What Are Normal Foot Biomechanics?

Ankle injuries are common in sports. Ankle injuries account for about 25% of all sports-related injuries. Ankle injury is mainly caused by ligament injury. The ankle ligament injury rate accounts for about 80% of the total ankle injury rate in sports. Ankle injury will not only affect the normal competition and training of athletes, but also cause chronic injury such as ankle instability and degenerative osteoarthritis if not handled properly.

Ankle injuries are common in sports. Ankle injuries account for about 25% of all sports-related injuries. Ankle injury is mainly caused by ligament injury. The ankle ligament injury rate accounts for about 80% of the total ankle injury rate in sports. Ankle injury will not only affect the normal competition and training of athletes, but also cause chronic injury such as ankle instability and degenerative osteoarthritis if not handled properly.

Anatomy of ankle joints prone to injury Ankle joints include tibial, tibiofibular, and talofibular articular surfaces, which mainly guarantee the functions of foot dorsiflexion, plantar flexion, flipping, and rotation. The ankle points formed by the medial malleolus and lateral malleolus of the distal tibia and fibula cannot be completely matched with the medial and lateral sides of the talus and ankle joint. This is the anatomical basis for the ankle joint to easily rotate. During the landing process, the ankle joint gradually changed from the plantar flexion position to the dorsal extension position. During this process, the contact area between the ankle joint surface continued to increase, and the unit area force continued to decrease. When the landing was stable, the inner and outer sides of the talus The contact area between the articular surface and the tibia and fibula is the largest. The stability of the ankle joint is closely related to the ligament.

The lateral ankle joint is reinforced by lateral ligaments. It starts from the lateral malleolus and ends in three bundles at the anterior and lateral sides of the talus, and at the rear of the talus. The lateral ligament is the weakest ligament in the ankle, and it is also a structure that is more likely to be damaged during landing. There is a strong and tough triangular ligament reinforcement inside the ankle joint. The anatomical structure of the triangular ligament is numerous and small, and its mechanism of maintaining joint biomechanical stability is complex.

Figure: Anatomy of the human ankle

Boden et al. Believe that the stability of the ankle joint mainly depends on the stability of the medial, lateral, and inferior tibiofibular joints. If two of these three structures are stable, the ankle joint is stable. When the ankle is in the plantar or dorsiflexion position, the triangular ligament will play a very important role in the rotation stability of the ankle and calf. Michelson et al. Believe that when the ankle joint is in extreme dorsiflexion and plantar flexion, the ankle joint is varus, and the triangular ligament can effectively limit the talar external rotation and ensure the stability of the ankle joint.

Progress in Biomechanics of Ankle Injury. Biological Modeling and 3D Finite Element Using biological modeling to study the stress distribution of the foot can provide foot physiology and pathology evidence for ankle joint floor injuries. The establishment of an appropriate ankle biomechanical model has become the focus of foot biomechanical research. Three-dimensional finite element technology can use CT or MRI scanning technology to obtain various three-dimensional coordinate values of the normal ankle joint, and then input the finite element analysis software to build a finite element model of the ankle joint. It can not only effectively simulate the human skeletal muscle system, but also infer the changes in the stress distribution of internal bone tissue and soft tissue. Compared with traditional biomechanical research, the 3D finite element method also has the advantages of low cost, wide application, and strong adaptability. Tao Kai et al. Used a three-dimensional finite element model to quantify the effects of plantar pressure distribution in different postures, stress distribution of soft tissues inside the ankle joint, and deformation of the arch during the landing on the biomechanical characteristics of the foot. Cheung et al. Used an MRI image to establish a highly anatomically similar ankle finite element model, and specifically quantified and analyzed the soft tissue stiffness of the plantar foot and the effect on plantar pressure and bone stress distribution. The use of this technology can increase theoretical support for the design of new sports insoles.

Kinematics of ankle injuries Kinematics of ankles in sports early focused on the use of high-speed cameras to analyze the landing process. High-speed photography can obtain the landing speed, angle, and exercise time of the ankle joint when the subject jumps to the ground, and then the landing impact force on the ankle joint can be calculated by Newton's law of motion. With the advancement of technology, there are new tools for the study of landing injury kinematics. At present, three-dimensional motion capture systems are mostly used in sports biomechanics experiments. The three-dimensional motion capture system can capture the trajectory of human motion through the markers on the subject. It can accurately output related kinematic parameters such as motion time, motion speed, acceleration, joint angular displacement and angular velocity in various directions through corresponding software. Yeow et al. Used a three-dimensional motion capture system combined with force plate technology to compare the differences in ankle joint angle and angular velocity between male and female athletes. Ergen et al. Used a three-dimensional motion capture system to study football players with ankle sprains and compared the effects of ankle brace and warm-up training on ankle joint protection. Jing Lanxiang and others used a three-dimensional motion capture system combined with force plate technology to study the dynamics and stiffness changes of the lower limb ankle joints after weight-bearing isometric training. And stiffness parameters while reducing the risk of ankle injury.

