Degenerative Cervical Myelopathy: From Basic Science to Clinical Practice

Degenerative Cervical Myelopathy: From Basic Science to Clinical Practice lays the foundation for understanding DCM manifestation, pathophysiology, diagnosis and treatment strategies. The book covers the latest basic and clinical research, updates on patient management strategies, and discusses promising neuroprotective therapies for the future of DCM care. Written by international experts across a range of topics related to degenerative cervical myelopathy, the book helps readers understand the challenges and future directions of patient management.

As degenerative cervical myelopathy (DCM) is the leading cause of spinal cord dysfunction and one of the most common indications for spinal surgery worldwide, the term DCM encompasses a group of chronic, non-traumatic spinal cord injuries that occur due to degenerative changes in the cervical spine (e.g. disc spondylosis or repetitive dynamic injury from hyper-mobility).

• Covers recent clinical trial advancements and the impact of trial findings
• Presents recent clinical guidelines for the management of degenerative cervical myelopathy, providing readers with insights regarding the translation of research from bench to bedside
• Provides readers with the skills needed to understand the translational pathway using real-life examples

• Language: English
• Publisher: Academic Press
• Release date: Nov 24, 2023
• ISBN: 9780323957915

Book preview

Preface

Michael G. Fehlings

Ten years ago, there was not a single comprehensive bench to bedside textbook dedicated to degenerative cervical myelopathy (DCM)—the term was yet to come into existence. Today, in 2023, I am delighted to see this textbook hit the shelves and provide the community with an overview of DCM from basic science to clinical practice. I have dedicated my career to the fields of neurosurgery and neuroscience with the aim of producing meaningful change in the lives of those living with spinal cord dysfunction. Throughout my career, I have encountered many patients living with DCM and have learned from every case. These patients inform the topics I study from a research perspective and how I approach clinical practice. The purpose of this textbook is to share my knowledge, as well as the expertise of the dedicated clinicians and researchers who wrote many of the chapters, with you.

In the last decade, there has been a rapid advancement in the understanding of and awareness for DCM, which is the most common cause of spinal cord impairment worldwide and one of the leading indications for spinal surgery. DCM encompasses a group of chronic, nontraumatic spinal cord injuries that occur due to degenerative changes in the cervical spine (e.g., disc spondylosis or repetitive dynamic injury from hypermobility) and genetically mediated conditions such as ossification of the posterior longitudinal ligament (OPLL). The natural history of DCM is typically one of progressive neurological dysfunctions, leading to difficulties performing activities of daily living such as eating, walking, and controlling bowel/bladder function. Significant pain is another common symptom for those living with DCM. Importantly, those affected by DCM report substantial reductions to their quality of life and independence. Despite the high incidence of DCM, little is known about the optimal management of this condition. With an aging population, the prevalence of this condition is expected to rise, further highlighting the current importance of this topic.

Recent efforts to enhance knowledge synthesis and translation have already begun to enhance outcomes for DCM patients. The overarching term of degenerative cervical myelopathy, coined by my lab in 2015, encompasses numerous related conditions, including cervical spondylotic myelopathy, OPLL, ossification of the ligamentum flavum, and degenerative disc disease. By placing these unique conditions under one umbrella, it was possible to view degenerative conditions affecting the cervical spine holistically as well as to generate robust diagnostic tools and care pathways for patients.

Following introduction of the DCM term, we have witnessed an explosion in research over the last 10 years. Advancements in our understanding of the pathophysiology, the application of advanced imaging modalities, and studies on surgical management led to the development of the first-ever clinical practice guidelines for this condition. Published in 2017, the guidelines provided recommendations on the surgical management of mild, moderate, and severe DCM. The guidelines project was critical for spurring awareness surrounding DCM management and enabling patients to become more active in the decision-making process.

More recently, the RECODE-DCM project identified the top 10 immediate priorities surrounding DCM. Topics such as raising awareness, better understand the natural history of DCM, and defining the optimal diagnostic criteria were included on the list. Importantly, the RECODE-DCM initiative served to raise awareness in the clinic, research labs, as well as with key healthcare stakeholders.

Within this textbook, I have attempted to have all contributors write their chapters to appeal to a broad audience. DCM touches a wide range of health professionals, trainees, and researchers, from family physicians who do the initial screening, radiologists who aid in diagnostics, neurosurgeons and orthopedic surgeons who lead surgical management, dedicated support staffs who facilitate care, rehabilitation teams who aid in the recovery of function, and basic, clinical and translational researchers. I hope this textbook will serve as a resource for trainees in clinical and scientific disciplines. As this condition becomes more common, it is critical that the healthcare ecosystem is prepared to address the challenges and all stakeholders are comfortable identifying and initiating care pathways for affected individuals.

This textbook includes perspectives on diagnosis, clinical decision-making, and multidisciplinary management that span the breadth of nonoperative management to operative intervention and pre- as well as postoperative rehabilitation. Imaging is critical to confirming the diagnosis of DCM—two chapters are focused primarily on imaging techniques including advanced magnetic resonance imaging approaches. Moreover, all the chapters on clinical decision-making include the use of various imaging modalities to facilitate management.

