The annulus fibrosus is the strong outer layer of an intervertebral disc, made up of concentric rings of fibrous cartilage. Its job is to contain the nucleus pulposus, the soft, gel-like center of the disc that acts as a shock absorber between vertebrae. When the annulus fibrosus tears or weakens, the nucleus can bulge or herniate outward, potentially pressing on nearby nerves and causing pain. While MRI is the primary imaging method for evaluating disc problems, musculoskeletal ultrasound can sometimes visualize disc herniations in the cervical and lumbar spine and is used in some clinical settings to guide injections near damaged discs.
Sonography Term