Simultaneous quantification of lower limb skeletal posture and ground reaction forces using upright computed tomography: Potential implications for osteoarthritis assessment and treatment

Understanding the transmission of forces through the joints of the lower limb under weight-bearing conditions is critical for assessing the progression of knee and ankle osteoarthritis, as well as for developing effective surgical and preventive strategies. This study presents the first simultaneous quantification of three-dimensional skeletal posture and ground reaction force vectors during quiet standing, utilizing upright computed tomography and a custom-made force plate. We constructed the force plate using two six-axis force sensors, and the coordinate system of the CT was aligned with that of the force plate using metal spheres attached to the edges of the force plate. This system enabled precise measurement of ground reaction force vectors relative to the skeletal posture. The present study demonstrated that the load-bearing axis (the line connecting the femoral head center to the midpoint of the distal tibial plafond) in healthy subjects during quiet standing is not identical to the actual line of force application. The analysis revealed that the force vectors generally pass slightly medioposterior to the femoral head center. By providing a detailed view of how force is transmitted through the lower limb joints, this system potentially offers new insights into joint loading patterns that possibly contribute to osteoarthritis development.