In closing, I wish to express my thanks to everyone who contributed to this textbook, including my colleagues from around the globe. For a number of these individuals, we have been working on various knowledge translation and research projects specific to DCM for over a decade. I am thankful that we were able to bring this book together to share with you. I would also like to express my gratitude to members of the Fehlings Lab, many of whom contributed directly to this textbook or to studies that are cited here. I am extremely proud of the research that you have completed, and it is incredibly special to see the findings from this work having a direct impact on the lives of individuals affected by DCM.

Chapter 1

Degenerative cervical myelopathy: an overview of the commonest form of spinal cord impairment in adults

Nader Hejrati¹,²,³,⁴, Karlo M. Pedro⁴,⁵ and Michael G. Fehlings⁶,⁷,⁸,    ¹Genetics and Development, Krembil Research Institute, University Health Network, Toronto, ON, Canada,    ²Eastern Switzerland Spine Center, Cantonal Hospital, St. Gallen, Switzerland,    ³Division of Neurosurgery and Spine Program, Department of Surgery, University of Toronto, Toronto, ON, Canada,    ⁴Division of Neurosurgery, Krembil Neuroscience Centre, Toronto Western Hospital, University Health Network, Toronto, ON, Canada,    ⁵Institute of Medical Science, University of Toronto, Toronto, ON, Canada,    ⁶University of Toronto, Toronto, ON, Canada,    ⁷Robert Campeau Foundation/Dr. C.H. Tator Chair in Brain and Spinal Cord Research at UHN, Toronto, ON, Canada,    ⁸Krembil Brain Institute, Toronto Western Hospital, University Health Network, Toronto, ON, Canada

Abstract

Degenerative cervical myelopathy (DCM) is a recently coined term that has been introduced to describe a number of age-related and congenitally associated degenerative changes of the cervical spine that ultimately result in cervical myelopathy. Despite the heterogeneous presentation of DCM (e.g., degenerative disk disease, hypertrophy of the ligamentum flavum, ossification of posterior longitudinal ligament), the commonality of these pathologic entities is that they eventually result in spinal cord dysfunction through static and dynamic injury mechanisms. With an ever-growing proportion of the world population reflecting an ageing demographic, DCM is becoming more prevalent and has evolved to the commonest form of spinal cord impairment in adults. The progressive nature of the disease results in neurological deficits that may contribute to significant impairments of activities of daily living and decline quality of life. In patients with moderate and severe forms of DCM, surgical decompression is the only proven therapy to halt progression of disease and offer some neurologic recovery. Clinical decision-making has been proven to be more challenging in patients with mild DCM, where a trial of structured rehabilitation might constitute a valid alternative strategy. Development of diagnostic tools capable of capturing the subpopulation of patients with mild DCM that warrant surgical intervention is of utmost importance. Owing to the inherent limited regenerative capacity of the spinal cord, patients often show only modest functional recovery following surgical decompression. Future research efforts will therefore have to focus on novel neurorestorative strategies including neuroprotective, neuroregenerative and neuromodulative therapies that aim at mitigating the harmful effects of chronic cord compression and regain lost neurologic function.

Keywords

Degenerative cervical myelopathy; pathobiology; neurologic recovery; imaging; neuroprotection; outcomes; surgery

Introduction

Degenerative cervical myelopathy (DCM) is a progressive neurological condition, which can result in life-changing consequences among affected individuals. The neurologic dysfunction results from an insult to the spinal cord as a result of progressive degeneration of the spinal axis and resultant spinal cord compression. In fact, DCM is considered to be the most common cause of nontraumatic spinal cord dysfunction worldwide [1], a condition for which restorative treatments have not yet been established. The prevalence of DCM has been previously reported at a minimum of 6.05 per 100,000 in North America [2]. However, it is likely that previous studies underestimate the true prevalence and incidence of DCM. Symptoms of DCM can be mild and patients themselves may fail to perceive functional deterioration due to mechanisms of behavioral adaption and neuroplasticity, which may result in a significant number of undetected cases [3]. With an increasing proportion of the world population reflecting an aging demographic, it is expected that age-related degenerative changes of the cervical spine, and subsequently DCM, will become more prevalent. It is therefore becoming increasingly evident that DCM represents a significant unmet need that must become an international public health priority [4,5].

The epidemiology of DCM mirrors the observed demographic shift in the spinal cord injury (SCI) patient population, which shows a greater preponderance in elderly individuals [6,7]. Of importance, a great proportion of elderly patients with traumatic SCIs have been reported to have preexisting degenerative changes of the cervical spine [8]. As a result, traumatic central cord syndrome, one of the most common types of incomplete SCI, has been associated with cervical hyperextension injuries in elderly individuals with preexisting cervical degenerative changes, and is commonly found after minor trauma with no evidence of spinal column injuries [9].

