Causalgia: a military pain syndrome.

Causalgia, officially known as complex regional pain syndrome type II, is a pain syndrome characterized by severe burning pain, motor and sensory dysfunction, and changes in skin color and temperature sensation distal to an injured peripheral nerve. The pain syndrome primarily tends to affect combat soldiers after they sustain wartime injuries from blasts and gunshots. Here, the authors provide a historical narrative that showcases the critical contributions of military physicians to our understanding of causalgia and to the field of peripheral nerve neurosurgery as a whole.

The role of socioeconomic status on outcomes following cerebellopontine angle tumor resection.

PURPOSE: It is well documented that the interaction between many social factors can affect clinical outcomes. However, the independent effects of economics on outcomes following surgery are not well understood. The goal of this study is to investigate the role socioeconomic status has on postoperative outcomes in a cerebellopontine angle (CPA) tumor resection population. MATERIALS AND METHODS: Over 6 years (07 June 2013 to 24 April 2019), 277 consecutive CPA tumor cases were reviewed at a single, multihospital academic medical center. Patient characteristics obtained included median household income, Charlson Comorbidity Index (CCI), race, BMI, tobacco use, amongst 23 others. Outcomes studied included readmission, ED evaluation, unplanned return to surgery (during and after index admission), return to surgery after index admission, and mortality within 90 days, in addition to reoperation and mortality throughout the entire follow-up period. Univariate analysis was conducted amongst the entire population with significance set at a p value <0.05. The population was divided into quartiles based on median household income and univariate analysis conducted between the lowest (Q1) and highest (Q4) socioeconomic quartiles, with significance set at a p value <0.05. Stepwise regression was conducted to determine the correlations amongst study variables and identify confounding factors. RESULTS: Regression analysis of 273 patients did not find household income to be associated with any of the long-term outcomes assessed. Similarly, a Q1 vs Q4 comparison did not yield significantly different odds of outcomes assessed. CONCLUSION: Although not statistically significant, the odds ratios suggest socioeconomic status may have a clinically significant effect on postsurgical outcomes. Further studies in larger, matched populations are necessary to validate these findings.

The impact of gender on long-term outcomes following supratentorial brain tumor resection.

PURPOSE: Gender is a known social determinant of health which has been linked disparities in medical care. This study intends to assess the impact of gender on 90-day and long-term morbidity and mortality outcomes following supratentorial brain tumor resection in a coarsened-exact matched population. MATERIALS AND METHODS: A total of 1970 consecutive patients at a single, university-wide health system undergoing supratentorial brain tumor resection over a six-year period (09 June 2013 to 26 April 2019) were analyzed retrospectively. Coarsened Exact Matching was employed to match patients on key demographic factors including history of prior surgery, smoking status, median household income, American Society of Anesthesiologists (ASA) grade, and Charlson Comorbidity Index (CCI), amongst others. Primary outcomes assessed included readmission, ED visit, unplanned reoperation, and mortality within 90 days of surgery. Long-term outcomes such as mortality and unplanned return to surgery during the entire follow-up period were also recorded. RESULTS: Whole-population regression demonstrated significantly increased mortality throughout the entire follow-up period for the male cohort (p = 0.004, OR = 1.32, 95% CI = 1.09 - 1.59); however, no significant difference was found after coarsened exact matching was performed (p = 0.08). In both the whole-population regression and matched-cohort analysis, no significant difference was observed between gender and readmission, ED visit, unplanned reoperation, or mortality in the 90-day post-operative window, in addition to return to surgery after throughout the entire follow-up period. CONCLUSION: After controlling for confounding variables, female birth gender did not significantly predict any difference in morbidity and mortality outcomes following supratentorial brain tumor resection. Difference between mortality outcomes in the pre-matched population versus the matched cohort suggests the need to better manage the underlying health conditions of male patients in order to prevent future disparities.

Resolution of hypoglossal nerve palsy after coil embolization of an anterior condylar confluence fistula.

A 69-year-old female presented with 2-year history of slurred speech, left-sided pulsatile tinnitus, and left-sided hypoglossal nerve palsy. Cerebral angiography demonstrated a left anterior condylar confluence fistula. She was treated with a transvenous coil embolization of the left condylar fistula pocket.

Eagle syndrome: a rare pathology presented in a 3-Dimensional reconstructed view.

