Inefficient urethral milking secondary to urethral dysfunction as an additional risk factor for incontinence after radical prostatectomy.

PURPOSE: Continence after radical prostatectomy is thought to depend completely on the striated urethral sphincter. However, some patients complain only of occasional post-void dribbling. Therefore, we determined whether urethral dysfunction may be another cause of incontinence.
MATERIALS AND METHODS: The sensory threshold of electric stimulation was measured by double ring electrodes in the membranous urethra and 2.5 cm. distal in 29 men before and in 29 after radical retropubic prostatectomy. In addition, voiding cystourethrography was performed in 66 patients before and in 49 after surgery to determine complete post-void urethral emptying or milking.
RESULTS: The mean sensory threshold of the membranous urethra was 15 +/- 3 mA. preoperatively versus 38 +/- 17 postoperatively (p <0.0001). The sensory threshold 2.5 cm. further distal was 12 +/- 5 mA. before and 10 +/- 4 after radical prostatectomy, which was not statistically significant. Postoperatively in completely continent patients and in those with dribbling the mean threshold was 32 +/- 12 and 43 +/- 18 mA. in the membranous urethra (p = 0.09), and 11 +/- 4 and 9 +/- 4 mA. in the bulbar urethra, respectively, which was not statistically significant. Of the 66 patients 36 (55%) showed post-void urethral milking before surgery but only 8 of 49 (16%) showed it postoperatively (chi-square test p <0.0001), including 7 who were completely continent and 1 who complained of occasional post-void dribbling.
CONCLUSIONS: After radical prostatectomy sensitivity of the membranous but not of the bulbar urethra is affected, correlating with postoperative continence. In addition, post-void dribbling seems to be associated with the loss of urethral milking. We conclude that preserving urethral function is another important continence factor after radical prostatectomy.