Manometric asymmetry in the anal canal in controls and patients with fecal incontinence

Manometric Asymmetry in the Anal Canal in Controls and Patients with Fecal Incontinence Nigel Williams, Ch.M., F.R.C.S., Josephine Barlow, M.Sc., Anthony Hobson, B.Sc., Nigel Scott, M.D., F.R.C.S., Miles Irving, M.D., F.R.C.S. From the Department of Surgery, University of Manchester, Hope Hospital, Salford, Manchester, United Kingdom

PURPOSE: This study was designed to ascertain the exis- tence of manometric asymmetry in the anal canal in con- trois and in patients with fecal incontinence. METHODS: A computerized manometric technique with an eight-channel perfusion catheter was used. Coefficient of variation (CV, a mathematical expression of the degree or magnitude of deviation of a set of data points from the mean) was developed in this study as an index of anal canal manometric asymmetry. RESULTS: At 1 cm from the anal verge, mean CV was 9.3 and 8.7 percent in asymptomatic control males and females, respectively. During a maximum voluntary squeeze effort, mean CV in control males was 9.3 percent and was not significantly different (P = 0.28) from that in control females (7.8 percent). In 14 consecutive female patients with fecal incontinence, mean CV at rest (1 cm from the anal verge) was 21 percent and was significantly higher (P < 0.01) than in control females. Similarly, during a maximum voluntary squeeze effort, mean CV in patients with fecal incontinence was 20.5 percent and was significantly higher (P < 0.01) than in the female control group (7.8 percent). CONCLUSION: It is concluded that CV, a method of expressing anal sphincter manometric asymmetry, is a useful manometric parameter in the assessment of anorectal function. [Key words: Internal anal sphincter; External anal sphincter; Vector manometry; Radial asymmetry; Sphincter symmetry; Anal fissure; Fecal incontinence]

Williams N, Barlow J, Hobson A, Scott N, Irving M. Mano- metric asymmetry in the anal canal in controls and patients with fecal incontinence. Dis Colon Rectum 1995;38: 1275-1280.

A nal m a n o m e t r y r emains one of the more com-

m o n inves t igat ions u s e d in assess ing anorec ta l

funct ion. i , 2 The mos t c o m m o n l y u s e d pa r ame te r s

f rom such a m a n o m e t r i c s tudy are the rest ing anal

canal p re s su re a n d the m a x i m u m anal canal p re s su re

fo l lowing a vo lun ta ry s q u e e z e effort. W h e r e micro-

ba l l oons are used , these p res su res c o m p r i s e the math-

emat ic c i rcumferent ia l m e a n of all p re s su res for that

surface area of the anal canal in direct contac t wi th the

ba l loon . Similarly, p e r f u s e d s ing le - lumen ca the ters

m e a s u r e anal canal p ressures at one loca t ion only.

Address reprint requests to Prof. Irving: Department of Surgery, University of Manchester, Hope Hospital, Salford, Manchester M6 8HD, United Kingdom.

