Osteoporosis

Osteoporosis, frequently found in immobilized patients and in postmenopausal women, is an imbalance in skeletal turnover so that bone resorption exceeds bone formation.

Reparación de una fractura

The fracture of a bone is usually caused by direct violence or by a strong twisting strain. When a bone fractures the two fragments separate and in so doing tear the arteries in the Haversian systems that cross the fracture line. This damage results in the leakage of blood into the fracture, where it is trapped and soon clots. After a short time, the Haversian arteries go into spasm, causing the death of active bone cells not only at the fracture site, but also for some distance along the shaft. About two days after the break, the blood clot is invaded by capillaries and fibroblasts. The fibroblasts differentiate into bone-forming cells, or osteoblasts, and cells that form periosteal tissue on the outside of the bone. New tissue, called callus, surrounds the fracture and replaces the dead bone. The dead bone is absorbed and replaced by new bone, formed by the osteoblasts in the callus, which is remodeled by cells, called osteoclasts, to its original shape. This remodeling process is so effective that after a few months it is difficult to detect the fracture site.

La estructura del hueso

This is the structure of bone. Spongy or cancellous bone form the center bulk of all our bones. Its honeycomb structure keeps bone light, in contrast to the heavier, compact bone, which gives it strength. Bone cells or osteocytes are contained in spaces called lacunae. The minute projections of bone cells trail into adjoining channels known as canaliculi. Tissue fluid, which fills the lacunae, allows the transfer of materials between bone cells and capillaries. Haversian systems, each about one-sixtieth of an inch wide, make up the structure of compact bone. Each system is formed by a series of rings called lamellae, which are deposits of mineral salts and collagen fibers. Haversian canals, which run through the center of each Haversian system, contain the blood and lymphatic vessels supplying the bone. Here arteries carrying oxygenated blood are shown in red. Veins carrying deoxygenated blood are shown in blue. The lymphatic vessels are shown in white. A section through the shaft of the femur, a long bone, shows a central mass of spongy bone surrounded by the branching tubular Haversian systems. Blood vessels on the bone surface reach into the center of each Haversian system supplying the bone cells.