540
TECHNICAL NOTES
February 1979
DISCUSSION
Fig. 2. Cross-sectional CT image of the central axis. The arrow indicates the opaque catheters.
The entire transfer of information from the minified CT scan to the 1:1 scale tracing on graph paper requires less than an hour. Given the traced cross-section, treatment planning may proceed to whatever degree of complexity the radiotherapist desires. Some possible considerations are: (a) Tissue inhomogeneities may be accounted for by including bone and air-filled cavities on the tracing. (b) Off-axis dosimetry is possible by choosing additional levels (e.g., the top and bottom of the portal) for transfer to graph paper. It should be noted, however, that central-axis isodose data may not be appropriate for these off-axis contours. (c) Interval CT studies may be done so that the treatment plan may be changed to account for shrinking tumor volumes. (d) If treatment is repeated, old portals can be marked with opaque catheters, thereby making it possible to locate them on the tracing. These steps enable the radiotherapist to use the valuable information available only on CT scans to his patient's best advantage. This method is quick, cheap, and applicable in virtually any radiotherapy department.
projected onto graph paper taped on a wall. By varying the distance from projector to graph paper, the size of the image can be changed until it exactly fits the AP and lateral dimensions obtained in Step 3. The image is thereby scale-corrected and a tracing of the projected image can be made on the graph paper. Body outline, tumor extent, and normal surroundingorgans are illustrated in whatever detail desired by the treatment planner. The treatment volume is then drawn onto this cross-sectional image and treatment planning can proceed.
1 From the Radiation Center, University of Louisville School of Medicine, 500 S. Floyd St. (B.M.B., T.E.B.), and the Department of Radiology, Jewish Hospital (D.B.S.),Louisville, Ky. 40202 (Reprint requests to University of Louisville). Accepted for publication in February 1978. 2 SO-185 rapid-processing copy film, Eastman Kodak, Rochester, N.Y. sjh
Radiographic Localization of the Acetabular Component of a Hip Prosthesis 1 Bernard Ghelman, M.D. The degree of anterior or posterior tilt of the acetabular cup can be established using fluoroscopy in patients with total hip prostheses. Since the technique is fast, painless, and requires minimal cooperation, it can be performed immediately following surgery. This method is suitable for postoperative evaluation of patients with total hip replacement and is also reproducible for serial analysis. INDEX TERM: Hip, prosthesis, 4 [4].454
Radiology 130:540-542, February 1979
The placement of total hip prostheses is essential in determining the postsurgical prognosis. Radiographic evaluation essentially involves assessment of (a) the position of the femoral and acetabular components; (b) the relationship of the prosthesis to the pelvis; and (c) the relative position of the prosthesis and standard imaginary planes. The relationship between the acetabular cup and the pelvic bones is radiographically uncertain at present because of anatomical variation of bony landmarks and the difficulty in reproducing patient position for periodic radiographic measurements. I have developed a fluoroscopic method which can determine the exact position of the acetabular component (cup) relative to specific planes of orientation. With this method, anatomical variation between patients is unimportant and little if any cooperation of the patient is necessary.
METHODS AND MATERIAL An adult pelvis was fitted with a prosthetic acetabular cup and examined under fluoroscopy. The circular wire in the base of the cup was examined with cephalad, neutral, and caudadangulation of the x-ray tube. When the anterior and posterior halves of the wire overlapped, the angle of the tube was recorded along with its cephalad or caudad direction. Overlap indicates that the beam is tangential to the plane passing through the opening of the cup. The angle of the tube indicates the degree of anteroposterior tilt of the cup in relation to a 'cross-section transverse or transaxial plane. When the halves of the wire overlap, the position of the tube determines which way the opening of the cup is facing, i.e., it is tilted forward (anterior) if overlap is observed with the tube caudad or backward (posterior) if the tube is pointing cephalad. The position of the acetabular component in relation to the horizontal plane affects measurements made by this method. The farther vertical the cup is inserted in respect to the ischioischial line (a line drawn between the farthest inferior tips of the ischial bones), the greater the apparent anteroposterior tilt in relation to the transverse plane. As the angle of the cup in relation to the ischio-ischial line is increased to 90°. a point is reached where overlap is impossible unless the base is parallel to the sagittal plane. The relationship between the fluoroscopic measurement of the anteroposterior tilt of the cup and the angulation of the cup to the ischio-ischial line was observed.
