Septic Arthritis

HPI:
 
The patient is a 41-year-old female with past medical history of diabetes who presents with right knee pain.  Patient states that approximately 2 days ago, she noticed that her knee was red, swollen, and has gotten sore to the point that she cannot walk.  Patient denies ever having symptoms like this before.  Patient denies any prior surgeries or trauma to the joint.
 
Physical exam:
 
Swelling and erythema over the right knee.  The patient is unwilling to walk in the exam room stating that she cannot secondary to pain.  The knee is warm to the touch with no overlying induration.  The patient has limited active and passive range of motion secondary to pain.  Patient has 2+ distal pulses with intact sensation to light touch in all dermatomes.
 
Radiographs:
 
Normal knee
 
Laboratory data:
 
CBC:  WBC 24K, Platelets 224
Serum glucose:  197
ESR:  39
CRP: 7.2
Joint aspiration: cloudy fluid, WBC 62K, gram stain negative, glucose 94
 
Diagnosis and Plan:
 
Septic arthritis.  Patient was started on vancomycin and orthopedics was consulted.  She was admitted to the hospital and taken to the OR later that night for washout.
 
Discussion:
 
Location:
 
The most commonly affected joints in descending order are the knee (>50%), hip, shoulder, elbow, ankle, sternoclavicular joint.
 
Risk Factors:
 
Greater than 80 years of age, presence of prosthetic joint, overlying skin infection, diabetes, rheumatoid arthritis, cirrhosis, HIV, history of gout or pseudogout, endocarditis, recent bacteremia, IV drug user, recent joint surgery.
 
Organisms:
 
Most common in all patients is Staphylococcus aureus which accounts for greater that 50% of infections. 
 
There are some specific patients that have high rates of other organisms that we should be aware:
 

• Healthy, sexually active adolescents and young adults:  Neisseria gonorrhea
• Neonates: gram negative bacilli
• Infants and elderly: group B strep
• Sickle cell disease: Salmonella
• IV drug users: Pseudomonas aeruginosa
• Immunocompromised host: Candida/fungal

 
ER Work-up:
 

• Plain radiographs
• CBC, ESR, CRP
• Joint aspirate with cell count and differential, gram stain, glucose
• Blood cultures (50% positive, even without fever)

 
Differential:
 
An emergency physician is only as good as the differential that they consider, therefore, we should maintain the following on their differential: gout, pseudogout, reactive arthritis, rheumatoid arthritis, Lyme disease, gonococcal arthritis, traumatic arthritis, cellulitis, bursitis.
 
Treatment:
 
There are no good randomized controlled trials for antibiotic treatment of septic arthritis.  Current recommendations are based on the most likely organism.  If you lucky enough to have a positive Gram stain, then you should treat gram-positive smear with vancomycin and gram negative smear with a third generation cephalosporin such as ceftriaxone.  Other specialized considerations are:
 

• Pseudomonas aeruginosa – ceftazidime and aminoglycoside
• Negative gram stain and immunocompetent – vancomycin
• Negative gram stain and immunocompromised, traumatic, or IV drug users - vancomycin and third-generation cephalosporin

 
Finally, once confirmed, orthopedic service should be consulted as these joints will need washout in the operating room.
 
Pearls:
 

• The likelihood of septic arthritis decreases significantly if the patient is able to bear weight and has no pain on passive range of motion
• Serum WBC count has low sensitivity
• Only approximately 60% of patients will have fever
• Sensitivity of CRP and ESR are 92% and 98% respectively
• IV antibiotics and orthopedic consultation are standard of care