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Rinchen Phuntsok, Chase W. Provost, Andrew T. Dailey, Douglas L. Brockmeyer and Benjamin J. Ellis

OBJECTIVE

Prior studies have provided conflicting evidence regarding the contribution of key ligamentous structures to atlantoaxial (AA) joint stability. Many of these studies employed cadaveric techniques that are hampered by the inherent difficulties of testing isolated-injury scenarios. Analysis with validated finite element (FE) models can overcome some of these limitations. In a previous study, the authors completed an FE analysis of 5 subject-specific craniocervical junction (CCJ) models to investigate the biomechanics of the occipitoatlantal joint and identify the ligamentous structures essential for its stability. Here, the authors use these same CCJ FE models to investigate the biomechanics of the AA joint and to identify the ligamentous structures essential for its stability.

METHODS

Five validated CCJ FE models were used to simulate isolated- and combined ligamentous–injury scenarios of the transverse ligament (TL), tectorial membrane (TM), alar ligament (AL), occipitoatlantal capsular ligament, and AA capsular ligament (AACL). All models were tested with rotational moments (flexion-extension, axial rotation, and lateral bending) and anterior translational loads (C2 constrained with anterior load applied to the occiput) to simulate physiological loading and to assess changes in the atlantodental interval (ADI), a key radiographic indicator of instability.

RESULTS

Isolated AACL injury significantly increased range of motion (ROM) under rotational moment at the AA joint for flexion, lateral bending, and axial rotation, which increased by means of 28.0% ± 10.2%, 43.2% ± 15.4%, and 159.1% ± 35.1%, respectively (p ≤ 0.05 for all). TL removal simulated under translational loads resulted in a significant increase in displacement at the AA joint by 89.3% ± 36.6% (p < 0.001), increasing the ADI from 2.7 mm to 4.5 mm. An AACL injury combined with an injury to any other ligament resulted in significant increases in ROM at the AA joint, except when combined with injuries to both the TM and the ALs. Similarly, injury to the TL combined with injury to any other CCJ ligament resulted in a significant increase in displacement at the AA joint (significantly increasing ADI) under translational loads.

CONCLUSIONS

Using FE modeling techniques, the authors showed a significant reliance of isolated- and combined ligamentous–injury scenarios on the AACLs and TL to restrain motion at the AA joint. Isolated injuries to other structures alone, including the AL and TM, did not result in significant increases in either AA joint ROM or anterior displacement.

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Marcus D. Mazur and Andrew T. Dailey

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Brandon Sherrod, Michael Karsy, Jian Guan, Andrea A. Brock, Ilyas M. Eli, Erica F. Bisson and Andrew T. Dailey

OBJECTIVE

The objective of this study was to investigate the effect of hospital type and patient transfer during the treatment of patients with vertebral fracture and/or spinal cord injury (SCI).

METHODS

The National Inpatient Sample (NIS) database was queried to identify patients treated in Utah from 2001 to 2011 for vertebral column fracture and/or SCI (ICD-9-CM codes 805, 806, and 952). Variables related to patient transfer into and out of the index hospital were evaluated in relation to patient disposition, hospital length of stay, mortality, and cost.

RESULTS

A total of 53,644 patients were seen (mean [± SEM] age 55.3 ± 0.1 years, 46.0% females, 90.2% white), of which 10,620 patients were transferred from another institution rather than directly admitted. Directly admitted (vs transferred) patients showed a greater likelihood of routine disposition (54.4% vs 26.0%) and a lower likelihood of skilled nursing facility disposition (28.2% vs 49.2%) (p < 0.0001). Directly admitted patients also had a significantly shorter length of stay (5.6 ± 6.7 vs 7.8 ± 9.5 days, p < 0.0001) and lower total charges ($26,882 ± $37,348 vs $42,965 ± $52,118, p < 0.0001). A multivariable analysis showed that major operative procedures (hazard ratio [HR] 1.7, 95% confidence interval [CI] 1.4–2.0, p < 0.0001) and SCI (HR 2.1, 95% CI 1.6–2.8, p < 0.0001) were associated with reduced survival whereas patient transfer was associated with better survival rates (HR 0.4, 95% CI 0.3–0.5, p < 0.0001). A multivariable analysis of cost showed that disposition (β = 0.1), length of stay (β = 0.6), and major operative procedure (β = 0.3) (p < 0.0001) affected cost the most.

CONCLUSIONS

Overall, transferred patients had lower mortality but greater likelihood for poor outcomes, longer length of stay, and higher cost compared with directly admitted patients. These results suggest some significant benefits to transferring patients with acute injury to facilities capable of providing appropriate treatment, but also support the need to further improve coordinated care of transferred patients, including surgical treatment and rehabilitation.

