Osteitis and osteomyelitis are infections of the bone and bone marrow, respectively. Because these terms are often used interchangeably in clinical settings, both conditions will be referred to as osteomyelitis here. Staphylococcus aureus accounts for the majority of acute osteomyelitis cases; however, there are a number of other pathogens associated with this condition. How the pathogen enters the bone determines the type of osteomyelitis: hematogenous and exogenous forms exist. Hematogenous osteomyelitis is caused by seeding from a remote source and is most common among IV drug users and children. Exogenous osteomyelitis is more common in adults and results from direct inoculation through trauma (posttraumatic osteomyelitis) or contiguous spread from infected adjacent tissue (contiguous osteomyelitis due to, e.g., diabetic foot, contaminated prosthetic device). Osteomyelitis may be either acute or chronic and presents with general signs of local inflammation, including swelling, pain, redness, and warmth. Systemic signs, such as fever and chills, are more indicative of an acute infection. Diagnosis of clinically suspected cases is supported via laboratory tests, biopsy, and/or imaging. The treatment of choice for hematogenous osteomyelitis is IV antibiotics. Surgery may be necessary to remove necrotic bone, abscesses, infected foreign bodies, or fistulae. While osteomyelitis in adults often assumes a chronic course and requires prolonged treatment, children typically make a quick and full recovery.
- Osteitis: a general term for inflammation of the bone
- Osteomyelitis: infection of the bone marrow
- Hematogenous osteomyelitis
- Exogenous osteomyelitis: more common in adults 
Epidemiological data refers to the US, unless otherwise specified.
Routes of infection
- Hematogenous osteomyelitis
- Exogenous osteomyelitis: usually due to multiple pathogens
- Microbial: highly virulent pathogens
|Most common pathogens causing osteomyelitis|
|Pathogens||Commonly affected groups|
|Staphylococcus aureus (most common cause)|
|Staphylococcus epidermidis|| |
|Pseudomonas aeruginosa|| |
|Pasteurella multocida|| |
|Fungi (e.g., Candida)|
- Onset: usually gradual, over several days
- Chief complaint: pain at the site of infection, possibly related to movement
- Possible localized findings: point tenderness, swelling, redness, warmth
- Possible systemic findings: malaise, fever, chills
- Common localization of hematogenous osteomyelitis
Subtypes and variants
- Definition: subacute osteomyelitis characterized by an intraosseous abscess; commonly affects the distal femur and proximal tibia
- Pathophysiology: hematogenous seeding of a distant infectious focus → subacute or chronic pyogenic infection of the bone → fibrous and granulation tissue formation around pyogenic focus → localized abscess
- Frequently asymptomatic or only mild symptoms
- Localized pain
- Diagnostics: well-circumscribed, thick-walled cystic lesion in the metaphysis and epiphysis of long bones on x-ray and contrast-enhanced MRI
- Treatment: surgical drainage
- Suspect osteomyelitis in patients with focal symptoms (point tenderness) accompanied by nonspecific signs and symptoms of inflammation.
- Initial work-up includes blood cultures, inflammatory markers, and x-ray imaging.
- Rule out possible primary sources of infection and/or sites of dissemination (e.g., dental infection, furuncle, urinary tract infections).
- Inflammatory markers
- Blood cultures: microbiological testing
- Early stages (< 2 weeks of symptoms onset): typically no pathological findings
- Later stages: bone destruction, sequestrum formation,
- MRI: the most sensitive diagnostic study
- Skeletal scintigraphy: visualizes areas of bone with increased bone turnover
- Radionuclide-labeled leukocyte scintigraphy: detects sites of infection or inflammation
- Sonography: to assess soft tissue involvement
Early stages of osteomyelitis are not visible on x-ray.
- Septic arthritis
- (e.g., , )
- (e.g., bone cyst)
The differential diagnoses listed here are not exhaustive.
- Bed rest and immobilization of the affected extremity
- Antibiotic treatment
|Initial empiric antibiotic treatment|
|In children||< 3 months of age|
|> 3 months of age|
|Pathogen-directed IV antibiotics (according to bone biopsy findings)|
|Methicillin-susceptible S. aureus (MSSA)|
|MRSA or S. epidermidis|| |
|Gram-negative pathogens (including Pseudomonas)|
|Secondary osteomyelitis (e.g., prosthetic joints or foreign bodies)||Rifampicin in addition to the antibiotic regimen|
Treatment of osteomyelitis should not be delayed, especially in children. Osteomyelitis can have detrimental effects on bone development, resulting in severe long-term complications.
- Course: recurring/chronic cases
- In children: growth impairment
We list the most important complications. The selection is not exhaustive.
- Quick, full recovery is common in children receiving appropriate antimicrobial treatment → > 95% of cases resolve completely. 
- Acute osteomyelitis in adults often transforms into chronic osteomyelitis.
- Chronic osteomyelitis