Historically, cervical myelopathy due to degenerative changes of the spine has been known by over 11 different names (e.g., cervical spondylotic myelopathy, cervical spinal myelopathy, cervical stenosis with myelopathy). Not surprisingly, this has generated clinical as well as research challenges, and importantly complicated awareness [10]. As a result, a multistakeholder consensus process was initiated involving spine surgeons, other healthcare professionals, DCM patients, and caregivers to identify a single name and definition for cervical myelopathy resulting from degenerative spinal column pathology [10]. As a consequence of these efforts, which have been led by the AO Spine RECODE-DCM initiative (Research objectives and Common Data Elements Degenerative Cervical Myelopathy), DCM was chosen as the unifying term that essentially defines progressive SCI caused by narrowing of the spinal canal.

DCM is an umbrella term describing various age-related and genetically associated degenerative conditions of the cervical spine (e.g., degenerative disk disease, cervical spondylotic myelopathy, and ligamentous aberrations such as ossification of the posterior longitudinal ligament or the ligamentum flavum) that ultimately result in cervical myelopathy (Fig. 1.1) [2]. On rare occasions, DCM may be associated with congenital disorders such as Ehlers–Danlos, Klippel–Feil, or Down syndrome. Despite their heterogeneity, the common feature of these pathological entities is that they eventually result in either chronic compressive, tractive, or shear forces to the spinal cord causing neurological dysfunction through static and/or dynamic injury mechanisms [2,9]. Intensive research efforts over the past decades have shed light on the complex microstructural processes involved in the pathobiology of DCM. As the clinical picture closely resembles that of spinal cord-injured patients, it is not surprising to see that the pathophysiology of DCM resembles that observed in traumatic SCI. In brief, the injury cascade is initiated as the spinal cord and its macro- and microvasculature experiences chronic stress through surrounding structures (e.g., osteophytes, disk, hypertrophied ligaments), thereby impeding spinal cord perfusion. This leads to ischemia-induced hypoxic endothelial cell death and disruption of the blood–spinal cord barrier, which ultimately renders the spinal cord permeable to the influx of inflammatory cells and blood-borne toxins [11–14]. Enhanced comprehension of the underlying pathomechanism of DCM has unveiled varied potential therapeutic targets, and therefore research strategies that we will discuss throughout this book.

Figure 1.1 An overview of the varied pathological changes in the cervical spine that may be involved in the development of degenerative cervical myelopathy. Medical illustration by Diana Kryski (Kryski Biomedia). Reprinted with permission from Nouri A, Tetreault L, Singh A, et al. Degenerative cervical myelopathy: epidemiology, genetics, and pathogenesis. Spine 2015;40:E675.

Diagnosis of degenerative cervical myelopathy

Magnetic resonance imaging (MRI) in conjunction with a thorough clinical neurological examination is the mainstay of a diagnostic workup in patients suspected with DCM. However, it is becoming increasingly evident that conventional MRI (T2 and T1 sequences), as well as the widely used (modified) Japanese Orthopedic Association scale, may be insensitive to capture microstructural pathology or detect clinical deterioration at an early stage of the disease, respectively [15]. Detection of neurological deterioration is particularly important in the subpopulation of patients with mild DCM who are initially managed nonoperatively. The most recent 2017 AO Spine practice guidelines suggest that both surgical intervention and a supervised trial of structured rehabilitation are equivalent treatment options in the management of patients with mild DCM; however, transition to surgical intervention is recommended if a patient neurologically deteriorates or fails to improve [16]. Timely recognition of functional deterioration or progression of (micro)-structural pathological changes to the spinal cord is therefore a crucial element in the management of patients with mild DCM. With a reported sensitivity rate of only 28% for anatomical MRI to detect deterioration, more sensitive tools are clearly warranted. Advanced MRI protocols have been investigated in DCM, including functional MRI, diffusion tensor imaging, magnetization transfer, myelin water fraction, T2*-weighted imaging, and MR spectroscopy, may hold the potential solutions to this problem [17]. One particular metric derived from T2*-weighted imaging that has shown promise as a biomarker of white matter injury is the T2* white matter to gray matter signal intensity ratio [18]. A combination of clinical assessments, such as the mJOA score, manual dexterity, grip strength, as well as gait and balance analysis in conjunction with advanced imaging modalities holds the potential to inform clinical decision-making and guide healthcare providers in the selection process of an appropriate treatment.

While standard radiographic features (such as computed tomography, MRI, and conventional radiographs), as well as baseline neurologic status, might be similar among different patients with DCM, there is a considerable degree of heterogeneity in patient’s individual functional recovery and outcome. These observations potentially suggest the existence of additional factors beyond what is currently being detected with contemporary diagnostic tools. As an example, molecular biomarkers, such as the apolipoprotein E (ApoE) allelic status have been shown to play a key role in the pathogenesis of DCM as well as predicting patient outcomes following surgery. Specifically, an ApoEε4 gene polymorphism, which can be easily detected using venous sampling, has been found to be associated with an increased risk of developing myelopathy in patients with chronic cord compression, as well as predicting worse functional outcomes following surgery in DCM patients compared to individuals who do not harbor the gene polymorphism [19,20]. With other promising biomarkers on the horizon (e.g., circulating microRNAs such as MIR21–5p) [21], genetic profiling might evolve to a strong ancillary tool expanding the clinician’s armamentarium for risk stratification and outcome prediction in patients with DCM.

