Use of Acetate Templates Over Digital Radiographs for Templating in Total Hip Arthroplasty: Technique and Its Validation.

PURPOSE: Acetate templates were commonly used for templating for total hip arthroplasty. With digital radiographs having replaced conventional analogue radiographs, newer techniques are required. We describe a method for templating images of digital radiographs using conventional acetate templates, which is independent of a magnification marker or PACS system.
METHODS: Fifty-one patients (64 hips) who were treated with primary THA were prospectively evaluated. Templating was done by keeping the acetate template directly over the digital image of the radiograph on a liquid crystal display (LCD) monitor, after calibrating the linear scale generated by the digital radiography machine. The size of prosthesis predicted on this templating technique was compared with the actual sizes used during the surgery. Inter-observer and intra-observer reliabilities were assessed. Our calibration method was further validated by comparing the size of the cup calculated on postoperative radiograph using digital templating software (mediCAD Hectec GmbH) and the actual size used during surgery.
RESULTS: Accurate size was predicted for 36.7% of the acetabular cup and 35.9% of femoral stems. The accuracy within ± one size was 89.9% for acetabular cups and 91.4% for femoral stems. Excellent inter-observer and intra-observer reliability were seen for both femoral and acetabular components.
CONCLUSION: The method described provides an accurate, reproducible, convenient and low-cost technique of preoperative templating. It combines the ease of using acetate templates with the convenience of being able to use digital images, without the need for expensive software. © Indian Orthopaedics Association 2020.