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Spinal instrumentation in infants, children, and adolescents: a review

JNSPG 75th Anniversary Invited Review Article

Stephen Mendenhall, Dillon Mobasser, Katherine Relyea and Andrew Jea

OBJECTIVE

The evolution of pediatric spinal instrumentation has progressed in the last 70 years since the popularization of the Harrington rod showing the feasibility of placing spinal instrumentation into the pediatric spine. Although lacking in pediatric-specific spinal instrumentation, when possible, adult instrumentation techniques and tools have been adapted for the pediatric spine. A new generation of pediatric neurosurgeons with interest in complex spine disorder has pushed the field forward, while keeping the special nuances of the growing immature spine in mind. The authors sought to review their own experience with various types of spinal instrumentation in the pediatric spine and document the state of the art for pediatric spine surgery.

METHODS

The authors retrospectively reviewed patients in their practice who underwent complex spine surgery. Patient demographics, operative data, and perioperative complications were recorded. At the same time, the authors surveyed the literature for spinal instrumentation techniques that have been utilized in the pediatric spine. The authors chronicle the past and present of pediatric spinal instrumentation, and speculate about its future.

RESULTS

The medical records of the first 361 patients who underwent 384 procedures involving spinal instrumentation from July 1, 2007, to May 31, 2018, were analyzed. The mean age at surgery was 12 years and 6 months (range 3 months to 21 years and 4 months). The types of spinal instrumentation utilized included occipital screws (94 cases); C1 lateral mass screws (115 cases); C2 pars/translaminar screws (143 cases); subaxial cervical lateral mass screws (95 cases); thoracic and lumbar spine traditional-trajectory and cortical-trajectory pedicle screws (234 cases); thoracic and lumbar sublaminar, subtransverse, and subcostal polyester bands (65 cases); S1 pedicle screws (103 cases); and S2 alar-iliac/iliac screws (56 cases). Complications related to spinal instrumentation included hardware-related skin breakdown (1.8%), infection (1.8%), proximal junctional kyphosis (1.0%), pseudarthroses (1.0%), screw malpositioning (0.5%), CSF leak (0.5%), hardware failure (0.5%), graft migration (0.3%), nerve root injury (0.3%), and vertebral artery injury (0.3%).

CONCLUSIONS

Pediatric neurosurgeons with an interest in complex spine disorders in children should develop a comprehensive armamentarium of safe techniques for placing rigid and nonrigid spinal instrumentation even in the smallest of children, with low complication rates. The authors’ review provides some benchmarks and outcomes for comparison, and furnishes a historical perspective of the past and future of pediatric spine surgery.

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Scott L. Parker, David N. Shau, Stephen K. Mendenhall and Matthew J. McGirt

Object

Revision lumbar fusion procedures are technically challenging and can be associated with tremendous health care resource utilization and cost. There is a paucity of data regarding specific factors that significantly contribute to increased cost of care. In light of this, the authors set out to identify independent risk factors predictive of increasing 2-year direct health care costs after revision lumbar fusion.

Methods

One hundred fifty patients undergoing revision instrument-assisted fusion for adjacent-segment disease (50 cases), pseudarthrosis (47 cases), or same-level stenosis (53 cases) were included in this study. Patient demographics, comorbidities, preoperative health states as assessed by patient-reported outcome questionnaires and perioperative complications were collected and analyzed. Two-year back-related medical resource utilization and direct health care costs were assessed. The independent association of all variables to increasing cost was assessed using multivariate linear regression analysis.

Results

There was a wide range ($24,935–$63,769) in overall 2-year direct costs for patients undergoing revision lumbar fusion (mean $32,915 ± $8344 [± SD]). Preoperative variables independently associated with 2-year direct health care costs included diagnosis of congestive heart failure, more severe leg pain (visual analog scale), greater back-related disability (Oswestry Disability Index), and worse mental health (12-Item Short Form Health Survey Mental Component Summary score). There was a 1.1- to 1.2-fold increase in cost for patients in the greatest quartiles compared with those in the lowest quartiles for these variables. Surgical site infection, return to the operating room, and spine-related hospital readmission during the 90-day global health period were postoperative variables independently associated with 2-year cost. Patients in the greatest versus lowest quartiles had a 1.7- to 1.9-fold increase in cost for these variables.

Conclusions

Revision lumbar fusion can be associated with considerable 2-year health care costs. These costs can also vary widely among patients, as evidenced by the 2.6-fold overall cost range in this series. Although comorbidities and preoperative severity of disease states contribute to cost of care, the primary drivers of increased cost include perioperative complications such as surgical site infection, return to the operating room, and readmission during the global health period. Measures focused on health service improvement will be most successful in reducing the cost of care for patients undergoing revision lumbar fusion.