A 42-year-old male presented with 3-month history of constant right-sided frontal headaches, severe right-sided intermittent sharp jaw pain, odynophagia, globus pharyngis, and worsening episodes of blurry vision in his right eye. Cervicocerebral angiography demonstrated a prominent, 4 cm right sided styloid process with close proximity to the right internal carotid artery (ICA). The patient was referred to otorhinolaryngology for styloidectomy and continued care.

The LACE + index as a predictor of 90-day urologic surgery outcomes.

PURPOSE: This study assessed the ability of the LACE + [Length of stay, Acuity of admission, Charlson Comorbidity Index (CCI) score, and Emergency department visits in the past 6 months] index to predict adverse outcomes after urologic surgery. METHODS: LACE + scores were retrospectively calculated for all consecutive patients (n = 9824) who received urologic surgery at one multi-center health system over 2 years (2016-2018). Coarsened exact matching was employed to sort patient data before analysis; matching criteria included duration of surgery, BMI, and race among others. Outcomes including unplanned hospital readmission, emergency room visits, and reoperation were compared for patients with different LACE + quartiles. RESULTS: 722 patients were matched between Q1 and Q4; 1120 patients were matched between Q2 and Q4; 2550 patients were matched between Q3 and Q4. Higher LACE + score significantly predicted readmission within 90 days (90D) of discharge for Q1 vs Q4 and Q2 vs Q4. Increased LACE + score also significantly predicted 90D emergency room visits for Q1 vs Q4, Q2 vs Q4, and Q3 vs Q4. LACE + score was also significantly predictive of 90D reoperation for Q1 vs Q4. LACE + score did not predict 90D reoperation for Q2 vs Q4 or Q3 vs Q4 or 90D readmission for Q3 vs. Q4. CONCLUSION: These results suggest that LACE + may be a suitable prediction model for important patient outcomes after urologic surgery.

Association of Overlapping, Nonconcurrent, Surgery With Patient Outcomes at a Large Academic Medical Center: A Coarsened Exact Matching Study.

OBJECTIVE: Assess the safety of overlapping surgery before implementation of new recommendations and regulations. BACKGROUND: Overlapping surgery is a longstanding practice that has not been well studied. There remains a need to analyze data across institutions and specialties to draw well-informed conclusions regarding appropriate application of this practice. METHODS: Coarsened exact matching was used to assess the impact of overlap on outcomes amongst all surgical interventions (n = 61,524) over 1 year (2014) at 1 health system. Overlap was categorized as: any, beginning, or end overlap. Study subjects were matched 1:1 on 11 variables. Serious unanticipated events were studied including unplanned return to operating room, readmission, and mortality. RESULTS: In all, 8391 patients (13.6%) had any overlap and underwent coarsened exact matching. For beginning/end overlap, matched groups were created (total matched population N = 4534/3616 patients, respectively). Any overlap did not predict unanticipated return to surgery (9.8% any overlap vs 10.1% no overlap; P = 0.45). Further, any overlap did not predict an increase in reoperation, readmission, or emergency room (ER) visits at 30 or 90 days (30D reoperation 3.6% vs 3.7%; P = 0.83, 90D reoperation 3.8% vs 3.9%; P = 0.84) (30D readmission 9.9% vs 10.2%; P = 0.45, 90D readmissions 6.9% vs 7.0%; P = 0.90) (30D ER 5.4% vs 5.6%; P = 0.60, 90D ER 4.8% vs 4.7%; P = 0.71). In addition, any overlap was not associated with mortality over the surgical follow-up period (90D mortality 1.7% vs 2.1%; P = 0.06). Beginning/end overlap had results similar to any overlap. CONCLUSION: Overlapping, nonconcurrent surgery is not associated with an increase in reoperation, readmission, ER visits, or unanticipated return to surgery.

Microsurgical treatment of tentorial dural fistulas causing thalamic venous hypertension: two illustrative sister cases.

This video is a presentation of technical tenets for the microsurgical clipping of a tentorial dural arteriovenous fistula presenting with thalamic venous hypertension. These cases are easily misdiagnosed and often supplied by the tentorial artery of Davidoff and Schecter. The cases shown in the video uniquely illustrate a supracerebellar infratentorial approach to identify and clip an arterialized tentorial vein utilizing intraoperative Doppler and fluorescein, with navigation and an intraoperative cerebral angiogram in a hybrid neuroangiography operative suite. Both patients were found to have thalamic edema on preoperative imaging, which significantly improved postoperatively.The video can be found here: https://youtu.be/HmUO6Ye53QI.

