How should I evaluate and treat a 7-year-old child with swelling of the hallux?

Evaluation and Management of Big Toe Swelling in a 7-Year-Old

Start with plain radiographs of the foot in two planes as the initial imaging study, then proceed to MRI if infection is suspected and radiographs are non-diagnostic. 1

Initial Clinical Assessment

Key Historical Features to Obtain

• Duration of swelling and rate of progression 2
• History of trauma, particularly stubbing injuries, which can cause occult compound Salter I fractures of the distal phalanx despite absence of obvious wounds 3
• Fever presence (present in 78% of pediatric foot/ankle bone and joint infections) 2
• Recent infections or bacteremia 4, 5
• Immunization status, particularly for Haemophilus influenzae type b 4
• Functional impairment: refusal to bear weight, limping, or pseudoparalysis 5

Physical Examination Priorities

• Localize swelling to specific anatomic structures (joint vs. bone vs. soft tissue) 1
• Assess for warmth, erythema, and tenderness over the hallux 2
• Evaluate range of motion of the metatarsophalangeal (MTP) joint 1
• Inspect for skin breaks, puncture wounds, or nail bed involvement that would indicate compound injury 3
• Palpate for fluctuance suggesting abscess formation 2

Diagnostic Imaging Algorithm

First-Line Imaging: Radiography

Plain radiographs of the foot (AP, lateral, and oblique views) are the mandatory initial study 1, though sensitivity for early osteomyelitis is low, with bone destruction taking up to 3 weeks to appear 1. Radiographs may show:

• Soft-tissue swelling (early finding) 1
• Periosteal reaction (nonspecific) 1
• Osteolysis or bone sequestration (late findings, seen in only 2 of 23 cases in one pediatric series) 2

Advanced Imaging: MRI Without and With IV Contrast

If infection (osteomyelitis or septic arthritis) is clinically suspected and radiographs are non-diagnostic, MRI of the area of interest is the next appropriate study 1. MRI has:

• Sensitivity of 82-100% and specificity of 75-96% for acute osteomyelitis 1
• Ability to detect subperiosteal abscesses, which complicate 43% (10 of 23) of pediatric foot/ankle osteomyelitis cases and are associated with sequelae 2
• Capability to identify concomitant osteomyelitis in 70% of septic arthritis cases 1

Contrast administration increases reader confidence and better delineates abscesses, though fluid-sensitive sequences alone may be sufficient for diagnosis 1.

Role of Ultrasound

Ultrasound has limited utility for hallux evaluation 1 but may:

• Detect joint effusions (though less relevant for small joints like the MTP) 1
• Identify subperiosteal collections in osteomyelitis 1
• Evaluate for soft-tissue abscesses 1

Ultrasound cannot evaluate bone marrow and is not sensitive for osteomyelitis 1.

Laboratory Evaluation

Essential Blood Tests

• C-reactive protein (CRP): elevated in 96% (22 of 23) of pediatric foot/ankle bone and joint infections 2
• Complete blood count with differential 4
• Blood cultures (positive in approximately 43% of cases, with Staphylococcus aureus identified in 43% of pediatric foot/ankle infections) 2, 4, 5
• Erythrocyte sedimentation rate (ESR) 4

Differential Diagnosis by Age and Presentation

Infectious Etiologies (Most Common in This Age Group)

• Acute hematogenous osteomyelitis (most common pathogen: S. aureus, followed by Kingella kingae in children under 5 years) 4, 5
• Septic arthritis of the MTP joint 1
• Cellulitis with or without underlying osteomyelitis 2
• Occult compound fracture with secondary infection (particularly after stubbing injury) 3

Traumatic Etiologies

• Salter I fracture of the distal phalanx (may be compound despite absence of obvious wound) 3
• Turf toe or plantar plate injury 1
• Soft-tissue contusion 1

Other Considerations

• Juvenile idiopathic arthritis (though typically polyarticular in this age group) 1
• Foreign body with reactive inflammation 1

Management Algorithm

When Infection is Suspected or Confirmed

Empiric antibiotic therapy should be started as soon as possible after obtaining blood cultures 4:

Antibiotic Selection (Age ≥3 months)

• First-line: IV cefazolin (anti-staphylococcal coverage) 4, 5
• Alternative: IV anti-staphylococcal penicillin (e.g., cloxacillin, nafcillin) 4
• Add vancomycin if methicillin-resistant S. aureus (MRSA) is prevalent locally or if the patient is critically ill 4

Surgical Intervention Indications

Orthopedic consultation is mandatory for 5:

• Septic arthritis requiring joint aspiration and possible debridement 5
• Subperiosteal abscess requiring surgical drainage (present in 43% of pediatric foot/ankle osteomyelitis cases) 2
• Clinical deterioration despite appropriate antibiotics 4

Early surgical drainage of abscesses is critical, as all three cases with sequelae (fusion, deformity) in one series were initially complicated by abscess 2.

Duration of Therapy

• Total duration: 3-4 weeks for uncomplicated osteomyelitis (shorter than the previously recommended 6 weeks) 5
• Transition to oral antibiotics when the patient is clinically improved with decreasing inflammatory markers 4, 5
• IV therapy duration: typically 3-7 days before oral conversion 4

When Trauma Without Infection is Suspected

• Immobilization and non-weight bearing for suspected fractures 1
• Consider prophylactic antibiotics for stubbing injuries with concern for occult compound fracture, even without obvious infection 3

Critical Pitfalls to Avoid

1. Do not dismiss stubbing injuries as benign: Salter I fractures of the distal phalanx can be compound despite absence of visible wounds, and all six cases in one series developed cellulitis and osteomyelitis when not treated promptly with antibiotics 3

2. Do not delay imaging if infection is suspected: Median time to diagnosis in pediatric foot/ankle infections is only 3.2 days, but early diagnosis is crucial to prevent complications 2

3. Do not rely on radiographs alone to exclude osteomyelitis: Sensitivity is low in early disease, and MRI is required for definitive evaluation 1

4. Do not miss subperiosteal abscesses: These complicate 43% of pediatric foot/ankle osteomyelitis cases and are strongly associated with long-term sequelae including fusion and deformity 2

5. Do not assume isolated arthritis: In children with septic arthritis, concomitant osteomyelitis is present in approximately 70% of cases on MRI, and femoral neck aspiration at the time of surgery improves diagnosis compared to preoperative MRI alone 1

Follow-Up Requirements

• Serial clinical examinations and inflammatory markers (CRP, ESR) during treatment 4, 5
• Long-term orthopedic follow-up is justified given the risk of sequelae (fusion, deformity) in complicated cases 2
• Repeat imaging if clinical deterioration or failure to improve after 48-72 hours of appropriate therapy 4