Giantism is a condition of abnormally increased height that usually results from excessive cartilage and bone formation at the epiphyseal plates of long bones. The most common type of giantism, pituitary giantism, results from excess secretion of pituitary growth hormone. However, the large stature of some individuals can result from genetic factors rather than from abnormal levels of growth hormone.

Acromegaly (ak'ro-meg'al-e) is also caused by excess pituitary growth hormone secretion. However, acromegaly involves growth of connective tissue, including bones, after the epiphyseal plates have ossified. The effect mainly involves increased diameter of all bones and is most strikingly apparent in the face and hands. Many pituitary giants also develop acromegaly later in life.

Dwarfism, the condition in which a person is abnormally short, is the opposite of giantism. Pituitary dwarfism results when abnormally low levels of pituitary growth hormone affect the whole body, thus producing a small person who is normally proportioned. Achondroplastic (a-kon'dro-plas'tik) dwarfism, involving a disproportionate shortening of the long bones, is more common than proportionate dwarfing and produces a person with a nearly normal-sized trunk and head but shorter-than-normal limbs. Most cases of achondroplastic dwarfism are the result of genetic defects that cause deficient or improper growth of the cartilage model, especially the epiphyseal plate, and often involve deficient collagen synthesis. Often the cartilage matrix does not have its normal integrity, and the chondrocytes of the epiphysis cannot form their normal columns, even through rates of cell proliferation may be normal.

Osteogenesis imperfecta (os'te-o-jen'e-sis im-per-fek'tah) a group of genetic disorders producing very brittle bones that are easily fractured, occurs because insufficient collagen is formed to properly strengthen the bones. Intrauterine fractures of the extremities usually heal in poor alignment, causing the limbs to appear bent and short. Several other hereditary disorders of bone mineralization involve the enzymes responsible for normal phosphate or calcium metabolism. They closely resemble rickets and result in weak bones.

Bacterial Infections

Osteomyelitis (os-te-o-mi-e-li'tis) is bone inflammation that often results from bacterial infection. It can lead to complete destruction of the bone. Staphylococcus aureus, often introduced into the body through wounds, is a common cause of osteomyelitis. Bone tuberculosis, a specific type of osteomyelitis, results from spread of the tubercular bacterium from the initial site of infection such as the lungs to the bones through the circulatory system.

Tumors

There are many types of tumors, with a a wide range of resultant bone defects and prognoses. Tumors can be benign or malignant. Malignant bone tumors can metastasize to other parts of the body, or they can spread to bone from metastasizing tumors elsewhere in the body.

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