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Common classification of prosthetic feet
Several commonly used prosthetic feet are classified as follows:
(1) SACH foot
SACH foot is soft calcaneus. Its ankle and mid foot parts are made up of inner wood core, which is covered with foam and made into feet. The heel of the SACH foot is fitted with a soft plastic foam wedge, that is, the soft heel. When the heel touches the ground, the soft heel deforms under pressure, and then the sole touches the ground, similar to the plantar flexion of the foot. During the forward rolling of the foot, the front foot part of the foam shell is similar to the dorsal extension of the toes. The movement of the false foot in the sagittal plane is realized by the elastic material on the foot.
SACH feet are lighter in weight. It can also be used in lower leg prosthesis. When it is used for thigh prosthesis, it is only suitable for patients walking on the flat ground or in the area with simple ground conditions. The flexible movement of the foot is limited to the heel and metatarsophalangeal joints, and it has no function of eversion and rotation. With the increase of the height of amputation and the complexity of ground conditions, this kind of foot is not suitable. In addition, because it is hard to follow the ground, it also has adverse effects on the stability of the knee joint.
(2) energy storage foot
The energy storage foot is developed on the ankle fixed soft heel foot with simple structure and light weight. It has been further improved in structure. Increased foot mobility in all directions. It stores energy during the support period and releases it when pedaling. The release rate of energy is related to the structure of feet and the energy storage materials used. This kind of artificial foot is designed for running, jumping and other sports. It is suitable for patients with high activity.
(3) Uniaxial foot
The uniaxial foot has a joint axis related to the human ankle joint. The foot can do dorsiflexion and plantar flexion around this axis. The structure of the foot also determines that it can only move in the sagittal plane. The range of motion and damping of the dorsiflexion and plantar flexion of the single axial foot can be adjusted by the buffer device located in the front and rear of the axle. They also affect the stability of the knee joint. The disadvantages of this kind of foot are heavy weight, long-term use or use in poor conditions, joint wear and tear.
(4) multi-axis foot
The multi-axis foot can move in three faces. Its function is realized by the deformation of elastic material located at ankle. The elastic material has the deformation ability in all directions, so the dummy foot can move in all directions. The pronation and valgus of the artificial feet enable the amputee to walk on the uneven ground wearing the artificial limbs. The rotating movement ability of the dummy foot can absorb the rotating moment produced by the uneven ground. This kind of artificial foot is suitable for all kinds of amputees living in non plain areas. The disadvantages are complicated structure and heavy weight of prosthesis.
(5) Hydraulic control foot
In theory, each movement of the joint can be controlled by hydraulic pressure. Because of the relationship between size and weight, the hydraulic control foot is only designed for the control of the false instep. If the false foot has a large range of dorsiflexion activities, it will make climbing, knee bending, pedaling and many other activities easier. But at the same time, we should prevent the knee from bending out of control. This is the task of hydraulic ankle control.
Technically, there are two ways of control: hydraulic control of ankle dorsiflexion and hydraulic control of knee flexion affected by ankle dorsiflexion. The hydraulic ankle allows the ankle to perform a wide range of dorsiflexion. The dorsiflexion of the dummy foot is not an uncontrolled free movement, nor a movement controlled by an elastic cushion, but a movement under the continuous damping of the hydraulic device. In the gait cycle, when the dummy foot is at any angle position, it is protected by hydraulic buffer and will not change suddenly. Through the hydraulic control of ankle dorsiflexion brake, the lower leg can not accelerate forward suddenly, so the knee joint will not bend suddenly. Through the continuous movement of ankle under the control of hydraulic pressure, the foot can continue to bend back, and the knee can continue to bend in a controlled way. The hydraulic control of knee joint affected by ankle dorsiflexion has the same effect in principle. Compared with the pure hydraulic ankle joint, the knee joint control has the following functions: locking the knee joint; controlling the movement of the knee joint; controlling the swing of the dummy foot. But it also has the disadvantages of heavy weight, easy to break and difficult to repair. This kind of artificial foot is suitable for those patients who regard the function as very heavy and do not care about the increase of weight.