A nomogram for predicting the need for sciatic nerve block after total knee arthroplasty

Purpose: Sciatic nerve block (SNB) is commonly performed in combination with femoral nerve block (FNB) for postoperative analgesia following total knee arthroplasty (TKA). Despite the fact that 10–20 % of TKA patients require SNB for postoperative posterior knee pain, there are no existing studies that suggest a model to predict the need for SNB. The aim of our study was to develop a prediction tool to measure the likelihood of patients undergoing TKA surgery requiring a postoperative SNB. Methods: With institutional review board approval, we obtained data from the electronic medical record of patients who underwent TKA at the Cleveland Clinic. A multivariable logistic regression was used to estimate the probability of requiring a postoperative SNB. Clinicians selected potential predictors to create a model, and the potential nonlinear association between continuous predictors and SNB was assessed using the restricted cubic spline model. Results: In total 6279 TKA cases involving 2329 patients with complete datasets were used for building the prediction model, including 276 (12 %) patients who received a postoperative SNB and 2053 (88 %) patients who did not. The estimated C statistic of the prediction model was 0.64. The nomogram is used by first locating the patient position on each predictor variable scale, which has corresponding prognostic points. The cut-off of 11.6 % jointly maximizes the sensitivity and specificity. Conclusion: This is the first study to be published on SNB prediction after TKA. Our nomogram may prove to be a useful tool for guiding physicians in terms of their decisions regarding SNB.