KR100751568B1 - Bone fixation device and buffer sleeve employed thereto - Google Patents

Abstract

A bone fixation device and a buffering sleeve used in the same are provided to induce synostosis and to make a bone fixing system maintain its function by making stress distributed evenly around a screw portion of an implant. A bone fixation device(100) includes a buffering sleeve(120) and an implant(110). The buffering sleeve(120) has a cylindrical shape, and comprises a hollow potion of which one end portion is open. The buffering sleeve(120) is inserted to bring the outer surface thereof into contact with the inner surface of a hole formed on a bone. One end of the implant(110) is inserted into the hollow portion of the buffering sleeve, and a screw portion is formed on the surface of the same end portion of the implant(110). The diameter of the screw portion of the implant increases from an end portion in a longitudinal direction thereof.

Description

BONE FIXATION DEVICE AND BUFFER SLEEVE EMPLOYED THERETO

1 is a state of use of a conventional compression screw used to treat hip fractures,

2 is a view schematically showing a bone fixation system according to an embodiment of the present invention,

3 is a view showing an implant portion of the bone fixation system shown in FIG.

4 is a view showing a buffer sleeve of the bone fixation system shown in FIG.

5 is an enlarged view of a portion A of FIG. 4;

6 is a view showing a state in which the bone fixation system shown in FIG.

7 is a view schematically showing a bone fixation system according to another embodiment of the present invention,

8 is a view showing a buffer sleeve of the bone fixation system shown in FIG.

9 is a view showing a state in which the bone fixation system shown in FIG.

10 is a cross-sectional view of the buffer sleeve used in the bone fixation system according to a third embodiment of the present invention,

11 shows an implant used in a bone fixation system according to a third embodiment of the invention, and

FIG. 12 is an enlarged view of a portion of the buffer sleeve shown in FIG. 10. FIG.

<Explanation of symbols for the main parts of the drawings>

50: bone tissue 100, 200: bone fixation system

110, 320: implants 120, 220, 310: buffer sleeve

112: screw portion 122: hollow portion

126, 316: outer surface of the buffer sleeve 130: bone affinity particles

The present invention relates to a bone fixation system and a buffer sleeve used therein, and more particularly, to fine movement between the surface of the implant and bone tissue inserted into a hole provided in the bone for treating a fracture of the bone, such as hip fracture. It relates to a bone fixation system that can prevent and promote bone fusion and the buffer sleeve used therein.

In general, bone fixation systems, such as compression screws, have implants that are inserted and secured into the bone using a screw system. The procedure of the fixation system is performed by first providing a hole having an appropriate diameter in the bone to be treated, and then inserting the implant into the bone by using a screw provided at the end of the implant.

In the case of using such a conventional screw fixation system, the amount of bone tissue around the implant is reduced and degeneration occurs. This is known to be due to an uneven distribution of stresses acting on bone tissue adjacent to the implant. The uneven distribution of stress is largely represented over the entire length of the implant and locally as the difference in stress concentration between the thread and the screw bone. Since the former is torqued around a point within the implant (center of rotation) when the side force is applied to the implant, relatively higher stress is applied to the bone tissue away from the center of rotation and relatively less to bone tissue near the implant. It occurs when a stress is applied. The latter is due to the phenomenon that the stress is concentrated in the bone tissue around the screw thread provided on the outer peripheral surface of the implant and the stress is reduced in the bone tissue around the screw bone.

According to Wolf's law, (1) when the stress applied to the bone tissue is reduced, bone resorption occurs until a new equilibrium is reached and the stress distribution is uniform (2). If the stress applied to the bone tissue is uniform, there is no change in the bone tissue. (3) If the stress applied to the bone tissue is increased within the physiological limit, the bone is formed until a new equilibrium state is reached and the stress distribution is uniform. 4) When the stress applied to the bone tissue is extremely increased, bone absorption occurs. These laws are known to coincide with real phenomena. Therefore, in order for the bone fixation system to be stably fixed to the bone tissue, a stress within an appropriate range should be applied to the bone tissue around the implant, and it should be understood that an extreme increase or decrease of the stress should be avoided.

