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The Relation of the Sacral Promontory to the Pelvic Inlet*
THE BBL.A.TlON OF TilE IACB.A.L PltOMOlfTOBY TO THE P:SLVIC INLET* HERBERT
THoMs, ]\t[.D., NEw HAVEN, Co~N.
(From the Department of Obstetrics and Oyneoolo,qy, Yale University Hchool of M nl·khw)
T
HE anatomist William Turner more than a half century ago wrote, "With the exception of the skull, no portion of the skeleton presents greater individual variations than the pelvis.'· The truth of this statement has been made greatly manift'st in our time, for through the use of roentgen methods has come the oppOl'tunit?' for the study of the bony pelvis on a far greater scale than was possible to our ancestors. The reason for such wide variation in this part of the skeleton must be sought in the fact that the pelvis is developed from a considerable number of bones and that during its growth to the adult state it is subjected to an indefinite number of nutritional, mechanical, and hormonal influences. The present study is eoneerned with but one aspect of pelvic variation and that is the pelvic relationships of the upper sacrum, and in particular the position of the promontor~~ of the sacrum in its relation to the plane of the pelvie inlet. In this investigation the roentgenologic findings in 200 primigravid women have been studied. These women were unselected and represent a group who were registered !or delivery in the prenatal (•linie of the New Haven Hospital during the year 1942. It is because of the wide variation in position of the sacral promontory in its relation to the bony pelvic canal that some modern investigators have found that for clinical purposes it is necessary to abandon the idea that the superior strait, as described in anatomie texts, should he considered as the plane of the obstetric pelvic inlet. Therefore, from an obstetric point of view the plane of the pelvic inlet is considered to he bolmded anteriorly by the upper posterior surfaee of the pubk symphysis and forward positions of the iliopectineal lines, laterally by the iliopectineal lines and posteriorly by 1he posterior portions of these lines and the anterior upper surface of 1lw sacrum a1 the point 1vhere the convergence of these lines t;ak~>s plac·P. The importanee of this plane in the mechanism of labor has heen emphasized h.v Caldwell, 1\ioloy and D'Esopo/ who state, "\V1.~ heliPYe that the Jlromontory is too nniitable in position to the plane of tlw inlPt to be used as a point of origin of such an important ohstetl'ie dianH'teJ' (the trne <'
110
1'HOMS:
RELATION OF SACRAL PROMONTORY TO PELVIC INLET
111
face of the first sacral vertebra where the continuation of the iliopectineal lines on either side meet each other.'' That a wide variation exists in the position of the promontory is seen in this study of its relation to the posterior end-point of the anteroposterior diameter of the plane of the pelvic inlet. In these 200 cases the promontory rested at or near this point in 61 instances, The The The The The
promontory promontory promontory promontory promontory
rested rested rested rested rested
1.0 1.5. 2.0 2.5 3.0
em. em. em. em. em.
above above above above above
this this this this this
point point point point point
in in in ln in
30 instances, 41 instances, 51 instances, 12 in&tances, 5 instances.
Fig. 1.-Small brachypellic type pelvis, anteroposterior 10.0 transverse lUi. Th e promontory rests 2.5 em. above the posterior end point of the true conjugate. The diagonal conjugate Is 12.0 em. from which It might be assumed that the true conjugate was 10.5 em., an error which might be costly.
F'rom this evidence it becomes apparent that the position of the forward edge of the sacral promontory is too unreliable to be considered as the posterior ~nd of the true conjugate diameter, for in this series it was at or close to this point in but 30.5 per cent of cases (Fig. 1). It also becomes obvious that because of this positional variation the value of the diagonal conjugate diameter as an index of the true conjugate diameter may be very much questioned. It is generally stated that the true con-
112
AMERICAN JOURNAL OE' OBS'l'E'l'RICS AND GYNECOLOGY
jugate diameter may be estimated from the formet· by deducting l.:i to 2.0 em. according to the height aiHl inclination of the symphysis pubis. Some texts omit the question of height and inclination and simply deduct 1.5 em. for the true conjugate diameter. The facts seem to be that the diagonal conjugate cannot be considered a reliable index to the true conjugate diameter and that in some cases information so obtained may be misleading (Fig. 2). In the p1·esent series this fact was emphasized by a comparison of Cases 21 and 54, which had identical diagonal conjugate diameters of 13.0 em. and true conjugates of 11.9 and 10.5, respectively.
