In the JournalsPerspective

Higher suggested cut-off values for PJI identified among obese patients

Higher suggested cut-off values for periprosthetic joint infection diagnosis were identified among obese patients who underwent revision total knee arthroplasty compared with patients who were not obese, according to study results.

Researchers collected body mass index, serum inflammatory markers and synovial fluid for 102 patients who underwent revision total knee arthroplasty (TKA) and analyzed for the highest area under the curve. Patients were classified as infected or non-infected and obese or non-obese and placed into four groups based on their classifications.

No differences in serum C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) or synovial values were observed between patients who were obese and non-obese, according to the researchers.

When using receiver operating characteristic curves, the researchers found a higher CRP cut-off value for diagnosing periprosthetic joint infection (PJI) in obese patients, as well as a smaller difference in ESR cut-off.

Compared with the traditional value, the suggested cut-off value for CRP performed better in every category among patients who were not obese with equal sensitivity. The suggested cut-off value achieved higher accuracy, specificity and positive predictive value among patients who were obese but demonstrated inferior sensitivity and negative predictive value.

According to the researchers, the suggested cut-off ESR values performed similarly to traditional ESR values, but with slight improvements in specificity.

Disclosure: See the study for a full list of all authors’ relevant financial disclosures.

Higher suggested cut-off values for periprosthetic joint infection diagnosis were identified among obese patients who underwent revision total knee arthroplasty compared with patients who were not obese, according to study results.

Researchers collected body mass index, serum inflammatory markers and synovial fluid for 102 patients who underwent revision total knee arthroplasty (TKA) and analyzed for the highest area under the curve. Patients were classified as infected or non-infected and obese or non-obese and placed into four groups based on their classifications.

No differences in serum C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) or synovial values were observed between patients who were obese and non-obese, according to the researchers.

When using receiver operating characteristic curves, the researchers found a higher CRP cut-off value for diagnosing periprosthetic joint infection (PJI) in obese patients, as well as a smaller difference in ESR cut-off.

Compared with the traditional value, the suggested cut-off value for CRP performed better in every category among patients who were not obese with equal sensitivity. The suggested cut-off value achieved higher accuracy, specificity and positive predictive value among patients who were obese but demonstrated inferior sensitivity and negative predictive value.

According to the researchers, the suggested cut-off ESR values performed similarly to traditional ESR values, but with slight improvements in specificity.

Disclosure: See the study for a full list of all authors’ relevant financial disclosures.

    Perspective
    Javad Parvizi

    Javad Parvizi

    These renowned investigators have performed a clinically relevant and important study. As they state, the diagnosis of periprosthetic joint infection (PJI) continues to pose a challenge to the medical community. C-reactive protein (CRP) is a serological marker that is used as part of a multi-prong approach for diagnosis of PJI. The values of the CRP is believed to be affected by numerous factors, including the presence of an inflammatory conditions such as rheumatoid arthritis, psoriasis and so on. These inflammatory conditions can elevate the level of CRP and other serological inflammatory markers considerably. Because of this concern, some clinicians rely less on these tests for diagnosis of PJI when a patient suffers from an inflammatory condition. What is interesting is that, in recent years, evidence is emerging to suggest that obesity is also a systemic inflammatory condition that does result in elevation of serological inflammatory markers such as CRP.

    The authors set out to investigate whether the values of CRP were higher in obese patients with PJI compared to non-obese patients. They did indeed find the latter to be the case. This study, as well as others, highlights the challenges of relying on a test, namely CRP, that is nonspecific for the diagnosis of PJI and was not designed for such a purpose. It compels us to continue to seek tests with better accuracy. The latter has been the driving factor behind efforts to identify molecular markers that hold better promise for diagnosis of PJI, one of the most devastating complications of joint arthroplasty.

    • Javad Parvizi, MD, FRCS
    • Vice Chairman of Research Rothman Institute at Thomas Jefferson University Hospital

    Disclosures: Parvizi has no relevant financial disclosures.