Surgical therapy for abnormalities of the urinary sphincter in the female.

THE ability to initiate and terminate micturition in a normal fashion and to maintain continence between voidings depends upon an intact corticoregulatory tract and an adequate urinary sphincter (Lapides, 1962). It has been demonstrated (Lapides et al., 1960 a ; Woodburne, 1960) that the urinarysphincter is a tubular structure (Fig. I ) approximately 3 cm. long in both the young male and female adult. The proximal end of the tube is continuous with the bladder fundus while the distal end merges into the bulbous urethra in the male, and the terminal centimetre of vaginal urethra in the female (Lyon and Smith, 1963). The tubular sphincter is lined by a mucous membrane consisting primarily of transitional epithelium and possesses a heavy outer coat of smooth muscle (Fig. 2). The smooth muscle fibres are direct extensions of the detrusor meshwork and are primarily longitudinal in nature. Unusually heavy concentrations of elastic tissue occur submucosally and between the longitudinal muscle fibres. The elastic fibres are found along the entire length of the urinary sphincter and are disposed in a circular fashion. While the fundus of the bladder is acting as a reservoir and storing urine, the lumen of the urinary sphincter is constricted by the inherent tonic compressing action of the smooth muscle and elastic fibres in its wall. Urine in the bladder is prevented from flowing through the conduit by the tightly apposed surfaces of the turgid urethral mucous membrane. The sphincteric action of the posterior urethra per se is quite efficient provided the intravesical pressure is low to moderate. When intravesical pressure rises to high levels the effectiveness of the posterior urethra must be increased in order to prevent leaking. This is readily accomplished by the activity of the striated muscles of the urogenital diaphragm and levator ani (Fig. 3) which compress and elongate the urinary sphincter. Both of these actions have been found to enhance urinary continence. The circumferential compression is applied mainly to the distal 2 cm. of the urinary sphincter. When the bladder converts from a storage to an evacuating organ, the urinary sphincter changes its configuration from an elongated, narrow conduit with obliterated lumen to a short, wide tube with a funnelled opening and a wide lumen (Fig. 3). The transformation occurs through relaxation of the periurethral striated muscle and active contraction of the detrusorurethral smooth muscle sheet. Because of this activity the resistance of the urinary sphincter is markedly decreased and the bladder can empty itself readily at low pressures.