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Rinchen Phuntsok, Benjamin J. Ellis, Michael R. Herron, Chase W. Provost, Andrew T. Dailey and Douglas L. Brockmeyer

OBJECTIVE

There is contradictory evidence regarding the relative contribution of the key stabilizing ligaments of the occipitoatlantal (OA) joint. Cadaveric studies are limited by the nature and the number of injury scenarios that can be tested to identify OA stabilizing ligaments. Finite element (FE) analysis can overcome these limitations and provide valuable data in this area. The authors completed an FE analysis of 5 subject-specific craniocervical junction (CCJ) models to investigate the biomechanics of the OA joint and identify the ligamentous structures essential for stability.

METHODS

Isolated and combined injury scenarios were simulated under physiological loads for 5 validated CCJ FE models to assess the relative role of key ligamentous structures on OA joint stability. Each model was tested in flexion-extension, axial rotation, and lateral bending in various injury scenarios. Isolated ligamentous injury scenarios consisted of either decreasing the stiffness of the OA capsular ligaments (OACLs) or completely removing the transverse ligament (TL), tectorial membrane (TM), or alar ligaments (ALs). Combination scenarios were also evaluated.

RESULTS

An isolated OACL injury resulted in the largest percentage increase in all ranges of motion (ROMs) at the OA joint compared with the other isolated injuries. Flexion, extension, lateral bending, and axial rotation significantly increased by 12.4% ± 7.4%, 11.1% ± 10.3%, 83.6% ± 14.4%, and 81.9% ± 9.4%, respectively (p ≤ 0.05 for all). Among combination injuries, OACL+TM+TL injury resulted in the most consistent significant increases in ROM for both the OA joint and the CCJ during all loading scenarios. OACL+AL injury caused the most significant percentage increase for OA joint axial rotation.

CONCLUSIONS

These results demonstrate that the OACLs are the key stabilizing ligamentous structures of the OA joint. Injury of these primary stabilizing ligaments is necessary to cause OA instability. Isolated injuries of TL, TM, or AL are unlikely to result in appreciable instability at the OA joint.

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Jian Guan, Michael Karsy, Andrea A. Brock, William T. Couldwell, John R. W. Kestle, Randy L. Jensen, Andrew T. Dailey, Erica F. Bisson and Richard H. Schmidt

OBJECTIVE

Overlapping surgery remains a controversial topic in the medical community. Although numerous studies have examined the safety profile of overlapping operations, there are few data on its financial impact. The authors assessed direct hospital costs associated with neurosurgical operations during periods before and after a more stringent overlapping surgery policy was implemented.

METHODS

The authors retrospectively reviewed the records of nonemergency neurosurgical operations that took place during the periods from June 1, 2014, to October 31, 2014 (pre–policy change), and from June 1, 2016, to October 31, 2016 (post–policy change), by any of the 4 senior neurosurgeons authorized to perform overlapping cases during both periods. Cost data as well as demographic, surgical, and hospitalization-related variables were obtained from an institutional tool, the Value-Driven Outcomes database.

RESULTS

A total of 625 hospitalizations met inclusion criteria for cost analysis; of these, 362 occurred prior to the policy change and 263 occurred after the change. All costs were reported as a proportion of the average total hospitalization cost for the entire cohort. There was no significant difference in mean total hospital costs between the prechange and postchange period (0.994 ± 1.237 vs 1.009 ± 0.994, p = 0.873). On multivariate linear regression analysis, neither the policy change (p = 0.582) nor the use of overlapping surgery (p = 0.273) was significantly associated with higher total hospital costs.

CONCLUSIONS

A more restrictive overlapping surgery policy was not associated with a reduction in the direct costs of hospitalization for neurosurgical procedures.

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Thomas J. Buell, Davis G. Taylor, Ching-Jen Chen and Bhiken I. Naik

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Vijay M. Ravindra, Kaine Onwuzulike, Robert S. Heller, Robert Quigley, John Smith, Andrew T. Dailey and Douglas L. Brockmeyer

OBJECTIVE

Previous reports have addressed the short-term response of patients with Chiari-related scoliosis (CRS) to suboccipital decompression and duraplasty (SODD); however, the long-term behavior of the curve has not been well defined. The authors undertook a longitudinal study of a cohort of patients who underwent SODD for CRS to determine whether there are factors related to Chiari malformation (CM) that predict long-term scoliotic curve behavior and need for deformity correction.

METHODS

The authors retrospectively reviewed cases in which patients underwent SODD for CRS during a 14-year period at a single center. Clinical (age, sex, and associated disorders/syndromes) and radiographic (CM type, tonsillar descent, pBC2 line, clival-axial angle [CXA], syrinx length and level, and initial Cobb angle) information was evaluated to identify associations with the primary outcome: delayed thoracolumbar fusion for progressive scoliosis.

RESULTS

Twenty-eight patients were identified, but 4 were lost to follow-up and 1 underwent fusion within a year. Among the remaining 23 patients, 11 required fusion surgery at an average of 88.3 ± 15.4 months after SODD, including 7 (30%) who needed fusion more than 5 years after SODD. On univariate analysis, a lower CXA (131.5° ± 4.8° vs 146.5° ± 4.6°, p = 0.034), pBC2 > 9 mm (64% vs 25%, p = 0.06), and higher initial Cobb angle (35.1° ± 3.6° vs 22.8° ± 4.0°, p = 0.035) were associated with the need for thoracolumbar fusion. Multivariable modeling revealed that lower CXA was independently associated with a need for delayed thoracolumbar fusion (OR 1.12, p = 0.0128).

