Talking about the full contact of the prosthesis socket and the weight bearing of the stump

When an amputee walks with a lower limb prosthesis, people always tend to pay attention to gait harmony. People only care about what happened to the stump when the stump has bruising, discoloration, weight bearing and blood circulation problems. The various changes of the residual limb are inseparable from the socket that accommodates the residual limb.

The socket is the most important part of the prosthesis. It directly touches the residual limb, supports the weight of the human body, and controls the movement of the prosthesis. Whether the prosthesis is comfortable or not depends entirely on whether the socket is suitable. The socket is an important structure that affects the wearing comfort and function of the prosthesis. Full contact and maximum stump load-bearing are the requirements of modern prosthetic assembly for socket. Unfortunately, it is often overlooked.

Weight bearing and movement are the most fundamental functions of lower limb prosthetics. The reliable "connection" between the residual limb and the socket ensures the realization of the function of the prosthesis. Any tiny "prosthetic joint" activity and "piston movement" between them will hinder the amputee's precise control of the prosthesis, thereby reducing the stability of standing and walking and increasing the patient's energy consumption. The full contact between the residual limb and the socket helps to achieve the goal of a firm connection between the residual limb and the socket. Full contact requires that the residual limb can at least be in contact and can withstand a certain amount of pressure. Otherwise, before installing the prosthesis, conservative or surgical methods should be considered to improve the quality of the residual limb.

Wearing an ideal prosthesis with the most weight-bearing stump, the amputee should be able to stand on the bottom of the socket with the stump, just like standing on the ground before the amputation. Using the stump to bear weight to the greatest extent is an important condition for the prosthesis to become physiological. The weight bearing of the stump not only has important biomechanical significance, but also through stump contact and weight bearing, the sensory nervous system of the amputee can directly feel the pressure and important information from the bottom end.

The weight bearing of the stump realizes the weight bearing of the stump bone. It has the physiological effect of preventing decalcification (passive osteoporosis). For children with amputees, it can also stimulate the growth of stumps.

The weight-bearing capacity of the stump depends on the amputation height and soft tissue quality, and depends on the surgical technique. Among calf amputees, long stumps can bear less than 20% of body weight; medium-length stumps with larger cross-sections can generally bear 30-60% of body weight; short stumps have higher load-bearing capacity, even up to 100%. The stump of the thigh stump also has about 20-30% weight bearing capacity. Various residual limbs obtained through joint severance, amputation of the cancellous bone near the joint, and amputation of the foot with part of the sole of the foot can fully bear weight after a short period of practice, and have 100% weight bearing capacity.

The problem of full contact between the calf and thigh prosthesis and the weight bearing of the stump is the most prominent in the assembly of the lower limb prosthesis. The calf prosthesis and thigh prosthesis free the stump by supporting the upper part of the stump, such as the proximal tibia, thigh, or ischium. This will inevitably lead to venous and lymphatic drainage disorders, causing swelling of the residual limb. The amputation of the thigh and calf passes through the tubular bone, and the stump has limited weight bearing capacity. The prosthesis must inevitably reduce the load of the stump through the upper end of the stump, but the degree of load-free should be reduced to the minimum, so that the stump can bear the maximum weight. In fact, the weight-bearing capacity of the stump is higher than generally thought.

The weight-bearing capacity of the stump in the prosthesis also depends on the shape and material of the socket. The silicone calf and thigh prosthetic technology provides conditions for full contact and stump bearing in terms of materials and technology. Nevertheless, in today's calf and thigh prosthetic assembly, there are still many receiving cavities that do not meet the requirements of full contact and stump load-bearing.

Some so-called "high-end" calf prostheses, although using very high-quality and expensive materials, have not achieved full contact, let alone stump bearing. The huge space between the end of the stump and the bottom of the socket is the root cause of the discoloration and swelling of the stump. As long as the bottom end is pressed lightly after putting on the inner sleeve, the amputee can easily know whether the socket is in full contact. Some amputees spontaneously put cotton silk on the bottom of the socket to maintain contact and pressure with the residual limb. Their knowledge of full contact has exceeded that of prosthetic technicians. Expensive materials do not represent the quality of high-end prostheses.

