Osteomyelitis is a severe infection causing inflammation within the bone and its internal marrow cavity. This condition occurs when microorganisms, most commonly bacteria, invade the bone, leading to a destructive inflammatory response. Because bone tissue has limited ability to expand, the swelling can compress blood vessels, restricting blood flow and causing localized tissue death. Early recognition is important because untreated osteomyelitis can lead to permanent damage and long-term complications.
Defining the Condition and Its Forms
Osteomyelitis is defined by the presence of infection and inflammation, typically caused by bacteria like Staphylococcus aureus. The inflammatory reaction impairs blood supply, which can lead to the formation of a piece of dead, infected bone called a sequestrum. This dead tissue acts as a reservoir for infection, making the condition difficult to cure with antibiotics alone.
The condition is broadly categorized into two main types based on duration. Acute osteomyelitis has a rapid onset, typically developing over days to a week, and is characterized by severe symptoms. This form is generally easier to treat successfully with prompt medical intervention.
Chronic osteomyelitis is a persistent infection that can linger for months or years, often resulting from an inadequately treated acute infection. It is characterized by persistent bone destruction and the presence of the sequestrum, which requires surgical removal. This form may present with less intense systemic symptoms but causes persistent pain and recurrent episodes of drainage.
Common Causes and Risk Factors
Infection can reach the bone through three primary pathways. Hematogenous spread occurs when pathogens travel through the bloodstream from a distant source of infection, such as a urinary tract infection or pneumonia. This route is the most common in children, often affecting long bones, while in adults it frequently targets the vertebrae.
Contiguous spread occurs when infection enters the bone directly from nearby soft tissue, often seen in diabetic foot ulcers or near prosthetic joints following surgery. Direct inoculation happens when bacteria are introduced straight into the bone through trauma, such as an open fracture, or during a surgical procedure.
Certain underlying health conditions increase the risk of bone infection. Diabetes is a major factor, especially when associated with poor blood sugar control and peripheral vascular disease, which impairs blood flow. Individuals with weakened immune systems (e.g., due to HIV or immunosuppressant medications) are also at higher risk. Intravenous drug use and conditions affecting blood cells, such as sickle cell disease, predispose individuals to this infection.
Recognizing the Signs
In acute cases, patients typically experience localized symptoms over the affected bone. These signs include severe, deep pain, which may worsen with movement or pressure, accompanied by swelling, warmth, and redness of the overlying skin.
Systemic symptoms often accompany localized signs, signaling a widespread infection. These can include an abrupt onset of fever, chills, and a general feeling of being unwell. Young children may exhibit irritability, lethargy, or a reluctance to use the affected limb.
In chronic osteomyelitis, systemic signs like fever may be less pronounced or absent, making identification difficult. The hallmark of the chronic form is often persistent or recurring bone pain and the presence of a draining sinus. This sinus is an abnormal tunnel that forms from the infected bone to the skin’s surface, releasing pus or fluid.
Diagnosis and Treatment Approaches
Diagnosing osteomyelitis requires laboratory tests and advanced imaging studies. Blood tests are often performed first to look for elevated inflammatory markers, such as C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR, though these do not confirm the presence of bone infection alone. Imaging is crucial, starting with plain X-rays, which may not show bone damage until the infection has been present for several weeks. Magnetic Resonance Imaging (MRI) is the most effective tool for identifying early signs of infection and soft tissue involvement.
The definitive step for diagnosis and pathogen identification is a bone biopsy, where a tissue sample is taken directly from the infected site for culture. Culturing the organism from the bone is necessary because surface cultures from draining wounds can be misleading. Identifying the specific bacteria allows providers to tailor the antibiotic treatment.
Treatment is aggressive and requires a multidisciplinary team of specialists. The primary treatment is a prolonged course of high-dose antibiotics, often administered intravenously (IV) for several weeks, commonly lasting four to six weeks. The specific antibiotic is chosen based on the results of the bone culture and sensitivity testing.
Surgical debridement is often necessary, involving the physical removal of all infected and dead bone tissue (sequestrum). Surgery eliminates the source of infection that antibiotics cannot penetrate due to poor blood supply. For extensive infections, procedures to restore blood flow or, in rare cases, amputation may be considered to prevent the spread of the infection.