OUTLET CONTRACTION OF THE *

By W. I. C. MORRIS, M.B., F.R.C.S.E., M.R.C.O.G.

There is no great unanimity in regard to the incidence or even the existence of outlet contraction. Stander (1946) states that contractions of the pelvic outlet occur in about 6 per cent, of all women. De Lee (1938) quoted figures as high as 26 per cent. (Stocker), but others, including Bourne and Williams (1939), are sceptical of the importance of outlet contraction, and emphasise that the head which passes the is unlikely to meet grave difficulty at the outlet. All of us, however, are familiar with the occasional unexpectedly stiff forceps operation, as a result of which we deliver with much soft tissue damage a still-born baby, or, perhaps worse, one which survives to develop signs of grave intra-cranial damage. A tentative diagnosis of outlet contraction in such a case may enable us to lay a flattering unction to our souls, but outlet contraction is a subtle condition which may result from a variety of deformities and abnormalities, and its detection before the occurrence of a disaster is often difficult. I propose to devote the major portion of this lecture to an examination of various diagnostic criteria which may give such forewarning, and to deal but briefly with other aspects of outlet contraction.

The Shape and Dimensions of the Fcetal Head in Labour

The first approach to this problem should be to obtain an accurate picture of the fcetal head in that stage of labour when it first meets the outlet resistance. As clearly demonstrated by Moir (1929, I932)' the head, moulded in the attitude of full flexion, approximates very closely to a cylinder, with bi-parietal, sub-occipito-bregmatic, and occipito-frontal diameters all more or less equal. As a reasonable be average the diameter of this cylinder in the full-term head may taken as 9-3 centimetres (3! inches), and so long as the head remai*1^ flexed, this is the largest diameter. During the normal mechanism 0 extension of the head an oblique measurement (not a true diamete1' of the cylinder) which we may accept as roughly 10 centimetres (4 inches) has to pass the outlet.

The Pelvic Outlet in Relation to the Fcetal Head The fcetal head enters the outlet at the inferior pelvic strait plane of least pelvic dimensions, i.e. the plane which cuts the ischi3 spines, the lower border of the symphysis , and (not infrequently/ * A Honyman Gillespie Lecture delivered in the Royal Infirmary on 27th J?ne 1946. OUTLET CONTRACTION OF THE PELVIS 91 the sacro-coccygeal joint. The axis of advance of the foetal head makes a bend almost equal to a right angle at this plane, changing from a own wards and backwards path to one which is downwards and orwards. This change of direction carries the advance into the canal of the outlet proper, bounded at the sides by the medial surfaces ?f the bodies of the ischia-; bounded posteriorly by the soft tissues the f pelvic floor and by the (a structure which is of negligible lrnPortance if normally mobile) ; and opening anteriorly through the gap between the conjoint rami of and pubis, referred to as e . The apex of the arch is closed the structures ?f pubic by the vestibule.

Types of Outlet Contraction

B?ny contraction of the outlet may result from :? (0) Absolute narrowing at the plane of least pelvic dimensions. (6) Narrowing below the level of this plane, i.e. narrowing of the pubic arch. 00 Combinations of the above.

Narrowing of the Plane of Least Pelvic Dimensions

first of these contractions may involve either the coronal or e sagittal measurements of the outlet. Williams (quoted Stander, WaS more imPressed by the frequency of coronal contractions, butut Moir (1941) considers narrowing in the sagittal plane to be at as important. In either case, the narrowing may result from a .5 funnel tendency reducing the more or less ?rmly from brim to outlet, or on the other hand, the contraction an isolated incident. Certain conditions are a .^e notoriously of the (C ,Cla general funnelling pelvis, e.g. the android pelvis We^> Moloy and D'Esopo, 1933, J934? x935)? high assimilation pe^. s> and spinal deformities such as dorso-lumbar kyphosis and anally spondylolisthesis. It is also recognised that the so-called "^mor contraction of the pelvis is often associated with funnel even more the brim j which reduces the outlet than (Stander, ^^nity, As an isolated incident, the coronal measurements of the plane ^ cav^ reduced by prominent ischial spines, inverted into the pelvic while the antero-posterior diameter may be reduced by unusual Convy>er?ence of jn the lower towards the symphysis pubis, especially o.- .at extremely common abnormality where the sacrum consists of vertebra:. S'*^d of alte aVrowi^ ?f the Pubic arch is usually independent any general ?f the pelvic shape. The effect of narrowing of the pubic arc^a.tl0nls *? deny the anterior of the bony hiatus to the head, It js ^ portion the symphysis pubis were prolonged downwards and back ards to an extent depending on the degree of narrowing. The 92 W. I. C. MORRIS influence of this intangible barrier (Fig. i) produces a reduction in the available antero-posterior diameter of the outlet canal dependent upon two factors :? (?) The extent of the pubic arch denied to the head. (?) The angulation between the plane of the pubic arch and the axis of the symphysis pubis. The more nearly this approaches i8o?, the less the influence of pubic arch narrowing, and vice versa.

afC^' Fig. i.?Showing effect of varying angle between axis of symphysis and plane of &TC^' Shaded area = portion of arch denied to head.

