A prerecorded program for the Ball pelvimetry technique Ebf*\NL’EL
A.
Pdvirtwtr~ uwd with approuch much Ic~.Y
FRIEDMAN,
M.D.,
MED.SC.D
run bp ,simpl$ed by a recently devised computer program. The program can any of several advanced programmable pocket or desk-top calcu1ator.y. This is more accurate than either the nomogram or the slide rule. and demander time and attention.
TH FC X-RAY cephalopelvimetric technique first described in 1935 by Ball and Marchbanks has several distinct advantages over other methods. It is capable of measuring the fetal head in any presenting position, providing a specific head volume in each case against which to judge the capacity of the pelvis based on measured dimensions. Moreover, it has essentially none of the technical drawbacks of other methods that require accurate positioning of the patient, precise placement of grids or rulings, or use of specially designed equipment. The geometric triangulation principles of the Ball technique have been previously outlined.’ Detailed expositions of how the measurements are made from the x-ray films are also available2. ” and need not be repeated here. Various aids have been introduced to simplify the mathematical manipulations needed to correct the film measurements for expected divergence error, to calculate the corresponding head volume and pelvic capacity. and to determine volume deficits where they exist. It is likely this useful clinical tool has not found greater acceptance among obstetricians and radiologists by virtue of the arithmetic involved. Nomograms*, ’ and a special slide rule’ have apparently not entirely resolved this problem. A recently devised computer program6 has generated utilitarian tables that are proving to be most helpful in clinical practice at this institution. The sheer bulk of paper and the need to reduplicate the tables periodically as they deteriorate with use and time are the only obvious disadvantages we have encountered to date.
From I5rarl
the Department v/ Obstetrics and Gynecology, Hospital or~d Harwzrd Medical Schoo!.
Receiwdjr .4ccepted
public&on ,Warch
January
be
A computer program has now been evolved for use with any of several advanced programmable pocket or desk-top calculators. The loo-step sequence shown in Table I was written specifically for the HP-65* unit; it can be readily modified for other equipment. When the prerecorded magnetic card containing this program is inserted into the calculator, the operator can proceed to compute volumes, capacities. and deficits merely by entering the paired arrays of measured dimensions and object-film distances. As each pair is entered, the corrected volume is derived and stored for subsequent use in determining the deficit or for later reference purposes. In this program, subroutine A is used for entering the three important pelvic dimensions (widest transverse and anteroposterior diameters of the inlet and interspinous diameter at the midplane)* and subroutine B for the two head &cumference measurements (obtained from the anteroposterior and lateral films, respectively). All necessar? corrections and conversions are automaCcally accomplished and the head volumes are averaged. After the five dimensions have been duly processed, subroutine C computes the deficits seriatim. To enter a new case, only the storage registers need to be cleared. The flow of data is as follows: The first measured pelvic dimension (the widest transverse diamet.er of the inlet) is entered (key A) along with it< object.-film distance (key R/S). The data are automatically subprogrammed (subroutine E) for purposes of correcting the measured dimension for magnificafion distortion and beginning the computation of the corresponding volume
Beth
23, 1976.
The program returns to the point from which it had branched, there to complete the volume calculation and to seek an appropriate storage register. It tests
IO, 1976.
Reprint requests: Emanuel A. Friedman, M.D., Department of Obstetrtis and Gynecology, Beth Israel Hospitul, 330 Brookline ‘41v., Boston, Massachusetts 02215.
*Hewlett-Packard
477
Company,
Cupertino,
California.
