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Minimally Invasive Spinal Deformity Surgery: Analysis of Patients Who Fail to Reach Minimal Clinically Important Difference
Journal Pre-proof Minimally invasive spinal deformity surgery: An analysis of patients that fail to reach minimal clinically important difference (MCID) Michael Y. Wang, MD, Juan Uribe, MD, Praveen V. Mummaneni, MD, Stacie Tran, MPH, G. Damian Brusko, BS, Paul Park, MD, Pierce Nunley, MD PhD, Adam Kanter, MD, David Okonkwo, MD, PhD, Neel Anand, MD, Dean Chou, MD, Christopher I. Shaffrey, MD, Kai-Ming Fu, MD, PhD, Gregory M. Mundis, Jr., MD, Robert Eastlack, MD, on behalf of the MIS-ISSG Group PII:
S1878-8750(20)30290-4
DOI:
https://doi.org/10.1016/j.wneu.2020.02.025
Reference:
WNEU 14300
To appear in:
World Neurosurgery
Received Date: 2 November 2019 Revised Date:
3 February 2020
Accepted Date: 4 February 2020
Please cite this article as: Wang MY, Uribe J, Mummaneni PV, Tran S, Brusko GD, Park P, Nunley P, Kanter A, Okonkwo D, Anand N, Chou D, Shaffrey CI, Fu K-M, Mundis Jr. GM, Eastlack R, on behalf of the MIS-ISSG Group, Minimally invasive spinal deformity surgery: An analysis of patients that fail to reach minimal clinically important difference (MCID), World Neurosurgery (2020), doi: https:// doi.org/10.1016/j.wneu.2020.02.025. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier Inc.
Failure to Achieve MCID in MIS Spine Deformity Minimally invasive spinal deformity surgery: An analysis of patients that fail to reach minimal clinically important difference (MCID) Michael Y Wang, MD,1 Juan Uribe, MD,2 Praveen V Mummaneni, MD,3 Stacie Tran, MPH,4 G. Damian Brusko, BS,1 Paul Park, MD,5 Pierce Nunley, MD PhD,6 Adam Kanter, MD,7 David Okonkwo, MD, PhD,7 Neel Anand, MD,8 Dean Chou, MD,3 Christopher I Shaffrey, MD,9 KaiMing Fu, MD, PhD,10 Gregory M. Mundis Jr., MD,11 Robert Eastlack, MD,12 on behalf of the MIS-ISSG Group 1
Department of Neurological Surgery, University of Miami Miller School of Medicine, Miami, FL, USA 2 Department of Neurosurgery, Barrow Neurological Institute, Phoenix, AZ, USA 3 Department of Neurological Surgery, University of California, San Francisco, CA, USA 4 Department of Orthopedic Surgery, San Diego Center for Spinal Disorders, La Jolla, CA, USA 5 Department of Neurological Surgery, University of Michigan, Ann Arbor, MI, USA 6 Department of Orthopedic Surgery, Spine Institute of Louisiana, Shreveport, LA, USA 7 Department of Neurological Surgery, University of Pittsburgh Medical Center, Pittsburgh, PA, USA 8 Department of Orthopedic Surgery, Cedars Sinai Hospital, Los Angeles, CA, USA 9 Department of Neurological Surgery, Duke University, Durham, NC, USA 10 Department of Orthopedic Surgery, Weill Cornell Medical College, New York, NY, USA 11 Department of Orthopedic Surgery, Scripps Clinic Torrey Pines, La Jolla, CA, USA 12 Department of Neurological Surgery, Scripps Clinic Torrey Pines, La Jolla, CA, USA Corresponding author: Michael Y. Wang MD, FACS Lois Pope Life Center Department of Neurological Surgery 1095 NW 14th Terrace, Miami, FL 33136 Tel.: (305) 243-3294 Fax: (305) 243-3337 Email: [email protected]
Running Title: Failure to Achieve MCID in MIS Spine Deformity
Key words: Minimal clinically important difference (MCID), Minimally invasive (MIS), Patient reported outcome measures (PROMs), Percutaneous, Scoliosis, Spinal deformity
1 ABSTRACT Background It is well known that clinical improvements following surgical intervention are variable. While all surgeons strive to maximize reliability and degree of improvement, certain patients will fail to achieve meaningful gains. We aim to analyze patients who failed to reach minimal clinically important difference (MCID) in an effort to improve outcomes for minimally invasive (MIS) deformity surgery. Methods Data was collected on a multi-center registry of MIS adult spinal deformity (ASD) surgeries. Patient inclusion criteria were: age>18 years, and coronal Cobb>20°, pelvic incidence-lumbar lordosis (PI-LL) >10º, or a sagittal vertical axis (SVA)>5 cm. All patients had minimum 2 years follow-up (N=222). MCID was defined as 12.8 or more points of improvement in the Oswestry Disability Index (ODI). Up to two different etiologies for failure were allowed per patient. Results We identified 78 cases (35%) where the patient failed to achieve MCID at long-term follow-up. A total of 82 identifiable causes were seen in these patients with 14 patients having multiple causes. In 6 patients, the etiology was unclear. The causes were sub-classified as neurological, medical, structural, under treatment, degenerative progression, traumatic, idiopathic, and floor effects. In 71% of cases, an identifiable cause was related to the spine whereas in 35% the cause was not related to the spine. Conclusions Definable causes of failed MIS ASD surgery are often identifiable and similar to open surgery. In some cases the cause is treatable and structural. However, it is also common to see failure due to pathologies unrelated to the index surgery.
2 INTRODUCTION There is a growing body of literature documenting the benefits of adult spinal deformity (ASD) surgery. These operations afford the ability to correct neural compression, segmental instability, and spinal imbalance, all of which can lead to relief of pain and functional loss.1-3 Similarly, minimally invasive surgery (MIS) options for managing ASD have also emerged and their efficacy has been shown in large case series and multi-center cohorts.4-6 However, the benefits that have been documented are aggregate measures, and the journey of each individual patient undergoing MIS ASD surgery is unique. Some patients will experience more improvement from an operation than others. Also, some patients initially experiencing improvement will lose the benefits of an operation over the course of time. All of these aspects of a post-operative population should be considered when analyzing the effects of operative interventions. In the context of surgical management for ASD, these issues may be particularly salient for two reasons. First, the interventions involve substantial morbidity, financial cost, and prolonged recovery times. As such, for the individual patient who fails to achieve meaningful improvement the risk-benefit analysis is, in retrospect, highly unfavorable. Second, MIS ASD surgery leverages newer techniques and technologies, so there is less experience to allow surgeons and patients to evaluate their efficacy from this perspective. In order to determine the extent of improvement gained following surgical intervention, the concept of minimal clinically important difference (MCID) has been described. This distinction aims to identify the smallest score on the Oswestry Disability Index (ODI), for example, that would meaningfully impact a patient’s quality of life.7 To date, there have been no studies published exploring the specific reasons why individual patients in a large multi-center cohort did not achieve improvement after MIS ASD surgery. This report analyzed a large experience at eight tertiary spine care centers in an effort to identify the causes underlying a failure to achieve and/or maintain MCID following MIS treatment of ASD.