Besides reducing the available antero-posterior diameter of the outlet, the closure of the anterior portion of the arch alters the genefa &e axis of the advance of the head, partially undoing the curve of birth canal, and compelling the head to emerge more posteriorly than usual. This has two important effects to be referred to later, viz. (a) The stimulus to internal rotation of the head is diminish^ (Moir, 1929, 1932). (b) Perineal trauma is more common and more severe.

Measurements of Pelvic Outlet in the Dried Pelvis 0) Measurements of Least Pelvic Plane.?Exact definition of ^ measurements is simple. The antero-posterior diameter is measure between the lower border of the symphysis pubis and the tip of OUTLET CONTRACTION OF THE PELVIS 93

are fused with the sacrum. When one or more pieces of the coccyx fixed the diameter requires to be measured to the lowest point. of the ischial ^crum,e transverse diameter is measured between the tips spines. Stander (1946) defines these as :?

. . . 11 centimetres Antero-posterior *5 . centimetres Transverse . . .10-5

Nicholson variations occur. It is suggested by (1938, 1943) area of this as a at *t is more profitable to calculate the plane are the axes, geometrical ellipse of which the foregoing measurements er measurements alone. Radiological than to rely on the linear women les by Ince and Young (1940) in 500 consecutive yielded can be with the average figure of 93-7 sq. cm. This compared is ea of a cross-section of a 9*3 cm. cylinder, which approximately 08 sq. cm. to obtain a (P) Measurement of Pubic Arch.?It is difficult of the arch. The method of stating the measurement J* lsfactory that is the USUa^ is to measure the base of the arch, technique this with dist ketween the ischial tuberosities, and to correlate e and the sacral thean,CGdistance between the mid-point of this diameter measurement of the This is referred to as the posterior sagittal diameter and e ' The distance between the inter-tuber-ischial ^ to as the anterior can also be measured and is referred sa .SymPhysis the ^^ameter of the outlet. By applied trigonometry, quotient of V diameter anter*or sagittal diameter by the inter-tuber-ischial can h at the to determine the angle subtended symphysis pubis bvt, e.used Nicholson lnter"tuber_ischial diameter (Ince and Young, 1940 ; and T a referred to as the sub-pubic er> !946), and this is sometimes an 1 of course. Figures & e- It can be measured by more direct means ^oted are

. 11 cm. Inter-tuber-ischial . 1946) cm. (Stander, sagittal . . 7 cm.-10 posterior 8? 1943) Sub-pubic angle . (Smout, index o~ a satisfactory These measurements do not provide very e of the arch. For example : Capacity pubic betweenuclwccxi is to beue mcdsuicumeasured (*) The inter-tuber-ischialluier-rUDer-iscniai diameter quari'mt defined and, ral masses, not between easily points, ? bony even are 1945). material, wide errors possible (Heyns, S^etal of the foetal head passing Moreoy ^ We consider the cylindrical body throu that major obstruction Ier> Pu^c arch it will be apparent any Win to the cylinder, 0g w^ere the converging rami become tangential gener iiUr the arch were ^ distance from the tuberosities. If pubic a ?0me uiamcici andanu strict lnier-iuuer-istnidi diameter angle> a<1 knowledgeKnowieage of01 thetne inter-tuber-ischial the S?K these with would enable us to predict points angle ischia and are accuSub-Pubicracy- However, the conjoint rami of the pubis 94 W. I. C. MORRIS seldom straight, but show a slight concavity directed medially near the symphysis, and in some cases a convexity towards the middle line in their ischial portions so that each conjoint ramus comes to have a- sigmoid curve. The inter-tuber-ischial diameter gives no information as to the possible existence or location of such a convexity. (b) The sub-pubic angle, however estimated, is of limited value. A narrow angle may be an indication of a narrow base to the pubic arch, but it is quite erroneous to assume that, for any given measurement of the base of the arch, the capacity of the arch is influenced adversely by a narrow angle (Nicholson and Tauber, 1946). The reverse is actually the case, for, if the inter-tuber' ischial diameter remain constant, the area- enclosed by the rami is greater with the smaller angle. This appears a paradox Fig. 2.?Sub-pubic angle. but a moment's reflection reveals geometrical accuracy (Fig. 2). It is therefore justifiable to fall back on a measuring expedient which is not scorned in engineering, namely, to use a gauge in assessing the calibre of an irregular aperture. Such a gauge would be a cylinder measuring 9*3 centimetres in diameter. In fitting it into the dried pubic arch, note could be taken of two points, namely :? (a) The distance between the lower border of the symphysis pub*5 and the circumference of the cylinder, i.e. waste space at ape* of pubic arch. (b) The distance separating the base of the pubic arch from parallel diameter of the cylinder.

