Comorbidity Index as a Risk Factor of Knee PJI Recurrence After Spacer Implantation

Background. Patient-related risk factors for periprosthetic joint infection (PJI) are currently investigated in detail. However, the influence of those factors on PJI recurrence and their confounding effect was not investigated. Identifying factors that influence PJI recurrence and establishing the role of each risk factor are important. The study aimed to analyze the comorbidity structure in patients with knee PJI and create, based on obtained data, a rating scale that allows predicting the probability of PJI recurrence after spacer implantation. Material and Methods. A single-center study was conducted based on retrospective data of 161 patients with PJI after primary total knee arthroplasty treated with staged reimplantation from January 2007 to January 2017. To clarify comorbidity structure and the most important risk factors, all patients were divided into two groups: patients with PJI recurrence after spacer implantation (group 1, n = 48) and patients who successfully passed spacer implantation (n = 113, group 2). Based on the obtained data, the frequency of comorbidities was analyzed. The list included 17 points that characterized the presence and severity of different comorbidities. Then, we conducted a logistic regression analysis to identify the significance of each factor and thresholds for the comorbidity index (CI) for the interpretation of the final score. With the presented scale, spacer implantation in the compared groups was analyzed. Results. The most significant comorbidities were anemia, chronic kidney disease, obesity, and cardiovascular pathology. The CI thresholds were calculated, which allowed interpretation of the obtained score. The distribution of patients by risk categories within each group was also analyzed, and differences between groups were determined. The CI value corresponding to the minimal risk of PJI recurrence was more common (p<0.0001) in group 1. Moreover, more than half of the patients with failed spacer implantation had a high risk of PJI recurrence according the CI value, and only 6.2% of patients who had successful treatment had CI high value (p<0.0001). Conclusion. The multivariate analysis of the presence and severity of concomitant pathologies enabled the development of a comorbidity scale with the calculation of an integral indicator (comorbidity index) and establishment of its threshold values. The proposed CI could be the basis for a combined relapse risk calculator and an algorithm for choosing the surgical treatment strategy in patients with knee PJI, which requires further investigation.