Mechanical Axis Deviation Angle Versus Hip-Knee-Ankle Angle in Total Knee Arthroplasty: Correlation and Reliability

Area of Science:

• Orthopedic Surgery
• Biomechanical Engineering
• Radiology

Background:

• Accurate assessment of coronal alignment is crucial in total knee arthroplasty (TKA) for optimal functional outcomes.
• Traditional alignment metrics like the Hip-Knee-Ankle angle (HKA) are widely used but can have limitations in reliability.

Purpose of the Study:

• To evaluate the relationship between the Mechanical Axis Deviation Angle (MAD-A) and the Hip-Knee-Ankle angle (HKA) in TKA patients.
• To compare the inter-observer reliability of MAD-A and HKA measurements for assessing coronal alignment.

Main Methods:

• MAD-A and HKA were measured preoperatively and postoperatively (6 weeks) using long-leg radiographs and CT scanograms in 108 knees undergoing primary TKA.
• MAD-A quantifies the angular deviation of the femoral mechanical axis from the ideal limb mechanical axis.
• Three independent observers performed measurements to assess inter-observer reliability.

Main Results:

• MAD-A measurements were consistently lower than HKA values (mean differences -1.4° to -6.2°).
• Both MAD-A and HKA showed strong positive correlations (r > 0.97, p < 0.001) at all time points.
• MAD-A demonstrated superior inter-observer reliability (ICC > 0.99) compared to HKA (ICC 0.966-0.988).
• Both HKA and MAD-A showed significant improvement post-TKA (p < 0.001).

Conclusions:

• MAD-A is strongly correlated with HKA and exhibits superior inter-observer reliability in TKA coronal alignment assessment.
• MAD-A may serve as a valuable complementary tool to HKA for alignment evaluation.
• Further research is warranted to establish normative MAD-A values across various knee pathologies.