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. We compared functional calibration methods with conventional methods in this group for 1) localization of the hip joint center (HJC) and knee axis orientation, 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 HJCs and knee axis orientation were compared between calibration methods, with CT serving as reference for HJC estimation. Gait kinematics were compared using statistical parameter mapping (SPM). Findings Functional calibration methods estimated the HJC closer to the CT reference (26±21mm more lateral) than the conventional method (38±21mm more medial). In the full sample, orientation of the knee joint axis was not different between calibration methods, but in adolescents with increased femoral anteversion, the knee was more internally rotated with the functional method (3.3±6.2°). During gait, SPM revealed significantly more hip flexion, more internal hip rotation during the stance phase, less knee varus-valgus motion, and larger knee flexion angles when applying the functional calibration method. Interpretation Functional calibration methods better approximated the HJC, and showed a knee axis orientation that was more towards the direction of the deformity. This resulted in less knee joint angle crosstalk during gait. Although differences between calibration methods on gait kinematics were within clinically acceptable limits for the sagittal plane, relatively larger differences on transversal hip kinematics may hold clinical importance.