541
TECHNICAL NOTES
Vol. 130
Technical Notes
Fig. 1. A. AP view of the pelvis of a 40-year-old woman with bilateral total hip replacements for long-standingrheumatoid arthritis. The right hip prosthesis is dislocated three days after surgery. B. Following reduction, the positions of the different components of the prosthetic devices appear to be satisfactory. The acetabular ischial angle is 35° on the right and 55° on the left.
Fig. 2. A-C. Cup of the right prosthesis seen with the beam angled 0° (A), 5° cephalad (B)! and 5° caudad (C). The anterior and posterior halves of the wire at the base of the cup overlap only when the x-ray beam is aimed cephalad. The corrected and projected posterior tilt of the right cup is 5°.
Fig. 3.
A-C.
Cup of the left prosthesis seen with the beam angled 0° (A), 15° cephalad (B), and 15° caudad (C). The halves of the wire overlap only when the beam is aimed caudad. The corrected anterior tilt of the left cup is 10°.
Measurements were obtained by positioning the cup at predetermined degrees of tilt and varying the angulation of the cup with the ischio-ischialline. The projected tilt at different degrees of acetabular ischial angulation was recorded (TABLE I). The correction factors used to obtain the actual angle of the anteroposterior tilt can be determined from the apparent angle noted at fluoroscopy (see figures given in TABLE I). The involved hip is easily examined under fluoroscopy with the patient supine and lying as comfortably as possible on the x-ray table. The knees should be extended and the hips kept flat to prevent pelvic tilting: the most convenient way of doing this is to make certain that the symphysis pubis and the lumbar
spinous processes are aligned. The examination is performed best with a remote-control x-ray unit that has tomographic capability. An anteroposterior view of the pelvis is now obtained to measure the acetabular ischial angle. The tube is centered over the hip so that both halves of the wire in the base of the cup are observed, and the fluoroscopic tube can be angled cephalad and caudad until overlap is noted. Figures 1-3 demonstrate how this method is applied.
DISCUSSION The present method of measurement of the acetabular component of a total hip prosthesis establishes the type and
542
TECHNICAL NOTES
TABLE I:
MEASUREMENT OFANTERIOR OR POSTERIOR TILT(ANTEVERSION/RETROVERSION) OFTHE ACETABULAR COMPONENT OF A HIPPROSTHESIS
r Corrected .anteroposterior tilt 00 50 10 0 150 20 0 25 0 30 0
00
50
100
150
20 0
25 0
00 50 10 0 15 0 20 0 25 0 30 0
00 50 10 0 15 0 20 0 25 0 30 0
00 50 10 0 15 0 20 0 25 0 30 0
00 50 100 150 20 0 25 0 30 0
00 50 100 150 20 0 25 0 30 0
00 50 100 150 20 0 25 0 33 0
....
A.
B.
C.
February 1979
Acetabular Ischial Angle 45 0 30 0 40 0 35 0
50 0
00 00 00 00 00 50 50 50 50 70 100 100 120 140 100 20 0 15 0 150 17 0 17 0 0 0 0 0 21 24 21 24 26 0 27 0 29 0 32 0 34 0 +35 0 33 0 35 0 +35 0 Projected Anteroposterior Tilt
,
55 0
60 0
65 0
70 0
75 0
00 70 140 22 0 29 0
00 10 0 16 0 24 0 30 0
00 10 0 19 0 32 0 34 0
00 120 22 0 35 0 0 +35
00 120 270 +35 0
Measure the acetabular ischial angle and the projected antero-posterior tilt of the cup. Find the number closest to the projected tilt in the column under the appropriate acetabular ischial angle. The corrected tilt is provided on the same line, on the left side of the table (interpolation may be necessary).
degree of tilt of the open face of the cup with respect to an imaginary transverse plane. Measurements can also be performed to establish the position of the cup relative to the sagittal plane if a fluoroscopic unit that moves in an arc crossing the pelvis is available. The best measurement would be one in which the beam moved through an arc perpendicular to the base of the cup. This method of measuring acetabular tilt permits intraoperative evaluation of the placement of the acetabular component. Determining the base of the prosthetic cup is simple when a metallic wire is present. Some cups which do not have such
a wire can also be evaluated by the parallel radiolucent grooves seen throughout the cup. When the x-ray beam is tangential to the plane of the cup, these qrooves are seen as a straight line. ACKNOWLEDGMENTS: I wish to thank Dr. Helene Pavlov for revising this text and Miss Marianne Angeletti for her technical assistance.
1 From the Department of Radiology, Hospital for Special Surgery, New York, N.Y. 10021. Received Dec. 13, 1977; accepted and revision requested Feb. 7, 1978; revision received Feb. 27. sjh
TECHNICAL NOTES
February 1979
DISCUSSION
Fig. 2. Cross-sectional CT image of the central axis. The arrow indicates the opaque catheters.
