Periprosthetic Joint Infection: There’s an App for That!

    How do you determine if your patient with a painful knee or hip following total joint arthroplasty has an infected prosthesis? You probably order any of a number of tests are currently used to evaluate the possibility of a periprosthetic joint infection (PJI). The problem is no single test is 100% sensitive or 100% specific in diagnosing PJI.

    Dr. Carlo Luca Romanò and his colleagues in Milan, Italy, took on the challenge of PJI diagnosis and in 2009, published their Combined Diagnostic Tool, which that uses the relative contributions of multiple diagnostic tests – including ESR, CRP, X-ray, and histology – to arrive at a PJI diagnosis.

    Diagnostic App in Development

    Now, they are working with a German software developer on an app designed to automatically calculate a patient’s probability of having a PJI.

    “Diagnosis of periprosthetic joint infection is often difficult due to conflicting results from different tests,” Dr. Romanò said. “Until now an empiric evaluation of the different ‘weight’ of each test is performed by every single surgeon on a rather subjective base.”

    “With the Combined Diagnostic Tool (CDT) App we would like to provide a simple tool on every smartphone that, based on each the sensitivity and specificity of each test, will be able to calculate in real time the chance of pathology in any given patient.” 

    According to Dr. Romanò, the algorithm on which the app is based has been previously validated in a clinical study on PJI. The next step, he said, is to unveil the first version of the app, with a pre-final graphical interface, which he and his team hope will occur at the Musculoskeletal Infection Society meeting in Philadelphia, Pennsylvania, in August 2013.

    Dr. Romanò says the strengths of the app are that it will be:

    • Easy to use
    • Available at no cost to the user
    • Repeatable and allow for comparable results across surgeons and centers
    • Based on data in the literature
    • Periodically updated

    He acknowledged that surgeons may be resistant because of the novelty of the approach and the possibility that the app could be seen as more of a “gadget” than a helpful diagnostic tool. Despite that, “we are really confident that the strengths of this innovation largely exceed possible limitations,” Dr. Romanò said.

    Risk Factors Before Surgery

    Whether a patient has developed a PJI following total joint arthroplasty is only part of the story. What about before the procedure? What can be done to prevent a PJI?

    Dr. Romanò and his colleagues are looking at that as well.

    For the past 5 years, Dr. Romanò’s group has been collecting data on risk factors for PJI. Independently, Javad Parvizi, MD, and his colleagues at The Rothman Institute in Philadelphia, Pennsylvania, have been studying the same data. The groups are pooling their research and collaborating on an app that will calculate a patient’s risk for infection after joint replacement.

    “This app will be based on an original nomogram and will include all known risk factors for developing post-surgical infections,” Dr. Romanò said. “We are going to validate it in the clinical setting before release,” which he estimates will occur in about 6 months.

    Dr. Romanò said that both apps are designed to replace largely empiric evaluations, anchoring the output of the clinical investigations to scientific data available from the literature according to a transparent algorithm.

    “Clinical scoring systems now rely on points and values that are often arbitrarily weighted, insufficiently validated, and approximate,” he said.

    “For example, a diabetic patient is scored as a host Type B according to Cierny-Mader or McPherson’s classifications, exactly as a patient with renal insufficiency. However, if we read the literature, the odds ratio for a periprosthetic infection is 4 to 6 for a diabetic patient and up to 16 for a patient with renal failure.

    ”Still more complex and unreliable is the evaluation of a patient with two or more co-morbidities, Dr. Romanò noted.

    He said the apps under development are aimed at giving more precise and scientifically based output to the following questions:

    • How much risk of developing an infection does this patient have?
    • How much can the patient reduce the risk of infection if he/she corrects this risk factor?

    Similarly, the CDT app is intended to answer these questions:

    • What is the chance that a patient with a painful prosthesis and these positive/negative tests as a PJI
    • How much will a certain test improve the ability to diagnose a PJI?
    • Is a certain test cost-effective?

    Although the risk factor app will be primarily released for professionals, Dr. Romanò said there can be a positive interaction among the surgeon, the patient, and the app in terms of making patients more conscious of their risk factors and the possibility for improving their general health status before undergoing elective surgery. This makes the patient “a more informed part of the decision process,” Dr. Romanò said.