John M Mathis Ali Shaibani and Ajay K Wakhloo

The spine and its anatomical components are complex. Authors have approached it from a variety of perspectives including surgical, anatomical, and diagnostic (imaging). Our interest in spinal anatomy concerns the treatment of pathological processes affecting the spine. This chapter describes spine anatomy that is of interest to the image-guided interventionist.

Physical Components

Bones

The spine is composed of 33 bones: there are 7 cervical vertebra, 12 thoracic vertebra, 5 lumbar vertebra, 5 sacral segments (fused), and 4 coccygeal segments (variably fused).1 Natural curvature is found throughout the spine (Figure 1.1). Viewed from the side, the cervical spine is convex forward, the thoracic spine is convex backward (centered at T7), the lumbar spine is convex forward, and the sacral bone is convex backward. The vertebrae progressively enlarge from the cervical through the lumbar regions. There is also variability in vertebra size at any particular level based on the individual's body size (Figure 1.2). The size of a vertebra is of extreme importance when one is performing vertebroplasty or kyphoplasty. In these procedures the most common side effects are created by cement leak. This results from natural or pathological holes in vertebra as well as overfilling. To avoid overfilling it is important to appreciate the volume range of vertebral bodies between the cervical and lumbar regions (Table 1.1). Theoretical volume calculations show vertebral body volumes ranging from 7.2 mL in the cervical spine to 19.6 mL in the lumbar region. These volumes are computed for a hollow cylinder with dimensions taken from each spine region. Because of the thickness of cortical and trabecular bone, the fillable volume is on the order of 50% of the theoretical volume. The fillable volume will again be diminished by the amount of the vertebral collapse following a compression fracture. As seen in Table 1.1, the 50% compressed volume for a C5 vertebra is between 1.8 and 2.2 mL. In the thoracic spine (T9), the 50% compressed volume is

Convex Thoracic Spine

Figure 1.1. The spine viewed from the lateral projection. Natural curvature varies from convex forward in the cervical and lumbar region to concave forward in the thoracic and sacral regions. The thoracic curvature is particularly prone to kyphosis with vertebral compression fractures in this territory.

Figure 1.1. The spine viewed from the lateral projection. Natural curvature varies from convex forward in the cervical and lumbar region to concave forward in the thoracic and sacral regions. The thoracic curvature is particularly prone to kyphosis with vertebral compression fractures in this territory.

3.8 mL. At L3 the 50% compressed volume is 4.9 mL. It is easy to see why very small volumes of cement sometimes can achieve adequate biomechanical augmentation for pain relief. These volumes differ considerably from region to region in the spine.

The spinal canal is formed by the posterior wall and the posterior elements of the vertebral body (pedicles and lamina). The pedicles join the vertebral body to the posterior lamina. The vertebral pedicle is a

Pedicle Lamina
Figure 1.2. Representative vertebrae from the cervical, thoracic, and lumbar regions. Relative vertebra body sizes and configuration changes are shown.

complex three-dimensional cylindroid structure that consists of a thin shell of compact bone (which is thickest on the medial surface) that surrounds a much larger center that is filled with cancellous bone.2-8 The pedicles are extremely important because they provide a safe tunnel through which the interventionist can gain access to the vertebral body for biopsy, vertebroplasty, and kyphoplasty. The pedicles in the cervical region are small and present a poor access to the vertebral body in this region. However, the thoracic and lumbar pedicles provide good potential access. Pedicles progressively increase in size from the upper thoracic (T4) to the lower lumbar (L5) spine. The angle of

Table 1.1. Vertebral volume estimates from the cervical to lumbar regions

Vertebral level

Theoretical volume (mL)

Fillable volume (mL)

50% Compressed volume (mL)

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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Responses

  • sofia
    Where is the pedicle and lamina on a vertebrae?
    7 years ago
  • JULIANE
    Which region a vertebrae is from?
    7 years ago
  • franziska
    Where are the pedicles on a vertebrae?
    6 years ago

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