BIO-FLEXIBLE SPINAL FIXATION APPARATUS FOR PREVENTING FATIGUE FRACTURE

Abstract

The present invention relates to a bio-flexible spinal fixation apparatus capable of realizing motions similar to general body mechanical motions during flexion and extension motions after spinal fixation surgery by configuring a center of a coil part of a rod to have a eccentricity at a certain distance from a center line of a straight part and a specific inclination, and conveniently performing an operation of setting a fixing position of the rod during spinal fixation surgery by machining the straight part section of the rod into a flat surface. The present invention includes a screw pike that includes a head part and a screw; a rod that has a straight part and a coil part wound to be inclined by a predetermined angle with an eccentricity from a center of the straight part; and a set screw.

Claims

1. A bio-flexible spinal fixation apparatus, comprising: a screw pike that includes a head part that has a receiving part penetrating in both sides and female threads formed on an inner circumferential surface of the receiving part and grooves formed in parallel at a bottom portion and a screw that extends to a bottom surface of the head part and is inserted into a spinal segment to be fixed; a rod that has a straight part seated in the groove of the screw pike and a coil part wound to be inclined by a specific angle based on a center separated by a predetermined distance with an eccentricity from a center of the straight part; and a set screw that has a fixing groove formed in the central portion and is fastened to the female thread of the head part of the screw pike to pressurize and fix the rod.

2. The bio-flexible spinal fixation apparatus of claim 1, wherein an upper surface of the straight part of the rod has a flat surface.

3. The bio-flexible spinal fixation apparatus of claim 2, wherein the flat surface of the rod is formed by a compression machining process in which a cross section is reduced.

4. The bio-flexible spinal fixation apparatus of claim 1, wherein a diameter of a cross section of the straight part of the rod is formed larger than that of a cross section of the coil part.

5. The bio-flexible spinal fixation apparatus of claim 4, wherein the diameter of the cross section of the straight part of the rod is ?4.5 mm, and the diameter of the cross section of the coil part is ?4.0 mm.

6. The bio-flexible spinal fixation apparatus of claim 1, wherein the screw pike is symmetrically inserted into both sides of the spine based on a center line of a human body, and a direction in which the coil part is wound is opposite to each other based on a center line of the straight part so that the coil part of the rod is symmetrically located on both sides of the spine based on the center line of the human body.

7. The bio-flexible spinal fixation apparatus of claim 2, further comprising: a washer that has a spherical projection provided on an upper side of the central portion to fit into a coupling hole of the set screw and is formed in a plane on the bottom surface to be in close contact with the flat surface of the rod in order to uniformly share a vertical load applied by a tightening force of the set screw to the flat surface of the rod, wherein the set screw has the coupling hole smaller in size than a fixing groove at a lower end of the central portion.

8. The bio-flexible spinal fixation apparatus of claim 1, further comprising: a washer that has a spherical projection provided on an upper side of the central portion to fit into a coupling hole of the set screw and has a spherical groove having a size receiving a spherical surface of the rod formed on the bottom surface to uniformly share a vertical load applied by a tightening force of the set screw to the flat surface of the rod, wherein the set screw has the coupling hole smaller in size than a fixing groove at a lower end of the central portion.

9. A bio-flexible spinal fixation apparatus, comprising: first to third pedicle arrays that include screws arranged vertically on each side with respect to a center line of a human body and inserted into a pedicle, and head parts having a plurality of opening grooves; first and second rod arrays that are seated in one of the plurality of opening grooves of head parts of each of the first to third pedicle screws constituting the first to third pedicle screw arrays and connecting the first to third pedicle screw arrays in a segmented form; and a fixing cap that is fastened to first to third pedicle screw head parts of the first to third pedicle screw arrays, respectively, and fixes the first and second rods each constituting the first and second rod arrays so that the first and second rods are not separated from the opening grooves, wherein the first and second rods include a straight part and a coil part formed in a center of the straight part, a center of the coil part is wound eccentrically in one direction while upward from the center of the straight part, and the coil part is wound so as to be inclined in one direction of medial or lateral from an imaginary center line of each of the first to third pedicle screws with respect to a prone position of a surgical patient on an operating table.

10. The bio-flexible spinal fixation apparatus of claim 9, wherein the opening grooves of the head parts of the first to third pedicle screws are formed of two, and when the coil parts of the first and second rods are symmetrically positioned in inner grooves of the two opening grooves based on the center line of the human body, the symmetrical coil parts are wound so as to be inclined laterally from the imaginary center line of the first to third pedicle screws.

11. The bio-flexible spinal fixation apparatus of claim 9, wherein the opening grooves of the head parts of each of the first to third pedicle screws are formed of two, and when the coil parts of the first and second rods are symmetrically positioned in outer grooves of the two opening grooves based on the center line of the human body, the symmetrical coil parts are wound so as to be inclined medially from the imaginary center line of the first to third pedicle screws.

