WO2020171794A1

WO2020171794A1 - Fixation element for osteosynthesis

Info

Publication number: WO2020171794A1
Application number: PCT/UA2019/000024
Authority: WO
Inventors: Вадим Николаевич ЧЁРНЫЙ; Роман Александрович МИРОНЕНКО; Сергей Юрьевич ЦОЦОРИН; Дмитрий Игоревич ВИНИЧЕНКО
Original assignee: Публичное акционерное общество "МОТОР СИЧ" (АО "МОТОР СИЧ")
Priority date: 2019-02-20
Filing date: 2019-02-20
Publication date: 2020-08-27

Abstract

A fixation element for osteosynthesis is made of a magnesium-based alloy containing zirconium, neodymium, zinc and silver. The technical result is biodegradation at a dissolution rate of 6-12 months in the body, and reduced toxicity.

Description

FIXING ELEMENT FOR OSTEOSYNTHESIS

FIELD OF TECHNOLOGY

The invention relates to medicine, namely to orthopedics, traumatology and medical equipment, and can be used in orthopedic traumatological operations, in particular in osteosynthesis. Fixing structures made of various materials are used for osteosynthesis. One of the elements of fixing structures are bone screws, which are used both as independent fixators and in conjunction with plates.

Since joint endoprostheses and screws are integrated into the musculoskeletal system of the body, they not only themselves are under the influence of constantly occurring static, cyclic and dynamic mechanical loads, but also transfer these loads to the surrounding bone tissue. Therefore, the materials intended for their manufacture must have a high level of biochemical and biomechanical compatibility with body tissues, good functional characteristics, and mechanical properties that ensure their tolerance to bone tissue, i.e. should not destroy it, be non-toxic. The main materials used for the manufacture of immersion implants are stainless steel and titanium alloys.

PRIOR ART

Various designs of fixing elements for osteosynthesis are known, for example, a device for a bone plate, including a bone screw as a fixator for insertion into a through hole [1], or, for example, a bone screw with an axially two-component screw head [2] having a base body, which is parallel to the longitudinal axis of the screw, the helical shaft to be fixed concentrically in the bone, and the screw head. The use of fixators of similar structures and materials for osteosynthesis requires repeated surgical interventions aimed at removing metal elements that have fulfilled their function. Often this is no less traumatic process than the osteosynthesis itself. The use of such metal retainers is limited by the possibility of bacterial contamination of these implants. Long-term presence of implants made of these alloys in the human body can lead to the accumulation of toxic elements and metallosis. There are also manifestations of allergic and locally irritating reactions of the body in the form of aseptic inflammation.

Bio-soluble polymer materials based on polyglycolic and polylactic acids, for example, amorphous polymer PLLA [3], [4], [5], are becoming more widespread.

Retainers made from materials of this type dissolve well in the body. Their disadvantages include the fact that after dissolving them in the bone tissue, a void remains, which can further lead to a violation of the supporting ability of the bone. The described conical shape of the screw, when inserted into the bone, can lead to injury to the bone tissue. Osteliasis is often observed around such implants.

Known medical implant for the human or animal body [6], selected as a prototype of the invention. The implant consists of at least a magnesium alloy. According to the invention, the magnesium alloy contains fractions of rare earth elements and lithium, and optionally also yttrium and aluminum. Preferably, the magnesium alloy contains lithium in a proportion of 0.01 to 7% by mass, aluminum in a proportion of 0.01 to 16% by mass, optionally yttrium in a proportion of 0.01 to 7% by mass, and rare earth elements in a proportion of 0.01 to 8% by weight.

The advantage of devices for osteosynthesis made of magnesium-based alloys is that they are bio-soluble in the body. However, an essential characteristic of such devices is the degree of their solubility in the human body. So, the disadvantage of the prototype is the insufficient level of solubility (14-15 months), which leads to metalosis and bone destruction. The presence of yttrium significantly increases the cost of the product, in addition, the presence of yttrium and especially lithium leads to complications due to their toxicity.

DISCLOSURE OF THE INVENTION

The basis of the invention is the task of improving the fixing elements used in osteosynthesis operations. The technical result is the biodegradation of the fixing elements, such as screws, with a dissolution rate in the body of 6 to 12 months and a decrease in their toxicity.

In a particular case of implementation of the invention, non-limiting examples of screws made of biodegradable material are proposed, which make it possible to avoid repeated operations with the removal of the screw, and make it possible to carry out osteosynthesis without complications.

