Septic arthritis of the acromioclavicular joint: Tc-99m leukocyte imaging.

A 62-year-old man presented to the hospital feeling generally unwell with rigors. He reported a painful right shoulder 1 day later. Ultrasound of the right shoulder was unremarkable. Blood cultures taken on admission grew Staphylococcus aureus. Because he had a history of right knee replacement complicated by infection with the same pathogen, a colloid/leukocyte scan was ordered to evaluate the possibility of prosthetic infection. Although the study revealed no prosthetic infection, it did show intense unmatched leukocyte uptake in the right acromioclavicular joint with a large soft tissue component. Computed tomography of the site was unremarkable. Surgical exploration confirmed septic arthritis of the right acromioclavicular joint with a large soft tissue component but no osteomyelitis. This is a rarely reported site for septic arthritis.