Stress urinary incontinence is caused predominantly by urethral support failure

An assessment of the relationship between urethral hypermobility as measured by ultrasound and the symptoms of stress urinary incontinence in primiparous women 9-18 months postpartum

Aim

The aim of the study was to estimate the relationship between bladder neck hypermobility as assessed by ultrasound and the occurrence of stress urinary incontinence as measured with the UDI-6 questionnaire in primiparous women 9-18 months postpartum.

Materials and methods

The study included 100 women 9-18 months after their first delivery, 19% of whom (study group) presented with urethral hypermobility. Ultrasound was used to determine the position and mobility of the bladder neck in order to assess the urethral hypermobility. A vector of ≥15 mm was defined as urethral hypermobility. Symptoms of stress urinary incontinence were assessed using question 3 of the UDI-6 questionnaire, in which the presence of symptoms was defined as a response rated from 1 to 4.

Results

We demonstrated a statistically significant relationship between urethral hypermobility and the symptoms of stress urinary incontinence with a statistical significance level of p <0.002.

Conclusions

Stress urinary incontinence is a common disorder in women, the pathophysiology of which is not fully understood. It has adverse effects on the quality of life, perception of one's own body and sexual function. Impairment of urethral fixation may play an important role in the pathophysiology of this common form of urinary incontinence. The study showed that urethral hypermobility, as assessed by ultrasound, contributes to stress urinary incontinence, as measured with the UDI-6 score. Although stress urinary incontinence is a multifactorial disorder influenced by anatomical changes and congenital anatomical features, it is easily diagnosed. Suburethral slings are an effective surgical technique; however, the incidence of postoperative voiding dysfunction or recurrent stress urinary incontinence is 10-20%. Therefore, an assessment of anatomical changes in stress urinary incontinence may help individualize the surgical strategy.

An anatomical pathway for restoration of bladder neck closure by a midurethral sling, according to the integral theory

A firm pubourethral ligament (PUL) is required to prevent the reflex posterior pelvic muscle forces forcibly opening out the posterior urethral wall on effort. A weak or loose PUL elongates on effort and this allows the posterior pelvic muscles to stretch open the posterior urethral wall causing urine loss, "stress urinary incontinence." Such forcible opening out of the urethra exponentially reduces the urethral resistance to flow inversely by the fourth power of the radius (i.e., 16 times). For example, if the radius doubles in size, the bladder pressure required for urine to flow out decreases by a factor of 16, from say, 160 to 10 cm H₂ O. A midurethral sling reinforces PUL to prevent the urethra opening out, thereby restoring both the distal urethral and bladder neck closure mechanisms.