3 METHODS A total of eight tertiary spine care centers with established expertise in MIS ASD surgery were selected to participate in the MIS-ISSG. All centers obtained local Institutional Review Board (IRB) approval for participation in this study and patient consent was obtained prior to enrollment in the database. In this series data was collected retrospectively through an annual review process and data was housed centrally with centralized image processing and analysis. All patients had the following data at baseline (pre-operative) and last follow-up: 36” anteroposterior (AP) and Lateral standing scoliosis X-Rays, Oswestry Disability Index (ODI), and separate Numeric Pain Scores (NPS) for leg and back pain. The NPS was conducted on a ten-point scale. In addition, the database included: patient demographics (age, gender, body mass index (BMI), smoking status, previous spine surgeries, and American Society of Anesthesia or ASA grade); data for surgical parameters (total operative time, any staging of procedures, total blood loss, surgical methodology, number of levels treated, and routes of approach); and clinical outcomes (length of stay, any blood transfusions, and major/minor complications allocated by subtype). For inclusion in the database patients had to be more than 18 years of age at the time of surgery. Radiographic inclusion criteria were a coronal Cobb angle of greater than or equal to 20°, a pelvic incidence-lumbar lordosis (PI-LL) >10º, or a sagittal vertical axis (SVA) greater than 5 cm. The coronal Cobb angle was determined by measuring the maximal coronal angulation between the two most angulated upper vertebral endplates on 36” standing X-Rays. Lumbar lordosis was measured between the upper endplates of L1 and S1 in the standing lateral position with 36’ X-Rays. The SVA was measured by dropping a plumb line from the anterior inferior aspect of the C7 vertebra. Data was combined from all centers in Microsoft Excel and data analysis was performed using SPSS software. A minimum of two years of clinical and radiographic follow-up was required for inclusion in the study. This study explored the specific aspects of patients who did not experience substantial gains in clinical improvement. To determine this, we used the criteria of minimal clinically important difference (MCID) as reported by Copay et al, defined as 12.8 or more points of improvement in the Oswestry Disability Index (ODI).7 Patients not meeting MCID at last follow-up were queried and the cause(s) of continued pain or lost function were categorized into distinct groups as shown in Table 1. The causes for failure to meet MCID were determined by
4 the treating surgeon and were based on the clinical post-operative course and follow-up radiographic studies. To identify primary causes of failure each patient was limited to a maximum of two etiologies for non-improvement.
RESULTS Patient Series Of the 222 patients in the database, 78 patients (35%) failed to meet MCID at final follow-up. The causes of their failure are shown in Table 1. Six patients (7.7%) had no identifiable cause, and 4 cases were identified as not meeting MCID due to a floor effect. This was particularly seen when the baseline ODI score was atypically low, making a 12.8 point decrease improbable. A total of 82 causes were identified, and 14 of the patients had more than one clearly identifiable cause. Causes were categorized into 17 subtypes, and these could more broadly be characterized as being: structurally related to deformity, neurological, medical, idiopathic, traumatic, degenerative progression, under treatment (defined as failure to achieve spinopelvic alignment, poor coronal correction, or inadequate construct length), and idiopathic. Causes Related to Spinal Deformity The etiology of failure could also be considered as related to the spinal deformity or not. The subtypes that were related to the deformity itself included 7 diagnoses. Adjacent segment disease was responsible in 10% of cases and was defined as new arthritic or stenotic symptoms proximal or distal to the fusion construct. Proximal junctional kyphosis (PJK) (6.4%) was defined as a new deformity occurring adjacent to the construct and was different from adjacent segment disease in that there was a kyphotic malalignment or fracture, as shown in Figure 1. Persistent axial pain (14%) was back pain that had no specific structural etiology identifiable, and it was distinct from other causes of pain at the site of surgery, such as a nonunion (7.7%) or hardware failure/fracture (3.8%), as shown in Figure 2. Under treatment is a category relatively unique to MIS ASD surgery. Given that MIS surgeons often are selective about the areas being fused, there is the possibility that simply not enough spinal segments or correction were incorporated into the index operation. This is distinct from adjacent segment disease and PJK and was responsible for 6.4% of cases. Causes Unrelated to Spinal Deformity
5 The most common causes of non-deformity failure were progression of arthritic conditions. This could occur in the extremities (12.8%), other areas of the spine remote from the thoracolumbar deformity (10%), or the sacroiliac (SI) joints (7.7%), as shown in Figure 3. Other medical complications developing in the early postoperative period (1.3%), in a delayed fashion (7.7%), and delayed death (1.3%) were also seen. Neural pain following surgery, from either nerve root injury or persistent radiculopathy, was seen in 3.8% and progression of central neurodegenerative diseases such as Parkinson’s Disease or stroke were seen in 5.1%. Trauma was surprisingly common as a cause of further morbidity and was seen in 6.4%.