lfl The former measurement should not exceed 1 centimetre, and a roomy arch the coronal diameter of the cylinder should be at least 1 centimetre in front of the ischial tuberosities (Figs. 3 and 4).

Measurement of the Pelvic Outlet in the Living SubJ?c1" & It is now expedient to discuss the measurement of the outlet ' the living subject. Two methods are available, clinical and radiologic Since the radiological method bares the as it were, it will profitable to dispose of it first, but not at length, since the subject has been covered so fully in the British literature by Moir (194*^ Nicholson (1936, 1938, 1943), Ince and Young (1940), Heyns 094^'e Williams and Phillips (1946), Kenny (1944) and Dewar (1946), wh* t0? the classical American work by Thorns, Caldwell and Moloy is well known to require comment. OUTLET CONTRACTION OF THE PELVIS 95

Radiological Measurement of Pelvic Outlet It is desirable to have three views of the pelvis. First-class metric technique is necessary. For ease of calculation, the system offers enormous advantages. (#) Postero-anterior view of pubic arch taken with the patient sitting well forward with the symphysis pubis in contact with the

FlG.FIG. 3.?Wide arch".

Fig. 4.?Narrow Arch.

a Lysholm grid intervening. A very accurate projection" can and the dia min^mum distortion be attained inter-tuber-ischial . may be read, although the examiner is often in doubt as to ^terGnt* irn Points to select in making this measurement. More by tant, however, the shape of the arch is accurately shown, and, on the film a transparency on which is outlined a cjj.^P^mposinge t^e -9*3 centimetre diameter, it is possible to assess the capacity of arc^arck- The interval in centimetres between the apex of the pubic anc^ the circumference of the circle, and the relationship of the c0r a diameter of the circle to the ischial tuberosities are noted. 0rmer measurement will be Used in assessing the effect of pubic 96 W. I. C. MORRIS arch narrowing in relation to the other bony boundaries of the outlet, the latter in assessing the effect of such narrowing upon the soft tissues. (b) Lateral.?The lateral film permits the measurement of the anterior and posterior sagittal measurements of the outlet, and oi the antero-posterior diameter of the least pelvic plane ; and gives an opportunity for calculating a corrected antero-posterior outW * diameter allowing for any narrowing of the pubic arch as follows A point is taken in the general line of the conjoint rami seen & profile, at a distance from the lower border of the symphysis equivalent to that of the waste space recognised in the pubic arch view, and the distance between this point and the tip of the sacrum is taken as the " Corrected antero-posterior diameter of the outlet." (See Figs. 5-15*) (c) Antero-posterior, either in a sitting posture or recumbent with the lumbar spine in lordosis. The diameter between the ischial spineS and, in some cases between the medial surfaces of the ischial tuberosities may be measured. This film should be taken before the foetus is sufficiently large to obstruct the X-rays.

IllustrativeIllustrative CasesCases

CaseCase i.?Mrsi.? Mrs H.H. ParaPara o.o. AgeAge 28.28. (Figs.(Figs. 55 andand 6.)6.)

Fig. 5. Fig. 6. 4 Outlet contraction due solely to antero-posterior shortening assocfcte with six-segment sacrum. Pubic arch fairly roomy.

Obstetrical conjugate . . . . n-o cm. Antero-posterior of outlet . . .9*8 cm. Corrected antero-posterior of outlet . . 9* 2 cm. OUTLET CONTRACTION OF THE PELVIS 97

Low forceps delivery after deep impaction of head in transverse diameter, following twenty-seven hours' labour. Living 6 lb. 5^ oz. baby. Both survived.

