Abstract
A “two-stage exchange” remains the gold standard for treatment of the infected THA in North America. Although there is interest in “one-stage exchange” this technique is predicated on the use of fixation of the revision implants with antibiotic loaded cement, which is not as popular in North America.
Diagnosis is critical and in general consists of a screening serum ESR and CRP followed by selective aspiration if the above are abnormal and/or if the clinical history is suspicious. The aspirated fluid is sent for a synovial fluid WBC (cut-off approximately 3,000 WBC/μL), differential (cut-off 80% PMN) and culture.
The basic tenets of treatment include:
Thorough debridement of all infected appearing cement and all foreign material
Placement of an interval antibiotic loaded spacer (note that the addition of antibiotics to bone cement is NOT FDA approved)
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4–6 g of antibiotics per pkg of cement; typically vancomycin + tobramycin
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Higher viscosity cement may be associated with higher elution
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Higher elution with combination of antibiotics
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Antibiotic spacers can be “articulating” or “static”. Potential advantages of an articulating spacer include greater patient comfort and an easier approach at the second stage exchange as leg length and soft tissue tension is maintained. However, these spacers are oftentimes more costly and can dislocate. May not be appropriate in cases where there is severe bone loss that cannot support partial weight bearing or if the abductors are compromised (higher risk of dislocation).
The first stage is followed by approximately 6 weeks of organism specific IV antibiotics. An interdisciplinary approach with an infectious disease specialist, internal medicine and a nutritionist optimises outcomes.
Our protocol then includes weekly ESR and CRP to monitor their trend. These labs are re-checked two weeks after cessation of antibiotics to ensure the trend has not changed. We have found that while the ESR and CRP are significantly lower than prior to the 1st stage, they often times DO NOT normalise and there is no specific cut-off value that predicts persistent infection. An intra-operative aspiration for synovial fluid WBC count and differential is obtained intra-operatively (cut-off values of approximately 3,000 WBC/μl and 80% PMN) and are the best tests to identify persistent infection.