6 DISCUSSION Key Results To our knowledge this is the largest series of MIS ASD cases evaluated for achievement and maintenance of MCID postoperatively. Numerous causes for these failures or lapses in MCID were identified in this series. The most obvious of these etiologies are structural issues, including adjacent segment disease, PJK, nonunion, and hardware failure, which occurred in 28% of the failures. These cases are potentially preventable or manageable with additional surgical intervention, which has been described in previous reports.8-11 One of the most common causes of continued pain or loss of function was the progression of arthritic conditions based on new clinical and radiographic findings during the follow-up period. This was seen commonly in areas of the spine that were likely not affected by the index surgery. For example, patients most commonly presented with new cervical myelopathy and subsequent radiographic evidence of degenerative disease requiring surgical treatment or with osteoporotic thoracic compression fractures quite distant from the surgical construct. Furthermore, patients requiring an ASD surgery are also likely to harbor severe systemic osteoarthritis. Hip and knee disease coincides with spine disease and alters gait while some patients have muscle contractures or paraspinal muscle atrophy causing a stooped posture, both of which can lead to pain. We saw this in our series, as many of our patients required additional surgical interventions for hip and knee arthritis (12.8%). Repeated injections or ablations of the SI joint were also a common cause of new or continued pain (7.7%). Thus, based on the evidence in these select patients, we attributed the failure to reach MCID as related to the natural progression of osteoarthritic disease. Comparison to Current Literature Fortunately, neurological problems as a result of the index surgery were uncommon at long term follow-up. It is well-known that short term neurological complaints are commonly seen after trans-psoas surgery,12,13 but this study demonstrates that it is not a major barrier to achieving long-term favorable results. However, we also saw progression of central nervous system disease with stroke or Parkinson’s Disease as a cause of failing to achieve long-term improvements. As with open surgery, MIS treatment of ASD can result in undertreatment of the deformity, particularly in the sagittal plane. This generally occurred in two scenarios. The first
7 is the limitation of the length of the spinal construct, either because the surgeon is trying to pinpoint the pain generator and treat less of the spine, or because of limitations of the surgical approach (e.g.: an inability to perform L5/S1 interbody fusion from a lateral approach). The second scenario is under treatment of the deformity itself, typically related to a lack of powerful correction measures to gain sagittal or coronal balance. Because the surgeons in this study were skilled in not only surgical technique, but also patient selection, the second scenario was uncommon. As with any series with long-term follow-up, patients in the series were susceptible to new pathologies. For example, a new cancer diagnosis was present in two of our patients. Both the neoplastic process itself as well as its medical treatments can reduce patient reported outcome measures (PROMs). Similarly, our patients were also subject to the risk of new traumatic events including falls and motor vehicle collisions. This was seen in 6.4% of our patients. It is however possible that the risk of suffering trauma or the risk of greater pain with trauma was increased due to having a long segment spinal fusion or elderly age confers an increased risk of traumatic falls. A concerning subset of patients were those where the cause could not be clearly identified. Within this group were patients who continued to experience axial back pain, which was in fact the most common diagnosis (14%). This subset of patients unfortunately exists in every postoperative surgical series, and many potential causes have been proposed. This includes soft tissue or muscular trauma, fibromyalgia, opiate-induced hyperalgesia, catastrophizing behaviors, stiffness due to lost spinal motion, among others. Study Limitations As with all retrospective studies this report has significant limitations. Nonetheless, data collection occurred on an annual basis and is likely a true representation of physician practices and outcomes at these eight centers. Other inherent limitations relate to sample size and lack of statistical power to validate some of the trends seen in this series. Another drawback of this study was its limitation to eight selective centers. As such, it is unclear if this report represents practice patterns across North America. Unfortunately, larger datasets lack granular data elements and would be unlikely to detect some of the findings seen in this multi-center study. Additionally, there likely exists some bias in the retrospective categorization of the etiologies related to failure. However, the etiologies were determined based on both clinical
8 symptoms and any radiographic evidence at each follow-up visit. Thus, in patients with other known medical or traumatic comorbidities and the absence of radiographic evidence of an etiology related to their spinal deformity surgery, the former is the more likely etiology contributing to a reduced improvement in overall quality of life. Furthermore, it should be noted that the fact that a patient did not meet MCID on an ODI does not mean that they did not benefit from surgery. Patients in this series could have experienced relief of severe radiculopathy yet still score poorly on the ODI. Therefore, the limitations of PROMs also have to be taken into account.
CONCLUSIONS Definable causes of failed MIS ASD surgery are similar to open surgery. In many cases the cause is treatable and structural. However, it is also common to see failure due to pathologies unrelated to the index surgery. Larger multi-center, prospective databases with increasingly granular data elements may help further elucidate the etiology of failed cases.
9 REFERENCES 1.
Lenke LG, Fehlings MG, Shaffrey CI, et al. Neurologic Outcomes of Complex Adult Spinal Deformity Surgery: Results of the Prospective, Multicenter Scoli-RISK-1 Study. Spine. 2016;41(3):204-212.
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Choi SH, Son SM, Goh TS, Park W, Lee JS. Outcomes of Operative and Nonoperative Treatment in Patients with Adult Spinal Deformity with a Minimum 2-Year Follow-Up: A Meta-Analysis. World neurosurgery. 2018;120:e870-e876.
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Haque RM, Mundis GM, Jr., Ahmed Y, et al. Comparison of radiographic results after minimally invasive, hybrid, and open surgery for adult spinal deformity: a multicenter study of 184 patients. Neurosurgical focus. 2014;36(5):E13.
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Scheer JK, Smith JS, Clark AJ, et al. Comprehensive study of back and leg pain improvements after adult spinal deformity surgery: analysis of 421 patients with 2-year follow-up and of the impact of the surgery on treatment satisfaction. Journal of neurosurgery Spine. 2015;22(5):540-553.
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Park P, Okonkwo DO, Nguyen S, et al. Can a Minimal Clinically Important Difference Be Achieved in Elderly Patients with Adult Spinal Deformity Who Undergo Minimally Invasive Spinal Surgery? World neurosurgery. 2016;86:168-172.
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Mundis GM, Jr., Turner JD, Deverin V, et al. A Critical Analysis of Sagittal Plane Deformity Correction With Minimally Invasive Adult Spinal Deformity Surgery: A 2Year Follow-Up Study. Spine deformity. 2017;5(4):265-271.
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Copay AG, Glassman SD, Subach BR, Berven S, Schuler TC, Carreon LY. Minimum clinically important difference in lumbar spine surgery patients: a choice of methods using the Oswestry Disability Index, Medical Outcomes Study questionnaire Short Form 36, and pain scales. The spine journal : official journal of the North American Spine Society. 2008;8(6):968-974.
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Reames DL, Kasliwal MK, Smith JS, Hamilton DK, Arlet V, Shaffrey CI. Time to development, clinical and radiographic characteristics, and management of proximal junctional kyphosis following adult thoracolumbar instrumented fusion for spinal deformity. Journal of spinal disorders & techniques. 2015;28(2):E106-114.
