| The human foot is the only part that contacts the ground during walking.After a long natural evolution process,it has formed a unique foot structure different from primates and other animals,which makes the human bipedal walking with both stability and flexibility.The foot is characterized by variable stiffness during gait.The bones,wrapped in muscles and ligaments,form the characteristic arch of the foot,the main structure of which is the joint.Among them,the hindfoot foot joints(tibiotalar joint and subtalar joint)are subjected to huge impact force at the initial stage of gait.In the gait process,joint posture has the function of motion regulation,which plays an important role in the smoothness and stability of gait.In addition,tibiotalar joint and subtalar joint are prone to various ankle diseases,such as ankle arthritis and ankle sprain,and ankle diseases will change the movement of the hindfoot joint to varying degrees.Quantification of the detailed three-dimensional kinematics of the hindfoot joint is critical to our understanding of the biomechanical function of complex arch structures in producing stable and efficient bipedal motion.In engineering,it can provide detailed reference for the development of rehabilitation assistant devices and the foot design of biped robots.In clinic,it has important guiding significance for preoperative diagnosis and postoperative evaluation of ankle joint disease.In this paper,the international advanced equipment biplanar dynamic X-ray system is used to study the three-dimensional 6-DOF movement of human hindfoot joint.We studied tibiotalar and subtalar joint movements during the stance phase of gait at normal speed and with heavy load,and hindfoot joint movements under a special movement condition(heel lift-down).In addition,3D-2D registration and semiautomatic tracking technology based on bone contour and gray intensity were successfully explored,and joint motion calculation algorithm based on semi-automatic tracking data was developed,which improved the accuracy and efficiency of image processing.It is of great significance for the application of biplanar dynamic X-ray system in the field of biomechanics.The main work and conclusions of this paper are as follows:(1)Exploration and application of 3D-2D semi-automatic registration methodBased on foot CT image,the image segmentation and model reconstruction are completed to obtain the virtual model for semi-automatic registration.Use the biplanar X-ray image sequence after distortion correction and calibration file reconstruction biplanar three-dimensional virtual environment,than complete the initial frame registration manually in the neutral position of the foot.Using the downhill simplex optimization algorithm and particle swarm optimization algorithm to find the virtual model and the X-ray image’s matching bone position.Automatic optimization algorithm and interpolation were performed on the image sequence in stages to complete semi-automatic registration,and the transformation matrix of the skeleton in the laboratory coordinate system was obtained.(2)3D motion calculation algorithm of foot joint based on 3D dynamic X-ray dataBased on the reconstructed skeleton model of the hind foot,customize the local anatomical coordinate system.The transformation from anatomical coordinate system to technical coordinate system and then from technical coordinate system to laboratory coordinate system is completed by using the relationship between coordinate systems.The joint angle is determined using the overall transformation from proximal to distal of the joint.The vectors between the origin of the distal ACS to the origin of the proximal ACS were projected onto each axis of the proximal skeletal ACS to quantify joint translation.(3)Kinematics research during the stance phase of gait and heel lift-down motion.In this paper,biplanar X-ray images of the feet of healthy subjects during the stance phase of gait(loaded and non-loaded)and during heel lift-down motion were collected,and three-dimensional 6-DOF analysis of the two joints of the hindfoot was performed.It was found that there was a kinematic coupling between dorsiflexion/plantar flexion in the sagittal plane and inversion/eversion in the frontal plane of the two joints of the hindfoot.The dorsiflexion/plantarflexion ROM was the largest in sagittal plane and the inversion/eversion ROM was the smallest in frontal plane,and the weight bearing significantly increased the inversion/eversion ROM during the stance phase of gait.The motion pattern of dorsiflexion-plantarflexion-dorsiflexion was observed in the sagittal plane,and the motion pattern of eversion-inversion-eversion was observed in the frontal plane.The rotational motion in the transverse plane was first adduction and then abduction.Loading increased the maximum plantarflexion angle,increased the maximum inversion angle,and decreased the maximum dorsiflexion angle,and also led to an earlier adduction of 0°.Weight-bearing significantly increased the medial and lateral translational ROM,and the talus moved outward,backward and downward with respect to the tibia under non-weight-bearing condition.The talus moves inward,forward,and downward with respect to the tibia during loading.The inversion/eversion ROM was the largest in the frontal plane of the subtalar joint,and the weight bearing increased the inversion/eversion ROM.The calcaneus shows slight plantarflexion,inversion,and abduction with respect to the talus during the stance phase of gait.The medial-lateral translational ROM of the subtalar joint was the largest,and the proximal and distal translational ROM was the smallest.During the stance phase of gait,the calcaneus moved inward,forward and downward relative to the talus,and the weight bearing would cause the calcaneus to move forward later relative to the talus during the full-foot touching stage.In the process of heel lifting and dropping,the tibiotalar joint presents the talus relative to tibia plantarflexion,inversion and adduction,and the subtalar joint presents the calcaneus relative to talus inversion and adduction,and the corresponding rotation angle increases first and then decreases.The dorsiflexion/plantarflexion ROM of tibiotalar joint was the largest,inversion/eversion ROM was the smallest.The inversion/eversion ROM of the subtalar joint was the largest,and the dorsiflexion/plantarflexion ROM was the smallest.The anteroposterior translational ROM of tibiotalar joint was the largest,while the medial-lateral translational ROM of subtalar joint was the largest. |
