Neurosurgical Diseases and Trauma of the Spine and Spinal Cord: Anesthetic Considerations

Cervical Spondylosis

Degenerative disease of the cervical spine affects more than 90% of individuals older than 65 years. The term cervical spondylosis refers to the nonspecific degenerative process of the spine that may result in degenerative listhesis, spinal stenosis, as well as neural foraminal encroachment ( Fig. 21.11 ).

In those individuals who eventually experience symptoms of cervical degenerative disease, radiculopathy is the most common. Cervical radiculopathy is defined as a neurologic condition characterized by dysfunction of a cervical spinal nerve, the nerve roots, or both. It is most commonly caused by lateral disk herniation, osteophyte overgrowth with narrowing of the lateral foramen (termed the lateral recess syndrome ), or cervical spinal instability caused by subluxation of a cervical vertebra ( Fig. 21.12 ).

MRI is the imaging modality of choice in the diagnosis of cervical radiculopathy; however, MRI is not indicated in the initial stages of management because the findings will not alter treatment. In general, medical management is attempted for 4–6 weeks, and if the patient remains symptomatic, an MRI study is appropriate. CT is of value primarily for defining the bony anatomy and for helping to distinguish whether the stenosis is due to soft or calcified lesions. Surgical treatment for cervical radiculopathy is indicated for severe clinical symptoms that medical therapy has failed to control combined with a compatible MRI study demonstrating nerve compression; for the persistence of pain despite medical management for at least 6 weeks; and for the presence of an evolving neurologic deficit.

Cervical Spondylotic Myelopathy

Cervical spondylotic myelopathy (CSM) is the most common type of spinal cord dysfunction in patients older than 55 years. Originally described more than 50 years ago, CSM is the result of narrowing of the cervical spinal canal due to a degenerative process or a congenital disorder. The primary pathophysiologic abnormality in CSM is a reduction in the sagittal diameter of spinal canal, with cervical myelopathy developing in nearly all patients in whom there is a greater than 30% reduction in the cross-sectional area of the cervical vertebral canal. Typical signs and symptoms of CSM are pain in the neck, shoulder, and subscapular areas; numbness or tingling in the upper extremities; motor weakness in the upper or lower extremities; sensory changes in the lower extremities; gait disturbances; bowel and bladder dysfunction; and spasticity, hyperreflexia, and clonus typical of an upper motor neuron lesion. The most common presentation of CSM is a spastic gait. Physical findings include atrophy of the muscles of the hand, hyperreflexia, electric-shock-like sensations down the arm or back after flexion of the neck (Lhermitte’s sign), and sensory loss. Plain films often show evidence of osteophyte formation, kyphosis, and subluxation. MRI remains the imaging modality of choice, providing information about the spinal canal (demyelination, spinal cord atrophy, and edema), intervertebral disks, vertebral osteophytes, and ligaments. Treatment of CSM initially involves nonoperative therapy; however, early surgery is associated with significant improvement in the neurologic prognosis. If surgical intervention is chosen, treatment considerations include anterior cervical discectomy and fusion (ACD&F), anterior cervical fusion (ACF), cervical laminoplasty, and posterior cervical decompression and fusion.

The anesthetic management of patients with cervical spine instability or myelopathy should consider the specific technique most appropriate for securing the airway, choice of anesthetic agents, hemodynamic monitoring needs, use of vasoactive medications, and positioning. For patients with symptomatic spinal stenosis, an awake fiberoptic intubation is often suggested; however, initial induction of anesthesia followed by fiberoptic intubation utilizing manual in-line stabilization with/without spinal cord monitoring is a viable option. The use of invasive (or advanced noninvasive) blood pressure monitoring is advocated to facilitate maintenance of an adequate spinal cord perfusion pressure (i.e., mean artery pressure ≥ 85 mm Hg) throughout the case. If electrophysiologic (EP) spinal cord monitoring is planned, the anesthetic strategy should select agents with minimal effects on the EP waveform potentials. The decision to extubate the patient following surgery should be made only in the absence of airway edema, neck hematoma, and depressed mental status.

Cervical Disk Herniation

Intervertebral disks are composed of a well-hydrated central nucleus pulposus surrounded by an outer anulus fibrosus. With age, the disks deteriorate, ultimately resulting in herniation when the anulus fibrosus breaks open or cracks, allowing the nucleus pulposus to extrude (see Fig. 21.12 ).

