Incontinence remains to be one of the most significant factors affecting quality of life after RP. In the present study, 57.5% of patients achieved early continence recovery, which was consistent with previous studies [4,9]. With the advances in knowledge of urinary continence mechanism, the main structure in continence is considered the external striated sphincter, which maintains a urethral closure pressure greater than bladder pressure. Sphincteric incompetence after RP may be a result of shorter MUL, loss of neural innervations, muscle damage and loss of the surrounding support tissue [10]. Though PPI is usually a temporary symptom, the lack of information predicting continence recovery leads to anxiety in patients and prevents early treatment for PPI. Therefore, to identify possible predictors of PPI and develop a risk scoring system can contribute to patient counseling and early intervention of PPI.
Advanced age has been proposed as an important predictor of continence recovery after surgery by some studies [4,11,12]. In contrast, our study revealed that there was not significant difference on ages between patients with and without early continence recovery. Nyarangi‑Dix et al [13] suggested that continence recovery in elderly men does not differ from younger men undergoing robot-assisted radical prostatectomy. Patient characteristics, surgeon experience and surgical techniques play an important role in continence recovery after RP. NVB sparing was confirmed to be an effective surgical technique for improving continence recovery [14,15]. Our study also revealed that patients treated with NVB sparing achieved significant better continence recovery.
We identified that preoperative MUL was an independent predictor of continence recovery. Coakley et al [16] firstly revealed that longer preoperative MUL was associated with faster continence recovery. The study reported 89% of patients with a MUL > 12 mm achieved continence recovery compared with 77% of patients with a preoperative MUL ≤ 12 mm in 12 months after surgery. A meta-analysis containing one randomized controlled trial and 12 cohort studies demonstrated that a longer preoperative MUL is significantly and positively associated with continence recovery after RP [17]. Matsushita et al [18] reported that the addition of preoperative MUL increased the AUC of model for predicting continence recovery, but the AUC was not good enough. Longer MUL including a greater amount of external striated sphincter, play an important role in maintaining and increasing the urethral closure pressures.
RP leads to damages in the structure and function of membranous urethra. However, the MUL-removal rates can vary greatly between different patients and surgeons. The postoperative MUL may be a more accurate parameter for predicting continence recovery than preoperative MUL. Since MRI is not routine performed after RP, only a few studies revealed that longer postoperative MUL was associated with a faster continence recovery after PR [7,9,19]. Postoperative MUL measured on cystourethrography was also identified to be an important predictor of continence recovery [20]. Kohjimoto et al [21] examined 179 prostate specimens of RP and identified that MUL removed with prostate was an independent predictor of continence recovery. Our study revealed that patients with higher MUL-removal rate suffered a significantly longer period of PPI. Therefore, blunt dissection of the urethra distal to the prostatic apex should be carried out for sparing the membranous urethra, which could contribute to improving continence recovery after RP [22].
In recent studies, several MRI parameters such as IPPL, bladder neck width were identified to be predictors of continence recovery after RP [8,9]. Lee et al. [8] reported that significant improvement in continence recovery was observed in patients with IPPL < 5 mm at all periods compared with those with IPPL ≥ 5 mm. In a cohort of 821 patients who underwent robot-assisted radical prostatectomy, IPPL measured by transrectal ultrasound was also identified to be a powerful predictor of continence recovery [23]. Our previous study also confirmed that patients achieved early continence recovery after LRP had a significant shorter IPPL [24]. The core condition of urinary continence is the balance of detrusor contractility and urethral pressure. Intravesical prostatic protrusion was identified to be associated with lower urinary tract symptoms and overactive bladder [25,26]. It is supposed that longer IPPL contributes to pathophysiological changes of bladder detrusor such as detrusor hyperactive, detrusor instability and subsequent bladder dysfunction, and then leads to a delay in continence recovery after RP. Furthermore, the impact of intravesical prostatic protrusion on more surgical damage of the internal sphincter during bladder neck dissections put forward as a possible contributor [25]. However, the underlying mechanisms by which IPPL affects continence recovery after RP remains unclear.
On the other hand, we revealed that square UVA was a strongly negative predictor of continence recovery after RP. The risk of PPI for patients with square UVA was 2.3 times higher than those with triangle UVA. However, the mechanisms resulting in the difference on the shape of UVA is unclear. It may be related to the procedure of dissociation proximal urethra and vesical-urethral anastomosis. We proposed that patient with square UVA may suffered more damage such as scarring and fibrosis to the membranous urethra, which may be caused by high tension anastomosis, subsequent tissue ischemia and mechanical damage to sphincter [27]. Compared to the triangle UVA, square UVA may be an important signal of insufficient urethral closure pressure. Haga et al [19] found that patients with triangle bladder neck had better urinary continence, but it failed to showed significant difference. Further research on the association between the shape of UVA and continence recovery after RP is necessary.
The present study has some limitations. The retrospective nature of the study and the selection of patients with postoperative MRI could have generated unanticipated biases. The postoperative MRIs were performed in different intervals after surgery, which may affect the urethral parameters. Furthermore, the present study included a relatively small number of patients. Finally, several surgeon and patient factors such as thermal dissection close to NVB, preoperative sphincter control are involved in continence recovery after RP.