Osteoid is a protein mixture secreted by osteoblasts that forms the organic matrix of bone. Bone is formed when osteoid mineralizes.
Osteoid is important in several disease processes:
- failure of osteoid to mineralize leads to osteomalacia in adults and rickets in children.
- focal accumulations of osteoid can lead to Milkman's pseudofractures, which are suggestive of osteomalacia.
- linear accumulations of osteoid may build perpendicular to the cortical margin and appear as Looser's zones or pseudofractures.
- osteoid osteoma is composed of osteoid and woven bone, both of which can be seen as interconnected trabeculae, sheets, or isolated islands.