Injuries to the Spinal cord and spinal Column

I. Introduction

Each year, approximately 10,000 new spinal cord injuries result in paralysis, with an estimated societal cost of $10 billion. The average age of the injured is 32 years with a 4:1 male-to-female ratio. Motor vehicle accidents account for 50% of the spinal cord injuries, sports 14%, falls 21%, and violence 15%. Of patients with spinal cord injuries, 44% also suffer from other significant trauma, with 14% having head and facial trauma. Half of all spinal cord injuries involve the cervical spine, most occurring between C4 and C7, with a 3-month mortality of 20%. Half of spinal cord injuries involve complete quadriplegia.

II. Anatomy and Biomechanical Definitions

A.

The spinal cord is a continuation of the brainstem (medulla). This area is the cer-vicomedullary junction, which is located at the foramen magnum of the skull. The spinal cord continues through the vertebral canal of the cervical, thoracic, and upper lumbar vertebra, generally ending at the L1 to L2 space. The spinal cord contains the upper motor neurons (UMNs) that synapse with lower motor neurons (LMNs) to form the nerve roots and cauda equina. The nerve roots in the cervical and lumbar regions fuse as the cervical and lumbar plexuses before separating again as specific nerves. Generally speaking, UMN lesions carry a worse prognosis than LMN lesions, as nerve roots have better capacity for repair than does the spinal cord.

B.

The spinal column is composed of 7 cervical, 12 thoracic, 5 lumbar, and 5 fused sacral vertebrae. With the exception of the sacral vertebra, the vertebral bodies articulate with each other across the intervertebral disc and facet joints, forming a functional spinal unit. The facet joints, associated ligamentous structures, and other bone articulations (e.g., the rib cage) determine the motion across two vertebral bodies. The motions are considered in the sagittal plane (flexion and extension), coronal plane (lateral flexion), and in the transverse plane (rotation). In the cervical spine, about 50% of flexion and extension occurs between the occiput and C1, whereas 50% of rotation occurs between C1 and C2. The remainder of cervical movement takes place in the subaxial (below C2) region. The thoracic spine has little motion because of the facet joint orientation and added stabilization of the rib cage. The facet joints of the lumbar spine have a more sagittal orientation and allow moderate motion in the sagittal plane while resisting rotation. The transition from the stiff thoracic spine to a mobile lumbar area accounts for the high number of injuries at the thoracolumbar junction.

C.

Injuries to the spinal column occur as a result of excessive forces applied to the spine. These forces can cause axial loading, hyperflexion, hyperextension, distraction, rotation, or a combination of forces. Injury to the spinal column can cause spinal instability, which can be defined on radiographic or clinical grounds. In the acute setting, radiographic features are most commonly used to determine spinal stability. This is reviewed later in the chapter.

D.

The conceptualization of the spine as a series of support columns increases our bio-mechanical understanding of stability. Three columns of the spine have been described for the lower thoracic and lumbar spine. The anterior column (anterior longitudinal ligament and the anterior two thirds of the vertebral body and disc),

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the middle column (posterior third of the vertebral body and disc, the posterior longitudinal ligament), and the posterior column (the facet joints, capsule, ligamentum flavum, and posterior ligaments) describe the main columns of overall biomechanical support (Fig. 18-1). The three-column theory may not be completely applicable to the cervical spine, but it is still generally used. Injuries or deficits of two of three columns denotes biomechanical instability.

E.

Spinal cord injuries can be separate and distinct from spinal column injuries. The diagnosis of a spinal cord injury (SCI) is made on clinical grounds and supplemented with diagnostic tests such as magnetic resonance imaging (MRI), myelo-graphy, or electrodiagnostic studies. The level of SCI frequently correlates with the level of spinal column injury. However, SCI can occur without spinal column injury.

F.

Spinal column injuries are bone or ligamentous disruptions that result in bone fractures or ligamentous instability. The loss of these stabilizing and supporting elements can result in compression and injury of neural elements. The diagnosis of spinal column injury is based on clinical and radiographic criteria, such as pain and ecchymosis at the level of fracture and plain film evidence of fracture. Spinal column injuries can occur without spinal cord injury.