Abstract
Elective spine surgeries are performed for a variety of conditions including degenerative, neoplastic, inflammatory, infective, and congenital pathologies. They can vary in complexity from minimally invasive single-level microdiskectomies to extensive multisegment instrumentations, often performed thorough combined approaches and in multiple stages. Anesthetic management of major spine surgeries, particularly for older patients with multiple comorbidities can be very challenging. Besides providing optimal conditions for the surgery and for neuroelectrophysiological monitoring, the anesthetist has to manage significant fluid shifts and blood losses, potentially difficult airways, and perioperative procedure-specific complications; has to take spinal cord protection measures; and also has to provide adequate postoperative pain relief. To contribute to a successful clinical outcome, the anesthetist should be aware not only of the anesthetic implications of the spine pathology but also of the level of invasiveness and potential complications of the intended surgical procedure, along with the specific approach and position required for its optimal surgical exposure. This chapter describes the anesthetic considerations for adult patients undergoing elective spine surgeries.
Keywords
Anesthesia, General, Spinal, Spine, Surgery
Outline
Introduction 400
Spine 400
Types of Spine Surgeries 401
Surgical Approaches to the Spine 403
Common Spine Disorders 403
Spine Degenerative Disease 403
Craniovertebral Junction Anomalies 409
Conditions Associated With Spinal Instability 409
Conditions Associated With Cervical Spine Limitation 411
Congenital Abnormalities Involving the Cervical Spine 411
Ossification of the Posterior Longitudinal Ligament 413
Inflammatory Spondyloarthropathies 413
Neoplasms of the Spine 414
Infections of the Spine 416
Spinal Deformity 416
Metabolic Bone Disease: Osteoporosis 417
Imaging in Spine Lesions 417
Positioning for Spine Surgeries 417
Neurophysiological Intraoperative Monitoring During Spine Surgeries 418
Somatosensory Evoked Potentials 418
Motor Evoked Potentials 419
Electromyography 419
Multimodality Monitoring 420
Effect of Anesthetic Drugs on Neuroelectrophysiological Monitoring 420
Preanesthetic Assessment and Optimization 420
General Examination 421
Cardiac Evaluation 421
Pulmonary Evaluation 421
Neurological Evaluation 421
Hepatic Evaluation 422
Renal Evaluation 422
Hemopoetic System 422
Medication and Allergy History 422
Evaluation of Airway and Cervical Spine Mobility 422
Special Considerations 423
Anesthesia Management 423
Anesthetic Techniques 424
Airway Management 425
Airway Considerations in Patients With Cervical Spine Disorders 425
Airway Management Strategy 425
Airway Devices, Techniques, and Maneuvers 425
One-Lung Ventilation 426
Monitoring 427
Anesthetic Considerations for Neuroelectrophysiological Monitoring 427
Fluid and Blood Loss Management 428
Minimizing Damage to the Spinal Cord 429
Postoperative Management 430
Tracheal Extubation 430
Postoperative Airway Obstruction 430
Postoperative Pain Relief 431
Thromboembolism Prophylaxis 431
Special Considerations 431
Neoplasms of the Spine 431
Cervical Spine Surgeries 432
Thoracic Spine Surgeries 434
Anterior Approaches 434
Posterior Approaches 434
Scoliosis Surgeries 435
Video-Assisted Thoracoscopy 435
Vertebroplasty and Kyphoplasty 436
Lumbar Surgeries 436
Complications 437
Conclusion 437
References 437
Introduction
Over the past few decades, spinal surgery has evolved into an extremely specialized field; highly complex instrumentation procedures are increasingly being performed, across all age groups, and often through minimally invasive approaches. Needless to say, successful outcome of these surgeries demands an equally intricate and well-planned anesthesia strategy, which is based on a comprehensive understanding of the causative pathology, along with a precise knowledge of the specific requirements and potential complications of the proposed surgical procedure. The first section of this chapter provides an overview of the relevant functional anatomy of spine; common spine pathologies that may require operative intervention; various types of spine surgeries, patient positions, and operative approaches; and commonly used neuromonitoring techniques. The next section describes the preoperative evaluation and anesthetic management of adult patients undergoing elective spine surgeries; the final section focuses on specific concerns pertaining to cervical, thoracic, and lumbar spine surgeries.
Spine
Vertebral Column and Spinal Cord
The vertebral column (VC) is composed of 33 vertebrae [cervical (C), 7; thoracic (T), 5; lumbar (L), 5; sacral (S), 5; coccygeal, 4], which are interconnected by intervertebral (IV) disks (except C1, C2) and stabilized by spinal ligaments. The first two cervical vertebrae (C1, atlas; C2, axis) form the upper cervical spine; third to seventh cervical vertebrae (C3-C7) form the subaxial spine. The spinal cord is enclosed within the vertebral canal, where it is protected by the cerebrospinal fluid (CSF) and meninges. It is organized into 31 segments: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal; each segment innervates a dermatome via a spinal nerve.
The craniovertebral junction (CVJ) or occipitoatlantoaxial (OAA) complex is formed by atlantooccipital and atlantoaxial joints, which are stabilized by ligaments (cruciate, apical, alar, and cruciform ligaments) and membranes (anterior and posterior atlanto-occipital membranes; tectorial membrane). Cruciate ligament is composed of transverse and cervical ligaments.
Movements of the Neck
There are two distinct types of neck movements: linear motion and rotation. The neck moves through 90 degrees from full flexion to full extension; one-third of this occurs at the OAA complex, and the rest at the lower cervical spine (C5-C7). Extension at OAA complex is limited by contact of the posterior arch of atlas with the occiput superiorly, and by arch of axis inferiorly. Neck rotation almost entirely originates at the atlantoaxial joints. The axis has a superiorly protruding, cone-shaped, odontoid process (dens), which articulates with the anterior arch of the atlas to form the median atlantoaxial joint, a unique pivot joint that enables rotation of atlas on the axis; facet joints between C1 and C2 vertebrae form the lateral atlantoaxial joints.
