Glossary

Hard disc - Disc displacement in which the displaced portion has undergone calcification or ossification and may be intimately associated with apophyseal osteophytes. Note: The term hard disc is most often used in reference to the cervical spine to distinguish chronic hypertrophic and reactive changes in the periphery of the disc from acute extrusion of soft, predominantly nuclear tissue. See: chronic disc herniation.

Herniated Disc - Extrusion of part of the nucleus pulposus material through a defect in the annulus fibrosus.

Herniated disc - 1. Localized displacement of disc material beyond the normal margins of the intervertebral disc space. 2. (Non-Standard) [Any displacement of disc tissue beyond the disc space]. Note: Localized means, by way of convention, less than 50% (180 degrees) of the circumference of the disc. Disc material may include nucleus, cartilage, fragmented apophyseal bone, or fragmented anular tissue.

Heterotopic Bone Formation - The occurrence of bone growth in an abnormal location.

Hook - For spinal applications, a metallic medical device used to connect spinal structures to a rod.

Hydroxyapatite (HA) - The lattice-like structure of bone composed of calcium and phosphorous crystals which deposits on collagen to provide the rigid structure of bone.