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Letter to the Editor. Class imbalance in machine learning for neurosurgical outcome prediction: are our models valid?

Victor E. Staartjes and Marc L. Schröder

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Revisions for screw malposition and clinical outcomes after robot-guided lumbar fusion for spondylolisthesis

Marc L. Schröder and Victor E. Staartjes

OBJECTIVE

The accuracy of robot-guided pedicle screw placement has been proven to be high, but little is known about the impact of such guidance on clinical outcomes such as the rate of revision surgeries for screw malposition. In addition, there are very few data about the impact of robot-guided fusion on patient-reported outcomes (PROs). Thus, the clinical benefit for the patient is unclear. In this study, the authors analyzed revision rates for screw malposition and changes in PROs following minimally invasive robot-guided pedicle screw fixation.

METHODS

A retrospective cohort study of patients who had undergone minimally invasive posterior lumbar interbody fusion (MI-PLIF) or minimally invasive transforaminal lumbar interbody fusion was performed. Patients were followed up clinically at 6 weeks, 12 months, and 24 months after treatment and by mailed questionnaire in March 2016 as a final follow-up. Visual analog scale (VAS) scores for back and leg pain severity, Oswestry Disability Index (ODI), screw revisions, and socio-demographic factors were analyzed. A literature review was performed, comparing the incidence of intraoperative screw revisions and revision surgery for screw malposition in robot-guided, navigated, and freehand fusion procedures.

RESULTS

Seventy-two patients fit the study inclusion criteria and had a mean follow up of 32 ± 17 months. No screws had to be revised intraoperatively, and no revision surgery for screw malposition was needed. In the literature review, the authors found a higher rate of intraoperative screw revisions in the navigated pool than in the robot-guided pool (p < 0.001, OR 9.7). Additionally, a higher incidence of revision surgery for screw malposition was observed for freehand procedures than for the robot-guided procedures (p < 0.001, OR 8.1). The VAS score for back pain improved significantly from 66.9 ± 25.0 preoperatively to 30.1 ± 26.8 at the final follow-up, as did the VAS score for leg pain (from 70.6 ± 22.8 to 24.3 ± 28.3) and ODI (from 43.4 ± 18.3 to 16.2 ± 16.7; all p < 0.001). Undergoing PLIF, a high body mass index, smoking status, and a preoperative ability to work were identified as predictors of a reduction in back pain. Length of hospital stay was 2.4 ± 1.1 days and operating time was 161 ± 50 minutes. Ability to work increased from 38.9% to 78.2% of patients (p < 0.001) at the final follow-up, and 89.1% of patients indicated they would choose to undergo the same treatment again.

CONCLUSIONS

In adults with low-grade spondylolisthesis, the data demonstrated a benefit in using robotic guidance to reduce the rate of revision surgery for screw malposition as compared with other techniques of pedicle screw insertion described in peer-reviewed publications. Larger comparative studies are required to assess differences in PROs following a minimally invasive approach in spinal fusion surgeries compared with other techniques.

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Letter to the Editor. Reappraising role of clinical evaluations in degenerative lumbar spine pathologies

Sunil Munakomi

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The five-repetition sit-to-stand test: evaluation of a simple and objective tool for the assessment of degenerative pathologies of the lumbar spine

Victor E. Staartjes and Marc L. Schröder

OBJECTIVE

Recently, objective functional tests have generated interest since they can supplement an objective dimension to clinical assessment. The five-repetition sit-to-stand (5R-STS) test is a quick and objective tool that tests movements frequently used in everyday life. The aim of this prospective study was to evaluate the validity and reliability of the 5R-STS test in patients with degenerative pathologies of the lumbar spine.

METHODS

Patients and healthy volunteers completed the standardized 5R-STS, Roland-Morris Disability Questionnaire (RMDQ), Oswestry Disability Index (ODI), visual analog scale (VAS) for back and leg pain, and EQ-5D for health-related quality of life (HRQOL). To assess convergent validity, the 5R-STS test times were correlated with these questionnaires.