12. The bio-flexible spinal fixation apparatus of claim 9, wherein an inclination of the coil parts of the first and second rods is 31.7??5?.

13. The bio-flexible spinal fixation apparatus of claim 9, wherein the opening grooves of the head parts of each of the first to third pedicle screws are formed in a shape corresponding to an appearance of the straight parts of the first and second rods.

14. The bio-flexible spinal fixation apparatus of claim 13, wherein the straight parts of the first and second rods have a circular cross section but have a flat cross section with a flat upper surface, and the opening grooves of the head parts of each of the first to third pedicle screws is formed in a circular shape to receive a circular cross section of a shaft.

15. The bio-flexible spinal fixation apparatus of claim 13, wherein the straight parts of the first and second rods are pressed so that lower surfaces of the straight parts have a circular cross section, and upper surfaces and left and right surfaces of the straight parts have a flat cross section, and the opening groove of the head part has a circular bottom portion and both side surfaces formed in the flat cross section to be formed to a size that receives a lower circular cross section and left and right flat cross sections of the straight part.

16. The bio-flexible spinal fixation apparatus of claim 9, wherein a screw part is formed on inner circumferential surfaces of the opening grooves of the head parts of each of the first to third pedicle screws, and the fixing cap is formed with a set screw so as to be fastened to a threaded part of the opening groove.

17. The bio-flexible spinal fixation apparatus of claim 16, further comprising: a washer that has a spherical projection provided on an upper side of the central portion to fit into the coupling hole of the cylindrical portion and a spherical groove that is provided on a bottom surface thereof and has a size receiving a spherical surface of a rod to uniformly share a vertical load applied by a tightening force of the set screw to flat surfaces of the first and second rods, wherein the set screw is formed of a cylindrical portion having a coupling hole penetrating through a central portion.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0043] FIG. 1 is a perspective view illustrating a configuration of a bio-flexible spinal fixation apparatus according to the related art.

[0044] FIG. 2 is a schematic diagram of the bio-flexible spinal fixation apparatus according to the related art mounted on a spinal segment.

[0045] FIG. 3 is an exemplary view illustrating various types of pedicle screw pike rods according to the related art.

[0046] FIG. 4 is a perspective view illustrating a configuration of a bio-flexible spinal fixation apparatus according to an embodiment of the present invention.

[0047] FIG. 5 is a front and right-side projection view illustrating a configuration of a left (L) rod, which is a main part of the bio-flexible spinal fixation apparatus according to the present invention.

[0048] FIG. 6 is a front and right-side projection view illustrating a configuration of a right (R) rod, which is a main part of the bio-flexible spinal fixation apparatus according to the present invention.

[0049] FIG. 7 is a cross-sectional view illustrating a configuration in which a washer is mounted on a set screw, which is a main part of the present invention.

[0050] FIG. 8 is a schematic cross-sectional projection view in which a rod and a set screw are coupled to a head part of a screw pike.

[0051] FIG. 9 is a diagram illustrating another example of a configuration in which the set screw and washer of FIG. 7 are integrated.

[0052] FIG. 10 is a view of a straight state before molding a coil part on the rod of the present invention.

[0053] FIG. 11 is a view after molding in which the coil part is wound twice around the rod of the present invention.

[0054] FIG. 12 is a diagram illustrating an example of machining a flat surface on a straight part of a rod, which is the main part of the present invention.

[0055] FIG. 13 is a diagram illustrating another example of machining the flat surface.

[0056] FIG. 14 is a graph showing a disc pressure profile in spinal fixation surgery using the bio-flexible spinal fixation apparatus according to the present invention.

[0057] FIG. 15 is a model diagram illustrating a state in which the bio-flexible spinal fixation apparatus according to the present invention is mounted on the spine.

BEST MODE

[0058] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying FIGS. 4 to 15.

[0059] A bio-flexible spinal fixation apparatus according to the present invention is implemented to simplify an operation of setting fixing position of a rod in a surgical operation of fixing the rod with a set screw, and to prevent the rod from leading to fatigue fracture by repeated stress.

[0060] A configuration of a bio-flexible spinal fixation apparatus according to a first embodiment of the present invention will be described with reference to FIGS. 4 to 10.

[0061] FIG. 4 is a perspective view illustrating a configuration of a bio-flexible spinal fixation apparatus according to an embodiment of the present invention, FIG. 5 is a front and right-side projection view illustrating a configuration of a left (L) rod, which is a main part of the bio-flexible spinal fixation apparatus according to the present invention, FIG. 6 is a front and right-side projection view illustrating a configuration of a right (R) rod, which is a main part of the bio-flexible spinal fixation apparatus according to the present invention, FIG. 7 is a cross-sectional view illustrating a configuration in which a washer is mounted on a set screw, which is a main part of the present invention, and FIG. 8 is a schematic cross-sectional projection view in which a rod and a set screw are coupled to a head part of a screw pike.

