A reader has asked that I write about osteomyelitis. This is a condition where the bone and/or bone marrow become infected, usually with bacteria. These bacteria cause a pyogenic reaction - the body produces pus that contains infection-fighting white blood cells. The bacteria that cause the infection vary based on the age of the patient and the location of the infection.

Osteomyelitis is a fairly uncommon condition that is actually becoming less frequent, perhaps because of earlier diagnosis and more effective therapy. Despite being less frequent, when present, it can cause serious problems.

There are conditions that can predispose one to develop osteomyelitis. It is more common in people with open fractures, diabetics, those with sickle cell disease, IV drug abusers, alcoholics, chronic steroid users and those with suppressed immune systems. It can also occur in people with chronic joint problems and those who have artificial joint replacements.

Osteomyelitis can be a localized condition or can spread through the bone and marrow. It can be classified using many criteria including the offending organism, how the infection was introduced to the bone, and its anatomic location.

It is also classified as acute (early infection) or chronic if it has progressed and failed treatment. Acute osteomyelitis can be further divided into hematogenous or contiguous types based on how the infection was contracted.

Hematogenous osteomyelitis is caused by bacteria getting into the blood stream at a remote site and traveling to the bone. This usually occurs in children in the part of the bone called the metaphysis. The metaphyses are found at the end of bones where bone lengthening occurs. Blood flow in these areas is slow which allows the bacteria to get a foothold.

Adults who get hematogenous osteomyelitis usually have some type of immune system suppression. It is more common in those who use IV drugs, have HIV and can even occur as a result of infected teeth.

The other type of acute osteomyelitis is caused by contiguous infection. The infection is spread from the skin surface to the bone through trauma, surgery or even just having an open sore on the skin. Surgeries that involve repairing or replacing joints can be prone to this type of infection. This is why performing orthopedic surgery in a sterile environment and not cutting through infected skin is so important. Contiguous infection is more common in adults and adolescents.

Chronic osteomyelitis results when treatment of the acute infection fails or the infection is not recognized in time. The immune reaction of the body can actually cause plugging of blood vessels and reduced circulation in the area of infection. This results in areas of bone being isolated from nutrients causing a smoldering infection.

There are many symptoms of osteomyelitis, but the most common are fever and swelling, tenderness and redness over the bone. Patients may feel like they have the flu with malaise and bone aches. Children may refuse to move the area associated with the infected bone.

Diagnosing osteomyelitis can be difficult. The evaluation typically involves some blood work and removal of bone tissue via needle or surgery to look for signs of infection. Unfortunately, these cultures may not grow bacteria in the lab.

Radiology studies are also very important in diagnosis. Regular X-rays may not show an abnormality in the bone for a few weeks. A bone scan is more sensitive. This test involves injecting a nuclear tracer into the body that travels to areas of inflammation.

MRI scans are also very good at picking up early infection. Depending on the site of suspected infection, CT scanning may also be of value. Ultrasound imaging is sometimes used in children.

Antibiotics are used to treat osteomyelitis. The choice of antibiotics is an educated guess and is based on the location of the infection as well as the age of the patient and route of infection. More specific treatment is tailored when and if the offending bacteria are able to be identified in the microbiology lab.

Since the infection can be quite isolated and the blood supply to the area may be compromised, antibiotic treatment may need to be given for weeks to months. Infections that do not respond may require surgery to remove the dead and infected tissue. Prior to effective antibiotic therapy, sometimes blow fly larvae would be inoculated into the infected bone to eat the dead tissue.

Early management of those with bacteria in the blood is critical to prevention of hematogenous osteomyelitis. Good wound management and surgical techniques are important to prevent the contiguous type.

Dr. John Roberts is a local physician. His column appears in Monday's edition of the Times, and he has a daily health tip on the front page. Dr. Roberts is one of the owners of Sagamore News Media, parent company of The Times.