A spine X-ray, or radiograph, is a two-dimensional medical image created by passing controlled amounts of radiation through the body. This technique provides a rapid evaluation of the vertebral column’s bony structures. By capturing the differential absorption of X-rays by dense tissues like bone, the images help assess the overall alignment and structural integrity of the spinal skeleton, allowing visualization of fractures, bony defects, and chronic changes.
The Essential Anatomy of the Spine
The human spine is a complex structure made up of 33 individual bones called vertebrae, organized into four distinct regions. These regions include the seven cervical vertebrae (neck), the twelve thoracic vertebrae (mid-back), and the five lumbar vertebrae (lower back). Below the lumbar section are the sacrum and the coccyx, which consist of fused vertebrae.
Each vertebral unit is composed of several bony elements visible on an X-ray. The largest component is the vertebral body, a cylindrical mass that bears the majority of the body’s weight. Extending backward from the body are the pedicles and laminae, which form the protective bony ring around the spinal cord.
The transverse processes project laterally, while the single spinous process extends posteriorly. Between each vertebral body is the intervertebral disc space, which holds the soft, cartilaginous disc. Since the disc is soft tissue, it is not directly visible on X-ray, but its presence is inferred by the uniform height of the space. The facet joints (zygapophyseal joints) connect adjacent vertebrae and control spinal motion.
Standard Views and Positioning
Different X-ray views are necessary for a complete three-dimensional assessment of spinal structures and alignment. The most common standard projection is the Antero-Posterior (AP) view, or the Postero-Anterior (PA) view. These frontal views assess the vertebral bodies, transverse processes, and the alignment of the spinous processes down the midline.
The Lateral view, taken from the side, is highly informative, clearly displaying the vertebral bodies in profile and the height of the disc spaces. This projection evaluates the natural curvatures of the spine, such as lordosis (cervical and lumbar) and kyphosis (thoracic). Oblique views are used to visualize the posterior elements, particularly the facet joints and the pars interarticularis.
Dynamic views are special lateral projections captured during maximum flexion and extension. These motion studies help determine spinal stability by revealing abnormal movement between adjacent vertebrae. Proper patient positioning is essential for all views to prevent rotation and ensure the entire area of interest is fully captured for accurate interpretation.
The Systematic Approach to Interpretation
A consistent, step-by-step method is necessary to ensure no subtle abnormality is missed when reviewing a spine X-ray. The process often follows the “A, B, C, S” mnemonic: Alignment, Bone, Cartilage/Disc Spaces, and Soft Tissues. This systematic review begins with the overall architecture of the spine before moving to the individual components.
Alignment
The assessment of spinal alignment starts with tracing three parallel, continuous lines on the lateral view. The anterior vertebral line follows the front edge of the vertebral bodies, and the posterior vertebral line tracks the back edge. The third line, the spinolaminar line, traces the junction of the spinous processes and the posterior wall of the spinal canal. Any interruption in the smooth course of these lines suggests a subluxation or fracture that has disrupted the normal relationship between vertebrae.
Bone
Following the alignment check, each vertebra must be inspected for changes in density, contour, and integrity. This involves scrutinizing the outer cortical margin of every vertebral body for breaks indicating a fracture. The internal trabecular pattern should be assessed for uniform density, as localized areas of increased or decreased opacity may suggest underlying disease. The height of each vertebral body is compared to adjacent ones, looking for the classic wedge shape of a compression fracture.
Cartilage/Disc Spaces
The third step focuses on the intervertebral disc spaces, which appear as gaps between the vertebral bodies. These spaces should be uniform in height and parallel throughout the spine, gradually increasing in height from the upper thoracic to the lower lumbar spine. Narrowing of a disc space suggests degeneration, while an abnormally widened space may indicate a ligamentous injury or fracture-dislocation. The endplates, the surfaces of the vertebral bodies contacting the disc, are also checked for irregularities or erosions.
Soft Tissues
Finally, the soft tissues surrounding the bony column are briefly assessed, acknowledging the limitations of X-ray imaging for non-osseous structures. On the lateral view of the cervical spine, the prevertebral soft tissue space (in front of the vertebral bodies) is examined for abnormal widening. Swelling here may indicate a hematoma or edema associated with an acute fracture. In the thoracic and lumbar regions, the paraspinal lines are checked for displacement or bulging, which can suggest a hematoma or mass effect.
Identifying Common Pathologies
Applying the systematic approach allows for the identification of common pathological findings visible on a spine X-ray. These findings often fall into three broad categories: degenerative changes, traumatic injuries, and alignment issues.
Degenerative Changes
The most frequent findings relate to age-related wear and tear, collectively known as spondylosis or degenerative disc disease. This condition manifests as disc space narrowing, where the intervertebral gap loses its normal height. Osteophytes, or bony spurs, form along the margins of the vertebral bodies as the body attempts to stabilize a deteriorating segment. Additionally, the facet joints may show signs of arthritis, appearing as joint space narrowing and sclerosis (increased bone density at the joint margins).
Traumatic Injuries
Traumatic findings range from minor stable fractures to unstable injuries that disrupt the spinal column. A compression fracture is common, where the vertebral body collapses, typically in the front, resulting in a wedge shape on the lateral view. Burst fractures are more severe, involving comminution of the vertebral body and often resulting in fragments extending into the spinal canal. A defect in the pars interarticularis, known as spondylolysis, may appear as a break or lucency in the neck of the “Scottie dog” sign on an oblique projection.
Alignment Issues
Abnormal spinal curvatures and vertebral slips are readily diagnosed on X-ray. Scoliosis is a lateral curvature of the spine best assessed on the AP view. Spondylolisthesis describes the forward slip of one vertebral body over the one beneath it, a finding most clearly seen on the lateral projection. This slippage is often measured to determine its severity and may be associated with a pars defect or advanced degenerative changes.