Accuracy of using radiographs for custom hip stem design

Area of Science:

• Orthopedic surgery
• Biomedical engineering
• Medical imaging

Background:

• Custom femoral stems improve hip implant fit and longevity.
• Current custom stem design relies on computed tomography (CT) scans, which are costly and time-consuming.
• Accurate prediction of femoral canal shape is crucial for effective custom stem design.

Purpose of the Study:

• To evaluate the accuracy of predicting femoral canal shape using biplane radiography.
• To compare the design and fit of custom femoral stems created from actual versus radiographically predicted canal shapes.
• To determine if radiographic prediction is a viable alternative to CT scans for custom uncemented femoral stem design.

Main Methods:

• An average femur shape was established from 50 femurs (100 total).
• Femoral canal shape was predicted from biplane radiographs by deforming the average shape to match radiographic outlines.
• Custom femoral stems were designed based on both actual and predicted canal shapes.
• Fit accuracy was assessed by comparing stem designs and evaluating fit after insertion into prepared canals.

Main Results:

• Radiographic prediction of femoral canal shape achieved an average accuracy of within 1 mm.
• Accuracy was higher in the proximomedial and distal canal regions (0.3 +/- 0.8 mm) compared to trochanteric regions.
• Minimal differences were observed between stems designed from actual and predicted canal shapes.
• Stem insertion revealed fit errors of approximately 1 mm in specific regions, regardless of the design method.

Conclusions:

• Biplane radiography provides sufficient accuracy for predicting femoral canal shape in femurs without significant abnormalities.
• This method enables the design of standard custom uncemented femoral stems, offering a simpler and potentially less expensive alternative to CT-based designs.
• The findings support the use of radiographic prediction for routine custom femoral stem design.