Signs and Symptoms
- Classical presentation: Acute onset of pain, warmth and swelling of a single joint
- Range of motion is usually decreased
- The knee is most commonly affected but any joint may be involved
- >1 joint may be involved in patients with pre-existing joint disease, other inflammatory conditions or severe sepsis and in some patients infected with certain pathogens (eg Neisseria gonorrhoeae, Neisseria meningitidis and Salmonella spp)
- Fever and chills may be present
- Children may present with more subtle symptoms:
- Anorexia, malaise, irritability
- Limp or refusal to walk
- Refusal to use the affected joint
- Redness and swelling of skin and soft tissue overlying the involved joint early in the disease
- Must always be part of the differential diagnosis in a patient with an acute monoarthritis
Etiology
Pathogens Causing Infectious Arthritis
Staphylococcus aureus
- Most common pathogen in infectious arthritis of both native and prosthetic joints
- Infections caused by methicillin-resistant S aureus (MRSA) are usually more aggressive, with involvement of >1 joint
- MRSA is common in intravenous (IV) drug users, elderly and orthopedic-associated infections
Staphylococcus epidermidis
- More common in prosthetic joint infection
Streptococci
- Most common Gram-positive aerobes causing infectious arthritis, next to S aureus
- Important infectious arthritis pathogens in patients with serious infections of the genitourinary or gastrointestinal tract
- Group B streptococci are a common cause of infectious arthritis in neonates while Streptococcus pyogenes and Streptococcus pneumoniae are common pathogens in children ≤5 years old who have infectious arthritis
Gram-negative Bacilli
- Common etiologic agents of infectious arthritis in intravenous drug users, elderly and immunocompromised persons
- Elderly patients frequently have underlying joint diseases and concomitant diseases like diabetes mellitus (DM) and rheumatoid arthritis
- Disease-modifying drugs used to treat rheumatoid arthritis (eg Infliximab and Etanercept) may predispose patients to the development of infectious arthritis
- Haemophilus influenzae was formerly a common pathogen in infectious arthritis in children aged 1 month-5 years but widespread vaccination against the organism has drastically reduced the number of cases
- Kingella kingae is the most common cause of bacterial arthritis in children younger than 2-3 years old
- P aeruginosa may be a cause of infectious arthritis in intravenous drugs users, premature infants and patients with central vascular catheters
Neisseria gonorrhoeae
- Possible etiologic agent in young, healthy, sexually active adults with infectious arthritis
- Incidence frequently related to socioeconomic status
Anaerobes
- More common in patients with DM and those with prosthetic joint infection
Mycobacterial sp and Fungi
- Much less common cause of infectious arthritis compared to bacteria
- Low immune system, recent travel and living in endemic areas are determinants for people susceptible to mycobacterial infections
- Infectious arthritis caused by these organisms usually presents with marked joint swelling, mild signs of acute inflammation and few systemic symptoms
- Tuberculous infectious arthritis may be more common in low-income groups while other mycobacterial species can cause infectious arthritis in human immunodeficiency virus (HIV)-infected persons
- Candida arthritis is more common in immunocompromised persons and is associated with the presence of a central vascular catheter
Pathophysiology
- Hematogenous spread is the most common route for infections to reach the joint space with penetrating trauma or inoculation as potential triggers
- Pathogenic bacteria enter the joints resulting to leukocyte infiltration and serous exudation
- As the synovitis worsens, increased vascular permeability and fibrin deposition cause articular damage leading to poor joint function
- Further worsening of inflammation causes purulent conversion of the exudate, articular cartilage involvement (destruction of the subchondral bone) and cellulitis in the surrounding soft tissue
Epidemiology
- Annual incidence rate varies from 1 to 35 cases per 100,000 individuals in different countries
- Higher incidence in children than adults
Risk Factors
- Newborns and adults >80 years old
- Recent joint surgery, prosthetic joints, arthroscopy, osteoarthritis, rheumatoid arthritis in a specific joint, direct joint injury, open reduction of fracture and intra-articular steroid injection
- Systemic diseases (eg rheumatoid arthritis, DM, malignancies), use of glucocorticoids and other immunosuppressive drugs
- Extra-articular site of infection that may have given rise to bacteremic seeding in a joint (eg pyelonephritis, pneumonia and skin infection)
- Alcoholism IV drug abuse
- Low socioeconomic status