Fig, 2.-Small mesatipellic type pelvis. anteroposterior 10.4. transverse 11.4. The promontory rests 2.0 em. above the posterior end point of the tru<:; conjugate. Roentgenogram shows a breech presentation in a primigravida. The cl!agonal coniugate Is 13.0 em. from whieh the true conjugate c·~timation of 11.5 gives an error of 1. .1 em.
In this series an attempt was made to find out if high positions of the promontory were associated with any particular pelvic grouping according to the division into dolichopellic, mesatipellic, brachypellic and platypellic types. In the series these groups were represented as follows: Dolichopellic type Mesatipellic type Brachypellic type Platypellic type
30 instance;; or 15% 84 instance;; or 42% 77 instances ur :38.5% 9 instances or 4.5%
THOMS:
RELATION OF SACRAL PROMONTORY TO PELVIC INLET
113
These findings correspond with the findings in 1,100 women previously published, 2 which were for these groups: 18.6 per cent, 45.9 per cent, 32.2 per cent, 3.2 per cent, respectively. In the 61 pelves in which the promontory was at or less than 1 em. above the pelvic inlet plane, the division was: Dolichopellic type Mesatipellic type Brachypellic type Platypellic type
8.2% 37.7% 45.9% 8.2%
Fig. 3.-The .p romontory Is located near the posterior end point of the true conjugate diameter. In this position It may very definitely lnfiuence the descent and position of the fetal head In its engagement in the true pelvis .
In the 71 pelves in which the promontory was 1 em. or more but less than 2 em. above the pelvic inlet plane, the division was : Dolichopellic type Mesatipellic type Brachypellic type Platypellic type
21.1% 38.0% 38.0% 2.8%
114
AMERICAN ,JOU RNAL 01<' OBSTE~rRICS AND GYNECOLOGY
In 68 pelves in which the promontol'y wa:,; 2 pelvic inlet plane, the division was: Doli('.hopellie type Mesat.ipellie ty pe Brachypellic type Platypellic t.ype
('Ill.
ot· more ahove the
I .J.. i'ri ; .)I ),IJC; ;
:{:?.4'1;. ~.w;,.
From this analysis it is apparent that no definite conclusions may he drawn, and that the high promontory position is somewhat, if hut slightly, associated with the dolichopellic and mesatipellic t:vpes ( If pelvis.
Fig. 4.-The promontory is located 3 em. above the posterior end point of the true conjugate diameter. Its influence if any in the descent and position of the fetal head in its engagement in the true pelvis would· not a ppear to be important.
In the present series also the reliability of the diagonal conjugate diameter as an index of the true conjugate diameter was determined. For this purpose 1.5 em. was deducted from the diagonal conjugate and a leeway of 0.25 em. + or - was allowed for the true conjugate. The result showed that the diagonal eonjugate could be used as a satisfactory criterion in 76 instances, or but 38 per cent of cases.
THOMS:
RELATION 01'' SACRAL PROMONTORY ·TO PELVIC INLET
115
Because of the variation in the ·position of the sacral · promontory, it is apparent thatthe U$Ual concept of the role played by this protuberance in ' the pelvic engagement of the fetus -and in the mechanism of labor must be somewhat modified. Except in those inst~tnces where the promontory is at or near the posterior limits of the plane of the pelvic inlet it is difficult to see how in high positions it can· play a very major part in the mechanism by which the fetal head settles into the pelvis. The fact is seen to advantage in Figs. 3 ·and 4. However, it should not be forgotten that in certain instances (probably rarely) even when the promontory occupies a somewhat high position it may project forward and the distance from the upper posterior symphysis to the promontory be less than that of the true conjugate diameter (Fig. 5) .
Fig. . :;,_:Rarely when the promontory Is located above the p()sterio; end point of the true conj,ugate a forward position exists which makes the aymphysts.promontory distance less than the true conjugate, in this Instance 11.5 '8lld 11.2 em., r.espectlvely.
A question arises as to whether high positions of the sacral promontory are definitely associated with the so-called assimilation pelvis. There did not seem to be any direct evidence of this in the series, but it should. be stated that the diagnosis of this type of pelvis from the single lateral roentgenogram cannot readily be made because all of th~ segments of the lumbar spine are not visible and in many instances the segmentational differences in the lower sacrum and roccy:s: are not easily disti:Jiguishable.
