Experimental Study No. 6: Correction of abnormal geometry and dysfunction by suspensory ligament reconstruction gives insights into mechanisms for anorectal angle formation
PETER PETROS (*) - MICHAEL SWASH (**)
(*) Royal Perth Hospital, University of Western Australia
(**) Dept of Neurology, The Royal London Hospital, London, UK
Abstract: Normalization of the anorectal angle after fecal incontinence cure by midurethral and posterior sling surgery is consistent with the
hypothesis that a normal anorectal angle requires balanced pelvic muscle forces.
Key words: Fecal incontinence; Muscle balance; Obstructed defecation; Anorectal angle; Integral theory.
It is generally believed that raised intra-abdominal pressure
presses the rectum down to increase the anorectal
angle.1 Study No. 3 demonstrated that levator plate contraction
was a likely factor in anorectal closure, and therefore
would have some influence on the shape of the anorectum.
In contrast, study No. 4 indicated that increased abdominal
pressure per se could not be a factor in anorectal closure,
and therefore would have little influence on the shape of the
anorectum.
This case report appears to support the Theory's concept
that the anorectal angle is a resultant of balanced muscle
forces acting against competent suspensory ligaments.
The patient was 49 years old, para 3. She presented with
difficulty with defecation, fecal incontinence, stress urinary
incontinence, nocturia and pelvic pain. The patient had
second degree vault prolapse, lax rectovaginal fascia and a
very deficient perineal body. Pre-operative ultrasound (Fig.
1) 
showed
an acute anorectal angle at rest, which was only minimally responsive to straining.
Defecating proctogram demonstrated an acute anorectal angle similar to that in
Fig. 1.
There was no rectocele or rectal intussusception.
Attempted evacuation was accompanied by straining against
an uneffaced ano-rectal angle, with no passage of barium.
Digital pressure applied to the perineal body under fluoroscopy
appeared to support the anterior vaginal wall, and to
straighten out the ano-rectal angle. This resulted in slight
opening of the anorectal canal, and the passage of a small
amount of rectal content.
There was no patient selection. The mean age of the group
(n = 80) was 60.6 years (range 24-88), mean parity 3 (range
0-6). All patients were assessed according to a standard
protocol involving a semiquantitative patient-administered
questionnaire, urinary diary, 24 hour pad testing, transperineal
ultrasound and urodynamics.
All the endoanal ultrasound
examinations were conducted by a specialist in
ultrasonic imaging (JA), using a transrectal Acuson 7 MHz
linear array axial sector scanner (focal range 0.5 cm to 8
cm). As this review conforms to the standards established by
the NHMRC for ethical quality review, ethics approval was
not sought.
The patient was cured of urinary and fecal incontinence
and was able to defecate normally. The post-operative
transperineal ultrasound examination (Fig.
2) ,
demonstrated a return to normal morphology.
It was radiologically demonstrated, in Study No. 2, that the anorectal closure muscles levator plate (LP), longitudinal muscles of the anus (LMA), and puborectalis muscle (PRM), stretch the rectal walls in opposite directions. It is hypothesized:
(1) That the balance of forward and backward forces determines the shape of the rectum, and anorectal angle.
(2) That lax pubourethral (PUL) and uterosacral (USL) ligaments will weaken the backward/downward muscle forces, distorting the anorectal angle by unbalanced forward (puborectalis) muscle contraction.
Both LP and LMA (Fig.
3 ),
rely on firm ligamentous insertion points to contract adequately: superiorly,
the uterosacral ligaments, 'USL', and inferiorly, external anal sphincter
and perineal body, 'PB' (Fig.
3) .
This inability to balance
the forward contraction of puborectalis muscle (PRM), may
explain the acute anorectal angle "A". We explain the use
of digital pressure to facilitate evacuation as follows: a
lax perineal body will prevent the levator plate from stretching
the anterior wall of rectum via a tensioned rectovaginal
fascia. This mechanism is a pre-requisite for normal evacuation.
Digital pressure on the posterior vaginal wall mimics
a firm perineal body, allowing levator plate 'LP', Fig.
3 to
stretch the rectovaginal fascia 'RVF' backwards, temporarily
restoring the anorectal opening mechanism.
CONCLUSION
Cut away from their ligament and muscle supports, the
pelvic organs have no shape or strength. Like a rope suspension
bridge, the forces stretching the organs against the
suspensory ligaments (Fig.
3) must
be balanced. Any imbalance may change the geometry, and even function of particular
organs. Restoration of normal anorectal geometry and
function by surgical reinforcement of the suspensory ligaments
and perineal body in this case supports this hypothesis.
- Parks AG. Anorectal incontinence. Proc Royal Soc Med 1975; 68: 681-90.
- Petros PE. New ambulatory surgical methods using an anatomical classification of urinary dysfunction improve stress, urge, and abnormal emptying. Int J Urogynecology 1997; 8: 270-278.
Correspondence to:
Prof. Peter Petros,
E-mail: kvinno@highway1.com.au