Focus

The same posterior muscle vectors act to open urethra and anus during micturition and defecation

  • PETER E. PETROS
  • MARK B. BUSH

Pelviperineology 2017;36(2):35-36

The generally accepted mechanism for micturition and defecation is that the pelvic floor muscles relax, detrusor contracts, urine and feces are expelled. To our knowledge, no EMG or imaging proof has ever been offered to validate this mechanism. X-ray and EMG evidence presented here confirms an alternative hypothesis, that only the forward acting pelvic muscles relax prior to micturition, m.pubococcygeus for micturition and m.puborectalis for defecation; prior to detrusor contraction, the same backward acting muscle vectors contract against competent uterosacral ligaments (USL) to open out the posterior urethral wall and anorectal angle. This exponentially decreases the internal resistance to fecal and urine flow. If USLs are loose, this mechanism weakens and the patient may complain of evacuation difficulties for bladder, bowel or both. Shortening and reinforcing the USLs has been demonstrated to reverse this cascade of events to cure the evacuation dysfunctions.

Keywords: Micturition; Defecation; Pelvic muscle contraction; Frictional resistance.