Radiologists should use the hip-knee-ankle angle rather than the mechanical axis deviation to describe knee alignment

Area of Science:

• Orthopedic surgery
• Radiology
• Biomechanical analysis

Background:

• Coronal knee alignment is critical for total knee arthroplasty (TKA) success.
• Mechanical axis deviation (MAD) is frequently reported, but its clinical relevance compared to hip-knee-ankle angle (HKAA) is debated.
• Understanding alignment predictors is key to improving TKA outcomes and longevity.

Purpose of the Study:

• To assess the predictive accuracy of mechanical axis deviation (MAD) for hip-knee-ankle angle (HKAA).
• To determine if patient height and sex influence the MAD's ability to predict HKAA.
• To compare the measurement time efficiency of MAD versus HKAA.

Main Methods:

• Retrospective review of 200 hip-to-ankle radiographs for TKA planning.
• Measurement of MAD and HKAA using PACS tools.
• Analysis using receiver operator characteristic (ROC) curves and linear modeling; paired t tests for time comparison.

Main Results:

• Strong correlation found between MAD and HKAA (r=0.99, p<0.001).
• MAD's predictive performance for HKAA was significantly affected by patient height (p=0.005) and sex (p<0.001).
• No significant difference in measurement time between MAD and HKAA (p>0.05).

Conclusions:

• Hip-knee-ankle angle (HKAA) is recommended over mechanical axis deviation (MAD) for assessing coronal knee alignment in TKA.
• HKAA offers greater clinical relevance and comparable measurement efficiency.
• Accurate alignment assessment is crucial for optimizing TKA outcomes and minimizing failure rates.