CaseCase o. 2.?Mrs2.?Mrs McS.McS. ParaPara o. AgeAge 24.24. (Figs.(Figs. 77 andand 8.)8.)

Fig.Fig. 7.7.

Fig. 8.

anf but Outlet to sacruqacrum, principally t0, contraction due partially s,x-segment narrow arch which shows 3 cm. waste spa ? cm. * I2.6 Obstetrical conjugate ? ^ 10*2 cm. A.P. of outlet ? cm. Corrected A.P. outlet ? ? 9?o V?L. g L1V. no. 2 98 W. I. C. MORRIS

Mid forceps delivery after forty-eight hours' labour with head obliquely L.O.A. Living 8 lb. 8 oz. baby. Both survived, but mother suffered severe perineal trauma and was unable to urinate for three weeks after delivery.

Case 3.?Mrs C. Para o. Age 29. (Figs. 9, 10 and n.)11.)

Fig. 9.

V 'v

f / /

1V 1 ' / 7 Fig. io.10. Fig. ii.

Outlet contraction associated (a) with narrow arch due chiefly to convex1^ of conjoint rami despite wide inter-tuber-ischial diameter, and (b) with comp^ete bony fusion of sacrum and coccyx. Conjugate of brim also small.

Obstetrical conjugate . , . . io-o cm. A.P. outlet ...... 9*2 cm. Corrected A.P. outlet .... 8*6 cm. OUTLET CONTRACTION OF THE PELVIS 99

Spontaneous vertex delivery after six and a half hours' labour of 6 lb. i2? oz. baby, in lithotomy position and following deep episiotomy. Both survived, forbid puerperium. Post-natal pelvic X-ray shows fracture of the sacro- coccyx with enlargement of diameters to :? A.P. outlet io-8 cm.

Corrected A.P. outlet . . . .10*2 cm.

Case 4.?Mrs McC. Para o. Age 40. (Figs. 12 and 13.)

Fig. 12.

Fig. 13 ^utlet contraction dependent on (a) very gross narrowing of arch, IOO W. I. C. MORRIS

{b) complete fusion of sacrum and coccyx. Obstetrical conjugate also small. Obstetrical conjugate .... io-i cm. A.P. outlet . . . . . io-i cm. Corrected A.P. outlet . . . .8*5 cm. After twenty-four hours' labour, head had not passed the brim, despite considerable moulding. Lower segment Caesarean section. 6 lb. iof ?z' baby. Both survived.

Case 5.?Mrs Mel. Para o. Age 28. (Figs. 14 and 15.)

Fig. 14.

Fig. 15. OUTLET CONTRACTION OF THE PELVIS io*

Twins. Outlet contraction dependent upon :? (

X-rays taken post-natally show dislocation of coccyx.

Obstetrical conjugate .... 11*7 cm. A.P. outlet . . . . . io-o cm.

Corrected A.P. outlet . . . . 8*8 cm.

Outlet contraction was recognised first in second stage of labour with rank breech impacted after thirty hours on sacral tip?no mobile coccyx Pfesent at that time?antero-posterior diameter of least pelvic plane equalled 8 centimetres. After legs brought down, natural forces delivered trunk of child, but head ^fcame completely impacted with long axis in antero-posterior diameter. ?rceps failed to deliver head and slipped off. After manual rotation to ng sub-occipito-frontal diameter of head into transverse of outlet, head ivered with strong jaw and shoulder traction following bi-lateral episiotomy. b- 2 J oz. baby still-born. Autopsy showed intra-cranial haemorrhage and actured vault of skull. 4 lb. 7^ oz. sister (also breech) delivered alive with a

Clinical Measurement of the Outlet "

The routine clinical measurements of the outlet are :? (a) The antero-posterior of the least pelvic plane. (^) The inter-tuber-ischial. 00 The posterior sagittal. The anterior sagittal.

addition are made to form of attempts subjective impressions

The amplitude of the pubic arch. ^ ) The distance between the ischial spines.