Korean Patent Laid-Open Publication Nos. 10-2004-0011624 and 10-2004-0092935 disclose compression screws that are one of bone fixation systems. 1 shows the state of use of the compression screw disclosed in these documents. The compression screw 10 is fixed to the femoral body 2 with a plurality of fixing screws. The lag screw 11 is inserted into the hole provided in the femoral ball head 3 through the through hole provided in the pressure screw and coupled thereto. Accordingly, the femoral head 3 is to remain coupled to the femoral body (2). However, since the pressing screw disclosed in this document directly contacts the bone tissue with the threaded portion of the lag screw, the stress is unevenly distributed in the bone tissue adjacent to the thread and the screw bone as described above. Therefore, if the condition is maintained for a long time, the amount of bone tissue around the lag screw is reduced and degenerate.

The present invention is to solve the above problems, to provide a bone fixation system that allows the bone fixation system to continuously maintain the function by inducing bone fusion by uniformly distributed stress in the bone tissue around the screw portion of the implant The purpose.

In order to solve the above technical problem, a bone fixing system comprising: a cushioning sleeve having a cylindrical shape, at least one end having a hollow portion open, the buffer sleeve is inserted into the outer surface in contact with the inner surface of the hole provided in the bone; And one end inserted into the hollow portion of the buffer sleeve, and an implant having a threaded portion provided on a surface of the one end, wherein at least a portion of the threaded portion of the implant has a diameter within a predetermined distance along the longitudinal direction from the distal end thereof. It has a tapered shape that is gradually larger, and a bone fixation system is provided in which the length of the hollow portion of the buffer sleeve is longer than the length of the threaded portion of the implant. The following relationship is established between the implant, the buffer sleeve and the bone tissue of the bone.

μ _{IB ㆍ} F _IB <μ _{OB ㆍ} F _OB

Here, F _IB is the compressive force that the implant exerts on the inner surface of the hollow portion of the buffer sleeve, μ _IB is the friction coefficient between the implant and the buffer sleeve, F _OB is the compressive force applied to the bone tissue, and μ _OB is the The coefficient of friction between the cushion sleeve and bone tissue.

The buffer sleeve may be made of polyethylene or polyether ether ketone (PEEK).

The outer surface of the buffer sleeve may be provided with a plurality of fine holes.

Preferably, the buffer sleeve includes a plurality of fine particles having bone affinity, and the bone affinity fine particles are distributed on the outer surface and the inside of the buffer sleeve. In addition, the bone-affinity fine particles are preferably distributed in the region adjacent to the outer surface and the outer surface of the buffer sleeve and not in the region adjacent to the inner surface of the buffer sleeve.

According to another aspect of the present invention, there is provided a bone fixation system, comprising: a cushioning sleeve having a cylindrical shape and having a hollow portion having at least one end opened, and having an outer surface inserted into and contacting an inner surface of a hole provided in a bone; And one end is inserted into the hollow portion of the buffer sleeve, the surface of the one end includes an implant provided with a thread, at least a portion of the threaded portion of the implant has a tapered shape whose diameter gradually increases along the longitudinal direction from the tip portion The inner surface of the shock absorbing sleeve has a shape corresponding to the thread of the implant, and the bone fixing system having a length of the hollow portion of the shock absorbing sleeve is longer than the length of the thread of the implant.

The outer surface of the buffer sleeve may be provided with a plurality of fine holes.

Preferably, the buffer sleeve is made of titanium, the inner surface of the buffer sleeve is preferably coated with plastic.

When the implant is inserted into the shock absorbing sleeve, the thread of the implant portion corresponds to the thread of the implant on the inner surface of the shock absorbing sleeve so that between the portion corresponding to the thread of the shock absorbing sleeve and the outer surface of the shock absorbing sleeve can be cut. The distance t between the portion to be made and the outer surface of the buffer sleeve may be small.

According to still another aspect of the present invention, a cylindrical buffer sleeve used in a bone fixation system and disposed between an implant having a screw portion and bone tissue, and is inserted and placed so that its outer surface comes into contact with an inner surface of a hole provided in a bone during a procedure. And a cushioning sleeve for use in a bone fixation system having a hollow portion into which the threaded portion of the implant is inserted.

The inner surface of the buffer sleeve has a shape corresponding to the threaded portion of the implant, the distance (t) between the portion of the inner sleeve of the buffer sleeve corresponding to the thread of the implant and the outer surface of the buffer sleeve is small, the buffer sleeve In the case where the implant is inserted into the implant, it is preferable to cut between the portion corresponding to the thread of the shock absorbing sleeve and the outer surface of the shock absorbing sleeve by the thread of the thread of the implant.

