How reliable are currently available methods of measuring the anorectal angle?

How Reliable are Currently Available Methods of Measuring the Anorectal Angle? Jose M. N. Jorge, M.D.,* Steven D. Wexner, M.D.,* Floriano Marchetti, M.D.,* Guillermo O. Rosato, M.D.,* Maureen L. Sullivan, M.D.,'~ David G. Jagelman, M.D.*

From the Departments of* Colorectal Surgery and ~ Radiology, Cleveland Clinic Florida, Fort Lauderdale, Florida

A prospective study was undertaken to compare two different methods of measuring the anorectal angle (ARA), balloon proctography (BP) and cinedefecography (CD), as well as to evaluate the reproducibility of this measurement using each technique. One hundred four consecutive patients (75 women and 29 men) with constipation (63 patients), fecal incontinence (25 patients), or rectal pain (16 patients) underwent both BP and CD. The ARA was measured by taking lateral radiographs of the pelvis during rest (R), squeeze (S), and push (P). The same interpretation process was performed 2 to 12 months later by the same observer, blinded as to diagnosis and initial measurements. There were highly significant differences in each measurement category, R (P < 0.0001), S (P < 0.0001), and P (P < 0.0004) between BP and CD. However, the correlation between the first and second measurements was excellent (P < 0.0001). BP was consistently more difficult to interpret because of balloon configuration. Although BP and CD have poor correlation with each other, each examination can be reliably interpreted. CD appears to be a superior examination because of the added ability to delineate recto- celes, intussusceptions, and other structural defects. [Key words: Defecography; Proctography; Balloon sphincterography; Anorectal angle; Constipation; Fecal incontinence]

Jorge JMN, Wexner SD, Marchetti F, Rosato GO, Sullivan ML, Jagelman DG. How reliable are currently available methods of measuring the anorectal angle? Dis Colon Rectum 1992;35:332-338.

p rior to the advent of specia l ized radiographic

techniques, the dynamic mechan i sms of defecation were largely speculative. The impor tance of

these radiologic techniques was first descr ibed in 1952 by Wallden. 1 However , these specia l ized

techniques were not inc luded in rout ine clinical practice until recently. With the i m p r o v e m e n t in

the technical aspects of radiology, both cinedefecography (CD) and bal loon p roc tography (BP)

Poster presentation at the meeting of The American Society of Colon and Rectal Surgeons, Boston, Massachusetts, May 12 to 17, 1991. Address reprint requests to Dr. Wexner: 3000 W. Cypress Creek Road, Fort Lauderdale, Florida 33309.

have b e e n used with increasing f requency in the

evaluation of functional disorders of the pelvic floor.Z, 3

The anorectal angle (ARA) was first descr ibed by

the late Sir Allan Parks as the essential c o m p o n e n t of fecal cont inence. 4 Since the first descr ipt ion of

the ARA, many authors have focused their at tention

on this angle in the interpretat ion of anorectal physiologic tests. 5'6 In fact, the m e a s u r e m e n t of

the ARA may be the mos t f requent ly assessed phys-

iologic variable. However , t echniques vary, and the

ARA is measu red differently by different research-

ers. Many authors def ine the ARA as the angle

f o rmed by the longitudinal axis of the rec tum and

the longitudinal axis of the anal canal. 6-9 However ,

others consider the lower poster ior border of the

distal part of the rec tum to define the rectal com- ponen t of the angle) '1~ 12 Compar ing these two

me thods of measuremen t , a significant difference

in the values of the ARA was demons t ra ted by Felt- Bersma et al. 13

Recently, a n u m b e r of investigators have chal-

l enged the tenet of Parks and ques t ioned the sig- nificance of the ARA in the main tenance of fecal cont inence. 13-15 Nonetheless , the configurat ional

changes of the ARA with voluntary contract ion or

relaxation of the pelvic f loor may be important.

