RU111429U1 - JOINT ENDOPROTHESIS Friction ASSEMBLY - Google Patents

Abstract

 The knot of the joint endoprosthesis friction with elements made with interacting smooth surfaces, characterized in that the elements of the endoprosthesis friction knot are made of monolithic isotropic pyrolytic carbon doped with boron.

Description

The invention relates to medical equipment and can be used in orthopedics to replace the affected natural joints of a person (hip, knee, ankle, toes, shoulder, elbow, wrist, fingers, maxillofacial, intervertebral disc).

One of the most amazing “inventions” of nature associated with the musculoskeletal system of a person is joints. If all the bones of the human skeleton were simply motionlessly connected to each other, such a person could not even move. Mobile joints of bones are called joints. Areas of bones adjoining in the joint (friction unit) are covered with well-sliding cartilage and hermetically covered by a shell - articular capsule (bag). To reduce friction, the cavity that partially separates the bones is filled with synovial fluid, which is secreted by the tissues of the joint bag and cartilage. Erasing with friction, cartilage also turns into grease. A healthy joint thus lubricates itself and maintains it in working condition. There are joints that can only bend and unbend (for example, the joints between the phalanges of a person’s fingers). Others may, in addition, make movements in different directions - to the sides, etc. Finally, the spherical joints (for example, the shoulder) can also rotate. But all joints are united by the presence of a friction unit.

Diseases and injuries of the musculoskeletal system differ from diseases and injuries of other organs, in particular, in the latter case, usually with the cure of the disease process, the patient's working capacity is restored. For diseases and injuries of the musculoskeletal system, the cure of the process, if preventive measures are not taken, often leaves behind “consequences” in the form of contractures, limitation of movements, etc., requiring “aftercare”, sometimes very long, or endoprosthetics.

Joint replacement is the most modern modern method of restoring joint mobility by replacing them fully or partially with artificial components. The most common at present are hip and knee endoprostheses, as well as mobile endoprostheses of the intervertebral discs. Endoprostheses of other human joints are in the stage of widespread use.

The number of diseases and injuries of the hip joint, according to WHO forecasts, will increase with increasing life expectancy and general aging of the population. By 2025, the number of people aged 60 and over will exceed one billion people. The urgency of the problem is increasing every year, as the level of damage and the detectability of diseases of the hip joint are constantly growing, both in the main age group and in the aging population. The proportion of diseases and injuries of the hip joint among the pathology of the musculoskeletal system will increase by 80%. In the United States alone, 300,000 new hip fractures are detected annually.

A similar picture is with diseases of the knee joint. Because of hemophilia, which affects up to 5% of the population, the knee joints are affected, and most often the only way to help is by joint replacement. In the total volume of operations on the joints, knee replacement is more than 25%.

For a long time, mankind dreamed of the possibility of treating the spine while maintaining its mobility - a function without which a person’s life is not complete. Until recently, this was impossible, and only now, at the modern level of technology, dynamic systems of stabilization of the spine have been developed. These systems provide restoration of the natural architectonics of the spine while maintaining its dynamic properties. The creation of a movable intervertebral disc for the treatment of the spine is the most advanced modern direction in the development of medical science and technology.

With the development of science and technology today it becomes possible to create an endoprosthesis of any human joint. And this area of medicine is becoming increasingly developed.

The development of endoprostheses was carried out in various directions of constructing prosthetic elements, methods of fixation, the use of various materials, various types of surface treatment and various options for the shape of implants.

Endoprosthesis materials used today were selected according to 3 essential criteria:

- biocompatibility (tolerance with the human body);

- resistance to corrosion;

- mechanical properties.

Currently, in the friction units of endoprostheses use:

- Metallic materials :.

These are mainly stainless steel or titanium alloys, which are used in the manufacture of the legs and heads of endoprostheses.

- Ceramic materials:

Alumina is the most used specifically for the production of a friction unit for endoprostheses due to its low coefficient of friction, which reduces the risk of wear.

- Polyethylene:

This thermoplastic macromolecule is used for the manufacture of elements of the friction unit of endoprostheses.

All known endoprostheses of the elbow, shoulder and knee joints for total arthroplasty for pathological diseases and the consequences of injuries, for example [1], the combination of metal - high molecular weight polyethylene as the main elements of the friction unit. Particles of polyethylene wear during the period from 5 to 20 years of operation of the endoprosthesis provoke bone destruction around the prosthesis, which requires a new surgical intervention (revision endoprosthetics).

