This infection occurs most commonly as a result of hematogenous seeding of the joint in the setting of bacteremia. A joint may be inadvertently inoculated with a pathogen at the time of surgery or trauma. In some patients, a severe soft tissue infection may spread to involve a nearby joint.
Common pathogens responsible for this infection include Staphylococcus aureus, Streptococcus species, gram-negative bacilli, and Neisseria gonorrhoeae.
Risk factors for this infection include old age, diabetes mellitus, recent joint surgery or procedure, skin infection, the presence of a prosthetic joint, or immunosuppression. Patients with rheumatoid arthritis or who abuse intravenous (IV) drugs are also at increased risk for this infection.
Patients present with a swollen, warm, stiff, and painful joint. Fever may be present. The majority of the time, a single joint (usually the knee) is involved. Symptoms develop over 1-2 weeks. If the infection is caused by N gonorrhoeae, patients classically also present with a rash and tenosynovitis. If the infection is due to fungi or mycobacteria, the symptoms may be subtler and may worsen more gradually.
Diagnosis can be made by arthrocentesis. Joint fluid should be sent for analysis including cell count, microscopic analysis for crystals, Gram stain, and bacterial culture. Additional cultures of the joint fluid can be obtained if an atypical pathogen is suspected by history or examination.
Treatment requires drainage of the joint (surgically or by repeated needle aspiration) in combination with antimicrobial therapy.
M00.80 – Arthritis due to other bacteria, unspecified joint
396234004 – Infective arthritis
Differential Diagnosis & Pitfalls
- Arthritis due to viral infections (eg, parvovirus B19, rubella, human immunodeficiency virus, chikungunya, Zika virus) – Arthritis may affect multiple joints and be associated with rash and other symptoms of a viral syndrome including fever.
- Lyme arthritis – May present with similar symptoms as septic arthritis, but usually with less pain. Serologic testing for Lyme disease may be performed in patients with a possible exposure history. Arthrocentesis to exclude septic arthritis due to typical pathogens should still be performed.
- Rheumatoid arthritis – Classically presents with symmetrical involvement of peripheral joints.
- Gout – Intracellular urate crystals seen in joint fluid (presence of crystals does not rule out concomitant septic arthritis).
- Calcium pyrophosphate deposition disease – Calcium pyrophosphate crystals seen in joint fluid (presence of crystals does not rule out concomitant septic arthritis).
- Reactive arthritis – Patients have a preceding illness (eg, diarrhea or urethritis) and may also present with enthesitis, dactylitis, or inflammatory back pain.
- Osteoarthritis – Usually symptoms are chronic and there are not usually inflammatory findings (red, hot, swollen joint) on examination.
- Injury (eg, meniscal tear) – Patient will usually relate a history of preceding trauma.
- Hemarthrosis – Patient will usually have a history of trauma or a bleeding disorder.