Pelviperineology

Figure 1. – The hypothesis: directional muscle forces activate anorectal closure and defecation. 3D schematic view of pelvic structures from above and behind. Broken lines = position of anorectal angle during defecation. Closure: Levator plate (LP) stretches the rectum backwards against an anus laterally compressed and anchored by puborectalis (PRM). The rectovaginal fascia (RVF) is stretched backwards by LP against the perineal body (PB). The downward vector LMA (longitudinal muscle of the anus) pulls down the now extended rectum to create the anorectal angle and water-tight closure. Defecation: PRM relaxes. LP and LMA open out the anorectal angle. Rectum (R) contracts to evacuate. PUL = pubourethral ligament; USL = uterosacral ligament; EAS = external anal sphincter. m. pubococcygeus (PCM) tensions distal vagina, PB and the anterior anal wall during closure and defecation.

Fig. 2. – Patient continent of urine and feces. Sitting lateral X-Ray, with radio-opaque dye in bladder (B), vagina (V), rectum (R) and levator plate (LP). A white diagonal line represents the superior border of LP. PB = perineal body; R = rectum; CX = cervix; ‘X’& Y= insertion of the pubourethral and uterosacral ligaments (black broken lines).

Fig. 3. – Straining, normal patient anorectal closure - same patient and labelling as Fig. 2. With reference to Figs. 1 & 2, arrows denote directional movement of the organs; P (curved arrow) = action of m.puborectalis; the forward and backward directional arrows pull against “X” (pubourethral ligament), and the downward arrow against “Y”(uterosacral ligament). The anterior wall of rectum appears to be anchored at “T”, the site of insertion of m.deep transversus perinei. The rectum ‘R’ is stretched backwards and rotated around an anus firmly anchored by m. puborectalis ‘P’.

Fig. 4. – Squeezing normal patient same patient and labelling as Fig. 2. Relative to Fig. 2, there is: indentation of bladder base; marked angulation of vagina and rectum; approximation of LP to rectum; upward stretching of levator plate (LP) to the horizontal position; all these movements are consistent with upward contraction of an underlying muscle, m.puborectalis (arrow).

Fig. 5. – Squeezing normal patient same patient and labelling as Fig. 2. Relative to Fig. 2, there is: indentation of bladder base; marked angulation of vagina and rectum; approximation of LP to rectum; upward stretching of levator plate (LP) to the horizontal position; all these movements are consistent with upward contraction of an underlying muscle, m.puborectalis (arrow).

Fig. 6. – “Pre-Evacuation strain” Same patient & labelling as fig 5, sitting position. With reference to the resting state, Fig. 5, note: forward stretching of distal vagina “V”; downward angulation of anterior border of levator plate (LP); the distal part of the posterior rectal wall has become vertical, consistent with forward contraction of puborectalis (black arrow); entry of material into anus “A”, consistent with the diagnosis of fecal incontinence; “pinching” of anterior rectal wall at “T”, consistent with anchoring by m. deep transversus perinei.

Fig. 7. – Squeeze Same patient as Fig 5, sitting position. All the organs and LP have been pulled upwards and forwards, consistent with contraction of the puborectalis muscle, PRM.

Fig. 8. – Defecation Same patient and labelling as Fig. 5, sitting position. Arrows denote directional movement of the organs consistent with stretching by muscle forces. Note: forward stretching of distal vagina “V”; backward stretching of proximal vagina, bladder (B) and rectum (R); downward angulation of levator plate (LP); marked widening of the anal canal (A) ; bulge at “T” consistent with anchoring by m. deep transversus perinei. EAS = position of external anal sphincter.