The entire transfer of information from the minified CT scan to the 1:1 scale tracing on graph paper requires less than an hour. Given the traced cross-section, treatment planning may proceed to whatever degree of complexity the radiotherapist desires. Some possible considerations are: (a) Tissue inhomogeneities may be accounted for by including bone and air-filled cavities on the tracing. (b) Off-axis dosimetry is possible by choosing additional levels (e.g., the top and bottom of the portal) for transfer to graph paper. It should be noted, however, that central-axis isodose data may not be appropriate for these off-axis contours. (c) Interval CT studies may be done so that the treatment plan may be changed to account for shrinking tumor volumes. (d) If treatment is repeated, old portals can be marked with opaque catheters, thereby making it possible to locate them on the tracing. These steps enable the radiotherapist to use the valuable information available only on CT scans to his patient's best advantage. This method is quick, cheap, and applicable in virtually any radiotherapy department.
projected onto graph paper taped on a wall. By varying the distance from projector to graph paper, the size of the image can be changed until it exactly fits the AP and lateral dimensions obtained in Step 3. The image is thereby scale-corrected and a tracing of the projected image can be made on the graph paper. Body outline, tumor extent, and normal surroundingorgans are illustrated in whatever detail desired by the treatment planner. The treatment volume is then drawn onto this cross-sectional image and treatment planning can proceed.
1 From the Radiation Center, University of Louisville School of Medicine, 500 S. Floyd St. (B.M.B., T.E.B.), and the Department of Radiology, Jewish Hospital (D.B.S.),Louisville, Ky. 40202 (Reprint requests to University of Louisville). Accepted for publication in February 1978. 2 SO-185 rapid-processing copy film, Eastman Kodak, Rochester, N.Y. sjh
Radiographic Localization of the Acetabular Component of a Hip Prosthesis 1 Bernard Ghelman, M.D. The degree of anterior or posterior tilt of the acetabular cup can be established using fluoroscopy in patients with total hip prostheses. Since the technique is fast, painless, and requires minimal cooperation, it can be performed immediately following surgery. This method is suitable for postoperative evaluation of patients with total hip replacement and is also reproducible for serial analysis. INDEX TERM: Hip, prosthesis, 4 [4].454
Radiology 130:540-542, February 1979
The placement of total hip prostheses is essential in determining the postsurgical prognosis. Radiographic evaluation essentially involves assessment of (a) the position of the femoral and acetabular components; (b) the relationship of the prosthesis to the pelvis; and (c) the relative position of the prosthesis and standard imaginary planes. The relationship between the acetabular cup and the pelvic bones is radiographically uncertain at present because of anatomical variation of bony landmarks and the difficulty in reproducing patient position for periodic radiographic measurements. I have developed a fluoroscopic method which can determine the exact position of the acetabular component (cup) relative to specific planes of orientation. With this method, anatomical variation between patients is unimportant and little if any cooperation of the patient is necessary.
METHODS AND MATERIAL An adult pelvis was fitted with a prosthetic acetabular cup and examined under fluoroscopy. The circular wire in the base of the cup was examined with cephalad, neutral, and caudadangulation of the x-ray tube. When the anterior and posterior halves of the wire overlapped, the angle of the tube was recorded along with its cephalad or caudad direction. Overlap indicates that the beam is tangential to the plane passing through the opening of the cup. The angle of the tube indicates the degree of anteroposterior tilt of the cup in relation to a 'cross-section transverse or transaxial plane. When the halves of the wire overlap, the position of the tube determines which way the opening of the cup is facing, i.e., it is tilted forward (anterior) if overlap is observed with the tube caudad or backward (posterior) if the tube is pointing cephalad. The position of the acetabular component in relation to the horizontal plane affects measurements made by this method. The farther vertical the cup is inserted in respect to the ischioischial line (a line drawn between the farthest inferior tips of the ischial bones), the greater the apparent anteroposterior tilt in relation to the transverse plane. As the angle of the cup in relation to the ischio-ischial line is increased to 90°. a point is reached where overlap is impossible unless the base is parallel to the sagittal plane. The relationship between the fluoroscopic measurement of the anteroposterior tilt of the cup and the angulation of the cup to the ischio-ischial line was observed.
