Osteomyelitis

What is Osteomyelitis?

Osteomyelitis is a term that doctors use to describe bone infections. It’s either a short-term or long-term swelling of the bone and its parts caused by harmful organisms, such as bacteria, fungi, and types of bacteria called mycobacteria. It’s interesting to note that this condition is not new. Studies of animal fossils have shown evidence of bone infection, indicating that osteomyelitis has a long history.

The term ‘osteomyelitis’ has been in use since 1844, thanks to a doctor named Nelaton. But before antibiotics like penicillin were introduced in the 1940s, treatment for this condition mainly involved surgery. Doctors would remove infected tissue (a process known as debridement), carve out a saucer-shaped area in bone (saucerization), and pack the wound. After surgery, the infected region would be left to heal on its own, which is referred to as healing by ‘secondary intention’. This method, however, led to a high death rate due to serious body-wide infections, also known as sepsis.

Thankfully, since the arrival of antibiotics, the number of people dying from osteomyelitis, including a type caused by a bacterium called staphylococcus, has decreased remarkably.

What Causes Osteomyelitis?

Healthy bones are usually very good at resisting infections. However, certain conditions can make the bones more vulnerable to disease. This can happen when a large amount of bacteria is introduced, or if there’s been damage to the bone (such as from an injury or poor blood supply), or when foreign objects enter the body. In these cases, the areas of the bone where bacteria can attach become exposed.

Certain bacteria, such as Staphylococcus aureus (often called “staph”), can stick to the bone by using special receptors known as adhesins. These adhesins allow the bacteria to connect to components of the bone, like laminin, collagen, fibronectin, and bone sialoglycoprotein. For example, staph bacterium can attach to bone cartilage using collagen-binding adhesin. It’s also been found that this bacterium can attach to medical devices that have been placed inside the bone using fibronectin-binding adhesin.

An interesting fact is that staph bacteria can survive inside cells of the bone (known as osteoblasts) once they have entered them. Some bacteria also have the ability to form a protective layer known as a biofilm around themselves and the surfaces they’re attached to. This ability of some bacteria to stick to the bone and medical devices, resist antibiotics due to their protective biofilm, and survive inside the cells might explain why bone infections can persist and why shorter courses of antibiotic treatment often fail.

Risk Factors and Frequency for Osteomyelitis

Osteomyelitis, a type of bone infection, is somewhat common but its exact frequency in the United States is not well known. However, it’s estimated that it accounts for 1 in 675 hospital admissions each year, which is about 50,000 cases. Some studies suggest the rate of osteomyelitis is 21.8 cases for every 100,000 people each year. The condition seems to be more common in men, although the reason for this is unclear. Its incidence also increases with age because older people often have other health conditions like diabetes or peripheral vascular disease that could contribute. Thankfully, advancements in medical imaging technologies like MRI and bone scans have greatly improved our ability to accurately diagnose and understand the specifics of the infection.

Signs and Symptoms of Osteomyelitis

Osteomyelitis is a condition that affects the bone and can vary in how it presents itself. For adults, it can sometimes be hard to diagnose and needs careful consideration. A detailed patient history and thorough physical examination serve as an essential starting point. Certain patients are more likely to get osteomyelitis, including those with blood infections, heart valve infection, users of intravenous drugs, those with a history of injury, and open fractures. The risk also increases in patients with persistent sores that don’t heal, especially in those with diabetes, poor blood circulation, nerve damage, or orthopedic devices.

Acute osteomyelitis frequently develops within two weeks, though its symptoms may start to show gradually over a few days. Local symptoms include redness, swelling, warmth, and a dull pain with or without movement at the infection site. Patients may also experience fever, chills or generally feel unwell. In some cases, it may cause a painful infection in a joint, particularly if the growth area of a bone is within the infected joint. Sharp pains in the neck or back paired with a fever, raised inflammation markers, blood infection or heart valve infection should raise concern for a specific type of osteomyelitis affecting the spinal vertebrae.

In contrast, chronic osteomyelitis symptoms typically occur over a much longer period, usually more than two weeks. These patients may also experience swelling, pain, and redness at the infection site, but they rarely have a fever. Deep or extensive sores that won’t heal after several weeks of treatment in diabetes patients or those in weak health are concerning signs. Doctors will typically focus on finding the source of the infection, checking sensory function, and examining the blood vessels in the extremities. For patients with osteomyelitis affecting the vertebrae, they may experience tenderness when the area is touched. The ‘probe-to-bone’ test is often performed, where a blunt sterile instrument is inserted into an ulcer to touch the bone, indicating that osteomyelitis is likely. This test is used in conjunction with the patient’s initial likelihood of having osteomyelitis to decide if additional tests like imaging or biopsy are needed to make a treatment decision.

