Ground Reaction Force on the Frontal Plane Directs to the Center of Mass During Gait: Analysis from Gait Database

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Category: Other; Basic Sciences/Biologics Introduction/Purpose: In recent years, a paradigm shift has emerged in the preoperative planning for lower extremity osteotomies or arthroplasty. The focus has shifted from the loading axis during static standing known as Mikulicz line, to the loading axis during gait. These methods assumed that ground reaction force (GRF) vector directed toward the center of mass (CoM) on the frontal plane in the stance phase of gait. However, no study has clarified the relationship between the CoM and GRF vector. Furthermore, it is unknown to what extent the GRF vector turns inward from the Mikulicz line. The aim of the study is to reveal the geometrical relation on the frontal plane between the GRF vector and the anatomical landmarks including joint centers and the CoM during gait. Methods: The analysis was performed using the AIST (National Institute of Advanced Industrial Science and Technology) gait database 2019 which includes the data of 10 m walk on barefoot with comfortable speed obtained using motion-capture-system and force plates. The stance phase data of right feet for 162 participants (Male/Female = 78/84) under 50 years old was extracted. On the frontal plane, the distance from the GRF vector to the right hip center (D_hip) and to the CoM (D_CoM) were evaluated in the time period between the first and the last peak of the vertical GRF because this period could be considered as a single stance phase. The angle between GRF vector and the line passing center of pressures and hip centers (Mikulicz-GRF_Angle) was also calculated. Results: The analysis focused on the time period corresponding to 22 - 79 % of the stance phase, representing a single stance phase. Throughout this phase, the GRF vector on the frontal plane consistently directed medially to the hip center. The average D_hip during the single stance phase was 7.6 ± 1.0 cm, with a range of 6.6-9.2 cm. D_CoM was 1.3 ± 0.2 cm, and its range was 0.9 - 1.6 cm. Mikulicz-GRF_Angle was 5.6 ± 0.7 degrees, with a range of 4.8 - 6.7 degrees. Conclusion: During the single stance phase of gait in healthy young adults, the GRF vector consistently directs toward their CoM rather than their hip center on the frontal plane. The loading axis during gait was oriented 4.8 - 6.7 degrees medially to the hip center. These findings should be considered during surgery aimed at kinematic alignment reconstruction of the lower extremity.