Templating digital radiographs using acetate templates in Total Hip Arthroplasty

Abstract

Introduction & objectivePreoperative templating in Total Hip Arthroplasty (THA) has traditionally been done with conventional radiographs. With conventional films being replaced by digital films, it has become difficult for surgeons to template the hip preoperatively, as digital templating involves special software, carries an additional cost and is not freely available. We describe a hybrid technique that involves the use of standard acetate templates, used over digital radiographs on a LCD monitor. Materials and methodsPreoperative digital radiographs of the pelvis were taken with a 30mm diameter spherical metal ball taped onto the greater trochanter. Viewing the digital radiographs on a flat screen LCD monitor, the metal ball on the image was magnified to 30mm as per the scale on the acetate template. The size of the acetabular cup and the femoral stem were then directly read using standard techniques with the acetate templates. To assess accuracy, digital films of 54 hips were retrospectively templated and the estimated size of the implant was compared with the actual size used at surgery. Reliability of the method was tested with Intraclass Correlation Coefficient (ICC). ResultsUsing this technique, it was possible to accurately predict the acetabular cup size in 38/54 (70%) of the hips and to within 1 size in 96% of the hips. The femoral component size was accurately predicted in 24/54 (44%) of the hips and to within 1 size in 82% of the hips. When assessed by two independent observers, there was good intraobserver reliability (ICC value=0.96) and interobserver reliability (ICC value=0.93) for the acetabular templating as well as for the femur (ICC value of 0.93 for intraobserver reliability and ICC value of 0.88 for interobserver reliability). ConclusionIt was possible to accurately and reliably predict the size of the acetabular cup and the femoral stem, using standard acetate onlay templates on digital radiographs, without the use of digital templating software.