Septic Arthritis

Question 1

Define septic arthritis.

Answer 1

infection within the joint capsule (typically a mono arthritis although 9% are polyarticular)

Question 2

Which are the most likely joints to be affected by septic arthritis in children and adults?

Answer 2

adults: knee
children: hip

shoulder in any case is indicative of serious underlying disease

Question 3

What elements of a pt. history increase the likelihood of septic arthritis

Answer 3

trauma
recent infection
overseas travel
injection drug use

Question 4

What are the clinical signs of acute septic arthritis?

Answer 4

abrupt onset
intense pain
swelling and erythema of the affected joint
restricted movement
signs of systemic infection eg. low-grade fever

Question 5

How does infection get within the joint capsule? (3)

Answer 5

hematogenous spread from distant infection
direct seeding from local trauma, surgery or injection
extension of infection in contiguous bone or soft tissues

Question 6

List some risk factors for septic arthritis.

Answer 6

age greater than 80 y
DM
Rheumatoid arthritis
prostetic joint
recent joint surgery
skin infection, cutaneous ulcers
IV drug abuse, alcoholism
previous intra-articular corticosteroid injection

Question 7

What are the most common organisms of septic arthritis?

Answer 7

gram positive (90%+)
gram-negative organisms (in high risk patients)
polymicrobial infections, anaerobes (IV drug use)

Staph aureus, Strep spp, TB, H. flu b, other gram negative, anaerobes and N. gonorrhoeae

Question 8

What are the two presentations of gonococcal arthritis?

Answer 8

(risk factors include pregnancy and menstruation)

gonococcal reactive arthritis: mulitple joints, wrist/hands, skin rash, rare to find organism in synovial fluid
gonococcal septic arthritis: monoarthrits, knees primarily, gonococci found in synovial fluid and blood, skin lesions may be present over the affected joint

Question 9

Why is quick diagnosis so important with septic arthritis?

Answer 9

infection can damage the affected joint very quickly and damage can be long lasting

Question 10

How is septic arthritis diagnosed?

Answer 10

prompt arthrocentesis with gram stain and culture

looking for turbid, yellow or viscous fluid, cell counts 50,000 to 15000 WBC >90% WBC; decreased WBC in ½ cases

other tests: blood culture (50% +), urine culture, throat swab, skin lesion swab, serologic tests for lyme, syphilis and brucellosis, G/C testing

CBC, acute phase reactants, biochemical analysis, RF, ANA

Question 11

What would imaging tell you about septic arthritis?

Answer 11

plain films show fluid int eh joint, joint space widening or soft tissue swelling

U/S can show effusion, MRI useful for deep joints; radioisotope scans not highly specific

Question 12

When should cultures be sent for unusual organisms?

Answer 12

hx. of TB exposure
hx. of trauma or animal bite
travel/living: fungal or lyme endemic
presence of immune suppression
mono arthritis that is refractor to conventional therapy

Question 13

What is the appropriate treatment of septic arthritis ?

Answer 13

empiric antibiotic treatment should be started as soon as joint aspiration samples have been taken

effective drainage is essential and repeat aspiration or surgical drainage may be required. maintain joint in optimal functional position

Question 14

What should empiric abx for septic arthritis cover?

Answer 14

S. aureus (vancomycin
expanded coverage for those at risk: gram neg or anaerobes (cefepime)

IV for first 2 weeks, 4 weeks treatment total (2 weeks for GC + chym. coverage)
poorer prognosis with older age, pre-existing joint disease and presence of synthetic material within the joint