To explore the risk factors of persistent pain after primary hip replacement and to develop a model for predicting the risk.

According to the inclusion criteria (follow-up time≥six months and completed data of primary hip replace ment) and exclusion criteria(postoperative deep infection, combining pelvic fractures or other multiple joints injuries and diseases), 475 patients receiving primary hip arthroplasty in three hospitals from January 2017 to December 2019 were selected as the research subjects. The clinical data of patients was collected through the electronic medical record system, and the relevant literatures at home and abroad were retrieved and combined with clinical practice. The risk factors that might be associated with persistent pain after primary hip arthroplasty were selected for the study. Among them, 342 cases were selected, and related risk factor analysis and risk prediction model were established. Chi-square test was used for univariate analysis, and logistic analysis was used for multivariate analysis. The model was applied to clinical practice and the remaining 133 patients were evaluated. The results were analyzed using the area under the receiver operating characteristic (ROC) and area under the curve (AUC) to evaluate the differential validity and predictive power of the risk prediction model.

Multi-factor logistic analysis showed that age≥75 years, body mass index (BMI), history of diabetes, displacement type, intraoperative blood loss, lower limb vein thrombosis and postoperative C-reactive protein (CRP)≥10 mg/L were the independent risk factors for the development of continuous pain after total hip arthroplasty (P<0.05). The risk prediction model for these factors was as follows: y=e^Logit(P)/[1+ e^Logit(P))], in which y is the probability of persistent pain and e is an exponential function. After evaluating the patients with the model, the total accuracy of the model was 72.18%. The differential validity of the model was evaluated by ROC curve, and the results showed that the AUC was 0.863, the sensitivity was 92.86%, and the specificity was 62.86%.

The major influencing factors for persistent pain after primary total hip arthroplasty are the age≥75 years, BMI, diabetes mellitus, the displacement type, intraoperative blood loss, lower limb vein thrombosis and postoperative CRP≥10 mg/L. The risk prediction model constructed according to the above influencing factors has good discriminant ability for the risk prediction of persistent pain after primary hip replacement, but still needs further confirmation by prospective study.