Howeve r , these m e t h o d s are unab l e to de tec t m a n o -

metr ic radial a s y m m e t r y in the anal canal that m a y

occur in pat ients wi th fecal i ncon t inence resul t ing

f rom t raumat ic sph inc te r damage . 3-5 By contrast , mul-

t i lumen p e r f u s e d ca the ters assess anal canal p ressures

o n a c ross-sec t ional bas is at e ach r eco rd ing s tat ion

f rom the anal verge . It is, therefore , poss ib le , wi th

mul t i l umen catheters to e x a m i n e the p ressures in

each q u a d r a n t of the anal canal. 6

The ex i s tence of radial var ia t ion in anal canal pres-

sure has b e e n p rev ious ly d o c u m e n t e d b y the d e m o n -

s t rat ion of s ignif icant m a n o m e t r i c a s y m m e t r y in the

anal canal wi th anter ior quad ran t p ressures b e i n g

l o w e r than those lateral ly and p o s t e r i o r l y ] Several

m a n o m e t r i c terms have b e e n i n t roduc e d in an at-

t empt to quant i fy and express anal canal m a n o m e t r i c

asymmetry . These inc lude the "pressure vector , ''8

w h i c h desc r ibes the d i rec t ional s u m m a t i o n of four

q u a d r a n t p ressures in the anal canal and also the idea

of a m a n o m e t r i c "vector s y m m e t r y index. "4 In the

lat ter t echnique , a f lexible e igh t -channe l pe r fus ion

ca the te r is u s e d to ob ta in m a n o m e t r i c da ta that is

s to red on a pe r sona l c o m p u t e r and ana lyzed b y soft-

wa re d e v e l o p e d b y Perry. 4 The e ight channe l s of

m a n o m e t r i c data are r econs t ruc ted to gene ra t e a

t h r e e -d ime ns iona l wire f rame m o d e l of anal canal

pressures , and vec to r s y m m e t r y index rep resen t s 4

"the ratio of the smal les t to the largest sec tor v o l u m e s

of the p re s su re vec torgram." Using this index, uni ty

was t aken to r ep re sen t a per fec t ly symmet r i c sph inc-

ter (i.e., a per fec t circle) a n d in a ser ies of 21 a symp-

tomat ic female cont ro ls the m e a n vec to r s y m m e t r y

i n d e x (VSI) was 0.76.

Manomet r i c a s y m m e t r y in the anal canal was inves-

t iga ted b y s tudying a s y m p t o m a t i c cont ro ls and pa-

t ients wi th fecal incon t inence . Coeff icient of var ia t ion

(CV), a ma thema t i c e xp re s s ion of the magn i tude o f

dev ia t ion of a set of da ta po in ts f rom the g r o u p mean ,

1275

1276

was developed as an indicator of manometric sphinc-

ter asymmetry.

MATERIALS A N D M E T H O D S

The study was approved by the Ethical Committee

of Salford Health Authority. All patients to be included

in the study gave informed consent.

Manometric procedures were performed in the left

lateral decubitus position. Bowel preparation was not

used before the manometr ic procedure. Manometry

was performed using an Amdorfer M3, eight-lumen

polyvinyl chloride catheter (Arndorfer Inc., Lec-

t romed UK Ltd, Letchworth, Herts, UK) connected to

a pneumohydraul ic capillary infusion system and per-

fused with sterile degassed water at 0.4 ml /min/chan-

nel using a perfusion pressure of 85 kPa. Perfusion

ports were located 3 cm from the catheter tip and

were arranged radially at 45 ~ intervals. The catheter

was graduated at 1-cm intervals, with larger gradua-

tions at 5-cm intervals. Channel 1 was identified by a

longitudinal line along the catheter. Each capillary

tube from the M3 eight-lumen catheter was connected

to a TNF-R disposable transducer (Viggo-Spectrum,

Swindon, Wiltshire, UK) and data transmitted to a PC Polygraf TM (PC Polygraf HR, Synectics Medical, En-

field, Middlesex, UK) with all eight channels set to

record manometric data. Data were then transmitted

to a personal computer on which the procedure was

monitored in real time and also stored directly on the

hard disk for subsequent review and analysis.

Before a manometr ic procedure the catheter-perfu-

sion system was calibrated to 50 m m H g using a meter

rule and then calibrated to the patient such that 0

m m H g was at the level of the anal verge. The catheter

was inserted into the anal canal to a distance of 6 cm

from the anal verge so channel 1 corresponded to

dorsal (as viewed in the lithotomy position) and left

until a steady manometric trace was obtained. Data

were collected using a station pull-through technique.

Once the patient was comfortable and the manomet-

ric trace had stabilized, recording was commenced at

6 cm from the anal verge. The station from the anal

verge was checked after each 1-cm withdrawal, and

radial orientation was maintained constant. Maximum voluntary squeeze effort was measured at the station of highest resting pressure. Each squeeze effort lasted be tween sLx and eight seconds, during which patients

were actively encouraged to maintain tonic activity,

and three such efforts were recorded.

WILLIAMS ETAL Dis Colon Rectum, December 1995

C o e f f i c i e n t o f Variation

CV was developed as a hypothetic value to de- scribe the magnitude or degree of deviation of all

eight individual data points from that which would

form a perfect circle, i.e., if all data points were equal,

then this would represent a perfect circle. Coefficient

of variation then represents the magnitude of devia-

tion away from a perfect circle as opposed to the

standard deviation of the eight manometric values, which, in the present context, represents the segment-

to-segment variability. Coefficient of variation was

calculated as follows:

Standard Deviation CV = X 100

Mean

where SD and mean are calculated from the eight

manometric values pertaining to that station.