In the cervical spine, the most common location of the herniation is at C5–C6, followed by C6–C7, and herniation is most common in individuals older than 40 years. The symptoms of a cervical disk herniation are neck pain and radicular symptoms, which consist of shoulder, arm, or hand paresthesias or pain, and muscle weakness in a dermatomal nerve root distribution. Patients may also present with symptoms of a cervical myelopathy if the herniation is centrally located. In patients in whom a disk herniation is suspected, plain films may demonstrate a narrowed disk space, osteophytes, or subluxation of the vertebra. An MRI study is the radiologic imaging modality of choice for evaluation of a suspected herniated cervical disk ( Fig. 21.13 ).

The primary treatment of a cervical disk herniation is medical management, at least initially. Cervical soft collars, anti-inflammatory agents, oral steroids, and physical therapy are all appropriate in the short term because more than 90% of patients with radiculopathic symptoms experience improvement with these measures. If nonsurgical therapy fails or the patient demonstrates progressive neurologic symptoms, surgical therapy is selected, typically an anterior cervical diskectomy and fusion (ACD&F), with or without anterior cervical plating.

Complications of surgery include thoracic duct injury, cerebrospinal fluid (CSF) leak, spinal cord or nerve root injury, vertebral artery injury, perforation of the esophagus or trachea, recurrent laryngeal nerve injury (vocal cord paralysis), postoperative hematoma, and wound infection. In instances in which there is a significant postoperative hematoma, the airway should be left secured until the patient is fully awake, the hematoma is not enlarging, and there is a tracheal cuff leak.

Syringomyelia

Syringohydromyelia refers to the cystic cavitation of the spinal cord. Two main forms have been described: syringomyelia and hydromyelia. In hydromyelia, there is primary dilatation of the central canal that is often associated with abnormalities at the foramen magnum such as tonsillar herniation (Chiari malformation) and basal arachnoiditis. In true syringomyelia, a cyst arises within the cord substance itself and does not communicate with the central canal or subarachnoid space. Common causes of true syringomyelia include trauma (most common), neoplasm, and arachnoiditis. In the typical presentation, an adult between the ages of 20 and 50 years complains of sensory loss (similar to central cord syndrome) in a “cape” distribution, cervical or occipital pain, wasting in the hands, and painless arthropathies. MRI is the investigation of choice and should include images of the cervical and thoracic spinal cord as well as the brain. Treatment focuses upon reestablishing normal CSF flow across the site of the injury. Therapeutic choices include a posterior fossa decompression and C1 laminectomy (with or without expansile duroplasty) in the presence of a Chiari malformation, fenestration of associated arachnoidal cysts, resection of an associated neoplasm, or placement of a shunt with direct drainage of the cyst into the subarachnoid space or pleural cavity. The airway management of patients with syringomyelia should consider the neurologic deficits commonly associated with this disease. In patients in whom syringomyelia is associated with the Chiari malformation, limitation of neck flexion and extension is vital in preventing further compression of neuronal structures. The limitation of neck motion during intubation by the use of fiberoptic bronchoscopy (either awake or after induction) is an appropriate choice.

Herniated Disk

Symptomatic thoracic disk herniations are rare, with an annual incidence of 1 per 1 million patients. Thoracic disk herniations occur most commonly at T8–T12, with a peak incidence between the ages of 40 and 60 years (mean, 46 years). The majority of disk herniations are located centrolaterally (94%) or laterally (6%) and manifest a variety of symptoms and signs, including pain (localized, axial, or radicular), myelopathy, sensory disturbances, and bladder dysfunction. The radiographic diagnosis is made through a combination of CT and MRI imaging. The majority of symptomatic thoracic disk herniations are effectively managed with nonoperative therapy alone. Indications for surgery include failure of a 4– 6-week trial of medical treatment; severe, persistent radicular pain; and significant neurologic deficits, particularly if there is any progression of symptoms. Thoracic spine operations are typically lengthy procedures (≥ 3 hours), often with clinically significant blood loss. Major surgical complications are uncommon; they include death from cardiopulmonary compromise, spinal instability requiring further surgery, and worsening of neurologic deficits.