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Kim YC, Lenke LG, Hyun SJ, Lee JH, Koester LA, Blanke KM. Results of revision surgery after pedicle subtraction osteotomy for fixed sagittal imbalance with
10 pseudarthrosis at the prior osteotomy site or elsewhere: minimum 5 years post-revision. Spine. 2014;39(21):1817-1828. 10.
Harimaya K, Mishiro T, Lenke LG, Bridwell KH, Koester LA, Sides BA. Etiology and revision surgical strategies in failed lumbosacral fixation of adult spinal deformity constructs. Spine. 2011;36(20):1701-1710.
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Hamilton DK, Kanter AS, Bolinger BD, et al. Reoperation rates in minimally invasive, hybrid and open surgical treatment for adult spinal deformity with minimum 2-year follow-up. European spine journal : official publication of the European Spine Society, the European Spinal Deformity Society, and the European Section of the Cervical Spine Research Society. 2016;25(8):2605-2611.
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Dakwar E, Vale FL, Uribe JS. Trajectory of the main sensory and motor branches of the lumbar plexus outside the psoas muscle related to the lateral retroperitoneal transpsoas approach. Journal of neurosurgery Spine. 2011;14(2):290-295.
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Cummock MD, Vanni S, Levi AD, Yu Y, Wang MY. An analysis of postoperative thigh symptoms after minimally invasive transpsoas lumbar interbody fusion. Journal of neurosurgery Spine. 2011;15(1):11-18.
11 FIGURE LEGENDS
Figure 1 Surgical case example of a patient with PJK. This patient had undergone a L2-5 lateral interbody fusion with L2-S1 mini-open instrumented fusion for flat back and scoliosis. A & B) One year following surgery the patient developed PJK and fracture at L2. C & D) An extension of fusion to T11 was required.
Figure 2 Surgical case example of persistent axial pain without a clear structural etiology. A & B) This 68 year old patient underwent a T10 to L5 MIS ASD surgery with MIS transforaminal lumbar interbody fusion (TLIF) at L3-5. C) The patient had no complications from surgery but continued to complain of axial pain which was improved from preoperatively, but with a less than 12.8 point ODI gain. Follow-up for 8 years included repeated tests and imaging for various causes including D) distal and E) proximal structural causes of axial pain. The workup was also negative for SI joint arthritis, nonunion, and hardware breakage. Ultimately, no clear etiology was identified.
Figure 3 Surgical case example of non-adjacent spinal disease progression. A & B) A 70 year-old male was treated with lateral interbody fusion (LIF), anterior column resection (ACR), and open T10 to pelvis posterior instrumented fusion. C) The patient later developed cervical myelopathy requiring an anterior C5 to T1 decompression and instrumented fusion.
Table 1: Etiologies of Non-Improvement Following Minimally-Invasive Correction of Adult Spinal Deformity Etiology of Non-Improvement
Category
Number
Percentage
Persistent axial pain in area of surgery w/o clear structural etiology
Idiopathic
11
14.0%
Other non-spinal arthritides
Degenerative progression
10
12.8%
Adjacent segment disease (ASD)
Structural
8
10.0%
Non-adjacent spinal fracture or stenosis (e.g.: cervical)
Degenerative progression
8
10.0%
Sacroiliac (SI) Joint pain
Degenerative progression
6
7.7%
Other severe medical comorbidities (e.g.: cardiac, pulmonary, neoplastic)
Medical
6
7.7%
Pseudarthrosis/nonunion
Structural
6
7.7%
Trauma causing other injuries
Traumatic
5
6.4%
Structural
5
6.4%
Undertreatment
5
6.4%
Neurological
4
5.1%
Hardware failure/fracture
Structural
3
3.8%
Nerve root injury or neve pain
Neurological
3
3.8%
Other medical complications from surgery
Medical
1
1.3%
Death
Medical
1
1.3%
Floor effect
Floor effect
4
5.1%
Could not be determined
6
7.7%
Total
92
Proximal junctional kyphosis (PJK) Undertreatment (spinal pain from other levels or incomplete correction of deformity) Other neurological degenerative disease (e.g.: Parkinson's or stroke)
Abbreviations: ACR: Anterior Column Resection AP: Anteroposterior ASA: American Society of Anesthesia ASD: Adult Spinal Deformity BMI: Body Mass Index IRB: Institutional Review Board LIF: Lateral Interbody Fusion MCID: Minimal Clinically Important Difference MIS: Minimally Invasive NPS: Numeric Pain Scores ODI: Oswestry Disability Index PI-LL: Pelvic Incidence-Lumbar Lordosis PJK: Proximal junctional kyphosis PROMs: Patient Reported Outcome Measures SI: Sacroiliac SVA: Sagittal Vertical Axis TLIF: Transforaminal Lumbar Interbody Fusion
1 Financial Disclosures Dr. Wang declares the following financial interests/personal relationships which may be considered as potential competing interests: grants from Department of Defense, personal fees from DePuy-Synthes Spine, Inc, personal fees from Stryker Spine, personal fees from K2M, personal fees from Spineology, other from DePuy-Synthes Spine, Inc, other from Children's Hospital of Los Angeles, other from Springer Publishing, other from Quality Medical Publishing, other from Vallum, other from Spinicity, other from Innovative Surgical Devices, outside the submitted work. Dr. Uribe declares the following financial interests/personal relationships which may be considered as potential competing interests: research support, stock options, and consulting fees from NuVasive, Inc. as well as consulting fees from SI-Bone outside of the submitted work. Dr. Mummaneni declares the following financial interests/personal relationships which may be considered as potential competing interests: personal fees from DePuy Spine, personal fees from Globus, personal fees from Stryker, other from ISSG, other from Spineart, other from Thieme Publishing, other from Springer Publishing, grants from NREF, grants from AO Spine, other from DePuy Spine, other from Spinicity, other from ISD, outside the submitted work. Dr. Park declares the following financial interests/personal relationships which may be considered as potential competing interests: personal fees from Globus, personal fees from NuVasive, personal fees from Allosource, grants from Pfizer, grants from Vertex, personal fees from Medtronic, outside the submitted work. Dr. Nunley declares the following financial interests/personal relationships which may be considered as potential competing interests: patents with royalties paid to K2M, a patent with royalties paid to LDR Medical, other from Amedica Corporation, other from ZimmerBiomet, other from K2M, other from Paradigm, other from Spineology, other from Vertiflex, other from Camber Spine, other from Integrity, other from Centinel Spine, outside the submitted work Dr. Kanter declares the following financial interests/personal relationships which may be considered as potential competing interests: other from Nuvasive, other from Zimmer Biomet, outside the submitted work. Dr. Okonkwo declares the following financial interests/personal relationships which may be considered as potential competing interests: consultant for NuVasive, Zimmer Biomet, and Stryker; is a patent holder with Zimmer Biomet; and receives royalties from Zimmer Biomet and
