A fistula is an abnormal connection between two parts inside of the body. Fistulas may develop between different organs, such as between the esophagus and the windpipe or the bowel and the vagina. They can also develop between two blood vessels, such as between an artery and a vein or between two arteries.

Some people are born with a fistula. Other common causes of fistulas include:

• Complications from surgery
• Injury
• Infection
• Diseases, such as Crohn's disease or ulcerative colitis

Treatment depends on the cause of the fistula, where it is, and how bad it is. Some fistulas will close on their own. In some cases, you may need antibiotics and/or surgery.

Each of your feet has 26 bones, 33 joints, and more than 100 tendons, muscles, and ligaments. No wonder a lot of things can go wrong. Here are a few common problems:

• Bunions - hard, painful bumps on the big toe joint
• Corns and calluses - thickened skin from friction or pressure
• Plantar warts - warts on the soles of your feet
• Fallen arches - also called flat feet

Ill-fitting shoes often cause these problems. Aging and being overweight also increase your chances of having foot problems.

Having HIV/AIDS weakens your body's immune system. It destroys the white blood cells that fight infection. This puts you at risk for opportunistic infections (OIs). OIs are serious infections that take advantage of your weak immune system. These infections are less common and less severe in healthy people.

There are many types of OIs:

• Bacterial infections, including tuberculosis and a serious related disease, Mycobacterium avium complex (MAC)
• Viral infections, such as cytomegalovirus (CMV) and hepatitis C
• Fungal infections, like yeast infections, cryptococcal meningitis, pneumocystis carinii pneumonia (PCP) and histoplasmosis
• Parasitic infections, such as crypto (cryptosporidiosis) and toxo (toxoplasmosis)

Having HIV/AIDS can make infections harder to treat. People with HIV/AIDS are also more likely to have complications from common illnesses such as the flu.

You can help prevent infections by taking your HIV/AIDS medicines. Other things that can help include practicing safe sex, washing your hands well and often, and cooking your food thoroughly.

Your legs are made up of bones, blood vessels, muscles, and other connective tissue. They are important for motion and standing. Playing sports, running, falling, or having an accident can damage your legs. Common leg injuries include sprains and strains, joint dislocations, and fractures (broken bones).

These injuries can affect the entire leg, or just the foot, ankle, knee, or hip. Certain diseases also lead to leg problems. For example, knee osteoarthritis, common in older people, can cause pain and limited motion. Problems in your veins in your legs can lead to varicose veins or deep vein thrombosis.

Metabolism is the process your body uses to make energy from the food you eat. Food is made up of proteins, carbohydrates, and fats. Chemicals in your digestive system (enzymes) break the food parts down into sugars and acids, your body's fuel. Your body can use this fuel right away, or it can store the energy in your body tissues. If you have a metabolic disorder, something goes wrong with this process.

Lipid metabolism disorders, such as Gaucher disease and Tay-Sachs disease, involve lipids. Lipids are fats or fat-like substances. They include oils, fatty acids, waxes, and cholesterol. If you have one of these disorders, you may not have enough enzymes to break down lipids. Or the enzymes may not work properly and your body can't convert the fats into energy. They cause a harmful amount of lipids to build up in your body. Over time, that can damage your cells and tissues, especially in the brain, peripheral nervous system, liver, spleen, and bone marrow. Many of these disorders can be very serious, or sometimes even fatal.

These disorders are inherited. Newborn babies get screened for some of them, using blood tests. If there is a family history of one of these disorders, parents can get genetic testing to see whether they carry the gene. Other genetic tests can tell whether the fetus has the disorder or carries the gene for the disorder.

Enzyme replacement therapies can help with a few of these disorders. For others, there is no treatment. Medicines, blood transfusions, and other procedures may help with complications.