The external urethral sphincter provides the voluntary conscious control of urination, encircling the membranous urethra as a sleeve of striated muscle that is tonically active to maintain continence. It works with the internal urethral sphincter (smooth muscle) and the levator ani to maintain urethral closure pressure above bladder pressure during filling. Sphincter damage during radical prostatectomy is the primary cause of post-prostatectomy stress urinary incontinence.
| Origin | Perineal membrane (inferior fascia of the urogenital diaphragm) |
|---|---|
| Insertion | Encircles the membranous urethra without true bony insertion |
| Nerve Supply | Pudendal nerve via the perineal branch (S2, S3, S4) |
| Blood Supply | Internal pudendal artery |
| Actions | Voluntary control of urethral closure — the primary voluntary continence mechanism; Relaxes during micturition to allow urine flow; Contracts reflexively during coughing and exertion to prevent stress incontinence |
|---|
The external sphincter must relax coordinately with the detrusor contraction during micturition — failure of this coordination (detrusor-sphincter dyssynergia) in spinal cord injury above the sacral cord produces obstructed voiding with elevated bladder pressures that risk upper urinary tract damage.
Post-prostatectomy incontinence from external sphincter damage affects 5 to 20 percent of men following radical prostatectomy for prostate cancer. Pelvic floor rehabilitation targeting the external sphincter before and after surgery significantly reduces the duration and severity of incontinence. Artificial urinary sphincter (AUS) device is the gold standard treatment for severe post-prostatectomy incontinence.
Not directly assessable by palpation. Function is assessed by urodynamic studies measuring urethral closure pressure during filling and voiding phases.
External sphincter damage during radical prostatectomy producing stress urinary incontinence managed with pelvic floor rehabilitation and artificial urinary sphincter implantation for severe cases.
