Osteomyelitis
What is Osteomyelitis?
Osteomyelitis is an infection in a bone. This infection can be caused by either bacteria or fungi. However, the most common cause is the staphylococcus group of bacteria. These bacteria are generally part of the normal flora living on the skin of healthy human beings. When they penetrate the body’s physical barrier (skin), the bacteria can cause a local infection that may spread to the bone. In other instances, bacteria will enter the bloodstream and travel to bones that may lead to a blood-borne (hematogenous) bone infection. Osteomyelitis therefore often begins as a blood or soft tissue infection that reaches a bone.
Risk Factors for Osteomyelitis
A deep local infection such as that from a penetrating or surgical wound is a risk factor for the development of an infection involving the bone (osteomyelitis). Individuals with a decreased immune response or a decreased capacity to fight off infection are at higher risk of having a soft-tissue infection invade the bone to form an osteomyelitis. Conditions that increase the risk of an osteomyelitis include:
- Advanced age
- Diabetes
- Sickle Cell
- Immunocompromised state
- HIV
- Organ Transplant
Clinical Presentation
Patients may present with symptoms of an infection such as a fever, although many bone infections are chronic symptoms limited to a draining wound. Patients may also have pain and swelling of the soft-tissue around the infected bone as the area becomes inflamed. Depending on the location of the bone infection, this can either present as leg, foot, or back pain. Patient history may reveal a recent infection or injury, such as a cut, surgical incision, or ulceration in the skin.
Physical Examination
The physical examination of patients with osteomyelitis can vary from minimal symptoms to marked pain, swelling, and discharge. Patients with acute osteomyelitis will often present with pain and swelling of the affected bone. Patients commonly have an open wound where the bacteria are able to penetrate the skin and reach the bone – or where drainage from an infected bone be discharged. In some patients, there may be pus drainage at the site of the infection. Patients may have difficulty bearing weight or utilizing the affected bone due to pain. In severe cases, there may be gangrene (dead tissue) at the site of infection.
Diagnosis
Osteomyelitis can be diagnosed using a variety of methods.
Imaging
X-ray imaging may be normal during the very early stages of infection. However, as the infection progresses, there will be a localized decrease in bone density. An MRI may be helpful to determine the extent of infection and may reveal a buildup of infected fluid (abscess) in bone and surrounding regions.
Blood Samples
A complete blood count will often reveal an increased White Blood Cell (WBC) count. WBCs are a part of the body’s immune response, so the increased WBC count is indicative of an infection. A blood test known as a blood culture may also identify bacteria in the bloodstream. However, a normal WBC count or a negative blood culture does not rule out an osteomyelitis. A positive blood or bone culture can be used to determine the type of bacteria responsible for the osteomyelitis, and guide the antibiotic treatment.
Bone Biopsy
In some instances, a sample of the optionally infected bone will need to be taken at surgery to confirm the presence of a bone infection – and identify the organism involved.
Treatment
Treatment of an osteomyelitis depends on the extent of the bone infection. Antibiotics are the first line of treatment. These may be administered orally or through an IV over the course of weeks. In cases of osteomyelitis where the blood (carrying the antibiotics) can reach the entire area of infected bone, a course of antibiotics may be all that is needed to eradicate the bone infection. However, one of the challenges of treating osteomyelitis is that the bacteria often wall off an area within the infected bone thereby preventing any bone and antibiotics from reaching the infected bone. In this situation, surgery to debride (clean out) or remove the infected area of bone will be necessary. In some patients with significant foot infections, the only way to truly eradicate the infection may be to perform an amputation.
Edited May 1, 2021