Treatment of degenerative cervical myelopathy

Surgical decompression of the spinal cord (with or without fusion) is the only proven therapy to halt progression of the disease and improve functional outcomes in patients with DCM. The 2017 multidisciplinary AO Spine guideline provided the first consensus-based recommendations for the management of patients with DCM. Accordingly, patients with mild DCM (mJOA 15–17) might be offered an initial trial of nonoperative management (i.e., structured rehabilitation and surveillance), whereas patients with moderate (mJOA 12–14) or severe DCM (mJOA 0–11) should be offered surgical intervention as first-line therapy [16]. While clinical decision-making in DCM patients with mild symptoms might not be as straightforward, the progressive nature of the disease suggests that a certain proportion of patients might necessitate a change in their therapeutic regimen if neurologic deterioration occurs during the course of nonoperative treatment [22]. Not only is it critical to identify the subpopulation of mild DCM patients that need to transition from nonoperative management to surgical intervention, but the early timing of surgery has also been shown to be a key element influencing functional recovery [23].

The election of the optimal surgical approach in patients with DCM has generated a source of vibrant debates and remains controversial. Over the past two decades, a number of cohort studies have been published only to add further to the complexity and equipoise between anterior and posterior surgical decompression. The highest evidence to date has only recently been published in a randomized controlled trial recapitulating earlier findings that an anterior cervical approach does not significantly improve patient-reported outcomes (Short Form 36) at 1 year following surgery when compared to posterior surgical approach [24]. As we will discuss further in detail in this book, it is important to note. However, that a number of patient-specific factors (such as modified K-line, sagittal alignment, location of the pathology) and surgeon-related factors (e.g., preference and skills) need to be considered when choosing the appropriate surgical strategy for an individual patient.

While surgical decompression continues to be a central component of DCM therapy, full restoration of neurologic function is rarely seen, particularly in patients with severe and long-standing functional deficits. Despite surgery, persistent myelopathic symptoms, such as impaired mobility, manual dexterity, muscle weakness, and autonomic dysfunction manifested as bladder/bowel sphincter dysfunction may contribute to significant impairments of activities of daily living and decline the quality of life [25]. As such, alternative therapeutic strategies are highly needed to counteract the postsurgical plateauing phase of functional recuperation. This is reflected in the recent James Lind Alliance priority setting partnership, which identified the following uncertainty as one of the top ten priorities in the field of DCM: Can novel therapies, including stem-cell, gene, pharmacological and neuroprotective therapies, be identified to improve the health and wellbeing of people living with DCM and slow down disease progression? [26]. It is therefore indispensable that future research endeavors focus on novel neurorestorative strategies in the field of DCM including neuroprotective (e.g., Riluzole, corticosteroids, immunomodulators), neuroregenerative (e.g., stem cell therapies), and neuromodulative strategies (e.g., spinal cord stimulation).

Overview of chapters

This book starts with an overview of the anatomy and physiology of the cervical spine and the cervical spinal cord, and then moves into the epidemiology, genetics and classification of DCM. We then discuss the pathophysiology of DCM, methods to assess the cervical alignment and deformity and clinical assessment tools to detect and monitor the disease. An overview of imaging modalities and electrophysiological techniques is then provided. This will be followed by a discussion of the natural history of DCM along with the primary care practitioner’s role in the assessment and management of DCM. Several chapters will focus on the therapeutic management of patients with DCM and include (1) an overview of management options related to current guidelines, (2) prehabilitation and rehabilitation strategies, (3) decision-making in the surgical management of DCM, and (4) a detailed discussion on anterior and posterior surgical approaches. Finally, a discussion on potential serological, genetic and imaging biomarkers, and nonoperative strategies, including neuroprotective and neuroregenerative therapies, will be provided. This book concludes with an overview of the state of the art and future directions of DCM. A summary of each chapter, highlighting the key points, is provided here.

Anatomy and physiology of the cervical spine and the cervical spinal cord

In this chapter, the authors discuss the structural and functional anatomy of the cervical spine, which can be divided into two main segments: (1) the craniocervical junction (CCJ) (Occiput to C2 (Atlas)) and the subaxial spine (C3–C7). The cervical spine as a whole is in charge of bearing the weight of the head and permitting movement of the neck and head. The cervical spine has a substantial level of anatomical variance despite exhibiting the majority of common vertebral characteristics. Its primary function is to support and facilitate the movement of the head and neck. More motion and flexibility, nevertheless, may come with a higher risk of harm to the spinal cord and its related neurovascular systems.

Epidemiology, genetics, and classification of degenerative cervical myelopathy

DCM represents a group of age-related degenerative disorders of the cervical spine that result in a form of chronic SCI, presenting with a diverse natural history. Classically, this condition was referred to as cervical spondylotic myelopathy. However, this term lacked precision and pathologic entities, such as ossification of the posterior longitudinal ligament and degenerative herniated disc disease, for example, were inconsistently included resulting in the reidentification of the term under DCM in 2015. There has been significant progress in detailing the epidemiological parameters and investigations of genetic factors that can be associated with the spectrum of the disease. This chapter explores this new classification and discusses the epidemiology and genetic factors under this new perspective.