The condition of the thigh prosthesis is slightly better. Although there are still a large number of absorbing cavities without stump contact, full-contact cavities have been widely promoted and used.

There is a large gap between the bottom end of the suction cavity and the end of the residual limb. It constitutes a confined space. The negative pressure generated in the confined space will suck the socket on the residual limb and play a hanging role. This is the reason why the socket was widely adopted in the early days. Wearing a prosthesis assembled with this socket, the external pressure on the stump is less than the pressure on the side and mouth shape of the stump, lymphatic and venous return are blocked, and stump edema is inevitably produced. Despite the serious shortcomings of this receptacle, it is still widely used in thigh prosthetic assembly. The main reason is that the manufacturing technology requirements of this socket are relatively low.

The full-contact socket retains the advantages of the suction socket and eliminates its adverse effects. The entire surface of the stump, especially the end of the stump, is in full contact with the socket. The end of the residual limb bears 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 legs are swinging, and the stump is pressed by the bottom of the cavity when the weight is supported to pump the blood out. The blood flows in and out alternately at the end of the residual limb so as to promote the blood circulation of the residual limb.

It is very simple to check whether the thigh cavity has achieved full contact and stump bearing. In the load-bearing support state, the amputee can not only detect the gap and pressure between the end of the stump and the bottom of the socket through the valve hole, but also judge whether the end of the stump is squeezed.

In order to achieve the stump contact and load-bearing, on the one hand, the stump must have a good soft tissue coverage, on the other hand, the shape of the socket must fit the stump very well. This puts forward higher requirements for both amputation technology and prosthetic assembly technology.

The currently widely used thigh prosthesis wear method has a very adverse effect on full contact and stump bearing. Nowadays, everyone wears prostheses with socks and valve holes. The soft tissue is pulled towards the stump. The weight-bearing capacity of the stump is weakened. The valve hole at the bottom of the socket even destroys the contact and load-bearing position there. Only by filling the valve hole at the bottom of the socket with a special valve can the full contact in the true sense be achieved. As long as there is no better way to wear a prosthesis, the weight-bearing capacity of the stump will not be fully utilized.

In our country, the assembly of lower limb prostheses has not been able to achieve full contact and stump load-bearing. There are not only cognitive reasons, but also prosthetic assembly technical reasons, and amputation technical reasons.

Many amputees and prosthetics technicians lack sufficient attention to this issue. They did not realize that full contact and weight bearing of the stump would affect the health of the amputee's stump and even the entire body. In order to avoid the troubles caused by the tenderness of the end of the stump to the prosthesis assembly, the prosthetic assembly technicians stand in their own position rather than the position of the amputee, simply suspend the stump in the socket, and are unwilling to pursue full contact and stump Load-bearing goals. The amputee accepted it because there was no tenderness.

Due to the lack of knowledge and the lack of pressure from the needs of amputees (special consumers), technicians lack the motivation to pursue advanced technology, and cannot technically achieve full contact and stump bearing.

Full contact and stump weight bearing put forward higher requirements on the quality of the stump. Due to the lack of understanding of the development of prosthetic technology in the medical field, the surgeon has not created a residual limb that can achieve full contact and stump weight. Bone spurs, neuromas, and terrible scars left after surgery hinder the application of new technologies.

We pursue the goal of full contact and stump weight-bearing, so as not to affect the circulation of the stump's arteries, veins, and lymph, and not to hinder nerve conduction. There is no full-contact and weight-bearing socket, and sooner or later it will cause chronic blood circulation disorder, causing swelling of the stump, until eczema, blisters, chronic ulcers appear, especially serious skin changes at the mouth of the socket. As a result, the residual limb loses its weight-bearing capacity and can only bear weight through the tighter upper part of the mouth, forming a vicious circle.

In the initial stage of stump bearing, the soft tissue at the end of the stump will shrink rapidly, which reduces the pressure on the end of the stump at the bottom of the socket. In the initial stage of prosthesis assembly, the bottom of the socket should be continuously adapted to adapt to the shape of the end of the stump to achieve the greatest degree of weight bearing on the stump.