Fur thermore , many clinicians cont inue to place c redence in the ARA, and rout ine m e a s u r e m e n t is of ten taken. However , few data exist as to the

reliability and reproducibi l i ty of the currently available me thods of m e a s u r e m e n t of the ARA. Accord-

ingly, the aims of this s tudy were to assess pro- spect ively the correlat ion b e t w e e n two different me thods of measur ing the ARA: BP and CD. In addition, the reproducibi l i ty of the ARA measuremen t using each of these two techniques was eval- uated. This s tudy was not des igned to assess the

332

Vol. 35, No. 4 ANORECTAL ANGLE 333

importance of the ARA in the mechanisms of continence and evacuation.

MATERIALS AND METHODS

One hundred four consecutive patients (75 women and 29 men) with a mean age of 61.4 (range, 18-85) years underwent both BP and CD between November 1989 and January 1991. Indi- cations included constipation (63 patients), incontinence (25 patients), and rectal pain (16 patients).

A n o r e c t a l Ang le M e a s u r e m e n t

The ARA, defined as the angle between the axis of the anal canal and the distal half of the posterior wall of the rectum, was then measured from the radiographs by an observer aware of the clinical history. The results were recorded and all markings removed from the films. Between 2 and 12 months later, the same interpretation process was performed by the same observer, at this point blinded as to clinical history.

Balloon Proctography Patients had a disposable phosphate enema (C.

B. Fleet, Lynchburg, VA). BP was performed by inserting a compliant, latex balloon (Lahr balloon; Sunburst, Ladson, SC) with an intraluminal, semi- rigid stent into the anal canal and rectum. The flexible, cylindric balloon was connected to a cal- ibrated reservoir of barium, the height of which corresponds to intra-anal pressure. Lateral radiographs were taken, with the patient seated on a water-filled commode, at rest (R) and during both squeeze (S) and push (P). This technique was originally described by Preston e t al . ~6 and was subsequently modified by Lahr e t al . I7 The exact techniques of BP are described in more detail elsewhere.l< 19

C i n e d e f e c o g r a p h y

CD was performed with the patient in the left lateral decubitus position on the fluoroscopic table. The rectal mucosa was first coated with 50 ml of a concentrated suspension of barium. This improved the contrast imagery obtained. After initial barium instillation, air was insufflated to contrast and outline the rectal mucosa. This technique has been described by other authors. 2~ Subse- quently, contrast medium of a consistency similar to stool (Anatrast~"; EZ-EM, Westbury, NY) was placed into the rectum. Usually, all 200 cc (500 g) were used unless the patient experienced rectal fullness prior to that point. Injection was continued as the tip was removed to coat the anal canal with barium. Radiographs were taken at R and during S and P. Then, the entire x-ray table was inclined upright 90 ~ and the patient was comfortably seated on a water-filled commode attached to the footrest. The patient was asked to evacuate, and, with the aid of fluoroscopy and video recording, the dynamics of evacuation were analyzed. This technique is described in more detail elsewhere, i' 1< 22-24

Statistics The paired t-test was used to compare BP and

CD in each of the three positions: R, S, and P. Correlation coefficients were calculated to ascer- tain the reproducibility of each exam. All statistical evaluation was performed by the Department of Biostatistics and Epidemiology.

RESULTS

The descriptive statistics for all 12 categories are presented in Table 1. It should be noted that fewer BPs than CDs were reinterpreted due to acquisition of knowledge about kinking, twisting, and malpo- sitioning of the balloon. This is further described in the discussion.

There were highly significant differences in each measurement category, R (P < 0.0001), S (P < 0.0001), and P (P < 0.0004), when BP was compared with CD. These differences were noted with both the first and the second sets of measurements (Figs. 1A-C, respectively).

However, there was excellent correlation between the initial and final measurements for all three categories (R, S, and P) and for both techniques, BP and CD (P < 0.0001). This is shown graphically in Figures 2A-C, respectively. Knowl- edge of the patient's history or clinical examination did not appear to influence the ability to interpret the ARA.