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Clark Watts, Robert C. Mendenhall, Stephen E. Radecki and Roger A. Girard

✓ This paper reports a national study of physicians in 24 medical and surgical specialties, and reveals the opinions of neurosurgeons and their professional colleagues with regard to the adequacy of the supply of neurosurgical manpower. Among neurosurgeons, 30.4% believe the supply to be excessive, 60.1% think it is about right, 7.5% believe that there is a shortage, and 2.0% have no opinion. Neurologists' opinions do not differ significantly from those of neurosurgeons, but physicians and surgeons in 22 other specialties are significantly less likely to regard the supply as excessive, and are more likely to perceive a shortage. Primary care physicians, as a group, are most likely to perceive a shortage, and least likely to indicate an excess. Among the 24 specialties studied, 9.3% of physicians believe the supply of neurosurgeons to be excessive, 55.1% think it is about right, 22.9% believe that there is a shortage, and 12.8% have no opinion.

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Scott L. Parker, Saniya S. Godil, David N. Shau, Stephen K. Mendenhall and Matthew J. McGirt

Object

Treatment effectiveness following spine surgery is usually gauged with the help of patient-reported outcome (PRO) questionnaires. Although these questionnaires assess pain, disability, and general health state, their numerical scores lack direct, clinically significant meaning. Thus, the concept of minimum clinically important difference (MCID) has been introduced, which indicates the smallest change in an outcome measure that reflects clinically meaningful improvement to patients. The authors set out to determine anterior cervical discectomy and fusion (ACDF)–specific MCID values for the visual analog scale (VAS), Neck Disability Index (NDI), 12-Item Short-Form Health Survey (SF-12), and EQ-5D (the EuroQol health survey) in patients undergoing ACDF for cervical radiculopathy.

Methods

Data on 69 patients who underwent ACDF for cervical radiculopathy were collected in the authors' web-based, prospective registry during the study enrollment period. Patient-reported outcome questionnaires (VAS–neck pain [NP]), VAS–arm pain [AP], NDI, SF-12, and EQ-5D) were administered preoperatively and 3 months postoperatively, allowing 3-month change scores to be calculated. Four established calculation methods were used to calculate anchor-based MCID values using the North American Spine Society (NASS) patient satisfaction scale as the anchor: 1) average change, 2) minimum detectable change (MDC), 3) change difference, and 4) receiver operating characteristic (ROC) curve analysis.

Results

Sixty-one patients (88%) were available at follow-up. At 3 months postoperatively, statistically significant improvement (p < 0.001) was observed for the following PROs assessed: VAS-NP (2.7 ± 3.3), VAS-AP (3.7 ± 3.6), NDI (23.2% ± 19.7%), SF-12 physical component score (PCS; 10.7 ± 9.7), and EQ-5D (0.20 ± 0.23 QALY). Improvement on the SF-12 mental component score (MCS) trended toward significance (3.4 ± 11.4, p = 0.07). The 4 MCID calculation methods generated a range of MCID values for each of the PROs: VAS-NP 2.6–4.0, VAS-AP 2.4–4.2, NDI 16.0%–27.6%, SF-12 PCS 7.0–12.2, SF-12 MCS 0.0–7.2, and EQ-5D 0.05–0.24 QALY. The maximum area under the curve (AUC) was observed for NDI (0.80), and the minimum AUC was observed for SF-12 MCS (0.66) and EQ-5D (0.67). Based on the MDC approach, the MCID threshold was 2.6 points for VAS-NP, 4.1 points for VAS-AP, 17.3% for NDI, 8.1 points for SF-12 PCS, 4.7 points for SF-12 MCS, and 0.24 QALY for EQ-5D. The mean improvement in patient scores at 3 months surpassed the MCID threshold for VAS-NP, NDI, and SF-12 PCS but not for VAS-AP, SF-12 MCS, and EQ-5D.

Conclusions

The ACDF-specific MCID is highly variable depending on the calculation technique used. The MDC approach seems to be most appropriate for MCID calculations in the ACDF population, as it provided a threshold value above the 95% confidence interval of nonresponders (greater than the measurement error) and was closest to the average change of most PROs reported by responders. When the MDC method was applied with the NASS patient satisfaction scale as the anchor, the MCID thresholds were 2.6 points for VAS-NP, 4.1 points for VAS-AP, 17.3% for NDI, 8.1 points for SF-12 PCS, 4.7 points for SF-12 MCS, and 0.24 QALY for EQ-5D.

