Digital pre-operative templating is more accurate in total hip replacement compared to analogue templating

We prospectively evaluated the accuracy of digital compared to analogue pre-operative templating in 50 consecutive primary hip replacements between April 2006 and June 2007. The senior author pre-operatively templated implant size using TraumaCad (Orthocrat Limited, Israel). Thirty-one Exeter primary hip and 19 hybrid hip replacements were performed. Hips were templated using radiographs calibrated against a spherical metal ball. For each hip, an AP pelvis view was used. Acetabular implants used were either Trident PSL or Exeter contemporary cup (Stryker). Femoral stem was Exeter (Stryker). Predicted implant sizes were documented. Post-operatively, the predicted implant size was compared to the implanted components. All post-operative films showed good fit of components and there were no intraoperative or post-operative fractures. The intra-rater reliability (ICC) of analogue templating was 0.96 and digital templating was 0.90. Accurate templating score for acetabular cup was 46% (digital) 43% (analogue), femoral offset was 80% (digital) 70% (analogue), femoral stem was 76% (digital) 60% (analogue). The differences between templating and actual implant sizes were plotted in Bland–Altman plot. Digital templating produced narrower confidence interval compared to analogue templating. Digital templating proved to be statistically, significantly more accurate compared to analogue templating for acetabluar cup and femoral stem. Our data indicate that digital templating is more reliable in predicting actual implant sizes for total hip arthroplasty when performed by the operating surgeon.