Organic matrix (Osteoid)

The organic matrix is called osteoid and is synthesized by osteoblasts. It mainly consists of type 1 collagen, which under normal conditions is deposited following an orderly lamellar pattern. The matrix also contains non-collagenous proteins which are vital for bone mineralization. Osteoid displays a typical red or pink color with Masson-Goldner trichrome stain.

In anomalous situations the deposit of collagen bundles may take place following a non-lamellar pattern called “woven-bone”. This irregular type of deposit takes place in states of high turnover or in cases of fracture repair and does not provide adequate mechanical support. It is characterized by lacking the typical birefringence of lamellar bone under polarized light, which is of great diagnostic utility.

Mineralized bone

The mineral component contains the greatest body stores of calcium and phosphorus in hydroxyapatite crystal form [Ca10(PO4)6(OH)2], which is deposited on the osteoid. Proteins binding with calcium include bone osteocalcin (GLA) and matrix GLA protein. These proteins delay mineralization allowing osteoid maturation. Mineralized bone is usually stained blue or green with Masson-Goldner trichrome stain.