The effect of functional calibration methods on gait kinematics in adolescents with idiopathic rotational deformity of the femur

Background: Due to anatomical deviations, assumptions of the conventional calibration method for gait analysis may be violated in individuals with rotational deformities of the femur. Functional calibration methods were compared with conventional methods in this group for 1) localization of the hip joint center and orientation of the knee axis, and 2) gait kinematics.Methods: Twenty-four adolescents with idiopathic rotational deformity of the femur underwent gait analysis and a CT scan. During standing, distance between hip joint centers and knee axis orientation were compared between calibration methods, with CT serving as reference for hip joint center estimation. Gait kinematics were compared using statistical parametric mapping.Findings: The conventional calibration method estimated the hip joint center closer to the CT reference (4 & PLUSMN;12 mm more lateral) than the functional calibration method (26 & PLUSMN; 20 mm more lateral). Orientation of the knee joint axis was 2.6 degrees less internal in the functional calibration method. During gait, statistical parametric mapping revealed significantly more hip flexion, less external hip rotation during the swing phase, less knee varus-valgus motion, and larger knee flexion angles when applying the functional method.Interpretation: Functional calibration methods were less accurate in determining the hip joint center location than the conventional calibration method and resulted in a knee joint axis that was less internally rotated. Impor-tantly, there was less knee joint angle crosstalk during gait when using the functional method. Although dif-ferences between methods on gait kinematics were within clinically acceptable limits for the sagittal plane, relatively larger differences on transversal hip kinematics may hold clinical importance.