Emphysematous osteomyelitis

1. Cause / Etiology

·         EO is a rare, severe form of osteomyelitis characterized by the presence of gas within bone (intraosseous gas), produced by gas-forming microorganisms.

·         Common causative organisms:

o    Anaerobes: Clostridium spp., Bacteroides spp.

o    Facultative anaerobes: Escherichia coli, Klebsiella pneumoniae, Enterobacter spp.

o    Fusobacterium, Peptostreptococcus, and others

·         Risk factors:

o    Diabetes mellitus (most common)

o    Peripheral vascular disease

o    Immunosuppression (e.g., malignancy, chemotherapy)

o    Alcoholism, trauma, surgery

o    Hematogenous spread or contiguous infection from nearby soft tissue

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2. Pathophysiology

·         Infection by gas-forming bacteria leads to:

o    Rapid tissue necrosis

o    Anaerobic fermentation → gas production (H₂, CO₂, N₂)

o    Accumulation of gas within the medullary cavity and cortex of bone

·         The gas can dissect through the Haversian systems and spread subperiosteally and into adjacent soft tissues.

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3. Epidemiology

·         Extremely rare, with fewer than 100 cases reported in the literature.

·         Most commonly affects:

o    Pelvis and femur

o    Also reported in the spine (vertebrae), tibia, and humerus

·         Diabetic patients represent the majority of reported cases.

·         Mortality can be high (~30%), especially with delayed diagnosis or poor host immune status.

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4. Clinical Presentation

·         Similar to typical osteomyelitis but often more severe:

o    Fever, chills, localized pain

o    Erythema, warmth, swelling over the affected bone

o    Draining sinus or abscess (in advanced cases)

o    Signs of sepsis or septic shock in some patients

May present subtly in immunocompromised patients

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5. Imaging Features

🩻 X-ray:

·         May show:

o    Patchy lytic bone destruction

o    Intraosseous gas (appears as radiolucent bubbles within bone)

o    Soft tissue gas or swelling

💻 CT scan:

·         Gold standard for detecting intraosseous gas

·         High sensitivity for:

o    Bone destruction

o    Air pockets in marrow and cortex

o    Associated soft tissue emphysema or abscess

🧲 MRI:

·         Useful for soft tissue assessment

·         Shows bone marrow edema, cortical destruction

·         Gas seen as signal voids on all sequences

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6. Treatment

·         EO is a surgical emergency in many cases.

·         Treatment consists of:

o    Broad-spectrum intravenous antibiotics, tailored once cultures are available (covering anaerobes and Gram-negatives)

§  Example: Piperacillin-tazobactam + metronidazole, or carbapenems

o    Surgical debridement or resection (especially if abscess or necrotic tissue is present)

o    Glycemic control in diabetic patients

o    Consideration for amputation in extensive disease or nonviable limb

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7. Prognosis

·         Prognosis depends on:

o    Timeliness of diagnosis

o    Host immune status

o    Presence of systemic sepsis

o    Degree of bone and soft tissue involvement

·         Mortality rate: ~30% in reported cases

·         High risk of long-term disability, especially with delayed treatment

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🔑 Summary Points

·         Emphysematous osteomyelitis is a rare but life-threatening infection marked by gas-producing bacteria invading bone.

·         Early recognition via CT imaging is critical.

·         Requires prompt antibiotics, often surgical debridement, and close multidisciplinary management.

·         High index of suspicion needed in diabetics and immunocompromised patients presenting with bone pain and systemic symptoms.

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