Research on dynamics Ankle joint injuries caused by jumping on the ground in sports are usually related to the impact of the ground on the soles of the feet exceeds the limit of the body's capacity. Therefore, the detection of ground reaction forces is used in the study of ankle landing injuries It occupies an important position. At present, the most commonly used ankle joint dynamics research at home and abroad is the three-dimensional force plate system. It can measure the distribution of vertical, front-to-back, and lateral forces on the landing surface, and can also calculate the torque and pressure center trajectories in the corresponding three directions with the help of related software. Lida et al. Used a three-dimensional force plate to simulate the absorption process of the ground impact force when the athlete jumped to the ground, and pointed out the effect of central motion control on the kinematic parameters of the ankle joint. Chu et al. Used a three-dimensional force plate combined with a motion capture system to study the movements that often cause joint sprains in sports, and obtained the ankle varus angle and ground reaction forces under various movements.

Madigan used a three-dimensional force plate to study the relationship between ground force and lower limb muscle fatigue. It was found that the fatigue of lower limb muscles before landing could affect the flexion amplitude of the lower limb joints, resulting in an increase in the impact of the ground on the lower limbs. The research of digital technology The development of plantar pressure measurement technology has passed the technology of foot print, plantar pressure scanning, force plate and force plate technology, pressure shoes and insole technology. Although the three-dimensional force plate can accurately measure the ground reaction force and distribution, it cannot measure the pressure at the "foot-shoe interface". The sole pressure insole solves this problem well. Because the insole is attached to the sole of the foot, it can measure continuous parameters of the "foot-shoe interface" pressure, and perform real-time monitoring and feedback. At present, the most widely used insoles in biomechanical research are the Belgian F-Scan insoles and the German Pedar insoles. The designer arranges the sensor according to the anatomical position of the sole of the foot, and adds a pad to make an insole. When a person wears this shoe to stand or walk, the output of the sensor changes. After processing the data, a continuous gait pressure curve can be obtained. . Fong et al. Used the sole pressure insole 3PS to detect the ankle spin torque in sports, and evaluated the risk of injury to the ankle in different postures when landing.

Study of surface electromyography. The movement of ankle muscles when jumping and landing in sports can provide power for joint movements and ensure joint coordination. When landing, insufficient muscle strength in the lower limbs can lead to inadequate movements in the landing posture, which increases the risk of ankle injury. In addition, chronic fatigue of the ankle muscles is also an important factor for sports personnel ankle injury caused by jumping. Osterberg et al. Studied the ankle muscle fatigue during repeated lifting tests and found that it is not the peak muscle strength that restricts the lifting movement from continuing to complete, but that the predetermined range of movement cannot be maintained due to muscle fatigue. There is a certain degree of correlation between surface electromyography activity and muscle activity and function, which can reflect neuromuscular activity to a certain extent. Surface electromyography (sEMG) technology is a method of collecting and analyzing electrical signals on the surface of muscles through an electromyograph. The application of sEMG signal characteristics can predict skeletal muscle fiber types, assess strength training, detect muscle damage, determine response time, exercise time and electromechanical delay of human activities and its relationship with muscle tissue metabolism. Niu et al. Studied the difference in the electromyographic activity of the lower limbs between athletes landing by detecting the surface EMG signals when the lower limbs landed. He pointed out that there was a significant difference in the activity of the flexors of the bilateral ankle joints when the athletes landed. Lida et al. Using surface electromyography to study the coordination of the lower limb muscles during the landing buffer process, it was confirmed that the role of central motion control in coordinating the motion of the ankle joint on the ground. An in-depth study of the biomechanical characteristics of the ankle joint and its influencing factors can better prevent ankle joint sports injuries in sports. The combination of kinematics, dynamics, surface electromyography, and finite element method of the ankle joint with new technical methods can provide a powerful help for the study of ankle joint injuries in sports.

Ankle Biomechanics Extended Reading

• Hu Gengdan, Wang Lejun, Niu Wenxin. Sports Biomechanics. Tongji University Press. December 2013, 1st edition.

• Niu WX, Yao J, Chu ZW, Jiang CH, Zhang M, Fan YB. Effects of ankle eversion, limb laterality, and ankle stabilizers on transient postural stability during unipedal standing. Journal of Medical and Biological Engineering . 2015, 35 (1) : 69-75.

• Niu WX, Wang LJ, Feng TN, Jiang CH, Fan YB, Zhang M. Effects of bone Young's modulus on finite element analysis in the lateral ankle biomechanics. Applied Bionics and Biomechanics . 2013, 10 (4): 189-95.

• Niu WX, Fan YB *. Terrain stiffness and ankle biomechanics during simulated half-squat parachute landing. Aviation, Space, and Environmental Medicine . 2013, 84 (12): 1262-7.

• Niu WX, Chu ZW, Yao J, Zhang M, Fan YB, Zhao QP. Effects of laterality, ankle inversion and stabilizers on the plantar pressure distribution during unipedal standing. Journal of Mechanics in Medicine and Biology . 2012, 12 (3): 1250055 (15 pages). (IF 2013 = 0.803)

• Niu WX, Wang Y, Yao J, Zhang M, Fan YB, Zhao QP. Consideration of gender differences in ankle stabilizer selection for half-squat parachute landing. Aviat Space Environ Med . 2011, 82 (12): 1118-24 .

• Niu WX, Wang Y, He Y, Fan YB, Zhao QP. Kinematics, kinetics, and electromyogram of ankle during drop landing: A comparison between dominant and non-dominant limb. Hum Mov Sci . 2011, 30 (3): 614- twenty three.

• Niu WX, Wang Y, He Y, Fan YB, Zhao QP. Biomechanical gender differences of the ankle joint during simulated half-squat parachute landing. Aviation, Space, and Environmental Medicine . 2010; 81 (8): 761-7.