Accuracy of preoperative templating for total hip arthroplasty using the Picture Archiving and Communication System

Preoperative planning is a key element in total hip arthroplasty. The magnification of pelvic radiographs is variable which can be corrected on digital imaging, by using a calibration marker of known diameter. The aim of this study is to determine the reliability and accuracy of the use of a calibration marker, for preoperative templating, in total hip arthroplasty. We assessed 59 preoperative antero-posterior pelvic radiographs in patients, due to undergo total hip arthroplasty, who previously had a total hip arthroplasty performed on the contralateral side. All radiographs were taken in our radiology department, using a 30 mm steel ball bearing as a calibration marker. The radiograph magnification was corrected using this calibration marker and the diameter of the in situ femoral prosthetic head was then measured and compared with the actual size as documented in the patients previous operative notes. It was noted during the review that in 41 patients, the marker was placed between the thighs and on top of the pelvis in the remaining 18 patients. The accuracy of measurements in group 1 (marker in between thighs) was within a mean of 1.56% (SD 4.78, 95% CI +0.053 to +3.075) of the actual size, as compared to −9.94% (SD 5.07, 95% CI −12.471 to −7.427) in group 2 (marker on top of the pelvis) (Fig. 3). The average magnification in group 1 was 101.56% (92.31–112.72%) and 90.05% (84.29–106.78%) in group 2. It is recommended that the calibration marker should always be placed between the patient’s thighs, allowing it to achieve a more level plane with the hip joint.