T he bones and joints of the human body, although designed to withstand a great deal of stress, are subject to a variety of disorders that can affect people of all ages. Some skeletal deformities are the result of congenital defects, and can be treated by physical therapy or surgery with varying degrees of success. Arthritis and related joint diseases, caused by wear and tear over the years, probably affect more people than any other skeletal disorder.
Man's erect posture makes the spine especially vulnerable to problems of alignment, often causing considerable pain. Bone tissue can also be invaded by tumors and by infections of the bone marrow. Also, stress to bones and joints can cause fractures or dislocations, which require prompt medical treatment to prevent deformity or loss of mobility.
A s the fetus develops in the womb, its bony skeleton first appears as soft cartilage, which hardens into bone before birth. The calcium content of the mother's diet aids the fetus in bone formation and in the development of the normal human skeleton. Thus the basic skeletal structure of an individual is formed before his birth. In some instances, the bones of the fetus develop abnormally, and such defects are usually noticeable soon after delivery.
The causes of skeletal birth defects are not always known. Some may result from hereditary factors; others have been traced to the mother's exposure to X rays, radiation, chemicals, drugs, or to disease during pregnancy. Among the more common birth defects are extra fingers, toes, or ribs, or missing fingers, hands, toes, feet, or limbs. Sections of the spine may be fused together, often without causing serious problems later in life, although some fused joints can hinder the motion of limbs. The sections of the skull may unite prematurely, retarding the growth of the brain.