Known mobile endoprostheses of the intervertebral disc [2]. Biomechanically and taking into account the type of rubbing surfaces, friction units are distinguished: metal-metal, metal-ceramic, metal-polyethylene. Currently, 4 different types of mobile intervertebral endoprostheses are approved for clinical use.

FlexiCore is an artificial disk (SpineCore, Inc., Summit, NJ) of a semi-fixed metal-to-metal construction with cobalt-chromium-molybdenum plates. The moving part is made in the form of a ball with a diameter of 13 mm. It is the center of rotation between the two plates. On the outer surface of the plates there are spikes for fixing to the vertebrae.

The Maverick prosthesis (Medtronic Sofamor Danek, Inc., Memphis, TN) is a semi-fixed metal-to-metal structure. The design of the prosthesis is similar to the model described above, but on its plates there is a protruding surface with holes for fixing screws to the vertebral bodies.

Friction nodes of the metal-metal type are potentially dangerous due to metal dust generated during the friction process. The use of metal implants is always complicated by galvanic-electric phenomena, leading to metallosis of surrounding tissues and corrosion of parts. Metals tend to cause bone resorption.

The ProDisc disc (Spine Solutions, Inc., New York, NY) was developed by Thierry Mamay in the late 1980s. "ProDisc" consists of metal plates and ultra-high molecular weight polyethylene. Polyethylene is fixed to the bottom plate. This is a semi-fixed drive. In the vertebral bodies, it is fixed by the central crest, which is on the plates.

The Charite disk (DePuy Spine, Raynham, MA) consists of two cobalt-chromomolybdenum plates and an ultra-high molecular weight polymer ellipsoid freely located between them. The plate is fixed to the bodies with spikes.

Friction units of the metal-polyethylene type can wear out over time and have “cold flow” and aging typical of plastic, which leads to deformation and destruction of the endoprosthesis. In addition, wear products of polymeric materials often cause malignant degeneration of surrounding tissues.

Today, the main materials for the manufacture of friction units for hip joint endoprostheses are: for cups - ultra-high molecular weight polyethylene UHMW PE ISO 5834/1 (ASTM F603), and for heads - hot-forged stainless steel FeCrNiMoMn ISO 5832/1 (ASTM F648), CoCrMo alloy ISO 5832/4 (ASTM F75) and Al ₂ O ₃ ceramic ISO 6474 (ASTM F603).

For example, hip joint endoprostheses are known [3, 4], which contain a friction unit in the form of a head and a cup made of ceramics. These joint prostheses have a low coefficient of friction in the joint and high wear resistance. However, there are serious limitations to the use of these endoprostheses. The natural fragility of ceramics does not allow to make the walls of the ceramic liner thinner than 5 mm. A common disadvantage of these prostheses is their low impact resistance. When jumping, running the patient, or during surgical procedures, shock loads affect the head and cup of the endoprosthesis, causing microcracks in the ceramics that grow during operation and cause the hinge element to fail. In addition, ceramics are not technologically advanced.

The metal-metal friction pair provides excellent friction indices, which reduces wear. The negative side is that it creates a diverse number of particles and, mainly, metal ions. These debris causes slight inflammation, but they can have very long-term toxicological effects, especially in the kidney, liver, or bone marrow. Therefore, they are contraindicated in women of childbearing age. The use of metal implants is always complicated by galvanic-electric phenomena, leading to metallosis of surrounding tissues and corrosion of parts. Metal endoprostheses, although convenient to manufacture and install, are not physiological. If nickel is excreted from the body, then cobalt is only 80-90%, and chromium is only a few percent. Even the most inert metal of titanium a few months after implantation is found in the lungs, liver, kidneys, lymph nodes, 4 years after implantation, its content in contacting tissues increases by more than 5 times. Metals tend to cause bone resorption. The difference in the physicomechanical properties of metals and bone tissue leads to loosening of the implants and the need for their revision (repeated operations).

Among traditional materials, the combination of polyethylene and Al ₂ O ₃ ceramics is considered the most optimal and most widespread [5]. The classical friction knot of a hip joint endoprosthesis, which we have chosen as a prototype [6], combines a polyethylene cup and a steel ball (cobalt chrome) or, better, a ceramic ball. The negative side of polyethylene is that it produces a large number of inflammatory microparticles, which lead to osteolysis.

With the use of endoprostheses, messages began to appear about the complications of this type of treatment. The main ones were infectious complications, osteolysis, instability of the acetabular and femoral components, fractures of the prosthesis legs, increased wear in the friction unit, occurrence of debris, metallosis, etc. The most vulnerable part of the hip joint prosthesis is the friction unit.