the actual measurements distinct from SlJ, ^ Measurements.?Of (as I believe that the one which can be ? only tajcJ^CtiveCf*n i impressions), is ine diameter iuyan^ approacnaPProach tot0 accuracy is the a-iiiciu-puaicnuiantero-posterior th e ^ least pelvic Two exist. Either the measure- ^ent plane. techniques may be made during vagina exa fiddle finger in contact with the sacra ^ t^e knuckle of the *^dex location of ? finger opposed to the symp ysis t^e which marked as in ?n;ugate * or n measuring alternatively external measurement may be with callipers from the lower of ^argin the symphysis to the lower en posterior surface of sacrum. is sacral must be Whichever technique adop ' tip ^entified by moving the coccyx bimanual y vaginal (or rectal) and . Hers, the of the examiner s diseng g d hand V?L. fingers applied L1V. NO. 2 ^ 2 102 W. I. C. MORRIS externally in the natal cleft. As pointed out by Moir (1941), the left lateral position is particularly suited to taking these measurements, and the rectum must be empty. With practice one can make the internal measurement very accurately. It is usually very close to the radiological measurement. Any error arising is on the safe side, the measurement being under-estimated by a few millimetres. Heyns (1945) claims that the external is at least as accurate as the X-ray measurement if a deduction of one centimetre be made to allow f?r the thickness of the sacrum and soft tissues. I find the inter-tuber-ischial diameter very difficult to measure. Thick skin, firm fat, and a bursa which allows the integument to move most freely over each large quadrilateral mass of , make it almost impossible to fix any definite points between which to take the measure- ment. To find myself differing in successive examinations of the a same patient by two centimetres in either direction is no rarity, and conviction of my fallibility in this respect has led me to abandon all attempts at making this measurement. The anterior sagittal and posterior sagittal diameters can be estimated only if it is possible to define the point where the inter-tuber' ischial diameter crosses the . I am seldom able to satisfy myself of this and accordingly I do not attempt measurement of these diameters. (b) Subjective Impressions.?So far as subjective impressions ai"e concerned, it is of course undesirable to rely on these, but probably less so than to take fallacious measurements. (i) The Pubic Arch. (a) External Palpation.?In a thin patient* 0 palpation of the pubic hiatus with the whole of the volar surfaces the fingers may enable one to assess the arch as wide or doubtful but if the patient be at all plump, the difficulties are such as to rend^ this a most fallible observation. A subjective impression of the widt of the inter-tuber-ischial diameter obtained by pushing the knuekleS in between the tuberosities is moderately accurate, but, as I have indicated, the inter-tuber-ischial diameter may be quite adequate and yet the rami may be so convex that the arch is functionally narro^' tbe (b) Vaginal Examination.?The fingers may be swept around tke arch from one to the symphysis and on towards y other tuberosity, noting the path traced. If the patient is not perfect %vl relaxed the tonicity of the levatores ani interferes very seriously this examination. Therefore, vaginal palpation is rather falli^e' although a very good impression is attained in the anaesthetised patie11 when attempts are made to introduce the whole hand into the vagina' when the cramping constriction of the fingers by a narrow arch I would like to record that I have readily recognised. always t0 able to get two fingers side by side into the apex of the arch, failure do which is occasionally described as indication of narrowing. (ii) Distance between Ischial Spines.?The ischial spines are ea^; to palpate on vaginal examination, and an attempt should be made OUTLET CONTRACTION OF THE PELVIS 103 assess their degree of prominence and of inversion into the pelvic cavity. If considerable, a suspicion of narrowing in this area must arise. Some idea of the actual diameter may be obtained by sweeping the fingers across the posterior vaginal fornix from one spine to the other.

Critical Summary of Available Procedures for Outlet Measurement To summarise, I believe that X-rays offer a complete range of Measurements, but that clinically, although various subjective lmpressions may be useful in experienced hands, the only reliable rneasurement is the antero-posterior diameter of the plane of least Pelvic dimensions. In this country, the man-power situation in respect radiographers hardly yet permits of routine X-rays, but it will be endeavour to demonstrate that with the one clinical measurement ?^ the antero-posterior diameter of the inferior strait of the pelvis it ?uld be possible to pick out the dangerous cases for full radiological .

Criteria for Diagnosis of Outlet Contraction It is difficult to define a precise criterion applicable to all cases, ams (quoted Stander, 1946), for example, considered outlet to exist in all cases where the inter-tuber-ischial diameter ^tractionasured clinically was less than 8 centimetres, but he appears to Ve been pre-occupied with contraction in the coronal plane. In any centres the of outlet contraction is made on the basis of diagnosis dictum that where the sum of the inter- tub .ms> (Stander, 1946) t|^er-1Schial and posterior sagittal diameters is less than 15 centimetres, sP?ntaneous delivery of a normal head is unlikely, pelves which n measured or fail to this standard ^ radiologically clinically attain 5 centimetres being regarded as contracted at the outlet.

