Case presentation A 92-year-old man presented to his primary care provider with complaints of pain in his left knee caused by osteoarthritis. The patient received an ultrasound-guided injection of 48 mg Hylan G-F 20 without complications. However, the patient complained of sharp pain and swelling in his left knee about 8 hours after the treatment and went to the emergency room 10 hours after the injection.
Pathological examination · The culture of the first synovial fluid sample (taken around 12 h after injection) revealed a tiny pink, a mucoid colony that did not grow on MacConkey agar 96 hours after the initial sample collection (Cover image a and b) · The organism was a Gram-negative bacillus that was catalase-positive and slightly oxidase-positive. Under a Wood's Lamp, colonies absorbed UV light and turned black (Cover image c).