Comparing urethral closure mechanisms

The ongoing debate in “International Urogynecology Journal” about urethral closure mechanisms is important, because without a clear understanding of the anatomy of closure and stress urinary incontinence, the surgeon can never understand how corrective surgery works, or how to systematically address complications of such operations. The two dominant mechanisms which explain urethral closure rely either on Enhorning’s ‘pressure transmission theory’, or musculo-elastic closure which relies on structurally sound suspensory ligaments. Pressure transmission hypotheses fail a simple test, “Why does the same raised intrabdominal pressure which ‘closes the urethra’ not stop micturition when the woman strains downwards?” Rather, it increases urine flow, a consequence of the relaxation of the forward closure muscle, pubococcygeus, which allows the posterior vectors levator plate/longitudinal muscle of the anus, to open out the urethra prior to micturition, while the raised pressure from straining drives the urine out faster.