Chapter 9: Vertebral Column

Detailed Chapter Overview

Chapter 9 provides a comprehensive and segmented exploration of the entire vertebral column, the central axis of the human skeleton. This chapter is critical, as spine radiography is essential for diagnosing a vast spectrum of conditions, from traumatic injuries and fractures to degenerative diseases like arthritis and scoliosis. The chapter systematically breaks down the spine into its distinct regions: cervical, thoracic, lumbar, sacrum, and coccyx. A major focus is placed on the unique anatomical characteristics of the vertebrae in each region—such as the bifid spinous processes of the cervical spine, the rib articulations of the thoracic spine, and the massive bodies of the lumbar spine. Understanding the spinal curvatures, both primary (kyphotic) and compensatory (lordotic), is fundamental to positioning and image interpretation. The chapter meticulously details the anatomy of the intervertebral foramina and zygapophyseal joints, explaining precisely which projections and patient rotations are required to visualize them as open spaces. It provides detailed, step-by-step instructions for a multitude of projections, from basic AP and lateral views to highly specialized techniques like the AP "Open-Mouth" for C1-C2, the "Swimmer's" lateral for the cervicothoracic region, and oblique views to demonstrate the lumbar "Scottie Dogs." Radiation protection is heavily emphasized, particularly for the cervical and lumbar regions. For every projection, rigorous evaluation criteria are established, ensuring the radiographer can produce diagnostically optimal images for this challenging and clinically significant area of the body.

In-Depth Study Guide

General Anatomy of the Vertebral Column

The vertebral column, or spine, is a complex, articulated pillar composed of 33 small, irregular bones in early life, which fuse into 26 distinct bones in the adult skeleton. It serves multiple critical functions: providing a flexible main support for the trunk, protecting the delicate spinal cord within its canal, and acting as a shock absorber for daily activities like walking and running.

• Divisions: The spine is segmented into five regions: 7 Cervical (neck), 12 Thoracic (upper back), 5 Lumbar (lower back), 5 Sacral (fused into one sacrum), and 3-5 Coccygeal (fused into one coccyx).
• Spinal Curvatures: The adult spine has four natural curves that give it strength and flexibility.
  • Primary Curves (Kyphotic): These are curves that are convex (curved outward) when viewed from the back. The thoracic and sacral regions have kyphotic curves, which are present at birth.
  • Compensatory Curves (Lordotic): These are curves that are concave (curved inward) when viewed from the back. The cervical and lumbar curves are lordotic and develop after birth as a child learns to hold their head up (cervical) and begins to walk (lumbar).
• Typical Vertebra: A typical vertebra consists of two main parts: an anterior, weight-bearing **body** and a posterior **vertebral arch**. The arch itself is formed by two short, thick **pedicles** and two flat **laminae**. The space enclosed by the body and arch is the **vertebral foramen**. When all vertebrae are stacked, these foramina form the continuous **vertebral canal**, which houses the spinal cord. Projecting from the arch are several processes: a single posterior **spinous process**, two lateral **transverse processes**, and four **articular processes** (two superior and two inferior) which form the zygapophyseal joints.
• Intervertebral Disks: Found between C2 and S1, these are tough fibrocartilaginous disks that separate the vertebral bodies. They consist of a tough outer layer (annulus fibrosus) and a soft, pulpy center (nucleus pulposus), acting as crucial shock absorbers.

Cervical Spine (C1-C7)

The most superior and most mobile section of the spine, supporting the skull and allowing for extensive head movement.

• Unique Features: All seven cervical vertebrae are distinguished by having three foramina: the single vertebral foramen and two **transverse foramina**, which allow for the passage of the vital vertebral arteries and veins. Additionally, the spinous processes of C2 through C6 are typically **bifid** (forked).
• Atlas (C1): This vertebra is unique as it is essentially a ring of bone with no body and no spinous process. It possesses large, concave superior articular processes that articulate with the occipital condyles of the skull, supporting the head.
• Axis (C2): The second cervical vertebra is easily identified by its prominent, tooth-like **dens** or **odontoid process**. This process projects superiorly from the body and acts as a pivot point for the rotation of the atlas (and thus, the head), allowing for the "no" motion.
• Zygapophyseal Joints: These facet joints are visualized only on a true lateral projection in the cervical spine.
• Intervertebral Foramina: These openings, through which spinal nerves exit, are best visualized on a 45-degree oblique projection. A key rule is that for AP obliques (LPO/RPO), the foramina demonstrated are those on the side **up** (farthest from the IR). For PA obliques (LAO/RAO), the foramina demonstrated are on the side **down** (closest to the IR).