RESULTS

Overall, 157 patients and 80 volunteers were enrolled. Direct correlation with RMDQ (r = 0.49), ODI (r = 0.44), and VAS for back pain (r = 0.31) and indirect correlation with the EQ-5D index (r = −0.41) were observed (p < 0.001). The 5R-STS test showed no correlation with VAS for leg pain and EQ-5D VAS (p > 0.05). In 119 individuals, the 5R-STS test demonstrated excellent test-retest reliability with an intraclass correlation coefficient of 0.98. The upper limit of normal, distinguishing patients with and without objective functional impairment, was identified as 10.35 seconds. A severity stratification classified patients with test times of 10.5–15.2, 15.3–22.0, or greater than 22.0 seconds as having mild, moderate, or severe functional impairment, respectively.

CONCLUSIONS

The 5R-STS test is a simple and effective tool to describe objective functional impairment. A patient able to perform the test in 10.4 seconds can be considered to have no relevant objective functional impairment.

Clinical trial registration no.: NCT03303300 (clinicaltrials.gov)

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Improving recovery after elective degenerative spine surgery: 5-year experience with an enhanced recovery after surgery (ERAS) protocol

Victor E. Staartjes, Marlies P. de Wispelaere, and Marc L. Schröder

OBJECTIVE

Enhanced recovery after surgery (ERAS) has led to a paradigm shift in various surgical specialties. Its application can result in substantial benefits in perioperative healthcare utilization through preoperative physical and mental patient optimization and modulation of the recovery process. Still, ERAS remains relatively new to spine surgery. The authors report their 5-year experience, focusing on ERAS application to a broad population of patients with degenerative spine conditions undergoing elective surgical procedures, including anterior lumbar interbody fusion (ALIF).

METHODS

A multimodal ERAS protocol was applied between November 2013 and October 2018. The authors analyze hospital stay, perioperative outcomes, readmissions, and adverse events obtained from a prospective institutional registry. Elective tubular microdiscectomy and mini-open decompression as well as minimally invasive (MI) anterior or posterior fusion cases were included. Their institutional ERAS protocol contains 22 pre-, intra-, and postoperative elements, including preoperative patient counseling, MI techniques, early mobilization and oral intake, minimal postoperative restrictions, and regular audits.

RESULTS

A total of 2592 consecutive patients were included, with 199 (8%) undergoing fusion. The mean hospital stay was 1.1 ± 1.2 days, with 20 (0.8%) 30-day and 36 (1.4%) 60-day readmissions. Ninety-four percent of patients were discharged after a maximum 1-night hospital stay. Over the 5-year period, a clear trend toward a higher proportion of patients discharged home after a 1-night stay was observed (p < 0.001), with a concomitant decrease in adverse events in the overall cohort (p = 0.025) and without increase in readmissions. For fusion procedures, the rate of 1-night hospital stays increased from 26% to 85% (p < 0.001). Similarly, the average length of hospital stay decreased steadily from 2.4 ± 1.2 days to 1.5 ± 0.3 days (p < 0.001), with a notable concomitant decrease in variance, resulting in an estimated reduction in nursing costs of 46.8%.

CONCLUSIONS

Application of an ERAS protocol over 5 years to a diverse population of patients undergoing surgical procedures, including ALIF, for treatment of degenerative spine conditions was safe and effective, without increase in readmissions. The data from this large case series stress the importance of the multidisciplinary, iterative improvement process to overcome the learning curve associated with ERAS implementation, and the importance of a dedicated perioperative care team. Prospective trials are needed to evaluate spinal ERAS on a higher level of evidence.

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Documented reversal of global ischemia immediately after removal of an acute subdural hematoma

Report of two cases

Marc L. Schröder, J. Paul Muizelaar, and A. John Kuta

✓ The authors report two cases of severe head injury with acute subdural hematoma, in which cerebral blood flow (CBF) and cerebral blood volume (CBV) measurements were obtained prior to evacuation of the subdural hematoma and again immediately after removal. The first patient, a 21-year-old man with a motor response localizing to pain, had a global CBF of 18.2 ml/100 gm/min and a decreased global CBV of 3.7 ml/100 gm at 2.3 hours after injury. Immediately after removal of the subdural hematoma (8.1 hours after injury), CBF and CBV measurements revealed increases to 35.5 ml/100 gm/min and 5.8 ml/100 gm, respectively. The second patient, a 49-year-old woman with a normal flexor motor response to pain, had preoperative global values of 15.8 ml/100 gm/min for CBF and 2.0 ml/100 gm for CBV at 3 hours after injury. Postoperatively (9.3 hours after injury), the CBF and CBV values increased to 41.6 ml/100 gm/min and 4.0 ml/100 gm, respectively. The first patient, with only borderline ischemia and removal of the subdural hematoma within 3 hours, made a good recovery, while the second patient, with prolonged lower levels of CBF, remained in a persistent vegetative state. The low values of preoperative CBV argue for compression of the microcirculation as the cause of ischemia.

