Stress urinary incontinence: Bladder neck closure (BNC)-The real bottom line rather than urethral support or function failure

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.