Abstract: Objective To assess the frailty status of older patients undergoing joint replacement surgery using the fatigue, resistance, ambulation, illnesses & loss of weight(FRAIL)scale. It further explored the impact of preoperative frailty on postoperative pressure injury and evaluated the effectiveness of combining FRAIL scores with common laboratory indicators in predicting postoperative pressure injury risk. Methods This cross-sectional study included 348 patients aged 60 years and older who were admitted to the Department of Orthopedics, Qilu Hospital of Shandong University, for joint replacement surgery between May 2021 and June 2023. Patients were divided into a training set(n=256)and avalidation set(n=92)based on admission time. The FRAIL scale was used to assess preoperative frailty, and the patients were divided into three groups: non-frail(0 points), pre-frail(1-2 points), and frail(3-5 points)groups. The Braden scale was used to assess pressure injury risk. Data on admission diagnoses, surgical procedures, and preoperative biochemical indicators were collected using the hospitals medical record management system. Univariate Logistic regression and least absolute shrinkage and selection operator(LASSO)regression were used to screen important predictive variables, and a multivariate Logistic regression model was constructed. A nomogram was constructed to visualise the model. The goodness-of-fit, calibration, and predictive ability of the model were evaluated using the Hosmer-Lemeshow test, receiver operating characteristic(ROC)curve, and area under the curve(AUC). Decision curve analysis(DCA)was employed to assess clinical utility. The Bootstrap method was used for internal validation and external validation was performed using the validation set. Subgroup analysis was performed based on age and surgical procedures. Results Among the 348 patients, 78 were non-frail, 204 were pre-frail, and 66 were frail. FRAIL score, neutrophils, ischaemia-modified albumin(IMA), and potassium ion concentration were independent predictors of postoperative pressure injury(P<0.05). For each 1-point increase in the FRAIL score, the risk of postoperative pressure injury increased by 1.719-fold(OR=1.719, 95%CI: 1.171-2.524, P=0.006), the OR for neutrophils was 1.222(95%CI:1.028-1.451, P=0.023), the OR for IMA was 1.117(95%CI: 1.051-1.187, P<0.001), and the OR for potassium ion concentration was 3.848(95%CI: 1.090-13.589, P=0.036). The Hosmer-Lemeshow test indicated good model fit(P=0.08), and the calibration curve showed good agreement. The AUC in the internal validation was 0.825, with a sensitivity of 0.889 and a specificity of 0.681; the AUC in the external validation was 0.834, with a sensitivity of 0.870 and a specificity of 0.681. DCA showed that using the prediction model resulted in higher net benefit within a probability range from 0.05 to 0.45. Subgroup analysis revealed that the FRAIL score had significant predictive value in patients aged 60-70 years and those undergoing unicompartmental knee arthroplasty. Conclusion Preoperative frailty is highly prevalent in older patients undergoing joint replacement surgery and is an independent risk factor for postoperative pressure injury. The prediction model combining FRAIL scores with common laboratory indicators showed good calibration and high predictive ability for changes in postoperative pressure injury risk, providing valuable reference for clinical decision making.

Key words: Orthopedice, Frailty, Older patients, Joint arthroplasty, Pressure injury