2 NuVasive. Dr. Anand declares the following financial interests/personal relationships which may be considered as potential competing interests: personal fees from Medtronics, other from Medtronics, other from Medtronics, other from Globus Medical, other from Globus Medical, other from GYS Tech, other from Paradigm Spine, other from Theracell, other from Elsevier, outside the submitted work. Dr. Chou declares the following financial interests/personal relationships which may be considered as potential competing interests: personal fees and other from Medtronic; and personal fees and other from Globus, outside the submitted work. Dr. Shaffrey declares the following financial interests/personal relationships which may be considered as potential competing interests: grants from ISSF Foundation, during the conduct of the study; personal fees from Medtronic, personal fees from NuVasive, personal fees from Zimmer Biomet, outside the submitted work. Dr. Fu declares the following financial interests/personal relationships which may be considered as potential competing interests: consultant for SI-Bone, DePuy, Globus. Dr. Mundis Jr. declares the following financial interests/personal relationships which may be considered as potential competing interests: personal fees from Nuvasive, personal fees from K2M, personal fees from Allosource, personal fees from Seaspine, personal fees from Viseon, outside the submitted work; patent Nuvasive with royalties paid, and a patent K2M with royalties paid. Dr. Eastlack declares the following financial interests/personal relationships which may be considered as potential competing interests: personal fees from Globus Medical, personal fees from Nuvasive, personal fees from Seaspine, other from Invuity, other from Aesculap, other from Baxter, other from K2M Stryker, other from Nuvasive, other from SI Bone, other from Titan, other from Aesculap, non-financial support from Seaspine, other from AO, other from Seaspine, other from Nuvasive, other from Nuvasive, other from Seaspine, other from Alphatec, outside the submitted work. The other authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Funding: This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
S1878-8750(20)30290-4
DOI:
https://doi.org/10.1016/j.wneu.2020.02.025
Reference:
WNEU 14300
To appear in:
World Neurosurgery
Received Date: 2 November 2019 Revised Date:
3 February 2020
Accepted Date: 4 February 2020
Please cite this article as: Wang MY, Uribe J, Mummaneni PV, Tran S, Brusko GD, Park P, Nunley P, Kanter A, Okonkwo D, Anand N, Chou D, Shaffrey CI, Fu K-M, Mundis Jr. GM, Eastlack R, on behalf of the MIS-ISSG Group, Minimally invasive spinal deformity surgery: An analysis of patients that fail to reach minimal clinically important difference (MCID), World Neurosurgery (2020), doi: https:// doi.org/10.1016/j.wneu.2020.02.025. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier Inc.
Failure to Achieve MCID in MIS Spine Deformity Minimally invasive spinal deformity surgery: An analysis of patients that fail to reach minimal clinically important difference (MCID) Michael Y Wang, MD,1 Juan Uribe, MD,2 Praveen V Mummaneni, MD,3 Stacie Tran, MPH,4 G. Damian Brusko, BS,1 Paul Park, MD,5 Pierce Nunley, MD PhD,6 Adam Kanter, MD,7 David Okonkwo, MD, PhD,7 Neel Anand, MD,8 Dean Chou, MD,3 Christopher I Shaffrey, MD,9 KaiMing Fu, MD, PhD,10 Gregory M. Mundis Jr., MD,11 Robert Eastlack, MD,12 on behalf of the MIS-ISSG Group 1
Department of Neurological Surgery, University of Miami Miller School of Medicine, Miami, FL, USA 2 Department of Neurosurgery, Barrow Neurological Institute, Phoenix, AZ, USA 3 Department of Neurological Surgery, University of California, San Francisco, CA, USA 4 Department of Orthopedic Surgery, San Diego Center for Spinal Disorders, La Jolla, CA, USA 5 Department of Neurological Surgery, University of Michigan, Ann Arbor, MI, USA 6 Department of Orthopedic Surgery, Spine Institute of Louisiana, Shreveport, LA, USA 7 Department of Neurological Surgery, University of Pittsburgh Medical Center, Pittsburgh, PA, USA 8 Department of Orthopedic Surgery, Cedars Sinai Hospital, Los Angeles, CA, USA 9 Department of Neurological Surgery, Duke University, Durham, NC, USA 10 Department of Orthopedic Surgery, Weill Cornell Medical College, New York, NY, USA 11 Department of Orthopedic Surgery, Scripps Clinic Torrey Pines, La Jolla, CA, USA 12 Department of Neurological Surgery, Scripps Clinic Torrey Pines, La Jolla, CA, USA Corresponding author: Michael Y. Wang MD, FACS Lois Pope Life Center Department of Neurological Surgery 1095 NW 14th Terrace, Miami, FL 33136 Tel.: (305) 243-3294 Fax: (305) 243-3337 Email: [email protected]
Running Title: Failure to Achieve MCID in MIS Spine Deformity
Key words: Minimal clinically important difference (MCID), Minimally invasive (MIS), Patient reported outcome measures (PROMs), Percutaneous, Scoliosis, Spinal deformity
1 ABSTRACT Background It is well known that clinical improvements following surgical intervention are variable. While all surgeons strive to maximize reliability and degree of improvement, certain patients will fail to achieve meaningful gains. We aim to analyze patients who failed to reach minimal clinically important difference (MCID) in an effort to improve outcomes for minimally invasive (MIS) deformity surgery. Methods Data was collected on a multi-center registry of MIS adult spinal deformity (ASD) surgeries. Patient inclusion criteria were: age>18 years, and coronal Cobb>20°, pelvic incidence-lumbar lordosis (PI-LL) >10º, or a sagittal vertical axis (SVA)>5 cm. All patients had minimum 2 years follow-up (N=222). MCID was defined as 12.8 or more points of improvement in the Oswestry Disability Index (ODI). Up to two different etiologies for failure were allowed per patient. Results We identified 78 cases (35%) where the patient failed to achieve MCID at long-term follow-up. A total of 82 identifiable causes were seen in these patients with 14 patients having multiple causes. In 6 patients, the etiology was unclear. The causes were sub-classified as neurological, medical, structural, under treatment, degenerative progression, traumatic, idiopathic, and floor effects. In 71% of cases, an identifiable cause was related to the spine whereas in 35% the cause was not related to the spine. Conclusions Definable causes of failed MIS ASD surgery are often identifiable and similar to open surgery. In some cases the cause is treatable and structural. However, it is also common to see failure due to pathologies unrelated to the index surgery.
