Sandbox:septic arthritis

Overview

Septic arthritis is a an important consideration in adults presenting with monoarticular arthritis in 80 to 90% of patients. It can involve any joint, but most commonly involves knee > hip > shoulder > ankle. Other joints such as sacroiliac joint, sternoclacicular or costoclavicular joints may be involved in patient with history of intravenous drug abuse (IVDA), penetrating trauma, animal or human bites and local steroid injections.

Classification

Classification Based on the Etiology

Septic arthritis can be classified into 2 types based on the etiology:

• Gonococcal septic arthritis
• Non gonococcal septic arthritis

Classification Based on the Presentation

Septic arthritis can be classified into 2 types based on the involvement of number of joints involved during presentation:

• Mono articular septic arthritis (MASA)
  • Most common type of presentation
• Poly articular septic arthritis (PASA)
  • Less common presentation (~15% of total septic arthritis cases)
  • commonly caused by staphylococcus aureus and other non gonococcal infections such as streptococci and gram negative bacteria.

Causes

Septic arthritis is due to intra articular seeding of living microorganisms. The most common etiological agent of all nongonococcal causes of septic arthritis in the United States is Staphylococcus aureus. Gram-negative bacilli account for 10 to 20% of septic arthritis causes. ~10% of patients with nongonococcal septic arthritis are due to polymicrobial cause of infections. Anaerobes are also can cause septic arthritis in few cases.

Most common cause of septic arthritis in children age < 2 years are Haemophilus influenzae (in immunized children), Staph. aureus, group A Streptococcal infections and Kingella kingae.

Causes of infection include

1. Hematogenous dissemination
2. Post operative wound infection such as after arthroscopic procedures
3. Intra articular steriod injections
4. Diagnostic punctures
5. Open traumatc injury to the joint

Common organisms

• Staphylococcus aureus
• Streptococcal pyogenous
• Streptococcal pneumonia
• Escherichia coli
• Staphylococcus epidermidis
• Borrelia burgdorferi

Pathophysiology

Presence of extreme vasularity and absence of limiting of basement membrane, promotes the easy access of infections into the synovial space.

Hematogenous spread: Septic arthritis most commonly develop as a result of hematogenous spreading bacteria into the vascular synovial membrane.

Direct inoculation: Direct inoculation of microorganisms may occur during joint surgery, particularly in association with knee and hip arthroplasties.

Contiguous spread: Bone infection can spread by breaking through its outer cortex and then into the intracapsular region that lead to joint infection. This kind of spread is more common in children as the small capillaries can cross the epiphyseal growth plate and permit extension of infection into the epiphysis and joint space.

Risk Factors

Common Risk Factors

Common risk factors that predespose septic arthritis are as follows:

• Age >60 years
• Recent history of bacteremia
• Degenerative joint diseases such as rheumatoid arthritis ( Prosthetic joint > Rheumatoid arthritis > Osteoarthritis)
• Corticosteroid therapy
• Diabetes mellitus
• Leukemia
• Cirrhosis
• Granulomatous diseases
• Hypogammaglobulinemia
• Intravenous substance abuse
• Chronic kidney disease
• Cytotoxic chemotherapy

Microorganism	Associated risk factors
Staphylococcus aureus	Rheumatioid arthritis Diabetes mellitus HIV patients
Streptococcus pyogenes Streptococcal pneumonia	Autoimmune diseases Chronic skin infections Trauma
Groups B Streptococcal infection	Immunocompromised patients Diabetes mellitus Malignancy Severe genitourinary or gastrointestinal infections
Neisseria gonorrhoeae	Complement deficiency Systemic lupus erythematosus Male homosexuality low socioeconomic status
Gram-negative bacilli Most common gram-negative organisms are Pseudomonas aeruginosa and Escherichia coli.	History of intravenous drug abuse Extremes of age Immunocompromised patients
Haemophilus influenzae	Unimmunized children
Anaerobes	Diabetes mellitus Patients with prosthetic joints

• Recent history of joint aspiration or local corticosteroid joint injection.
• History of Rhematoid arthritis
• History of diabetes mellitus

Epidemiology and Demographics

Females are more at risk in getting gonorrheal arthritis and four fold risk compared to men, due to the asymptomatic nature of gonorrheal infection in women.

In children hip is most commonly involved.

PASA is more common in men when compared to women.

Diagnosis

Appearance of the Patient

Patient with septic arthritis usually appears toxic and with joint pain that involved

Vital Signs

• Low grade fever
• Hyperthermia over the joint involved
• Tachycardia
• Tachypnea

Skin

• Warm over the joint

• Erythema over the around the joint that involved

Extremities

Most commonly involves knee > hip > shoulder > ankle. Other joints such as sacroiliac joint, sternoclacicular or costoclavicular joints may be involved in patient with history of intravenous drug abuse (IVDA), penetrating trauma, animal or human bites and local steroid injections.

• Swelling of the joint that involved
• Decreased range of motion

Laboratory Tests

Septic arthritis should not be excluded even though the patient have low fever and normal WBC.

Diagnosis of septic arthritis depends maily on the arthrocentesis and isolation of the pathogen from aspirated joint fluid.

Prognosis

Prognosis of septic arthritis depends on several factors.

Poor prognostic factors include age >50 years, history of rheumatoid arthritis as an underlying disease, staph. aureus is the causative agent.