Unlike a thoracic disk herniation, a lumbar disk herniation is very common, occurring in 2% of the general population at some time in their lives. Sciatica, resulting from a herniated lumbar disk, is the most common cause of radicular leg pain in the adult working population. Fortunately, the symptoms of sciatica typically resolve within 2 months from the onset in patients who are treated medically, and surgery is rarely necessary. The majority of lumbar herniations occur at the L4–L5 or L5–S1 spinal levels, most often posterolaterally, where the posterior longitudinal ligament is thinnest. The symptoms of a lumbar disk herniation range from lower back pain to radiculopathy with leg pain, weakness, and paresthesias. With a large centrally located disk herniation, the cauda equina syndrome may occur, resulting in lower back pain, bilateral lower extremity sensorimotor deficits, bladder dysfunction, sexual dysfunction, and perirectal sensory loss. The presence of cauda equina syndrome warrants urgent medical attention. MRI is the imaging modality of choice for suspected herniation of an intervertebral disk, as it clearly defines the local anatomy ( Fig. 21.14 ).

The majority of patients with lumbar disk herniations are treated medically. With such treatments, more than 75% of patients recover within 6–8 weeks. Accepted indications for surgical therapy include the cauda equina syndrome; significant motor deficits; severe pain unresponsive to medical therapy; failure of conservative therapy after 2–3 months; and large extruded disk fragments. Surgical options include diskectomy only, diskectomy with spinal fusion, hemilaminotomy, and/or laminectomy. Anesthetic management should consider the presence of presurgical neurologic deficits, the requirement for a meticulous positioning technique, identification of comorbidities that may increase the risk of complications, and the amount of anticipated blood loss. Invasive blood pressure monitoring is appropriate in those patients with serious comorbidities; however, noninvasive blood pressure monitoring is usually adequate in otherwise healthy patients scheduled for a lumbar procedure for disk herniation.

Lumbar Spondylosis

Lumbar spondylosis is a general term referring to changes in the vertebral joint characterized by progressive degeneration of the intervertebral disk, with subsequent changes in the bones and soft tissues. Disk degeneration, ligamentous and facet hypertrophy, spinal stenosis, and spondylolisthesis are the characteristic pathologic changes that result. The clinical spectrum of spondylosis includes spinal instability, spinal stenosis, and degenerative spondylolisthesis. Spinal stenosis, the most common of the spondylitic disorders, is a common indication for spinal surgery in adults older than 65 years.

Lumbar Spinal Stenosis

The etiology of lumbar spinal stenosis may be congenital, acquired, or a combination of both. The patient with congenitally short pedicles typically has a shallow spinal canal that predisposes to spinal stenosis later in life as the typical degenerative changes in the spine occur, such as disk protrusion, facet joint degeneration and hypertrophy, ligamentous hypertrophy, and spondylolisthesis ( Fig. 21.15 ).

Lumbar stenosis most commonly occurs at the L4–L5 spinal level, followed by the L3–L4 level. Clinical symptoms of lumbar spinal stenosis include the gradual onset of leg and buttock pain combined with lower extremity sensorineural deficits. These symptoms progress over a period of months. The initial diagnostic investigation should include AP, lateral, flexion, and extension plain films. Suggestive findings on plain films include disk space narrowing and erosion and sclerosis of the vertebral end plates. MRI, the imaging modality of choice in lumbar stenosis, typically shows degenerative changes such as facet joint and ligamentous hypertrophy, disk herniation, and nerve root impingement. The initial approach for patients with the symptoms of spinal stenosis is medical management. Surgical therapy is indicated in patients for whom conservative treatment has failed or who have severe and debilitating pain, significant motor deficits, or symptoms of myelopathy.

Degenerative Spondylolisthesis

Spondylolisthesis is a term referring to the anterior displacement of one vertebra on another associated with degenerative changes in the presence of an intact neural arch ( Fig. 21.16 ). Spondylolisthesis may be congenital or acquired. Degenerative spondylolisthesis is a common condition—particularly in individuals older than 50 years—with a reported incidence as high as 8.7%. Women are affected four to six times more commonly than men. The development of spondylolisthesis is associated with the presence of degenerative intervertebral disks, laxity of ligaments, and facet joint pathology.

