Bone is a composite material, consisting of inorganic and organic components as well as the cellular elements discussed previously. Inorganic matrixThe inorganic matrix of bone consists of a calcium hydroxyapatite, which is in a crystalline structure. This serves to: - Mineralize the osteoid produced by osteoblasts,
- Provide strength and hardness to the bone,
- House the body's mineral reserves, including:
- 99% of the body's calcium,
- 85% of its phosphorous,
- 65% of its sodium and magnesium
Organic matrixThirty-five percent (35%) of bone is organic. The organic matrix is composed of the bone cells that you have just learned about, and of protein. Ninety percent (90%) of bone protein is Type I collagen which has a triple helical structure, and ten percent (10%) consists of noncollagenous proteins. Abnormalities of collagen formation may occur and lead to bone fragility. Watch a flash movie depicting the normal sequence of collagen synthesis on the American Society for Bone and Mineral Research Bone Curriculum webpage. This newborn male is observed to have shortened, excessively bowed limbs. He cries with even gentle manipulation of his arms and legs. Xrays reveal multiple fractures in various stages of healing. What abnormality of bone could result in this clinical picture? | | This infant has a severe form of osteogenesis imperfecta (OI). This genetic disorder is caused by abnormalities of collagen formation resulting in brittle bones that are easily fractured. This child was diagnosed with limb fractures by prenatal ultrasound. Children with a less severe form of OI may present with fractures caused by minimal trauma. This clinical picture must be differentiated from child abuse (where the history may be inconsistent with the pattern of injury observed). | Close |
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