116
AMERICAN JOURNAL OF OBSTETRICS AND GYNECOLOGY
In conclusion, it may be stated that because of the variation in position of the sacral promontory the estimation of the true conjugate diameter based upon the length of the diagonal conjugate diameter iR subject to error and pelvic capacity so determined should not be expressed in exact terms. In the present series the estimation of l he tnw conjugate diameter based on the length of the diagonal <•on;iugate was only approximately correct in 38 per eent of cases. Bt~eause of t}w nu·iation in position of the sacral promontory the part pla.ved hy this protuberance in the engagement of t.ht• fetal head may he either import:mt or unimportant. This study emphasizes again that roentgenologie methods are an important adjunct to the usual diagnostic obstetric pro<'edures, for with the added knowledge that they furnish many of the mechanical problem" of labor will be better understood and operative inter·ferenee mad(; :1 more intelligent proeedur<'. In our own c1inic the experience obtained by the routine use of roentgen pelvimetry in 2,000 primigravid womPn delivered during the past seven :Vt'ars (•onfirms this opinion with in~ rreasing strength.
References 1. Caldwell, W. E., Moloy, N.C., and
763, 1935. :?. ThomR, H.: AM. J. 0RST. &
D'F;~opo,
GYNE~<.
D. A.:
AM . •T. 0Rs·r. & Hy;,·T,. 30:
42: 9!i7, 19±1.
THE EFFECT OF COMPLEMENTING THE DIET IN PREGNANCY WITH CALCIUM, PHOSPHORUS, IRON, AND VITAMINS A AND D':' PRED
L.
ADAIR,
J. DmcK:IfANN, IVI.D., HERBERT ~lrnn;1., M.S.. l':lvr,viA KRAMFR, Pn.n ...\.'\P EDNA LORANG, B.8 .. CHICAGO, ILL.
IVI.D.,
·wrLLIAl\i
M.D., FLoRENCE Duh'XLE,
HERE have been a number of reports concernitJg- the ealcium. phos phorus, iron, nitrogen, and vitamin requirenwnts of the T woman, but the actual number of patients studied is eomparatin;ly small. D
pregnant
A series of metaholi(· studies were made hy m; as a part of an iuvostiga tion of the therapeutic value of added amounts of ealeium, phosphornH. iron, and vitamins A and D. The patients were divided into fom groups: ( 1) Control. (2) These patients received a proprietary ct>real for its cium, phosphorus, and iron rontent.
£•td-
*Read at a meeting of the Chicago Gynecological Society, Januat·y Hi. 1943. This study was supported in pazt by a grant from Mead .Johnson anrl <:ompany, who also supplied the special cereal and vitamins.
THoMs, ]\t[.D., NEw HAVEN, Co~N.
(From the Department of Obstetrics and Oyneoolo,qy, Yale University Hchool of M nl·khw)
T
HE anatomist William Turner more than a half century ago wrote, "With the exception of the skull, no portion of the skeleton presents greater individual variations than the pelvis.'· The truth of this statement has been made greatly manift'st in our time, for through the use of roentgen methods has come the oppOl'tunit?' for the study of the bony pelvis on a far greater scale than was possible to our ancestors. The reason for such wide variation in this part of the skeleton must be sought in the fact that the pelvis is developed from a considerable number of bones and that during its growth to the adult state it is subjected to an indefinite number of nutritional, mechanical, and hormonal influences. The present study is eoneerned with but one aspect of pelvic variation and that is the pelvic relationships of the upper sacrum, and in particular the position of the promontor~~ of the sacrum in its relation to the plane of the pelvie inlet. In this investigation the roentgenologic findings in 200 primigravid women have been studied. These women were unselected and represent a group who were registered !or delivery in the prenatal (•linie of the New Haven Hospital during the year 1942. It is because of the wide variation in position of the sacral promontory in its relation to the bony pelvic canal that some modern investigators have found that for clinical purposes it is necessary to abandon the idea that the superior strait, as described in anatomie texts, should he considered as the plane of the obstetric pelvic inlet. Therefore, from an obstetric point of view the plane of the pelvic inlet is considered to he bolmded anteriorly by the upper posterior surfaee of the pubk symphysis and forward positions of the iliopectineal lines, laterally by the iliopectineal lines and posteriorly by 1he posterior portions of these lines and the anterior upper surface of 1lw sacrum a1 the point 1vhere the convergence of these lines t;ak~>s plac·P. The importanee of this plane in the mechanism of labor has heen emphasized h.v Caldwell, 1\ioloy and D'Esopo/ who state, "\V1.~ heliPYe that the Jlromontory is too nniitable in position to the plane of tlw inlPt to be used as a point of origin of such an important ohstetl'ie dianH'teJ' (the trne <'
110
1'HOMS:
RELATION OF SACRAL PROMONTORY TO PELVIC INLET
111
face of the first sacral vertebra where the continuation of the iliopectineal lines on either side meet each other.'' That a wide variation exists in the position of the promontory is seen in this study of its relation to the posterior end-point of the anteroposterior diameter of the plane of the pelvic inlet. In these 200 cases the promontory rested at or near this point in 61 instances, The The The The The
promontory promontory promontory promontory promontory
rested rested rested rested rested
1.0 1.5. 2.0 2.5 3.0
em. em. em. em. em.
above above above above above
this this this this this
point point point point point
in in in ln in
30 instances, 41 instances, 51 instances, 12 in&tances, 5 instances.