The problem is solved by the fact that the fixing element for osteosynthesis, made of a biodegradable casting alloy based on magnesium, according to the invention, contains zirconium, neodymium, zinc, silver in the following ratio of ingredients, wt. %:

zirconium 0, 4-1, 0

neodymium 2, 2-2, 8

zinc 0, 1-0, 7

silver 0.03-0.5

amount of impurities <0.2

magnesium rest. Magnesium and its biodegradation products have very good biocompatibility, and devices for implantation based on a magnesium alloy of the proposed composition are metabolized by the body and do not have a pathological effect on the surrounding tissues and the body as a whole. Magnesium ions Mg2 +, as biodegradation products, interact with phosphate ions contained in the organic body and form layers of magnesium phosphate, which contributes to the formation of bonds between implants and the mineral phase of newly formed bone tissue [7], [8]. Excess magnesium ions are easily excreted through the kidneys, and non-toxicity makes it possible to consider it as a material for an implant that can be completely biodegradable in a natural way.

With the introduction of microadditives of silver, the strength and ductility of the alloy increases. Microadditives of silver grind the structure of the alloy, reducing its solubility. Thus, it is possible to regulate the solubility and obtain the required duration of its dissolution in the body. In addition, the presence of silver in the magnesium alloy enhances the bactericidal properties of implantable devices. The bactericidal properties of metallic silver and its alloys are associated with the release during bio-dissolution of silver ions Ad + into the space around the fixing element during the interaction of alloys in the electrolytic conditions of the human or animal organism. The amount of silver ions formed during dissolution depends on the composition of the alloy and its structure. In other words, the structure of the obtained alloy determines the characteristics of bio-solubility, mechanical and bactericidal properties. It is the combination of the claimed alloy ingredients and their ratio that ensure the achievement of a new technical result - the production of a casting alloy with solubility in the human body within 6-12 months. This is achieved by the fact that with the stated content of ingredients, an additional amount of fine-grained intermetallic compounds (MgZr) i ₂ Nd is formed, in which part of the zirconium is replaced by silver. These intermetallic compounds are uniformly distributed over the entire metal cross section and increase the electrochemical potential between the metal matrix and intermetallics with different electrochemical potentials, which leads to an increase in the solubility of such an alloy to the required level when it is in the body. In terms of mechanical properties, the alloy is close to the mechanical properties of bone.

IMPLEMENTATION AND USE OPTIONS

To confirm the declared properties of fixation elements for osteosynthesis, characterized by the use of a new material, tests were first carried out on samples. Samples were smelted in crucible furnaces IPM-500, refining of melts with VI-2 flux was carried out in dispensing (distribution) furnaces. The obtained alloys of different compositions were poured into cave-clay molds and cast samples (10 x 5 mm) were obtained for dissolution testing, which were subjected to heat treatment according to the Tb mode. The samples were placed in artificial blood (venofundin) and kept until complete dissolution of the samples at a temperature of 37 ° C, the stability of which was ensured by an UT-15 ultra-thermostat.

The test characteristics are shown in the tables. Table 1 - composition of the investigated alloys. Table 2 - test results.

Table 1

table 2

Analysis of the results of the solubility of the investigated alloys (Table 1) showed that the prototype alloy (Option 1) has a low dissolution rate - 14.1 months (Table 2). This leads to the formation of metallosis, destruction of the bone after it grows together.

In the proposed alloy, when the content of elements is less than the lower limit (option 2), an insufficient amount of intermetallic compounds (volume percent of intermetallic compounds <0.3 wt%). As a result, the electrochemical potential arising between the metal matrix and the intermetallic phase is insufficient for the required solubility of the alloy. The solubility of this alloy is 13.5 months. This dissolution rate of implants is low and leads to the occurrence of metallosis (saturation of the bone with metal).

When the content of elements in the alloy is within the stated limits (options 3 and 4), an intermetallic phase is formed, the volume fraction of which is 0.3 - 0.5 wt%. This amount of intermetallic phase is sufficient for the occurrence of the necessary electrochemical tension between the metal matrix and intermetallic compounds, which ensures the solubility of the alloy within 6 - 12 months (option 3 - 12.0 months, option 4 - 6.0 months, Table 2) ... This rate of dissolution of fixing elements for osteosynthesis is sufficient for reliable bone fusion and excludes the formation of metallosis.

When the content of elements exceeds the upper limit (option 5), an excess amount of the intermetallic phase is formed, the volume fraction of which exceeds 0.5 wt%, as a result of which the electrochemical tension between the metal matrix and intermetallic compounds increases, which leads to an increase in the solubility of the alloy (<5 months) , which is not enough for reliable bone healing in fractures.

The fixing element for osteosynthesis can be made in the form of screws having the following design features, examples of which are shown in the drawings: figure 1 - cancellous screw, figure 2 - cortical screw.

Example 1. The fixing element is made in the form of a cancellous screw (Fig. 1), which is used directly to fasten the fractured bone, and can be used in the treatment of fractures of various localization, for example, the femoral neck, heel bone.

The screw consists of a head 1 and a rod 2 with a thread 3. The special features of the screw are that the rod has a full thread in the distal part, which allows compression of small fragments of bones by increasing the area of screw compression. The threaded part is made with an outer diameter of 6.5 mm, an inner diameter of 3 mm, a thread pitch of 2.75 mm, a special profile of turns with angles of 25 ° and 5 °, passing into the inner diameter of a thread with radii R0.8MM and R1, 2MM, and the head with a diameter of 8 mm has a spherical configuration at the bottom, in contact with the bone.