Therefore, for each station recording eight channels of manometr ic data, the mean, standard deviation,

and CV were calculated and tabulated. The method of

calculating CV was identical for data obtained both at

rest and during max imum voluntary squeeze effort.

Statistical Analysis

Mean values represent the algebraic mean of all

eight values obtained at manometry and are followed

by standard error of the mean (SEM) in parentheses.

Manometric data were normally distributed, and as-

sessment was performed using parametric tests. Com-

parison of male and female controls and be tween patient groups was performed using unpaired t-test.

Data within individual groups were analyzed using

paired Student's t-test.

RESULTS

Patients

Nine male controls (median age, 62 (range, 28-83)

years) and 11 female controls (median age, 53 (range, 29-71) years) were studied. All patients had a normal

bowel habit. Two female controls were nulliparous, three were primiparous, and six were multiparous. All

primiparae and multiparae had delivered vaginally, with forceps-assisted delivery being necessary in one multiparous and one primiparous female.

Fourteen consecutive female patients (median age, 60 (range, 35-77) years) with fecal incontinence (FD were studied. Age distribution was not significantly different (t = 0.95; P = 0.35) be tween female controls and female patients with fecal incontinence. All pa-

Vol. 38, No. 12 ANAL CANAL MANOMETRIC ASYMMETRY

T a b l e 1. Comparison of Coefficient of Variation of Manometric Data During a Resting Pull-Through

1277

Coefficient of Variation Station from Anal Verge (cm)

6 5 4 3 2 1

Control males 48.4 25.7 23.7 21.0 11.2 9.3 Control females 41.4 33.6 28.6 22.8 13.2 8.7 Females-FI 36.9 37.9 39.6 29.0 28.2 21.0 t Value* 0.37 0.38 1.02 1.00 2.03 3.33 P Value 0.72 0.71 0.32 0.33 0.06 0.003

* Comparison of female controls (11) with females with fecal incontinence (FI; 14).

8o

oXg.

o 60 g

>

"6 40

13=d' o "'=9

~ 2o o

0 i i l l i i i

6 5 4 3 2 1 0

Station from the anal verge/cm

Figure 1. Coefficient of variation along the anal canal in controls (mean _+ SEM).

tients were parous. Two patients had delivered one

child, five had delivered two children, six had deliv-

ered three children, and one patient had delivered

four children. Traumatic delivery was reported by

three patients, two had had forceps-assisted delivery,

and two reported having had an episiotomy to facil-

itate childbirth.

Resting: Male Controls

Mean resting pressure (MRP (SEM)) increased with

decreasing distance from the anal verge and was

highest at 1 cm from the anal verge (61.9 (4.77)

mmHg). CV was highest at 6 cm from the anal verge,

with a mean value of 48.4 percent for the nine male

controls (Table 1). There was a sharp decrease in CV

from 6 to 5 cm, but this failed to achieve statistical significance (t = 1.82; P = 0.11). The incremental

decrease in CV for each 1-cm interval from 5 to 3 cm

was not statistically significant (Fig. 1). Although the

decrease in mean CV from 3 (20 percent) to 2 cm (11.2 percent) appeared large, it was not significant (t =

1.73; P = 0.12). The mean CV then decreased further

to 9.3 percent at 1 cm.

Resting: Female Controls

MRP increased with decreasing distance from the

anal verge so it was highest at 1 cm (63.9 (5.43)

mmHg). Maximum CV was at 6 cm from the anal

verge (mean CV, 41.4 percent) in female controls.

This gradually decreased with decreasing distance

from the anal verge (Fig. 1; Table 1). Although there

was a sharp reduction in mean CV from 6 (41.4 per-

cent) to 5 cm (33.2 percent), this failed to achieve

statistical significance (t = 1.30; P = 0.22). The de-

crease in CV among 5, 4, 3, and 2 cm was not signif-

icant at any station. The lowest value for CV in the

anal canal (8.7 percent) was at 1 cm from the anal

verge and was significantly lower (t = 2.47; P = 0.03)

than that at 3 cm.

V o l u n t a r y S q u e e z e Effor t : C o n t r o l s

Maximum voluntary squeeze pressure (MSP) in

male controls was 188.8 (10.4) mmHg and in female

controls was 142.8 (7.38) mmHg (Table 2). Mean CV

of manometric data during MSP in men was 9.3 (1.27)

percent and in female controls was 7.8 (0.57) percent.