Pathophysiology of degenerative cervical myelopathy

This chapter discusses the pathophysiology of DCM. It provides a concise review of the etiology of DCM and then review potential genetic risk factors in humans and animal models. It will then lead over to a thorough discussion of the microstructural processes involved in DCM that result from chronic compression of the spinal cord, including ischemia, blood–spinal cord barrier disruption, and neuroinflammation. Systemic implications, such as recent associations between DCM and gastrointestinal dysfunction, cytokines, chemokines, and microRNAs as potential biomarkers of DCM progression, as well as neurobehavioral recovery following surgical decompression, are then discussed. The chapter concludes with an overview of the main animal models used in basic science to reproduce the natural history of DCM and study therapeutic strategies.

Clinical assessment tools

In this chapter, the science of clinical measurement is introduced and applied to the assessment of DCM. We begin by introducing the theoretical framework of constructs as well as items, and then provide knowledge of how to appraise and choose tools for a clinical assessment. The assessments that we focus on are measurements of either the patients’ level of impairment or their quality of life. Comprehensive data on the measurement properties of all DCM tools available is presented and discussed, and a deep dive into the tools in the DCM core measurement set, as well as emerging assessments, is featured.

Imaging for degenerative cervical myelopathy

Currently, conventional MRI (T2 and T1 weighting) remains the modality of choice in the assessment of DCM as it has been shown to be useful in visualizing the precise location of stenosis, and can provide insights into the extent of intramedullary damage through T2-weighted hyperintensity or T1-weighted hypointensity. However, cervical stenosis causing spinal cord compression or deformation is common, while the majority of individuals do not develop symptoms or signs of myelopathy. Although sensitive in detecting spinal cord compression, conventional MRI has demonstrated low specificity for DCM. In addition, signal intensity changes present on conventional MRI have poor sensitivity for myelopathy and correlate poorly with the severity of neurological deficits. Quantitative neuroimaging techniques can overcome this limitation by providing reproducible maps of quantitative values proportional to tissue microstructure such as myelin, axonal density, tissue vascularization, iron deposition, and metabolic profiling. In this chapter, we will discuss recent advances in quantitative MRI techniques (e.g., T2*-weighted MRI, diffusion tensor imaging, magnetization transfer, functional MRI) that may hold the potential to provide sensitive biomarkers of spinal cord tissue integrity as well as underlying pathology, and can ultimately aid in clinical decision-making.

Neurophysiology and advanced dynamic assessments in degenerative cervical myelopathy

Early diagnosis and management of DCM is essential to prevent further disease progression. Current diagnosis relies heavily on unspecific clinical and imaging assessment tools, which may not be able to detect early signs of impairment in patients with DCM. Advanced objective diagnostics have emerged as promising tools to detect early signs of impairment in DCM, beyond the presence of evident clinical symptoms. In this sense, advanced neurophysiological techniques (i.e., contact heat evoked potentials) allow the assessment of silent damage within the spinal cord as related to impairment in both descending and ascending white matter tracts. Moreover, advanced dynamic assessments of spinal cord stress include spinal cord motion analysis by means of phase-contrast MRI and measures of cerebrospinal fluid pressure dynamics. Collectively, these advanced clinical assessment tools represent valuable measures for early diagnosis of DCM and hold the potential to improve the prediction and monitoring of disease progression.

Assessment of cervical alignment and deformity

The successful management of cervical deformity relies on proper assessment. The symptoms and signs are as essential a part of the assessment as the radiological parameters. In this chapter, the details of patient history and examination are considered, alongside the radiological parameters to be evaluated. Specific considerations for the craniocervical junction, subaxial spine, and cervico-thoracic junction are detailed and the targets for surgical correction defined.

Natural history and patient trajectory in degenerative cervical myelopathy

The increased availability of MRI has unveiled a subpopulation of patients with DCM with mild symptoms of myelopathy who may have minimal or no impairment during daily activities. Despite the notion of the progressive nature of the degenerative disease, the natural history of DCM remains poorly understood. Thus, evidence supporting clinical decision-making in patients with mild forms of DCM, where a trial of structured rehabilitation has been suggested as an alternative option to surgical decompression, remains a challenge that warrants further investigation. In this chapter, we will summarize the evidence on the natural history of DCM and discuss potential risk factors in the progression of DCM, such as anatomic, genetic and environmental (e.g., trauma) factors. Sensitive biomarkers are needed to capture the subpopulation of patients with mild DCM who are at particular risk of disease progression and to personalize treatment approaches.

Role of the primary care practitioner in the assessment and management of degenerative cervical myelopathy

This chapter examines the importance of primary care in managing DCM. Primary care is often the point of first contact for patients with DCM; however, the diagnosis is often delayed or missed. The barriers to diagnosing and managing DCM in primary care (awareness, knowledge, system/access) will be discussed. A practical clinical approach to diagnosing and managing DCM will be outlined that can be utilized by clinicians. Future strategies and solutions for improving the primary care management of DCM will be reviewed.