Example 2. The fixing element is made in the form of a cortical screw (Fig. 2), used for bone osteosynthesis, when fixing various fractures, both independently and together with plates, for example, for fixing plates on the forearm.

The screw consists of a head 1 and a rod 2 with a thread 3. The special features of the screw are that the rod has a full thread in the distal part, the threaded part is made with an outer diameter of Q 4 mm, an inner diameter of 3 mm, a thread pitch of 1.5 mm, a special profile turns with angles 35 ° and 10 °, passing into the inner diameter of the thread with radii R 0.6 mm and R 1.0 mm, and the head with a diameter Q 6 mm has a spherical configuration in the lower part in contact with the bone.

The proposed sizes of the screw heads and their spherical shape allow them to be immersed into the bone tissue almost completely, i.e. the contact of the screw with soft tissues will be reduced. This reduces the corrosive effect of the electrolyte environment of the body on the screw and ensures the required stay of the screw in the bone.

Implementation of screws from a biodegradable alloy in the proposed composition of ingredients corresponds to the deformation properties of this material. Given the properties of the material from which the screw is made and its design features, the screw is used in this way.

When installing screws, the use of drills and taps is recommended. The drill is used to form a channel through the bone fragments that need fixation. With a larger diameter drill, a bed for the screw head is formed. The tap is used to prepare the thread in the channel. The screw is screwed into the canal using a screwdriver and additional force is applied to create compression between the bone fragments that are synthesized. The patient is observed on for 3-9 months and control bone consolidation at the fracture site. During this period, resorption of the screw occurs.

The cancellous screws made in accordance with the invention have been used for minimally invasive fixation of a calcaneus fracture in patients.

Conclusions after the end of treatment and rehabilitation of the patient.

When carrying out osteosynthesis using screws made of the claimed magnesium alloy, the proliferative activity of cells that take part in the formation of bone tissue is not disturbed. The strength and plasticity of the screw is satisfactory. The mechanical strength of the screw corresponds to the mechanical strength of the bone. The base alloy (Md) has improved adhesion of the implant to the osteocyte and does not retard cell development. Due to the presence of silver microadditions in the alloy, no inflammatory complications were observed in the area of implant insertion. No signs of intoxication were observed in the patient. During the biodegradation of the screw (over approximately 9 months), the bone canal was completely restored. No manifestations of allergic and locally irritating reactions of the body in the form of aseptic inflammation were observed.

Compression of small fragments of bones by increasing the area of screw compression ensured satisfactory fusion of bone tissue. The proposed dimensions of the screw head and its spherical shape make it possible to immerse it in the bone tissue almost completely, i.e. reduced contact of the screw with soft tissues. This ensured a decrease in the corrosive effect of the electrolyte environment of the body on the screw and compliance with the required residence time of the screw in the bone.

SOURCES OF INFORMATION:

[1] Patent EP0507162 (A1), publ. 1992-10-07, Bone plate device, IPC: A61 B17 / 56; A61 B17 / 70; A61 B17 / 80;

[2] Patent EP1191891 (A1), publ. 2002-04-03, Bone screw with axially two-part screw head, IPC: A61 B17 / 58; A61 B17 / 80; A61 B17 / 86; (IPC1-7):

A61B17 / 86;

[3] (http://www.arthrex.com/knee/biocomposite-interference-screws);

[4] Patent US3739773 (A), publ. 1973-06-19, Polyglycolic acid prosthetic devices, IPC: A61 B17 / 11; A61 F13 / 00; A61L17 / 14; A61L31 / 06;

C08G63 / 08; D01 F6 / 62;

[5] Lavery et al., "Mechanical Characteristics of Poly-L-Lactic Acid Absorbable Screws and Stainless Steel Screws in Basilar Osteotomies of the First Metatarsal", The Journal of Foot and Ankle Surgery, vol. 33, No. 3, pp. 249-254,1994.

[6] W002100452 (A1), publ. 2002-12-19, Medical implant for the human or animal body, IPC A61 L27 / 04; A61 L27 / 58;

[7] B.H. The black. "Prospects for the use of biodegradable magnesium-based alloys in osteosynthesis." Zaporozhye Medical Journal, 2013, Ns6 (81), pp.76-79;

[8] Witte F. The history of biodegradable magnesium implants: A review ta

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Claims

CLAIM

1. Fixing element for osteosynthesis, made of magnesium-based alloy, characterized in that the alloy contains zirconium, neodymium, zinc, silver, with the following ratio of ingredients, wt. %: zirconium 0.4 - 1.0

neodymium 2.2 - 2.8

zinc 0.1 - 0.7

silver 0.03 - 0.5

amount of impurities <0.2

magnesium rest.

2. The fixing element according to claim 1, characterized in that it is made in the form of a cancellous screw or a cortical screw.