Like the frame of a car, the bones and connecting tissues of your skeletal system provide a solid structure for your body. It protects your internal organs and serves as the attachment point for your muscles, enabling movement. Many diseases affect the skeletal system, including joint conditions, structural bone abnormalities, infectious diseases and tumors.
Your bones intersect at joints, which have different capacities for movement. The most mobile joints are lined with a smooth tissue called cartilage and contain fluid to prevent bone-on-bone friction. Joint disorders are the leading type of skeletal system disease. Osteoarthritis is the most common form, affecting at least 27 million Americans, according to the Centers for Disease Control and Prevention. It is caused by wear and tear that erodes joint cartilage, causing stiffness and pain. Rheumatoid arthritis is an autoimmune disease in which the body mistakenly attacks joint tissues. Psoriatic arthritis occurs in some people with the skin condition psoriasis. Gout is a common form of episodic arthritis, occurring when sandlike crystals are deposited in one or more joints.
Structural Bone Disorders
Several diseases can affect bone structure, leaving bones weakened and more likely to break. In osteoporosis, the most common structural bone disease, the bones are less solid and more fragile than normal. According to the U.S. surgeon general, 1.5 million older Americans suffer fractures each year due to osteoporosis. People with Paget disease of bone have unusually thick bones, but they are soft and prone to break because of their abnormal structure. Vitamin D deficiency may also disrupt normal bone formation, a condition known as rickets or osteomalacia. Scoliosis is a common skeletal disorder characterized by abnormal curvature of the spine, although the bones themselves are normal.
The skeletal system can be affected by infectious diseases. Osteomyelitis describes a bone infection, usually caused by bacteria. Septic arthritis is a joint infection, which is also typically caused by bacteria but is sometimes due to a virus or fungus. Certain bacterial infections of the intestine or reproductive system can also affect the joints, a condition known as reactive arthritis. Joint inflammation and arthritic pain are also common with infectious illnesses like Lyme disease, chronic hepatitis C and infectious mononucleosis.
Cancerous and noncancerous tumors can affect the bones and other tissues of the skeletal system. The most common cancerous bone tumors are metastatic. These tumors originate from a cancer elsewhere in the body -- such as the breast, lung or colon -- that has spread to the bones. Cancerous tumors that originate from bone are rare, with fewer than 3,000 cases per year in the United States, according to 2015 statistics from the American Cancer Society. Osteosarcoma is the most common form of bone cancer, usually affecting the large bones of the leg or arm. Noncancerous bone tumors are more common and usually affect children and young adults.