Research objectives and common data elements for degenerative cervical myelopathy: from research priorities to global action

This chapter outlines a knowledge translation initiative called RECODE-DCM (Research objectives and Common Data Elements for DCM), which aims to accelerate the acquisition and implementation of knowledge that can change outcomes. RECODE-DCM was originally established to address three key barriers to knowledge discovery: First, What to research? Identifying the top research priorities in DCM and addressing an imbalance in research activity and critical knowledge gaps. Second, What to call the condition? Agreeing on a unifying index term and addressing the widespread variation in terminology hampering evidence searching and interpretation. Third, what to measure in DCM trials? Forming a minimum dataset for DCM trials, to ensure studies are comparable and therefore meaningful. These important questions were addressed by mobilizing a diverse, global, and multidisciplinary community including people living with DCM.

Overview of management options for degenerative cervical myelopathy

An expanding body of evidence exists defining optimal management strategies for patients with DCM. Current guidelines recommend surgical intervention for severe or moderate cases of DCM. In patients with mild DCM, or radiographic compression without myelopathy, either surgical intervention or structured nonoperative intervention can be pursued. Once the decision is made to operate, the choice of surgical approach (anterior vs. posterior vs. combined) is influenced by patient and disease characteristics. Recent research efforts have attempted to weigh the efficacy and complication profile of different surgical approaches in situations in which clinical equipoise may exist. This chapter reviews the treatment options available in the management of DCM, and the available evidence behind each strategy.

Defining the position of rehabilitation in the management of degenerative cervical myelopathy

The role of rehabilitation and rehab professionals in the management of DCM is relatively new and under-established. While the DCM population presents with a number of rehabilitation challenges, few resources have been put forth to provide DCM patients with specific multidisciplinary intervention for clinical management. In this chapter, we review the current use of rehabilitation in the management of DCM and the current literature that defines the field of outcome assessments in DCM. We use these findings to help define the role of rehab as it relates to close monitoring of a progressive disease. We then take this evidence one step further and consider the most meaningful way to apply this new knowledge to how current management of DCM can be enhanced by building stronger multidisciplinary support, earlier detection of disease, and opportunities to enhance neuroplasticity. We also aim to expose the nuances of DCM and how this disease has a slightly different presentation from traumatic SCI. Hence, modified rehab approaches need to be considered as the application of existing rehab models from traumatic SCI is insufficient.

Decision-making in surgical management of degenerative cervical myelopathy

Surgical decompression of the spinal cord and fusion of the spinal column can arrest the progression of this pathological condition and can sometimes permit recovery of spinal cord function. Many patients with mild DCM symptoms are treated expectantly. Numerous reports suggest that DCM surgery has a high complication rate, while there may be appreciable differences in the morbidity between different surgical approaches (e.g., anterior versus posterior) for DCM. For these and other historical reasons, there is uncertainty as to the optimal surgical approach (anterior versus posterior) for treating DCM. This is particularly true in older patients. Both operative approaches are in widespread use in contemporary surgical practice. Moreover, laminoplasty (a motion-preserving type of posterior approach) is gaining recognition as an effective surgical approach for many patients with DCM. In this chapter, we will discuss the varied factors that need to be considered in the decision-making process of the appropriate surgical approach for patients with DCM.

Anterior surgical approaches to treat degenerative cervical myelopathy

This chapter focuses on anterior surgical approaches to the cervical spine for patients with DCM. Knowledge of pertinent surgical anatomy and surgical techniques are key essentials to achieving adequate decompression while maintaining low operative morbidity. The anterior surgical approaches discussed in this chapter include anterior cervical discectomy and fusion, anterior cervical corpectomy and fusion, and cervical disk arthroplasty. We will also draw comparisons to the multiple grafts and devices that are used during surgery and discuss complications associated with the anterior approach.

Posterior surgical approaches to treat degenerative cervical myelopathy—cervical laminectomy±fusion

In this chapter, we will discuss cervical laminectomy as a safe and effective surgical treatment for DCM that allows single or multilevel decompression of the spinal canal. The impact on the posterior ligamental complex and paraspinal muscle health post-laminectomy must be considered so that concomitant use of adjuncts (such as instrumented fusion) can be employed to prevent complications such as post-laminectomy kyphosis. Complications can include intraoperative SCI, dural tear, postoperative infection or wound breakdown, post-laminectomy kyphosis, and injury to the vertebral arteries.

Posterior surgical approaches to treat degenerative cervical myelopathy—cervical laminoplasty

Cervical laminoplasty is an effective and useful technique for the surgical treatment of DCM, and this procedure has been used worldwide with satisfactory outcomes. Herein, we will discuss two of the most commonly used techniques: open-door laminoplasty and double-door laminoplasty. Recent studies compared the surgical results between the two approaches, but both procedures are demonstrated to achieve comparable functional improvement. While laminoplasty is associated with favorable outcomes, there are a number of complications to consider including closure of expanded laminae, segmental motor paralysis, and axial neck pain. To enhance the efficacy and safety of laminoplasty, the frequency of these complications should be minimized by carefully evaluating technical considerations as well as focusing upon appropriate patient selection.

