overall practice that is cranial surgery. C and D: Mortality rate and adverse discharge disposition for spinal surgeries (y axis) shown for 4 groups of surgeons categorized by total surgical volume (1st quartile < 110 cases per year, 2nd quartile 110–157 cases per year, 3rd quartile 158–225 cases per year, 4th quartile > 225 cases per year). The x axis shows neurosurgeon specialization subcategorized into quintiles according to the percentage of overall practice that is spinal surgery.

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    Scatter plots displaying mortality rates (green represents lower, red represents higher) as a function of case volume (x axis) and percent spinal or cranial surgery specialization (y axis) among surgeons with at least 1 patient fatality. The cranial data (left) illustrate a clear trend toward lower mortality rates with increasing specialization; however a weaker trend toward increased case volume is noted. In the spine data (right), a clear trend toward lower mortality rates can be seen with both increasing volume and increasing specialization. Histograms summarizing mortality rates as a function of case volume (above the scatter plots) and specialization (to the right of scatter plots) are provided as summary statistics.

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