Annulus fibrosus

A tough, fibrous outer ring of the intervertebral discs in the spine.

The annulus fibrosus is a structured, concentric layer of fibrocartilage that surrounds the nucleus pulposus within intervertebral discs. Its primary role is to absorb mechanical stress and provide stability to the spine. The annulus fibrosus is composed of multiple layers of collagen fibers and is designed to withstand tensile forces, ensuring the integrity of the disc throughout a range of movements.

Terminologia Anatomica

annulus-fibrosus

System

Musculoskeletal system

Function

The annulus fibrosus plays a critical role in the function and health of the spine. It acts as a shock absorber, allowing the intervertebral discs to distribute loads and pressures that occur during everyday activities such as walking, running, and lifting. This structure helps maintain proper alignment of the vertebrae and prevents them from grinding against each other. Moreover, the annulus fibrosus contributes to the flexibility of the spine, enabling a wide range of motion while providing a necessary boundary to contain the soft nucleus pulposus. This combination of flexibility and strength helps protect the spinal cord and surrounding nerves from injury.

Location

Situated between the individual vertebrae in the spinal column, the annulus fibrosus encases the nucleus pulposus, forming the intervertebral discs that connect adjacent vertebrae. Each disc is located in the spaces between vertebrae, spanning from the cervical region to the lumbar region of the spine. The annulus fibrosus encompasses the entire outer edge of the disc, anchoring it to the endplates of the vertebrae above and below. It is generally thicker in the anterior region of the disc, providing additional support to the spine's curvature.

Did You Know?

The annulus fibrosus is made up of 15 to 25 layers of collagen fibers, arranged in a crosshatch pattern for added strength.
Injuries to the annulus fibrosus can lead to conditions like herniated discs, which can cause pain and nerve compression.
The dehydration of the nucleus pulposus with age can lead to changes in the annulus fibrosus, affecting its functionality and the overall health of the spine.
Unlike many other tissues in the body, the annulus fibrosus has a limited blood supply, which can slow healing processes.