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    Management of the Infected Total Hip Arthroplasty

    Dr. Gwo-Chin Lee discusses the current options for diagnosing and treating a patient with an infected total hip replacement.

    Infection of a total hip arthroplasty (THA) is a catastrophic complication that causes significant morbidity and mortality. It is also very costly to treat.

    Speaking at ICJR’s annual Winter Hip & Knee Course, Gwo-Chin Lee, MD, reviewed the keys to successful management of an infected THA, including a systematic approach to accurate diagnosis and appropriate and timely treatment.

    Diagnosis

    In a consensus document from 2011, a workgroup of the Musculoskeletal Infection Society defined periprosthetic joint infection (PJI) as follows:

    Major criteria:

    • A sinus tract communicating with the prosthesis

    OR

    • Positive cultures from at least 2 sites surrounding the prosthesis
    • Minor criteria – 4 out of 6 needed for a diagnosis of infection:
    • Elevated erythrocyte sedimentation rate (ESR) /elevated C-reactive protein (CRP) level
    • Elevated synovial white blood cell (WBC) count
    • Presence of purulence in affected joint
    • Positive culture from 1 site surrounding the prosthesis
    • Greater than 5 neutrophils per HPS (400x magnification) in frozen section

    This definition reflects the tools that are the cornerstone for diagnosing PJI: ESR, CRP, synovial WBC, culture and sensitivity, intraoperative frozen section, and imaging studies. Culture and sensitivity testing, Dr. Lee said, are most important for determining whether an infection is treatable. In addition, synovial enzymes and biomarkers are newer tests being used to diagnose a PJI.

    Dr. Lee said that any patient with a painful joint arthroplasty should have ESR and CRP tests done, and if abnormal, an aspiration will be needed for further work-up. Joint aspiration off antibiotics is still the most efficient way to diagnose PJI, but orthopaedic surgeons should beware of false positive and false negative results.

    The synovial WBC count can vary with duration since surgery, but in general, 12,800 WBC/µL within 6 weeks post-THA is considered normal. In the chronically infected hip. a count above 3000 WBC/ µL is considered infected. In the acute setting, a CRP greater than 93 mg/L is indicative of acute infection.

    Recent advances have been made to improve yield of testing for the infecting microorganism. Dr. Lee discussed the benefits of two such advances, polymerase chain reaction (PCR) and sonication of an extracted prosthesis:

    • PCR has been shown to be a very sensitive tool to detect some of the very low virulence organisms.
    • Sonication has been shown to disrupt biofilm, thereby improving yield.
    • In patients who have previously been on antibiotics, sensitivity has been shown to be greatly increased with the use of sonication.
    • Sonication in combination with CRP and frozen histology has been shown to yield the maximum sensitivity and specificity.

    Treatment

    Although not all infected THAs are the same, Dr. Lee said the treatment principles do not change:

    • Accurate diagnosis with the organism identified
    • Patient staging
    • Surgical debridement
    • Local antibiotic delivery
    • Staged surgical reconstruction

    The success of irrigation and debridement and prosthesis retention decreases with time, and one study showed 8 of 13 procedures were successful within 28 days of initial THA. Studies also show that the type of organism does not have an effect on the success rate of irrigation and debridement procedures. At this time, it does not seem possible to determine the optimal conditions that would make prosthesis retention successful, as opposed to an exchange procedure.

    The surgical technique in the treatment of infected THA includes aggressive debridement in which all non-viable tissue, including bone, is removed. Dr. Lee emphasized the importance of using an extensile approach to achieve complete visibility of the joint.

    During the extraction procedure, be sure to take multiple tissue cultures. Tissue cultures have been shown to yield better results than swabs, and taking an odd number of cultures prevents a “tie” between culture results.

    The use antibiotics in the cement is important, with powder antibiotics preferred over liquids. Make sure to achieve a high dose of antibiotic in the joint and surrounding tissues to eradicate infection.

    The use of spacers is the standard of care today for two-stage re-implantation for infected THA. The use of spacers is important in maintaining limb length, and articulating spacers improve patient mobility. Spacers help with local delivery of antibiotics and makes for an easier re-implantation procedure.

    The possible complications of spacers include dislocation, periprosthetic fracture, and persistent infection. The size and length options for spacers are limited, and one option for the use of a smaller stem in a spacious femoral canal has been to add a batch of cement to the proximal canal to increase rotational stability.

    In the reconstruction phase, after the infection has been eradicated, the surgeon must ask “what is lost” and consider bone loss, pelvic discontinuity, and abductor deficiency. All must be properly addressed during the re-implantation procedure.

    Historically, by applying the standard of care principles, 90% infection control can be achieved at 10 to 15 years of follow-up. But, Dr. Lee said, more current research suggests that the aggregated success rates may be lower, and in the ideal patient may yield success rates of approximately 80%.

    Newer initiatives such as implants that deliver antibiotics may provide some protection against infection, but cost becomes a factor. The use of molecular genetic detection of infection such as IL-6 and procalcitonin combined with CRP and leukocytes may help determine whether failures truly are due to infections or if they are aseptic.

    Dr. Lee said US-based surgeons may also want to rethink their standard of care regarding single- versus two-stage revision. Research from Europe suggests that single-stage revisions are quite successful.

    Dr. Lee’s presentation can be found here.