Discussion on the full contact of the prosthetic receiving cavity and the bearing of the stump
When amputees walk with lower limb prostheses, people always tend to pay attention to the harmony of gait. Only when there are swelling, discoloration, load-bearing and blood circulation problems in the residual limb, people care about what happened to the residual limb. The changes of the stump are closely related to the reception cavity which absorbs and contains the stump.
The receiving cavity is the most important part of the prosthesis. It directly contacts with the stump, supports the weight of human body and controls the movement of the prosthesis. Whether the prosthesis is comfortable or not depends on whether the receiving cavity is suitable. The receptive cavity is an important structure that affects the comfort and function of the prosthesis. Full contact and maximum load-bearing of the stump are the requirements of modern prosthetic assembly. Unfortunately, it is often overlooked.
Bearing and movement are the most fundamental functions of lower limb prosthesis. The reliable "connection" between the stump and the receiving cavity ensures the realization of the function of the prosthesis. Any tiny "dummy joint" and "piston movement" between them will hinder the amputee's precise control of the prosthesis, thus reducing the stability of standing and walking, and increasing the patient's energy consumption. The full contact between the stump and the receiving cavity is helpful to achieve the goal of firm connection between the stump and the receiving cavity. Full contact requires that the residual limb can at least contact and bear certain pressure. Otherwise, before installing the prosthesis, we should consider to improve the quality of the residual limb by conservative or surgical methods.
The amputee should be able to stand on the bottom of the receiving cavity with the amputee, just like standing on the ground before the amputation. It is an important condition for the prosthesis to use the stump to bear the most weight. It is not only of great biomechanical significance, but also through the contact and bearing of the stump, the amputee's sensory nervous system can directly feel the important information of the pressure and movement from the bottom.
The weight bearing of the stump realizes the weight bearing of the skeleton of the stump. It has the physiological function of preventing decalcification (passive osteoporosis). For child amputees, it can also stimulate the growth of stumps.
The bearing capacity of the stump depends on the height of the amputation and the quality of the soft tissue, as well as the surgical technique. Among the amputees, the load-bearing capacity of the long stump is less than 20% of the body weight; the large section of the middle stump can generally bear 30-60% of the body weight; the load-bearing capacity of the short stump is higher, even up to 100%. The stump of the thigh has about 20-30% load-bearing capacity. All kinds of stumps obtained by amputation of joint, osteoporotic part near the joint and foot amputation with part of sole reserved can fully bear weight after short time practice, and have 100% bearing capacity.
The problem of full contact and load-bearing of leg and thigh prosthesis is the most prominent in the lower limb prosthesis assembly. The lower leg prosthesis and the thigh prosthesis can free the upper part of the stump by supporting the upper part of the stump, such as the proximal tibia, thigh or Ischia. This will inevitably lead to venous and lymphatic reflux disorders, resulting in swelling of the stump. The position of thigh and leg amputation passes through tubular bone, and the bearing capacity of the stump is limited. It is inevitable for the prosthesis to reduce the load of the stump by carrying the weight on the upper end of the stump, but the load-free degree should be minimized to make the stump bear the maximum load. In fact, the bearing capacity of the stump is higher than the general imagination.
The bearing capacity of the stump in the prosthesis also depends on the shape and material of the receiving cavity. The technology of silicone leg and thigh prosthesis provides conditions for full contact and bearing of stump in material and technology. However, in today's lower leg and thigh prosthesis assembly, there are still many receiving cavities which do not meet the requirements of full contact and residual load-bearing.
Some so-called "high-grade" leg prostheses, although using very high-quality and expensive materials, have not achieved full contact, let alone bearing of the stump. The huge space between the end of the stump and the base of the receiving cavity is the root cause of the discoloration and stasis of the stump. It is easy for amputees to know whether the receiving cavity is in full contact as long as the bottom end is pressed lightly after the inner sleeve is put on. Some amputees spontaneously pad cotton threads on the bottom of the receiving cavity to maintain contact and pressure with the stump. Their knowledge of total contact has surpassed that of prosthetic technicians. Expensive materials do not represent the quality of high-grade prostheses.
The condition of thigh prosthesis is a little better. Although there are still a large number of suction receptacles without end contact, full contact receptacles have been widely used.
There is a large gap between the bottom of the suction receiver and the end of the stump. It forms a confined space. The negative pressure generated in the confined space will absorb the receiving cavity on the stump and play a role of suspension. This is the reason why the receiving cavity was widely used in the early stage. The external pressure on the stump is less than that on the side and mouth of the stump. The lymphatic and venous return is blocked, which inevitably leads to the edema of the stump. In spite of its serious disadvantages, the receiving cavity is still widely used in the assembly of thigh prosthesis. The main reason is that the fabrication technology of the receiving cavity is low.
The full contact receiver retains the advantages of the suction receiver and eliminates its adverse effects. The whole surface of the stump, especially the end of the stump, is in full contact with the receiving cavity. The end of the stump is subjected to axial pressure from the bottom of the cavity. In the process of walking, the blood is sucked to the end of the stump by negative pressure when the leg is swinging, and the blood is pumped out when the stump is compressed by the cavity bottom during the load-bearing support. Blood flows in and out of the end of the stump so repeatedly and alternately, promoting