RU2382619C2 - Intervertebral immobile implant from isotropic pyrolytic carbon - Google Patents

Abstract

FIELD: medicine.

SUBSTANCE: implant is made from monolithic isotropic pyrolytic carbon, without legating elements or legated with boron or silicon, with limit of compression strength not less than 450 MPa.

EFFECT: increase of biocompatibility, biomechanical properties, improvement of implant osteointegration in bone tissues and reduction of traumatism during operation by means of implants from isotropic pyrolytic carbon.

4 cl, 2 tbl, 2 dwg

Description

The invention relates to medical equipment and can be used in spinal surgery to correct injuries and instability in the bodies of human vertebrae in all parts of the spine (cervical, thoracic, lumbar).

With irreversible changes in the anatomical structure of the intervertebral discs or vertebral bodies due to illness or injury, they resort to prosthetics. For prosthetics of intervertebral discs, fixed and movable implants are used. Prosthetics with fixed implants leads to bone ankylosis between the vertebral bodies and interbody fusion.

A fixed implant should recreate the biomechanical properties of the natural disc. After implant placement, the height of the disc gap is restored and the intervertebral foramen is increased, which prevents compression of the roots.

In addition, the materials from which the implants are made must satisfy a number of requirements:

- Lack of toxicity and corrosion;

- durability;

- manufacturability;

- Wear resistance;

- Physico-mechanical properties close to bone.

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 requirements for a fixed implant are very high. It should not break. In addition, it should be biologically inert to the body, not lead to the development of the inflammatory process.

Initially, autobone in the form of cylindrical or rectangular implants was used for fixed implants.

Bagby and Kuslich in 1992 instead of bone autoimplants for the first time used a cylindrical implant filled with autobone (VAK, Spine-Tech, Minneapolis, MN). The cylindrical implant had a circumferential thread, which allowed it to be screwed between the locking plates and form a rigid fixation immediately after the operation. Subsequently, various designs of metal implants were developed. Currently, the following prosthesis designs are widely used [1]:

1. Metal:

- Threaded cylindrical cages (HAC, Spine-Tech, Minneapolis, MN; RTFC, Surgical Dynamics, Norwalk, CT; and Inter Fix, Sofamor Danek Group, Memphis, TN).

- Rectangular titanium cages (Harms titanium-mesh cage, DePuy-Acromed, Cleveland, OH).

- Implants made of porous titanium nickelide [2,3].

The use of metal implants is always complicated by galvanoelectric phenomena, leading to metallosis of surrounding tissues and corrosion of parts. Metals tend to cause bone resorption.

2. Made of plastic:

- Implants that are susceptible to biological resorption. They consist of a polyactide acid (PLA) polymer, which decomposes into CO ₂ and water [4].

- PEEK - a plastic semi-crystal of a polyaromatic linear polymer. It has osteoconductive and osteoinductive properties, as well as elasticity that is practically no different from the elasticity of the human bone [5].

- Rectangular synthetic fiber cages (Brantigan carbon fiber cages, DePuy-Acromed, Cleveland, OH; and Femoral Ring Allograft-FRA Spacer, Synthes, Paoli, PA).

Plastic implants can wear out over time and exhibit “cold flow” and aging typical of plastic, which leads to deformation and destruction of the implant. In addition, wear products of polymeric materials often cause malignant degeneration of surrounding tissues.

3. Ceramic implants [5, 6], selected as a prototype.

There are serious limitations to the use of ceramic implants. The natural fragility of ceramics does not allow making the walls of ceramic implants less than 5 mm. A common disadvantage of these implants is their low impact resistance. When jumping, running the patient, or during surgical procedures, the implant is subjected to shock loads, causing microcracks in the ceramics, which grow during operation and can cause the destruction of the implant.

The aim of the invention is to increase biocompatibility, biomechanical properties, improve osseointegration of the implant in bone tissue and reduce trauma during surgery using implants made of isotropic pyrolytic carbon.