Stability of the Spine
Stability of the spine is defined as “its ability to maintain normal inter-vertebral alignment and prevent excessive movement between vertebrae during normal physiological loading, so that spinal cord or nerve roots are not damaged or irritated, and deformity or pain does not occur.” This stability is provided by IV disks (anterior and vertical stability), facet joints (posterior stability), and various spinal ligaments, especially the anterior longitudinal ligament (ALL) and the posterior longitudinal ligament (PLL). The broad ALL, situated on the anterior surface of the vertebral bodies and IV disks, prevents hyperextension of the spine. The slender PLL, which lies within the vertebral canal, on the posterior surface of the vertebral bodies and IV disks, prevents hyperflexion of the VC.
Spine stability is most commonly assessed by the “three-column spine model” proposed by Denis, which involves evaluation of lateral spine radiographs in both flexion and extension. According to this model, the sagittal spine is divided into three columns. The anterior column is formed by the ALL, anterior half of body, and anterior annulus fibrosus of the IV disk; the middle column by PLL, posterior wall of vertebral body, and posterior annulus fibrosus of the IV disk; and the posterior column is formed by the posterior arch, ligamentum flavum, supraspinous, and interspinous ligaments. The spine is considered to be potentially unstable if two or more columns are disrupted. Spinal instability can result in injury to the spinal cord and/or nerve roots, progressive spinal deformity, neurologic loss, and chronic pain.
Stability of the CVJ depends fundamentally on the integrity of the dens, supporting ligaments and membranes, especially cruciate and alar ligaments. The thick, strong transverse ligament that is attached between the two bony tubercles on the inner anterolateral aspect of atlas, functions as a restraining band on the dens, to provide odontoid stability anteriorly and free spinal cord motion posteriorly. Normally, it does not allow >3 mm of translation between dens and the anterior arch of the atlas; this anterior atlas–dental interval (AADI) is measured on a lateral neck radiograph as the distance between the posterior surface of the anterior arch of atlas and the anterior surface of dens.
For proper functioning of the spinal cord, a minimum canal lumen is required, both at rest and during movement. Cord compromise occurs if the spinal canal space is decreased; neurologic injury occurs if this reduction is persistent. Area of the vertebral canal at C1 level can be divided into one-third odontoid peg, one-third cord, and one-third space (Steel’s rule of thirds). The area composed of the cord and space, allows for some encroachment of the spinal lumen without compromising the cord, and is referred to as “space available for the cord” (SAC) or posterior atlas–dens interval (PADI). It is a good predictor for potential neurological compromise and is measured on a lateral neck radiograph at the C1 level, as the distance between posterior surface of the dens and anterior surface of posterior arch of the atlas (normal PADI >20 mm).
At lower cervical levels, progressive narrowing of the canal combined with an increase in diameter of the spinal cord, causes a reduction in the SAC, with the spinal cord filling approximately 75% of the cross-sectional area of the canal at C4-C7 levels.
Types of Spine Surgeries
Common spine pathologies that can require surgical intervention include degenerative disorders, neoplasms, infections, trauma, inflammatory arthropathies, and congenital malformations ( Table 24.1 ) These interventions are often classified, according to their level of invasiveness, as simple decompression, simple spine fusion, and complex spine fusion (arthrodesis and instrumentation) ( Table 24.2 ).
| Degenerative disorders Disk herniation Spondylosis with radiculopathy and myelopathy Spondylolisthesis Spinal stenosis Craniovertebral junction anomalies Congenital malformations Ossified posterior longitudinal ligament Inflammatory spondyloarthropathies Rheumatoid arthritis Ankylosing spondylitis Neoplasms Metastatic tumors Primary tumors: Intramedullary: ependymoma, astrocytoma, hemangioblastoma Intradural–extramedullary: meningioma, peripheral nerve sheath tumors (schwannoma, neurofibroma), arachnoid cysts, hamartoma Extradural: Bone-forming tumors: osteoid osteoma, osteoblastoma, osteosarcoma Cartilage-forming tumors: chondroma, osteochondroma, chondrosarcoma Giant cell tumors: osteoclastoma Round cell tumors: Ewing sarcoma, malignant lymphoma and myeloma Vascular tumors: hemangioma, hemangioendothelioma Tumor like lesions: aneurysmal bone cyst, eosinophilic granuloma Infections Vertebral osteomyelitis Epidural abscess Granulomatous infections: Pott spine, fungal lesions Spinal deformity Scoliosis Kyphosis Axial skeleton fractures, dislocations, and metabolic disorders Osteoporotic fractures Vascular malformations Arteriovenous malformation Spinal arteriovenous dural fistula Trauma Muscular dystrophies |
| Simple Decompression Simple spine fusion : a single surgical approach and fusion of <2 disk levels Complex spine fusion : fusion of >2 disk levels, 360 degrees spine fusion by single incision, or a combined anterior–posterior fusion technique |
The aim of spinal decompression procedures is to increase the functional space for compressed neural elements ( Table 24.3 ). Spinal fusion involves joining of two vertebrae by insertion of graft material into the decompressed site. It has two major indications: first for the management of disorders that compromise the structural integrity of the spine, e.g., degenerative and inflammatory pathologies or vertebral fractures (traumatic or pathological—tumors, infection) and second, in combination with decompression procedures, to stabilize the spine when its native stability has been compromised, e.g., following multilevel decompression or an osteotomy. Several types of graft materials are available, such as autologous bone graft (iliac crest, fibula, ribs, humerus, femur), nonstructural allograft (demineralized bone matrix), or synthetic bone graft substitutes [titanium; ceramics such as hydroxyapatite and beta-tricalcium phosphate; polyaryletheretherketone (PEEK)]. Autologous bone autografts and vertebral interbody cages (titanium, PEEK, etc.) are commonly used for spinal fusion after anterior cervical diskectomy (ACD) or corpectomy.