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Stephen K. Mendenhall, Andrew Huh, Janit Pandya, Vincent Alentado, Karl Balsara, Chang Ho and Andrew Jea

OBJECTIVE

The revelation of normative radiographic measurements for the developing pediatric spine is incomplete. The purpose of this analysis was to determine the normal range of asymmetry of the lateral atlantodental interval (LADI) and define age- and sex-related differences.

METHODS

A total of 3072 children aged 0–18 years who underwent CT scanning of the cervical spine were identified at Riley Hospital for Children between 2005 and 2017. Patients were stratified by sex and age (in years) into 36 cohorts. Following this stratification, patients within each group were randomly selected for inclusion until 15 patients in each group had been measured (quota sampling). A total of 540 patients were included for study. Right and left linear measurements were performed in the CT axial plane at the C-1 midlateral mass level.

RESULTS

The overall mean difference between the right and left LADI was 0.09 ± 1.23 mm (range -6.05 to 4.87 mm). The magnitude of this asymmetry remained statistically insignificant across age groups (p = 0.278) and sex (p = 0.889). The intraclass correlation coefficient was 0.805 (95% CI 0.779–0.829).

CONCLUSIONS

Asymmetry of the LADI is not unusual in asymptomatic children. There is no appreciable difference in magnitude of this asymmetry across age ranges and sex. Measurement of LADI asymmetry shows “good” reliability and is easy to perform. Pediatric neurosurgeons, emergency department physicians, and radiologists should be aware of normative values of asymmetry when interpreting CT scans of the cervical spine. This may prevent unnecessary further workup with dynamic CT or MRI.

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Scott L. Parker, Saniya S. Godil, Scott L. Zuckerman, Stephen K. Mendenhall, Noel B. Tulipan and Matthew J. McGirt

Object

Suboccipital decompression is a common procedure for patients with Chiari malformation Type I (CMI). Published studies have reported complication rates ranging from 3% to 40%, with pseudomeningocele being one of the most common complications. To date, there are no studies assessing the effect of this complication on long-term outcome. Therefore, the authors set out to assess the effect of symptomatic pseudomeningocele on patient outcomes following suboccipital decompression for CM-I.

Methods

The study comprised 50 adult patients with CM-I who underwent suboccipital craniectomy and C-1 laminectomy with or without duraplasty. Clinical presentation, radiological studies, operative variables, and complications were assessed for each case. Baseline and 1-year postoperative patient-reported outcomes were assessed to determine improvement in pain, disability, and quality of life. The extent of improvement was compared for patients with and without development of a postoperative symptomatic pseudomeningocele.

Results

A symptomatic pseudomeningocele developed postoperatively in 9 patients (18%). There was no difference with regard to clinical, radiological, or operative variables for patients with or without a postoperative pseudomeningocele. Patients without a pseudomeningocele had significant improvement in all 9 patient-reported outcome measures assessed. On the other hand, patients with pseudomeningocele only had significant improvement in headache (as measured on the Numeric Rating Scale) and headache-related disability (as measured on the Headache Disability Index) but no improvement in quality of life. Twenty-nine (71%) of 41 patients without a pseudomeningocele reported improvement in health status postoperatively compared with only 3 (33%) of 9 patients with a postoperative pseudomeningocele (p = 0.05).

Conclusions

Surgical management of CM-I in adults provides significant and sustained improvement in pain, disability, general health, and quality of life. Development of a postoperative symptomatic pseudomeningocele has lingering effects at 1 year, and it significantly diminishes the overall benefit of suboccipital decompression for CM-related symptoms. Further research is needed to accurately predict which patients may benefit from decompression alone without duraplasty.

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Tim Adamson, Saniya S. Godil, Melissa Mehrlich, Stephen Mendenhall, Anthony L. Asher and Matthew J. McGirt

OBJECTIVE

In an era of escalating health care costs and pressure to improve efficiency and cost of care, ambulatory surgery centers (ASCs) have emerged as lower-cost options for many surgical therapies. Anterior cervical discectomy and fusion (ACDF) is one of the most prevalent spine surgeries performed, and the frequency of its performance is rapidly increasing as the aging population grows. Although ASCs offer significant cost advantages over hospital-based surgical centers, concern over the safety of outpatient ACDF has slowed its adoption. The authors intended to 1) determine the safety of the first 1000 consecutive ACDF surgeries performed in their outpatient ASC, and 2) compare the safety of these outpatient ACDFs with that of consecutive ACDFs performed during the same time period in the hospital setting.

