Computed tomography scanogram compared to long leg radiograph for determining axial knee alignment

Area of Science:

• Orthopedic surgery
• Radiology
• Biomechanics

Background:

• Supine computed tomography scanogram (CTS) is frequently used for knee alignment measurement.
• Validation of CTS against weight-bearing long leg radiograph (LLR) is lacking for native and post-unicompartmental knee replacement (UKR) knees.

Purpose of the Study:

• To quantify differences in knee alignment measurements between CTS and LLR.
• To assess the accuracy of CTS as an alternative to LLR.

Main Methods:

• 40 knees (17 native, 23 post-UKR) underwent both supine CTS and weight-bearing LLR.
• Mechanical and anatomical tibio-femoral axes were measured.
• Bland-Altman analysis and intraclass correlation (ICC) assessed agreement and reliability.

Main Results:

• CTS and LLR demonstrated high reliability (ICC > 0.9) for both axes.
• Significant and clinically relevant differences were observed between CTS and LLR measurements for both mechanical and anatomical axes in native and post-UKR knees.

Conclusions:

• While reliable, CTS is not an accurate substitute for LLR in knee alignment assessment.
• CTS should not replace LLR for measuring mechanical or anatomical knee axes.