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[Conditions](https://durgical.com/en/conditions/) · [Knee](https://durgical.com/en/conditions/)

# 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

Tap one to see what it is and open it in 3D.

- [Joint capsule](https://durgical.com/en/anatomy/articular-capsule-of-knee-joint/)

## Microorganisms that cause it

- [Neisseria gonorrhoeae](https://durgical.com/en/microbiology/neisseria-gonorrhoeae/)
- [Staphylococcus aureus](https://durgical.com/en/microbiology/staphylococcus-aureus/)

## In histology

- [Synovial joints: capsule, synovial membrane and articular cartilage](https://durgical.com/en/histology/synovial-joints-capsule-synovial-membrane-and-articular-cartilage/)

## In the clinical exam

- [Joint examination: inspection, palpation and range of motion](https://durgical.com/en/clinical-exam/joint-examination-inspection-palpation-and-range-of-motion/)
- [Knee effusion: patellar tap and bulge sign](https://durgical.com/en/clinical-exam/knee-effusion-patellar-tap-and-bulge-sign/)

## Why it happens

- [Patterns of acute inflammation: serous, fibrinous, purulent, abscess, ulcer](https://durgical.com/en/general-pathology/patterns-of-acute-inflammation-serous-fibrinous-purulent-abscess-ulcer/)
- [When leukocytes injure tissue: proteases, oxidants and NETs](https://durgical.com/en/general-pathology/when-leukocytes-injure-tissue-proteases-oxidants-and-nets/)
- [Inflammation: the cardinal signs and its five steps](https://durgical.com/en/general-pathology/inflammation-the-cardinal-signs-and-its-five-steps/)
- [Cartilage: hyaline, elastic, fibrocartilage](https://durgical.com/en/histology/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

- [Osteomyelitis](https://durgical.com/en/conditions/osteomyelitis/)
- [Gout](https://durgical.com/en/conditions/gout/)

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Septic Arthritis](https://www.ncbi.nlm.nih.gov/books/NBK538176/) (StatPearls (NCBI Bookshelf), 2024).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/conditions/septic-arthritis-of-the-knee/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/conditions/septic-arthritis-of-the-knee/