X-ray Diagnosis of Outlet Contraction Relieve it is possible with modern developments in radiological pejJ. to of contracted ^ be fairly precise. The diagnosis outlet lT^etrye made with confidence in case where the i^ea complete any X-ray t^e of the antero-posterior or of the transverse diameter of S^rementsane ?f of least pelvic dimensions is less than 9*3 centimetres. It is, rse> obviously correct that provided the disparity between the CoUldUKmentS ^ n0t t0? ?reat> narrow measurements in one direction compensated for by an increase in the direction at right ^ngles to *t? if we assume further of the head to be So f moulding possible. aS contraction conc below the plane of least pelvic dimensions is * as thg11 suggest that the measurement which I have referred to corrected antero-posterior diameter of the outlet can be taken ic>4 W. I. C. MORRIS as an index of outlet contraction. However, the critical figure in this respect is larger than 9*3 centimetres, for although the head may pass the plane of least pelvic dimensions well flexed, with its outline cylindrical and its diameter 9*3 centimetres, the classical mechanism of extension brings across the antero-posterior of the outlet an oblique measurement in the neighbourhood of 10 centimetres. I therefore hold that no matter what the actual size of the antero-posterior diameter of the plane of least pelvic dimensions, the outlet is to be regarded as contracted in any case where the corrected antero-posterior diameter is less than 10 centimetres. I admit that this whole system is based on rather theoretical arguments, but in my hands it has proved a rough but useful guide.

Clinical Diagnosis of Outlet Contraction

ofl I believe that firm diagnosis of outlet contraction can be made the clinical grounds in cases where the antero-posterior diameter of plane of least pelvic dimensions is under 10 centimetres. This does not necessarily imply a contraction of the plane of least pelvlC dimensions, but if the antero-posterior of this plane is less than 10 centimetres, the antero-posterior diameter of the outlet will certainly be inadequate at the time of extension of the head. On the other hand, from my studies in X-ray pelvimetry, I believe that if the anterO' posterior diameter of the plane of least pelvic dimensions measure 11-5 centimetres or more, serious antero-posterior narrowing of outlet can be ruled out, since even in the narrowest pubic arches corrected antero-posterior outlet diameter very seldom differs by more than 1-5 centimetres from the antero-posterior diameter of the inferi?r ^e pelvic strait. It will be noted that this figure of 11-5 centimetres is same as the average figure given by Stander for this measurement. The question then arises how far one is justified in assuming W an antero-posterior diameter of li*S centimetres for the inferior stra entirely rules out outlet contraction. Obviously this would be a rathe^ dangerous assumption if it could be shown that serious reduction the diameter between the ischial spines were likely to occur in associat^11y with such a large antero-posterior diameter. Whilst it is entire t*1 possible that such reduction could occur, my own is impression ^ it is unlikely. Furthermore, it can be shown mathematically that ellipse in which the long axis has a measurement of 11*5 centimetr an sho will have area greater than a 9*3 centimetre circle for all axes greater than 7-7 centimetres, which would represent a very gr?^ contraction of the diameter between the ischial spines, difficult sU ^ overlook on vaginal examination. I have no records of any measurement less than 8 centimetres, while the smallest diame recorded by Ince and Young (1940) in their survey is 7*5 centimetr^ I therefore suggest that, whilst an antero-posterior diameter of centimetres does not rule out the possibility of a contraction in OUTLET CONTRACTION OF THE PELVIS 105 least pelvic plane, it does indicate that severe insurmountable con- traction in this area is very unlikely. As a working rule, I suggest that in all cases in which the antero- posterior diameter from the lower border of the symphysis to the tip ? the sacrum is 11 5 centimetres or over, outlet contraction is very Unlikely unless the ischial spines appear to be particularly prominent and inverted; when this measurement is less than 11 *5 centimetres, tV? . ne pelvis should be regarded as suspect and referred for radiological examination ; when the diameter is less than 10 centimetres, the outlet ls definitely contracted.

