Determining femoral component position using CAS and measured resection

Area of Science:

• Orthopedic surgery
• Biomedical engineering
• Medical device technology

Background:

• Computer-assisted surgery (CAS) is increasingly utilized in total knee arthroplasty (TKA).
• Accurate femoral component sizing and rotational alignment are critical for TKA outcomes.
• The reliability of different CAS referencing methods for femoral component placement requires evaluation.

Purpose of the Study:

• To assess the accuracy of CAS in determining femoral component size and rotational alignment in TKA.
• To compare the effectiveness of different rotational referencing methods (epicondylar axis, posterior condylar axis, anteroposterior axis) within CAS.
• To evaluate the impact of surgeon's clinical judgment on CAS-guided TKA procedures.

Main Methods:

• Retrospective review of 50 primary TKAs using a femur-first, measured resection CAS workflow.
• Analysis of femoral component size and rotational alignment based on surgeon's final decisions.
• Comparison of CAS-recommended size and rotation against actual implanted component using various landmark references.

Main Results:

• The femoral component was downsized in 52% of cases compared to CAS recommendations.
• The posterior condylar axis (PCA) matched the implanted rotation within 1 degree in 64% of cases.
• Epicondylar axis (32%) and anteroposterior axis (26%) showed lower accuracy for rotational alignment compared to PCA.

Conclusions:

• CAS provides valuable data but does not supersede surgeon's clinical judgment in TKA.
• Femoral component downsizing is common, indicating potential overestimation by CAS.
• The posterior condylar axis is a more reliable landmark for rotational alignment in CAS-assisted TKA compared to other references.