Post-prostatectomy incontinence (PPI) remains a troublesome complication and compromises the quality of life in patients with prostate cancer. Various parameters are evaluated to identify the risk factors for PPI. Membranous Urethral Length (MUL) in preoperative magnetic resonance imaging (MRI) is a well-established predictor for PPI[1]. Pelvic floor muscle training (PFMT) speeds the recovery of PPI, and preoperative PFMT helps in early recovery of continence[2]. The internal anal sphincter (IAS) activity investigated through digital examinations, such as the length and the sphincteric muscle power, could be an alternative measurement for the pelvic floor function. This study aimed to identify the associations between the characteristics of IAS and PPI.

Consecutive patients with prostate cancer who received radical prostatectomy were recruited in this prospective study from July 2018 to August 2020. All patients underwent either robotic-assisted laparoscopic radical prostatectomy (RaLP) or laparoscopic radical prostatectomy (LRP). 

Medical information was collected by chart review. The activity of IAS was evaluated through digital examinations by a single experienced physician. The length of IAS was examined at the end of the first postoperative month, while the strength of IAS was measured before the operation and during every postoperative follow-up. We marked the strength of IAS on a three-score system (1 point:  loose, 2 points: competence, and 3 points: good contraction). Manometry was also performed on the same schedule as the strength of IAS. Anatomic parameters of the pelvic floor were acquired from preoperative MRI. Continence was defined as either completely pad-free or safety pad only. Associated analysis was performed to evaluate the potential impacts of various clinical parameters on the early resuming of continence at the end of the first and the third month after radical prostatectomy.

86 patients were enrolled in this cohort, and the mean age was 67.0 ± 5.9 years old. The mean thickness of pelvic floor muscle in MRI was 3.38 ± 0.68 cm and the mean length of IAS at the end of the first postoperative month in all subjects was 3.93 ± 1.04 cm. Most patients had either a competent (45.8% patients with 2 points) or a well contracted anal sphincter (47.0% patients with 3 points) after surgery. The percentage of the continent population at the end of the first month and the third month were 46.5% and 81.4%, respectively. The clinical parameters between the continent group and incontinent group were shown in Table 1. In the multivariate analysis (Table 2), both the length and muscle power of IAS were significantly associated with early continence at the end of the first month (OR 2.05 and 2.79, respectively). The sphincteric length remained a positive contribution to continence at the end of the third month. Meanwhile, prior transurethral surgery negatively influenced the restoration of continence in the third month.

The length of IAS played a crucial role in the early recovery of continence at the end of the first and third postoperative months. Although the muscle power of IAS was strongly correlated to continence at the end of the first month, we did not see a significant impact of muscle strength on early continence at the end of the third month. This result might suggest that patients with weaker sphincteric strength at the end of the first month might benefit from adequate PFMT and subsequently regain the continence in the third month. 

Interestingly, greater MUL did not contribute to early continence within three months in our cohort. Many factors might shorten the MUL and subsequently alter the activity of the external urethral sphincter after radical prostatectomy. A tumor located at the prostate apex, various surgical techniques for anastomosis, and different degrees of fibrotic change would compromise the function of the external urethral sphincter. Therefore, preoperative MUL might not be a precise indicator for the dynamic process of postoperative continence recovery. On the other hand, our results showed that the length of IAS at the end of the first postoperative month could act as a reliable marker. With a cuff-off level of 3.7 cm, the length of IAS could be a powerful predictor of early continence (p<0.001).

The length and strength of the IAS could act as dynamic predictors for early recovery of PPI. Adequate PMFT could eliminate the disadvantages of shorter preoperative MUL and initially impaired postoperative pelvic floor muscle power, to aid early continence recovery after prostatectomy.

Mungovan SF, Sandhu JS, Akin O, Smart NA, Graham PL, Patel MI. Preoperative Membranous Urethral Length Measurement and Continence Recovery Following Radical Prostatectomy: A Systematic Review and Meta-analysis. Eur Urol. 2017 Mar;71(3):368-378.
Chang JI, Lam V, Patel MI. Preoperative Pelvic Floor Muscle Exercise and Postprostatectomy Incontinence: A Systematic Review and Meta-analysis. Eur Urol. 2016 Mar;69(3):460-7.