Methicillin-Resistant Staphylococcus Aureus Septic Arthritis of the Knee Secondary to Steroid/Anesthetic Injection

Abstract

Septic arthritis is a common infectious disease affecting the joints. Bacteria may gain entrance into the synovial fluid of the joint hematogenously, by local/direct extension, or may enter the joint fluid traumatically or as the result of injection into the joint space. Staphylococcus aureus remains the most common cause of septic arthritis from secondary bacteremias from a distant primary focus. The hematogenous seeding of joints is a recognized complication of S. aureus endocarditis in normal hosts and intravenous drug abusers. S. aureus is a common skin colonizer, and is the most common organism associated with traumatic or iatrogenic septic arthritis where bacteria from the skin are introduced into the synovial fluid of the joint via percutaneous instrumentation [1–4]. There have been reports of iatrogenic septic arthritis secondary to arthroscopy or needle aspiration/injection of joints. Normally, the joint space and synovial fluid are sterile, but organisms may gain entrance to the joint space if a suboptimal sterile technique is used during the joint aspiration/injection procedure. Aerobic gram-negative bacilli, e.g., Serratia, Enterobacter, Pseudomonas aeruginosa, etc., are the most common gram-negative organisms involved in iatrogenic septic arthritis. These organisms share in common an aquatic habitat and frequently contaminate aqueous solutions associated with arthroscopic or joint aspiration instruments. Therefore, the recovery of aerobic gram-negative bacilli from synovial fluid of a patient with recent joint instrumentation in the absence of a hematogenous source should suggest iatrogenic introduction of the organism via contaminated fluids or solutions. In contrast, the recovery of clostridia, propionibacteria, or S. aureus from a recently instrumented patient with septic arthritis in the absence of contiguous or hematogenous focus should suggest the skin as a source of the organism [5–10]. S. aureus from an antibiotic susceptibility perspective may be considered as being methicillin sensitive (MSSA) or methicillin resistant (MRSA). Although staphylococci differ in their susceptibility to methicillin, they cause the same spectrum of infection. During the past several decades, there has been an increase in MRSA recovered from a variety of clinical sites in colonized and infected patients. This increase has been attributed, in part, to the selective pressure caused by overuse of certain antibiotics, e.g., ciprofloxacin, imipenem, and ceftazidime. Although MRSA and MSSA are common skin colonizers, they are also known pathogens and capable of serious disease [5]. S. aureus introduced into joint space may result in destruction and loss of function of that joint. For this reason, careful attention should be given to aseptic technique when joint instrumentation procedures are undertaken [1]. We present a case of iatrogenic MRSA septic arthritis of the knee in a normal host. Because the patient had no other source of contiguous or distant S. aureus infection, we believe that the MRSA was introduced during the instillation of steroids/anesthetic into the affected knee joint. To our knowledge, this is the second known case of MRSA septic arthritis, and the first case of iatrogenic MRSA septic arthritis to be reported. Case Report. The patient was a 73-year-old woman with a past medical history of osteoarthritis. Because of pain in her knees, she received bilateral steroid/anesthetic injections from her medical doctor. Her left knee pain worsened, and she returned to her physician. At that time, her left knee was not erythematous, but was mildly swollen with no frank effusion, and a range of flexion to 40°. Arthrocentesis was performed and a 5-mL turbid straw-colored synovial fluid obtained and sent for culture and susceptibility and cell count. The patient was reinjected with lidocaine for the pain. She was then referred for an MRI which revealed osteoarthritis with marked chondromalacia and subarticular edema of the medial aspect of the knee, significant joint effusion, and complex tear of the medial collateral ligament. The synovial fluid gram stain revealed gram-positive cocci and grew methicillin-resistantStaphylococcus aureus(MRSA). The patient was started on vancomycin, 1 g (IV) q 12 hours. The patient underwent arthroscopic lavage, and gross pus was noted to exude from the knee joint. The exudate was sent for culture and sensitivity and cell count. Preoperatively, the patient remained afebrile, and had the following laboratory results: white blood cell count 18,200/mm3, hemoglobin 11.7g/dL, hematocrit 35%, and platelet count 421,000/mm3. The cell count from the pus collected from the left knee during surgical debridement was 188,000/mm3 (93% polymorphonuclear cells, 3% lymphocytes, and 4% monocytes). The gram stain revealed gram-positive cocci in pairs and clusters which grew MRSA. The patient tolerated the procedure well, her knee was immobilized, and large-bore Hemovac was left in knee to drain. The patient was hospitalized and received vancomycin, 1 g (IV) q 12 hours for 5 days. On postoperative day 3, the Hemovac drain was removed, and the patient continued physical therapy for her knee. The patient was discharged home on hospital day 5 on minocycline, 100 mg (PO) q 12 hours to complete 3 weeks of therapy. Discussion. Iatrogenic septic arthritis is increasing with the increasing popularity of arthroscopic procedures and the instillation of steroids into joints for osteoarthritis or rheumatoid arthritis. The introduction of instruments into a normally sterile space or body fluid requires the utmost attention to sterile technique to avoid the introduction of organisms colonizing the overlying skin into the joint space. Careful attention must also be given to ensure that cleansing and irrigating fluids associated with the instruments used for injection or visualization of joints are sterile to avoid the introduction of aerobic gram-negative bacilli that thrive in an aquatic environment, i.e., Enterobacter, Serratia, etc. [1–4]. The patient described above presented with an acute monoarticular septic arthritis of the knee joint that occurred several days after an injection of steroid into the knee joint. The synovial fluid findings were diagnostic of septic arthritis and the synovial fluid grew MRSA. Treatment options for MRSA are limited at the present time. Vancomycin and minocycline are only two currently available antibiotics that are predictably effective in infections caused by MRSA. Both vancomycin and minocycline penetrate into synovial fluid achieving near serum concentrations. The treatment in this patient initially consisted of joint drainage in conjunction with intravenous vancomycin. After the drain was removed, the patient was continued with oral minocycline. The patient has regained most of her joint function and continues to do well. We believe this is the first case of iatrogenic MRSA septic arthritis of the knee from steroid injections. This is the second case of non-bacteremic MRSA septic arthritis reported to date. This case serves as a reminder to clinicians performing arthroscopy, doing joint aspirations, or injecting steroids into joints, that constant vigilance must be maintained to be certain irrigating fluids are sterile, to minimize the possibility of introducing aerobic gram-negative bacilli into the joint fluid, and that scrupulous aseptic technique is used to minimize the possibility of introducing skin organisms, e.g., S. aureus, into the synovial fluid. As colonization and infection caused by MRSA increases, clinicians should be aware of the potential for MRSA infection with patients undergoing percutaneous procedures with MRSA skin colonization.