Nonoperative management of degenerative cervical myelopathy

This chapter examines current evidence-based treatment strategies for the nonoperative management of individuals living with asymptomatic DCM, or individuals with moderate-to-severe DCM, when the risks of surgical decompression outweigh the potential benefits. The chapter reviews principles and treatment strategies of the nonoperative management of individuals with DCM, while being focused on the restoration of upper and lower extremity motor and sensory function. The chapter closes with a review of secondary health conditions related to DCM, emphasizing the importance of their early recognition and effective management in order to improve individuals’ functional outcomes, quality of life and participation. Major knowledge gaps and opportunities for future research are underlined.

Neuroregenerative strategies for degenerative cervical myelopathy

DCM compromises neurological function to an extent that cannot be recovered through endogenous plasticity and regeneration. Despite the severe neuropathology arising from chronic spinal cord compression, very few studies have focused on regenerative strategies for DCM. Here, we describe the parallels in pathology and pathophysiology between DCM and traumatic SCI, as well as highlight that regenerative strategies are appropriate given the severity of injury. Modulation of the extracellular environment and cell-intrinsic approaches to regeneration are explored, in addition to potential roles for cell and gene therapies.

State of the art and future directions of degenerative cervical myelopathy

In this chapter, we will discuss advanced neuroimaging techniques, molecular-based diagnostics, and genetic tools, which hold the potential to become the cornerstone for effective management and treatment of DCM in the future. Despite the remarkable advances already achieved thus far, it will be necessary to continue global efforts to identify the ideal therapy especially in mild cases, establish a uniform diagnostic framework, and design management paradigms adapted to each individual patient situation.

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Chapter 2

Anatomy and physiology of cervical spine and cervical spinal cord

Mohammed Ali Alvi¹,², Ali Moghaddamjou¹,² and Michael G. Fehlings³,⁴,⁵,⁶,    ¹Institute of Medical Science, University of Toronto, Toronto, ON, Canada,    ²Division of Neurosurgery and Spine Program, Department of Surgery, University of Toronto, Toronto, ON, Canada,    ³Division of Genetics and Development, Krembil Brain Institute, University Health Network, Toronto, ON, Canada,    ⁴University of Toronto, Toronto, ON, Canada,    ⁵Robert Campeau Foundation/Dr. C.H. Tator Chair in Brain and Spinal Cord Research at UHN, Toronto, ON, Canada,    ⁶Krembil Brain Institute, Toronto Western Hospital, University Health Network, Toronto, ON, Canada

Abstract

The cervical spine is made up of the craniocervical junction (occiput to C2 (atlas)) and the subaxial spine (C3 to C7) are the two main segments of the cervical spine. The cervical spine as a whole is in charge of bearing the weight of the head and permitting movement of the neck and head. The cervical spine has a substantial level of anatomical variance despite exhibiting the majority of common vertebral characteristics. The cervical spine's primary function is to support and facilitate the movement of the head and neck. Given the minimal weight-bearing force at this level, large vertebral bodies are not required. Hence, a greater range of motion is more important than vertebral size and rigidity. More motion and flexibility, nevertheless, may come with a higher risk of harm to the spinal cord and its related neurovascular systems. In the current chapter, the authors discuss the structural and functional anatomy of the cervical spine.

Keywords

Cervical spine; craniovertebral junction; CCJ; subaxial cervical spine; neck; vertebra

Introduction

For accurate diagnosis and adequate management of any cervical spine pathology, a thorough understanding of the anatomy of the cervical spine is necessary. Clinicians and surgeons need to be able to understand the intricate anatomy and biomechanics, from the osseous structure to the soft tissue components that collectively support, maintain, and shield the spinal cord. The correct surgical planning and operating procedure for patients who are managed surgically depend on having a thorough understanding of the complex anatomy in this area. To give physicians a thorough review they can rely on and refer to while treating patients with cervical spine disorders, we discuss the cervical spine anatomy in this chapter with a focus on the osseous, muscular, ligamentous, and neurovascular components.

The cervical spine is typically divided into the craniovertebral junction, which includes the first cervical vertebra (C1), also known as the atlas, and the second vertebra (C2), also known as the axis; and the subaxial cervical spine which extends from the third cervical vertebra (C3) to the seventh cervical vertebra (C7), and the cervicothoracic junction (CTJ).

Osseous anatomy

Craniocervical junction

Occipital bone

The occipital bone runs from the clivus anteriorly to the lambdoid suture posteriorly. The embryologic genesis of the occipital bone is in four major cartilaginous centers that are laid down in the chondro-cranium around the foramen magnum and a fifth membranous element [1]. The transverse sinus may be roughly located using the superior nuchal line, and the inion, which is present in the midline along this line, resembles the torcular herophili. The most precise marking for the confluence of the sinuses may be the insertion of the semispinalis capitis [2].