| Diskectomy : removal of an intervertebral disk; may be performed via an anterior approach (cervical spine) or a posterior approach (thoracic, lumbar spine) Microdiskectomy : performed for decompression of nerve roots affected by a simple pathology. A small incision is made over the appropriate interspace and an operating microscope is used to retract the nerve root to allow disk material to be excised; bone is not usually removed Corpectomy : removal of one or more vertebral bodies in addition to their adjacent intervertebral disks Laminotomy : partial resection of laminae of two adjacent vertebrae, to decompresses the spinal cord/nerve root and also provide access for posterior removal of a laterally herniated disk Laminoforaminotomy : removal of a small portion of a unilateral lamina and facet joint (facetectomy), for enlarging the intervertebral foramen. A key hole foraminotomy decompresses only individual nerve roots (but not spinal cord) by creating a small keyhole in the lamina to access the nerve root Laminaplasty : involves expansion of the spinal canal by drilling bilateral troughs in multiple laminae; hinging them and swinging them open like a door and fixing them in position with small plates or sutures. Since the posterior elements are not removed completely, it is perceived to be associated with a decreased incidence of postlaminectomy kyphosis Laminectomy : complete removal of the vertebral lamina, spinous process, portion of the enlarged facet joints, and thickened ligaments overlying the spinal cord and nerves. Its primary indication is decompression of the dorsal epidural space and for intradural pathologies such as spinal cord neoplasms and vascular malformations |
Internal spine fixation is used to reconstruct the compromised columns within a spinal motion segment (two adjacent vertebrae and their interconnecting tissues), so as to provide temporary immobilization and provisional stability, until osseous fusion occurs across the affected spinal levels. Various devices such as screws, wires, plates, and rods are used for this purpose. Screws are used in a variety of applications, such as transpedicular, transarticular, lateral mass, pars interarticularis, translaminar, and odontoid screw fixation. Sublaminar and spinous process wiring are used for posterior spinal fixation; rods are used for posterior fixation of the thoracolumbar spine. Plates find application in anterior or posterior fixation of the cervical spine (e.g., lateral mass plates) and for ventrolateral fixation of the thoracolumbar spine.
Lumbar interbody fusion procedures (fusion of at least two vertebrae) are usually indicated in patients with scoliosis, spondylolisthesis, spinal fractures, or multiple severe degenerative disk disease; to restore and stabilize the sagittal alignment of the spine; and to distract the neuroforaminal space. Posterior lumbar interbody fusion (PLIF) involves a bilateral laminectomy, diskectomy, and placement of bone graft into the decorticated disk space. In transforaminal lumbar interbody fusion (TLIF), a unilateral graft is placed via the neural foramen, after complete removal of the facet joint on that site. Anterior lumbar interbody fusion (ALIF), lateral lumbar interbody fusion (LLIF), and axial lumbar interbody fusion (Ax-LIF) are indirect decompression procedures that decompress the spinal nerves by increasing the height of the disk space by placing a spacer. These procedures may be followed by additional stabilization of vertebrae with pedicle or facet screws, rods, spinous process clamps, etc.
Newer techniques such as arthroplasty, nucleoplasty, dynamic stabilization, etc., avoid fusion altogether and attempt to restore stability by dynamic internal fixation, in which the implanted hardware has the capacity to bear loads previously borne by disks, facets, and ligaments. Cervical disk arthroplasty, performed for single-level cervical disk degenerative disease, involves diskectomy and decompression of the epidural space, followed by insertion of an artificial disk into the disk space.
In recent years, minimally invasive surgeries (MISs) have emerged as an alternative to open spine procedures. These techniques use smaller incisions and respect anatomic planes, and hence cause much less collateral damage as compared with open procedures. They are associated with a lower stress response, lesser postoperative pain with reduced narcotic requirements, faster recovery, and a shorter hospital stay than open procedures; however, there are no differences in long-term outcome between the two techniques. Although their operative times tend to be longer in the early learning phases, with experience they can be performed in equal or shorter times. Common MIS procedures are video-assisted thoracoscopic surgery (VATS), endoscopic cervical diskectomy and foraminectomy, lumbar microdiskectomy, laproscopic-assisted lumbar spinal surgery for diskectomy and anterior fusion, vertebroplasty, kyphoplasty, etc. VATS is the minimally invasive alternative to open thoracotomy; it finds application in anterior diskectomy and biopsy, during anterior spine release, and for instrumentation during combined anterior–posterior approach in spine deformity correction surgeries. In vertebroplasty and kyphoplasty, a hollow-bore needle is inserted percutaneously into a collapsed vertebral body, under fluoroscopic guidance. In vertebroplasty, a cementing agent, e.g., polymethylmethacrylate, is injected to strengthen the structure and increase the stability of the vertebral body. In kyphoplasty, the height of the compressed vertebral body is increased prior to injection of the cement, by inserting a balloon through the needle and inflating it to expand the vertebral body. It is used for treatment of destructive vertebral lesions, e.g., metastatic carcinoma and multiple myeloma.