2 INTRODUCTION There is a growing body of literature documenting the benefits of adult spinal deformity (ASD) surgery. These operations afford the ability to correct neural compression, segmental instability, and spinal imbalance, all of which can lead to relief of pain and functional loss.1-3 Similarly, minimally invasive surgery (MIS) options for managing ASD have also emerged and their efficacy has been shown in large case series and multi-center cohorts.4-6 However, the benefits that have been documented are aggregate measures, and the journey of each individual patient undergoing MIS ASD surgery is unique. Some patients will experience more improvement from an operation than others. Also, some patients initially experiencing improvement will lose the benefits of an operation over the course of time. All of these aspects of a post-operative population should be considered when analyzing the effects of operative interventions. In the context of surgical management for ASD, these issues may be particularly salient for two reasons. First, the interventions involve substantial morbidity, financial cost, and prolonged recovery times. As such, for the individual patient who fails to achieve meaningful improvement the risk-benefit analysis is, in retrospect, highly unfavorable. Second, MIS ASD surgery leverages newer techniques and technologies, so there is less experience to allow surgeons and patients to evaluate their efficacy from this perspective. In order to determine the extent of improvement gained following surgical intervention, the concept of minimal clinically important difference (MCID) has been described. This distinction aims to identify the smallest score on the Oswestry Disability Index (ODI), for example, that would meaningfully impact a patient’s quality of life.7 To date, there have been no studies published exploring the specific reasons why individual patients in a large multi-center cohort did not achieve improvement after MIS ASD surgery. This report analyzed a large experience at eight tertiary spine care centers in an effort to identify the causes underlying a failure to achieve and/or maintain MCID following MIS treatment of ASD.
3 METHODS A total of eight tertiary spine care centers with established expertise in MIS ASD surgery were selected to participate in the MIS-ISSG. All centers obtained local Institutional Review Board (IRB) approval for participation in this study and patient consent was obtained prior to enrollment in the database. In this series data was collected retrospectively through an annual review process and data was housed centrally with centralized image processing and analysis. All patients had the following data at baseline (pre-operative) and last follow-up: 36” anteroposterior (AP) and Lateral standing scoliosis X-Rays, Oswestry Disability Index (ODI), and separate Numeric Pain Scores (NPS) for leg and back pain. The NPS was conducted on a ten-point scale. In addition, the database included: patient demographics (age, gender, body mass index (BMI), smoking status, previous spine surgeries, and American Society of Anesthesia or ASA grade); data for surgical parameters (total operative time, any staging of procedures, total blood loss, surgical methodology, number of levels treated, and routes of approach); and clinical outcomes (length of stay, any blood transfusions, and major/minor complications allocated by subtype). For inclusion in the database patients had to be more than 18 years of age at the time of surgery. Radiographic inclusion criteria were a coronal Cobb angle of greater than or equal to 20°, a pelvic incidence-lumbar lordosis (PI-LL) >10º, or a sagittal vertical axis (SVA) greater than 5 cm. The coronal Cobb angle was determined by measuring the maximal coronal angulation between the two most angulated upper vertebral endplates on 36” standing X-Rays. Lumbar lordosis was measured between the upper endplates of L1 and S1 in the standing lateral position with 36’ X-Rays. The SVA was measured by dropping a plumb line from the anterior inferior aspect of the C7 vertebra. Data was combined from all centers in Microsoft Excel and data analysis was performed using SPSS software. A minimum of two years of clinical and radiographic follow-up was required for inclusion in the study. This study explored the specific aspects of patients who did not experience substantial gains in clinical improvement. To determine this, we used the criteria of minimal clinically important difference (MCID) as reported by Copay et al, defined as 12.8 or more points of improvement in the Oswestry Disability Index (ODI).7 Patients not meeting MCID at last follow-up were queried and the cause(s) of continued pain or lost function were categorized into distinct groups as shown in Table 1. The causes for failure to meet MCID were determined by
4 the treating surgeon and were based on the clinical post-operative course and follow-up radiographic studies. To identify primary causes of failure each patient was limited to a maximum of two etiologies for non-improvement.
RESULTS Patient Series Of the 222 patients in the database, 78 patients (35%) failed to meet MCID at final follow-up. The causes of their failure are shown in Table 1. Six patients (7.7%) had no identifiable cause, and 4 cases were identified as not meeting MCID due to a floor effect. This was particularly seen when the baseline ODI score was atypically low, making a 12.8 point decrease improbable. A total of 82 causes were identified, and 14 of the patients had more than one clearly identifiable cause. Causes were categorized into 17 subtypes, and these could more broadly be characterized as being: structurally related to deformity, neurological, medical, idiopathic, traumatic, degenerative progression, under treatment (defined as failure to achieve spinopelvic alignment, poor coronal correction, or inadequate construct length), and idiopathic. Causes Related to Spinal Deformity The etiology of failure could also be considered as related to the spinal deformity or not. The subtypes that were related to the deformity itself included 7 diagnoses. Adjacent segment disease was responsible in 10% of cases and was defined as new arthritic or stenotic symptoms proximal or distal to the fusion construct. Proximal junctional kyphosis (PJK) (6.4%) was defined as a new deformity occurring adjacent to the construct and was different from adjacent segment disease in that there was a kyphotic malalignment or fracture, as shown in Figure 1. Persistent axial pain (14%) was back pain that had no specific structural etiology identifiable, and it was distinct from other causes of pain at the site of surgery, such as a nonunion (7.7%) or hardware failure/fracture (3.8%), as shown in Figure 2. Under treatment is a category relatively unique to MIS ASD surgery. Given that MIS surgeons often are selective about the areas being fused, there is the possibility that simply not enough spinal segments or correction were incorporated into the index operation. This is distinct from adjacent segment disease and PJK and was responsible for 6.4% of cases. Causes Unrelated to Spinal Deformity
5 The most common causes of non-deformity failure were progression of arthritic conditions. This could occur in the extremities (12.8%), other areas of the spine remote from the thoracolumbar deformity (10%), or the sacroiliac (SI) joints (7.7%), as shown in Figure 3. Other medical complications developing in the early postoperative period (1.3%), in a delayed fashion (7.7%), and delayed death (1.3%) were also seen. Neural pain following surgery, from either nerve root injury or persistent radiculopathy, was seen in 3.8% and progression of central neurodegenerative diseases such as Parkinson’s Disease or stroke were seen in 5.1%. Trauma was surprisingly common as a cause of further morbidity and was seen in 6.4%.
