Overview
Definition:
Osteomyelitis is an infection of bone and bone marrow, typically caused by bacteria but can also be viral, fungal, or parasitic
In children, it most commonly affects long bones and is often hematogenous in origin.
Epidemiology:
Incidence varies, but it is more common in children aged 1-12 years
Boys are affected slightly more than girls
Staphylococcus aureus is the most common causative organism
Other common pathogens include Streptococcus pyogenes, Streptococcus pneumoniae, and Haemophilus influenzae type b (less common now due to vaccination)
Salmonella species are common in children with sickle cell disease.
Clinical Significance:
Prompt diagnosis and treatment are crucial to prevent long-term complications such as bone deformities, growth disturbances, chronic osteomyelitis, and dissemination of infection
Understanding optimal MRI timing and therapy duration is key for effective management and favorable outcomes in pediatric patients.
Clinical Presentation
Symptoms:
Fever and malaise are common systemic symptoms
Localized bone pain, tenderness, and swelling are characteristic
Limp or refusal to bear weight on the affected limb is frequent in lower extremity osteomyelitis
Irritability and poor feeding may be observed in infants
Pseudoparalysis may occur in young children.
Signs:
Localized warmth and erythema over the affected bone
Tenderness to palpation is a key finding
A palpable mass or fluctuance may suggest an abscess
Joint effusion may be present if the infection is near a joint.
Diagnostic Criteria:
No single criterion is diagnostic
Diagnosis relies on a combination of clinical findings, laboratory tests, and imaging
The modified Cierny-Mader staging system, though primarily for adults, can be adapted
Pediatric osteomyelitis is often categorized as acute, subacute, or chronic based on duration and presentation.
Diagnostic Approach
History Taking:
Detailed history of recent trauma, preceding infections (e.g., skin infections, URI), and underlying medical conditions (e.g., sickle cell disease, immunodeficiency)
Duration of symptoms is important for classifying the type of osteomyelitis.
Physical Examination:
Thorough examination of the affected limb, assessing for tenderness, swelling, erythema, warmth, and range of motion
Palpation for any fluctuance
Examination of adjacent joints
Assessment of vital signs.
Investigations:
Initial lab tests include complete blood count (CBC) with differential (elevated WBC count), erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) (elevated)
Blood cultures are essential if bacteremia is suspected
Radiographs (X-rays) may be normal in early stages but can show periosteal reaction, cortical destruction, or sequestrum formation later
**MRI is the gold standard for early diagnosis and assessment of extent.** MRI shows bone marrow edema, periosteal elevation, and soft tissue involvement
It is highly sensitive and specific
**MRI timing is crucial
it can detect changes as early as 24-48 hours after infection onset.** Bone biopsy (surgical or percutaneous) for culture and histology is definitive but not always required if clinical and imaging findings are clear.
Differential Diagnosis:
Septic arthritis (usually more acute joint involvement, effusion, limited range of motion), trauma (fracture, contusion), transient synovitis, bone tumors (e.g., Ewing sarcoma, osteosarcoma), cellulitis, juvenile idiopathic arthritis, sickle cell crisis.
Management
Initial Management:
Empirical antibiotic therapy should be initiated promptly after obtaining blood cultures and, if possible, a bone biopsy aspirate
Initial antibiotics should cover the most likely pathogens (e.g., S
aureus, Streptococcus species).
Medical Management:
Antibiotic therapy: Intravenous antibiotics are typically given for 4-6 weeks, followed by oral antibiotics for a variable duration (totaling at least 6-8 weeks in most cases of acute osteomyelitis)
Dosing is weight-based and adjusted for renal function
Common empiric choices include vancomycin (for MRSA coverage), nafcillin or oxacillin (for MSSA), clindamycin, or cefazolin
For specific identified pathogens, therapy is tailored
Duration of therapy is guided by clinical response, normalization of inflammatory markers (ESR, CRP), and imaging findings
**MRI can be repeated at 2-4 weeks to assess response
persistent or worsening edema indicates treatment failure or need for surgical intervention.** A minimum of 6-8 weeks of total therapy is standard for acute osteomyelitis
Chronic osteomyelitis may require longer courses or surgical debridement.
Surgical Management:
Indications include failure to respond to antibiotics, presence of a significant abscess, involvement of the joint, or progressive bone destruction
Surgical options include drainage of abscesses, debridement of necrotic bone (sequestrectomy), and bone grafting if necessary
Surgical intervention may be required even after appropriate antibiotic therapy.
Supportive Care:
Pain management with analgesics
Immobilization of the affected limb may be necessary
Physical therapy is important for regaining function after acute treatment.
Complications
Early Complications:
Septic arthritis (if infection extends into joint), spread of infection to adjacent soft tissues (abscess formation), bacteremia with seeding to other organs (e.g., endocarditis).
Late Complications:
Chronic osteomyelitis, pathological fracture, growth disturbances, limb length discrepancy, joint contractures, osteonecrosis, and in rare cases, osteosarcoma transformation (post-irradiation osteosarcoma, not typical for primary osteomyelitis).
Prevention Strategies:
Prompt treatment of skin infections and other sources of potential bacteremia
Maintaining good hygiene
Early recognition and management of symptoms suggestive of osteomyelitis.
Prognosis
Factors Affecting Prognosis:
Prompt diagnosis and initiation of appropriate therapy are the most critical factors
Age of the patient, virulence of the organism, presence of underlying medical conditions, and extent of bone involvement also influence prognosis.
Outcomes:
With appropriate and timely treatment, most children with acute osteomyelitis have an excellent prognosis and full recovery
However, delayed treatment can lead to significant long-term morbidity.
Follow Up:
Regular follow-up is essential for at least several months to monitor for recurrence, assess growth and development of the affected limb, and ensure complete functional recovery
Follow-up imaging may be required
Monitoring of inflammatory markers is also important.
Key Points
Exam Focus:
Remember S
aureus is the most common pathogen in children
MRI is the investigation of choice for early detection, usually showing edema within 24-48 hours
Antibiotics are typically IV for 4-6 weeks, followed by oral for a total of at least 6-8 weeks
Consider surgical drainage for abscesses or non-response
CRP and ESR are key inflammatory markers.
Clinical Pearls:
Always consider osteomyelitis in a child with localized bone pain and fever, especially if there is limping or refusal to bear weight
Don't hesitate to get an MRI if initial X-rays are negative but suspicion remains high
Tailor antibiotic therapy once cultures return
Monitor inflammatory markers closely for treatment response.
Common Mistakes:
Delaying MRI imaging despite clinical suspicion
Underestimating the duration of antibiotic therapy, especially oral consolidation
Inadequate coverage for S
aureus
Not considering surgical intervention when indicated
Misinterpreting normal initial X-rays as ruling out osteomyelitis.