Fig. 1.-Small brachypellic type pelvis, anteroposterior 10.0 transverse lUi. Th e promontory rests 2.5 em. above the posterior end point of the true conjugate. The diagonal conjugate Is 12.0 em. from which It might be assumed that the true conjugate was 10.5 em., an error which might be costly.
F'rom this evidence it becomes apparent that the position of the forward edge of the sacral promontory is too unreliable to be considered as the posterior ~nd of the true conjugate diameter, for in this series it was at or close to this point in but 30.5 per cent of cases (Fig. 1). It also becomes obvious that because of this positional variation the value of the diagonal conjugate diameter as an index of the true conjugate diameter may be very much questioned. It is generally stated that the true con-
112
AMERICAN JOURNAL OE' OBS'l'E'l'RICS AND GYNECOLOGY
jugate diameter may be estimated from the formet· by deducting l.:i to 2.0 em. according to the height aiHl inclination of the symphysis pubis. Some texts omit the question of height and inclination and simply deduct 1.5 em. for the true conjugate diameter. The facts seem to be that the diagonal conjugate cannot be considered a reliable index to the true conjugate diameter and that in some cases information so obtained may be misleading (Fig. 2). In the p1·esent series this fact was emphasized by a comparison of Cases 21 and 54, which had identical diagonal conjugate diameters of 13.0 em. and true conjugates of 11.9 and 10.5, respectively.
Fig, 2.-Small mesatipellic type pelvis. anteroposterior 10.4. transverse 11.4. The promontory rests 2.0 em. above the posterior end point of the tru<:; conjugate. Roentgenogram shows a breech presentation in a primigravida. The cl!agonal coniugate Is 13.0 em. from whieh the true conjugate c·~timation of 11.5 gives an error of 1. .1 em.
In this series an attempt was made to find out if high positions of the promontory were associated with any particular pelvic grouping according to the division into dolichopellic, mesatipellic, brachypellic and platypellic types. In the series these groups were represented as follows: Dolichopellic type Mesatipellic type Brachypellic type Platypellic type
30 instance;; or 15% 84 instance;; or 42% 77 instances ur :38.5% 9 instances or 4.5%
THOMS:
RELATION OF SACRAL PROMONTORY TO PELVIC INLET
113
These findings correspond with the findings in 1,100 women previously published, 2 which were for these groups: 18.6 per cent, 45.9 per cent, 32.2 per cent, 3.2 per cent, respectively. In the 61 pelves in which the promontory was at or less than 1 em. above the pelvic inlet plane, the division was: Dolichopellic type Mesatipellic type Brachypellic type Platypellic type
8.2% 37.7% 45.9% 8.2%
Fig. 3.-The .p romontory Is located near the posterior end point of the true conjugate diameter. In this position It may very definitely lnfiuence the descent and position of the fetal head In its engagement in the true pelvis .
In the 71 pelves in which the promontory was 1 em. or more but less than 2 em. above the pelvic inlet plane, the division was : Dolichopellic type Mesatipellic type Brachypellic type Platypellic type
21.1% 38.0% 38.0% 2.8%
114
AMERICAN ,JOU RNAL 01<' OBSTE~rRICS AND GYNECOLOGY
In 68 pelves in which the promontol'y wa:,; 2 pelvic inlet plane, the division was: Doli('.hopellie type Mesat.ipellie ty pe Brachypellic type Platypellic t.ype
('Ill.
ot· more ahove the
I .J.. i'ri ; .)I ),IJC; ;
:{:?.4'1;. ~.w;,.
From this analysis it is apparent that no definite conclusions may he drawn, and that the high promontory position is somewhat, if hut slightly, associated with the dolichopellic and mesatipellic t:vpes ( If pelvis.
Fig. 4.-The promontory is located 3 em. above the posterior end point of the true conjugate diameter. Its influence if any in the descent and position of the fetal head in its engagement in the true pelvis would· not a ppear to be important.