[0062] As illustrated in FIGS. 4 to 6, the bio-flexible spinal fixation apparatus in this embodiment includes: a plurality of screw pikes 10 that include a head part 12 that has a U-shaped receiving groove 14 penetrating in a longitudinal direction and having a female screw formed on an inner circumferential surface thereof and two grooves 16a and 16b formed at the bottom of the receiving groove 14 and screws 18 that are symmetrically inserted into a spinal segment based on a center line of a human body; a straight part 22 that is seated in the grooves 16a and 16b of the screw pike 10; a rod 20 that has a coil part 24 wound to the left (L) or right (R) based on a center with a certain eccentricity d from a center of the straight part 22 and is coupled to the screw pike 10; a set screw 30 that is fastened to the receiving groove 14 of the head part 12 and has a wrench groove 32 formed in a central portion; and a washer 40 that is integrally coupled to a bottom surface of the set screw 30 and applies a fixed load to the straight part 22 of the rod 20 with uniform sharing when the set screw 30 is fastened.

[0063] In the bio-flexible spinal fixation apparatus of the present invention described above, the screw pikes 10 are symmetrically inserted into both sides of a spine 500 segment in a transverse direction based on a center line of a human body, and the rod 20 is seated in the grooves 16a and 16b of the receiving groove 14 in a zigzag manner to connect each spinal segment in the longitudinal direction.

[0064] In the embodiment of the present invention, the coil part 24 of the rod 20 is wound twice, and the straight parts 22 on both sides have a flat surface 26 whose upper portion is flat to set the standard for the fixing position of the rod 20. When the rod 20 is fixed with the flat surface 26 facing upward, the coil part 24 is automatically erected at an inclination of about 31.7??5? from the center line of the straight part 22, and the coil parts 24 of the rods 20 on both sides of the left and right are symmetrically fixed on both sides based on the center line of the human body.

[0065] As illustrated in FIG. 7, the set screw 30 has a through hole 34 having a wing part 36 formed at the center of the bottom surface. The washer 40 has an angular shape with a size to be inserted into the receiving groove 14, and a spherical projection 42 is formed on the upper portion to fit into the through hole 34 of the set screw 30. In this case, the wing part 36 of the through hole 34 and the spherical projection 42 are configured to have a gap, so that the set screw 30 rotates and is fastened to a female screw of the head part 12, but the washer 40 descends without rotating and presses the flat surface 26 of the rod 20 with a uniform load. Accordingly, it is possible to prevent scratch areas generated on a contact surface of the rod 20 due to rotational force resulting from fastening of the set screw 30 from leading to a notch due to repetitive elastic operation of the rod 20.

[0066] In more detail, as illustrated in FIG. 8, even though the tightening force is provided through the set screw 30, since a rotating surface of the set screw 30 contacts only the washer 40, scratches caused by the rotating surface of the set screw 30 are not transmitted to the rod 20. In addition, since the uniformly shared load pressed by the washer 40 is applied to the entire contact surface area of the flat surface 26 of the rod 20, it is possible to prevent the repeated stress occurred when a human waist is bent and stretched as in the related art from concentrated on the point contact area and sequentially leading to the fatigue fracture.

[0067] Meanwhile, a configuration of another embodiment of the washer 40 integrally coupled to the set screw 30 is illustrated in FIG. 9.

[0068] In this embodiment, a structure is proposed in which a spherical groove 44 of a size capable of surrounding an outer diameter of the rod is formed on the bottom surface of the washer 40.

[0069] According to the spherical groove 44 of the washer 40, in case that a flat surface 26 is not formed on the straight part 22 of the rod 20 and seated in the grooves 16a and 16b of the head part 12, the spherical groove 44 is in surface contact t with the straight part 22 of the spherical cross section without the flat surface 26 to uniformly share the load of the set screw 30 to the straight part 22.

[0070] FIG. 10 is a view of a straight state before molding the coil part 24 on the rod of the present invention, FIG. 11 is a view after molding in which the coil part 24 is wound twice around the rod of the present invention, FIG. 12 is a diagram illustrating an example of machining a flat surface on a straight part of a rod, which is the main part of the present invention, and FIG. 13 is a diagram illustrating another example of machining the flat surface.