Quantifying a novel three-dimensional marker of scoliosis.

BACKGROUND: Scoliosis causes abnormal spinal curvature and torsional rotation of the vertebrae and has implications for human suffering and societal cost. In differential geometry, Writhe describes three-dimensional curvature. Differential geometric quantities can inform better diagnostic metrics of scoliotic deformity. This evaluation could help physicians and researchers study scoliosis and determine treatments. METHODS: Eight adult lumbar spine CT scans were analyzed in custom MATLAB programs to estimate Writhe and Cobb angle. Five patients exhibited scoliotic curvature, and three controls were asymptomatic. Vertebral centroids in three-dimensional space were determined, and Writhe was approximated. A T-test determined whether the affected spines had greater Writhe than the controls. Cohen's D test was used to determine effect size. RESULTS: Writhe of scoliotic spines (5.4E-4 ± 2.7E-4) was significantly higher than non-scoliotic spines (8.2E-5 ± 1.1E-4; p = 0.008). CONCLUSION: Writhe, a measure of curvature derived from 3D imaging, is significantly greater in scoliotic than in non-scoliotic spines. Future directions must include more subjects and examine writhe as a marker of scoliosis severity, progression, and response to treatment.

The obesity paradox and ventriculoperitoneal shunting in aneurysmal subarachnoid hemorrhage patients undergoing microsurgical clipping.

BACKGROUND: Aneurysmal subarachnoid hemorrhage (aSAH) can be devastating. Identifying predisposing factors is paramount in reducing aSAH-related mortality. Obesity's negative impact on health is well-established. However, the controversial "obesity paradox" in neurosurgery suggests that obesity may confer a survival advantage in SAH. We hypothesized that obesity would have a negative impact on outcomes following surgical clipping in aSAH. METHODS: A single-institution retrospective review was performed of aSAH patients undergoing surgical clipping from 2017 to 2021. Demographics and clinically relevant variables were collected. Obesity was defined as body mass index >30. Primary outcome was death or severe disability (mRS 4-6) at last follow-up. Secondary outcome was VPS placement. Multivariable Cox proportional-hazards model identified predictors of poor outcome. Kaplan-Meier curves identified survivorship differences between obese and non-obese patients. RESULTS: Poor outcome occurred in 11 of 52 total patients (21.2 %). There were no differences in demographics or distribution of Hunt Hess (HH), modified Fisher Grade (mFG), or external ventricular drain (EVD) placement between obese and non-obese patients. On univariate analysis, hypertension, older age, and non-obesity were predictive of poor outcome. On multivariable analysis, only obesity remained significant, suggesting a protective effect from poor outcome (HR 0.45 [0.21-0.95], p = 0.037). VPS placement occurred in 6 (11.5 %) patients for which obesity was not a significant predictor. CONCLUSIONS: Obesity may have a protective effect against poor outcome following surgical clipping in aSAH. Additionally, obesity does not appear to increase rate of EVD conversion to VPS. Thus, our study suggests that obesity should not preclude patients from open surgical intervention when clinically appropriate.

Varying Degree of Overlap Following the Critical Steps of Lumbar Fusion and Short-term Outcomes.

STUDY DESIGN: Retrospective cohort. OBJECTIVE: The present study analyzes the impact of end-overlap on short-term outcomes after single-level, posterior lumbar fusions. SUMMARY OF BACKGROUND DATA: Few studies have evaluated how "end-overlap" (i.e., surgical overlap after the critical elements of spinal procedures, such as during wound closure) influences surgical outcomes. METHODS: Retrospective analysis was performed on 3563 consecutive adult patients undergoing single-level, posterior-only lumbar fusion over a 6-year period at a multi-hospital university health system. Exclusion criteria included revision surgery, missing key health information, significantly elevated body mass index (>70), non-elective operations, non-general anesthesia, and unclean wounds. Outcomes included 30-day emergency department visit, readmission, reoperation, morbidity, and mortality. Univariate analysis was carried out on the sample population, then limited to patients with end-overlap. Subsequently, patients with the least end-overlap were exact-matched to patients with the most. Matching was performed based on key demographic variables-including sex and comorbid status-and attending surgeon, and then outcomes were compared between exact-matched cohorts. RESULTS: Among the entire sample population, no significant associations were found between the degree of end-overlap and short-term adverse events. Limited to cases with any end-overlap, increasing overlap was associated with increased 30-day emergency department visits ( P =0.049) but no other adverse outcomes. After controlling for confounding variables in the demographic-matched and demographic/surgeon-matched analyses, no differences in outcomes were observed between exact-matched cohorts. CONCLUSIONS: The degree of overlap after the critical steps of single-level lumbar fusion did not predict adverse short-term outcomes. This suggests that end-overlap is a safe practice within this surgical population.