541
TECHNICAL NOTES
Vol. 130
Technical Notes
Fig. 1. A. AP view of the pelvis of a 40-year-old woman with bilateral total hip replacements for long-standingrheumatoid arthritis. The right hip prosthesis is dislocated three days after surgery. B. Following reduction, the positions of the different components of the prosthetic devices appear to be satisfactory. The acetabular ischial angle is 35° on the right and 55° on the left.
Fig. 2. A-C. Cup of the right prosthesis seen with the beam angled 0° (A), 5° cephalad (B)! and 5° caudad (C). The anterior and posterior halves of the wire at the base of the cup overlap only when the x-ray beam is aimed cephalad. The corrected and projected posterior tilt of the right cup is 5°.
Fig. 3.
A-C.
Cup of the left prosthesis seen with the beam angled 0° (A), 15° cephalad (B), and 15° caudad (C). The halves of the wire overlap only when the beam is aimed caudad. The corrected anterior tilt of the left cup is 10°.
Measurements were obtained by positioning the cup at predetermined degrees of tilt and varying the angulation of the cup with the ischio-ischialline. The projected tilt at different degrees of acetabular ischial angulation was recorded (TABLE I). The correction factors used to obtain the actual angle of the anteroposterior tilt can be determined from the apparent angle noted at fluoroscopy (see figures given in TABLE I). The involved hip is easily examined under fluoroscopy with the patient supine and lying as comfortably as possible on the x-ray table. The knees should be extended and the hips kept flat to prevent pelvic tilting: the most convenient way of doing this is to make certain that the symphysis pubis and the lumbar
spinous processes are aligned. The examination is performed best with a remote-control x-ray unit that has tomographic capability. An anteroposterior view of the pelvis is now obtained to measure the acetabular ischial angle. The tube is centered over the hip so that both halves of the wire in the base of the cup are observed, and the fluoroscopic tube can be angled cephalad and caudad until overlap is noted. Figures 1-3 demonstrate how this method is applied.
DISCUSSION The present method of measurement of the acetabular component of a total hip prosthesis establishes the type and
542
TECHNICAL NOTES
TABLE I:
MEASUREMENT OFANTERIOR OR POSTERIOR TILT(ANTEVERSION/RETROVERSION) OFTHE ACETABULAR COMPONENT OF A HIPPROSTHESIS
r Corrected .anteroposterior tilt 00 50 10 0 150 20 0 25 0 30 0
00
50
100
150
20 0
25 0
00 50 10 0 15 0 20 0 25 0 30 0
00 50 10 0 15 0 20 0 25 0 30 0
00 50 10 0 15 0 20 0 25 0 30 0
00 50 100 150 20 0 25 0 30 0
00 50 100 150 20 0 25 0 30 0
00 50 100 150 20 0 25 0 33 0
....
A.
B.
C.
February 1979
Acetabular Ischial Angle 45 0 30 0 40 0 35 0
50 0
00 00 00 00 00 50 50 50 50 70 100 100 120 140 100 20 0 15 0 150 17 0 17 0 0 0 0 0 21 24 21 24 26 0 27 0 29 0 32 0 34 0 +35 0 33 0 35 0 +35 0 Projected Anteroposterior Tilt
,
55 0
60 0
65 0
70 0
75 0
00 70 140 22 0 29 0
00 10 0 16 0 24 0 30 0
00 10 0 19 0 32 0 34 0
00 120 22 0 35 0 0 +35
00 120 270 +35 0
Measure the acetabular ischial angle and the projected antero-posterior tilt of the cup. Find the number closest to the projected tilt in the column under the appropriate acetabular ischial angle. The corrected tilt is provided on the same line, on the left side of the table (interpolation may be necessary).
degree of tilt of the open face of the cup with respect to an imaginary transverse plane. Measurements can also be performed to establish the position of the cup relative to the sagittal plane if a fluoroscopic unit that moves in an arc crossing the pelvis is available. The best measurement would be one in which the beam moved through an arc perpendicular to the base of the cup. This method of measuring acetabular tilt permits intraoperative evaluation of the placement of the acetabular component. Determining the base of the prosthetic cup is simple when a metallic wire is present. Some cups which do not have such
a wire can also be evaluated by the parallel radiolucent grooves seen throughout the cup. When the x-ray beam is tangential to the plane of the cup, these qrooves are seen as a straight line. ACKNOWLEDGMENTS: I wish to thank Dr. Helene Pavlov for revising this text and Miss Marianne Angeletti for her technical assistance.
1 From the Department of Radiology, Hospital for Special Surgery, New York, N.Y. 10021. Received Dec. 13, 1977; accepted and revision requested Feb. 7, 1978; revision received Feb. 27. sjh