The buffer sleeve may be made of titanium, and preferably, the inner surface of the buffer sleeve is coated with a plastic material.

The length of the hollow portion of the cushioning sleeve may be longer than the length of the screw portion of the implant.

Hereinafter, with reference to the accompanying drawings, a preferred embodiment of the present invention will be described in detail.

2 is a view schematically showing a bone fixation system according to an embodiment of the present invention, Figure 3 is a view showing an implant portion of the bone fixation system shown in Figure 2, Figure 4 is a bone shown in Figure 2 It is a figure which shows the buffer sleeve of a fixed system.

As shown in Figures 2 and 3, the implant 110, which is fixed in a threaded manner, has a thread 112 at its end. The cross section of the threaded portion 112 of the implant 110 is preferably circular. This is because when the cross section of the threaded portion 112 of the implant 110 is circular, a uniform compressive force can be applied in all directions with respect to the inner surface of the hollow portion 122 of the buffer sleeve 120. In addition, the thread portion 112 of the implant 110 preferably has a tapered shape in which the cross-sectional area decreases toward the tip portion, which means that the thread portion 112 of the implant 110 is a hollow portion 122 of the buffer sleeve 120 during the procedure. It is intended to be easily inserted into. In addition, if the area of the tapered portion is long, the expansion pressure on the inner surface of the hollow portion can be adjusted according to the insertion degree of the screw portion (112). For example, the entire threaded portion 112 may be tapered. The implant 110 may be mainly formed of a material such as titanium or ceramic, but is not necessarily limited thereto, and any material that is harmless to the human body may be used as long as it guarantees the function of the implant.

The buffer sleeve 120 has a generally cylindrical shape and has a hollow portion 122 into which the implant 110 is inserted. Since the depth of the hollow part 122 is longer than the length of the threaded part 112 of the implant 110, a predetermined empty space may exist between the lower end of the implant 110 and the bottom of the hollow part 122 even after the procedure. In particular, when the threaded portion 112 of the implant 110 is tapered, the threaded portion 112 is formed on the inner surface 126 of the buffered sleeve 120 according to the degree of insertion of the threaded portion 112 into the buffer sleeve 120. The pressure you apply varies. An empty space provided on the bottom of the hollow portion 122 provides a free space in which the implant 110 can be further inserted. As shown in Figures 2 and 4, the lower portion of the buffer sleeve 120 may be formed slightly smaller than the other diameter portion to be easily inserted into the hole provided in the bone tissue.

When the implant 110 is inserted into the hollow portion 122 of the shock absorbing sleeve 120, the shock absorbing sleeve 120 expands due to the pressure applied to the inner surface 126 of the hollow part 122 by the outer surface of the implant 110. It is desirable to be able to. When the buffer sleeve 120 is expanded, not only the friction force between the outer surface of the buffer sleeve 120 and bone tissue is increased, but the stress applied to the bone tissue by the outer surface of the buffer sleeve 120 is increased, thereby promoting bone tissue growth. Because there is. Therefore, the buffer sleeve 120 may be made of a material having a lower mechanical rigidity than the material forming the implant 110. In addition, in order to apply an appropriate stress to the bone tissue around the buffer sleeve 120, expansion must occur at a certain level or more. For example, engineering plastics with less rigidity than metals or ceramics may be used. However, because the implant is embedded directly into the bone tissue, the material should be harmless to the human body, and in order to be firmly fixed, the surface should be easily compatible with the bone tissue. For example, a material such as polyethylene or polyether ether ketone (PEEK) may be considered. In addition, titanium may be used as a material of the buffer sleeve 120. In this case, the wall thickness of the buffer sleeve 120 may be formed relatively thin as compared with the case made of plastic.

In order for the implant to function properly, the frictional force between the surface of the implant 110 and the inner surface 126 of the buffer sleeve 120 and the frictional force between the outer surface of the buffer sleeve 120 and bone tissue should be established as follows.