Cervical Spine Projections:

• AP Axial: Requires a 15-20 degree cephalad CR angle to open the intervertebral disk spaces, which are naturally angled due to the lordotic curve.
• AP "Open-Mouth": A critical view to visualize the relationship between C1 and C2 (specifically the dens and its articulation) without superimposition of the upper incisors and the base of the skull.
• Lateral (Grandy Method): Always performed at a 72-inch SID to minimize magnification and improve recorded detail. It is crucial that the entire C1 through C7 segment is visualized.
• "Swimmer's" Lateral (Twining Method): A specialized projection used when the C7-T1 region is obscured by the patient's shoulders on a standard lateral view. It involves positioning one arm up and one arm down to separate the shoulders.
• AP/PA Obliques: Require a 45-degree patient rotation and a 15-20 degree CR angle (cephalad for AP, caudad for PA) to clearly demonstrate the intervertebral foramina.

Thoracic Spine (T1-T12)

• Unique Features: The defining characteristic of the thoracic vertebrae is the presence of **costal facets** on their bodies and transverse processes. These facets are the articulation points for the 12 pairs of ribs, making the thoracic spine more rigid and less mobile than the cervical or lumbar regions.
• Zygapophyseal Joints: To visualize these joints, a steep 70-degree oblique position from the coronal plane is necessary.
• Intervertebral Foramina: These are visualized only on a true lateral projection.

Thoracic Spine Projections:

• AP: Patient is supine. To achieve a more uniform radiographic density over the length of the thoracic spine, a wedge filter can be used, or the anode heel effect can be applied (placing the cathode end over the thicker lower thoracic region).
• Lateral: Patient is positioned in a true lateral with arms forward to avoid superimposition. A **breathing technique** (low mA, long exposure time of 2-3 seconds) is highly recommended. The patient breathes gently during the exposure, which blurs out the overlying lung markings and rib shadows, resulting in a clearer view of the vertebral bodies.
• Obliques: A 70-degree oblique from the AP or PA position is required to open up and visualize the zygapophyseal joints.

Lumbar Spine (L1-L5)

• Unique Features: The lumbar vertebrae are the largest and strongest, characterized by massive, kidney-bean-shaped bodies designed to support the significant weight of the upper body.
• Pars Interarticularis: A critical anatomical region, this is the part of the lamina located between the superior and inferior articular processes. It is a common site for stress fractures, a condition known as **spondylolysis**.
• "Scottie Dog": On a correctly positioned 45-degree oblique view, the posterior elements of a lumbar vertebra create a recognizable shape resembling a Scottie dog. Radiographers must be able to identify the parts of the "dog" as they correspond to specific anatomy:
  • **Ear:** Superior Articular Process
  • **Nose:** Transverse Process
  • **Eye:** Pedicle
  • **Neck:** Pars Interarticularis (a "collar" on the dog can indicate a fracture or spondylolysis)
  • **Leg:** Inferior Articular Process
• Zygapophyseal Joints: These are clearly demonstrated on a 45-degree oblique projection.
• Intervertebral Foramina: As with the thoracic spine, these are visualized only on a true lateral projection.

Lumbar Spine Projections:

• AP: The patient should be supine with their knees flexed and feet flat on the table. This maneuver reduces the natural lumbar lordotic curve, bringing the vertebrae closer to the IR and opening the intervertebral disk spaces for better visualization.
• Lateral: A lead shield placed on the tabletop behind the patient is crucial for absorbing scatter radiation, which significantly improves image contrast and detail.
• Obliques (RPO/LPO): The patient is rotated 45 degrees. In these posterior oblique positions, the zygapophyseal joints demonstrated are those on the side **down** (closest to the IR). For example, an RPO will show the right-sided joints.
• L5-S1 "Spot" View: A localized view focusing on the lumbosacral junction, which is a common site for pathology. On the lateral projection, a 5-8 degree caudad CR angle is often necessary to open the L5-S1 joint space, which is angled inferiorly.