Prosthetic Joint Infections

Question 1

What are the common pathogens causing PJI?

Answer 1

coagulase-negative Staphylococcus (CoNS), and Staph aureus

Question 2

how does the patient present in acute PJI?

Answer 2

signs of joint inflammation + fever (septic arthritis)

Question 3

how does the patient present in chronic PJI?

Answer 3

loosening of prosthesis (on XR) + sinus tracts

Question 4

what is considered early PJI?

Answer 4

within first 3 months, usually acquired during implantation

Question 5

what is consider delayed PJI?

Answer 5

during initial 3 – 24 months, also acquired during implantation but usually caused by less virulent organisms

Question 6

what is considered late PJI?

Answer 6

greater than 24 months post-op, typically acquired from haematogenous seeding

Question 7

What are the synovial fluid studies WBCs cut offs in PJI?

Answer 7

• Knee : WBC > 1.7 x 10^3 (> 65% PMN);

- Hip : WBC > 4.2x 10^3 (> 80% PMN)

Question 8

How is PJI diagnosed?

Answer 8

NEJM 2009 diagnostic criteria: ≥ 1 of

1) Sinus tract communicating w/ prosthesis
2) Gross purulence in joint space

3) Periprosthetic tissue specimen:
- Acute inflammation on histopathology
- Isolation of same microorganism from ≥2 c/s OR same in substantial amounts

4) Joint aspirate (synovial fluid):
- Isolation of same microorganism from ≥2 c/s OR same in substantial amounts
- Note: joint aspiration should be as aseptic as possible (i.e. perform in OT), and try to hold off abx before doing c/s, in order to increase yield

Question 9

How is PJI treated?

Answer 9

Medical

• C/s directed IV abx, ≥ 6/52
• Consider adding rifampicin in cases of rifampicin susceptible Staph, as biofilm often makes abx ineffective without Sx removal of the film
• LT (lifelong) suppressive abx may be considered in pts who undergo debridement but are not candidates for removal of prosthesis, e.g. spine operations, AAA graft

Surgical

• Debridement of wound
• Replacement arthroplasty – best outcome
• KIV arthrodesis may be required if: poor skin coverage, involvement of resistant organisms, or recurrent infection