Spondylolisthesis is typically asymptomatic; however, clinical symptoms may develop and are related to the presence of spinal stenosis causing lower back pain, radiculopathy, and neurogenic claudication (lower extremity pain, paresthesias, and weakness associated with walking or standing). The evaluation of patients with spondylolisthesis incorporates clinical symptoms in combination with anatomic abnormalities detected on radiologic imaging studies, because stenosis is commonly present without symptoms. The severity of spondylolisthesis is determined by evaluation of the extent of slip and the slip angle using plain films. The extent of slip is subsequently expressed as a percentage of anterior displacement of the inferior end plate of the vertebral body above with the superior end plate of the vertebral body below. The slip angle is generally less than 30 degrees in patients with degenerative spondylolisthesis, but it may progress in about one-third of patients.

The initiating pathophysiologic event in the development of degenerative spondylolisthesis is deterioration of the intervertebral disk leading to a narrowing of the disk space, which in turn results in buckling of the ligamentum flavum with consequent microinstability of the motion segment. Owing to the loss of normal ligamentous restriction, the vertebra develops an anterior listhesis ( Fig. 21.17 ) or, occasionally, a posterior listhesis.

The diagnosis of degenerative spondylolisthesis is based on a combination of plain films and MRI. MRI of the lumbosacral spine is indicated in the presence of neurologic signs and symptoms. MRI detects the presence of ligamentous hypertrophy, spinal cord compression, nerve root impingement, pathologic disk anatomy, and synovial cysts, all of which may be the source of back pain, neurologic deficits, or both.

Definitive therapy in patients with degenerative spondylolisthesis is based on the clinical signs and symptoms combined with the findings from imaging studies. In nearly all cases of lower back pain, with or without neurologic deficits, nonoperative therapy is preferred as the initial treatment for at least the first 4 to 6 weeks. If conservative therapy fails, a trial of epidural steroids and other pain management interventions is appropriate. The indications for surgery include: persistent or recurrent back or leg pain or neurogenic claudication that interferes with the daily activities of life and is unresponsive to 12 weeks of nonsurgical therapy; a progressive neurologic deficit; and symptoms of spinal stenosis. Surgical treatment considerations include the choice of surgical approach (anterior, posterior, or a combination approach) and the specific spine procedure. Surgical decompression with or without lumbar fusion and instrumentation is the usual procedure of choice.

The anesthetic management of patients undergoing operations for lumbar spinal stenosis and degenerative spondylolisthesis must consider the specific surgical procedure and approach planned, the anticipated length of surgery, the anticipated blood loss, whether spinal cord monitoring will be utilized, and any associated comorbidities. Total intravenous anesthesia (TIVA) is often the preferred anesthetic technique, particularly if spinal cord monitoring of motor-evoked potentials is planned. Meticulous attention to patient positioning is important in reducing the incidence of postoperative complications (e.g., nerve injury, blindness).

Osteomyelitis

Spinal infections may involve the vertebral body, the intervertebral disk, the neural arch, or the posterior elements. Vertebral osteomyelitis is the most common of the spinal infections, whereas epidural abscesses are relatively rare. Vertebral osteomyelitis preferentially involves the anterior and middle spinal columns. Although the treatment of vertebral osteomyelitis is usually nonsurgical, surgical intervention may at times be warranted.

Clinically, the symptoms and laboratory findings in patients with vertebral osteomyelitis are nonspecific, with little evidence of a systemic process. The diagnosis relies upon a high index of clinical suspicion in combination with the results of radiologic, microbiologic and pathologic tests. Bacteremic spread is the most likely route of vertebral osteomyelitis and is related to the rich arterial blood supply to the vertebral body, particularly near the longitudinal ligament. Vertebral osteomyelitis most commonly affects the lumbar spine, followed by the thoracic spine, cervical spine, and sacral spine. Patients often complain of localized back pain and paravertebral muscle spasms, with mild neurologic deficits reported in about one-third of patients; other patients demonstrate a severe neurologic deficit or an incomplete spinal cord syndrome. Laboratory tests reveal a leukocytosis in more than half of the patients, an elevation in the erythrocyte sedimentation rate (ESR), and an increase in C-reactive protein (CRP) and procalcitonin levels; ^, the ESR and CRP are sensitive markers for infection, but nonspecific.

The initial radiologic signs of osteomyelitis are usually absent; after several weeks, radiographic imaging reveals a reduction in disk height and vertebral end plate erosions, followed by the appearance of osteolytic areas, paravertebral soft tissue shadows, and eventual vertebral body collapse. The most sensitive early radiologic imaging technique is a nuclear bone scan using technetium Tc 99m MDP (methylene diphosphonate) with single-photon emission computed tomography. MRI is the gold standard imaging modality for the diagnosis of osteomyelitis, providing accurate detail regarding the intervertebral disk, vertebral marrow, neurologic structures, and paraspinal soft tissue pathology. Typical MRI findings in vertebral osteomyelitis and diskitis include loss of end-plate definition and decreased signal in the disk and adjacent vertebral bodies ( Fig. 21.18 ).

