Patellar Subacute Hematogenous Osteomyelitis in Children Due To K. Kingae: A Report of Two Cases

Abstract

Isolated osteomyelitis of the patella is a rare condition mainly occurring in the pediatric population. Diagnosis is often delayed as clinical presentation manifests with vague anterior knee pain, sometimes with mild local signs of inflammation but frequently without any local signs at all. While falls on the knee can explain mild knee pain, erythema, swelling and persistent peripatellar pain should raise a high index of suspicion for local infection. We present two cases of subacute osteomyelitis of the patella in young children. In both cases bone lesions presented as an osteolytic lesion of the patella. After open biopsy of the lesion, bacteriological analysis confirmed infection with Kingella kingae.Keywords: Osteomyelitis; Kingella kingae; Trauma; Bone edema; Intravenous antibiotics; Radiographic; PCR Level of EvidenceCase reports, level IV. Case Report 1A 14-month-old Caucasian girl was admitted to the emergency department (ED) of our hospital due to persistent limping for more than 2 weeks. There was no history of trauma. A febrile episode (38.7°C) had occurred approximately 2 weeks before presentation at the ED, but as symptoms had decreased progressively no investigations into the cause of infection and no treatment had been undertaken. On admittance to our hospital, the child was afebrile and walked with a stiff knee. Clinical examination revealed right-sided knee pain, slight prepatellar edema, and a mild knee joint effusion. Laboratory results showed a white blood cell count of 17,000 cells/mm 3 , normal Creactive protein (2 mg/dL) and erythrocyte sedimentation rate (11 mm/h), but a high platelet count (520.000cells/mm 3 ). Conventional radiograph showed no significant abnormality. MRI demonstrated prepatellar soft tissue swelling, joint effusion, synovial enhancement and bone edema, all signs compatible with septic arthritis (Figure 1). Moreover, MRI revealed an osteolytic lesion located in the upper part of the right patella with anterior erosion of the cortical bone. The child underwent joint aspiration where a small quantity of mildly opaque liquid was extracted; the joint cavity was then thoroughly irrigated and the patient was immediately started on intravenous antibiotics (cefuroxime). A switch to oral antibiotics was undertaken after 3 days and treatment was continued for another 20 days. No pathogen was cultivated from the joint fluid, but K. kingae specific rtPCR gave a positive result. At the final clinical control, 12 months after surgery, the child did not complain about any pain and gait was normal. The clinical exam did not reveal any tenderness, swelling or erythema around the knee and the range of motion of the right knee joint was normal. Radiographs showed a normal patella without pathological findings.