Traumatic spinal fractures are a leading cause of morbidity in the trauma population. They must be assessed and managed differently than other spinal pathology including degenerative, neoplastic or infectious. Establishing stability, restoring alignment and decompression of neural elements are critical to the successful management of traumatic spinal injury. In this chapter, we will review the relevant anatomy, biomechanics of injury and principles of management to avoid complications in the treatment of traumatic spinal fractures.
Keywordsthoracolumbar junction, TLICS, burst fracture, spinal fusion, spinal cord injury, radiculopathy, cauda equina syndrome
Traumatic spinal fractures are a leading cause of morbidity in the trauma patient.
Spinal stability is defined as the ability of the spine to resist displacement of structures under physiologic loads so as to prevent injury or irritation to neural elements.
The spine is divided into three regions with specific anatomic properties that must be considered in traumatic spinal fracture repair.
The traumatic spine must be assessed and managed differently than degenerative pathology.
The complications or sequelae of traumatic spinal fractures can be mitigated with appropriate preoperative and perioperative considerations for the trauma patient.
The goal in the management of spinal fractures is the restoration of alignment, the preservation of neurologic function, and the mitigation of posttraumatic pain.
Traumatic spinal fractures represent a minority of injuries seen in the trauma population, but they account for a substantial cost to the health care system and represent a burden on society. Depending on the population studied, variation in the literature exists regarding the order of the common mechanisms of injury. The most common mechanisms include motor vehicle accident and high-energy fall from a height. Injuries caused by violent assaults vary depending on the region of the United States that is studied. The character and location of injury to the spine correlate with the mechanism of injury. The thoracolumbar junction is the most common site of injury, comprising over 80% of all spinal traumas. The highest number of complete motor and sensory neurologic deficits are found in cervical spine injuries. Prehospital immobilization and the early recognition and management of acute spinal fractures are critical to reduce the morbidity of this traumatic injury. Preoperative complications often result from failure to identify spinal fractures and/or ligamentous injuries, whereas postoperative complications often result in delayed instability after either conservative or operative treatment of spinal injuries resulting in posttraumatic kyphosis or delayed painful angulation of the posttraumatic spine. Neurologic deficits can also occur and/or be detected in the postoperative period. As such, vigilance in the postoperative follow-up is necessary regardless of whether operative or nonoperative treatment was chosen.
The spine is a complex structure that exists as a combination of three subsystems: (1) the vertebrae providing an osseous structural frame; (2) intervertebral discs, apophyseal joints, and ligaments providing dynamic support; and (3) the coordination of muscle response through neural control. Instability occurs with anatomic disruption by trauma or disease of any one or combination of these systems. Panjabi and White elegantly defined spinal stability as “the ability of the spine to resist displacement of vertebral structures under physiologic loads such that neither damage nor irritation to neural elements can occur, while also preventing the development of deformity or pain due to structural change” ( Fig. 61.1 ).
The spine is composed of 25 vertebrae further divided into three distinct regions, each with its own common size, orientation, and relationship to surrounding structures that contribute to the functionality of the axial skeleton: (1) cervical, (2) thoracic, and (3) lumbosacral segments.
The vertebrae are composed of an inner highly porous, cancellous bone and a dense outer cortical shell. The vertebral end plates provide an even distribution of mechanical loads, and prevent disc extrusion into the vertebral bodies. The posterior elements of the vertebrae include a neural arch and transverse, spinous, and articular processes (inferior and superior facets). The neural arch is a ringed structure with its anterior portion attached to the vertebral body (pedicles) and the posterior half (laminae). The superior articular process of the vertebra below and inferior articular process of the vertebra above comprise the facet joint of each motion segment and limit the extent of torsion and shear. The orientation of these facet joints changes, depending on the spinal region, thereby modulating their respective functions. Most of the axial load sharing occurs in the vertebral body and intervertebral discs, or anterior column, with 10% to 20% distributed posteriorly to the facet. This value can go to as high as 70% during hyperextension. The transverse and spinous processes provide attachment points to ligaments and skeletal muscles that are responsible for spinal motion.
The intervertebral disc is composed of two parts: an inner gelatinous nucleus pulposus and an outer annulus fibrosis. The compressive loads are distributed across the gelatinous structure in between the vertebral bodies. Flexion and lateral bending result in loading conditions that cause as much as a 50% increase in annulus deformation and that cause increases in nuclear pressure such that traumatic annulus tearing and subsequent herniation of the disc material can occur.