478
Friedman
Table
I. Programmed
LBLA ST08 E
LBLl RCL2 1
:TO3 RCLl 1
:TO8 gDSZ RCL3 RTN RCL3 ST02 RTN
:TO8 @= CT01 RCL3 ST01 RTN
steps for Ball pelvimetry
LBLB ST08 2 ST07 E ENT
LBL2 RCL5 RCL4
LBLC RCLl RCL6
l
X
;TO6 RCL5 RTN
RIS RCL2 RCL6 RIS RCL3 RCL6 RTN
:TO5 RCL4 1 :TO8 gDSZ CT02 RCL5 ST04 RTN
LBLE RCL8 RIS ST06 & 100 ENT ENT RCL6
g=
RTN
each of the first three registers in turn and enters the derived volume into the first one it locates that contains no previously entered volume. Since this is the first entry, the capacity corresponding to the widest transverse inlet diameter would be stored in the first register. Next, a second dimension (the anteroposterior diameter of the inlet, key A) and its object-film distance (key R/S) are entered; the volume is computed and stored in the second register (subprogram 1). Entering the third pelvic dimension (interspinous diameter, key A) and its object-film distance (key R/S) complete the calculations of pelvic capacities as this volume is stored in the third register. One of the measured head circumferences (from the anteroposterior film, key B) with its corresponding
object-film distance (key R/S) is then entered, branched (subprogram E) for divergence correction, and furthei corrected for fetal scalp volume (by adding 2 cm. to the corrected cranial circumference). Initial computation of the head volume from the corrected circumference
is undertaken, utilizing the steps shared in common with the calculation of volume from diameters. Returning to the point from which it branched, the program completes the volume calculation and proceeds to seek an appropriate storage register; the first head volume is stored in the fourth register. The remaining head circumference (from the lateral film, key B) ancl its object-film distance (key R/S) are handled in the same way, and the calculated volumes stored in the fifth register (subprogram 2). When both head volume storage registers are occupied, they are automatically averaged and the mean head volume stored in the sixth register. Finally, subprogram C determines the deficits between the mean head volume and the pelvic capacity as derived first from the widest transverse inlet diameter (key C), then from the anteroposterior inlet diameter (key R/S), and last from the interspinous diameter (key R/S again). This approach is much more accurate than either the nomogram or the slide rule in clinical use. It is much lessdemanding in terms of time and attention than the aforementioned generated tables. The expense of a programmable calculator is offset by the advantages of the information it provides through the intermedium of this program, and of course by the many other uses to which it can be put.
REFERENCES
1. Ball, R. P., and Marchbanks, S. S.: Roentgen pelvimetry and fetal cephalometry: A new technique, Radiology 24: 77, 1935. 2. Friedman, E. A., and Taylor, M. B.: A modified nomographic aid for x-ray cephalopelvimetry, AM. J. OBSTET. GYNECOL. 105: 1110, 1969. 3. Ball, R. P.: Roentgenography: Pelycephalometry, in Glasser, O., editor: Medical Physics, Chicago, 1950, Year Book Medical Publishers, Inc., vol. II, p. 940.
4. Holmquest, H. J.: Nomogram for roentgenographic mensuration, Radiology 31: 198, 1938. 5. Schwartz, G. S.: A simplified method of correcting roentgenographic measurement of the maternal pehis and fetal skull, Am. J. Roentgenol. 71: 115, 1954. 6. Klapholz, H.: A computerized aid to Ball pelvimetry, AM. J. OBSTET. GYNECOL. 121: 1067, 1975.
A.
Pdvirtwtr~ uwd with approuch much Ic~.Y
FRIEDMAN,
M.D.,
MED.SC.D
run bp ,simpl$ed by a recently devised computer program. The program can any of several advanced programmable pocket or desk-top calcu1ator.y. This is more accurate than either the nomogram or the slide rule. and demander time and attention.
TH FC X-RAY cephalopelvimetric technique first described in 1935 by Ball and Marchbanks has several distinct advantages over other methods. It is capable of measuring the fetal head in any presenting position, providing a specific head volume in each case against which to judge the capacity of the pelvis based on measured dimensions. Moreover, it has essentially none of the technical drawbacks of other methods that require accurate positioning of the patient, precise placement of grids or rulings, or use of specially designed equipment. The geometric triangulation principles of the Ball technique have been previously outlined.’ Detailed expositions of how the measurements are made from the x-ray films are also available2. ” and need not be repeated here. Various aids have been introduced to simplify the mathematical manipulations needed to correct the film measurements for expected divergence error, to calculate the corresponding head volume and pelvic capacity. and to determine volume deficits where they exist. It is likely this useful clinical tool has not found greater acceptance among obstetricians and radiologists by virtue of the arithmetic involved. Nomograms*, ’ and a special slide rule’ have apparently not entirely resolved this problem. A recently devised computer program6 has generated utilitarian tables that are proving to be most helpful in clinical practice at this institution. The sheer bulk of paper and the need to reduplicate the tables periodically as they deteriorate with use and time are the only obvious disadvantages we have encountered to date.
From I5rarl
the Department v/ Obstetrics and Gynecology, Hospital or~d Harwzrd Medical Schoo!.
