TVT surgery involved the procedures of penetrating the paraurethral and retropubic cavity with a needle. These penetrations were blind procedures. The operators had no obvious target in terms of where to penetrate with the needle. Therefore, these were difficult techniques for inexperienced operators. Although TOT surgery also involved blind penetrating procedures, there was an obvious target, namely, the obturator foramen. This might make TOT surgery easier than TVT surgery for inexperienced operators. With TVT surgery, cystoscopy is essential after puncture. On the other hand, with TOT surgery, which is less likely to involve bladder damage, it is not essential. These differences could explain the difference in surgical duration between the two groups.
In the comparison of the urinary residual volume on post-operative day 1, it was higher with TVT surgery than TOT surgery. This does not conflict with previous reports by researchers[7
], and it is commonly understood that, because the angle of the curve of the suburethral hammock is more acute with TVT surgery, a higher urinary residual volume is observed. However, a dissection around the urethra is performed more widely with TOT surgery. Therefore, it is natural that edematous changes in the urethra after surgery would become predominant with TOT surgery, which could contribute to increased residual urine. The results of the present study indicate that the range of dissection did not influence the residual urine.
No differences were observed between both surgeries in comparison of the urinary residual volume in post-operative month 3. Chene[11
] et al. measured the angles of slings placed in TVT surgery and TOT surgery several months after the surgeries. The values were 116.3 ± 6.62° with TVT surgery (n = 28) and 130.75 ± 7.23° with TOT surgery (n = 30). A significantly more acute angle was observed with TVT surgery (p = 0.001). Despite the fact that the angle of the curve of the suburethral hammock was unchanged, there was no difference in the long-term urinary residual volume and, therefore, another factor other than the angle of the curve of the hammock must influence the long-term urinary residual volume. Midurethral sling surgery is performed to fix the urethra and involves few anatomic changes in surrounding tissues such as the bladder and external sphincter urethral muscle. The voiding functions and the cooperation system of the bladder and external sphincter urethral muscle would be adapted to post-operative urethral changes. This adaptation might reduce the difference between the two operative methods. In fact, Richter et al. [12
] reported that there would be no large difference between TVT surgery and TOT surgery in terms of long-term results.
With TVT surgery, a learning curve in terms of the surgical duration was found to be around 15 cases. On the other hand, with TOT surgery, the presence of a learning curve was not confirmed in any of the cases studied. This might be because the surgeon had already completed the learning curve for TVT surgery (introduced in 2004 at our hospital) by the time TOT surgery was introduced at our hospital (2006). This study had a certain limitation. There was a bias because it would be more reasonable to test the learning curve of TOT surgery in urologists who do not have prior experience of TVT surgery. However, the results indicated that the technique of TVT surgery could be applied to TOT surgery. Moreover, a study on the items of number of days of catheter placement, number of days of hospitalization, hemorrhage volume, urinary residual volume on post-operative day 1, urinary residual volume in post-operative month 3, post-operative subcutaneous hematoma, and post-operative urinary retention except for surgical duration revealed that both operative methods yield excellent outcomes in the early stages. The absence of a learning curve also indicated that both operative methods could be performed safely in the early stages of the introduction of surgery and could consistently obtain excellent surgical performance.
In this study, there was no difference in the post-operative ICIQ-SF value and the response rate of the two surgeries. However, the post-operative ICIQ-SF values were 1.48 ± 2.63 with TVT surgery and 3.16 ± 4.79 with TOT surgery, showing viability. This might be because the cases of UUI as a complication accounted for 20% or more in each group and, therefore, the ICIQ-SF value, which indicates the QOL impairment of overall incontinence numerically, showed a wide range even after surgery.
For TVT surgery, there is a case report that patients died due to intestinal puncture. In the present study, no serious complications such as bladder mispuncture, nerve and vascular damage, wound infection, or exposure of the sling occurred in either group. Moreover, de novo urgency, which has been reported as highly frequent, at 0.8 to 47.2%[13
], was not observed in this study. In terms of surgery for not malignancy but rather QOL disorder, these midurethral sling surgeries should naturally be required to be highly safe. The present study indicated that short- and long-term safety levels were high.
As is clear from the results of the present study, the efficacy and safety of TVT surgery and TOT surgery are generally well established, and few differences were observed in the frequency of complications between the selected operative methods. There will always be a debate over which operative method is best to be selected for those with little experience of midurethral sling surgery in the future. However, we have demonstrated that the introduction procedure (starting with TVT surgery followed by introduction of TOT surgery) at our institution can obtain satisfactory surgical performance.
Post-operative recurrence was observed in only 1 case of TOT surgery. An improvement of stress urinary incontinence was observed immediately after surgery, but a recurrence of stress urinary incontinence was observed after post-operative month 3. There is a report in which aging is defined as a risk factor of post-operative recurrence of stress urinary incontinence; however, the case of recurrence that we encountered this time was a case of a 62-year-old female who had no particular previous history. There are few reports on the predictive factors of post-operative recurrence and poor surgical effect[15
], and it will be necessary to clarify them in future studies. Moreover, for unsuccessful cases of TOT surgery, there is a report that an improvement of urinary incontinence was observed by performing TVT surgery subsequently[16
]. The development of additional treatment for unsuccessful cases is a goal for future study.
There are several limitations in this study. The limitations included a small number of the cases involved, a short post-operative follow-up duration, and poor examinations of pre- and post-operative voiding functions. We must analyze midurethral sling surgery more carefully on the basis of these results.