Achieving this goal is ensured by the fact that:

- the stationary intervertebral implant is made of monolithic isotropic pyrolytic carbon, without alloying elements or alloyed with boron or silicon, with a compressive strength of at least 450 MPa;

- the inner part of the implant is filled with porous carbon material;

- the porous carbon material is made in the form of a foam based on a carbon nanocomposite;

- the implant has 4 spikes of titanium on each end.

These differences of the proposed implant give him a number of important advantages compared to the prototype.

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;

- immutability under the influence of biological environments 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 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 isotropic pyrolytic carbon 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. Hemgoltz using strong fine-grained graphite MPG-6, syntactic carbon foam, carbon felt Karbotekstim-M and carbon fabric TGN-2M, all carbon materials were not torn off 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 best for use as implants.

Isotropic pyrolytic carbon has a uniform, isotropic, crystalline structure. Due to its unique properties (high density, strength, wear resistance, biological compatibility with blood and body tissues), isotropic pyrolytic carbon 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. Now work is underway on the production of dental implants and elements of the hip joints from this material.

The main physicomechanical and thermophysical properties of isotropic pyrolytic carbon are given in table 1.

The lumbar spine that is the most loaded in a person is subjected to heavy loads. Loads vary from 400 N in a standing position to 7000 N when lifting weights. Biomechanical studies have shown that the vertebral body (without the phenomena of osteoporosis) normally withstands a load of up to 10,000 N. The physico-mechanical properties of isotropic pyrolytic carbon are closest to the properties of the bone, as shown in Table 2. Moreover, the load that an isotropic implant can withstand pyrolytic carbon is more than 30,000 N, which is more than 3 times higher than the maximum physiological loads. The table shows that the physico-mechanical properties of titanium are an order of magnitude higher than the properties of bone. Therefore, with the same deformations, various stress states will arise in titanium and bone, which is the main reason for the loosening of metal implants.

The use of isotropic pyrolytic carbon for the manufacture of implants will significantly increase their biomechanical properties.

To improve osseointegration on each end of the implant there are 4 spikes made of titanium, which cut into the bone tissue of the vertebrae and provide primary fixation of the implant. Secondary and complete fixation of the implant is achieved due to the germination of bone tissue in the porous carbon material, which in this process serves as a matrix.

According to the generally accepted technique for installing fixed implants, their internal space is filled with a bone autograft for germination of bone tissue and for ensuring interbody fusion. An autograft is taken from the ilium or rib from the patient himself, which leads to additional invasiveness of the operation. When using fixed pyrolytic carbon implants filled with a porous carbon material, it is not necessary to take the autograft from the patient. This allows you to reduce the morbidity during the operation.

Another advantage of the manufacture of isotropic pyrolytic carbon implants is their manufacturability and relatively low cost. Isotropic pyrolytic carbon is processed on turning, milling, drilling, grinding and polishing machines using standard cutting tools. The fine-grained structure of isotropic pyrolytic carbon allows the manufacture of products with a thickness of 0.8-1 mm with edges of 0.03 mm and to obtain surfaces of 12-13 grade of purity.

The invention is illustrated by drawings. Figure 1 shows a fixed implant to replace the intervertebral disc, figure 2 fixed implant to replace one or more vertebral bodies. A stationary implant consists of a sleeve of isotropic pyrolytic carbon 1, the inner space of which is filled with porous carbon material 2, for example, foam based on a carbon nanocomposite. The implant has four spikes 3 of titanium on each end.

Implement the invention as follows.

Isotropic pyrolytic carbon is obtained by pyrolysis of hydrocarbons at high temperature by deposition on the inner surface of a cylindrical graphite substrate. After the end of the process of producing a sleeve of isotropic pyrolytic carbon by machining, a fixed implant with titanium rods at each end is obtained. The inside of the implant is filled with porous carbon material. The implant is washed in a special solution in an ultrasonic bath at a temperature of about 100 ° C. Then the implant is packaged and sterilized either in a consumer container or immediately before the operation by any method.

