Prosthetic joint infections

[Clin Microbiol Rev 2014;27:302-45, Clin Infect Dis 2013;56:e1-25, Europ J Nuclear Med Molecular Imaging 2019;46:971-88]

Diagnosis:

- Infection can be confirmed if presence of at least one of the following [Bone Joint J 2021;103-B(1):18-25]:

• clinical features: sinus tract communicating with joint prosthesis or visualization of the prosthesis
• isolation of same organism from ≥ 2 cultures, or from 1 culture if virulent organism (e.g. S. aureus, β-hemolytic Strep, aerobic Gram negative bacilli), of intraoperative joint fluid or periprosthetic tissue
• gross purulence in joint space (leucocyte count >3000 cells/uL with > 80% PMNs)
• acute inflammation (≥ 5 PMNs in ≥ 5 HPF) or visible organisms on histological exam.

- Infection is likely if presence of at least one clinical feature or raised CRP plus one of the other findings [Bone Joint J 2021;103-B(1):18-25]:

• clinical features:  radiological signs of loosening within first 5 years after implantation, previous wound healing problems, history of recent fever or bacteremia, purulence around the prosthesis
• CRP > 10mg/L
• isolation of same organism from 1 culture of joint aspirate or intraoperative joint fluid or periprosthetic tissue
• purulence in joint space (leucocyte count >1500 cells/uL with > 65% PMNs)
• acute inflammation (≥ 5 PMNs in single HPF) or visible organisms on histological exam
• positive WBC scan.

- A diagnostic arthrocentesis should be done in all patients unless surgery is imminently planned and antimicrobials can be safely withheld prior to surgery. Synovial analysis should include:

• cell count and differential
• culture - aerobic and anaerobic. If immunosuppressed or chronic infection, also consider fungal/mycobacterial cultures
• crystal analysis.

- Asymptomatic pyuria or bacteriuria, in the absence of urinary tract infection, is not associated with development of prosthetic joint infection, therefore pre-operative screening of asymptomatic patients by urinalysis and/or urine culture, is NOT recommended.

- Preoperative swabs of sinus tracts are discouraged due to poor concordance with operative cultures.

- Blood cultures recommended if febrile or acute onset of symptoms.

- ESR, CRP - low sensitivity for diagnosis but if initially elevated, may be useful to monitor response.

- Imaging - Plain x-ray not useful for diagnosis of early infection but may identify loosening of prosthesis or osteolysis. Other imaging studies (bone scan, WBC scan, MRI, CT scan) should not be routinely used. Bone scan is sensitive for detecting failed implant but nonspecific for detecting infection. May remain abnormal for two years or more after implantation. Consider combined WBC scan and bone marrow scan to improve accuracy.

- Antimicrobial therapy should ideally be discontinued ≥ 2 weeks prior to joint revision surgery. Pre-operative antibiotic prophylaxis does not need to be deferred until after intraoperative cultures have been taken unless there is a high suspicion of infection and pre-op cultures are negative or not obtained.

Intraoperative:

- Gram stain of synovial fluid has poor sensitivity (< 26%). Use of intraoperative Gram stain to rule out prosthetic joint infection is NOT recommended.

- Histopathological exam of periprosthetic tissue can be a useful adjunct with good specificity, though sensitivity is limited.

- Cultures of periprosthetic tissue x 5-6 samples recommended; isolation of a virulent organism (e.g. S. aureus, β-hemolytic Strep, aerobic Gram negative bacilli) ) from 1 sample, or same organism from ≥ 2 samples, is considered diagnostic. Isolation of skin flora organisms (e.g. CoNS, Cutibacterium spp) from only one of several cultures should be interpreted with caution, and requires evaluation of other available evidence.

NB: Cultures should be sent for aerobic and anaerobic culture and kept for 14 days.

- Swab cultures have low sensitivity and should be avoided. Cultures of superficial wound or sinus tract exudate often contaminated from surrounding skin so should not be done.

- Tailor therapy to C&S results. If bacterial cultures negative, but patient septic/not improving, recommend empiric therapy, and discuss value of specialized bacterial, fungal and mycobacterial cultures with microbiologist.

- Polymicrobial infections may occur in up to 20% of cases.

Treatment options:

1. Debridement + replacement of liner and implant retention (DAIR) of prosthesis followed by prolonged systemic antibiotic therapy - option for patients with early postoperative (within 30 days) or acute hematogenous infection with symptoms for < 3 weeks, stable implant, bone and soft tissue in good condition (e.g. no sinus tract), and known susceptible organism.
2. One-stage exchange: removal of infected prosthesis and implantation of new prosthesis +/- antibiotic- impregnated cement in same surgery, followed by systemic antibiotic therapy. Option for patients with adequate remaining bone stock, satisfactory condition of soft tissue, no severe comorbidities, and absence of difficult to treat organism (MRSA, enterococci, Pseudomonas aeruginosa, fungal, mycobacterial).
3. Two-stage exchange: removal of infected prosthesis, placement of temporary antibiotic-impregnated cement spacer and administration of systemic antibiotic therapy, and reimplantation of new prosthesis 6-12 weeks later. Option for patients medically able to undergo multiple surgeries. Post re-implantation duration of antibiotic therapy:
   • until intraoperative cultures come back negative (as long as antibiotics were stopped ≥ 2 weeks prior to surgery), or
   • 6-12 weeks if positive intraoperative cultures.
4. Removal of prosthesis without replacement or arthrodesis followed by 4-6 weeks of systemic antibiotic therapy (rifampin is not necessary since all foreign material has been removed) in patients with serious comorbidities where repeat surgery not an option. In some cases of uncontrolled infection, amputation may be necessary. Give antimicrobial therapy for 24-48 hours after amputation, or for 4-6 weeks after if residual infected bone or soft tissue, e.g. prosthesis extends above level of amputation.
5. Long term antibiotic suppression in patients where surgery is contraindicated.