Postgrad Med J: first published as 10.1136/pgmj.25.284.255 on 1 June 1949. Downloaded from 255

THE CLINICAL VALUE OF X-RAY PELVIMETRY By HUMPHREY G. E. ARTHURE, M.D., M.R.C.O.G., F.R.C.S. Assistant Obstetric Physician, Charing Cross Hospital; Surgeon to In-patients, Queen Charlotte's Maternity Hospital, London Introduction pected disproportion includes the following pro- Routine radiographic studies of the in jections: have provided valuable information (I) Antero-posterior projection, with the patient about the variations in shape and size of the supine. This film gives a general picture of the female pelvis. Improvements in technique and in- pelvis, from which gross contraction, tilting or creased experience of pelvimetry have made it asymmetry will be apparent, and from which the possible accurately to predict the outcome of general convergence or otherwise of the side walls labour in a high proportion of cases (9i per cent. of the pelvis can be noted. of 600 cases referred to the radiologist at Queen (2) Supero-inferior projection, with the patient Charlotte's Hospital). It is an opportune time, sitting, but reclining backwards so that the brim therefore, to discuss the ways in which is parallel to the casette. This film shows the true may assist the clinician, and to assess the value and shape of the brim and from it the brim diameters reliability of pelvimetric methods. are calculated. Difficulty may be experienced in Radiography may be used to confirm the deciding which line on the film should be taken as presence or absence of disproportion, but it must the anterior margin of the , and in such never be thought that it can supplant clinical cases the difficulty must be resolved by checking methods. measurements of diameters the measurement of the obstetric conjugate on the X-ray pelvic by copyright. may be more accurate than clinical measurements, lateral film. As Chassar Moir (I947) has pointed but it must clearly be recognized that accurate out, the most prominent point on the sacrum is prediction of the outcome of labour cannot be made in every case, however precise the measure- ments of the pelvis and foetal head may be. It is impossible to foretell the strength of the uterine contractions, the possible expansion of the pelvi- diameters in labour and the mouldability of ths "4.5 foetal head. There must, therefore, be a border- 145 line of cases in which the outcome of labour group http://pmj.bmj.com/ depends on factors which are unknown until labour occurs. In such cases a successful outcome may depend on the skill of the obstetrician who will be 6 better armed to overcome obstetric difficulties if he has accurate knowledge of the pelvic architec- FIG. 2.-Reconstruction chart of brim. ture.. Furthermore, it must be remembered that dystocia is more often due to imperfect uterine often below the pomontory. A' reconstruction. action than to actual disproportion. chart is then drawn, which shows the exact size on October 1, 2021 by guest. Protected It is convenient to discuss problems of dis- and shape of the brim, and on this chart a circle or proportion under two headings; disproportion at ellipse with a diameter of 9.5 cm. may be super- the brim and at the outlet. These present different imposed, representing an average foetal head at problems both in diagnosis and management. term. Consideration of disproportion in midcavity is un- It will be seen that the greatest transverse necessary if, firstly, brim disproportion is taken to diameter usually lies behind the mid point of the include those cases which have an antero-posterior antero-posterior diameter, and is sometimes quite diameter shorter than and slightly below the level close to the sacrum. For this reason, Chassar of the obstetric conjugate; and, secondly, if the Moir has designated the diameter Which intersects outlet is considered not as a single plane, but as the conjugate at the mid point as the available the lower pelvic strait. transverse diameter of the brim. From these films also the prominence of the Radiological Technique ischial spines can be observed, and the ischial The standard technique at Queen Charlotte's bispinous diameter calculated, if the distance from Hospital (Rohan Wliams, x943) in cases of sus- the plane of the brim is worked out from the lateral Postgrad Med J: first published as 10.1136/pgmj.25.284.255 on 1 June 1949. Downloaded from 256 POST GRADUATE MEDICAL JOURNAL June '949 film. This diameter may also be determined from the subpubic arch is narrow. In such a case the the antero-posterior projection. foetal head will be forced to emerge further back (3) Lateralprojection, with the patient erect. In than usual, and much of the