creation date: 2026-05-14 16:53
tags: Pathologies Incomplete
Osteomyelitis
Background
Definitions
Osteomyelitis is an infection of the bone.
Acute osteomyelitis: symptom durations of days to weeks
Chronic osteomyelitis: symptoms over months or years
Hematogenous osteomyelitis: spread of pathogens to bone through bacteremia which may or may not still be present at time of diagnosis of osteomyelitis
Nonhematogenous osteomyelitis: contiguous spread of infection to bone from adjacent joint or soft tissue infection, or by direct inoculation such as due to trauma
Native bone infection: infection in absence of hardware
Orthopedic device-associated infection: infections associated with orthopedic hardware
Risk Factors, Etiology, and Microbiology
Hematogenous osteomyelitis occurs in the setting of bacteremia. Vertebral osteomyelitis is the most common form but may occur at other site.
Risk factors for hematogenous osteomyelitis include:
- Endocarditis
- Indwelling intravascular devices (vascular catheters, cardiovascular devices)
- Orthopedic hardware
- Injection drug use
- Hemodialysis
- Sickle cell disease
Nonhematogenous osteomyelitis occurs most commonly in younger patients in the setting of trauma and surgery. In older patients, in the setting of contiguous tissue spread (eg. diabetic foot wounds).
Risk factors include:
- Poorly healing soft tissue wounds
- Presence of orthopedic hardware
- Diabetes
- Peripheral vascular disease
- Peripheral neuropathy
Pathogenesis
Hematogenous route
In pediatric populations, the metaphysis of long bones is vulnarable. This occurs as the metaphyseal sinusoidal vessels make sharp hairpin loops that create a calm region of blood flow suitable for bacterial settlement.
In adults, the metaphyseal and epiphyseal vessels connect and thus bacteria can seed in epiphysis or subchondral bone.
Once seeded, bacteria use adhesins, biofilm formation, and toxins to establish infection. Immune response and subsequent increased intraosseous pressure causes thrombosis and ischemic bone death.
Contiguous spread
Unlike hematogenous spread, this infects the cortex of the bone rather than the medullary cavity. Common clinical scenarios include:
- Diabetic foot ulcers
- Decubitus ulcers
- Periodontal disease
- Septic arthritis
Clinical Presentation
Signs & Symptoms
The typical presentation includes:
- Gradual onset of dull pain at involved site (may be masked if neurologic compromise)
- Tenderness, warmth, erythema, swelling - particular in context of associated soft tissue infection
- Draining sinus tract (high specificity, nearing pathognomonic)
History & Physical Exam
History should include past history of:
- Hardware
- Indwelling instruments
- Hemodialysis
- IV injections
Medical history relevant include:
- Diabetes
- Endocarditis
Diagnosis
Criteria
Definitive diagnosis of osteomyelitis requires:
- Isolation of bacteria or fungus from bone specimen
- Histologic evidence of inflammation and osteonecrosis
A diagnosis can be inferred with clinical and radiographic findings typical of osteomyelitis and one of the following:
- Positive blood cultures with typical pathogen (eg. S. aureus)
- Bone histopathology
- Persistently elevated inflammatory markers and no suspected alternative diagnosis (nonspecific, may lead to false positives)
Work-up
Imaging studies
Initial study consist of plain radiograph. X-rays can be normal in up to 80% of patients in first 2 weeks of infection and 30-50% of bone loss must have occurred before it is visible on x-ray.
Early x-ray findings include:
- Soft tissue swelling
- Focal osteopenia/lytic lesion
- Periosteal reaction
Chronic findings include:
- Sequestrum - dense sclerotic dead bone fragment within a lucent lesion (necrotic bone surrounded by radiolucent halo)
- Involucrum - thick shell of periosteal new bone surrounding sequestrum (appears like cortical thickening)
- Cloaca - opening/defect in involucrum through which pus exit
- Cortical disruption - obliteration or complete loss of normal cortical signal
- Sclerosis - generalized increased bone density from reactive bone formation
Further imaging consist of MRI. Findings can be highly sensitive and can find associated soft tissue infection.
Cultures
Bone biopsies are obtained either intraoperatively during debridement or percutaneously. They should be obtained if feasible and particularly helpful if:
- Diagnostic uncertainty
- Concern for antibiotic-resistant organism
- Failure of empiric antibiotic therapy
- Suspicion of atypical pathogen (eg. tuberculosis, fungus, Brucella spp.)
Blood cultures are generally not useful except if hematogenous infection is suspected. Similarly, wound swabs are not helpful.
Inflammatory markers
Specificity of markers are poor (approximately sensitivity 45-79% for both ESR and CRP). These are elevated in context of osteomyelitis:
- ESR
- CRP
- WBC count
Differential
Differential diagnosis includes:
- Soft tissue infection
- Charcot arthropathy
- Osteonecrosis
- Fracture
- Bone tumour
- Sickle cell vaso-occlusive pain crisis
- Synovitis, acne, hyperostosis, and osteitis (SAPHO) syndrome
- Complex regional pain syndrome
Red Flags / Complications
Infectious complications include:
- Sinus tract formation
- Contiguous soft tissue infection
- Abscess
- Septic arthritis
- Systemic infection
Noninfectious complications include:
- Bone damage causing bone deformity
- Increased risk for bone fracture
- Carcinoma at site of chronic osteomyelitis
Management
Treatment may include surgery and antimicrobial therapy. The details of management of specific types of osteomyelitis may be found in their respective pages.