Testing for Osteomyelitis

When your doctor suspects you might have osteomyelitis, which is an infection in the bone, they might order lab tests and use imaging to see what’s happening inside your body. Lab tests can include looking for a higher-than-normal number of white blood cells, as well as checking levels of ESR and C-reactive protein. The reason they check C-reactive protein levels is because they tend to change based on how you’re responding to treatment. If the osteomyelitis has come through the bloodstream and is affecting certain areas like the vertebrae, clavicle, or pubis, blood cultures might come back positive.

The x-ray, or plain radiograph, is usually the first imaging tool, but can take around two weeks to show signs of osteomyelitis. Even then, x-rays are mainly used to rule out other possible causes of pain like cancer spreading to the bone or bones breaking due to osteoporosis. X-rays aren’t great for early detection of this infection because roughly 50-75% of the bone’s structure has to be lost before it shows up on the scan.

So, where x-rays have their limitations, magnetic resonance imaging (MRI) is on the other end of the spectrum. This tool has a high sensitivity and specificity – technical terms for accuracy and precision in medical testing – for finding osteomyelitis. In fact, MRI can see the infection just 3 to 5 days after it starts. Unfortunately though, the presence of surgical hardware can limit its use. However, if you’ve had symptoms for at least a week and your MRI comes back negative, it can practically rule out the disease. Special nuclear imaging is useful when metal hardware in the body prevents the use of MRI.

Other less common imaging methods include positron emission tomography (PET), which is expensive and not routinely available, leukocyte scintigraphy, gallium scan, and computed tomography (CT scan). A CT scan provides a better look at the bone and surrounding structures than an x-ray, but isn’t as good as an MRI for seeing the infection early. It’s also more expensive than an x-ray, but is a great option when an MRI can’t be used. CT scans are typically used to see how much of the bone has been destroyed, to guide biopsies, and in patients who can’t get an MRI.

On the other hand, a bone biopsy can confirm the diagnosis of osteomyelitis, pinpoint the bacteria causing it, and steer the direction of antibiotic treatment. There are two ways to get a bone biopsy – an open method and a percutaneous method. An open biopsy is more preferred, but it doesn’t always need to be done, especially if blood cultures are positive and images show evidence of osteomyelitis. If you’ve been given antibiotics before the biopsy, your doctor might pause treatment for 48 to 72 hours to make it easier to find the bacteria. But, this isn’t always necessary because these infections usually happen in areas where the bone’s cells have died or been damaged.

In the percutaneous method, your doctor uses a needle to extract a sample of the infected bone tissue. It’s preferred that his procedure be done before antibiotics are started, to increase the likelihood of finding the bacteria. Ideally, your doctor will collect two samples, one for examining the tissue under a microscope and the other to see what kind of bacteria grows in the lab.

Treatment Options for Osteomyelitis

Osteomyelitis is an infection in your bone and it can be caused by several different types of bacteria. Most commonly, a bacterium called Staphylococcus aureus is the culprit. Also, a resistant version of this bacteria, known as MRSA, is being increasingly associated with this condition. Other common bacteria include coagulase-negative staphylococcus, beta-hemolytic streptococcus, and various types of aerobic and anaerobic gram-negative bacilli.

There are also less common causes of osteomyelitis that become more likely under certain conditions or in certain individuals. For example, a bacterium called Mycobacterium tuberculosis, which is known to cause tuberculosis in the lungs, can also spread to your spine, causing osteomyelitis there. Among other less common culprits are different types of fungi and mycobacteria, which are more typical in immunocompromised patients. Salmonella and S. aureus bacteria are implicated in causing osteomyelitis among people with sickle cell disease.

Treating osteomyelitis usually involves a team of different medical professionals. The main strategies are to control the infection through surgery and to use antibiotics for an extended length of time. In some cases, the infected bone may need to be removed because antibiotics struggle to penetrate the infected tissue. Additionally, removal of any implants present, such as artificial joints, might also be necessary, if they are infected. On the other hand, sometimes, the infected implant may still remain in place if it’s stable and the infecting bacteria are very susceptible to antibiotics. Where surgery is not feasible due to the location of the infection, antibiotics alone might be used over several months.

