Predictive value of postoperative NLR, PLR and LMR for early periprosthetic joint infection after total joint arthroplasty: a pilot study

Background： The purpose of this study was to evaluate the predictive value of the postoperative neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR) and lymphocyte-to-monocyte ratio (LMR) for early periprosthetic joint infection (PJI). Methods : During the period from January 2008 to December 2016, 104 patients (26 early PJI cases and 78 non-PJI cases) who underwent total joint arthroplasty at the Department of Orthopedics in our hospital were enrolled in this study. All of the relevant clinical information and laboratory indexes were reviewed from our hospital follow-up system. The time when any abnormal symptoms or signs occurred, including fever, local swelling or redness around the surgical site between the 2nd and 4th weeks after surgery, was defined as the “suspect time”. We compared laboratory parameters, including NLR, PLR, LMR, erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), between the two groups. The trends of NLR, LMR, PLR, CRP and ESR were also reviewed after surgery. The predictive ability of these parameters at the suspect time for early PJI was evaluated by multivariate analysis and receiver operating characteristic (ROC) curve analysis. Results : NLR, PLR and LMR returned to preoperative levels within two weeks after surgery in the two groups. In the early PJI group, NLR and PLR were significantly increased during the incubation period of infection or infection, and LMR was significantly reduced, although 61.5% (16/26) of the patients had normal white blood cells. Interestingly, ESR and CRP were still relatively high two weeks after surgery, and the change in these two indexes was not obvious when infection occurred. NLR and PLR were significantly correlated with early PJI (Odds ratio (OR) N LR =88.36, OR PLR =1.12, P NLR =0.005, P PLR =0.01), and NLR had great predictive ability for early PJI, with a cut-off value of 2.77 (sensitivity=84.6%, specificity=89.7%, 95% CI=0.86-0.97) . Conclusions: ESR and CRP are not sensitive for the diagnosis of early PJI due to their persistently high levels after arthroplasty. The postoperative NLR at the suspected time has a great ability to predict early PJI, and more attention should be paid to it.