[0071] As illustrated in FIGS. 10 and 11, in the embodiment of the present invention, a structure in which a diameter of a cross section of the straight part 22 section of the rod 20 is larger than that of a cross section of the coil part 24 section is proposed. Clinically observed at a point where a long-term period has elapsed after spinal fixation surgery, this is to ensure that the fixing operation of the rod 20 maintains maximum rigidity within an allowable range in order to delay the time when the fatigue fracture of the straight part 22 occurs or semi-permanently maintain. In this embodiment, a structure in which the diameter of the cross section of the straight part 22 is ?4.5 mm and the diameter of the cross section of the coil part 24 is ?4.0 mm is proposed.

[0072] In addition, as illustrated in FIG. 12, the straight part 22 of the rod 20 whose diameter has been increased to maintain rigidity is machined to flatten the upper surface by pressing with a machine such as a compression press so that there is no loss of diameter. As illustrated in FIG. 13, as another example of the flat surface 26, except for the lower round surface, both the upper and side surfaces may be pressed with a compression press or the like to be machined in an angular shape.

[0073] As described above, according to the configuration of the rod 20, as illustrated in FIG. 15, since the operation of setting the fixing position in which the coil parts 24 of the rods 20 on both sides are not biased to one side and are maintained symmetrically based on the center line of the human body may be easily performed based on the flat surface 26 of the rod, it is possible to simplify the coupling operation of the rod 20.

[0074] As shown in the disc pressure profile graph illustrated in FIG. 14, a high pressure appears on the front side of the disc in the case of flexion motion, and a high pressure appears on the rear side of the disc in the case of extension motion. In the case of neutral, it is common that the pressure on the front and rear sides of the disc appears at a similar level. In the bio-flexible spinal fixation apparatus of the present invention, given that the operation of setting the fixation position of the rod 20 is correctly implemented, due to the characteristics in which the coil part 24 is wound around the center with a constant eccentricity d from the center of the straight part 22, a uniformly unloading effect that the pattern of the overall graph is similar appears even though the pressure value is slightly reduced compared to the normal disc pressure profile.

[0075] In addition, the spine does not move by only one specific segment, but the motion of each segment is combined overall to perform motions such as flexion and extension. Conventionally, the motion of each segment is called a range of motion (ROM), and it is a result of a general spinal biomechanical analysis that the ROM of the operated segment is relatively small, and the ROM of the upper and lower adjacent segments of the operated segment is larger. Therefore, the acceleration of adjacent segment degeneration above and below the operated segment is also due to these unnatural mechanical motions of the spine.

[0076] According to the structure of the rod 20 of the present invention in which the straight part 22 and the coil part 24 are configured to have a central eccentricity and a specific inclination, the ROM of the operated segment is relatively maximized, and the adjacent segment ROM is minimized, compared to surgery using a rigid rod. In addition, as a result of finite element analysis of a case in which the bio-flexible spinal fixation apparatus of the present invention is mounted on the posterior portion of the spine between the segments of the spine 500 and the interbody fusion cage is used in the anterior portion of the spine, it was demonstrated that the load sharing ratio between the anterior portion and the posterior portion approaches the normal load sharing mechanism ratio as a ratio of 7:3 or 7.5:2.5. As a result, it is possible to minimize the adjacent segment degeneration above and below the operated segment.

[0077] Explaining the operating method of the rod, since the coil part 24 is wound around the center with a certain eccentricity d from the center of the straight part 22 of the rod 20, the rod 20 is operated in such a way that the motion is greater in the case of the flexion which is the motion of bending the waist forward and the motion is smaller in the case of extension which is the motion of stretching the waist backward, thereby deriving results similar to the actual biomechanical movement of the spine.

[0078] Rather than the structure in which the center of the coil part is wound eccentrically with the center of the straight part, if the shape of the rod has the spring structure in which the coil part and the straight part are wound concentrically around the same central axis as in a general spring, since the degree or size of the motion appears similarly during the flexion and extension, the motion of the waist becomes unnatural.

[0079] However, by the coupling structure of the straight part and coil part of the rod according to the present invention, since the spine is prevented from being biased to one side and the bending of the waist when the spine is bent backward is further limited than the motion when the spine is bent forward, and the load sharing between a plurality of fused spinal segments is similar to the normal load sharing mechanism, thereby it realizes the effect of relieving the burden on the waist.

[0080] Hereinabove, specific embodiments of the present invention have been described. However, the spirit and scope of the present invention is not limited to these specific embodiments, and it will be understood by those of ordinary skill in the art that various modifications and variations are possible within the scope of not changing the gist of the present invention.

DESCRIPTION OF REFERENCE SIGNS

[0081]

TABLE-US-00001 10: Screw pike 12: Head part 14: Receiving groove 16a, 16b: Groove 20: Rod 22: Straight part 24: Coil part 26: Flat surface 30: Set screw 32: Wrench groove 34: Through hole 36: Wing part 40: Washer 42: Spherical projection 44: Spherical groove 500: Spine