Septic arthritis

Disease Description (Causes and Symptoms)

• Definition and causes
  • A disease in which bacteria that have invaded the joint multiply in the synovium (joint capsule), causing acute inflammation (bacterial arthritis, septic arthritis).
  • Common causative organisms: Staphylococcus aureus (most common), streptococci, and gram-negative bacilli (particularly in high-risk patients and hospital-acquired infections); Neisseria gonorrhoeae and others when sexual activity is the cause.
  • Routes of infection: hematogenous spread (most common), direct contamination due to direct trauma, surgery, or injection, and spread from adjacent tissues (such as osteomyelitis).
• Pathophysiology (brief)
  • Bacteria invade the synovium → strong inflammatory response (large numbers of white blood cells, enzymes, and cytokines) → increased intra-articular pressure and activation of cartilage-degrading enzymes → damage to cartilage and joint structures and loss of function.
• Main symptoms
  • Acute monoarticular symptoms (mainly in the knee, hip, shoulder, wrist, etc.): severe joint pain, joint swelling and tenderness, redness and warmth, limited joint movement (especially limited passive movement), and possible systemic fever and chills.
  • In children and older adults, symptoms may be nonspecific (lethargy, fever, immobility).

Treatment

• Immediate diagnostic and therapeutic measures
  • When suspected, prompt arthrocentesis (joint fluid testing): cell count (WBC), Gram stain, cultures (joint fluid and blood), and crystal examination. Arthrocentesis is important for both diagnosis and decompression.
• Antibiotic treatment
  • Start empirical antibiotics immediately (intravenously), then switch or adjust them according to the culture results.
  • Empirical selection varies according to patient characteristics, route of infection, and the local prevalence of MRSA:
    • Suspected community-acquired infection with low MRSA risk: consider a third-generation cephalosporin (e.g., ceftriaxone) targeting MSSA and streptococci, or nafcillin/oxacillin.
    • If there is a risk of MRSA (older age, hospitalization, recent antibiotic use, IV drug use, etc.): include MRSA coverage with vancomycin or daptomycin, etc.
    • High risk of gram-negative infection or hospital-acquired infection: additionally consider a broad-spectrum beta-lactam (e.g., cefepime, piperacillin–tazobactam), etc.
    • If gonococcal arthritis is suspected in an adult: IV ceftriaxone is recommended (as directed by a specialist).
  • Treatment duration
    • Primary infection (native joint): total treatment usually 3–4 weeks (generally, 1–2 weeks of initial IV treatment followed by an additional total of 2–4 weeks after switching to oral treatment)—determined based on the clinical course and inflammatory markers (CRP).
    • Prosthetic joint infection or severe osteoarticular damage: 4–6 weeks or longer; long-term treatment may be necessary in some cases.
• Drainage and surgery
  • If repeated drainage through arthrocentesis is possible, conservative treatment may be attempted.
  • Arthroscopic lavage or open drainage (surgery) is necessary for joints that are difficult to access internally (e.g., the hip), when there is no improvement with arthrocentesis or endoscopic drainage, or when an abscess or necrotic tissue is present.
  • Prosthetic joint infection: if early (within several weeks), DAIR (debridement, antibiotics, and implant retention; retention without replacement) may be considered; delayed or chronic infection may require one-stage or two-stage revision surgery (removal and reinsertion of the implant).
• Supportive management
  • Pain management, fever management (antipyretics), joint stabilization and partial non-weight-bearing initially, followed by early joint movement and rehabilitation to restore range of motion.
  • Monitoring: clinical symptoms, CRP/ESR, follow-up blood cultures, and repeat arthrocentesis if necessary.
• Special situations
  • Children: the causative organisms, treatment dosage, and duration may differ, so consultation between pediatrics and orthopedics is recommended.
  • For immunocompromised patients, people with diabetes, skin infections, IV drug users, etc., a broader evaluation and broad-spectrum antibiotics should be considered.

Outpatient Visit Checklist (Preparation and Example Questions)

• Items to prepare (bringing these can help with the consultation)
  • List of current medications (including antibiotics, anticoagulants, and immunosuppressants), and information about medication allergies
  • Copies of recent test results (blood tests and imaging studies) and medical certificates
  • Records of when symptoms began and how they have changed (degree of pain, fever pattern, ability to walk, etc.)
  • History of recent surgery, injections, trauma, skin infection, or sexual activity (can be provided anonymously if necessary)
  • Whether you have a prosthetic joint and information about its manufacturer and implantation date (if applicable)
• Information about tests that may be performed as an outpatient
  • Blood tests (CBC, CRP, ESR, blood cultures), and, if necessary, arthrocentesis and joint fluid testing, as well as imaging such as X-ray, ultrasound, CT, or MRI.
• Example questions (questions that patients may ask healthcare professionals during the consultation)
  • Regarding symptoms: "What is causing this joint pain and swelling?", "How can we determine for sure whether it is an infection?"
  • Regarding tests: "Is joint fluid testing dangerous? What can we learn from the test?"
  • Regarding treatment: "Do I need to start antibiotics right away? Will I need inpatient treatment?"

Examples of General Questions to Ask the Doctor

• What are the expected side effects of this antibiotic? (e.g., nephrotoxicity, bone marrow suppression)
• Do I need surgery in my current condition? If so, when would be the appropriate time?
• What is the expected treatment duration and prognosis (likelihood of functional recovery)?
• Do I need to continue treatment even if the blood and joint cultures are negative?
• How should I undergo rehabilitation to restore joint function after the infection?
• What is the risk of other complications (sepsis, chronic joint damage, osteonecrosis, etc.)?

Examples of Disease-Specific Questions

• If it occurs in a young adult who is sexually active: "Could this arthritis be caused by Neisseria gonorrhoeae? Should I also be tested for sexually transmitted infections? Do I need to notify my guardian or recent partner?"
• If the patient has a prosthetic joint or a history of recent joint surgery: "Could this be a prosthetic joint infection? Can the implant be retained, or will it need to be removed?"

(Note) Because diagnosis and treatment vary depending on the patient's condition, culture results, local antibiotic resistance rates, and underlying diseases, it is important to consult the treating healthcare professionals and establish an individualized plan.