Eburnation

Eburnation is a pathological process observed in bone where the normal lamellar structure is replaced by a dense, structureless, ivory-like material. This occurs when the bone's reparative mechanisms are activated in response to chronic irritation, such as that seen in osteoarthritis or fracture healing. The term derives from the Latin word "eburneus," meaning "ivory."

The process involves the progressive deposition of dense avascular bone tissue. This new bone lacks the typical microscopic organization found in healthy bone, appearing smooth and homogeneous. Eburnation is often found in areas subjected to prolonged mechanical stress or inflammation. For example, in joints affected by osteoarthritis, the cartilage wears away, exposing the underlying bone to friction and pressure. The bone then responds by thickening and hardening, forming a polished, ivory-like surface in an attempt to protect itself.

Radiographically, eburnation appears as a zone of increased bone density, often with a smooth, sclerotic surface. While it represents a bone's attempt to stabilize and repair itself, it can also contribute to joint stiffness and limited mobility. In the context of fractures, eburnation can be seen at the fracture site as part of the healing process, forming dense callus. However, the term is most commonly associated with degenerative joint disease.