Surgical Approaches to the Spine
Spine surgeries can be performed through anterior, posterior, lateral, or combined anterior–posterior approaches ( Table 24.4 ). Anterior approach is used for exposure of ventral spine and spinal cord; anterior approaches for thoracic and lumbar spine may require invasion of thoracic and abdominal cavities, respectively. Posterior approach is used for dorsal spinal column surgeries; lateral approach is commonly used in thoracic spine surgeries. Combined anterior–posterior approaches are infrequently used and are typically indicated for correction of multilevel collapse, unstable three-column injury, and severe kyphosis, scoliosis, and infective or neoplastic conditions.
| Anterior Approaches | Posterior Approaches | Other Approaches | |
|---|---|---|---|
| Cervical Spine | |||
| Craniocervical junction | Transoral approach (transoral odontoidectomy) Transpalatal approach Transmandibular approach Retropharyngeal approach Position: Supine | Occipitocervical fusion ± fixation (keel plate, transarticular screws, polyaxial screws, wires, etc.) for occipitocervical instability, basilar invagination C1-C2 athrodesis ± fixation (transarticular screws, lateral mass screws, laminar screws, wires, etc.) for C1-C2 instability Position: prone, (rarely sitting) | Lateral: Transcondylar approach |
| Subaxial cervical spine | Standard anterior cervical disketomy approach for anterior cervical discoidectomy/corpectomy; fusion ± fixation (plate) Cervical disk arthroplasty Position: Supine | Subaxial approach for subaxial spine for decompression (laminectomy, laminotomy, foraminotomy, laminaplasty); fusion ± fixation (lateral mass, transarticular, translaminar screws, plates, wires) Minimally invasive foraminotomy Position: Prone | |
| Thoracic Spine | |||
| Cervicothoracic junction C7-T3 | Transmanubrial approach (sternal splitting approach) (Anterolateral cervical approach combined with a median sternotomy) Position: supine | Dorsal midline (laminectomy) and transpedicular approaches, for decompression; fusion ± fixation (pedicle screws, cage) Vertebroplasty Kyphoplasty Position: prone | Posterolateral approaches: Costotransversectomy Position: prone or lateral decubitus Lateral extracavitary approach Position : prone |
| T2-T12 | Transthoracic approach for thoracotomy (T2-T12) Retropleural approach (T2-T10) Thoracoscopic approach (endoscopic) Position: lateral decubitus | ||
| Lumbar Spine | |||
| Thoracolumbar junction | Thoracolumbar retroperitoneal approach Position: right lateral decubitus | Posterior midline approach Position: prone | |
| L1-L5 vertebrae | Transperitoneal (transabdominal) approach: Anterior lumbar interbody fusion Position: supine Retroperitoneal approach: Lateral lumbar interbody fusion (LLIF) Position: Lateral decubitus (usually left side up) Endoscopic transperitoneal approach. Position: supine | Decompression: Posterior midline approach for diskectomy, laminectomy, laminotomy, fenestration procedure (bilateral laminectomy), hemilaminectomy, lumbar pedicle subtraction/extension osteotomy, Transparaspinal approach for dumbbell-shaped spinal tumors Fusion: Posterolateral fusion Posterior lumbar interbody fusion Transforaminal lumbar interbody fusion Axial lumbar interbody fusion Fixation: Transpedicular screws, translaminar screws, rods Endoscopic microdiskectomy Lumbar disk arthroplasty Position: prone | |
Common Spine Disorders
Spine Degenerative Disease
Degenerative disorders usually affect midcervical and lumbar regions, and are the most common indication for spine surgeries. These disorders basically represent a continuum of changes, which start as a soft disk herniation, progress to spinal instability and/or spondylolisthesis, and eventually cause spinal stenosis and spondylotic myelopathy ( Table 24.5 ). Their pathophysiology can be explained by the Kirkaldy–Willis “three-joint complex model,” in which degenerative changes in one component of a motion segment (an IV disk and two facet joints) lead to accelerated degeneration of the other two joints, and eventually to degeneration of other components of the VC also. These changes are classified into early degeneration, destabilization, and restabilization phases.
| Radiculopathy : Any pathological change or functional disturbance in a spinal nerve root Myelopathy : Any pathological change or functional disturbance in the spinal cord Spinal stenosis : Narrowing of the spinal canal (central canal stenosis), neural foramina (foraminal stenosis), and/or the lateral recesses Spondylosis : Chronic degenerative process of the spine, characterized by disk space narrowing and osteophyte formation at vertebral endplates and facet joints, which may result in varying degrees of stenosis of the central spinal canal and root canals Sponylolisthesis : Anterior displacement of one vertebra on another, in the presence of an intact neural arch, due to degenerative, traumatic, or congenital causes |
Early degeneration phase: The IV disk is usually the first victim of degeneration—a decrease in its water content along with replacement of its collagen and proteoglycans by fibrous tissue leads to disk desiccation. Consequently, small circumferential tears develop on dorsolateral aspect of the annulus, which eventually enlarge into radial tears; nucleus pulposus protrudes through these defects and causes disk bulge, herniation, protrusion, or disk extrusion with free fragments in the spinal canal. Most disk herniations occur in a dorsolateral direction into the spinal canal and can cause impingement of a nerve root. These degenerative processes further induce a focal inflammatory reaction, which causes irritation and inflammation of the nerve roots; over time chronic edema and fibrosis of the nerve results in radiculopathy. Sometimes a central herniation may occur and can cause cord compression and myelopathy. Besides IV disks, the facet joints also undergo degenerative changes. At this stage, most patients respond to conservative measures.
Destabilization phase: It is characterized by instability and abnormal motion of the spine. A decrease in the height of IV disks because of progressive degeneration predisposes to buckling of ALL and PLL, and infolding of the ligamentum flavum; accelerated degeneration also leads to subluxation of facet joints. Gradually, the natural mobility of the spine is lost and dysfunctional motion segments are created, which eventually results in spondylolisthesis and spinal instability. At this stage, a fusion procedure may be required to stabilize the spine.
