Osteomyelitis is an infection that causes inflammation within the bone and bone marrow, typically caused by bacteria. Because bone is rigid, inflammation can lead to tissue death and chronic infection if not addressed quickly. Diagnosis involves a combination of clinical assessment, laboratory tests, and advanced imaging to confirm the presence and extent of the disease. No single test can definitively diagnose a bone infection in all patients.
Clinical Evaluation and Initial Suspicion
Diagnosis begins with a thorough clinical evaluation of the patient’s history and current symptoms. Providers look for specific risk factors, such as recent surgery, trauma, existing infections elsewhere in the body, or a compromised immune system. This background helps establish the initial suspicion for a bone infection.
During the physical examination, the doctor looks for localized symptoms over the suspected infection site. These signs often include persistent and severe pain, swelling, warmth, and redness of the overlying skin. A fever and a limited range of motion in the affected limb are also common findings, especially in cases of acute osteomyelitis.
In children, symptoms can be less specific, sometimes presenting only as an unexplained limp or a reluctance to use the affected limb. Chronic bone infections or those in patients with diabetes may present with vague symptoms or a draining wound, making the initial evaluation challenging. Recognizing these signs is necessary before proceeding to further testing.
Screening with Laboratory Markers
Once a bone infection is suspected, blood tests are used to identify systemic inflammation and infection. These markers do not specifically diagnose osteomyelitis but provide strong supportive evidence and help track the body’s response to the infection.
The Erythrocyte Sedimentation Rate (ESR) and C-Reactive Protein (CRP) are the two most commonly monitored inflammatory markers. CRP measures a protein produced by the liver that increases rapidly in response to inflammation and infection. ESR measures how quickly red blood cells settle, with a faster rate indicating the presence of inflammatory proteins.
Both ESR and CRP are typically elevated in acute osteomyelitis, though they lack specificity, meaning other inflammatory conditions can also cause high results. The White Blood Cell (WBC) count is also monitored, as an elevated number of white cells indicates the body is actively fighting an infection. Consistently high levels of CRP and ESR are often used to monitor the effectiveness of treatment over time.
Visualizing the Infection Through Imaging
Imaging studies are important for localizing the infection, assessing the extent of bone damage, and guiding the diagnostic process. Plain film X-rays are often the initial step due to their accessibility and low cost. However, X-rays may not show visible changes, such as bone destruction, until the infection has been present for 10 to 14 days in adults.
Magnetic Resonance Imaging (MRI) is considered the most sensitive imaging modality for diagnosing osteomyelitis, particularly in its early stages. MRI can detect changes in the bone marrow, such as edema, which can appear within days of the onset of infection. It also provides detailed images of the soft tissues, helping to identify abscesses or the spread of infection beyond the bone itself.
When an MRI is contraindicated, or if the infection site is unclear, other imaging techniques are used.
Computed Tomography (CT) Scans
Computed Tomography (CT) scans offer excellent detail of the bone structure. This is useful for identifying fragments of dead bone, known as sequestra, or for surgical planning.
Nuclear Medicine Scans
Nuclear medicine scans, such as bone scans or white blood cell scans, involve injecting a radioactive tracer. The tracer accumulates in areas of increased bone metabolism or infection. This method can effectively pinpoint the precise location of inflammation when the source of infection is vague.
Confirming the Diagnosis with Biopsy
While clinical findings, blood tests, and imaging studies can strongly suggest osteomyelitis, the definitive diagnosis requires obtaining a sample of the infected bone or tissue. This procedure is called a bone biopsy. The biopsy is often performed using a needle guided by imaging, or sometimes through an open surgical procedure.
The biopsy serves a dual purpose: providing a histopathological sample and a culture. The pathology examination confirms the presence of bone destruction and inflammatory cells characteristic of osteomyelitis. The tissue culture identifies the specific microorganism, usually a bacterium, that is causing the infection.
Identifying the causative germ guides the treatment plan, as it allows doctors to select the most effective, targeted antibiotics. Surface cultures from a draining wound are often unreliable and may miss the true pathogen within the bone. Obtaining the biopsy sample before starting antibiotics is preferred, as prior treatment can interfere with the culture results.