Household income is associated with return to surgery following discectomy for far lateral disc herniation.

BACKGROUND: Numerous studies have demonstrated that household income is independently predictive of postsurgical morbidity and mortality, but few studies have elucidated this relationship in a purely spine surgery population. This study aims to correlate household income with adverse events after discectomy for far lateral disc herniation (FLDH). METHODS: All adult patients (N.=144) who underwent FLDH surgery at a single, multihospital, 1659-bed university health system (2013-2020) were retrospectively analyzed. Univariate logistic regression was used to evaluate the relationship between household income and adverse postsurgical events, including unplanned hospital readmissions, ED visits, and reoperations. RESULTS: Mean age of the population was 61.72±11.55 years. Mean household income was $78,283±26,996; 69 (47.9%) were female; and 126 (87.5%) were non-Hispanic white. Ninety-two patients underwent open and fifty-two underwent endoscopic FLDH surgery. Each additional dollar decrease in household income was significantly associated with increased risk of reoperation of any kind within 90-days, but not 30-days, after the index admission. However, household income did not predict risk of readmission or ED visit within either 30-days or 30-90-days postsurgery. CONCLUSIONS: These findings suggest that household income may predict reoperation following FLDH surgery. Additional research is warranted into the relationship between household income and adverse neurosurgical outcomes.

Characterizing the Next Generation of Neurosurgeons: A Descriptive Analysis and Publicly Available Web Application of Neurosurgery Residency Programs' Website Data.

OBJECTIVE: Neurosurgery program websites serve as a valuable resource for applicants. However, each website exists in isolation, and it can be difficult to understand the general trends in U.S. neurosurgery resident demographics. In the present study, we collected data from program websites and analyzed the trends in the demographics of the current U.S. neurosurgery residents. METHODS: We used a program list obtained from the American Association of Medical Colleges Electronic Residency Application System to extract data from the current resident complement listed in each program's website, including program, year in program, medical school, sex (male vs. female), graduate and/or PhD degrees, and assessed the trends during 7 years of resident data using linear regression. RESULTS: We identified 116 neurosurgery residency programs in the United States, with 111 providing information on their current resident complement, yielding a dataset of 1599 residents. Of these 1599 residents, 348 (22%) were female, 301 (19%) had a graduate degree in addition to an MD or DO degree, 151 (9.4%) had a PhD degree, 300 (19%) had matched at the program affiliated with their medical school, and 121 (7.6%) had graduated from a foreign medical school. The proportion of matriculating female residents had increased an average of 2.1% annually (95% confidence interval, 0.6%-3.7%) from 2015 to 2021. The other demographic data had not changed significantly during the same period. CONCLUSIONS: In addition to summarizing the current resident demographics, our analysis identified a significant increase in the proportion of female residents between 2015 (15.1%) and 2021 (25.6%). This publicly available dataset should enable additional analyses of the evolution of neurosurgery resident demographics.

Interhemispheric gravity-assisted approach for microsurgical resection of a splenium arteriovenous malformation.

The parietal interhemispheric approach employing gravity retraction with skeletonization of bridging veins provides an excellent operative window for safe, curative resection of splenial arteriovenous malformations.

Postoperative Outcomes and Resource Utilization Following Open vs Endoscopic Far Lateral Lumbar Discectomy.