Receiwdjr .4ccepted
public&on ,Warch
January
be
A computer program has now been evolved for use with any of several advanced programmable pocket or desk-top calculators. The loo-step sequence shown in Table I was written specifically for the HP-65* unit; it can be readily modified for other equipment. When the prerecorded magnetic card containing this program is inserted into the calculator, the operator can proceed to compute volumes, capacities. and deficits merely by entering the paired arrays of measured dimensions and object-film distances. As each pair is entered, the corrected volume is derived and stored for subsequent use in determining the deficit or for later reference purposes. In this program, subroutine A is used for entering the three important pelvic dimensions (widest transverse and anteroposterior diameters of the inlet and interspinous diameter at the midplane)* and subroutine B for the two head &cumference measurements (obtained from the anteroposterior and lateral films, respectively). All necessar? corrections and conversions are automaCcally accomplished and the head volumes are averaged. After the five dimensions have been duly processed, subroutine C computes the deficits seriatim. To enter a new case, only the storage registers need to be cleared. The flow of data is as follows: The first measured pelvic dimension (the widest transverse diamet.er of the inlet) is entered (key A) along with it< object.-film distance (key R/S). The data are automatically subprogrammed (subroutine E) for purposes of correcting the measured dimension for magnificafion distortion and beginning the computation of the corresponding volume
Beth
23, 1976.
The program returns to the point from which it had branched, there to complete the volume calculation and to seek an appropriate storage register. It tests
IO, 1976.
Reprint requests: Emanuel A. Friedman, M.D., Department of Obstetrtis and Gynecology, Beth Israel Hospitul, 330 Brookline ‘41v., Boston, Massachusetts 02215.
*Hewlett-Packard
477
Company,
Cupertino,
California.
478
Friedman
Table
I. Programmed
LBLA ST08 E
LBLl RCL2 1
:TO3 RCLl 1
:TO8 gDSZ RCL3 RTN RCL3 ST02 RTN
:TO8 @= CT01 RCL3 ST01 RTN
steps for Ball pelvimetry
LBLB ST08 2 ST07 E ENT
LBL2 RCL5 RCL4
LBLC RCLl RCL6
l
X
;TO6 RCL5 RTN
RIS RCL2 RCL6 RIS RCL3 RCL6 RTN
:TO5 RCL4 1 :TO8 gDSZ CT02 RCL5 ST04 RTN
LBLE RCL8 RIS ST06 & 100 ENT ENT RCL6
g=
RTN
each of the first three registers in turn and enters the derived volume into the first one it locates that contains no previously entered volume. Since this is the first entry, the capacity corresponding to the widest transverse inlet diameter would be stored in the first register. Next, a second dimension (the anteroposterior diameter of the inlet, key A) and its object-film distance (key R/S) are entered; the volume is computed and stored in the second register (subprogram 1). Entering the third pelvic dimension (interspinous diameter, key A) and its object-film distance (key R/S) complete the calculations of pelvic capacities as this volume is stored in the third register. One of the measured head circumferences (from the anteroposterior film, key B) with its corresponding
object-film distance (key R/S) is then entered, branched (subprogram E) for divergence correction, and furthei corrected for fetal scalp volume (by adding 2 cm. to the corrected cranial circumference). Initial computation of the head volume from the corrected circumference
is undertaken, utilizing the steps shared in common with the calculation of volume from diameters. Returning to the point from which it branched, the program completes the volume calculation and proceeds to seek an appropriate storage register; the first head volume is stored in the fourth register. The remaining head circumference (from the lateral film, key B) ancl its object-film distance (key R/S) are handled in the same way, and the calculated volumes stored in the fifth register (subprogram 2). When both head volume storage registers are occupied, they are automatically averaged and the mean head volume stored in the sixth register. Finally, subprogram C determines the deficits between the mean head volume and the pelvic capacity as derived first from the widest transverse inlet diameter (key C), then from the anteroposterior inlet diameter (key R/S), and last from the interspinous diameter (key R/S again). This approach is much more accurate than either the nomogram or the slide rule in clinical use. It is much lessdemanding in terms of time and attention than the aforementioned generated tables. The expense of a programmable calculator is offset by the advantages of the information it provides through the intermedium of this program, and of course by the many other uses to which it can be put.
REFERENCES
1. Ball, R. P., and Marchbanks, S. S.: Roentgen pelvimetry and fetal cephalometry: A new technique, Radiology 24: 77, 1935. 2. Friedman, E. A., and Taylor, M. B.: A modified nomographic aid for x-ray cephalopelvimetry, AM. J. OBSTET. GYNECOL. 105: 1110, 1969. 3. Ball, R. P.: Roentgenography: Pelycephalometry, in Glasser, O., editor: Medical Physics, Chicago, 1950, Year Book Medical Publishers, Inc., vol. II, p. 940.
4. Holmquest, H. J.: Nomogram for roentgenographic mensuration, Radiology 31: 198, 1938. 5. Schwartz, G. S.: A simplified method of correcting roentgenographic measurement of the maternal pehis and fetal skull, Am. J. Roentgenol. 71: 115, 1954. 6. Klapholz, H.: A computerized aid to Ball pelvimetry, AM. J. OBSTET. GYNECOL. 121: 1067, 1975.