The main reason for the failure of implanted hip arthroplasty is the gradually developing aseptic instability, i.e. the weakening of the tight fit of the elements of the endoprosthesis in the bone bed, leading to loosening. The modern concept of “triggering” the biological mechanisms of aseptic instability of joint endoprostheses is that the aseptic inflammatory process in the tissues surrounding the endoprosthesis is the body’s response to tissue clogging by endoprosthesis wear products that integrates cell responses that lead to osteolysis. Osteolysis initiates instability of fixation of components of endoprostheses, which is exacerbated by the development of fatigue processes in the areas of attachment of components in the bones [7].

It can be imagined that a higher level of endoprosthetics will be based on new principles of designing friction units utilizing wear products, and the use of anti-friction materials that are “friendly” to the body and whose dispersions do not cause tissue inflammation.

The aim of the invention is to increase the biocompatibility, biomechanical properties and wear resistance of the friction unit of joint replacements.

Achieving the goal of increasing the biocompatibility, biomechanical properties and wear resistance of the joint endoprosthesis friction unit containing elements made with interacting smooth surfaces is ensured by the fact that the elements of the endoprosthesis friction unit are made of monolithic isotropic pyrolytic carbon doped with boron (hereinafter referred to as IPA).

The problem of developing biocompatible materials for endoprostheses has always been the most important and difficult. The materials from which the implants are made must satisfy a number of requirements:

- Lack of toxicity and corrosion;

- Physico-mechanical properties close to natural tissues;

- durability;

- Wear resistance;

- Manufacturability.

Inconsistency of the material in at least one of the parameters reduces the functional value of the implant and the duration of its functioning. The optimal combination of material characteristics ensures biocompatibility (including biomechanical) of the implant.

The development of the technique for producing numerous types of carbon materials along with the revealed compatibility with living tissue has led to the intensification of research, the development of new and composite materials based on carbon for medicine. To date, it has been reliably established that carbon materials do not have competitors in the degree of satisfaction of biochemical and physical-mechanical requirements for medical devices.

These requirements include:

- lack of toxicity and carcinogenicity;

- invariability under the influence of biological media of arbitrary activity;

- the absence of corrosion phenomena in contact with living tissues;

- proximity of physical and mechanical properties;

- the absence of fatigue stresses and, as a consequence, the durability of the implant;

- the presence of osteogenic activity at the surface of the implant;

- low wear under friction and the indifference of wear products that accumulate in the lymph nodes;

- the ability to stimulate tissue growth or regeneration of the underlying tissue;

- electrical conductivity close to tissue, without the release of ions into the environment;

- the possibility of obtaining a surface of almost any class of cleanliness and simple manufacture of a porous structure;

- Unconditional and quick sterilization of any kind.

None of the metals, plastics or types of ceramics currently used for endoprostheses and implants can fulfill these requirements.

The affinity of carbon materials with biological tissues is determined not only by low chemical activity, but also by the manifestation of bioactivity, as a result of which the surface of carbon materials is covered with an oriented and organized film of protein origin, similar to the replaced tissue.

The rate and orientation of the deposited film of protein origin depends on the surface properties of the carbon material. For example, the surface energy of the ILI is 50 erg / cm ² , but in contact with blood plasma or lymph decreases sharply to 20-30 erg / cm ² . This value of free surface energy is most beneficial for prolonged contact with biological media.

The materials used for the manufacture of endoprostheses and implants, in terms of the normal electrochemical potential in blood plasma, can be arranged in the following series: glassy carbon (+0.329 mV), platinum (+0.332 mV), gold (+0.334 mV), pyrographite (+0.344 mV) . It is known that glassy carbon has an amorphous structure, and pyrographite is close to a single crystal. We can say that in this way all carbon materials with different structures, having a normal electrochemical potential ranging from +0.329 mV to +0.344 mV, i.e. comparable with these indicators of the most passive of all elements of gold and platinum. Carbon materials are closest in electrochemical potential to the biological environment of a living organism.

As shown by morphological studies conducted on rabbits at the Moscow Research Institute of Eye Diseases. Helmholtz using durable fine-grained graphite MPG-6, syntactic carbon foam, carbon felt Karbotek-stim-M and carbon fabric TGN-2M, all carbon materials were not torn away during the year, did not change their shape and were overgrown with a connecting film of protein origin.

Therefore, in terms of biocompatibility, toxicity and corrosion, carbon materials are the best for use as endoprostheses.