The most important part of the occipital bone is the foramen magnum, which consists of three parts: the squamosal part that makes up the dorsal aspect of the foramen magnum's dorsal side; the basal or clival portion which makes up the anterior aspect, and the condylar part that connects the two parts [3]. The opisthion refers to the most posterior edge of the foramen magnum while basion refers to the foramen magnum's most anterior midline. The foramen magnum's sagittal diameter approximately measures 35.4 mm. The transverse diameter is a little bit smaller at its equator. The occipital condyles, which are part of the condylar portion, are located slightly above and anterior to the foramen magnum's equator. The angles at the craniocervical junction (CCJ), together with the shape of these condyles on either side of the foramen magnum, allow the skull to articulate with the cervical spine [4].

C1—atlas

The atlas, or first cervical vertebra (C1), derives from the fourth occipital and first cervical sclerotomes. It is the only vertebrae that lack a body and is made up of three ossification sites: the anterior arch or centrum and two neural arches that fuse later in life to form a unified posterior arch, completing the osseous ring that surrounds the spino-medullary junction [5]. It is critical to recognize that this ring is incomplete in up to 5% of patients in order to avoid causing a durotomy or spinal cord injury when approaching the CCJ posteriorly [6,7]. An anterior tubercle on the ring serves as the longus colli muscle's attachment point. This section of the atlas also gives rise to two important membranes: the anterior atlanto-occipital (AAO) membrane, which connects the atlas to the occipital bone, and the anterior atlantoaxial ligament, which runs from the atlas to the axis immediately inferior. A subtle indentation on the posterior aspect of the anterior tubercle, on the inner aspect of the anterior arch at the midline, allows for articulation with the dens of the axis. The transverse ligaments, which attach to the posterior aspect of the dens of the axis, have insertion sites just anterior and medial to the lateral masses on the inner aspect of the ring. The transverse process extends laterally from each lateral mass. The vertebral arteries are housed in the transverse process at this level before they leave the vertebral column and pass through the foramen magnum to become intracranial structures. A portion of the population has an anatomical variation known as an arcuate foramen or ponticulus-posticus, which is an osseous bridge covering the ridge containing the vertebral artery (VA). This variation is estimated to be 3%–15% prevalent in the population. The posterior tubercle, on the other hand, serves as an attachment site for the suboccipital membrane and the rectus capitis posterior minor muscle. The posterior atlanto-occipital (PAO) membrane runs from the superior border of the atlas' posterior arch to the anterior surface of the rim of foramen magnum [8,9]. The anterior and posterior arches are semicircular structures that are formed by the lateral aspects of the anterior and posterior tubercles. The lateral masses are created by the intersection of these arches on the rings' lateral-most aspect. Each lateral mass consists of an articular process on the superior and inferior aspect of the lateral mass. The VA runs through a subtle groove just posterior to the lateral mass. The superior articular process has a concave shape and is oriented inferiorly and medially; this allows for articulation with the occiput bilaterally. On the inferior aspect, the processes are oriented inferiorly and laterally with a sloped angle, allowing for articulation with the superior articular processes of C2 (axis) [10,11]. The orientation of the atlanto-occipital joints at caudal angles of 129° from lateral to medial allows for limited rotation, as opposed to the atlantoaxial joint, which has a cranially biased angulation of between 130° and 135°, allowing for much greater rotation. The articulation also allows for lateral bending [12,13].

C2—axis

The axis, which is the second cervical vertebra, is made up of five ossification sites, including two in the dens or odontoid process and one each in the body and each vertebral arch. The axis is the first bifid vertebra in the cervical spine and bears a broad, deeply concave spinous process on its caudal edge. The dens extends cephalad from the axis body, where it is articulated. An oval facet on the ventral surface of the dens articulates with the dorsal surface of the anterior tubercle of the atlas. Almost half of the head and cervical spine's rotatory movement is made possible via this articulation. The alar ligaments, which bridge the atlas and link medially to the posterior occipital condyles, are attached at two little prominences on the posterior aspect of the dens. The atlantoaxial complex is stabilized by these ligaments, which insert laterally at the base of the skull. The apical ligament is attached to the apex of the dens, which in turn is connected to the anterior aspect of foramen magnum in the midline. The transverse ligament, a structure that spans the anterior arch of the atlas and prevents lateral movement of the dens, serves as the principal stabilizer of the dens to the atlas. The transverse ligament of the atlas runs over a transverse groove in the dorsal part of the dens. The atlantoaxial complex is further stabilized by the transverse ligament's cephalad and caudal projections at the midline, known as the cruciform ligaments. The rectus capitis posterior major and obliquus capitis inferior muscles attach to the axis' posterior bifid spinous process. There are superior and inferior articular processes on the lateral sides of the axis, and they both articulate with corresponding parts of the surrounding vertebrae. In agreement with the inferior aspects of the lateral masses of the atlas, the superior facet slopes inferiorly laterally. The spinal canal of the cervical spine in this region has a larger sagittal diameter than the lower cervical spine, providing enough room for the dens and the spinal cord. The spinal cord takes up one-third of the canal's diameter, the dens occupies another third, and the remaining third is free space that prevents the cord from being compressed, according to Steel's rule of thirds