Restabilization phase: In this stage, the spine becomes more stable due to formation of osteophytes (bony spurs), but it also leads to stenosis of the spinal canal and neural foraminae. Osteophytes form at vertebral end plates, facet joints, and uncovertebral joints; end plate osteophytes grow across disk spaces and merge with osteophytes of adjacent vertebrae to form bridging osteophytes. Posterior or posterolateral osteophytes can cause compression of the thecal sac and/or spinal cord. Hypertrophy of ligament flavum, PLL, and facet joints occurs. These processes cause narrowing of the spinal canal lumen and/or neural foraminae; spondylotic radiculopathy and myelopathy occur due to extrinsic compression and mechanical distortion of the cord and/or spinal nerve roots ( Table 24.5 ). Clinically, patients may present with symptoms of radiculopathy due to spinal nerve entrapment and/or with neurogenic claudication (pain that is exacerbated by walking or standing, and relieved with postural changes) due to central canal and lateral recess stenosis.
Severe cord compression results in direct neuronal injury and initiates a secondary cascade of events including ischemia, excitotoxicity, and apoptosis, which result in irreversible changes in the cord, which is possibly the reason why some patients do not recover following decompressive surgery.
Degenerative Disease of Cervical Spine
Most cervical disk herniations occur posterolaterally at C5-6 and C6-7 levels and cause compression of C6 and C7 roots, respectively. Most patients respond to conservative management; however, surgery may be required if they have progressive neurological deficits or intractable pain. Surgical options include anterior decompression–ACD, which may be combined with fusion (ACDF), and possibly anterior cervical plating; cervical disk arthroplasty; or posterior decompression techniques such as laminectomy and laminoforaminotomy.
Cervical spondylotic radiculopathy (CSR) can occur because of lateral disk herniation, osteophyte overgrowth with stenosis of the lateral foramen (lateral recess syndrome), or cervical spinal instability caused by subluxation of a cervical vertebra. Patients usually complain of neck pain, brachalgia (arm pain), and radicular symptoms such as shooting pain that radiates from the shoulder to the arm, or hand; paresthesias; and/or muscle weakness in a dermatomal nerve root distribution.
Cervical spondylotic myelopathy (CSM) is the cumulative manifestation of three processes: “static compression,” “dynamic compression,” and the consequent “ischemic changes in the cord” ( Figs. 24.1 and 24.2 ). In static cord compression, degenerative processes encroach into the spinal canal, leading to cervical canal stenosis, cord compression, and restricted cord movements. Symptoms of myelopathy develop in nearly all patients who have a greater than 30% reduction in the cross sectional area of the cervical vertebral canal.
Dynamic cord compression occurs due “stretch-associated injury” during repetitive, normal, or abnormal movements of a compressed cord, especially in the presence of an unstable cervical spine. According to “Poisson effect,” the spinal cord shortens and thickens during extension and stretches during flexion of the neck. Hyperextension narrows the spinal canal by buckling the ligament flavum and shingling the laminae, hence thickening of a spondylotic cord in extension makes it more susceptible to posterior compression from the infolded ligamentum flavum or lamina. Conversely, a stretched spinal cord may be subjected to higher intrinsic pressures during flexion, if it abuts against a prominent disk, vertebral body, or ventral osteophyte complex, which protrudes into the vertebral canal. In addition, severely spondylotic segments may be fused and hence stable, but their adjacent segments tend to be hypermobile and can cause dynamic cord compression; hypermobility is most commonly observed at C3-C4 levels. Similarly, retrolisthesis of vertebrae can result in pinching of the cord between inferior posterior margin of the vertebral body and superior edge of the lamina caudad to it; this compression is worsened in extension and relieved during flexion, which tends to reduce the retrolisthesis.
Clinically, patients present in several ways, with varying combinations of pure myelopathy, myelopathy and radiculopathy, hyperactive reflexes, pain, spasticity, and /or sphincter disturbances. The earliest motor symptoms usually occur due to weakness of hand muscles, with difficulty in performing tasks that require fine manipulation, e.g., closing of shirt buttons, writing, etc.; unsteadiness in gait and spastic weakness tend to occur in more advanced cases. Clustering of CSM into five clinical syndromes has been described: central cord syndrome, Brown–Séquard syndrome, anterior cord syndrome, transverse lesion syndrome, and brachialgia, and cord syndrome, which are described elsewhere in the book.
Surgical intervention in CSR and CSM may be required in patients who have acute neurological deterioration, progressive neurological worsening, or intractable radicular pain and correlative imaging. The surgical goal in CSR is decompression of affected nerve root or roots; in CSM, cord decompression is followed by stabilization and restoration of VC alignment. Generally, the anterior approach (ACDF) is preferred in patients with less than three levels of ventral disease ( Fig. 24.3 ); patients with more than three levels of compression are generally treated by posterior decompression (laminectomy, laminoplasty); a concomitant arthrodesis should be considered in younger patients, because of the risk of a delayed swan neck deformity after a laminectomy.
Radiologically, predictors of a poor neurological outcome after surgery include multilevel T2W1 hyperintensity within the cord parenchyma and a flattened banana-shaped cord on axial images with an anterior–posterior cord compression ratio of <0.4 (ratio of anteroposterior to transverse diameter of cord).
Degenerative Disorders of the Lumbar Spine
Most lumbar disk herniations occur posterolaterally at L4-5 and L5-S1 levels and cause compression of the L5 and L6 nerve roots, respectively ( Fig. 24.4 ); patients usually complain of lower back pain, sciatica (pain radiating to the lower limbs), motor weakness, and/or paresthesias. While treatment is usually conservative, a diskectomy may be required in patients with intractable pain; emergency surgery may be required if a patient develops cauda equina syndrome due to a central disk herniation or has acute development or progression of motor deficits.