Certain patients may need extra care before a surgical intervention can take place, such as those with significant peripheral vascular disease who may require revascularization of the affected limb. Other considerations include controlling diabetes and other factors that may hinder healing, like tobacco use, malnutrition, chronic hypoxia, immune deficiencies, chronic lymphedema, and peripheral neuropathy.

Antibiotic therapy for osteomyelitis should ideally be guided by tests showing which type of bacteria is causing the infection. In the absence of these test results, doctors typically start off the treatment with a broad-spectrum antibiotic that can work against many types of bacteria. Once the specific bacteria and their susceptibility to antibiotics are identified, the treatment is adjusted to target the bacteria effectively.

Typically, osteomyelitis is treated with four to six weeks of antibiotic therapy, depending on the severity of the infection. If the infected bone has been surgically removed and clean margins ensure that no infection is left, the duration of the antibiotic therapy can be shortened to two weeks.

In some cases, vacuum-assisted wound closure devices may be used, especially in cases where large or deep wounds remain after removing the infected tissue. These devices help promote wound healing. Hyperbaric oxygen therapy, although not routinely used, can be an option for treating osteomyelitis in certain cases.

What else can Osteomyelitis be?

When a doctor suspects that a patient may have a bone infection, known as osteomyelitis, they also need to consider various other potential diagnoses. These conditions can often present with similar symptoms, and might include:

• Charcot arthropathy, a condition more common in people with diabetes
• SAPHO syndrome, which stands for Synovitis, Acne, Pustulosis, Hyperostosis, and Osteitis
• Different types of arthritis, including rheumatoid arthritis
• Metastatic bone disease, a condition where cancer has spread to the bones
• Bone fractures, including those caused by disease (pathological) or stress
• Gout, which is a type of arthritis caused by excess uric acid
• Avascular necrosis of the bone, a condition that happens when blood flow to a bone is interrupted or reduced
• Bursitis, which is inflammation of the fluid-filled sacs that cushion your joints
• Sickle cell vaso-occlusive pain crises, which are painful episodes occurring in people with sickle cell anemia

What to expect with Osteomyelitis

Aggressive early treatment tends to lead to a good outcome for people with acute osteomyelitis, a severe kind of bone infection. However, it’s worth noting that the infection might come back years after successful treatment. This can happen if the same area is injured again, or if the person’s immune system is weakened.

In adults, chronic osteomyelitis, which is a long-lasting bone infection, can reappear in around 30% of cases after a year. However, when the infection is caused by a bacteria called P. aeruginosa, the chance of it returning can be as high as 50%.

When osteomyelitis affects an area with an artificial joint or prosthetic, treatment can be more challenging. This often means more surgeries and a longer course of antibiotics, which can lead to greater discomfort and health issues.

Many steps are taken to prevent infections after surgery. This includes good preparation before the operation, using operating rooms with specialized airflow systems, and giving patients antibiotics before the surgery starts. These are usually first-generation (like cefazolin) or second-generation (like cefuroxime) cephalosporins, a type of antibiotics. It’s recommended to administer these antibiotics intravenously (through a vein) half an hour before the surgery starts. These measures have been shown to reduce the chance of getting an infection after surgery from 0.5% to 2%, which in turn improves the patient’s outcome.

Possible Complications When Diagnosed with Osteomyelitis

Early treatment of osteomyelitis, which includes taking antibiotics, is crucial to prevent complications. These are a variety of issues that can occur if osteomyelitis isn’t properly treated:

• Septic arthritis, which is a serious infection in a joint.
• Pathological fractures, which are broken bones caused by a disease.
• Squamous cell carcinoma, a type of skin cancer.
• Sinus tract formation, a channel that forms under the skin due to infection or disease.
• Amyloidosis, a rare disease that causes protein to build up in your organs.
• Abscess, a swollen area of tissue filled with pus.
• Bone deformity, changes to the shape or size of a bone.
• Systemic infection, an infection that affects the whole body.
• Contiguous soft tissue infection, an infection in the tissues adjacent to the affected bone.

Preventing Osteomyelitis

It’s crucial for patients to understand that their treatment might take a long time. Following the doctor’s guidance closely is really important to make sure wounds heal properly and to lower the chances of the same problem happening again. This understanding plays an important part in the care every patient receives.