What is osteomyelitis?
It is an infection of the bone and bone marrow. The word osteomyelitis is a combination of the Greek words osteon (bone), and myelos (marrow), plus the suffix itis (inflammation).
What causes osteomyelitis?
Osteomyelitis is an infection of the bones. The original site of infection is often elsewhere in the body, and the infection then spreads to the bone via blood. This is known as haematogenous osteomyelitis and is the most common form of osteomyelitis. A recent minor trauma that results in a blood clot could cause the bone to be susceptible to infection. Most cases are due to bacteria - approximately 60% of all cases are caused by Staphylococcus aureus. Other bacteria that may play a role include E. Coli (intravenous drug abusers), Salmonella (important in sickle cell disease), Strep. Pneumoniae, H. influenzae and Brucella. Fungi can also be responsible for the infection and Tuberculosis bacilli are an important cause of osteomyelitis in some areas. Pus can be produced within the bone and this can result in a bone abscess, which then deprives the bone of its blood supply. In adults, haematogenous osteomyelitis is very rare and osteomyelitis usually follows and open injury where bone was contaminated. In children, the long bones are usually affected.
Who gets osteomyelitis and who is at risk?
Diabetics and those who have had a recent trauma near or to a bone are more susceptible to osteomyelitis. Certain conditions also increase the risk of developing this kind of infection. These include the abuse of intravenous drugs such as heroin, surgery, sickle cell anaemia, injury, the presence of a foreign body (such as a bullet or a screw placed to hold together a broken bone), kidney dialysis, and untreated infections of tissue near a bone. For example, extreme cases of untreated sinus or dental infections can lead to osteomyelitis of the bones of the skull.
Symptoms and signs of osteomyelitis
Symptoms include pain or tenderness in the bone accompanied by pain on motion, swelling and warmth in the overlying area, fever, nausea and generally feeling unwell.
Acute osteomyelitis is an infection that develops and peaks over a fairly short time. Patients who develop osteomyelitis when it spreads from a nearby area of soft tissue infection might simply note that the original wound or infection heals poorly. In children, acute osteomyelitis usually occurs as pain in the affected bone, or they might notice that pressure over the infected area causes tenderness. They will also have fever and chills and won't use the limb.
Adult patients with osteomyelitis of the spine usually have dull, aching pain in the back for a long time, but no fever. Some patients experience pain in the chest, abdomen, arm or leg. This occurs when inflammation in the spine causes pressure on a nerve root leading to one of these other areas. The lower back is the most common area for osteomyelitis. When it is caused by tuberculosis (TB), osteomyelitis usually affects the thoracic spine. This is the part of the spine that runs from about the base of the neck down to where the ribs stop.
There are two main ways that infecting bacteria find their way to bone: via the bloodstream (haematogenous osteomyelitis), and spreading from nearby infected soft tissue.
Most infections that are spread via the bloodstream are due to the bacteria Staphylococcus aureus, which travel through the bloodstream to reach the bone. Due to the pattern of blood circulation in adults, the long bones in the arms and legs are less well served by the circulatory system than in children. These bones are therefore unlikely to develop haematogenous osteomyelitis in adults. Instead, the bones of the spine (vertebrae) receive a higher blood flow, so osteomyelitis in adults is most likely to affect the spine. Drug addicts may have osteomyelitis in the pubic bone or clavicle (collarbone).
In children, the most likely site of infection is within one of the long bones, particularly one of the bones of the lower leg (tibia), or the bone of the upper arm (humerus), or the thigh bone (femur). This is because in children these bones have extensive blood circulation, making them more vulnerable to invasion by bacteria.
When bacteria spread from nearby infected soft tissue, Staphylococcus aureus is responsible for about half of all cases. This often occurs when recent surgery or injury results in a soft-tissue infection. The bacteria can then spread to nearby bone, causing osteomyelitis. Patients with diabetes are particularly at risk of getting osteomyelitis from this source, because the disease interferes with nerve sensation and good blood circulation. This makes diabetics prone to foot wounds that do not heal well, and infection can then spread to bone.
Although osteomyelitis often presents as an acute illness, it may also present as a mild disease and the inability to move the affected limb. This is called “pseudo-paralysis” and is more often seen in children.
When osteomyelitis is not properly treated, a chronic (long-term) type of infection may occur. In this case, the infection may come and go for a long time, despite treatment during its active phases. An abnormal opening in the skin overlaying the area of bone infection, called a sinus tract, might sometimes drain pus. This type of infection may also result in areas of dead bone, called sequestra. These areas occur when the infection prevents the blood supply from reaching parts of the bone, causing the bone tissue to die. Such sequestra do not have the cells called osteocytes that normally help the bone to grow or remain strong.
How is osteomyelitis diagnosed?
Diagnosis of osteomyelitis involves several procedures.
The history of a hot painful area overlying a bone suggests the diagnosis. This is then confirmed by clinical examination and tests. A full blood count that shows high levels of white blood cells (responsible for fighting infection) indicates that an infection is present. Blood is also cultured in a laboratory - a process that allows any bacteria present to multiply. A specimen from the culture is then specially treated and examined under a microscope to identify the bacteria causing the infection. Tests are also done to determine to which medicines the organisms are sensitive.
In addition to the above tests, a scan called magnetic resonance imaging, or MRI, can be done. Particular radioactive elements can also be injected into the bloodstream, followed by a series of x-rays, called radionuclide scanning. This will reveal areas of bone inflammation with a 90% sensitivity.
If there are pockets of pus in the bone, or a soft tissue infection, they can act as sources for samples that can be cultured to allow medical staff to see what bacteria are present. A long, sharp needle can be used to obtain a specimen of bone (biopsy), which staff can then test for bacteria.
Can osteomyelitis be prevented?
All infections should be treated quickly and thoroughly. All wounds near to, or associated with, fractures should be scrubbed thoroughly in a theatre. No deep wounds should be treated at home, but should rather be seen to by a doctor – even more so if you fall in the “high-risk” category.
How is osteomyelitis treated?
Antibiotics are medications used to kill bacteria. They are usually administered through a needle in a vein (intravenous drip) for at least part of the time and then followed by oral antibiotics. Bed rest is usually recommended for part or all of that time. Occasionally, a patient will have such extensive osteomyelitis that he or she will need surgery to drain any pockets of pus, and to clean the infected area. Antibiotic beads that slowly release antibiotics in the area of the infection can also be inserted during the operation.
The progression of osteomyelitis depends on how quickly an infection is identified, and whether you have other underlying conditions that complicate the infection. If you receive treatment in time, there is very little chance of developing chronic, or long-term, osteomyelitis. Those who have chronic osteomyelitis may require antibiotics regularly for the rest of their lives.
What is the outcome of osteomyelitis?
If sterility of the lesion is achieved within two to four days, a good result can be expected in most cases if there is no compromise of the patient’s immune system. The disease may spread to adjacent bones and joints as a complication. Recurrence of bone infections often results in anaemia, weight loss and weakness. Rarely it may cause kidney problems and even lead to cancer.
Progression of the disease to the chronic form may also occur. It is especially common in the lower extremities and in people in whom the circulation is impaired. These people often require extensive surgery, excision of bone and tissue, and sometimes amputation.
Reviewed by Dr Sirk Loots, orthopaedic surgeon.