The difference in CV during MSP between male and

female controls was not significant (t = 1.11; P =

0.28).

Resting: Fecal Incontinence

MRP at 1 cm from the anal verge was significantly

lower (t = 4.32; P < 0.01) in female patients with FI

(32.5 mmHg) than in control females (63.9 mmHg). Similarly, MRP at 2 cm from the anal verge was also

significantly lower (t = 3.09; P = 0.005) in female patients with FI (30.9 mmHg) than in control females

(51.0 mmHg) (Fig. 2). In patients with FI, mean CV in

the anal canal was maximum (39.6 percent) at 4 cm from the anal verge (Fig. 3). Between the two groups

1278 WILLIAMS E T A L Dis Colon Rectum, December 1995

Table 2. Maximum Squeeze Pressures (MSP) and Coefficient of Variation (CV/%) During MSP in Patient Groups

Parameter Male Controls Female Controls Females-FI

MSP/mmHg 188.8 (7.38) 142.8 (7.38) 66.3 (3.85)* CV/% 9.3 (1.27) 7.8 (0.57) 20.5 (1.49)*

Numbers in parentheses are standard errors of the mean. * P < 0.01; female controls vs. female fecal incontinent (FI).

80

(3) T

E E 60

L

e)

b. 40

c

L

c 20 oo �9

~ = Control = FI

* * ~ p= 0.005

*

* p= 0.0003

I I I I I t I

6 5 4 3 2 1 0


Figure 2. Comparison of resting pressure profile in the anal canal in female controls and female patients with fecal incontinence (FI).

60

[] = FI A = Controls

�9 .~ 4o

> * p= 0.06 "6 ~-* p= 0.003

E ._ o 20 �9 0

0 I I I I I I I

6 5 4 3 2 1 0


Figure 3. Comparison of coefficient of variation in the anal canal in female controls and female patients with fecal incontinence (FI).

there was no statistically significant differences in manometric CV at rest at the 6, 5, 4, and 3 cm stations (Table 1). The difference in CV between female con-

trois and patients with FI was significant (t = 3.33; P = 0.003) at 1 cm from the anal verge. At 2 cm from

the anal verge, the difference in CV between the two groups (13.2 vs. 28.2 percent) failed to achieve statis-

tical significance (t = 2.03; P = 0.06).

Voluntary Squeeze Effort: Fecal Incont inence

In female patients with FI, MSP was 66.3 (3.85) m m H g and CV during MSP was 20.5 (1.49) percent.

MSP was significantly higher in the female control population (142.8 vs 66.3 mmHg) compared with

those with FI (t = 9.19; P < 0.01). Mean CV in the anal canal during MSP was 20.5 percent in the FI group

and 7.8 percent in the female control group (Fig. 4),

and this difference was highly significant (t = 7.96;

P < 0.01).

DISCUSSION

By recording eight channels of manometric data, it is possible to construct a composite three-dimen-

sional manometric profile of the anal canal. The station pull-through generates eight channels of mano-

metric data at each specified station from the anal verge. The eight channels of manometric data can be

thought of as representing eight points describing a

circle. Analysis and manipulation of these data points can then provide mathematic expressions of sphincter

symmetry. To further analyze this manometric data and provide an index of sphincter symmetry, the

mathematic concept of CV has been evaluated. The

coefficient of variation is expressed as a percentage. This concept is very similar to the parameter termed "pressure vector ''8 but not nearly as complex as Perry et al. 4 "vector symmetry index," which involves the complex mathematic calculation of "pressure vector volume" in each quadrant of the anal canal. All of

these indices aim to provide an expression of manometric sphincter symmetry. Calculation of CV can be performed on all manometric raw data, whether this is at rest or during a maximum voluntary squeeze effort. Thus it should be possible to provide an index of the

Vol. 38, No. 12

5 0

40 c- O

' - 30

0

E 20 �9

O ,+.-

0 �9 10

0

A It A

I I

Cont ro l FI

ANAL CANAL MANOMETRIC ASYMMETRY 1279

resting CV at 1 cm from the anal verge be tween the

two groups. This finding may have relevance to the

development of fecal incontinence in patients follow-

ing internal anal sphincter injury, whether this follows forceful anal dilation 1~>/2 or unintentional damage by

use of oversized retractors or stapling devices. 13 In-

deed, endosonographic evidence of anatomic injury to the internal anal sphincter after Lord's procedure

can be demonstrated in more than 90 percent of Control vs FI patients. 14 The present data suggesting abnormalities

p= <0.00001 of anal canal resting pressure and manometric sym-

metry may be a reflection of internal anal sphincter

dysfunction and are consistent with the observations

above.

