Soft-tissue emphysema following surgical procedures needs prompt and accurate diagnosis in order not to miss severe infections, such as clostridial myonecrosis and necrotizing fasciitis. We report the case of a 32-year-old patient who developed massive crepitation of the right leg and thoracic wall after knee arthroscopy had been performed a few days earlier. He was readmitted under suspicion of gas gangrene. This could not be ruled out by preoperative examinations as a subacute infection existed in the range of the infrapatellar incision. A mini-arthrotomy was carried out to exclude necrotizing soft tissue infection and to rinse the joint. An intercompartment emphysema could be confirmed intraoperatively. The postoperative course was uneventful. The main differential diagnoses of benign soft Tissue emphysema are summarized and treatment options are recommended.