DISCUSSION

The ARA is the result of the anatomic configuration of the pelvic floor muscles, formed predomi- nantly by the anteriorly directed pull of the puborectalis as it loops around the anorectal junction to form a strong U-shaped sling. 25

The importance of the ARA as a mechanism that helps to maintain the state of continence has been emphasized by several authors. < 26, 27 In theory, the

334 JORGE ET AL

Table 1. Descriptive Statistics

Dis Colon Rectum, April 1992

Variable n Mean SD SE Median Min. Max.

Initial Balloon R 102 127.5 22.3 2.2 128.5 71 172 Balloon S 102 111.8 21.2 2.1 110.0 60 172 Balloon P 100 130.8 24.1 2.4 132.0 71 180 Cinedef. R 98 107.2 23.8 2.4 105.0 58 155 Cinedef. S 98 93.1 24.2 2.4 88.5 50 146 Cinedef. P 95 118.2 27.3 2.8 122.0 45 180

Final Balloon R 69 120.1 19.9 2.4 120.0 77 156 Balloon S 76 107.1 19.0 2.2 106.5 75 152 Balloon P 72 124.3 24.6 2.9 125.5 35 180 Cinedef. R 100 102.9 22.8 2.3 100.0 55 150 Cinedef. S 100 89.1 23.3 2.3 84.5 44 155 Cinedef. P 98 114.1 28.0 2.8 117.0 57 180

Listed are the measurements for both balloon proctogram and cinedefecogram (Cinedef.) during rest (R), squeeze (S), and push (P). Both initial and final measurements are shown, n = number of patients. Note that far fewer balloon proctograms than cinedefecograms could be reinterpreted in radiographs in which kinking, twisting, or vertical balloon displacement occurred. The mean, median, minimum (Min.), and maximum (Max.) are an�9 angle values (o). SD and SE are standard deviation and standard error, respectively.

INITIAL MEASUREMENT OF RESTING FINAL MEASUREMENT OF RESTING

160 �9 140 ." .. .-~.,...o

120 " " # " . : ' , ,

100 �9 , . # � 9 1 4 9 , kU B0 ~ 0 f �9 .:

A 80 100 120 140 160 180

BALLOON PROCTOGRAM

140 " �9 " � 9 �9

120 �9 �9 I , =, ~ W It" ~'~ '. 80 , �9 I �9 . �9

~- 60 ~ �9 �9149

80 100 120 140 160

BALLOON PROCTOGRAM

INITIAL MEASUREMENT OF SQUEEZE FINAL MEASUREMENT OF SQUEEZE

~ 14080 , . . . : <~ 160 . 120 " �9 |'':" �9 " �9 ~D 140 "�9 �9 �9 ,,o, ~ 0,20 ~:.'" Ioo ";.:~ �9 ~ ioo ..:,.., "

W 80 "~ �9 �9

�9 .-.'- '~. ~ eo . . .. .

60 80 100 120 140 160 180 80 100 120 140 160 B

BALLOON PROCTOGRAM BALLOON PROCTOGRAM

INITIAL MEASUREMENT OF PUSH

<= 1~0 f 160 . . ,. �9 " . . . . . : , . . j ~ :

0 " t , . "s �9 "

1oo . .,-.. �9 .

~ 6 0 �9 �9 " " �9

~ 4 O 80 100 120 140 160 180

C BALLOON PROCTOGRAM

FINAL MEASUREMENT OF PUSH

160 �9 �9 � 9 �9

140 ' �9 " m. 120 " "." ~ "

I O0 �9 o �9 "~ �9 80

60F, , , " '', , ,1 40 60 80 100 120 140 160 180

BALLOON PROCTOGRAM

Figure 1. Balloon proctogram was compared with cinedefecogram twice. Significant differences were found for measurements made during rest (A; P < 0.0001), squeeze (B; P < 0.0001), and push (C; P < 0.0004).