μ _{IB ㆍ} F _IB <μ _{OB ㆍ} F _OB

Here, F _IB is the compressive force applied by the implant 110 to the inner surface 126 of the hollow portion 122 of the buffer sleeve 120, μ _IB is the friction coefficient between the implant 110 and the buffer sleeve 120, F _OB Is the compressive force applied by the buffer sleeve 120 to the bone tissue, and μ _OB is the coefficient of friction between the buffer sleeve 120 and the bone tissue. That is, the frictional force between the outer surface of the buffer sleeve 120 and the bone tissue should be relatively greater than the frictional force between the threaded portion 112 of the implant 110 and the inner surface 126 of the hollow portion 122.

Since the thread 112 of the implant 110 and the inner surface 126 of the hollow portion 122 should have a relatively small frictional force, the inner surface 126 of the hollow portion may be generally smooth. The outer surface of the buffer sleeve 120 should be relatively rough because the friction force should be relatively large.

Another way to satisfy the above relationship is to increase the bond strength between the outer surface of the buffer sleeve 120 and bone tissue. To this end, the buffer sleeve 120 may be provided with a bone affinity around the outer surface. FIG. 5 is an enlarged view of a portion indicated by circle A in FIG. 4. As shown, the bone affinity 130 in the form of particles is distributed on the outer surface of the buffer sleeve 120 and the inner region adjacent to the outer surface. As the bone affinity 130, phosphate hydroxide, calcium phosphate, animal bone powder, and other kinds of calcium phosphate having properties that promote bone growth may be used. In addition, although it does not actively promote bone growth like ceramic particles and metal particles, the in-growth of the bone has been proved, and the friction sleeve 120 is expanded to the bone by widening the friction and surface area of the buffer sleeve 120. Particles that aid in fast and tight fixation can also be used.

The bone affinity particles 130 are preferably distributed on the outer surface and the inner region of the buffer sleeve 120. As time passes, the bone affinity particles 130 are dissolved and absorbed into the bone. At this time, since the bone grows into the space where the bone affinity particles 130 were, the buffer sleeve 120 may be firmly fixed to the bone. have. In addition, since the bone affinity particles are not only distributed on the outer surface of the buffer sleeve 120 but also to the inner region adjacent thereto, the bone affinity particles 130 distributed on the outer surface are continuously absorbed into the bones. Can promote growth.

Preferably, the bone affinity particles 130 are distributed much in the region near the outer surface, and relatively less in the region near the inner surface 126. When the particles are arranged in this manner, the strength of the buffer sleeve 120 can be properly maintained. For example, when the inner layer of the buffer sleeve 120 is first formed of a plastic material in which the bone affinity particles 130 are not mixed, and then the outer layer of the buffer sleeve 120 is formed of the plastic material in which the bone affinity particles are mixed. As shown in FIG. 5, the buffer sleeve 120 in which the bone affinity is distributed may be manufactured.

FIG. 6 illustrates a state in which the bone fixation system shown in FIG. 2 is operated.

First, a hole for inserting and fixing the implant into the bone tissue 50 of the bone is provided. The buffer sleeve 120 is embedded in the hole provided in the bone tissue 50, and the implant 110 is installed so that the threaded portion 112 is inserted into the hollow portion 122 of the buffer sleeve 120. Since the tip portion of the screw portion 112 is tapered, it can be easily inserted. When the implant 110 is inserted into the buffer sleeve 120, the outer circumferential surface of the implant 110 exerts a pressure on the inner surface of the hollow portion 122 provided in the buffer sleeve 120, the pressure is a buffer made of a material such as plastic The sleeve 120 is inflated and the outer surface of the buffer sleeve 120 applies a predetermined stress to the surrounding bone tissue 50. In addition, the stress of the buffer sleeve 120 is applied to the bone tissue 50 by making the diameter of the hole drilled to insert the buffer sleeve 120 into the bone tissue slightly smaller than the outer diameter of the buffer sleeve 120 during the operation of the bone fixation system. You can also adjust the size of the. As mentioned above, according to Wolf's Law, an appropriate stress must be applied for bone tissue to grow. However, bone resorption occurs again when too much stress is applied. Therefore, the difference in diameter between the two is selected such that the stress that the outer surface of the buffer sleeve 120 exerts on the bone tissue 50 after the implant 110 is inserted into the buffer sleeve 120 is within a range capable of promoting bone growth. It is good to be.

