The external urethral sphincter is the voluntary component of urinary continence, under pudendal nerve control. In males, it surrounds the membranous urethra below the prostate — the zone most vulnerable in radical prostatectomy.
| Origin | Inferior pubic rami and perineal body — via the deep perineal pouch structures |
|---|---|
| Insertion | Encircles the urethra — forming a complete ring around the membranous urethra in males and the mid-urethra in females |
| Nerve Supply | Pudendal nerve — perineal branch (S2, S3, S4) |
| Blood Supply | Internal pudendal artery |
| Actions | Voluntary urinary continence — maintains urethral closure at rest and during straining; Contracts during cough and Valsalva to prevent stress urinary incontinence |
|---|
Preservation of the external urethral sphincter during radical prostatectomy is the primary determinant of post-operative continence. Nerve-sparing prostatectomy preserves the perineal branches to the EUS. In females, EUS weakness from pudendal neuropathy after childbirth contributes to stress urinary incontinence. Pelvic floor physiotherapy targets EUS strengthening.
Tested by voluntary interruption of the urinary stream or by cystometry and sphincter EMG.
External urethral sphincter damage during radical prostatectomy producing post-operative stress urinary incontinence, managed by pelvic floor physiotherapy or artificial urinary sphincter implantation.