Coefficient of variation of the manometric data dur-

ing a maximum voluntary contraction was signifi-

cantly (P < 0.01) higher in w o m e n with fecal incon-

tinence than in control females. These findings a r e

consistent with data available in the literature, as dam-

age to the anal sphincter complex may sometimes result from obstetric factors. 15 17 Although such dam-

age may be detected and confirmed by electrophysi- ologic studies, 18 newer techniques such as anal en-

dosonography can be used to diagnose such sphincter defects. 14 Endosonic defects that are visual-

ized have been correlated and confirmed by dissec-

tion of resected specimens 19 and at surgical explora-

tion. 2~ However, despite the rapidly increasing

popularity of anal endosonography, the technique

does not offer a universal panacea to the practicing coloproctologist because it is unable to differentiate

be tween a physiologically relevant sphincter defect and an occult finding. Many asymptomatic patients

are known to have sphincter dysfunction following childbirth, is If such asymptomatic patients were

found to have anatomic defects at anal endosonogra-

phy, it would not be possible to conclusively assess

the significance of such a defect purely on sono- graphic evidence alone.

The study of patients with proven obstetric damage to the external anal sphincter is of great value and

provides an in v ivo model of a documented sphincter defect. In a study of nine patients with fecal incontinence resulting from obstetric injury Roberts et aL 5

reported a mean resting asymmetry of 32.2 -+ 3.0 percent and squeeze asymmetry of 29.2 + 4.2 percent in the anal canal. Following sphincter repair in this cohort, they report an increase in resting pressure but no significant change in squeezing pressure or resting

asymmetry, despite symptomatic improvement. In contrast, Dreznik et al. 21 found that, following ante-

Female subjects

Figure 4. Comparison of coefficient of variation during maximum squeeze pressure in control females with those with fecal incontinence (FI) during a station pull-through.

manometric symmetry of the anal canal at rest and

during a maximum voluntary squeeze effort.

Coefficient of variation in this study was highest in

the proximal anal canal and decreased with decreas-

ing distance from the anal verge. There was a significant reduction in CV of the manometr ic data as the catheter passed into the anal canal high-pressure zone

(usually at 2 cm). The lowest CV was at 1 cm from the anal verge in both men and w o m e n controls, and this

corresponded to the area of highest mean resting

pressure. There were no significant differences in CV

along the anal canal in men and women. Coefficient

of variation in the control group was approximately

10 percent in both men and women. This correlates well with the findings of Call e t aL 9 who used a similar

manometr ic apparatus and observed a vector symmetry index of 0.80, 0.77, and 0.75 in 20 control males and 21 nulliparous and 18 multiparous females, re -

s p e c t i v e l y . There were no significant differences between the three groups in the study by Cali et al. 9 The slightly lower vector symmetry index in multiparous

w o m e n was taken to be a result of the effect of vaginal delivery on the external anal sphincter but was not found to be statistically significant and could, therefore, justify the inclusion of asymptomatic parous females in the control group.

There was a highly significant difference in the

1280

rior sphincter reconstruction in 28 patients with ob-

stetric injury, there was an increase in both resting and squeezing pressures "in all quadrants. ''21 They

concluded that "squeeze pressure may not be the

most important determinant of success" and qualified

this with "sphincter profile may also influence out- come to a lesser extent." Similarly, Blatchford et aL 22

performed sphincteroplasty in nine women with doc-

umented obstetric injury to the anal sphincter. Fol-

lowing sphincteroplasty all patients had significant

improvement in continence. More startling, however,

was the change in vector symmetry index before

(VSI = 0.42) and after (VSI = 0.67) sphincteroplasty

(P < 0.005), despite no significant change in resting

or squeezing pressures. The authors concluded that

"sphincter symmetry is an important factor in the

continence mechanism independent of anal canal

pressure."

