Improvement in early urinary continence recovery after robotic-assisted radical prostatectomy based on postoperative pelvic anatomic features: a retrospective review

Robotic-assisted radical prostatectomy (RARP) has been widely used as the most advanced treatment for localized prostate cancer [1, 2]. Urinary incontinence after RARP arguably has the most significant impact on quality of life postoperatively [3], and 4–22% of patients reported not achieving urinary continence within 12 months after RARP [4‐8]. Recent studies have reported that a patient’s preoperative status and certain anatomic characteristics are predictors of urinary continence postoperatively, therefore, it is indicated that surgical techniques and urinary incontinence after RARP are significantly related [6, 9‐12]. The membranous urethral length (MUL) is an important factor that directly correlates with the sphincter’s functional mechanism. The urethral sphincter is composed of an external striated sphincter and an internal smooth muscle layer, both of which are important increasing urethral closure pressure [13]. Previous studies showed that MUL preservation is important because it relates to urinary continence after open or laparoscopic radical prostatectomy [9, 10]. Preoperative MUL has been shown to be an important predictor of urinary continence recovery [14]. Early recovery of urinary continence after RARP has been shown to depend on postoperative MUL [15]. However, MUL is almost completely determined by the anatomic characteristics of the patient’s original pelvic floor shape [14].

Therefore, we investigated the impact of postoperative MUL on urinary continence recovery after RARP and the association between MUL and other anatomic characteristics of the pelvic floor shape, as measured with magnetic resonance imaging (MRI), with incontinence improvement after RARP.

Baseline clinical and pathological characteristics of the 73 patients who underwent RARP and postoperative MRI and 301 patients in the whole series are summarized in Table 1. At 1 month after RARP, urinary continence was restored in 27.4% of 73 patients who underwent RARP and postoperative MRI. Urinary continence improved over time, with 53.4, 68.5, and 84.9% of patients achieving urinary continence at 3, 6, and 12 months, respectively. When patients were divided into two groups (early versus late recovery of continence) based on urinary continence at 3 months after RARP, no significantly different clinical characteristics or surgical outcomes were observed (Table 2). We evaluated the association between postoperative pelvic anatomic features on MRI and urinary continence at 3 months (Fig. 2). The mean MUL (18.5 mm for the early continence group vs. 16.9 mm for the late continence group), levator muscle width (LMW) (7.1 mm for the early continence group vs. 6.5 mm for the late continence group), and BNW (7.2 mm for the early continence group vs. 5.4 mm for the late continence group) were significantly different between groups (all p < 0.05).

Because 64 patients reached complete urinary continence after RARP during the observation period, multivariate logistic regression analysis was used to identify prognostic MRI measurements predicting early complete urinary continence at 3 months after RARP. Multivariate logistic regression analysis evaluated clinical characteristics and perioperative parameters together with MRI parameters, and the results are summarized in Table 3. On the multivariate analysis, MUL (odds ratio [OR], 1.227; 95% confidence interval [CI], 1.011–1.489; p = 0.038) and BNW (OR. 1.585; 95% CI 1.050–2.393; p = 0.028) were associated with the period of early complete urinary continence.

A previous study reported that the most significant factor affecting quality of life after RARP was urinary incontinence [3]. In the present study, urinary incontinence was identified in 15.1% patients at 1 year after RARP, which was consistent with previous reports [4‐8]. Recent studies have reported that several anatomic characteristics are preoperative predictors of postoperative urinary incontinence, and surgical techniques are significantly associated with urinary incontinence after RARP [6, 9‐12]. Recent advances in knowledge of the pelvic structure have led to increased understanding of the urinary continence mechanism [13]. In brief, the external striated sphincter is the main structure in maintaining a urethral closure pressure that is greater than bladder pressure. Several authors have evaluated the impact of pre- and postoperative MUL and found that continence recovery was slower in men with short MULs [10, 14, 18].

Postoperative MUL as measured on urethrovesicography has been reported to be the most important predictive factor for recovery of urinary continence in the early postoperative period after RARP, and it is greater with preservation of the neurovascular bundle, thus allowing early recovery of urinary continence [15]. However, the measurement of postoperative MUL and other anatomic characteristics of the pelvic floor shape on urethrovesicography seems to be inaccurate and limited; hence, we evaluated the postoperative MRI findings. The development of MRI has enabled more accurate measurement of anatomic characteristics of the pelvic floor shape. Furthermore, MRI allows a minimally invasive examination of anatomical structures at the points of radiation exposure and pain. MRI findings of MUL and LMW have been shown to be useful and independent predictors of postoperative continence recovery [9]. Pre- and postoperative MUL measured by MRI were significantly associated with urinary continence recovery after RARP, and pre- to postoperative MUL change was also associated with urinary continence recovery at 6 months after RARP [19]. Our results showed that postoperative MUL as evaluated on MRI was significantly associated with early urinary continence recovery, indicating that the residual MUL also influenced recovery of continence at 3 months after RARP.

Multiple intraoperative maneuvers have been proposed to improve urinary continence, including bladder neck preservation [20], and novel reconstruction of tissue around the vesicourethral anastomosis [21]. The posterior musculofascial plate plays a significant role as a dynamic support structure for the prostatomembranous urethra [22, 23]. Multilayer posterior reconstruction measured by postoperative MRI could potentially restore anatomic and functional defects more effectively and provide stronger posterior support to improve the recovery of urinary continence after RARP [24]. The posterior construction of bladder wall, including BNW thickness, also plays an important role as a dynamic support structure for early urinary continence recovery. Our results showed that postoperative BNW thickness on MRI was significantly associated with early urinary continence recovery. This study is the first to report that preserving MUL longer and making BNW thicker at surgery were important for early recovery continence after RARP.

Our study had several limitations. First, this study had a retrospective design and a relatively small sample size, and all surgeries were performed by the three different surgeons. However, the same RARP protocol was used during the study period. Second, urinary continence status was evaluated based on the number of pads that patients used, which is relatively subjective. Measurement of the 24-h pad weight is considered to be the most accurate test [25], but it is difficult to apply in practice. In this study, we evaluated whether patients used no pads or pads for protection; hence, the severity of urinary incontinence was measured by a self-reported number of pads used. Finally, other parameters affecting urinary incontinence might have been underestimated because we focused on the impacts of postoperative MUL, LMW, and BNW on urinary incontinence.

Postoperative MUL as measured on MRI was significantly associated with early urinary continence recovery after RARP. Postoperative MUL was longer and BNW was thicker in patients who experienced early continence recovery (by 3 months after RARP). MUL and BNW on postoperative MRI were also related to the period of complete continence. Thus, surgeons’ efforts to preserve longer MUL and thicker BNW are recommended during surgery to achieve optimal continence outcomes after RARP.