A Caution in regard to the Diagnostic Criteria In the foregoing examination of criteria upon which to class a Pelvic outlet contracted, one's attention has been entirely focussed ^Pon the average measurement of the foetal head when moulded in exion. It is hardly necessary to emphasise that variations about the measurements are common, that partial or complete extension ^eanthe head can occur, and that accordingly outlet disproportion is in cases where the pelvic diameters are larger than the figures Possibleave quoted. Disproportion may also arise in breech deliveries when, nough the after-coming head may pass the pelvic brim in flexion, e . that it is to allow time for may result In fact impossible moulding disaster if the outlet be at all narrow. In parenthesis, it should be how frequently the head of the baby delivered by the breech ^?teda dolichocephalic shape. There is no cylinder here, but a disparity Measurements between the diameter and ^ bi-parietal sub-occipito egmatic diameter of a centimetre or more, with a sub-occipito frontal ameter which even in a 6 lb. baby may be as much as 11-5 centimetres, as in brim so at the outlet it is th ^erefore, contraction, apparent disproportion is more important than actual contraction, and that ^ae breech is a particularly dangerous presentation. A which I ^ further point to be noted is that in the calculations made I have deliberately chosen to ignore the soft tissues. There i?aVeno doubt that, in many of the cases diagnosed as contracted outlet a SQ/r stiff forceps, the major obstruction has been due to primigravid t'SSUes- ^ is to exclude the of faults in the Soft possibility mistaking passa?es f?r faults in the hard that I have deliberately neglected the s?ft tissues in making my calculations.

Labour in Contracted Outlet

If we assume a head of average size, of average consistence, and Renting in flexion, then outlet contraction may show itself in ways. Its chief influence is the second stage of labour, ^ariousit during .ut is not without effect ^ upon the first and third stages, especially those cases where the outlet contraction is an expression o a io6 W. I. C. MORRIS generalised funnel tendency. The head then meets resistance frort1 converging pelvic walls in the early portion of its descent, and there of is a tendency to the development during the first stage of labour uterine inertia, often wrongly labelled primary, and often associated of with hour-glass spasm of the uterus, so justly feared as a cause difficulty in the first and second stages of labour, and not infrequently a cause of disaster when it persists into the third stage. Nevertheless, it is the terminal second stage which is. characteristic' ally obstructed by a contracted outlet. The effect upon the mechanist of labour at this point is too complex for analysis in a short paper of this type, but to summarise one may say that outlet contraction influences the mechanism of labour adversely by interference with the mutually interdependent functions of descent and of intern^ rotation of the head, not only by absolute narrowing but also by the alteration in the axis of the birth canal. It should be noted that the common incomplete rotation of the occiput to the front is not necessarily per se a cause of major dystocia, in contracted outlet.

Damage to Maternal Passages in Contracted Outlet (a) Soft Passages.?In association with the altered axis of descend lfI damage to perineum and posterior vaginal wall occurs frequently association with a narrow pubic arch, which is the commonest cause of a complete perineal tear, especially in the case where the biparieta sot diameter is forced to emerge behind the tuberosities, when the tissues lack the protection given when this diameter is safely enclose between the conjoint rami. In antero-posterior shortening combined with or due to narro^ arch, laceration of the lateral vaginal wall commonly occurs, often an with very severe haemorrhage, difficult to control. I have seen apparently simple laceration at the lateral colpo-vulvar junctio^j partially overlapped and concealed by the labium minus, associate with wide separation of the lateral vaginal wall from the underly^ tissues, with very serious paravaginal bleeding. At other times one finds the major damage on the anteri?r vaginal wall, placed laterally. Unless bleeding occurs, laceratio*1* in this area will usually escape notice, but they should be looke for in patients where one sees the vestibule with the tense and an#1*11*' t lower end of the vagina being rolled out of the vulva in advance of descending head. I believe that waste space at the apex of the pu^lC^ arch is in some degree a protection against this form of trauma, with sequela of stress incontinence of urine. (b) Bony Passages.?Young (1940) has rightly pointed out th^' ' with the softening of the pelvic joints normal in pregnancy, a delive dlS through narrow passages can spring the symphysis pubis with astrous results to the sacro-iliac joints. From bitter clinical experien one is well aware how serious may be the results of a delivery throng OUTLET CONTRACTION OF THE PELVIS 107 a narrow outlet upon the patient's locomotion. A considerable legacy crippling is left by many a forceps delivery, not forgetting COccygodynia, with or without fracture of the coccyx or the last piece the sacrum.

The Management of Outlet Contraction

(

(i) To allow labour at term. (ii) To induce labour prematurely. (iii) To carry out elective Caesarean section.

