External Urethral Sphincter Detail

musculus sphincter urethrae externus detail

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.

Nerve: Pudendal nerve — perineal branch (S2, S3, S4) Blood Supply: Internal pudendal artery Region: Abdomen

Anatomical Data

Origin, Insertion & Supply

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

Biomechanics

Function & Actions

Actions	Voluntary urinary continence — maintains urethral closure at rest and during straining; Contracts during cough and Valsalva to prevent stress urinary incontinence

Clinical Relevance

Clinical Notes

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.

Palpation

Tested by voluntary interruption of the urinary stream or by cystometry and sphincter EMG.

Pathology

Common Injuries & Conditions

EUS Injury in Radical Prostatectomy

External urethral sphincter damage during radical prostatectomy producing post-operative stress urinary incontinence, managed by pelvic floor physiotherapy or artificial urinary sphincter implantation.