Lumbar spondylosis manifests as spinal stenosis, spinal instability, or degenerative spondylolisthesis. Lumbar stenosis usually occurs at L3-L4 and L4-L5 levels and causes neurogenic claudication. Degenerative spondylolisthesis usually involves L5-S1 or L4-L5 levels ( Fig. 24.5 ). Although conservative management is tried initially, most patients ultimately require surgical decompression of the neural elements; fusion may be considered in cases of segmental instability or deformity.
Craniovertebral Junction Anomalies
CVJ anomalies such as basilar invagination, atlantoaxial dislocation, atlantooccipital dislocation, and occipitalization of the atlas can occur in association with congenital or acquired conditions ( Table 24.6 ); these abnormalities cause spinal instability, cord compression, and myelopathy ( Fig. 24.6 ). Compression of brainstem and upper cervical spine can result in respiratory impairment due to damage of the respiratory center and weakness of respiratory muscles including diaphragm; impaired lower cranial nerve function results in a poor gag and cough reflex, with frequent aspiration and pulmonary infection. A further deterioration in respiratory function, as determined by pulmonary function tests and evaluation of diaphragmatic movements, is observed after the surgery, which increases the risk of prolonged ventilatory support and delayed tracheal extubation in these patients.
| Congenital : Chiari maliformations Syringomyelia Down syndrome Congenital atlantoaxial dislocation Os odointoideum Klippel–Feil syndrome Skeletal dysplasias: Morquio syndrome, spondyloepiphyseal dysplasia, osteogenesis imperfecta, diastrophic dwarfism, achondroplasia Neurofibramatosis type 1 Occipitalization of the atlas Acquired : Traumatic: fracture of odontoid, occipital condyles Inflammatory: rheumatoid arthritis, ankylosing spondylitis, psoriatic arthritis Enteropathic arthritis: Crohn disease, ulcerative colitis Neoplasms: primary or secondary |
Conditions Associated With Spinal Instability
Spinal instability can occur due to various reasons, such as trauma, tumors, infection, degenerative disorders, inflammatory diseases, or congenital conditions. The most commonly affected regions are cervical (C1, C2, and C4-C6) and thoracolumbar junction (T11 to L2). While an unstable spine should maintain in a fixed position, not all movements are necessarily associated with a potential for neurological compromise. For example, if the vertebral body collapses because of infection or tumor, but the posterior elements are preserved, then the spine is stable in extension, but flexion increases the deformity and can force the diseased tissue or the buckled PLL into the spinal canal.
Atlantoaxial Instability
In atlantoaxial instability (AAI), subluxation of atlas on the axis reduces the spinal canal diameter and increases the risk of cervicomedullary cord compression and myelopathy ( Fig. 24.7 ). It can occur in association with trauma, tumors, degenerative, inflammatory [e.g., rheumatoid arthritis (RA), ankylosing spondylitis (AS)], or congenital disorders ( Table 24.6 ). Pathologies that cause ligamentous disruption or laxity tend to cause greater cervical instability than C1-C2 fractures with intact ligaments.
AAI can be anterior (80%), posterior (10%), vertical, or rotatory and may be mobile and reducible or fixed and irreducible. In reducible AAI, the subluxation increases with flexion and decreases on extension of the neck; in irreducible AAI, it persists on extension of the neck. In anterior AAI, atlas moves forward on the axis, because of degradation or laxity of transverse ligament. The subluxation worsens with neck flexion when the head and atlas dislocate ventrally on the axis, to increase the AADI (normal <3 mm). In vertical AAI, destruction of C1 lateral mass causes upward migration of dens into the foramen magnum; cord myelopathy and compression of cervicomedullary junction, occur due to basilar invagination. In posterior AAI, destruction of the odontoid peg causes backward movement of C1 on C2. Vertical and posterior AAI are worsened by neck extension. Lateral or rotatory subluxation results from degenerative changes in C1/C2 facet joints and causes compression of spinal nerves and the vertebral artery (VA).
Radiologically, an AADI >3.0 mm in adults indicates AAI; AADI >9.0 mm is usually associated with cord compression. A PADI <14 mm increases the risk of spinal cord compression and neurological compromise; this risk increases by up to 10-fold in patients with coexisting upper cervical cord compression. Perioperatively, patients with AAI have an additional risk of neurological damage due to dynamic cord compression because of neck movement during airway control or surgical positioning. Prone positioning causes a modest degree of extension of the cervical spine and may aggravate a preexisting cord compression and myelopathy. Furthermore, the increase in vena caval pressures and increased resistance to venous outflow in the prone position can further reduce the spinal cord flow and worsen the positioning-induced ischemia. In patients with severely compromised canal lumens and long-standing myelopathy, hyperextension of the cervical spine during direct laryngoscopy (DL) can result in “central cord syndrome” due to dynamic cord compression. In this syndrome, acute lateral corticospinal tract injury occurs due to combined anterior and posterior compression of the central spinal cord (anteriorly by impinging osteophytes; posteriorly by infolded ligamentum flavum). It is characterized by disproportionately greater motor deficit in distal upper extremities compared to lower extremities (man in a barrel syndrome) and variable sensory deficit below the lesion; a positive Lhermitte sign (electric shock–like sensation that runs down the back and into the limbs, on flexion or extension of the neck), and bladder dysfunction are also very common.
Lower Cervical Spine Instability
A diagnosis of subaxial cervical spine instability is made, in the presence of one of the following radiological criteria :
- 1.