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Conflicts of interest in randomized controlled trials reported in neurosurgical journals

Victor E. Staartjes, Anita M. Klukowska, Elena L. Sorba, and Marc L. Schröder

OBJECTIVE

Randomized controlled trials (RCTs) form the basis of today’s evidence-based approach to medicine, and play a critical role in guidelines and the drug and device approval process. Conflicts of interest (COIs) are commonplace in medical research, but little is known about their influence. The authors aimed to evaluate the extent and influence of COIs in recent RCTs published in core neurosurgical journals using a cross-sectional analysis.

METHODS

Through review of 6 general neurosurgical journals, all interventional RCTs published from January 2009 to January 2019 were identified. Because it is difficult to objectively assess study outcome, the authors opted for a strict rating approach based on the statistical significance of unambiguously reported primary endpoints, and the reported statistical protocol.

RESULTS

A total of 129 RCTs met the inclusion criteria. During the study period, the Journal of Neurosurgery published the largest number of RCTs (n = 40, 31%). Any potential COI was disclosed by 57%, and a mean of 12% of authors had a personal COI. Nonfinancial industry involvement was reported in 10%, while 31% and 20% received external support and sponsoring, respectively. Study registration was reported by 56%, while 51% of studies were blinded. Registration showed an increasing trend from 17% to 76% (p < 0.001). The median randomized sample size was 92 (interquartile range 50–153), and 8% were designed to investigate noninferiority or equality. Sixty-three RCTs (49%) unambiguously reported a primary endpoint, of which 13% were composite primary endpoints. In 43%, study outcome was positive, which was associated with a noninferiority design (31% vs 3%, p = 0.007) and a composite primary endpoint (46% vs 9%, p = 0.002). Potential COIs were not significantly associated with study positivity (69% vs 59%, p = 0.433). In the multivariate analysis, only a composite primary endpoint remained predictive of a positive study outcome (odds ratio 6.34, 95% confidence interval 1.51–33.61, p = 0.017).

CONCLUSIONS

This analysis provides an overview of COIs and their potential influence on recent trials published in core neurosurgical journals. Reporting of primary endpoints, study registration, and uniform disclosure of COIs are crucial to ensure the quality of future neurosurgical randomized trials. COIs do not appear to significantly influence the outcome of randomized neurosurgical trials.

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Objective functional impairment in lumbar degenerative disease: concurrent validity of the baseline severity stratification for the five-repetition sit-to-stand test

Anita M. Klukowska, Marc L. Schröder, Martin N. Stienen, and Victor E. Staartjes

OBJECTIVE

The five-repetition sit-to-stand (5R-STS) test provides a new dimension of clinical assessment by capturing objective functional impairment (OFI). Through the utilization of data from two prospective studies, the authors sought to evaluate the concurrent validity of the proposed 5R-STS baseline severity stratification (BSS) for OFI with the following levels based on time to completion in seconds: none, ≤ 10.4; mild, 10.5–15.2; moderate, 15.3–22.0; and severe, > 22.0 seconds.

METHODS

Patients with degenerative diseases of the spine performed the 5R-STS test and completed visual analog scales (VASs) for back and leg pain, the Oswestry Disability Index (ODI), the Roland-Morris Disability Questionnaire (RMDQ), and EQ-5D questionnaires. The degree of OFI severity was assessed based on the previously proposed BSS, and its association with patient-reported scales was evaluated using ANOVA as well as crude and adjusted linear regression models.

RESULTS

Our sample included 240 patients, of whom 101 exhibited no OFI, whereas 80, 34, and 25 were judged to have mild, moderate, and severe OFI, respectively. A higher baseline severity was strongly associated with loss of working ability (p < 0.001), as well as results of all patient-reported scales (p ≤ 0.001), with the exception of the VAS for leg pain (p = 0.556). Crude and adjusted regression analyses corroborated these findings, although only patients with moderate and severe OFI as judged by using the 5R-STS BSS demonstrated clinically relevant differences compared with patients without OFI.