BACKGROUND: Operative approaches for far lateral disc herniation (FLDH) repair may be classified as open or minimally invasive. The present study aims to compare postoperative outcomes and resource utilization between patients undergoing open and endoscopic (one such minimally invasive approach) FLDH surgeries. METHODS: A total of 144 consecutive adult patients undergoing FLDH repair at a single, university health system over an 8-year period (2013-2020) were retrospectively reviewed. Patients were divided into 2 cohorts: "open" (n = 92) and "endoscopic" (n = 52). Logistic regression was performed to evaluate the impact of procedural type on postoperative outcomes, and resource utilization metrics were compared between cohorts using χ 2 test (for categorical variables) or t test (for continuous variables). Primary postsurgical outcomes included readmissions, reoperations, emergency department visits, and neurosurgery outpatient office visits within 90 days of the index operation. Primary resource utilization outcomes included total direct cost of the procedure and length of stay. Secondary measures included discharge disposition, operative length, and duration of follow-up. RESULTS: No differences were observed in adverse postoperative events. Patients undergoing open FLDH surgery were more likely to attend outpatient visits within 30 days (P = 0.016). Although direct operating room cost was lower (P < 0.001) for open procedures, length of hospital stay was longer (P < 0.001). Patients undergoing open surgery also demonstrated less favorable discharge dispositions, longer operative length, and greater duration of follow-up. CONCLUSIONS: While both procedure types represent viable options for FLDH, endoscopic surgeries appear to achieve comparable clinical outcomes with decreased perioperative resource utilization. CLINICAL RELEVANCE: The present study suggests that endoscopic FLDH repairs do not lead to inferior outcomes but may decrease utilization of perioperative resources.

Prognosticators of Functional Outcome After Supratentorial Minimally Invasive Intracranial Hemorrhage Evacuation With Tubular Retractor Systems.

BACKGROUND AND OBJECTIVES: Prognosticators of good functional outcome after minimally invasive surgical (MIS) intracranial hemorrhage (ICH) evacuation are poorly defined. This study aims to investigate clinical and radiographic prognosticators of poor functional outcome after MIS evacuation of ICH with tubular retractor systems. METHODS: Single-center retrospective review of adult (age ≥18 years) patients who underwent surgical evacuation of a spontaneous supratentorial ICH evacuation using tubular retractors from 2013 to 2022 was performed. Clinical and radiographic factors, such as antiplatelet/anticoagulant use, initial NIH Stroke Scale, ICH score, premorbid modified Rankin Scale (mRS), intraventricular hemorrhage (IVH) severity according to the modified Graeb scale, and preoperative/postoperative ICH volume, were collected. The main outcome was poor functional outcome, defined as mRS score of 4-6 within 1 year postoperatively. RESULTS: Eighty-eight patients were included. Clinical follow-up data were available for 64 (73%) patients. Of those, 43 (67%) had a poor functional outcome. On multivariate Cox regression, postoperative ICH volume ≥15 mL (hazard ratio [HR] = 2.46 [95% CI: 1.25-4.87]; P = .010) and higher modified Graeb score (HR = 1.04 [95% CI: 1-1.1]; P = .035] significantly increased the risk of poor functional outcome. Elevated postoperative ICH volume was predicted by the presence of lobar ICH (vs nonlobar, OR = 3.32 [95% CI: 1.01-11.55]; P = .043) and higher preoperative ICH volume (OR = 1.05 [1.02-1.08]; P < .001). A minimum of 60% ICH evacuation yielded an improvement in mRS 4-6 rates (HR 0.3 [95% CI: 0.1-0.8], P = .013). In patients without IVH and with a >80% ICH evacuation, the rate of mRS 4-6 was 42% compared with 67% in the whole patient sample ( P = .017). CONCLUSION: Increased IVH volumes and residual postoperative ICH volumes are associated with poor functional outcome after MIS ICH evacuation. Postoperative ICH volume was associated with lobar ICH location as well as preoperative ICH volume. These factors may help to prognosticate patient outcomes and improve selection criteria for MIS ICH evacuation techniques.

Flow diversion for the treatment of intracranial bifurcation aneurysms: a systematic review and meta-analysis.

BACKGROUND: Flow diversion (FD: flow diversion, flow diverter) is an endovascular treatment for many intracranial aneurysm types; however, limited reports have explored the use of FDs in bifurcation aneurysm management. We analyzed the safety and efficacy of FD for the management of intracranial bifurcation aneurysms. METHODS: A systematic review identified original research articles that used FD for treating intracranial bifurcation aneurysms. Articles with >4 patients that reported outcomes on the use of FDs for the management of bifurcation aneurysms along the anterior communicating artery (AComA), internal carotid artery terminus (ICAt), basilar apex (BA), or middle cerebral artery bifurcation (MCAb) were included. Meta-analysis was performed using a random effects model. RESULTS: 19 studies were included with 522 patients harboring 534 bifurcation aneurysms (mean size 9 mm, 78% unruptured). Complete aneurysmal occlusion rate was 68% (95% CI 58.7% to 76.1%, I2=67%) at mean angiographic follow-up of 16 months. Subgroup analysis of FD as a standalone treatment estimated a complete occlusion rate of 69% (95% CI 50% to 83%, I2=38%). The total complication rate was 22% (95% CI 16.7% to 28.6%, I2=51%), largely due to an ischemic complication rate of 16% (95% CI 10.8% to 21.9%, I2=55%). The etiologies of ischemic complications were largely due to jailed artery hypoperfusion (47%) and in-stent thrombosis (38%). 7% of patients suffered permanent symptomatic complications (95% CI 4.5% to 9.8%, I2=6%). CONCLUSION: FD treatment of bifurcation aneurysms has a modest efficacy and relatively unfavorable safety profile. Proceduralists may consider reserving FD as a treatment option if no other surgical or endovascular therapy is deemed feasible.