6 DISCUSSION Key Results To our knowledge this is the largest series of MIS ASD cases evaluated for achievement and maintenance of MCID postoperatively. Numerous causes for these failures or lapses in MCID were identified in this series. The most obvious of these etiologies are structural issues, including adjacent segment disease, PJK, nonunion, and hardware failure, which occurred in 28% of the failures. These cases are potentially preventable or manageable with additional surgical intervention, which has been described in previous reports.8-11 One of the most common causes of continued pain or loss of function was the progression of arthritic conditions based on new clinical and radiographic findings during the follow-up period. This was seen commonly in areas of the spine that were likely not affected by the index surgery. For example, patients most commonly presented with new cervical myelopathy and subsequent radiographic evidence of degenerative disease requiring surgical treatment or with osteoporotic thoracic compression fractures quite distant from the surgical construct. Furthermore, patients requiring an ASD surgery are also likely to harbor severe systemic osteoarthritis. Hip and knee disease coincides with spine disease and alters gait while some patients have muscle contractures or paraspinal muscle atrophy causing a stooped posture, both of which can lead to pain. We saw this in our series, as many of our patients required additional surgical interventions for hip and knee arthritis (12.8%). Repeated injections or ablations of the SI joint were also a common cause of new or continued pain (7.7%). Thus, based on the evidence in these select patients, we attributed the failure to reach MCID as related to the natural progression of osteoarthritic disease. Comparison to Current Literature Fortunately, neurological problems as a result of the index surgery were uncommon at long term follow-up. It is well-known that short term neurological complaints are commonly seen after trans-psoas surgery,12,13 but this study demonstrates that it is not a major barrier to achieving long-term favorable results. However, we also saw progression of central nervous system disease with stroke or Parkinson’s Disease as a cause of failing to achieve long-term improvements. As with open surgery, MIS treatment of ASD can result in undertreatment of the deformity, particularly in the sagittal plane. This generally occurred in two scenarios. The first
7 is the limitation of the length of the spinal construct, either because the surgeon is trying to pinpoint the pain generator and treat less of the spine, or because of limitations of the surgical approach (e.g.: an inability to perform L5/S1 interbody fusion from a lateral approach). The second scenario is under treatment of the deformity itself, typically related to a lack of powerful correction measures to gain sagittal or coronal balance. Because the surgeons in this study were skilled in not only surgical technique, but also patient selection, the second scenario was uncommon. As with any series with long-term follow-up, patients in the series were susceptible to new pathologies. For example, a new cancer diagnosis was present in two of our patients. Both the neoplastic process itself as well as its medical treatments can reduce patient reported outcome measures (PROMs). Similarly, our patients were also subject to the risk of new traumatic events including falls and motor vehicle collisions. This was seen in 6.4% of our patients. It is however possible that the risk of suffering trauma or the risk of greater pain with trauma was increased due to having a long segment spinal fusion or elderly age confers an increased risk of traumatic falls. A concerning subset of patients were those where the cause could not be clearly identified. Within this group were patients who continued to experience axial back pain, which was in fact the most common diagnosis (14%). This subset of patients unfortunately exists in every postoperative surgical series, and many potential causes have been proposed. This includes soft tissue or muscular trauma, fibromyalgia, opiate-induced hyperalgesia, catastrophizing behaviors, stiffness due to lost spinal motion, among others. Study Limitations As with all retrospective studies this report has significant limitations. Nonetheless, data collection occurred on an annual basis and is likely a true representation of physician practices and outcomes at these eight centers. Other inherent limitations relate to sample size and lack of statistical power to validate some of the trends seen in this series. Another drawback of this study was its limitation to eight selective centers. As such, it is unclear if this report represents practice patterns across North America. Unfortunately, larger datasets lack granular data elements and would be unlikely to detect some of the findings seen in this multi-center study. Additionally, there likely exists some bias in the retrospective categorization of the etiologies related to failure. However, the etiologies were determined based on both clinical
8 symptoms and any radiographic evidence at each follow-up visit. Thus, in patients with other known medical or traumatic comorbidities and the absence of radiographic evidence of an etiology related to their spinal deformity surgery, the former is the more likely etiology contributing to a reduced improvement in overall quality of life. Furthermore, it should be noted that the fact that a patient did not meet MCID on an ODI does not mean that they did not benefit from surgery. Patients in this series could have experienced relief of severe radiculopathy yet still score poorly on the ODI. Therefore, the limitations of PROMs also have to be taken into account.
CONCLUSIONS Definable causes of failed MIS ASD surgery are similar to open surgery. In many cases the cause is treatable and structural. However, it is also common to see failure due to pathologies unrelated to the index surgery. Larger multi-center, prospective databases with increasingly granular data elements may help further elucidate the etiology of failed cases.
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11 FIGURE LEGENDS
Figure 1 Surgical case example of a patient with PJK. This patient had undergone a L2-5 lateral interbody fusion with L2-S1 mini-open instrumented fusion for flat back and scoliosis. A & B) One year following surgery the patient developed PJK and fracture at L2. C & D) An extension of fusion to T11 was required.
Figure 2 Surgical case example of persistent axial pain without a clear structural etiology. A & B) This 68 year old patient underwent a T10 to L5 MIS ASD surgery with MIS transforaminal lumbar interbody fusion (TLIF) at L3-5. C) The patient had no complications from surgery but continued to complain of axial pain which was improved from preoperatively, but with a less than 12.8 point ODI gain. Follow-up for 8 years included repeated tests and imaging for various causes including D) distal and E) proximal structural causes of axial pain. The workup was also negative for SI joint arthritis, nonunion, and hardware breakage. Ultimately, no clear etiology was identified.
