Working Diagnosis:
Distal fibular osteomyelitis with a large periosteal abscess and ankle joint synovitis.

Treatment:
Immediately following review of the magnetic resonance imaging findings, the patient was admitted to the hospital. She was treated with intravenous cefazolin for 7 days and underwent urgent incision, drainage, and irrigation of the distal fibula.

Intraoperative cultures grew methicillin-sensitive Staphylococcus aureus.

She was discharged in a hard cast with touchdown weight-bearing precautions and transitioned to oral cephalexin for 4 weeks.

Outcome:
At 2 months postoperatively, she demonstrated notable right calf weakness, muscle atrophy, and an antalgic gait.

Four-month postoperative radiographs demonstrated resolution of the periosteal reaction, consistent with treated osteomyelitis.

Following completion of an intensive home physical therapy program, she regained full strength and range of motion and returned to unrestricted sports participation.

Author's Comments:
Acute hematogenous osteomyelitis is an uncommon but important cause of atraumatic extremity pain in children. Early symptoms may mimic more common musculoskeletal injuries, which can delay diagnosis. Distal fibular involvement is less common than involvement of other long bones and may further contribute to diagnostic uncertainty.1

Persistent fever, inability to bear weight, progressive pain, and severe localized tenderness should raise concern for infection even when initial radiographs are normal. Magnetic resonance imaging remains the gold standard imaging modality for the early diagnosis of osteomyelitis and can identify bone marrow edema, abscess formation, and associated soft tissue involvement before radiographic changes become apparent.1-2

In pediatric patients, osteomyelitis most commonly results from hematogenous seeding during transient bacteremia and is not typically associated with underlying immunodeficiency. Prompt diagnosis, targeted antibiotic therapy, and surgical intervention when indicated are essential to prevent complications and optimize functional outcomes.1-2

Editor's Comments:
Acute osteomyelitis is an uncommon but important cause of atraumatic extremity pain in children and remains a "can't miss" diagnosis for sports medicine clinicians. The most common mechanism of pediatric osteomyelitis is hematogenous spread, with bacterial seeding occurring in areas of rich metaphyseal blood supply adjacent to the growth plate.1

Persistent fever, inability to bear weight, progressive pain, and severe localized bony tenderness should raise suspicion for infection despite initially normal radiographs or an apparently benign musculoskeletal presentation. This was demonstrated in the present case, where distal fibular osteomyelitis initially mimicked a lateral ankle sprain. Magnetic resonance imaging remains the imaging modality of choice when osteomyelitis is suspected because of its ability to detect early bone and soft tissue involvement.1-2

This case also highlights the importance of rehabilitation following treatment. Although the patient experienced calf weakness, muscle atrophy, and gait abnormalities during recovery, dedicated physical therapy ultimately facilitated restoration of strength, function, and return to sport.

References:
1. Peltola H, Pääkkönen M. Acute osteomyelitis in children. N Engl J Med. 2014 Jan 23;370(4):352-60. doi: 10.1056/NEJMra1213956. PMID: 24450893.

2. Clinical Practice Guideline by the Pediatric Infectious Diseases Society and the Infectious Diseases Society of America: 2021 Guideline on Diagnosis and Management of Acute Hematogenous Osteomyelitis in Pediatrics

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