Septic Arthritis of the Knee !
Septic arthritis of the knee is an infection inside the knee joint, usually by bacteria; it is a medical emergency that can destroy the joint.
Updated 2026-10-23
Structures involved
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Microorganisms that cause it
In histology
In the clinical exam
- Joint examination: inspection, palpation and range of motion
- Knee effusion: patellar tap and bulge sign
Why it happens
- Patterns of acute inflammation: serous, fibrinous, purulent, abscess, ulcer
- When leukocytes injure tissue: proteases, oxidants and NETs
- Inflammation: the cardinal signs and its five steps
- Cartilage: hyaline, elastic, fibrocartilage
What it is
Infection inside the knee joint, most often bacterial. Medical emergency.
Causes
- Staphylococcus aureus most common
- Neisseria gonorrhoeae in young sexually active adults
Risk factors
- Prior joint injection or surgery
- Immunosuppression
- Diabetes
Symptoms and signs
- Acute hot, swollen, painful knee
- Limited motion
- Fever (may be absent)
Diagnosis
- Clinical
- Acute monoarthritis
- Tests
- Joint aspiration for cell count, Gram stain, and culture
Treatment
- Acute
- Urgent joint drainage and intravenous antibiotics.
- Surgical
- Arthroscopic or open lavage.
Complications
- Cartilage destruction
- Osteomyelitis
- Sepsis
Related conditions
Educational information, not medical advice. For any symptom, see a health professional.
Sources: Septic Arthritis (StatPearls (NCBI Bookshelf), 2024).
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Representative model, for educational purposes only.
