Acetate templating on calibrated standing digital radiograph improves accuracy of preoperative templating for total hip arthroplasty

Abstract

Background: The accuracy of preoperative templating with respect to leg length, femoral offset, and the size of femoral and acetabular components is essential to the success of total hip arthroplasty (THA). Traditionally, templating has been performed using printed film with acetate templates. However, preoperative templating designed by different prosthetic manufacturers cannot be used directly on the film due to varying acetate template amplification ratios. Computer-based templating needs specialized digital templating software, which has cost implications. To address these shortcomings, we bring forward several questions: (1) the accuracy of traditional manual templating combined with the calibrated digital radiograph for preoperative templating, (2) the inter- and intraobserver reliability of this method.

Hypothesis: Using calibrated digital radiograph with traditional manual templating improves the accuracy and reproducibility of preoperative templating for THA.

Patients and methods: We designed a stepwise method that combines the traditional manual templating with standing digital radiograph calibrated by a scaling ball. Two separate observers (XJL, QYG) analyzed data of 82 patients (109 THAs) who had undergone THA with preoperative templating using the calibrated digital templating. The intra- and interobserver reliability was assessed by intraclass correlation coefficient.

Results: The size of the acetate template acetabular based on our method was identical to the actual implanted acetabular size in 55.0% (XJL 110/218 [50.5%]; QYG 130/218 [59.6%]) of the cases indicating moderate accuracy. The intraclass correlation coefficient (ICC) for acetabular templating indicated almost perfect interobserver (ICC=0.918 [95% CI, 0.893-0.937]) and intraobserver agreement (ICC=0.932 [95% CI, 0.912-0.947]). While the exact implanted femoral size was predicted in 55.3% (XJL 122/218 [56.0%]; QYG 119/218 [54.6%]) of the cases. The ICC for femoral component templating indicated almost perfect interobserver (ICC=0.944 [95% CI, 0.927-0.957]) and intraobserver agreement (ICC=0.909 [95% CI, 0.883-0.930]).

Discussion: This new stepwise method may prove to be a more reliable preoperative design choice to accurately calibrate magnification with radiograph, and could solve the incompatibility of the preoperative template designed by different prosthetic companies for direct use with the x-ray film. The method described is practical, convenient, cost-effective and does not require specialized equipment or software, thus making it particularly suitable for use in underdeveloped settings.

Level of evidence: Level IV, case series without controls.

Keywords: Calibration; Standing digital radiograph; THA; Templating.