Effective medical therapy begins after making an accurate and rapid diagnosis, followed by 4–6 weeks of a combination of intravenous and oral antibiotic therapy. ^{, ,} Surgical therapy is required for most cases of vertebral osteomyelitis; the most common indications include: making a definitive identification of the causative organism; progressive neurologic deficits; spinal instability; progressive spinal deformity; and failure of medical therapy.

Epidural Abscess

Epidural abscesses are relatively rare infections, occurring in about 1 in 10,000 hospital admissions. Local spread of bacteria into the epidural space is responsible for about one-third of cases, and bacteremic seeding of the epidural space occurs in about 50% of cases. The clinical manifestations of an epidural abscess include back pain, fever, and neurologic deficits; half of patients with epidural abscesses are initially misdiagnosed at the time of presentation (range, 11–75%). Neurologic deficits are late manifestations of the infection, and when present, require rapid treatment. As in vertebral osteomyelitis, laboratory findings are nonspecific, with a leukocytosis present in two-thirds of patients; however, blood culture results may be positive and patients may appear to be systemically septic. Epidural abscesses are commonly located in the posterior regions of the thoracolumbar spine, and often involve multiple spinal segments.

Spinal epidural abscesses are diagnosed from clinical and radiologic findings in combination with results of culture of drainage material. ^, Plain radiographs provide diagnostic assistance in less than 20% of the cases, although there may be evidence of coexisting osteomyelitis. MRI with gadolinium enhancement is the radiologic imaging test of choice. This modality can be used to identify the exact location and extension of the epidural infection and to detect spinal cord compression and surrounding edema. Once the diagnosis is confirmed, systemic antibiotic therapy is often combined with surgical drainage. ^, The most common surgical procedure performed for the treatment of a spinal epidural abscess is a posterior decompressive laminectomy with evacuation of the epidural abscess or phlegmon. Neurologic outcome depends on the patient’s preoperative neurologic condition and the provision of early surgical treatment.

Rheumatoid Arthritis

Rheumatoid arthritis (RA) is the most common of the inflammatory diseases, affecting approximately 1% of the world’s population. RA is characterized by a chronic, systemic, autoimmune inflammatory state resulting in symmetrical pain, heat, swelling, and destruction in synovial joints of the hands and feet, wrists, elbows, hips, knees, ankles, and the cervical spine. The T cell-mediated inflammatory state of RA affects synovial tissues throughout the body, resulting in hypertrophy of joint tissue and erosion of articular cartilage and subchondral bone. The cervical spine is often affected, with involvement of the synovial joints of the cervical spine, particularly those surrounding the C1–C2 articulation. The synovitis weakens the surrounding supportive structures, resulting in axial instability that may lead to subluxation of the C1–C2 articulation and spinal cord compression. Atlantoaxial subluxation affects as many as one-fourth of patients with RA and is the most common cervical spine manifestation of RA.

Clinically, patients with RA involving the cervical spine may complain of cervical neck pain, headaches, and limitation of neck movement. In severe disease, subaxial subluxation may cause progressive cervical myelopathy with spasticity of the legs, motor weakness, and incontinence, or symptoms of nerve root compression. The diagnosis of cervical spine involvement in RA relies upon typical radiologic findings, including atlantoaxial subluxation, narrowed disk spaces, erosion of vertebral end plates, apophyseal joint erosion with blurred facets, and spinal osteoporosis. A CT scan is of value for detecting the extent of cervical spine bony destruction, whereas MRI is useful for identification of spinal cord pathology and soft tissue abnormalities.

Surgery is indicated in the presence of myelopathy; severe neck pain with a neurologic deficit; and excessive subluxation of C1–C2 with spinal canal stenosis, vertebral artery compromise, and spinal cord compression. Patients demonstrating symptoms of myelopathy, particularly in the presence of C1–C2 subluxation, require urgent posterior spinal decompression and instrumented fusion; current options may include C1 lateral mass screws in conjunction with C2 pedicle, pars or translaminar screws or C1–C2 transfacet screws and bone grafting. The presence of subaxial subluxation (C3–C7) warrants realignment and stabilization from a posterior approach, particularly when multiple levels are involved. An anterior approach may be appropriate as an alternative technique, especially in the case of significant kyphotic deformity. In select cases, a combined anterior and posterior approach may need to be utilized.