BALLOON PROCTOGRAM RESTING CINEDEFECOGRAM RESTING

""

12o ..~ .. 100 % :'.'" <~

80 �9 �9 " " �9 100 ~ �9 ~ "

u. 80 100 120 140 160 180 ,T 60 80 100 120 140 160

INITIAL MEASUREMENT INITIAL MEASUREMENT

BALLOON PROCTOGRAM SQUEEZEp_ CINEDEFECOGRAM SQUEEZE

... 140 "~= o. �9 �9 140 , � 9 * �9 . 120 . �9 �9

100 I � 9149 �9149 �9 ~176 * 100 " ; �9 80 �9 �9 �9

�9 ~ 8 0 6 0 " "

60 80 100 120 140 160 180 ~- 40 60 80 100 120 140


BALLOON PROCTOGRAM P U S H CINEDEFECOGRAM PUSH

120 120 ; . ~1OO8o " , ~ ' �9 , loo , ; "

60 80 �9 �9 Z 40 60 ,

80 100 120 140 160 180 ~ 40 60 80 100 120 140 160 180


Figure 2. Note the excellent correlation between the initial and final measurements for both techniques, BP and CD, and for all three categories, R (A), S (B), and P (C) (P < 0.0001).

ARA is c o m p o s e d of the anterior wall o f the rectum, wh ich occ ludes the upper anal canal as a "flap valve. ''4 Alternatively, the ARA may funct ion as a sphincter at the level of the anorectal ring. 28 How- ever, the clinical s ignif icance of the ARA remains

controversial. Incont inent patients have larger ARAs at rest than do const ipated patients; however , this may be a c o n s e q u e n c e of pelvic f loor laxity rather than the primary cause of incont inence .2,15, 28 Whether patients with const ipat ion have an in-


creased ARA compared with controls is also subject to controversy.*' 9, 12 Goeil4 found that the measure-

ments of the ARA did not differ substantially be-

tween symptomatic patients and asymptomatic controls. He concluded that there is probably no

apparent relationship between clinical symptoms and measurements in defecography.

There is a wide range of normal values for the

ARA at rest and during squeezing and straining. The resting ARA ranges from 70 ~ to 140 ~ (mean, 92-114~ 2'18'22 During squeezing, the voluntary

contraction of the pelvic floor muscle decreases the angle to 75 ~ to 90 ~ Conversely, during evacuation, relaxation of the muscles increases the angle

to between 110 ~ and 180 ~ (mean, 113-135~ Many authors have noted that the ARA does not seem to be affected by age or gender, n' 13, 29 How-

ever, Skomorowska and Hegedus 3~ found that the

ARA was significantly larger in male than in female

patients. Furthermore, they considered that quantification of the ARA was of no value in men, due

to the wide range of values in this group. Many methods exist by which the ARA can be

measured. In the present study, the posterior edge of the rectal wall was used to define the rectal component of the ARA, instead of the longitudinal axis of the rectum. The reason for the use of this latter technique is that the central rectal axis alleg- edly better represents the axis along which expulsion forces exert their effect. However, this axis may not reflect the actual axis of the expulsion forces in the presence of asymmetries of the outline of the distal rectum, e.g., a large anterior rectocele. Furthermore, these asymmetries, as well as an indistinct junction of the upper and lower rectum, can cause difficulties in the ARA measurement when the central rectal axis method is used. 31

This problem also exists if the ARA is determined by a computer. We agree with other authors that the ARA is best measured where the puborectalis sling actually makes its angulation impression. 2'32

This generally corresponds to the distal segment of the posterior edge of the rectal wall. According to this criterion, the ARA tends to be significantly smaller than when the longitudinal axis of the rectum is used. 13' 31, 32 However, even if the poste-

rior edge is measured, difficulty in accurate ARA measurement may occur with both BP and CD. This problem is illustrated in Figures 3 and 4, respectively.