Spinal ligaments provide low resistance to motion under physiologic loads, while distributing uniaxial tensile loads from one bone to another during loads beyond this range. These tasks are performed by seven subaxial spinal ligaments, which can be divided into intrasegmental systems that hold the functional spinal unit together and intersegmental systems that hold multiple vertebrae together. The posterior ligamentous complex (PLC) and paraspinal muscles form the posterior tension band of the spinal column that counterbalances the compressive force on the anterior column.
The occiput–C1 articulation is the most important segment involved in flexion-extension of the cervical spine ( Fig. 61.2 ). The occipital condyles articulate with the lateral masses of C1 to permit flexion and extension with limited rotation and lateral bending. There are several critical ligamentous structures at this segment that hold the occiput and cervical spine together; they are beyond the scope of this chapter. The hypoglossal nerve traverses the medial-superior aspect of each occipital condyle through the hypoglossal canal. As many as 40% of patients with occipital condyle fractures have lower cranial nerve injuries, primarily CN XII, some of which can develop in a delayed fashion. Osseous and/or ligamentous fractures at this segment can lead to atlanto-occipital dissociation, which is frequently a fatal injury.
The atlas, or C1 vertebra, is the first of the cervical vertebrae and exists as a bony ring surrounding the spinal cord. The anterior and posterior arches are located anterior and posterior, respectively, to the lateral masses that articulate with the occiput. The vertebral arteries course laterally to the bony ring through the transverse foramina. A burst fracture that includes a fracture through both arches is known as a Jefferson fracture. Most of these fractures can be managed conservatively. The extent of ligamentous injury can be extrapolated by the overhang of the C1 lateral mass on C2. Although this threshold has recently come into question, a bilateral combined value of greater than 7 mm indicates a significant ligamentous disruption that implies instability requiring fixation at this level. This radiographic finding is known as the rule of Spence.
C2 is composed of a vertebral body, the odontoid process or dens, and the foramen transversarium. The odontoid process is tightly held to the ventral portion of the C1 ring by the transverse atlantal ligament. The C1–C2 complex allows more rotation than any other spinal segment. This region accounts for approximately 50% of all rotation of the cervical spine. C2 fractures are classified as odontoid fractures (Types I–III), hangman’s fractures (bilateral traumatic spondylolisthesis through the pars interarticularis), facet fractures, or injuries to the foramen transversarium. Between 50% and 70% of fractures at this level are odontoid fractures and are associated with other spine injuries in 34% of patients. Anderson and D’Alonzo classified these fractures into three types. Type I is a fracture through the upper part of the odontoid process, which likely results from an avulsion of one of the alar ligaments and is considered stable. Type II fractures represent nearly 70% of all odontoid fractures and occur at the junction between the odontoid process and the vertebral body. These were later subclassified to account for treatment consequences of the subtle differences in fracture pattern. These fractures are generally considered unstable; however, treatment remains controversial because many authors have reported significant healing with conservative measures. Type III odontoid fractures extend into the body of the axis and are often managed conservatively unless significant comminution and/or displacement occurs. Hangman’s fractures, or bilateral traumatic spondylolisthesis through the pars interarticularis, are the second most common type of axis fractures. These fractures result from either axial loading from the skull—through the occipital condyles and the C1–C2 lateral masses, where they converge at the base of C2, passing through the weak pars interarticularis —or from hyperextension and distraction (execution by hanging).
The subaxial cervical spine spans from C3 to C7. The lordosis of the cervical spine affords greater mobility in this segment. The facet joint complex is coronally oriented and provides stability to the subaxial spine, and injury to the facet capsule or fracture can result in decreased biomechanical stability. The PLC provides support during flexion-extension, whereas the facets support axial rotation as well as flexion and extension. Superior articulating facets transition from a posteromedial orientation at C3 to a posterolateral orientation at C7. Facet fractures range from minor nondisplaced fractures to varying degrees of subluxations and dislocations. A variety of classification systems have been developed to describe subaxial cervical injuries with little consensus. The following subtypes of injury are based on the AOSpine system (Subaxial Cervical Spine Injury Classification System). Compression injuries result in compression fractures, with or without retropulsion (burst) of the vertebral body and/or the spinous processes and laminae. Tension band injuries involve either the anterior or posterior tension band of the cervical spine. These injuries can include osseous and/or ligamentous structures. They involve fractures or disruptions through the vertebral body or disc with an intact posterior hinge that prevents displacement. Translational injuries result from displacement of one vertebral body over another in any direction, often resulting in vertebral body and/or posterior element fractures. The vertebral arteries are encased by the transverse foramina from C6 to C1. As such, fractures through the transverse foramina or hyperextension of the cervical spine can lead to blunt vascular injury.