CONCLUSIONS

The degree of OFI—based on the 5R-STS BSS—is strongly associated with measures of back pain, subjective functional impairment, and health-related quality of life. However, leg pain severity is not reflected within the dimension of OFI measured by the 5R-STS. The proposed BSS appears to be a concurrently valid and clinically relevant measure of OFI in patients with degenerative spinal pathologies.

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Magnetic resonance imaging–based synthetic computed tomography of the lumbar spine for surgical planning: a clinical proof-of-concept

Victor E. Staartjes, Peter R. Seevinck, W. Peter Vandertop, Marijn van Stralen, and Marc L. Schröder

OBJECTIVE

Computed tomography scanning of the lumbar spine incurs a radiation dose ranging from 3.5 mSv to 19.5 mSv as well as relevant costs and is commonly necessary for spinal neuronavigation. Mitigation of the need for treatment-planning CT scans in the presence of MRI facilitated by MRI-based synthetic CT (sCT) would revolutionize navigated lumbar spine surgery. The authors aim to demonstrate, as a proof of concept, the capability of deep learning–based generation of sCT scans from MRI of the lumbar spine in 3 cases and to evaluate the potential of sCT for surgical planning.

METHODS

Synthetic CT reconstructions were made using a prototype version of the “BoneMRI” software. This deep learning–based image synthesis method relies on a convolutional neural network trained on paired MRI-CT data. A specific but generally available 4-minute 3D radiofrequency-spoiled T1-weighted multiple gradient echo MRI sequence was supplemented to a 1.5T lumbar spine MRI acquisition protocol.

RESULTS

In the 3 presented cases, the prototype sCT method allowed voxel-wise radiodensity estimation from MRI, resulting in qualitatively adequate CT images of the lumbar spine based on visual inspection. Normal as well as pathological structures were reliably visualized. In the first case, in which a spiral CT scan was available as a control, a volume CT dose index (CTDIvol) of 12.9 mGy could thus have been avoided. Pedicle screw trajectories and screw thickness were estimable based on sCT findings.

CONCLUSIONS

The evaluated prototype BoneMRI method enables generation of sCT scans from MRI images with only minor changes in the acquisition protocol, with a potential to reduce workflow complexity, radiation exposure, and costs. The quality of the generated CT scans was adequate based on visual inspection and could potentially be used for surgical planning, intraoperative neuronavigation, or for diagnostic purposes in an adjunctive manner.

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Association of time to surgery with leg pain after lumbar discectomy: is delayed surgery detrimental?

Alessandro Siccoli, Victor E. Staartjes, Marlies P. de Wispelaere, and Marc L. Schröder

OBJECTIVE

While it has been established that lumbar discectomy should only be performed after a certain waiting period unless neurological deficits are present, little is known about the association of late surgery with outcome. Using data from a prospective registry, the authors aimed to quantify the association of time to surgery (TTS) with leg pain outcome after lumbar discectomy and to identify a maximum TTS cutoff anchored to the minimum clinically important difference (MCID).

METHODS

TTS was defined as the time from the onset of leg pain caused by radiculopathy to the time of surgery in weeks. MCID was defined as a minimum 30% reduction in the numeric rating scale score for leg pain from baseline to 12 months. A Cox proportional hazards model was utilized to quantify the association of TTS with MCID. Maximum TTS cutoffs were derived both quantitatively, anchored to the area under the curve (AUC), and qualitatively, based on cutoff-specific MCID rates.

RESULTS

From a prospective registry, 372 patients who had undergone first-time tubular microdiscectomy were identified; 308 of these patients (83%) obtained an MCID. Attaining an MCID was associated with a shorter TTS (HR 0.718, 95% CI 0.546–0.945, p = 0.018). Effect size was preserved after adjustment for potential confounders. The optimal maximum TTS was estimated at 23.5 weeks based on the AUC, while the cutoff-specific method suggested 24 weeks. Discectomy after this cutoff starts to yield MCID rates under 80%. The 24-week cutoff also coincided with the time point after which the specificity for MCID first drops below 50% and after which the negative predictive value for nonattainment of MCID first surpasses ≥ 20%.

CONCLUSIONS

The study findings suggest that late lumbar discectomy is linked with poorer patient-reported outcomes and that—in accordance with the literature—a maximum TTS of 6 months should be aimed for.