METHODS

A total of 1000 consecutive patients who underwent ACDF in an ACS (outpatient ACDF) and 484 consecutive patients who underwent ACDF at Vanderbilt University Hospital (inpatient ACDF) from 2006 to 2013 were included in this retrospective study of patients' medical records. Data were collected on patient demographics, comorbidities, operative details, and perioperative and 90-day morbidity. Perioperative morbidity and hospital readmission were compared between the outpatient and inpatient ACDF groups.

RESULTS

Of the first 1000 outpatient ACDF cases performed in the authors' ASC, 629 (62.9%) were 1-level and 365 (36.5%) were 2-level ACDFs. Mean patient age was 49.5 ± 8.6, and 484 (48.4%) were males. All patients were observed postoperatively at the ASC postanesthesia care unit (PACU) for 4 hours before being discharged home. Eight patients (0.8%) were transferred from the surgery center to the hospital postoperatively (for pain control [n = 3], chest pain and electrocardiogram changes [n = 2], intraoperative CSF leak [n = 1], postoperative hematoma [n = 1], and profound postoperative weakness and surgical reexploration [n = 1]). No perioperative deaths occurred. The 30-day hospital readmission rate was 2.2%. All 90-day surgical morbidity was similar between outpatient and inpatient cohorts for both 1-level and 2-level ACDFs.

CONCLUSIONS

An analysis of 1000 consecutive patients who underwent ACDF in an outpatient setting demonstrates that surgical complications occur at a low rate (1%) and can be appropriately diagnosed and managed in a 4-hour ASC PACU window. Comparison with an inpatient ACDF surgery cohort demonstrated similar results, highlighting that ACDF can be safely performed in the outpatient ambulatory surgery setting without compromising surgical safety. In an effort to decrease costs of care, surgeons can safely perform 1- and 2-level ACDFs in an ASC environment.

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Scott L. Parker, Saniya S. Godil, Stephen K. Mendenhall, Scott L. Zuckerman, David N. Shau and Matthew J. McGirt

Object

Current health care reform calls for a reduction of procedures and treatments that are less effective, more costly, and of little value (high cost/low quality). The authors assessed the 2-year cost and effectiveness of comprehensive medical management for lumbar spondylolisthesis, stenosis, and herniation by utilizing a prospective single-center multidisciplinary spine center registry in a real-world practice setting.

Methods

Analysis was performed on a prospective longitudinal quality of life spine registry. Patients with lumbar spondylolisthesis (n = 50), stenosis (n = 50), and disc herniation (n = 50) who had symptoms persisting after 6 weeks of medical management and who were eligible for surgical treatment were entered into a prospective registry after deciding on nonsurgical treatment. In all cases, comprehensive medical management included spinal steroid injections, physical therapy, muscle relaxants, antiinflammatory medication, and narcotic oral agents. Two-year patient-reported outcomes, back-related medical resource utilization, and occupational work-day losses were prospectively collected and used to calculate Medicare fee–based direct and indirect costs from the payer and societal perspectives. The maximum health gain associated with medical management was defined as the improvement in pain, disability, and quality of life experienced after 2 years of medical treatment or at the time a patient decided to cross over to surgery.

Results

The maximum health gain in back pain, leg pain, disability, quality of life, depression, and general health state did not achieve statistical significance by 2 years of medical management, except for pain and disability in patients with disc herniation and back pain in patients with lumbar stenosis. Eighteen patients (36%) with spondylolisthesis, 11 (22%) with stenosis, and 17 (34%) with disc herniation eventually required surgical management due to lack of improvement. The 2-year improvement did not achieve a minimum clinically important difference in any outcome measure. The mean 2-year total cost (direct plus indirect) of medical management was $6606 for spondylolisthesis, $7747 for stenosis, and $7097 for herniation.

Conclusions

In an institution-wide, prospective, longitudinal quality of life registry that measures cost and effectiveness of all spine care provided, comprehensive medical management did not result in sustained improvement in pain, disability, or quality of life for patients with surgically eligible degenerative lumbar spondylolisthesis, stenosis, or disc herniation. From both the societal and payer perspective, continued medical management of patients with these lumbar pathologies in whom 6 weeks of conservative therapy failed was of minimal value given its lack of health utility and effectiveness and its health care costs. The findings from this real-world practice setting may more accurately reflect the true value and effectiveness of nonoperative care in surgically eligible patient populations.