The anesthetic approach for a patient undergoing surgery for RA should take into account the airway concerns unique to these patients, including limitation of neck and temporomandibular joint movement (limiting visualization of the larynx), arthritic involvement of the cricoarytenoid joints (preoperative hoarseness and stridor) with a narrowed tracheal inlet, atlantoaxial subluxation with potential vertebral artery compromise, basilar impression (from rostral advancement of the odontoid process with compression of the spinal cord or medulla), and instability of the lower cervical spine. Accordingly, an awake fiberoptic intubation or video-assisted laryngoscopy may be considered to minimize further neurologic injury during the induction of anesthesia and positioning of the patient.

Ankylosing Spondylitis

Ankylosing spondylitis (AS) is considered the prototypical seronegative spondyloarthropathy; it is characterized by a progressive inflammatory involvement of the spine and axial skeletal joints, which may result in severe spinal deformity ( Fig. 21.20 ). The disease is three times more common in men than in women. In addition to axial skeletal disease, AS involves enthesopathy (inflammation at the sites of tendon and ligamentous insertions), the presence of human leukocyte antigen (HLA-B27), and the absence of rheumatoid nodules and rheumatoid factor in serum (seronegative). The regions of the spine most often involved in AS are the sacroiliac, costovertebral, zygapophyseal, and discovertebral joints. Ankylosing spondylitis-associated fractures are most commonly seen in the lower cervical spine (C6–C7), although they may also occur in the lumbar and thoracic segments. Diseases associated with AS include peripheral polyarthritis, C1–C2 subluxation, valvular heart disease, aortitis, restrictive pulmonary disease, upper lobe pulmonary fibrosis, colitis, renal amyloidosis, osteoporosis, psoriasis, uveitis, and iritis.

Surgery is indicated for individuals with severe spinal deformities that adversely affect normal activities and in patients who have spinal instability due to spondylodiskitis or spinal fracture. In patients with AS who are scheduled for corrective spine surgery or for unrelated surgical procedures, careful preoperative assessment is essential. A thorough history should focus on the patient’s habits, lifestyle, and medications (e.g., use of opioids, nonsteroidal anti-inflammatory agents). Areas of particular focus should include: kidney, pulmonary, gastrointestinal, and nutritional assessment. In addition cervical spine flexibility and airway anatomy must be carefully evaluated in AS patients, as the potential for a difficult airway is increased. The presence and severity of cervical kyphosis should be noted as patients with marked neck flexion may mandate a fiberoptic airway approach or other advanced airway technique.

Hyperextension

Hyperextension injuries are most common in the cervical region and are a common cause of lower cervical neck injuries ( Fig. 21.22 ). Hyperextension injuries may result from facial or frontal trauma, whereby the forces separate the vertebral body and the adjacent lower end of the intervertebral disk. Hyperextension injuries result in disruption of the anterior and middle spinal columns in tension, reducing the AP diameter of the spinal canal and compressing the spinal cord between the posterior aspect of the vertebral body and the ligamentum flavum and lamina. Elderly individuals with cervical spondylosis are particularly susceptible to hyperextension injuries, and even moderate hyperextension may produce cord injury. The vertebral arteries may be damaged in cervical extension injuries, particularly in people with severe spondylosis. Hyperextension injuries are typically unstable owing to the disruption of the stabilizing ligamentous elements and injury to the intervertebral disks.

Compression

Compression injuries occur after impact forces containing a significant axial load (e.g., falls on the occiput) and result in wedge compression fractures, burst fractures ( Fig. 21.23 ), and ligamentous rupture. Wedge compression fractures, most common in the thoracolumbar region, result from pure flexion injury, whereby the posterior ligamentous complex remains intact. Compression injuries with burst fractures often cause serious neurologic damage from retropulsion of bone fragments, ligaments, and disk material into the spinal canal. Compression injuries associated with flexion may produce the so-called teardrop fracture, in which the vertebra is dislocated anteriorly, with an associated avulsion of the superior aspect of the vertebra and posterior longitudinal ligament damage, usually with significant neurologic damage.

