Osteomyelitis is inflammation of the bone caused by an infection, usually from bacteria but sometimes from fungi. Left untreated, it may progress to a severe infection and gangrene that may require surgical removal of bone or amputation of a limb.

The infection that leads to osteomyelitis usually can be traced to one of two sources:

• The bloodstream. An infection from somewhere in the body travels through the bloodstream to bone in another area.

• Direct injury. An injury such as a puncture wound, an animal bite or an open fracture from a car accident directly infects nearby bone.

When a bone is initially infected, the condition is known as acute osteomyelitis. An infected bone is likely to be filled with pus that collects in an abscess. This abscess prevents the blood from reaching the bone. If acute osteomyelitis is left untreated and continues over a long period of time, it can progress to chronic osteomyelitis, which may result in the death of the bone tissue (osteonecrosis). Once the tissue in the bone is dead, cells sent by the immune system cannot reach the infection to combat it.

Chronic osteomyelitis can impair the patient’s ability to use a limb or joint, and can spread to other parts of the body. Eventually, an infected bone may force amputation of a limb. Chronic osteomyelitis of the spine is particularly dangerous and has the potential to damage the nerves. In rare cases, osteomyelitis can even be fatal.

The bones most often infected in osteomyelitis differ depending on a person’s age. In children, long bones are most often affected. These bones, such as the femur (thigh bone), are longer than they are wide. Adults are most likely to experience osteomyelitis in the vertebrae (spinal bones) and the pelvis. They are also at increased risk of malignant external otitis, a severe ear infection that can spread to the skull and jawbone.