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Classification and function of lower limb prosthesis
There are many products of lower limb prosthesis. Different parts of amputation, different conditions of amputated stumps and different prostheses are suitable for installation. According to different amputation parts, the lower limb prosthesis can be divided into six types: foot prosthesis, Sam prosthesis, leg prosthesis, knee amputation prosthesis, thigh prosthesis and hip prosthesis.
1. Sam prosthesis
The SAM prosthesis is only suitable for the specific Sam amputation. SAIM's amputation site passes through the ankle joint, and the end of the stump can fully bear the weight of the body, which has the bearing characteristics of the foot stump. Sam's prosthesis is supported by the end of the stump. If the end of the stump can not bear the whole body weight, the lower leg prosthesis should be installed.
2. Leg prosthesis
The corresponding amputation site of the leg prosthesis is above the SAM amputation and below the knee joint disconnection. For some amputees who can not fully bear the weight at the end of the stump after Sam's amputation, they also need to install the leg prosthesis. If the amputation part is too close to the knee joint, the remaining leg stump below the knee joint is too short and less than 5cm in length, and it is not suitable to assemble the leg prosthesis, but it should be installed according to the bearing capacity of the end. The number of lower leg prostheses is the largest. The structure and material of prosthesis are also various. According to different structures, the lower leg prostheses can be divided into long prostheses with thigh hinge and short prostheses without thigh hinge. Compared with the long leg prosthesis, the short leg prosthesis has great advantages in many aspects. Generally, most of the amputees are suitable to install the short leg prosthesis. However, sometimes there are some special situations, such as the short leg stumps. Because of the work requirements, the load of the stumps is large, the weight of the stumps knee joint needs to be reduced and the load-free, the stumps knee joint is unstable, and the load-bearing capacity of the stumps is low. As long as one of them is met, a long prosthesis with thigh circumference shall be installed.
3. Foot prosthesis
Foot prosthesis is suitable for foot amputation. If the ankle joint and heel (the last third of the length of the foot) are retained, the foot prosthesis can be installed. If you just amputate your toes, there is no hindrance to not installing a prosthesis.
There are two characteristics of the stump suitable for the installation of the foot prosthesis: one is that it can bear the weight of the whole body; the other is that even without the prosthesis, the amputee can walk. However, in practice, these conditions are not always satisfied. The pain, scar and deformity on the stump often bring great pain to the amputee. If this happens, even if the best prosthesis is is installed, it is difficult to achieve the desired effect. Therefore, the residual limb must be repaired by surgical method first. Although foot amputees can walk without prostheses, wearing them can significantly improve their ability to stand and walk. After wearing the prosthesis, both the walking function and appearance are more close to normal. In addition, the foot prosthesis is is light and easy to wear and take off. Amputees are as easy to wear as shoes.
4. Hip prosthesis
When the amputation site is higher than the trochanter of femur and even passes through pelvis, a hip prosthesis with hip joint, knee joint, ankle and artificial foot can be installed. The receiving cavity of the hip prosthesis contains the pelvis, so as to achieve the purpose of bearing, suspending and controlling the movement of the prosthesis. Due to the large number of components in the assembly of hip prosthesis and the heavy weight of prosthesis, it is advisable to select light weight components. If possible, the weight of the prosthesis can be greatly reduced by using light shell structure. The current prosthetic technology can be used to install prostheses for amputees passing through any part of the lower limbs and restore their basic functions. The lower the amputation site, the better the functional recovery. For the patients with congenital limb deficiency or short limb deformity, the corresponding prosthesis can also be installed to restore and improve their functions.
5. Knee amputation prosthesis
The corresponding amputation site is the knee joint amputation. The characteristic of the amputated leg is that the end can bear the weight completely. In some cases, the amputation near the knee joint through the lower leg condyle or the thigh condyle can also obtain the stump with complete bearing at the end. They can also be fitted with knee amputated prostheses. This kind of stump is long in length, balanced in muscle strength, and can control the prosthesis well.
6. Thigh prosthesis
The corresponding amputation site of the thigh prosthesis is is above the knee amputation and below the trochanter of the femur. Under special circumstances, it is not allowed to install the short leg stump and the amputated knee stump of the knee amputated prosthesis, and the thigh prosthesis can be installed.
The main factors that determine the function of thigh prosthesis are the receptive cavity, knee joint, ankle and artificial foot. The receptive cavity and knee joint play a particularly important role. With the change of their forms and structures, a large number of different prosthetic products have evolved.
In China, transverse elliptical (quadrilateral) ischial support is still the main receiving cavity. In the world, cat-cam with ischial inclusion is widely used. From the support of the sciatic bone to the inclusion of the sciatic bone, the progress of the receptive cavity technology has brought a lot of good news to amputees wearing thigh prostheses. Wearing the ischium to contain the acceptor cavity, the force of the residual limb is more uniform, more in line with the physiological load-bearing state; the blood circulation of the residual limb is no longer blocked; the movement control ability of the residual limb to the artificial limb is higher. This kind of advanced receiving cavity technology is also being gradually popularized in China.
There are many kinds of prosthetic knee joints, including uniaxial joint and polyaxial joint. There are friction control, air pressure control and hydraulic control to control the swing of the joint; the control mode includes feedback control through real-time sensor detection and microprocessor data processing, as well as adjustment control with or without feedback. For amputees with different physique and activity, the joints are designed for both the elderly with low activity and the young with sports. In terms of materials, there are stainless steel materials with high strength and weight, titanium alloy materials with better strength and weight.