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Owoicho Adogwa, Scott L. Parker, David N. Shau, Stephen K. Mendenhall, Clinton J. Devin, Joseph S. Cheng and Matthew J. McGirt

Object

Over the past decade, there has been a dramatic increase in the number of spinal fusions performed in the US and a corresponding increase in the incidence of adjacent-segment disease (ASD). Surgical management of symptomatic ASD consists of decompression of neural elements and extension of fusion. It has been shown to have favorable long-term outcomes, but the cost-effectiveness remains unclear. In this study, the authors set out to assess the cost-effectiveness of revision surgery in the treatment of ASD over a 2-year period.

Methods

Fifty patients undergoing neural decompression and extension of fusion construct for ASD-associated back and leg pain were included in the study. Two-year total back-related medical resource utilization, missed work, and health state values (quality-adjusted life years [QALYs], calculated from the EQ-5D with US valuation) were assessed. Two-year resource use was multiplied by unit costs based on Medicare national allowable payment amounts (direct cost), and patient and caregiver workday losses were multiplied by the self-reported gross-of-tax wage rate (indirect cost). Mean total 2-year cost per QALY gained after revision surgery was assessed.

Results

The mean (± SD) interval between prior fusion and revision surgery for ASD was 3.07 ± 2.02 years. A mean cumulative 2-year gain of 0.76 QALYs was observed after revision surgery. The mean total 2-year cost of extension of fusion constructs was $47,846 ± $32,712 (surgery cost: $24,063 ± $300; outpatient resource utilization cost: $4175 ± $3368; indirect cost: $19,607 ± $32,187). Revision decompression and extension of fusion was associated with a mean 2-year cost per QALY gained of $62,955.

Conclusions

In the authors' practice, revision decompression and extension of fusion provided a significant gain in health state utility for patients with symptomatic ASD, with a 2-year cost per QALY gained of $62,995. When indicated, revision surgery for ASD is a valuable treatment option for patients experiencing back and leg pain secondary to ASD. The findings provide a value measure of surgery that can be compared with future cost-per-QALY-gained studies of medical management or alternative surgical approaches.

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Scott L. Parker, Stephen K. Mendenhall, David N. Shau, Owoicho Adogwa, William N. Anderson, Clinton J. Devin and Matthew J. McGirt

Object

Spine surgery outcome studies rely on patient-reported outcome (PRO) measurements to assess treatment effect, but the extent of improvement in the numerical scores of these questionnaires lacks a direct clinical meaning. Because of this, the concept of a minimum clinically important difference (MCID) has been used to measure the critical threshold needed to achieve clinically relevant treatment effectiveness. As utilization of spinal fusion has increased over the past decade, so has the incidence of same-level recurrent stenosis following index lumbar fusion, which commonly requires revision decompression and fusion. The MCID remains uninvestigated for any PROs in the setting of revision lumbar surgery for this pathology.

Methods

In 53 consecutive patients undergoing revision surgery for same-level recurrent lumbar stenosis–associated back and leg pain, PRO measures of back and leg pain were assessed preoperatively and 2 years postoperatively, using the visual analog scale for back pain (VAS-BP) and leg pain (VAS-LP), Oswestry Disability Index (ODI), Physical and Mental Component Summary categories of the 12-Item Short Form Health Survey (SF-12 PCS and MCS) for quality of life, Zung Depression Scale (ZDS), and EuroQol-5D health survey (EQ-5D). Four established anchor-based MCID calculation methods were used to calculate MCID (average change; minimum detectable change; change difference; and receiver operating characteristic curve analysis) for 2 separate anchors (health transition index of the SF-36 and the satisfaction index).

Results

All patients were available for 2-year PRO assessment. Two years after surgery, a significant improvement was observed for all PROs assessed. The 4 MCID calculation methods generated a range of MCID values for each of the PROs (VAS-BP 2.2–6.0, VAS-LP 3.9–7.5, ODI 8.2–19.9, SF-12 PCS 2.5–12.1, SF-12 MCS 7.0–15.9, ZDS 3.0–18.6, and EQ-5D 0.29–0.52). Each patient answered synchronously for the 2 anchors, suggesting both of these anchors are equally appropriate and valid for this patient population.

Conclusions

The same-level recurrent stenosis surgery-specific MCID is highly variable based on calculation technique. The “minimum detectable change” approach is the most appropriate method for calculation of MCIDs in this population because it was the only method to reliably provide a threshold above the 95% confidence interval of the unimproved cohort (greater than the measurement error). Based on this method, the MCID thresholds following neural decompression and fusion for symptomatic same-level recurrent stenosis are 2.2 points for VAS-BP, 5.0 points for VAS-LP, 8.2 points for ODI, 2.5 points for SF-12 PCS, 10.1 points for SF-12 MCS, 4.9 points for ZDS, and 0.39 QALYs for EQ-5D.