Nomogram for Poor 3-Month Functional Recovery After Total Knee Arthroplasty Using Cartilage Damage and Synovial Fluid Biomarkers: Development and Internal Evaluation

Introduction: This study aimed to develop and internally evaluate a multidimensional nomogram incorporating intraoperative cartilage damage and perioperative synovial fluid biomarkers to estimate the probability of poor functional recovery at 3 months after total knee arthroplasty (TKA). Materials: A retrospective cohort of 360 patients undergoing primary unilateral TKA was included in this study. Methods: IL-6, TNF-α, COMP, and total BDNF were measured in perioperative synovial fluid specimens collected after induction of anesthesia and before skin incision and were assessed together with intraoperative Outerbridge cartilage damage grade and routinely available demographic and clinical variables. The primary outcome was functional recovery at 3 months, defined by the WOMAC function subscale. Least Absolute Shrinkage and Selection Operator (LASSO) regression was used for predictor selection, and a nomogram was developed using multivariable logistic regression. Model performance was evaluated using area under the curve (AUC), calibration, and decision curve analysis (DCA). Results: Six predictors were retained in the final model: age, body mass index (BMI), preoperative WOMAC function score, Outerbridge grade, log(IL-6), and log(COMP). The nomogram showed promising discrimination in the held-out internal test set (AUC = 0.861, 95% CI: 0.782–0.934) and acceptable calibration (Hosmer–Lemeshow test, P = 0.45). Bootstrap optimism correction yielded a bias-corrected AUC of 0.842. DCA suggested potential net benefit across the evaluated threshold probabilities. Conclusion: The nomogram integrates clinical characteristics, intraoperative cartilage damage, and perioperative synovial fluid biomarkers to estimate the probability of poor functional recovery at 3 months after TKA. It should be regarded as a development-stage perioperative prediction model that requires prospective external validation before any clinical application.