The accuracy of external calibration markers in digital templating using the double marker and single marker method: a comparative study.

BACKGROUND: Digital templating is an essential step in the preoperative planning of total hip arthroplasty (THA). Previous studies have suggested that templating with the double marker method may be more accurate than a single marker method in the general population and in obese patients. The purpose of this study was to compare the accuracy in the preoperative component selection between the King Mark calibration device and the conventional metal ball method. Additionally, we examined whether King Mark offered any advantage over the standard metal ball in the preoperative selection of component sizes for obese patients.
METHODS: We retrospectively reviewed patients who underwent preoperative digital templating for THA in our center from January 2014 to January 2016 with King Mark device and marker ball. We compared the preoperative template component size and offset with the intraoperative definite implant size. The accuracy was defined as the difference between preoperative and intraoperative component sizes. The overall accepted calibration was defined as an exact match ± one size. Patients were stratified into two cohorts according to the calibration method: standard marker ball technique and King Mark technique.
RESULTS: 126 THA underwent digital calibration. 79 patients underwent a preoperative templating using the King Mark calibration device. 47 patients were templated using a conventional marker ball. The overall adequate preoperative planning of the acetabular cup (exact or ± 1 size match) in the King Mark group did not differ from the single marker method (74.7% and 74.5%, respectively, p = 0.979). No significant difference was noted in the overall accepted calibration of the femoral stem (exact or ± 1 size match) between the marker ball group and the King Mark group (58.2% and 70.2%, respectively, p = 0.179). The King Mark group showed a better preoperative planning for the stem's offset compared to the marker ball group (77.2% % and 61.7%, respectively, p = 0.062). For the obese patient cohort, no significant difference was noted between the King Mark group and the marker ball group in the exact prediction of the acetabular cup and the femoral stem, (p = 0.31 and p = 0.15, respectively).
CONCLUSIONS: Our study found no difference between the King Mark method and the conventional metal ball method in the ability to accurately predict component sizes. In the subgroup of obese patients, the King Mark technique offered no advantage for accurately predicting component sizes.