Accuracy of Total Hip Arthroplasty Templating Using Set Calibration Magnifications

Area of Science:

• Orthopedic Surgery
• Medical Imaging
• Biomedical Engineering

Background:

• Pre-operative templating for total hip arthroplasty (THA) is crucial for accurate surgical planning.
• Calibration markers, while beneficial, introduce cost, availability issues, and potential errors.
• Surgeons often use a fixed 118% magnification to mitigate calibration inaccuracies.

Purpose of the Study:

• To evaluate the accuracy of THA templating using standardized magnifications (118% and 119%).
• To assess the influence of body mass index (BMI) on templating accuracy.

Main Methods:

• Retrospective analysis of 119 consecutive THA cases from a single surgeon.
• Anteroposterior radiographs were templated using 118% and 119% magnification without calibration hardware.
• Templated cup sizes were compared to implanted sizes, with post-operative calibration using femoral head diameter.

Main Results:

• At 118% magnification, 61.1% of acetabular cups matched templated sizes, with 96.3% within two sizes.
• At 119% magnification, 52.5% of cups matched, with 100% within two sizes.
• No significant difference in cup size prediction accuracy between 118% and 119% (p=0.49).

Conclusions:

• Standardized magnifications of 118% or 119% provide reliable acetabular cup size prediction in THA without calibration equipment.
• Increasing BMI showed a trend towards increased magnification error but did not significantly affect templating accuracy within two sizes.