Introduction: Septic osteomyelitis commonly occurs hematogenously in either end of tubular bones in children. As involvement of patella among non-tubular bones is extremely rare, adequate diagnosis could be challenging. Although most of pediatric osteomyelitis can be treated with antibiotic therapy alone, the necessity of surgical treatment in patellar osteomyelitis is not known. We hereby reported a 9-year-old girl with septic osteomyelitis of the patella caused by methicillin-susceptible Staphylococcus aureus.
Case Report: Four days prior to admission, she had left knee pain after her gymnastic class. Two days after, she received acupuncture, but the pain did not resolve. As she developed high fever, she was referred to our hospital for further management. Physical examination revealed knee tenderness in front and absence of patellar floating. Initially, septic arthritis was suspected and joint fluid was aspirated. It was negative for gram staining with mildly elevated leukocytosis. Next day, magnetic resonance imaging revealed patellar osteomyelitis with periosteal abscess extending to patellar tendon. Blood culture and aspirated pus grew methicillin-susceptible Staphylococcal aureus. Because of persistent bacteremia, she underwent debridement and drainage. After removing the bursa and curettage of necrotic tissue of patella, a cavity defect remained from under the periosteum to the patellar tendon, where the abscess was drained. Soon after surgery, bacteremia was resolved. She was treated with cefazolin followed by cephalexin for 6 weeks as acute bacterial osteomyelitis.
Conclusion: Development of vascular system in patella progresses between 5 and 12 years of age and regresses afterwards. During this period, patellar osteomyelitis should be considered in differential diagnosis. Careful physical examination and imaging study are helpful in distinguishing patellar osteomyelitis from other common pediatric diseases of knee. While the majority of childhood septic osteomyelitis can be treated with antibiotics medically, our case and cases in literature suggested that patellar osteomyelitis often required surgical intervention.
Midori Tanikawa, Takemi Murai, Yuta Aizawa, Yuho Horikoshi, Kazue Kinoshita, Yoshihiko Morikawa, Norikazu Ohta and Satoshi Shimomura