CONCLUSIONS

This investigation demonstrates the long-term outcome and natural history of CRS after SODD. The durability of the effect of SODD on CRS and curve behavior is poor, with late curve progression occurring in 30% of patients. Factors associated with CRS progression include an initial pBC2 > 9 mm, lower CXA, and higher Cobb angle. Lower CXA was an independent predictor of delayed thoracolumbar fusion. Further study is necessary on a larger cohort of patients to fully elucidate this relationship.

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Jian Guan, Michael Karsy, Andrea A. Brock, William T. Couldwell, John R. W. Kestle, Randy L. Jensen, Andrew T. Dailey and Richard H. Schmidt

OBJECTIVE

Recently, overlapping surgery has been a source of controversy both in the popular press and within the academic medical community. There have been no studies examining the possible effects of more stringent overlapping surgery restrictions. At the authors’ institution, a new policy was implemented that restricts attending surgeons from starting a second case until all critical portions of the first case that could require the attending surgeon’s involvement are completed. The authors examined the impact of this policy on complication rates, neurosurgical resident education, and wait times for neurosurgical procedures.

METHODS

The authors performed a retrospective chart review of nonemergency neurosurgical procedures performed over two periods—from June 1, 2014, to October 31, 2014 (pre–policy change) and from June 1, 2016, to October 31, 2016 (post–policy change)—by any of 4 senior neurosurgeons at a single institution who were authorized to schedule overlapping cases. Information on preoperative evaluation, patient demographics, premorbid conditions, surgical variables, and postoperative course were collected and analyzed.

RESULTS

Six hundred fifty-three patients met inclusion criteria for complications analysis. Of these, 378 (57.9%) underwent surgery before the policy change. On multivariable regression analysis, neither overlapping surgery (odds ratio [OR] 1.072, 95% confidence interval [CI] 0.710–1.620) nor the overlapping surgery policy change (OR 1.057, 95% CI 0.700–1.596) was associated with overall complication rates. Similarly, neither overlapping surgery (OR 1.472, 95% CI 0.883–2.454) nor the overlapping surgery policy change (OR 1.251, 95% CI 0.748–2.091) was associated with numbers of serious complications. After the policy change, the percentage of procedures in which the senior assistant was a postresidency fellow increased significantly, from 11.9% to 34.2% (p < 0.001). In a multiple linear regression analysis of surgery wait times, patients undergoing surgery after the policy change had significantly longer delays from the decision to operate until the actual neurosurgical procedure (p < 0.001).

CONCLUSIONS

At the authors’ institution, further restriction of overlapping surgery was not associated with a reduction in overall or serious complications. Resident involvement in neurosurgical procedures decreased significantly after the policy change, and this study suggests that wait times for neurosurgical procedures also significantly lengthened.

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Jian Guan, Chad D. Cole, Meic H. Schmidt and Andrew T. Dailey

OBJECTIVE

Blood loss during surgery for thoracolumbar scoliosis often requires blood product transfusion. Rotational thromboelastometry (ROTEM) has enabled the more targeted treatment of coagulopathy, but its use in deformity surgery has received limited study. The authors investigated whether the use of ROTEM reduces transfusion requirements in this case-control study of thoracolumbar deformity surgery.

METHODS

Data were prospectively collected on all patients who received ROTEM-guided blood product management during long-segment (≥ 7 levels) posterior thoracolumbar fusion procedures at a single institution from April 2015 to February 2016. Patients were matched with a group of historical controls who did not receive ROTEM-guided therapy according to age, fusion segments, number of osteotomies, and number of interbody fusion levels. Demographic, intraoperative, and postoperative transfusion requirements were collected on all patients. Univariate analysis of ROTEM status and multiple linear regression analysis of the factors associated with total in-hospital transfusion volume were performed, with p < 0.05 considered to indicate statistical significance.

RESULTS

Fifteen patients who received ROTEM-guided therapy were identified and matched with 15 non-ROTEM controls. The mean number of fusion levels was 11 among all patients, with no significant differences between groups in terms of fusion levels, osteotomy levels, interbody fusion levels, or other demographic factors. Patients in the non-ROTEM group required significantly more total blood products during their hospitalization than patients in the ROTEM group (8.5 ± 4.2 units vs 3.71 ± 2.8 units; p = 0.001). Multiple linear regression analysis showed that the use of ROTEM (p = 0.016) and a lower number of fused levels (p = 0.022) were associated with lower in-hospital transfusion volumes.

CONCLUSIONS

ROTEM use during thoracolumbar deformity correction is associated with lower transfusion requirements. Further investigation will better define the role of ROTEM in transfusion during deformity surgery.