The presence of a large rectocele at rest or of an

Figure 3. Note the difficulty in interpretation of the ARA owing to balloon configuration.

Figure 4. Note the difficulty in interpretation of the ARA with CD owing to rectal configuration.

overdistended rectum can affect the measurement by erroneously decreasing the ARA. This latter problem can be avoided by injecting only the min- imal amount of barium paste necessary to allow the patient to experience rectal fullness; a 200-cc (500- g) maximum should be used. Conversely, an in- completely filled rectum can affect ARA measure-

336 JORGE E T AL

ment because of indistinct puborectalis impression. Likewise, when the posterior wall of the rectum is irregular owing to a posterior rectocele, perineal hernia, or double puborectalis/levator impression, the definition of the rectal component of the angle is more difficult (Fig. 5).

Significant discrepancies in the ARA values with regard to the technique used were observed in the present study. When BP was compared with CD, there were highly significant differences in each measurement category (R, S, and P). This occurred during both the initial and final sets of measurements. These discrepancies were more pro- nounced in two distinct circumstances. First, the balloon remained vertically displaced in the rectum instead of following the edge of the posterior wall (Figs. 6A and B). In this case, the CD angle was invariably more acute than the BP angle. Sec- ond, kinking of the balloon caused an erroneously more acute BP angle (Figs. 7A and B).

In patients with fecal incontinence, frequently the ARA could not be determined because of the inability to retain the balloon inside the rectum. BP also has other limitations: it cannot detect either intussusception or rectocele (Fig. 8). Moreover, BP cannot measure the adequacy of evacuation. Con- versely, CD permits quantification of evacuability and of rectal emptying dynamics. In addition, cer-

Dis Colon Rectum, April 1992

Figure 5. Note the difficulty in interpretation of the cinedefecogram owing to the posterior asymmetry.

Figure 6. Note the difficulty in interpretation of BP when the balloon stands vertically displaced in the rectum. A. Note that the gas bubble in the rectum is posterior to the balloon (arrow). B. The discrepancy in the ARA measurements can be schematically shown by overlapping the images of CD and BP.

tain sigmoid pathology, notably a nonemptying sigmoidocele, can be seen with CD but not with BP. Furthermore, Cherry 19 has shown that poor correlation coefficients exist between BP and per- fused manometry.

The reproducibility of ARA measurement has been questioned in several recent studies. 14'31'33 Ferrant e t aL ~5 found that the variation in ARA measurements which occurred between observers was as large as the range of angles in the entire group of patients. They concluded that a n y normal range could be defined because of such wide in-


B Figure 7. In some cases, the difficulty in interpretation of BP is due to kinking of the balloon. Panel A shows the radiograph, and Panel B shows the problem schematically.

terobserver variation. However, the present study showed that, despite the inherent inaccuracies pre- viously noted, both BP and CD could be reliably reinterpreted (P < 0.0001). This excellent correlation existed for radiographs obtained with the patient at rest as well as during squeezing and pushing. Therefore, knowledge of the patient's clinical history did not appear to affect the accuracy of interpretation.

Figure 8. Rectal wall abnormalities such as rectocele (ar- rows) cannot be demonstrated by BP.

C O N C L U S I O N S

Although BP and CD have poor correlation with each other, each examination can be reliably reinterpreted. CD appears to be a superior examination for several reasons. First, it is the only diagnostic test that provides anatomic detail, such as mucosal prolapse, intussusception, rectocele, and perineal hernia.34.35 Conversely, BP does not allow assess- ment of anatomic detail. Second, CD is easier to interpret since problems such as kinking or twisting, noted on BP, are not encountered. Third, evacuation can be better assessed using CD. There- fore, overall, the utility of BP is questionable.

A C K N O W L E D G M E N T S

The authors wish to express their appreciation to Geri Locker, BS, and Kirk Easley, MS, who performed all statistical analyses.

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How reliable are currently available methods of measuring the anorectal angle?