Male stress urinary incontinence (SUI) is a distressful complication of prostatic surgery either for prostate cancer or benign prostatic hyperplasia. Adjustable Transobturator male system (ATOMS) is increasingly used for the surgical treatment of male SUI. This system is based on ventral compression of the bulbar urethra by a filling a cushion. Compared to the artificial urinary sphincters the advantages of this system are its simplicity, the much lower risk of urethral atrophy or erosion, and the possibility of postoperative adjustment (1). However, its mode of action is not well understood. Our hypothesis is that the compression produced by the cushion filling produces a stretching effect on the bulbar urethra that increases urethral resistance and enhances the residual sphincteric activity, and also that different response to serial filling of the cushion intraoperatively after ATOMS placement could help to define the patients with best postoperative results.

We performed intraoperative measurement in a consecutive series of patients intervened with ATOMS  to evaluate the relationship between cushion filling volume and intraurethral bulbar pressure at the place of ATOMS contact.

Study design: Cross sectional study

Materials and methods: We carried out a cross sectional study in nine male patients submitted to ATOMS placement of for moderate and severe SUI. There were no exclusion criteria regarding leakage severity, concomitant radiotherapy, history of urethral stricture or previous SUI surgery. Surgical technique and perioperative care followed the original description (1). Perioperative intraurethral pressure measurement was carried out after ATOMS placement but before closing the incision, so that we could be sure the measurement was performed at the level at which the ATOMS system compresses the urethra. We measured this pressure by a T-DOC ® air charged catheter (Laborie, Mississaugua, Canada), connected to a Solar ® urodynamic equipment (MMS, Enschede The Netherlands). Initial pressure was measured with empty cushion, followed by 5 ml serial filling until 30 ml. Finally, the cushion was completely unfilled, and afterwards filled again up to atmospheric pressure (slightly different in every case determined by the anatomic position and the degree of pressing when the mesh arms are tied to the cushion). Finally, we measured the pressure with 4 ml additional to atmospheric pressure. Baseline data including pad-test, former radiotherapy was blind to intraoperative measurements.

Sample size was calculated based on data published by Ito et al (2). Assuming that the standard deviation of maximum urethral pressure in adult men is 7.75 cm H20 with a precision of ± 4 cm H2O and a confidence interval of 95 %, thus the minimum sample size should be 7 patients. 

We carried out a regression analysis of filling cushion values on intraurethral pressures, and calculated the Pearson correlation coefficient between preoperative pad-test, cushion volume and intraurethral pressure. We also performed a multivariate cluster analysis to search for different filling patterns. Six-months after surgery, once postoperative ATOMS adjustment was completed, we registered whether continence was achieved and postoperative pad-test. Continence was evaluated according to the clusters identified. The significance level was set at 95 % bilateral..

The regression analysis showed a significant direct relationship between cushion volume and intraurethral pressure (beta coefficient=0.072 cm H20/ml, p=0.000). It was also observed that intraurethral pressure rises scarcely and uniformly with filling under 15 ml (73 ± 22.7 cm H2O) but above 20ml there is a wide variability of the increment (233 ± 108.9 cm H2O) (Figure 1). The median intraurethral pressure at atmospheric pressure was 51 ± 22.7 cm H20, and at atmospheric pressure plus 4 ml was 80 ± 23.1 cm H2O). There is a correlation between intraurethral pressure baseline with ATOMS placed unfilled and filled at atmospheric pressure (p=0.038), and also between intraurethral pressure before ATOMS placement and with ATOMS placed and filled at atmospheric pressure plus 4 ml (p=0.047).  

Cluster analyses defined two patterns. Pattern one formed by 6 patients with distensible urethras and mild to moderate SUI in the pad-test, and Pattern two formed by 3 patients with rigid urethras and severe SUI baseline. The six patients in Cluster one (100%) achieved continence, but only one patient in Cluster two (33%) did so.

Intraurethral resting pressure must be adequate to maintain continence. Urethral pressure measurements have pointed out that normal urethral resting pressure is 70 ± 7.75 cm H20 (2). According to Laplace law intraurethral pressure is proportional to the tension of its wall. This tension increases in direct proportion to the degree to which the wall is stretched (3). This may be the mechanism by which ATOMS increases intraurethral pressure. Also, ultrasound images have shown that ATOMS filling elongates transversal urethral diameter whereas reduces antero-posterior diameter (Figure 2). Tissue biomechanics inform us that the relationship between tension and stretch depends on the histologic composition of tissues. Elastin fibres and muscle tissues allow great deformations without a proportional boost of tension. These fibres have a high compliance. Other fibres like collagen allow initial deformation without a high tension. However, once they reach their working length, they resist strongly further stretching with sharply rising their tension. Our cluster analysis confirms the existence of two patterns. Pattern one fits with normal urethras where elastin and muscle fibres are predominant and whose maximum intraoperative intraurethral pressure was 250 cm H20, and pattern two formed by rigid urethras where collagen is predominant and maximum intraurethral pressure reached values of 425 cm H2O. In these urethras an overfilling does not guarantee a continence status. This explains the finding previously reported that mean cushion filling is higher in incontinent than continent patients (1). The patients in cluster two are those with higher baseline SUI severity and also those with worst postoperative results.

We confirm the hypothesis that ATOMS system leads to continence by increasing intraurethral pressure owing to the stretching effect on urethral wall caused by cushion filling, thus increasing urethral resistance. The response to serial filling of the cushion intraoperatively depends on urethral rigidity and reflects baseline SUI severity and precludes postoperative results.

Angulo JC, Cruz F, Esquinas C, Arance I, Manso M, Rodríguez A et al. Treatment of male stress urinary incontinence with the adjustable transobturator male system: Outcomes of a multi-center Iberian study. Neurourol Urodyn. 2018;37(4):1458-1466
Ito T, Sakakibara R, Uchiyama T, Zhi L, Yamamoto T, Hattori T. Videomanometry of the pelvic organs: a comparison of the normal lower urinary and gastrointestinal tracts. Int J Urol. 2006;13(1):29-35
Zinner NR, Ritter RC, Sterling A.M, Donker PJ. The physical basis of some urodynamic measurements. J Urol 1977; 177: 682-689