Septic Arthritis in a Non-Prosthetic Joint Due to Mycobacterium Fortuitum: A Case Report
Authors: Materon Solangel Rodriguez , Trynz Samantha , San Giovanni Thomas P. 
Published: November 2022

Category: Midfoot/Forefoot; Basic Sciences/Biologics; Trauma; Other Introduction/Purpose: Septic arthritis is an emergent medical condition. Bacteria, especially Staphylococcus aureus and Streptococcus species, most commonly cause it. There is an increased risk of Septic Arthritis in patients on immunosuppressive therapy and with underlying joint disease. We present a case of right foot septic arthritis in an at-risk patient with a history of rheumatoid arthritis on etanercept therapy by the rare pathogen: Mycobacterium fortuitum. Mycobacterium Fortuitum is an acid- fast bacilli that should be considered in patients with therapy resistant skin and soft tissue infections; however, there have been some reports of progression to osteomyelitis and septic arthritis in prosthetic joints. To our knowledge, this is the first case of septic arthritis in a non-prosthetic joint due to Mycobacterium fortuitum. Methods: A 58-year-old male with history of rheumatoid arthritis on etanercept presented to our clinic for 2 months of right foot pain after a puncture wound from a gardening hoe while in open footwear. The patient was treated at two different health centers where the wound was irrigated and closed. The physical exam displayed a healed dorsolateral wound over the naviculo- cuneiform area, swelling, fluctuance and warmth. An MRI suggested septic arthritis with an abscess confirmed by ultrasound. During surgery, pus was found at the Chopart's, naviculocuneiform and cuboideonavicular joints with drainage to the plantar side. The area was thoroughly irrigated. The patient was discharged with a VAC and a 6-week course of intravenous cefepime. The culture returned positive for Staphylococcus aureus and Mycobacterium fortuitum. Antibiotic was switched to ceftriaxone, doxycycline, and bactrim. After 6 weeks of treatment, the patient returned full weight-bearing with no pain and healed wounds. Results: Septic Arthritis is an orthopedic emergency; the most common cause is Staphylococcus aureus. Mycobacterium fortuitum is a rapidly growing acid-fast bacilli. Infection with M. Fortuitum is caused by bacterial colonization following drug injection, mesotherapy, surgical procedures, trauma, or domestic animal bites. It usually causes skin and soft tissue infections and can disseminate to the respiratory system. While there are multiple publications indicating that M. fortuitum causes prosthetic joint infection, we did not find any reports of septic arthritis in absence of a prosthesis. In our patient, a puncture wound had introduced the bacteria into many midfoot joints. His immunosuppressive therapy and rheumatoid arthritis history were important risk factors. Patients with history of inflammatory arthropathy have a higher risk of failure after a single surgical debridement. Antibiotic treatment of M. Fortuitum is also challenging because it has been reported to have resistance to several drugs. It is usually susceptible to sulfonamides. Conclusion: Bacterial septic arthritis requires timely diagnosis, drainage, and proper antibiotic treatment to avoid devastating outcomes. The most common cause is Staphylococcus aureus, however, a high index of suspicion should be maintained and other bacterial causes should not be ruled out. Different stains should be done for various organisms in order to choose the proper antibiotic treatment. Careful approach and treatment should always be taken in patients at higher risk of atypical microorganisms.