All anterior or all posterior elements are destroyed
- 2.
There is >3.5 mm horizontal displacement between two points on adjacent vertebrae, on a lateral X-ray (translation)
- 3.
More than 50% compression of the vertebral body, interspinous widening, loss of facet parallelism, and loss of normal cervical lordosis
- 4.
There is >11 degrees angulation between adjacent vertebrae.
Conditions Associated With Cervical Spine Limitation
Cervical spine mobility can be restricted because of a cervical pathology, prior cervical spine fusion procedure, or due to presence of a neck immobilization device (e.g., cervical collar) ( Table 24.7 ). Patients with cervical spine limitation (CSL) can have a limited range of neck extension, flexion, or both, and pose problems during airway control.
| Congenital : Klippel–Feil syndrome, Goldenhar syndrome, diffuse idiopathic hyperosteosis Inflammatory : Rheumatoid arthritis, ankylosing spondylitis Degenerative : Degenerative spine disease, osteoarthritis Iatrogenic : Immobilization of cervical spine with a halo traction/cervical collar, prior surgical fusion Fracture/trauma |
Congenital Abnormalities Involving the Cervical Spine
A common feature of most congenital cervical spine abnormalities is cervical spine instability, as a consequence of failed osseous fusion, ligamentous laxity, or excessive ossification of the cervical spine. Many of these conditions are also associated with an actual or potential reduction in the lumen of the spinal canal; a spinal canal is considered congenitally stenotic if its midsagittal diameter is <13 mm on a lateral cervical spine radiograph (normal—17–18 mm) or when the Torg–Pavlov ratio (ratio of sagittal diameter of spinal canal to the corresponding vertebral body) is <0.8. Patients with congenitally narrow spinal canals tend to have an earlier onset of degenerative spine changes, and consequently an increased risk of cord compression and myelopathy; they are usually symptomatic by the third decade.
Down syndrome: Approximately 20% patients with Down syndrome develop AAI because of ligamentous laxity, muscle hypotonia, and cervical vertebral anomalies; most of them have clinically significant cervical spondylosis and cervical myelopathy by 40 years of age. Furthermore, their anesthetic management is influenced by other associated multisystemic manifestations ( Table 24.8 ).
| Rheumatoid arthritis | Difficult airway: Atlantoaxial instability, restricted cervical mobility, restricted mouth opening due to temporomandibular joint involvement, cricoarytenitis Cardiac: Ischemic heart disease, heart failure, pericarditis, valvular dysfunction, cardiomyopathy; increased cardiovascular risks in patients with seropositive disease and those with heart failure, poorly controlled disease, rheumatoid cachexia Pulmonary: Restrictive lung disease, pulmonary hypertension, pleural effusion, pulmonary fibrosis, respiratory myopathy Hematological: Anemia of chronic disease (normocytic, normochromic) and from treatment toxicity (gastrointestinal hemorrhage, myelosuppression). Thrombocytopenia Hepatic: Hepatic fibrosis Renal: Chronic renal failure due to drug toxicity, glomerulonephritis, tubulointerstitial nephritis Chronic steroid use, may need stress dose |
| Ankylosing spondylitis | Restricted movements of spine and sacroiliac joints (bamboo spine, chin-on-chest deformity) Difficult airway Restrictive lung disease: Pulmonary fibrosis, poor chest wall compliance Aortitis and aortic insufficiency |
| Scoliosis | Cardiorespiratory: Restrictive lung disease → pulmonary hypertension; right-sided heart failure → cor pulmonale Vital capacity <40%, highly predictive of postoperative ventilation Neuromuscular or congenital scoliosis: Greater extent of cardiopulmonary compromise, congenital cardiac anomalies, mitral valve regurgitation, haemopeoetic and coagulation abnormalities |
| Down syndrome | Difficult airway Cardiac: Atrioventricular septal defects, ventricular septal defects, patent ductus arteriosus, atrial septal defect, Tetralogy of Fallot, pulmonary vascular disease Respiratory system: Recurrent respiratory tract infections, subglottic stenosis, enlarged tongue, enlarged tonsils and adenoids, obstructive sleep apnea Central nervous system: Developmental delay and moderate to severe mental retardation, microcephaly, epilepsy (5–10%) Skeletal system: Atlantoaxial instability, generalized hypotonia Endocrine system: Hypothyroidism Hematology: Acute lymphoblastic leukemia, acute myeloid leukemia, polycythemia Obesity Difficult peripheral access |
| Neoplasms | Often not isolated to spine, may affect bone marrow, brain, heart, lungs, liver, kidneys Systemic toxicity of chemotherapeutic drugs. Respiratory: infection, pleural effusion, pulmonary toxicity from alkylating agents (cyclophosphamide, chlorambucil, busulfan) or antimetabolites (methotrexate, azathioprine); cardiac: myocardial injury due to chemotherapy (busulfan, cyclophosphamide, mitomycin); metabolic: hypercalcemia, syndrome of inappropriate secretion of antidiuretic hormone (small cell lung tumors, carcinoma of the prostate, pancreas, and bladder, and central nervous system neoplasms) |
| Muscle weakness (dystrophies) | May have compromised respiratory function, medical treatment should be optimized |
Klippel–Feil syndrome: These patients may present with the classic triad of cervical fusion abnormalities, short neck, and a low-lying hairline (KS syndrome), or only with cervical fusion abnormalities (KF variant). Associated abnormalities such as scoliosis, Chiari I malformations, cervical cord dysraphism, Sprengel deformity, synkinesis, genitourinary, and cardiovascular disorders may also be present. In addition to CSL due to cervical ankylosis, other complications such as instability, hypermobility, and symptomatic cervical spine stenosis at the fused segments can make airway management rather difficult.
