Internal and External Validation of a 90-Day Percentage Erection Fullness Score Model Predicting Potency Recovery Following Robot-assisted Radical Prostatectomy

Abstract

Background: We previously reported a new post-radical prostatectomy (RP) prediction model for men with normal baseline erectile function (EF) using 90-d postoperative erection fullness to identify men who might benefit from early EF rehabilitation.

Objective: To prospectively internally and externally validate the use of this risk assessment model in predicting 1- and 2-yr post-RP EF recovery.

Design, setting, and participants: We randomly assigned 297 patients with a preoperative International Index of Erectile Function 5 score of 22-25 undergoing robot-assisted RP by a single surgeon to a training set and internal validation set at a ratio of 2:1. A prospective external validation set included 91 patients treated by five high-volume surgeons.

Outcome measurements and statistical analysis: Potency was defined as erections sufficient for intercourse. To predict 1- and 2-yr potency recovery, logistic regression models were developed in the training set based on 90-d erection fullness of 0-24% or 25-100%. The resultant models were applied to the internal and external validation sets to calculate risk scores for 1- and 2-yr potency for each patient. Predictive validity was assessed using receiver operating characteristic (ROC) curves.

Results and limitations: Percentage erection fullness was an independent predictor of 1- and 2-yr potency recovery in all data sets. Internal validation confirmed strong reliability in predicting 2-yr potency outcomes (area under the ROC curve [AUC] 0.87) and external validation illustrated similar reliability in predicting 1-yr potency outcomes (AUC 0.80). In the external validation, the model predicted a mean 1-yr potency recovery rate of 39.7% (standard deviation 3.2%), compared to the actual rate of 36.26%. Limitations include the short follow-up for this cohort.

Conclusions: We present internal and external validation of a 90-d percentage erection fullness score, confirming that this metric is a robust predictor of post-RP EF recovery.

Patient summary: Percentage erection fullness at 3 mo after radical prostatectomy discriminates patients with a low or a high probability of recovery of erectile function (EF), which can facilitate identification of a need for early EF rehabilitation.

Keywords: Erectile function; Erections; Fullness; Potency; Radical prostatectomy; Validation.