Calibration Markers for Digital Templating in Total Hip Arthroplasty

Area of Science:

• Orthopedic Surgery
• Medical Imaging
• Biomechanical Engineering

Background:

• Digital templating with external calibration markers is standard for total hip arthroplasty (THA) planning.
• Accurate calibration is crucial for precise implant sizing and positioning.
• Magnification effects in digital radiography can impact surgical planning accuracy.

Purpose of the Study:

• To determine the geometrical basis of magnification in digital radiography for THA.
• To compare magnification accuracy between external and internal calibration markers.
• To investigate the influence of marker position, patient weight, and BMI on magnification.

Main Methods:

• Derived a formula to calculate magnification using internal and external calibration markers.
• Analyzed 100 digital pelvic radiographs.
• Calculated intraclass correlations to assess agreement and relationships between variables.

Main Results:

• A weak correlation (r = 0.297-0.361) was found between magnification of internal and external calibration markers.
• Intraclass correlations for measured and calculated values were high (0.882-1.000).
• Weak correlations were observed between marker magnification and patient weight/BMI (r = 0.420-0.428).

Conclusions:

• The poor correlation between external and internal calibration markers highlights limitations in current THA templating methods.
• Existing calibration techniques may require refinement for improved accuracy.
• Further research is needed to fully understand the influence of patient factors like weight and BMI on radiographic magnification.