Neurofibromatosis (NF): Patients with type 1 NF develop progressive cervical kyphosis, because of an intrinsic ligamentous abnormality or abnormal bony architecture, and can pose problems in airway control.
Arnold Chiari malformations (types I–IV): These are characterized by crowding of the posterior fossa by neural elements and herniation of the hindbrain through foramen magnum. Abnormal CSF flow through the foramen magnum can lead to development of a cervical cord syrinx. ACM type I is most commonly observed in adults, often in association with other abnormalities, e.g., occipitalization of C1, fusion of C1-C2, Klippel–Feil deformity, or cervical spina bifida occulta.
Achondroplasia: Achondroplastic dwarfs have a high incidence of AAI, cervical stenosis, and foramen magnum stenosis.
Skeletal dysplasias: In these conditions, the dens is hypoplastic, aplastic, or is not fused with the axis (os odontoideum), which leads to varying degrees of AAI, cord compression, and myelopathy.
Syringomyelia refers to cystic cavitation of the spinal cord ( Fig. 24.8 ). In communicating syringomyelia, primary dilatation of the central canal occurs, mostly in association with foramen magnum abnormalities, e.g., tonsillar herniation (Chiari malformation). In noncommunicating syringomyelia, the cyst arises within the cord substance itself and does not communicate with the central canal or subarachnoid space. Patients typically complain of sensory loss in a “cape” distribution (similar to central cord syndrome), cervical or occipital pain, wasting of hand muscles, and painless arthropathies. Surgical options include removal of known causes, decompression, laminectomy, duraplasty, shunting, excision of syrinx, and a suboccipital craniotomy.
Goldenhar syndrome is a type of mandibular hypoplasia associated with underdeveloped vertebrae, often in the neck and CSL.
Ossification of the Posterior Longitudinal Ligament
Ossification of the posterior longitudinal ligament (OPLL) is most commonly observed in the cervical region ( Fig. 24.9 ); it begins as focal areas of fibrosis, which progresses to calcification and finally ossification; the dura may also be involved in some patients. Patients are asymptomatic initially, but in later stages, develop symptoms of myelopathy (due to spinal cord compression or ischemia) and/or radiculopathy (by nerve root compression or stretching). In addition, they may have impaired glucose intolerance and/or respiratory compromise due to ossification of costotransverse and costovertebral ligaments. Surgical decompression is indicated in patients with moderate to severe myelopathy and can be performed through an anterior or a posterior approach (laminaplasty). Complete quadriplegia or rapid neurological deterioration, advanced age, poor medical condition, and/or presence of intrinsic spinal cord abnormalities on T2-weighted magnetic resonance imaging (MRI) are predictive of a poor postoperative outcome.
Inflammatory Spondyloarthropathies
Rheumatoid Arthritis
RA is a chronic, systemic, autoimmune disorder in which T-cell-mediated inflammation results in deforming symmetrical polyarthropathy and multiple extra-articular manifestations ( Table 24.8 ). Cervical spine instability and stiffness is commonly observed in patients with severe, long-standing RA. AAI is a consequence of progressive erosion of bone, cartilage, and ligaments by pannus formation; stiffness occurs due to chronic inflammation, thickening, and calcification. RA also affects the lower cervical spine and results in severe CSL, complex instability patterns including subaxial stepladder deformity, cervical canal stenosis, cord compression, and myelopathy. In addition, RA can also disrupt the temporomandibular joints, leading to limitation of mouth opening and difficulty in DL. Involvement of the cricoarytenoid joints may result in dyspnea, stridor, hoarseness, and occasionally severe upper airway obstruction. Patients with RA with myelopathy often have a very high morbidity and mortality, hence early surgical stabilization is indicated.
Ankylosing Spondylitis
AS is a systemic, inflammatory, progressive, seronegative arthropathy, which commonly affects the VC and can result in severe CSL ( Table 24.8 ). It causes recurrent episodes of inflammation in IV disks, ligaments, and facet joints; subsequently, fusion of adjacent vertebral segments results in fixed kyphotic deformity (bamboo spine), and in advanced disease, development of a “chin-on-chest” deformity (fixed flexion deformity at CVJ, limited forward gaze, as well as eating and swallowing difficulties). The rigid, fused spine is highly susceptible to fractures following apparently minor injuries, especially at lower cervical spine levels (C6-C7). AAI occurs in approximately 21% patients and is attributed to hypermobility in spinal segments adjacent to the fused elements. Restricted chest expansion due to costovertebral joint involvement can adversely affects the pulmonary function; involvement of the lumbar spine and sacroiliac joints spine causes persistent lower back discomfort, radiculopathy, and stiffness. These patients may have systemic manifestations also; those pertinent to the anesthetist include aortic valve insufficiency, cardiac conduction defects, and pulmonary fibrosis. Surgery is indicated in presence of severe spine deformities, spinal instability, or a spinal fracture. Patients with a “chin-on-chest” deformity may require an extension osteotomy and posterior cervical spine stabilization.
Neoplasms of the Spine ( Table 24.1 )
Metastatic extradural tumors are the most common spine tumors and usually involve the thoracic vertebral bodies; metastasis usually occurs from the breast, lung, renal, gastric, or hematopoietic/lymphoid tissue, by hematogeneous seeding or direct extension of the tumor.
Intramedullary tumors (10%) are located within the substance of the spinal cord and are usually malignant ( Fig. 24.10 ); most of them are subtypes of gliomas, such as ependymoma, astrocytoma, and hemangioblastomas. Ependymoma and astrocytoma may occur in association with NF types 1 and 2; hemagiomas may be part of von Hippel-Lindau syndrome.
