Periprosthetic Joint Infection

Question 1

What is the incidence of PJI in TKA and THA?

Answer 1

1% to 2% following primary TKA
6% following revision TKA
0.3% to 1.3% following primary total hip arthroplasty (THA)
3% following revision THA

Question 2

What lab values are a/w PJI?

Answer 2

> 10,700 cells/ul less than 4 weeks from surgery

>1150 cells/ul >4 weeks from surgery

Question 3

What is the sensitivity and specificity of an intra-operative frozen section for PJI?

Answer 3

sensitivity 85% and specificity 90% to 95%

>5 PMNs/hpf is probable for infection

Question 4

What are the advantages of an articulating spacer versus a block spacer?

Answer 4

1) decreased reimplantation exposure time
2) better maintenance of joint space and motion
3) decreased quad shortening
4) better patient satisfaction
Both spacer types have equivalent functional outcomes and rate of infection recurrence

Question 5

Increasing the porosity of a cement spacer for an infected total knee arthroplasty leads to?

Answer 5

Increased elution of abx; Palacos has greater elution than Simplex

Question 6

What are the MSIS criteria for PJI?

Answer 6

1) A sinus tract communicating with the prosthesis
2) A pathogen is isolated by culture from two separate tissue or fluid samples obtained from the affected prosthetic joint
(3) Four of the following six criteria exist:
(a) Elevated ESR and CRP (ESR > 30 mm/hour; CRP > 10 mg/L)
(b) Elevated synovial fluid WBC count (> 3000 cells/μL)
(c) Elevated synovial fluid neutrophil percentage (> 65%)
(d) Presence of purulence in the affected joint (no longer)
(e) Isolation of a microorganism in one periprosthetic tissue or fluid culture
(f) > 5 neutrophils per high-powered field in 5 high-power fields observed from histologic analysis of periprosthetic tissue at ×400 magnification