In the present series also the reliability of the diagonal conjugate diameter as an index of the true conjugate diameter was determined. For this purpose 1.5 em. was deducted from the diagonal conjugate and a leeway of 0.25 em. + or - was allowed for the true conjugate. The result showed that the diagonal eonjugate could be used as a satisfactory criterion in 76 instances, or but 38 per cent of cases.
THOMS:
RELATION 01'' SACRAL PROMONTORY ·TO PELVIC INLET
115
Because of the variation in the ·position of the sacral · promontory, it is apparent thatthe U$Ual concept of the role played by this protuberance in ' the pelvic engagement of the fetus -and in the mechanism of labor must be somewhat modified. Except in those inst~tnces where the promontory is at or near the posterior limits of the plane of the pelvic inlet it is difficult to see how in high positions it can· play a very major part in the mechanism by which the fetal head settles into the pelvis. The fact is seen to advantage in Figs. 3 ·and 4. However, it should not be forgotten that in certain instances (probably rarely) even when the promontory occupies a somewhat high position it may project forward and the distance from the upper posterior symphysis to the promontory be less than that of the true conjugate diameter (Fig. 5) .
Fig. . :;,_:Rarely when the promontory Is located above the p()sterio; end point of the true conj,ugate a forward position exists which makes the aymphysts.promontory distance less than the true conjugate, in this Instance 11.5 '8lld 11.2 em., r.espectlvely.
A question arises as to whether high positions of the sacral promontory are definitely associated with the so-called assimilation pelvis. There did not seem to be any direct evidence of this in the series, but it should. be stated that the diagnosis of this type of pelvis from the single lateral roentgenogram cannot readily be made because all of th~ segments of the lumbar spine are not visible and in many instances the segmentational differences in the lower sacrum and roccy:s: are not easily disti:Jiguishable.
116
AMERICAN JOURNAL OF OBSTETRICS AND GYNECOLOGY
In conclusion, it may be stated that because of the variation in position of the sacral promontory the estimation of the true conjugate diameter based upon the length of the diagonal conjugate diameter iR subject to error and pelvic capacity so determined should not be expressed in exact terms. In the present series the estimation of l he tnw conjugate diameter based on the length of the diagonal <•on;iugate was only approximately correct in 38 per eent of cases. Bt~eause of t}w nu·iation in position of the sacral promontory the part pla.ved hy this protuberance in the engagement of t.ht• fetal head may he either import:mt or unimportant. This study emphasizes again that roentgenologie methods are an important adjunct to the usual diagnostic obstetric pro<'edures, for with the added knowledge that they furnish many of the mechanical problem" of labor will be better understood and operative inter·ferenee mad(; :1 more intelligent proeedur<'. In our own c1inic the experience obtained by the routine use of roentgen pelvimetry in 2,000 primigravid womPn delivered during the past seven :Vt'ars (•onfirms this opinion with in~ rreasing strength.
References 1. Caldwell, W. E., Moloy, N.C., and
763, 1935. :?. ThomR, H.: AM. J. 0RST. &
D'F;~opo,
GYNE~<.
D. A.:
AM . •T. 0Rs·r. & Hy;,·T,. 30:
42: 9!i7, 19±1.
THE EFFECT OF COMPLEMENTING THE DIET IN PREGNANCY WITH CALCIUM, PHOSPHORUS, IRON, AND VITAMINS A AND D':' PRED
L.
ADAIR,
J. DmcK:IfANN, IVI.D., HERBERT ~lrnn;1., M.S.. l':lvr,viA KRAMFR, Pn.n ...\.'\P EDNA LORANG, B.8 .. CHICAGO, ILL.
IVI.D.,
·wrLLIAl\i
M.D., FLoRENCE Duh'XLE,
HERE have been a number of reports concernitJg- the ealcium. phos phorus, iron, nitrogen, and vitamin requirenwnts of the T woman, but the actual number of patients studied is eomparatin;ly small. D
pregnant
A series of metaholi(· studies were made hy m; as a part of an iuvostiga tion of the therapeutic value of added amounts of ealeium, phosphornH. iron, and vitamins A and D. The patients were divided into fom groups: ( 1) Control. (2) These patients received a proprietary ct>real for its cium, phosphorus, and iron rontent.
£•td-
*Read at a meeting of the Chicago Gynecological Society, Januat·y Hi. 1943. This study was supported in pazt by a grant from Mead .Johnson anrl <:ompany, who also supplied the special cereal and vitamins.