As time passes, the bone affinity particles 130 provided on the outer surface of the buffer sleeve 120 may be dissolved and absorbed into the bone tissue 50. At this time, the bone grows into the space where the bone affinity particles 130 were located. Therefore, the buffer sleeve 120 may be firmly fixed to the bone tissue (50). In addition, since the bone affinity particles 130 are distributed not only on the outer surface of the buffer sleeve 120 but also on the inner region adjacent thereto, the bone affinity particles 130 distributed on the outer surface are absorbed by the bone tissue 50. Afterwards, it is possible to promote internal growth of the bone tissue 50 continuously.

Figure 7 schematically shows a bone fixation system according to another embodiment of the present invention. FIG. 8 is a view showing a cushioning sleeve of the bone fixation system shown in FIG. 7.

The bone fixation system 200 according to the present embodiment has the same technical configuration as the above-described embodiment except that the buffer sleeve 220 has a cylindrical spring shape. Therefore, in the following description, the same reference numerals are used for the components having the same configuration as the above-described embodiment.

The buffer sleeve 220 has a structure such as a tension spring (see FIG. 8). If the buffer sleeve 220 is made of such a structure, the buffer sleeve 220 can be easily inserted into the hole provided in the bone tissue (50). That is, by inserting the buffer sleeve 220 to make the diameter smaller by inserting the buffer sleeve 220 before inserting it into the hole provided in the bone tissue 50, the buffer sleeve 220 can be inserted into the hole of the bone tissue 50 more easily. have.

The buffer sleeve 220 may be made of plastic as in the above-described embodiment. Preferably, the buffer sleeve 220 of the present embodiment is made of titanium. When the buffer sleeve 220 is made of titanium, in order to promote the growth of the bone tissue 50 and increase the binding force between the buffer sleeve 220 and the bone tissue, the outer surface of the buffer sleeve 220 is provided with a plurality of fine holes Good to do. In addition, the inner surface of the buffer sleeve 220 may be coated with plastic to reduce friction with the implant.

The buffer sleeve 220 may be inflated by elasticity after being inserted, and its outer surface may contact the inner surface of the hole provided in the bone tissue 50. On the other hand, the diameter in the state that the load is not applied to the buffer sleeve 220 may be smaller than the diameter of the hole provided in the bone tissue (50). The relationship between the diameter of the hole provided in the bone tissue 50 and the diameter of the unloaded state of the buffer sleeve 220 is preferably selected in the range that can be applied to the appropriate stress on the bone tissue.

9 is a view showing a state in which the bone fixation system shown in FIG.

In the embodiment shown in Figure 9 the diameter of the buffer sleeve 220 in the unloaded state is smaller than the inner diameter of the hole provided in the bone tissue (50). Therefore, the buffer sleeve 220 can be very easily inserted into the hole provided in the bone tissue (50). When the implant 110 is inserted, the buffer sleeve 220 is expanded by the threaded portion 112 of the implant 110, and the outer surface of the buffer sleeve 220 exerts a compressive force on the bone tissue. In general, the buffer sleeve 220 is disposed in the space between the threads of the thread 112 of the implant 110, so that the entire diameter of the bone fixation system can be reduced.

Figure 10 shows a buffer sleeve according to another embodiment of the present invention, Figure 11 shows an implant used with the buffer sleeve shown in FIG.

As shown in FIG. 10, the buffer sleeve 310 according to the present exemplary embodiment has an inner surface 312 corresponding to the threaded portions 322 and 324 of the implant 320. Therefore, the thickness between the inner surface 312 and the outer surface 316 of the buffer sleeve 310 is not constant. The thickness t between the portion 314 corresponding to the thread 322 of the implant 320 and the outer surface 316 of the cushioning sleeve 310 at the inner surface 312 of the cushioning sleeve 310 depends on the characteristics of the implant. Appropriately selected. For example, if this thickness t is very thin, the inner surface 312 and outer surface 316 of the buffer sleeve 310 when the threaded portions 322, 324 of the implant 320 are inserted into the buffer sleeve 310. Can be cut between. Then, the bone fixation system after the procedure may have the same shape as the above-described embodiment (see FIG. 9).

In this embodiment, the buffer sleeve 310 may be made of titanium, and as in the above-described embodiment, the inner surface 312 of the buffer sleeve 310 may be coated with plastic to reduce friction with the implant 320. Can be.

Although the invention has been described in detail based on the embodiments shown in the accompanying drawings, it is apparent that various modifications are possible without departing from the scope of the invention. Nothing described herein is intended to narrow the scope of the invention to the scope of the appended claims. The foregoing examples are for illustrative purposes only and are not intended to exclude those having other embodiments.