Endoscopic fenestration of a giant frontal arachnoid cyst: Operative technique and anatomical nuances.

Endoscopic fenestration is best as it is minimally invasive and does not require hardware in the surgical site (Figure 1). This case shows the safety of endoscopic fenestration and the utility of operative adjuncts (J Korean Med Sci. 1999;14:443; Neurosurg Focus. 2005;19:E7).

A Scoping Review of the Literature on the Relationship Between Social and Structural Determinants of Health and Neurosurgical Outcomes.

In the present study, we performed a scoping review of the social and structural determinant of health (SSDOH)-related academic literature from neurosurgery. To identify the studies to include or consider for our systematic review, we worked with a medical librarian to develop detailed search strategies for each database. The search was limited to studies reported from January 1, 1990 to December 3, 2020. All reports retrieved from the database searches were exported and stored in EndNote X.9 bibliographic and reference manager (Clarivate, Philadelphia, Pennsylvania, USA). The reports were screened by title and abstract independently by two of the co-authors (G.G. and A.O.). Any disagreements between the 2 reviewers were resolved by a third reviewer, who was unaware of the decisions of the primary reviewers. The search resulted in 5940 studies. After exclusions during data extraction, 99 studies remained for the final analysis. From the 99 included studies, 6 social determinants were analyzed, with 3 studies evaluating the highest level of educational attainment, 14 studies evaluating gender, 52 studies evaluating race, and 41 studies evaluating economic stability. Studies referencing SSDOH were found in 8 subspecialties, with 40 studies in spine surgery, 4 studies in functional neurosurgery, 14 studies in vascular neurosurgery, 27 studies in cranial oncology, 5 studies in spinal oncology, 5 studies in pediatric neurosurgery, 1 study in trauma, and 3 studies in general/unspecified subspecialties. Research gaps included the remaining neurosurgical subspecialties and numerous other SSDOHs. These gaps should be areas of future study, with the goal of aligning research with new healthcare initiatives and ensuring consideration of SSDOHs.

Postoperative outcomes and the association with overlap before or after the critical step of lumbar fusion.

OBJECTIVE: This study assesses how degree of overlap, either before or after the critical operative portion, affects lumbar fusion outcomes. METHODS: The authors retrospectively studied 3799 consecutive patients undergoing single-level, posterior-only lumbar fusion over 6 years (2013-2019) at a university health system. Outcomes recorded within 30-90 and 0-90 postoperative days included emergency department (ED) visit, readmission, reoperation, overall morbidity, and mortality. Furthermore, morbidity and mortality were recorded for the duration of follow-up. The amount of overlap that occurred before or after the critical portion of surgery was calculated as a percentage of total beginning or end operative time. Subsequent to initial whole-population analysis, coarsened exact-matched cohorts of patients were created with the least and most amounts of either beginning or end overlap. Univariate analysis was performed on both beginning and end overlap exact-matched cohorts, with significance set at p < 0.05. RESULTS: Equivalent outcomes were observed when comparing exact-matched patients. Among the whole population, the degree of beginning overlap was correlated with reduced ED visits within 30-90 and 0-90 days (p = 0.007, p = 0.009; respectively), and less 0-90 day morbidity (p = 0.037). Degree of end overlap was correlated with fewer 30-90 day ED visits (p = 0.015). When comparing only patients with overlap, degree of beginning overlap was correlated with fewer 0-90 day reoperations (p = 0.022), and no outcomes were correlated with degree of end overlap. CONCLUSIONS: The degree of overlap before or after the critical step of surgery does not lead to worse outcomes after lumbar fusion.