Figure 3 Surgical case example of non-adjacent spinal disease progression. A & B) A 70 year-old male was treated with lateral interbody fusion (LIF), anterior column resection (ACR), and open T10 to pelvis posterior instrumented fusion. C) The patient later developed cervical myelopathy requiring an anterior C5 to T1 decompression and instrumented fusion.
Table 1: Etiologies of Non-Improvement Following Minimally-Invasive Correction of Adult Spinal Deformity Etiology of Non-Improvement
Category
Number
Percentage
Persistent axial pain in area of surgery w/o clear structural etiology
Idiopathic
11
14.0%
Other non-spinal arthritides
Degenerative progression
10
12.8%
Adjacent segment disease (ASD)
Structural
8
10.0%
Non-adjacent spinal fracture or stenosis (e.g.: cervical)
Degenerative progression
8
10.0%
Sacroiliac (SI) Joint pain
Degenerative progression
6
7.7%
Other severe medical comorbidities (e.g.: cardiac, pulmonary, neoplastic)
Medical
6
7.7%
Pseudarthrosis/nonunion
Structural
6
7.7%
Trauma causing other injuries
Traumatic
5
6.4%
Structural
5
6.4%
Undertreatment
5
6.4%
Neurological
4
5.1%
Hardware failure/fracture
Structural
3
3.8%
Nerve root injury or neve pain
Neurological
3
3.8%
Other medical complications from surgery
Medical
1
1.3%
Death
Medical
1
1.3%
Floor effect
Floor effect
4
5.1%
Could not be determined
6
7.7%
Total
92
Proximal junctional kyphosis (PJK) Undertreatment (spinal pain from other levels or incomplete correction of deformity) Other neurological degenerative disease (e.g.: Parkinson's or stroke)
Abbreviations: ACR: Anterior Column Resection AP: Anteroposterior ASA: American Society of Anesthesia ASD: Adult Spinal Deformity BMI: Body Mass Index IRB: Institutional Review Board LIF: Lateral Interbody Fusion MCID: Minimal Clinically Important Difference MIS: Minimally Invasive NPS: Numeric Pain Scores ODI: Oswestry Disability Index PI-LL: Pelvic Incidence-Lumbar Lordosis PJK: Proximal junctional kyphosis PROMs: Patient Reported Outcome Measures SI: Sacroiliac SVA: Sagittal Vertical Axis TLIF: Transforaminal Lumbar Interbody Fusion
1 Financial Disclosures Dr. Wang declares the following financial interests/personal relationships which may be considered as potential competing interests: grants from Department of Defense, personal fees from DePuy-Synthes Spine, Inc, personal fees from Stryker Spine, personal fees from K2M, personal fees from Spineology, other from DePuy-Synthes Spine, Inc, other from Children's Hospital of Los Angeles, other from Springer Publishing, other from Quality Medical Publishing, other from Vallum, other from Spinicity, other from Innovative Surgical Devices, outside the submitted work. Dr. Uribe declares the following financial interests/personal relationships which may be considered as potential competing interests: research support, stock options, and consulting fees from NuVasive, Inc. as well as consulting fees from SI-Bone outside of the submitted work. Dr. Mummaneni declares the following financial interests/personal relationships which may be considered as potential competing interests: personal fees from DePuy Spine, personal fees from Globus, personal fees from Stryker, other from ISSG, other from Spineart, other from Thieme Publishing, other from Springer Publishing, grants from NREF, grants from AO Spine, other from DePuy Spine, other from Spinicity, other from ISD, outside the submitted work. Dr. Park declares the following financial interests/personal relationships which may be considered as potential competing interests: personal fees from Globus, personal fees from NuVasive, personal fees from Allosource, grants from Pfizer, grants from Vertex, personal fees from Medtronic, outside the submitted work. Dr. Nunley declares the following financial interests/personal relationships which may be considered as potential competing interests: patents with royalties paid to K2M, a patent with royalties paid to LDR Medical, other from Amedica Corporation, other from ZimmerBiomet, other from K2M, other from Paradigm, other from Spineology, other from Vertiflex, other from Camber Spine, other from Integrity, other from Centinel Spine, outside the submitted work Dr. Kanter declares the following financial interests/personal relationships which may be considered as potential competing interests: other from Nuvasive, other from Zimmer Biomet, outside the submitted work. Dr. Okonkwo declares the following financial interests/personal relationships which may be considered as potential competing interests: consultant for NuVasive, Zimmer Biomet, and Stryker; is a patent holder with Zimmer Biomet; and receives royalties from Zimmer Biomet and
2 NuVasive. Dr. Anand declares the following financial interests/personal relationships which may be considered as potential competing interests: personal fees from Medtronics, other from Medtronics, other from Medtronics, other from Globus Medical, other from Globus Medical, other from GYS Tech, other from Paradigm Spine, other from Theracell, other from Elsevier, outside the submitted work. Dr. Chou declares the following financial interests/personal relationships which may be considered as potential competing interests: personal fees and other from Medtronic; and personal fees and other from Globus, outside the submitted work. Dr. Shaffrey declares the following financial interests/personal relationships which may be considered as potential competing interests: grants from ISSF Foundation, during the conduct of the study; personal fees from Medtronic, personal fees from NuVasive, personal fees from Zimmer Biomet, outside the submitted work. Dr. Fu declares the following financial interests/personal relationships which may be considered as potential competing interests: consultant for SI-Bone, DePuy, Globus. Dr. Mundis Jr. declares the following financial interests/personal relationships which may be considered as potential competing interests: personal fees from Nuvasive, personal fees from K2M, personal fees from Allosource, personal fees from Seaspine, personal fees from Viseon, outside the submitted work; patent Nuvasive with royalties paid, and a patent K2M with royalties paid. Dr. Eastlack declares the following financial interests/personal relationships which may be considered as potential competing interests: personal fees from Globus Medical, personal fees from Nuvasive, personal fees from Seaspine, other from Invuity, other from Aesculap, other from Baxter, other from K2M Stryker, other from Nuvasive, other from SI Bone, other from Titan, other from Aesculap, non-financial support from Seaspine, other from AO, other from Seaspine, other from Nuvasive, other from Nuvasive, other from Seaspine, other from Alphatec, outside the submitted work. The other authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Funding: This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.