Your Diagnosis, Please
A previously healthy 3-year-old male presented to an urgent care clinic with 1 day of left knee swelling and erythema. He was diagnosed with cellulitis and discharged home on oral clindamycin. Two days later, he developed fever and progressive left knee swelling, refused to bear weight, and was brought to the Emergency Center for evaluation.
He had no significant medical or surgical history and was fully immunized. He was born in the United States and lived in Houston, Texas. He had not travelled outside of Texas and had no ill contacts. He enjoyed playing outdoors, had a minor fall 1 week prior to the development of symptoms but had no obvious abrasions or penetrating trauma to the knee. His diet contained no raw meat or unpasteurized dairy products.
His temperature was 38.6°C and heart rate was 110 beats/min, but other vital signs were normal for age. Physical examination was notable for a tender and swollen left knee with decreased range of motion (ROM)—both flexion and extension—and surrounding erythema.
His complete blood cell count showed 16,570 white blood cells/mm3 (with a differential of 67% neutrophils, 28% lymphocytes, 5% monocytes and 0% eosinophils), hemoglobin of 11.4 g/dl, hematocrit of 32.1% and a platelet count of 555,000/mm3. His chemistry panel was unremarkable; however, C-reactive protein and erythrocyte sedimentation rate were elevated at 7 mg/l and 37 mm/h, respectively (normal: <1 mg/l and <20 mm/h). An ultrasound of the left knee demonstrated a small joint effusion. Bedside aspiration of the affected joint revealed cloudy fluid with 66,700 white blood cells (74% neutrophils) and 22,000 red blood cells. The Gram stain showed no organisms.
He was admitted to the inpatient pediatric service and continued on treatment with intravenous (IV) clindamycin. The patient underwent an arthrotomy of the knee with irrigation and drain placement. Purulent fluid was noted in the joint space; postoperatively, the antibiotic regimen was changed to IV vancomycin and ceftriaxone. By hospital day (HD) 2, his fever had resolved. However, on HD 4, he continued to have significant pain and swelling of his left knee. A magnetic resonance imaging (MRI) revealed a large joint effusion with nonspecific osteitis of the distal femoral and proximal tibial epiphyses that did not meet MRI criteria for osteomyelitis. A second arthrotomy revealed hemarthrosis with no purulence. Following this second washout, he was transitioned from vancomycin to IV clindamycin and began to have decreased pain and improved ROM. On HD 10, he was discharged home on oral clindamycin and cefdinir. At the time of discharge, the following studies showed no growth or were negative: bacterial culture from the initial joint aspiration; aerobic, anaerobic, fungal and mycobacterial cultures from both operative procedures; and broad-range polymerase chain reactions (PCRs) (University of Washington Medical Center, Seattle, Washington) from the second arthrotomy for bacteria and acid-fast bacteria (AFB). After 15 days of antibiotic therapy, he continued to have marked swelling of the knee, severely restricted ROM and some pain. A subsequent result revealed the diagnosis of the patient.