Septic Arthritis

Snapshot

A 22-year-old man presents to his primary physician’s office for worsening knee pain. He reports that his symptoms began approximately 1 week ago and has worsened to the point of not being able to bend the knee. He states to being sexually active with multiple partners and inconsistently using condoms. On physical exam, the left knee is erythematous, swollen, and tender to palpation. There is decreased range of motion on the affected joint. Laboratory testing demonstrates an elevated erythrocyte sedimentation rate and C-reactive protein. An athrocentesis is obtained and demonstrates a white blood cell count of 55,000 cells/μL and gram-negative organisms. Empiric antibiotics are administered and orthopedic surgery is consulted.

Introduction

Clinical definition
- infection of a joint leading to arthritis that can be caused by
  - bacteria
  - fungi
  - mycobacteria
Epidemiology
- risk factors
  - increasing age
  - diabetes mellitus
  - rheumatoid arthritis
  - prosthetic joints
  - intravenous drug abuse
  - skin infection
  - alcohol use
  - sexual activity
Etiology
- Staphylococcus aureus
  - most common cause
- streptococci
  - second most common cause of nongonococcal arthritis
- Neisseria gonorrhoeae
  - suspect in healthy and sexually active young patient
- Pseudomonas aeruginosa
  - typically seen in healthcare-associated infections
- Borrelia burgdorferi
  - typically seen in patients in endemic areas
- Mycobacterium tuberculosis
Pathogenesis
- infectious agent can be spread to the joint via
  - the blood (hematogenously)
  - direct inoculation
  - contiguously from the adjacent skin (e.g., cellulitis and cutaneous ulcers)
- once the infectious agent arrives to the synovial membrane an inflammatory response ensues
Prognosis
- dependent on a number of comorbid conditions (e.g., age and immunosuppresion)
ranges 10-15%

Presentation

Imaging

Studies

Differential

Treatment

Complication