Post prostatectomy urinary incontinence is one of serious complications impairing patients’ quality of life after robot-assisted radical prostatectomy (RARP). Previous studies reported that several preoperative and postoperative factors and operating procedures were associated with urinary continence recovery after RARP (1). Preoperative membranous urethral length (MUL) is one of predicting factors for continence recovery after RARP. In contrast, little has been investigated about the clinical impacts on postoperative continence recovery of preserved MUL during surgery, even though urinary continence seems depending on residual rather than preoperative MUL because it is impossible to preserve the original membranous urethra after surgery. Herein, this is the first study to investigate surgical procedures of RARP including semiquantitative preserved MUL associating with urinary continence recovery by reviewing the operation video database.

A single-center retrospective study, approved by the institutional ethical committee, was conducted for patients with clinically localized prostate cancer receiving RARP by transperitoneal approach at our institution between March 2016 and October 2019. Baseline patient characteristics and perioperative and pathological outcomes were obtained from medical records. The day of continence recovery was registered when social continence was attained (a small 20-mL pad required daily) according to previous literature (2). Urethral balloon catheters were removed in all patients on postoperative day 6. All patients were instructed to perform pelvic floor exercises postoperatively. Reviewing the RARP video database was carried out independently by five researchers performing RARP and surgical skill outcomes including preservation of cavernous nerves of the penis, puboprostatic ligament and endopelvic fascia, residual MUL, bunching suture of the dorsal vein complex (DVC) and vesicourethral anastomotic leakage were collected. Preserved MUL was evaluated semiquantitatively on a video screen by counting how many 16-Fr urethral catheters (16/3 mm, every 0.5 piece) were equivalent to, during incision into urethra under the condition that the prostate was pulled to the head side by the 3rd arm (figrue1A).
Kaplan–Meier analysis with log-rank test was used to compare the urinary continence recovery rate, stratified by the residual MUL. Univariate and multivariate analysis were performed using the Cox proportional hazards model.

A total of 213 patients (median age 68 years) were included. The median console times, bleeding amount were 176min and 100ml respectively. Bilateral, unilateral and non-nerve-sparing operations were performed in 23, 45 and 145 patients, respectively, the bunching of DVC in 100 patients and bilateral, unilateral and non-fascia-sparing in 64, 33 and 116 patients respectively. The median residual MUL was 10.7 mm and the median postoperative follow-up period was 186 days (interquartile range: 7–349 days). 
In univariate analysis, a residual MUL of ≥16 mm, a body mass index of <23.1 kg/m2, and a resected prostate volume of <44.3 g were statistically significant factors that influenced urinary continence recovery and all of them also remained statistically significant in the multivariate analysis (HR 1.87, p = 0.022; HR 0.54, p = 0.001; and HR 0.57, p = 0.005, respectively) (Table 1). Kaplan–Meier curves were drawn for the cumulative rates of urinary continence with respect to the residual MUL. A residual MUL of ≥16 mm was a statistically significant factor that influenced urinary continence recovery (log-rank test, p = 0.026). The cumulative continence recovery rates at 12 months for patients with ≥16 mm and <16 mm residual MUL were 79.0% and 66.5%, respectively (Figure 1B).

This is the first study to demonstrate semiquantitatively that longer residual MUL contributed to postoperative urinary continence. A previous study investigating male urethral function during micturition using transrectal ultrasonography revealed that the anterior and lateral sides of the whole urethra inside the prostate was surrounded by a thick muscle unit and the distal of these muscle unit in the prostatic urethra stretched to outside of the apex of the prostate forming the external urethral sphincter muscle (3). Preserving this muscle as much as possible may be important to preserve urinary continence, because these muscle unit were injured by incision into the urethra at apex of the prostate.

These results suggest that patients with longer residual MUL in RARP have a significantly higher postoperative urinary continence recovery rate. Surgical procedure focusing on preserving longer MUL can have great impact on the urinary continence.

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