cases in which the baby presents by the vertex, and the corrected antero-posterjor Qf fhg outlet is 9 centimetres or more, the first alternative generally be chosen. So far as induction of labour is concerned, I e personally that it has little place, owing firstly to the difficulty (even ^th the use of X-rays) in estimating the size of the head in relation h?k^e out^et? and secondly to the fact that the head of a premature y is ill-fitted to withstand the trauma resulting from an induction out too late- Elective Csesarean section obviously has a field, ieXamP^e? *n cases where the corrected antero-posterior of the outlet is ess than 9 centimetres, in the elderly primigravida at term, in , . gravid breech presentation, in the presence of an unusually large Wlth a hard and in the of heart disease with failure 0j. head, subject one0rnPensati?n ; while, in the absence of a living child, a history of more still-births may compel Caesarean section. However, ea^or?aSe ^aS t0 k0 on its own into account not arSued merits, taking Pe*v*c measurements but also the factors of parity, age, 1Ve relat^n^fertility, psycho-somatic background, relative size of brim ?Ut^et or absence of at the etc presence disproportion brim, pla^ Management of Labour.?Vaginal delivery having been nned, the keynote of management should be conservatism without UteC-raSt.ination- temptation to employ oxytocics in the face of *nert*a must be most resisted. own is to ern ^ firmly My tendency tab Su*table analgesic drugs during the first and second stages of Until the head either is showing or is easily palpable through the per?^reum- Once this stage is reached, I interfere rather earlier than CaSG dec re?ar"ded as normal, especially if the pains are poor and -aSln^' The procedure involves first postural treatment, that ^ adopted that a^0Pti?n ?f an exaggerated lithotomy position in the hope of the innominate bones about the sacro-iliac joint will Rationln f0U enlargement of the antero-posterior outlet diameter. This is ln by the primigravida (and occasionally in the parous patient) of a is s^c Performance very deep episiotomy, which, in its turn ee ed by the application of forceps. io8 W. I. G. MORRIS

In contracted outlet I advocate a very strict cephalic application of the forceps, without attempts to correct incomplete rotation of the occiput. With a truly conservative management, it is unusual to encounter a genuine occipito-posterior position, though directly lateral positions are extremely common. Kielland's forceps are ideal in such cases, but, with the head well down, the Haig Ferguson instrument,

Case 6.?(Fig.^16).6.?(Fig.^6).

Fig. 16.

of to from difficult outs* X-ray damage resulting forceps ^ hospital. Patient almost completely crippled with bilateral sacro-iliac supra-pubic pain on walking and changes of posture. despite its generous pelvic curve, is usually quite successfully app^e(^aI"e to the sides of ,the head in any position. Milne Murray's forceps awkward unless the traction rods are removed. Delivery should be completed by traction, the precise axis suitable being discovered in each case by trial and error. Forcl forceps rotation is unnecessary, the head generally rotating spontane OUTLET CONTRACTION OF THE PELVIS 109 ously during traction. Occasionally it emerges permanently occipito- ateral, and still more rotation to bring the occiput directly 0r infrequently obliquely posterior occurs at the vulva. In my experience these are not the disasters to the soft tissues which they are usually imagined *? be. If moderate traction with the forceps fails to cause any advance, Attention is given to the patient's posture, the knees being still further ^awn up in an attempt to enlarge the available antero-posterior space. Progress is made after this, a second episiotomy, utterly removing ^n? t*ssue allows of the I resistance, usually completion delivery, ave never resorted to pubiotomy, nor to symphysiotomy, nor to derate fracture of the lower sacrum. Craniotomy is a last resort and very seldom required. ^aesarean section may sometimes be adopted during labour. It ha s a place in the true funnel pelvis, when its performance is more 0rnmonly indicated on account of faults in the powers, rather than e outlet disproportion. The lower segment operation is obligatory, > since the head has entered the pelvic cavity, its upward dislodgment aY be so difficult that digital pressure from the vagina by an assistant is after such but the s reclu*rec^ Morbidity high procedures, has to risT be taken occasionally.

Summary

The shape and dimensions of the moulded foetal head are dlscussed. outlet is described in relation to the foetal head Pe^v*c briefly 3- Types of outlet contraction are discussed. ?Methods of measuring the outlet in a dried pelvis, and in the liv>ng subject are examined critically. method of determining an antero-posterior diameter of the corrected in of arch obstruction is described. g respect pubic Criteria for the diagnosis of contracted outlet are laid down. 7 Tu effects of outlet contraction on labour, and the clinical agernent of contracted outlet are very briefly examined.

Acknowledgments

to the1Alrn^>^>SS^^e *? reac^ a paper on this subject without admitting one's indebtedness inflUe ^erican authors who have dealt so fully with this subject, whilst one has been most the lucid of Professor Chasser Moir T ,Personally profoundly by writings ls a Mio js pleasure also to express gratitude to my colleagues Dr M. J. D. Noble, ^est, mT^16 ^?r construc^on ?f t^ie illustrative models and to Miss I. R. ?R-, who is radiographer to the Ayrshire Central Hospital. iio W. I. C. MORRIS

REFERENCES

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