Post-infectious arthritis can be divided into different categories based on cause and clinical course:

1. By type of triggering infection:
   • Bacterial infections: Often caused by pathogens such as Chlamydia, Salmonella, Shigella, or Yersinia.
   • Viral infections: For example, after infections with hepatitis B virus or parvovirus B19.
   • Fungal infections: Rarer, but possible in immunocompromised patients.
2. By course:
   • Acute post-infectious arthritis: Sudden onset of symptoms that may subside within a few weeks.
   • Chronic post-infectious arthritis: Symptoms last longer than six months and can lead to permanent damage.

The cause of post-infectious arthritis lies in a misreaction of the immune system, where the body's own structures are attacked:

• Infectious triggers:
  • Common bacterial pathogens include Chlamydia trachomatis, Salmonella enteritidis, and Campylobacter jejuni.
• Immunological reaction:
  • The immune system reacts to certain features of the pathogens that resemble the body's own structures (molecular mimicry).
• Genetic predisposition:
  • The HLA-B27 gene increases the risk of developing post-infectious arthritis.

The symptoms typically appear two to four weeks after infection and can vary in severity:

• Joint complaints:
  • Pain, swelling, and redness, usually asymmetrical.
  • Mainly affects the knee, ankle, and hip joints.
• Systemic symptoms:
  • General feeling of illness, fatigue, and mild fever.
• Skin and eye involvement:
  • Conjunctivitis or skin rashes, such as keratoderma blennorrhagicum.
• Movement restrictions:
  • Restriction of joint mobility, especially after periods of rest.

The diagnosis is made through a combination of medical history, clinical examination, and additional tests:

- Medical history:

- The doctor inquires about recent infections and current complaints.

- Physical examination:

- Examination of the affected joints for swelling, warmth, and movement restrictions.

- Laboratory diagnostics:

- Elevated inflammation markers such as CRP and ESR.

- Detection of specific antibodies against triggering pathogens.

- HLA-B27 test to clarify genetic predisposition.

- Imaging techniques:

- X-ray: Visualization of joint damage or calcifications.

- Ultrasound: Detection of effusions and inflammations.

Conservative Therapy

The conservative treatment is the primary focus and aims to alleviate symptoms and treat the underlying infection:

• Medication Therapy:
  • Nonsteroidal anti-inflammatory drugs (NSAIDs) for reducing inflammation and relieving pain.
  • Corticosteroid injections for severe inflammation.
  • Antibiotics for confirmed bacterial infections.
• Physiotherapy:
  • Exercises to restore mobility and prevent joint stiffness.
• Pain Management:
  • Complementary measures such as cold or heat applications.

Surgical Therapy

Surgical treatment is rarely necessary but indicated in severe or chronic cases:

• Arthroscopy:
  • Removal of inflammatory fluids from the joint.
• Synovectomy:
  • Removal of the inflamed joint lining in cases of persistent discomfort.

The following measures are helpful in preventing post-infectious arthritis:

1. Hygiene measures: Regular hand washing and avoiding contaminated food.
2. Early detection and treatment: Seek medical clarification early if symptoms of infection occur.
3. Strengthening the immune system: Healthy diet, adequate sleep, and regular exercise.
4. Vaccinations: Protection against infections such as hepatitis B.
5. Risk minimization: Timely medical consultation in case of genetic predisposition.