The operation of installing the implant is as follows.

Implants can be implanted from anterior or posterior approaches. Rear access is used when it is necessary to remove osteophytes or herniated discs. In these cases, the implants can be installed from the rear access, without the need to make an additional incision in the abdominal wall (through the abdomen).

Most often, implants are nevertheless placed through anterior access to the spinal column; an incision is made along the anterolateral wall of the abdomen. Large blood vessels and organs are carefully shifted to the side, the desired intervertebral disc or one or more vertebral bodies is removed, and an implant is placed in this place. Between the vessels and the disc space, a hemostatic sponge is laid, drainage is established. The wound is sutured in layers.

After implant placement, the surgeon performs monitoring using a mobile x-ray machine.

In the manufacture of implants made of isotropic pyrolytic carbon, biocompatibility, biomechanical properties will be improved, osseointegration of the implant in bone tissues will be improved, and trauma during surgery will be reduced.

1. Zdeblik T.A., Phillips F.M. Intercorporal cell products // Spine. - 2003. - Aug. 1; 28 (Appendix 15): p. 2-7. (Zdeblick TA., Phillips F.M. Interbody cage devices. Spine. 2003 Aug. 1; 28 (15 Suppl): S2-7).

2. Epifantsev A.G. Surgical treatment of spondylolisthesis using porous titanium nickelide implants: Abstract. dis ... cand. honey. sciences. - Kemerovo, 1993 .-- 13 p.

3. Simonovich A.E. The use of porous titanium nickelide implants in the surgery of degenerative lesions of the lumbar spine // Spinal Surgery. - 2004. - No. 4. - S.8-17.

4. Van Dyck M., Smith T.H., Burger E.H., Weisman P.I. Bioresorbable cells from poly-L-lactic acid for lumbar intracorporal fusion: radiographic, histological and histomorphometric analysis in goats during a 3-year follow-up // Spine. - 2002. - Dec. one; 27 (23): 2706-14. (Van Dijk M., Smit T.N., Burger EH, Wuisman PI Bioabsorbable poly-L-lactic acid cages for lumbar interbody fusion: three-year follow-up radiographic, histologic, and histomorphometric analysis in goats. Spine. 2002 Dec .1; 27 (23): 2706-14).

5. Cho D., Liau V., Lee V. et al. Preliminary experience with the use of polyteretherketone (PEEK) cage in the treatment of cervical disc disease // Neurosurgery. - 2002 .-- 51: 1343-1350. (Cho D., Liau W., Lee W., et al. Preliminary experience using a polyetheretherketone (PEEK) cage in the treatment of cervical disk disease. Neurosurgery. 2002; 51: 1343-1350).

6. Gruntovsky G.Kh. The rationale and clinical use of ceramic implants in the surgical treatment of certain diseases and injuries of the musculoskeletal system: Abstract. Dis .... doctor med. sciences. -X., 1988 .-- 28 p.

7. Gruntovsky G.Kh. Primary stable spinal fusion with corundum ceramic endoprostheses in patients with osteochondrosis of the lumbar spine // Osteochondrosis. - M., 1992. - P.18-23.

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 (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) × l0 ³ 450 0.3 Isotropic pyrolytic carbon

Claims (4)

1. An implant of an intervertebral column of a fixed structure for replacing an intervertebral disc or one or several vertebral bodies, characterized in that it is made of monolithic isotropic pyrolytic carbon without alloying elements or alloyed with boron or silicon, with a compressive strength of at least 450 MPa. 2. The implant according to claim 1, characterized in that the inner part of the implant is filled with porous carbon material. 3. The implant according to claim 2, characterized in that the porous carbon material is made in the form of a foam based on a carbon nanocomposite. 4. The implant according to claim 1, characterized in that the implant has 4 spikes of titanium on each end.

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