Are we overestimating internal rotation gait by conventional modelling?

Area of Science:

• Biomechanics
• Gait Analysis
• Orthopedics

Background:

• Determining the knee joint axis (KJA) is crucial for analyzing gait and informing clinical decisions.
• Conventional KJA methods rely on regression equations or direct landmark placement.
• Functional KJA calibration offers a promising alternative, but its clinical relevance needs evaluation.

Purpose of the Study:

• To compare hip rotation estimates during gait using functional KJA calibration versus conventional methods.
• To assess the clinical relevance of differences in hip rotation measurements.

Main Methods:

• Prospective study of 95 subjects, including 71 with potential rotation malalignment.
• 3D gait analysis was performed using both conventional (knee alignment device) and functional (calibration movements) KJA determination methods.
• Mean hip rotation in stance (mHipRotSt) was calculated for each method, with procedures repeated.

Main Results:

• A systematic and substantial difference was found between functional and conventional hip rotation estimates (slope: 0.63, intercept: 0.31°).
• Functional methods yielded smaller errors (1-2°) compared to the conventional device (around 5°).
• The conventional method showed more consistent results when compared to frontal plane video-taping.

Conclusions:

• The systematic discrepancy in hip rotation measurements between functional and conventional KJA calibration is clinically significant.
• Misjudgments in patient rotation can occur, potentially impacting corrective procedures like derotation osteotomy.