Development of a clinical risk score for common peroneal nerve palsy after total knee arthroplasty using a Japanese nationwide database.

PURPOSE: This study aimed to develop a clinical risk score to stratify the risk of post-operative common peroneal nerve palsy (CPNP) following total knee arthroplasty (TKA), based on pre-operative factors.

METHODS

We conducted a retrospective cohort study of adult patients undergoing primary TKA using a Japanese nationwide database (from 2014 to 2024). The outcome was post-operative CPNP identified by International Classification of Diseases, Tenth Revision codes. Candidate predictors included 24 clinical and hospital-level variables. Least Absolute Shrinkage and Selection Operator (LASSO) regularization was applied for predictor selection. Multivariable logistic regression was used as the primary model, with penalized and Firth logistic models as sensitivity analyses. Model performance and internal validation were assessed using the area under the curve (AUC), calibration, and bootstrap resampling.

RESULTS

A total of 328,314 patients were eligible and CPNP occurred in 340 cases (0.10%). LASSO identified four predictors, and a 0-7 point risk score was developed: knee valgus deformity (3 points), knee contracture (2 points), low BMI < 18.5 (1 point), and spinal disorder (1 point). The observed risk rose from 0.09% (score 0) to 0.56% (score 3), and to 0.68% for scores ≥ 3, while categories of score ≥ 4 were sparsely populated. The risk score showed limited discrimination (AUC = 0.55) but favourable calibration (intercept = - 0.001, slope = 1.03).

CONCLUSION

We developed a clinical risk score for CPNP after TKA based on knee valgus deformity, knee contracture, low BMI, and spinal disorder. This score may support pre-operative risk assessment and informed consent in high-risk patients.