IPU has a homogeneous, isotropic, crystalline structure. IPU due to its unique properties (high density, strength, wear resistance, biological compatibility with blood and body tissues) has found application in medicine. The main elements of artificial heart valves are made from it. To date, hundreds of thousands of artificial heart valves have been manufactured, delivered and successfully operate in the world. And this is one of the most responsible human implants. The locking element of the artificial heart valve experiences the most severe loads. It should withstand about 40 million double strokes per year in a chemically active environment of native blood. Moreover, the experimentally established resource of the friction unit of the artificial heart valve is at least 100 years.

In terms of the coefficient of friction in liquid media under conditions of mechanical water compaction, IPU is 5 times higher than carbon materials of antifriction purpose of traditional technology. The low coefficient of friction IPA in combination with chemical inertness and impermeability to liquids ensures the performance of mechanical seals in aggressive environments. In dry friction mode, the control unit has no signs of wear after 2000 start-up-stop cycles under severe acceleration conditions to a critical speed of the gas-dynamic bearing shaft and emergency braking

The given example of the implementation of the complex of medical and technical properties of IPA as a structural material of an artificial heart valve gives an idea of the potential possibilities of using its bioengineering properties in medical technology, in particular in friction units of endoprostheses.

The main physicomechanical and thermophysical properties of IPA are given in table 1. Table 2 shows the proximity of the physicomechanical properties of bone and IPA, in contrast to titanium and ceramics.

Biomedical studies have shown that IPA is not toxic to the body, does not change the functions of the central nervous system, liver, kidneys, protein and fat metabolism, general reactivity, does not have carcinogenic, mutagenic, embryotropic and other actions. The collagen-fiber capsule growing on the implant passes into the bone and muscle tissues, the structure of which retains the structure characteristic of the norm. Unlike metals, electrically neutral IPA is not transferred by electrochemical reactions to the lymph nodes and other parts of the body, does not cause immunosuppression and other changes in the immune system, and does not lead to demineralization of adjacent bone tissue. Therefore, even those minor wear particles that are formed during the operation of the friction unit of the endoprosthesis will not adversely affect the surrounding tissue.

Another of the advantages of manufacturing a friction unit from IPA is manufacturability and relatively low cost. IPU is processed on turning, milling, drilling, grinding and polishing machines using standard cutting tools. The fine-grained structure of the IPA allows the manufacture of products with a thickness of 0.8-1 mm with edges of 0.03 mm and to obtain surfaces of grade 12-13.

The proposed invention is as follows.

IPA is obtained by the pyrolysis of hydrocarbons with the addition of boron-containing halides at high temperature by depositing a special graphite substrate on the inner surface. With a flat form of the substrate, a plate is obtained, with a cylindrical one, a sleeve. Then, from the blanks of the IPA of the necessary form by machining, the elements of the friction unit of the joint endoprosthesis are made.

The friction unit of an endoprosthesis of a joint, for example, a hip, containing a cup and a head, works as follows.

Using conventional surgical procedures, the hip joint prosthesis is fixed in the patient’s femur and pelvic bones. When the patient’s leg moves, the head of the hip joint endoprosthesis moves inside the cup. In this case, smooth, for example, spherical surfaces interact - the outer one at the head and the inner one at the cup, made of IPA. Due to this, minimal friction forces and minimal wear of rubbing surfaces are achieved with high biocompatibility and optimal biomechanical properties of the joint endoprosthesis.

Table 1 Physico-mechanical and thermophysical properties of isotropic pyrolytic carbon No pp Characteristic Properties one Density, kg / m ³ (1.80-2.10) × 10 ³ 2 Microhardness, MPa 1000-1500 3 Bending Strength, MPa 300-360 four The limit of compressive strength, MPa 450-600 5 Thermal conductivity, W / m × ° K 23-25 6 The coefficient of thermal linear expansion, ° K ^-1 (293-473 ° K) 5.5 × 10 ^-6 7 Electrical resistivity, Ohm × m (1.4-1.5) × 10 ^-5 table 2 Physico-mechanical properties of materials Modulus of elasticity, GPa Density, kg / m ³ Tensile strength, MPa Poisson's ratio Material 110 4,5 × 10 ³ 600 0.32 Titanium 350 3.99 × 10 ³ 500 0.3 Ceramics fifteen 2.4 × 10 ³ one hundred 0.3 Bone 20-23 (1.8-2.1) × 10 ³ 350 0.3 Isotropic pyrolytic carbon

Claims (1)

The knot of the joint endoprosthesis friction with elements made with interacting smooth surfaces, characterized in that the elements of the endoprosthesis friction knot are made of monolithic isotropic pyrolytic carbon doped with boron.