Using the bone fixation system according to the present invention, because the buffer sleeve is disposed between the screw portion and the bone tissue of the implant and the stress is uniformly distributed in the bone tissue around the screw portion of the implant, bone fusion is induced and the bone fixation system continues to function I can keep it.

Claims (16)

As a bone lock, A shock absorbing sleeve having a cylindrical shape and having a hollow portion having at least one end thereof inserted into and disposed such that an outer surface thereof contacts an inner surface of a hole provided in the bone; And One end is inserted into the hollow portion of the buffer sleeve, the implant is provided with a screw portion on the surface of the one end Including, At least a portion of the threaded portion of the implant has a tapered shape that gradually increases in diameter within a predetermined distance along the longitudinal direction from the distal end portion, Bone fixation device that the following relationship is established between the implant, the buffer sleeve and the bone tissue of the bone: μ _{IB ㆍ} F _IB <μ _{OB ㆍ} F _OB Here, F _IB is the compressive force that the implant exerts on the inner surface of the hollow portion of the buffer sleeve, μ _IB is the friction coefficient between the implant and the buffer sleeve, F _OB is the compressive force applied to the bone tissue, and μ _OB is the Coefficient of friction between cushioning sleeve and bone tissue. The method according to claim 1, The buffer sleeve is a bone fixing device, characterized in that made of polyethylene or polyether ether ketone (PEEK). The method according to claim 1, The outer surface of the buffer sleeve is a bone fixing device characterized in that it comprises a plurality of fine holes and small projections. The method according to claim 1, The buffer sleeve is provided with a plurality of fine particles having bone affinity, the bone affinity bone fixing device is distributed on the outside and inside of the buffer sleeve. The method according to claim 4, The bone affinity particles are distributed in the region adjacent to the outer surface and the outer surface of the buffer sleeve, bone anchoring device, characterized in that not distributed to the region adjacent to the inner surface of the buffer sleeve. As a bone lock, A shock absorbing sleeve having a cylindrical shape and having a hollow portion having at least one end thereof inserted into and disposed such that an outer surface thereof contacts an inner surface of a hole provided in the bone; And One end is inserted into the hollow portion of the buffer sleeve, the surface of the one end includes an implant provided with a thread, At least a portion of the screw portion of the implant has a tapered shape whose diameter gradually increases along the longitudinal direction from the tip portion, the inner surface of the buffer sleeve has a shape corresponding to the screw portion of the implant. The method according to claim 6, The outer surface of the buffer sleeve is a bone fixing device characterized in that it comprises a plurality of fine holes and projections. The method according to claim 7, The buffer sleeve is a bone fixing device, characterized in that consisting of titanium. The method according to claim 8, The inner surface of the buffer sleeve is a bone fixing device, characterized in that coated with plastic. The method according to claim 9, Characterized in that the distance (t) between the portion corresponding to the thread of the implant and the outer surface of the buffer sleeve is small on the inner surface of the buffer sleeve so that the portion between the thread corresponding to the thread of the buffer sleeve and the outer surface of the buffer sleeve is cut. Bone Lock. A cylindrical cushioning sleeve used in a bone fixation system and disposed between an implant having a thread and bone tissue, During the procedure, the outer surface is inserted and disposed so as to contact the inner surface of the hole provided in the bone, and has a hollow portion into which the threaded portion of the implant is inserted. The inner surface of the cushioning sleeve has a shape corresponding to the threaded portion of the implant, the distance (t) between the portion corresponding to the thread of the implant and the outer surface of the cushioning sleeve in the inner surface of the buffer sleeve is small, the thread of the buffer sleeve Between the portion corresponding to and the outer surface of the buffer sleeve, The outer surface of the buffer sleeve is a buffer sleeve, characterized in that provided with a plurality of fine holes and projections. delete delete The method according to claim 11, The buffer sleeve is a buffer sleeve used in the bone fixation system, characterized in that consisting of titanium. The method according to claim 14, The inner surface of the buffer sleeve is a buffer sleeve used in the bone fixation system, characterized in that the coated with a plastic material. The method according to claim 11, The length of the hollow portion of the buffer sleeve is a buffer sleeve used in the bone fixation system, characterized in that longer than the length of the threaded portion of the implant.

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