Clinical and functional anatomy of the urethral sphincter

Continence and micturition involve urethral closure. Especially, insufficient strength of the pelvic floor muscles including the urethral sphincter muscles causes urinary incontinence (UI). Thus, it is most important to understand the main mechanism causing UI and the relationship of UI with the urethral sphincter. Functionally and anatomically, the urethral sphincter is made up of the internal and the external sphincter. We highlight the basic and clinical anatomy of the internal and the external sphincter and their clinical meaning. Understanding these relationships may provide a novel view in identifying the main mechanism causing UI and surgical techniques for UI.