antero-posterior this the femoral shafts do not obscure the diameter is wasted. symphysis , and the postural tone of the (b) The anterior border of the sacrum is abdominal muscles tends to engage the foetal head normally concave, but variations are common, so into the brim. From this film measurements are that it may be roughly straight or even slightly made of the antero-posterior diameter of the brim convex; in this case it is usually the second sacral (from the upper posterior margin of the symphysis segment which projects more than the promontory, to the most prominent anterior margin of the.upper forming a conjugate which must be considered in- sacrum), and of the antero-posterior diameter of stead of the true conjugate of the brim. There are the outlet (from the lower posterior margin of the two sacral variations which may shorten the symphysis to the anterior margin of the lowest part antero-posterior ,diameter of the outlet; firstly, of the sacrum, or to the coccyx if the sacro- the deeply hollowed sacrum in which the sacro- coccygeal junction is fixed). coccygeal shelf projects forward to lie almost The lateral film also gives information on the under the ischial spines ; secondly, a long sacrum inclination of the pelvic brim to the lumbar spine. having perhaps six segments instead of five, which This can be measured as the angle between the may be comparatively straight without a prominent true conjugate and the anterior margin of the fifth sacro-coccygeal shelf, yet because it is often more lumbar vertebra. A very large angle may account vertical than normal, the antero-posterior diameter for delayed engagement of the foetal head and of the outlet may be seriously shortened. perhaps asynclitism, but the angle will be con- (4) Subpubic arch projection, taken with the siderably reduced by drawing up the knees, a patient sitting well forwards, so that the arch is point to be remembered in the management of the parallel with the casette. The manner in which first stage of )abour. the foetal head will fit into the arch de-

subpubic by copyright. ,A reconstruction chart is made from the lateral pends on the angle of the arch and on the curvature film of the median or sagittal plane of the pelvis, of the descending pubic rami. These factors are and from this the curve of the pelvic canal can be best assessed by using a disc with a diameter of http://pmj.bmj.com/

FIG. 4.--Lateral reconstruction chart. on October 1, 2021 by guest. Protected studied, using a disc representing the average FIG. 6.-Subpubic arch reconstruction chart. foetal head at term. It must, however, be re- membered that part of the antero-posterior 9.5 cm. representing the average foetal head at diameters may not be available to the foetal head, term: When the arch is wider than normal (90go and it is best to observe the general shape and lie or more) the disc occupies the whole of the arch, of the symphysis and descending pubic rami in with an average arch (about 850) there is a gap of front, and of the sacrum behind. 0.5 to I cm. between the circumference of the disc (a) The symphysis tends to slope backwards and the symphysis; when the arch is narrow (less roughly parallel with the backward inclination of than 80o) there will be a still wider gap. The the sacrum; if it has a greater backward slope length of this gap is measured on the film and than. usual, the antero-posterior diameter of the reduced to actual size, which will represent the outlet will be shortened. The descending pubic distance an average-sized unmoulded foetal head rami normally slope backwards more than the will lie from the lower border of the symphysis symphysis, but this is variable, and a marked during delivery. backward slope is particularly unfavourable when This distance can be marked off on the lateral Postgrad Med J: first published as 10.1136/pgmj.25.284.255 on 1 June 1949. Downloaded from June I949 ARTHURE : The Clinical Value of X-Ray Pelvimetry

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FIG. 9.