C O N C L U S I O N S

The discovery of significant anal sphincter mano-

metric asymmetry at rest and during a maximum vol-

untary squeeze effort in patients with fecal inconti-

nence, in this study, represents an important and

interesting finding and adds further credence to the

findings of others that anal sphincter manometric

asymmetry is an important parameter in the assess-

ment of anorectal function. Indeed, the concept of

sphincter symmetry appears to be pivotal in our un-

derstanding of the mechanisms of continence, and

assessment of such a manometric index could prove

to be of benefit in patient management in the future.

REFERENCES

1. Parks TG. The usefulness of tests in anorectal disease. World J Surg 1992;16:804-10.

2. Read NXV, Bannister JJ. Anorectal manometry: techniques in health and anorectal disease. In: Henry MM, Swash M, eds: Coloproctology and the pelvic floor. London: Butterworths, 1985:65-87.

3. Coller JA. Clinical application of anorectal manometry. Gastroenterol Clin North Am 1987;16:17-33.

4. Perry RE, Blatchford GJ, Christensen MA, Thorson AG, Attwood SE. Manometric diagnosis of anal sphincter injuries. Am J Surg 1990;159:112-7.

5. Roberts PL, Coller JA, Schoetz DJ Jr, Veidenheimer MC. Manometric assessment of patients with obstetric injuries and fecal incontinence. Dis Colon Rectum 1990;33: 16-20.

WILLIAMS E T A L Dis Colon Rectum, December 1995

6. McHugh SM, Diamant NE. Anal canal pressure profile; a reappraisal as determined by rapid pullthrough technique. Gut 1987;28:1234-41.

7. Taylor BM, Beart Jr RW, Phillips SF. Longitudinal and radial variations of pressure in the human anal sphincter. Gastroenterology 1984;86:693-7.

8. Sakaniwa M, Sawaguchi S, Okhawa H, Ikebukuro K. Computerised analysis of anorectal manometry. Prog Pediatr Surg 1989;24:21-32.

9. Cali RL, Blatchford GJ, Perry RE, Pitsch RM, Thorson AG, Christensen MA. Normal variation in anorectal manometry. Dis Colon Rectum 1992;35:1161-4.

10. Lord PH. A new regime for the treatment of haemorrhoids. J R Soc Med 1968;61:935-6.

11. Hancock BD. Lord's procedure for haemorrhoids; a prospective anal pressure study. Br J Surg 1981;68: 729-30.

12. Snooks SJ, Henry MM, Swash M. Fecal incontinence after anal dilatation. Br J Surg 1984;71:617-8.

13. Molloy RG, Moran KT, Coulter J, Waldron R, Kirwan WO. Mechanism of sphincter impairment following low anterior resection. Dis Colon Rectum 1992;35:462-4.

14. Speakman CT, Burnett SJ, Kamm MA, Bartram CI. Sphincter injury after anal dilatation demonstrated by anal endosonography. Br J Surg 1991;78:1429-30.

15. Deen K1, Kumar D, Williams JG, OlliffJ, Keighley MR. The prevalence of anal sphincter defects in fecal incontinence; a prospective endosonic study. Gut 1993;34: 685-8.

16. Jorge JM, Wexner SD. Etiology and management of fecal incontinence. Dis Colon Rectum 1993;36:77-97.

17. Sfrensen M, Tetzschner T, Rasmussen OO, Bjarnesen J, Christiansen J. Sphincter rupture in childbirth. Br J Surg 1993;80:392-4.

18. Snooks SJ, Setchell M, Swash M, Henry MM. Injury to innervation of pelvic floor sphincter musculature in childbirth. Lancet 1984;2:546-50.

19. Sultan AH, Nicholls RJ, Kamm MA, Hudson CN, Beynon J, Bartram CI. Anal endosonography and correlation with in-vitro and in-vivo anatomy. Br J Surg 1993;80: 508-11.

20. Deen KI, Kumar D, Williams JG, Olliff J, Keighley MR. Anal sphincter defects: correlation between endoanal ultrasound and surgery. Ann Surg 1993;218:201-5.

21, Dreznik Z, FleshmanJW, Kodner 1J, Fry RD. Restoration of squeeze pressure with sphincter repair to achieve continence [meeting abstract]. Dis Colon Rectum 1990; 33:P22.

22. Blatchford GJ, Perry RE, Christensen MA, Thorson AG. The effect of sphincteroplasty on manometric vector symmetry [meeting abstract]. Dis Colon Rectum 1990; 33:P22.

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Manometric asymmetry in the anal canal in controls and patients with fecal incontinence