The thoracic spine is aligned in kyphosis and structurally rendered more rigid by the rib cage that articulates with it ( Fig. 61.3 ). The mobility of the lordotic cervical spine meets the rigidity of the thoracic spine at the C7–T1 disc space, creating unique biomechanical properties of the cervico-thoracic junction that predispose this region to high-velocity injuries. The facets transition from a coronal orientation in the upper thoracic spine to a sagittal orientation in the lumbar spine. The apex of the thoracic kyphosis is at approximately the T8 vertebral level, which also corresponds to the narrowest cross-sectional area of the spinal canal. The thoracolumbar junction (T10–L2) is another biomechanical transition zone from a stiff rostral kyphotic thoracic spine to a more flexible caudal lordotic lumbar spine, which predisposes this region to high-velocity injuries.
The Subaxial Cervical Spine Injury Classification (SLIC) system describes the morphology of upper thoracic spine fractures as well as those of the cervical spine; included are categories for compression, burst, distraction, and rotational-translational injuries. Compression injuries are due to axial loading and result in loss of height of the anterior column (a flexion teardrop fracture). High axial loading forces will disrupt the posterior wall of the vertebral bodies and result in burst fractures with retropulsion of bone from the posterior aspect of the vertebral body into the spinal canal, which may cause significant neurologic injuries. Distraction injuries result from hyperextension of the thoracic spine, which may cause anterior ligamentous structures, including the anterior longitudinal ligament (ALL), to avulse the anterior inferior corner of the vertebral body, resulting in an extension teardrop fracture and a wider intervertebral space seen on imaging. Rotational-translational injuries are characterized by one vertebral body being rotated or translated beyond physiologic thresholds with respect to another. Unilateral and bilateral facet dislocations, floating lateral masses, and bilateral pedicle fractures are representative of this type of injury.
The lumbar spine is distinguished by the largest vertebral bodies in the spine, which subserve the largest axial loads. The pedicles are robust and increase in angulation from 0 degrees at L1 to 30 degrees at L5. The transverse processes originate increasingly anteriorly at more caudal segments and are attached to ligaments in the rigid pelvis at the more caudal segments. High-velocity injuries including falls from a height make the transverse processes prone to fracture. The facets are sagittally oriented to facilitate flexion and extension along this highly mobile lordotic segment.
A variety of classification systems have been developed over time to describe different injury patterns in the lumbar spine. The Thoracolumbar Injury Classification and Severity Score (TLICS) classifies injuries of the thoracolumbar junction and, by extension, the lumbar spine according to morphology, neurologic status, and integrity of the PLC to guide treatment decisions. The morphology of fractures includes compression, burst, translation, and rotation. Compression fractures of the vertebral body are visualized as a loss of height on radiographic imaging. The presence of short tau inversion recovery (STIR) signal on magnetic resonance imaging (MRI) distinguishes acute from chronic fractures in the anterior column. Burst fractures are compression fractures with retropulsion of the vertebral bone dorsally into the spinal canal. Translation/rotation injuries are sustained by rotational forces applied simultaneously with a flexion movement at the thoracolumbar spine, leading to complete disruption of the PLC and extension through the anterior disc and vertebral body. These are often associated with facet fractures and are usually unstable. Fracture dislocations are defined by the translation of the cephalad vertebrae compared with the adjacent caudal vertebrae. The facets are often disarticulated or fractured, and displacement of the vertebral body can range from 10% to complete spondyloptosis. Another fracture pattern similar to flexion-distraction injuries is the eponymous Chance fracture. In this injury, the fracture line extends from the posterior spinous process through the pedicles, vertebral body, and the PLC. The injury primarily involves bone, but can occur through the soft tissues as a so-called “ligamentous Chance fracture” ( Figs 61.4 and 61.5 ).