Implications of component size and calibration error on digital templating for total hip arthroplasty. A visual matrix from a simple mathematical model.

OBJECTIVE: Preoperative digital templating is a standard procedure in total hip arthroplasty. Deviations between template size and final implant size may result from inaccurate calibration, templating as well as intraoperative decisions. So far, the explicit effect of calibration errors on templating has not been addressed adequately. MATERIALS AND METHODS: A mathematical simulation of calibration errors up to ± 24% was applied to the templating of acetabular cups (38 to 72 mm diameter). The effect of calibration errors on template component size as deviation from optimal size was calculated. RESULTS: The relationship between calibration error and component size deviation is inverse and linear. Calibration errors have a more pronounced effect on larger component sizes. Calibration errors of 2-6% result in templating errors of up to two component sizes. Common errors of up to 12% may result in templating errors of 3-4 sizes for common implant sizes. A tabular matrix visualizes the effect. CONCLUSION: Calibration errors play a significant role in component size selection during digital templating. Orthopedic surgeons should be aware of this effect and try to identify and address this source of error.