Osteomyelitis: Clinical sciences

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Introduction0:00–0:37

Osteomyelitis refers to an infection of the bone, which is typically caused by bacteria, such as Staphylococcus aureus. Osteomyelitis develops by one of three routes; direct inoculation of the bone, like from an open fracture; contiguous infection, like from an infected foot ulcer overlying the bone; or hematogenous spread, like from bacteremia due to endocarditis.
Moreover, acute osteomyelitis develops within days to weeks of infection, whereas chronic osteomyelitis is characterized by long standing infection over months or even years.
If your patient presents with chief concerns suggesting osteomyelitis, you should first perform an ABCDE assessment to determine if the patient is unstable or stable.

Unstable0:37–1:10

If unstable, stabilize the airway, breathing, and circulation, obtain IV access, and start IV fluids. Next, put your patient on continuous vital sign monitoring, including blood pressure, heart rate, and oxygen saturation.
Finally, if needed, provide supplemental oxygen, and don’t forget to start broad-spectrum antibiotics.Okay, now let’s go back to the ABCDE assessment and take a look at stable individuals.

Stable1:10–1:53

In this case, first, obtain a focused history and physical examination. Next, order labs, including CBC, CRP, and ESR.
Patients typically report fever, as well as pain, redness, and swelling at the site of the infection. Additionally, the physical exam usually reveals erythema, warmth, and purulent drainage, as well as tenderness to palpation over the affected bone area.
Finally, labs usually show leukocytosis and elevated CRP and ESR. With these findings, you should suspect osteomyelitis.Your next step is to order imaging, such as an X-ray or MRI.

Suspect osteomyelitis1:53–2:31

An MRI is the best imaging study to diagnose osteomyelitis, so make sure to order one if the X-ray results are normal but there's high clinical suspicion.
Additionally, a bone biopsy can help you reveal the histopathologic changes specific to osteomyelitis, and bone cultures, or deep tissue cultures, can reveal the causative pathogen.
Together, histopathological examination and microbiological examination of bone are the gold standard when it comes for diagnosing osteomyelitis!Alright, first let’s take a look at acute osteomyelitis!

Acute osteomyelitis2:31–3:13

In this case, your patient will usually report symptoms lasting for up to 6 weeks. The X-ray can be normal or may show overlying soft tissue swelling with cortical bone destruction and an underlying lucent bony lesion; MRI typically reveals bone marrow edema and overlying periosteal and subcutaneous edema.
Finally, the bone biopsy will reveal neutrophil-rich infiltrate and thrombosis of small blood vessels. With these findings, you can diagnose acute osteomyelitis!On the other hand, we may have chronic osteomyelitis.

Chronic osteomyelitis3:13–4:08

These patients will report symptoms lasting for a time period that’s longer than 6 weeks. In these individuals, the X-ray typically demonstrates a lucent lesion with a surrounding poorly defined sclerotic border and overlying periosteal thickening; MRI shows a bony abscess with a thickened enhancing rim, as well as surrounding bone marrow and soft tissue edema.
This type of abscess is also known as a Brodie abscess. Finally, the bone biopsy reveals lymphocyte- and plasma cell-rich inflammatory infiltrate, bone marrow fibrosis, along with bone necrosis and new bone formation.
With these findings, diagnose chronic osteomyelitis! Now, regardless of acute versus chronic, once you diagnose osteomyelitis, begin empiric antibiotics that cover the most likely pathogens, and that have good bone penetration.

Empiric management4:08–5:10

Since the most common causative pathogen of osteomyelitis is Staphylococcus aureus, initiate the treatment with antistaphylococcal penicillins or first-generation cephalosporins.
However, if you suspect methicillin-resistant Staphylococcus aureus, your choice should be vancomycin! Additional antibiotic coverage might be needed in patients with certain risk factors!
For example, if your patient has a history of hemoglobinopathies like Sickle Cell Disease, they’re at higher risk for osteomyelitis from Salmonella.
Those who have stepped on a nail may have contracted Pseudomonas, while individuals with prosthetic joints are at risk for infection with Staphylococcus epidermidis.
So make sure to add empiric antibiotic coverage for these organisms as well. Alright, once you initiate antibiotics, you need to assess the source of infection!

Source of infection5:10–7:48

The first and most obvious source is direct inoculation. This is common with open traumas like an open bone fracture, a bite or other puncture wound, and recent orthopedic surgery.If the patient has no source of direct inoculation, look for a source of contiguous infection.
This type of osteomyelitis is common in patients with skin infections, like diabetic foot ulcers, vascular ulcers in patients with peripheral artery disease, or pressure ulcers in individuals with limited mobility.
Additionally, keep in mind that infections of teeth, gums, sinuses, and ears can spread and cause an infection of the adjacent bony structures of the head and neck.
Here’s a clinical pearl to keep in mind! The probe-to-bone test is one way to assess a diabetic foot ulcer for contiguous osteomyelitis.
In this test, use a sterile, blunt metal instrument to probe the ulcer. If you reach the bone, which feels like a gritty, hard resistance to the probe, then the test is positive for osteomyelitis.
And another clinical pearl! Actinomyces israelii is an important bacterium to consider.
Make sure to cover for it when selecting antibiotics for osteomyelitis affecting bony structures of the head and neck. While this bacterium is in the normal flora of the nose and throat and doesn’t normally cause disease, it can become pathogenic and lead to contiguous spread of infection.Finally, if there’s no identifiable source of direct inoculation or contiguous infection, consider osteomyelitis from hematogenous spread.
This is common in individuals with underlying bacteremia, like from endocarditis or a central venous catheter infection.
Unlike other causes of osteomyelitis where blood cultures are often negative, in these patients, blood cultures typically identify the bacteria responsible for the infection.
Here’s a high-yield fact! Vertebral Osteomyelitis is a specific type of osteomyelitis caused by hematogenous spread, which affects the spine and is typically associated with Staphylococcus aureus infection.
Patients with vertebral osteomyelitis often report fever and focal back pain. However, be sure to rule out Pott disease, which occurs due to the hematogenous spread of tuberculosis infection from the lungs to the vertebrae!Now, once you identify the source of infection and you get your biopsy results back, it’s time to tailor your management.

Management7:48–8:14

First, tailor antibiotics based on culture results. Additionally, you can consult the surgical team for debridement of necrotic tissue; removal of infected orthopedic hardware, if present; and, in severe cases, amputation of an affected limb.Alright, as a quick recap… Osteomyelitis is considered acute if it presents within days to weeks or less of a bony infection; whereas chronic osteomyelitis is characterized by long-standing infection, for months or years.

Review8:14–9:05

Once you diagnose osteomyelitis with an X-ray, MRI, or bone cultures, begin empiric antibiotics and assess for the source of infection.
Direct inoculation is associated with open traumas; contiguous spread is seen in ulcers; while hematogenous spread occurs due to bacteremia.
Once the infection source is identified and culture results are available, tailor antibiotics and consult your surgery team for possible debridement of necrotic tissue; removal of infected orthopedic hardware; or even amputation of an affected limb.
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