-Lateral X-ray. Head free and occiput slightly posterior; no disproportion. J.une 1949 ARTHURE : The Clinical Value of X-Ray Pelvimetry 259, Postgrad Med J: first published as 10.1136/pgmj.25.284.255 on 1 June 1949. Downloaded from reconstruction chart on the line of the descending accurate cephalometry, the clinician can often pubic rami, and the available antero-posterior compare cephalic diameters with the pelvis in the diameter is measured from the lowest anterior lateral film, provided the head is central, and more use might be made of radiography'in the' course of' x/ trial labour, to determine the progress of the head through the brim, and the degree of moulding. Indications for Radiography Although Munro Kerr (1942) has advocated routine radiography in all primigravidae, most obstetricians believe they can exclude dispropor- tion with certainty in a large majority of cases by- clinical methods. Yet most of them would admit -that they have occasionally missed disproportion, even though they have applied their usual methods of examination, and some are ready to look for the cause of unexpectedly difficult labour in postnatal radiography. X-rays may be used to confirm gross pelvic abnormality, to provide accurate information in cases of suspected disproportion, or to exclude disproportion with certainty when the pelvis is FIG. 7.--Lateral reconstruction chart in same case as thought to be normal. In the latter group may be Fig. 6, showing available A.P. diameter. mentioned patients who are difficult to examine, margin of the sacrum to this point. Recently, primigravidae with breech presentations, and and Rohan Williams patients who have previously had a difficult or Morris (I947), Allen (I947) by copyright. (I949) have given considerable attention to this prolonged labour 'or a . It is available antero-posterior diameter of the lower certainly helpful to both obstetrician and patient pelvic strait, and Morris considers the outlet is to have X-ray evidence that disproportion will not contracted when this diameter is less than io cm. occur, and this evidence will probably lessen un-- Forecast graphs. Chassar Moir (I947) has necessary surgical procedures. A number of advocated the use of graphs to assess the capacity patients have now been delivered at Queen Char- of the pelvis at three planes. He has prepared lotte's Hospital, as at other maternity hospitals, graphs for various biparietal diameters of the foetal without undue difficulty, having previously had a head, determined by postnatal measurement, and Caesarean section for disproportion diagnosed on without the benefit of has shown that a line may be drawn each graph X-rays. http://pmj.bmj.com/ for different sizes of the foetal head, on the lower Confirmation of obvious pelvic abnormality is side of which a great preponderance of difficult nowadays almost a routine before deciding on deliveries will be plotted. Caesarean section, and in not a few of these cases Cephalometry. As yet no series of forecasts have X-rays show that normal delivery is feasible in been published using antenatal cephalometry in spite of a flattened brim, an asymmetric pelvis or conjunction with pelvimetry, and there are two a narrow outlet. difficulties. Firstly, many patients are X-rayed One of the common indications for radiography early in before cephalometry is feasible; is the high head that cannot be pushed into the on October 1, 2021 by guest. Protected and, secondly, in patients X-rayed at or after the brim. It is well known that this is often due. to 36th week of pregnancy, measurements of the bad flexion and that engagement will readily occur foetal diameters can only be made in about half when the patient is examined sitting up. But it the cases because of unfavourable positions of the may be difficult to feel the head in this position,. head. Cephalometric methods are then only and the obstetrician may be uncertain whether it approximate, as is estimation of further growth in will or will not quite engage. It.is best to resolve the last month. this difficulty with a lateral X-ray in the erect Nevertheless, cephalometry should be practised position and a full pelvimetry if the head is not whenever possible, and provided its limitations are found to be engaged. -If the biparietal diameter is recognized, the additional knowledge will further smaller than the obstetric conjugate it may usually narrow down the borderline group. The clinical be stated that there is no brim disproportion. aphorism that 'the foetal head is the best SuCh a procedure will often obviate the necessity pelvimeter' must be applied to radiology, if the 'for a trial labour, which is not infrequently accom- best results are to be achieved. -Even without panied by defective uterine action, when both 26o POST GRADUATE MEDICAL JOURNAL ' June I949 Postgrad Med J: first published as 10.1136/pgmj.25.284.255 on 1 June 1949. Downloaded from patient and obstetrician are wondering about the perhaps a stillborn child. Labour may be surgic- possibility of Caesarean section. ally induced about the 38th week in cases of marked outlet contraction confirmed by X-rays, 'The Value of Radiography in Borderline but in most cases of minor contraction this is un- Cases necessary and it may reasonably be expected that Minor degrees of disproportion may be dis- forceps aid will overcome difficulty