Hyperflexion

Hyperflexion injuries may be divided into flexion–compression and flexion–distraction injuries. The direction of the applied load determines the particular injury pattern. Simple flexion–compression fractures results in wedge fractures of the vertebral body that cause a loss of anterior vertebral body height, creating a wedge shape. These injuries are typically stable, unless significant loss of vertebral body height results. Severe flexion–distraction injuries occur from a combination of flexion and distraction loads, with the center of rotation located anteriorly. This injury results in characteristic subluxations or dislocations (see Fig. 21.22 ) of the vertebral bodies with disruption of the posterior longitudinal ligament, causing significant spinal instability. Herniation of the intervertebral disks is commonly seen after severe flexion injuries, as is dislocation of the facet joints, particularly if enough of a rotational component is involved.

Rotation

Flexion and extension injuries that include significant rotational forces may result in severe spinal injuries, including subluxation, dislocation, and fracture–dislocations. Serious injuries to the vertebral bodies and intervertebral disks are often involved in the process ( Fig. 21.24 ).

Rotational spinal injuries often result in severe injuries to the spinal cord and cauda equina. In particular, hyperflexion–rotation forces associated with dislocation may produce either unilateral or bilateral locked facets. Bilateral facet dislocations (locked facets) are associated with major neurologic injury and often require surgical reduction and stabilization. These are most often seen in the lower cervical spine (C5–C7). Fractures of the vertebral peduncles may be associated with bilateral facet dislocations. Unilateral facet dislocations may be associated with no neurologic injury; however, they may be associated with nerve root compression or an incomplete SCI.

Shear

Some degree of spinal translation is involved in most spinal injuries, including spinal fractures and ligamentous tears. The shear mechanism typically involves all three columns of the spine and is associated with a higher incidence of facet dislocation.

Avulsion

Avulsion injuries are typically stable injuries. Examples of avulsion injuries include the odontoid type 1 fracture, in which the tip of the odontoid process is fractured or chipped, and the hyperextension teardrop fracture.

Combined

Combined injuries, resulting from various vectors of force such as axial loading, rotation, and flexion or extension, chiefly affect the cervical region and commonly produce ligamentous tears and distraction (an increase in distance between individual components of adjacent vertebrae. For example, a combined injury, or whiplash, involves rapid acceleration–deceleration forces resulting in extreme extension followed by flexion and is often associated with rotation, compression, and tearing forces. This kind of acceleration lesion distorts the spinal components, damaging the soft tissues of the neck, muscles, and anteroposterior ligaments, and sometimes involves nerve roots and disks.

Traumatic spondylolisthesis of the axis occurs with motor vehicle accidents when the driver’s face or chin hits the steering wheel. The extreme hyperextension of the neck produces shear stresses on the C2–C3 vertebral units, resulting in fracture of the neural arches with dislocation between C2 and C3. However, the avulsed arches decompress the cervicomedullary junction, so patients seldom experience neurologic deficits and usually have a good prognosis.

Mid-thoracic to upper thoracic spinal injuries are much less common than injuries of the cervical or thoracolumbar regions, because of the protection and fixation of the thoracic area by the rib cage and sternum. The greater mobility of the vertebral column at the thoracolumbar junction contributes significantly to the frequency of spinal injuries in this region. Injury to the thoracolumbar spinal column can result in wedge fractures of the vertebrae, with destruction of the laminae, pedicles, and facets. Protrusion of the vertebral body or disk material into the spinal cord may occur. The addition of torque results in fracture–dislocations of the vertebral column. Lumbar fractures have been reported to occur much less often and are the result of flexion and compression forces. Neurologic injuries that involve only the cauda equina have a high potential for significant neurologic recovery.

Penetrating wounds of the spine may cause significant damage, including direct and indirect spinal cord injury through transmitted energy. Many of these injuries produce damage to both the spinal cord and nerve roots as a result of associated shear stress; compression and contusion of cord tissue by bony impingement, herniated disks, or intraparenchymal bone fragments; or ischemia caused by interruption of the vascular supply. However, no consistent relationship exists between actual trauma to supporting structures and injury to the spinal cord. Thus, a patient may present with a stable spine without bony or ligamentous injury and still sustain SCI or may have serious fractures and an unstable spine without neurologic deficits. In adults, the areas most susceptible to injury are the lower cervical spine (C5–C7) and the thoracolumbar junction (T12– L1), regions of the spine coinciding with the areas of greatest spinal column mobility.