although covered by careful pelvic examination, because of occasionally at the expense of a dislocated coccyx. a high head that cannot be pushed into the brim, When a persistent occipito-posterior occurs in or simply on routine radiographic examination. labour it is an advantage to know if the pelvis is Evidence of such disproportion was found in about anthropoid, as then a face to pubes delivery may be I8 per cent. of cases referred to the radiologist at safely achieved, whereas with an android pelvis it is Queen Charlotte's Hospital, and in these the better to rotate the occiput. The accepted teaching chances of normal or difficult delivery are about and practice in cases of deep transverse arrest is to equal. Problems at the brim must be considered rotate the head manually and deliver it through separately from problems at the outlet, but both the lower pelvic strait with the long axis antero- may give rise to uncertainty in the generally posterior. Yet X-rays have shown that in 30 contracted pelvis. per cent. of these cases the ischial bispinous (a) Brim disproportion. There is no doubt that diameter is actually greater than the antero- clinical estimation of the shape and size of the posterior diameter of the outlet. This is a forcible brim is less accurate than pelvimetry. X-rays argument in favour of drawing the head through may be unnecessary when the head is engaged or this plane in the transverse diameter in these can.be pushed into the brim, but when this cannot particular cases, allowing rotation to occur after be done radiography will provide more information the head has passed the ischial spines. Such than can be obtained by examination under an practice might well reduce the high foetal mortality anaesthetic at the 36th week, with less discomfort associated with deep transverse arrest. to the patient. This procedure should be don- demned as strongly as indiscriminate surgical by copyright. induction. Conclusions Although the pelvic joints may expand some- The use of radiography in borderline cases has what during pregnancy, there is little evidence been criticized on the grounds that unnecessary that appreciable expansion occurs during labour, interference will increase. This should not be so and the mouldability of the foetal head cannot be if X-rays are done well and are interpreted with assessed until labour occurs. Trial labour is, intelligence. It is true that unnecessary Caesarean therefore, the best procedure for borderline brim ·section has sometimes been done when the disproportion, unless the age or history of the obstetrician has been misled by bad X-rays, but patient causes a bias in favour of elective Caesarean this should make us improve our X-ray diagnostic section. The outcome of trial labour must be methods and learn from our mistakes. The chief http://pmj.bmj.com/ determined mainly by clinical examination, but value of radiology may be the exclusion of dis- sometimes a head will mould to such an extent proportion, but valuable information can also be that the vertex reaches the pelvic floor before the gained in the borderline case, and forewarning of greatest diameter has passed the brim. X-rays in possible dystocia should at least ensure that these labour may still be of value in assessing the patients are confined in hospital, where facilities progress of the head. are available for a- Caesarean section or difficult It is sur- and for resuscitation of the (b) Outlet disproportion. perhaps forceps delivery, baby on October 1, 2021 by guest. Protected prising that accurate measurements of the pelvic if the need arises. otitlet are difficult to achieve by clinical methods, but X-rays sometimes show that this is so. ACKNOWLEDGMENTS Furthermore, the foetal head cannot be used as a pelvimeter except during delivery, and for this I wish to record my thanks to Dr. Rohan reason trial labour, as usually understood, has no Williams for his kind assistance and helpful place in outlet disproportion. Much greater ex- criticism, and for providing the illustrative pansion of the pelvic diameters is possible at the material. outlet than at the brim, and cases of absolute dis- proportion necessitating Caesarean section are BIBLIOGRAPHY rarely seen except in osteomalacic pelves or in ALLEN, P. (I947), Brit. 7. Radiol., 20, 45 and 205. dwarfs. Caesarean section CHASSAR MOIR, J. (I947), Y. Obst. and Gyn. Brit. Emp., x, 20. achondroplasiac may, MORRIS, W. I. C. (I947), Edin. Med.J., 54, 90. however, be the best treatment for a patient who- MUNRO-KERR, J. M. (I948), .7. Obs t.and Gyn. Brit. Emp., 4, 401. has -previously had a difficult forceps delivery with ROHAN WILLIAMS, E. (I943), Brit. J. Radiol., x6, 173.