WO2008082085A1

WO2008082085A1 - Rod multiaxiale connecting peidcle screws

Info

Publication number: WO2008082085A1
Application number: PCT/KR2007/006072
Authority: WO
Inventors: Jong Wuk Jang
Original assignee: Medyssey Co., Ltd.
Priority date: 2006-11-28
Filing date: 2007-11-28
Publication date: 2008-07-10
Also published as: KR100797755B1; KR20070011197A

Abstract

A multiaxial spinal fixation device includes a connecting rod integrally having rod portions and an elastic portion, which is disposed between the rod portions and is elastically deformable in response to an external force, a pedicle screw having a head, in which one end of the connecting rod is seated, and an elastic member added to the head. The connecting rod can suitably adjust the elastic restoring force in forward/backward and lateral directions and is thus optimally adopted to alleviate the symptoms of a patient and is optimally applied to a connecting region. It is also possible to connect three or more vertebrae to reduce the number and the structure of restorative elements, thereby minimizing the burden on the patient's body.

Description

Description ROD MULTIAXIALE CONNECTING PEIDCLE SCREWS

Technical Field

[1] The present invention relates to a multiaxial spinal fixation device having a pedicle screw and a connecting rod, and more particularly, to a multiaxial spinal fixation device, in which the structure of a connecting rod is improved to facilitate a surgical operation and manufacture thanks to the simple structure, and an elastic member is interposed between the pedicle screw and the connecting rod. The multiaxial spinal fixation device of the invention can be suitably arranged in a region of the spine to be connected while minimizing the effect on the human body after the surgical operation. Background Art

[2] The spine or vertebral column is composed of 34 bones or vertebrae which engage with each other in a jointed manner to bend and resist pressure. Spinal discs are placed between respective vertebrae to perform a cushioning function.

[3] As a representative symptom of back pain patients, a spinal disc is damaged and the nerves between respective vertebrae are pinched, thus causing pain.

[4] When part of the spine is damaged, a patient has difficulty engaging in personal activities. Even if the degree of damage is not severe, pain is caused when the damaged part of the spine is pressed or touched by an adjacent part.

[5] Accordingly, a patient who has a fracture or a damage in part of the spine needs a surgical operation for supporting adjacent spinal regions using an artificial restorative device so that the damaged region is not pinched or pressed. The spine supporting artificial device to be used includes pedicle screws, which are implanted into the spine at positions above and under the damaged spinal region, to act as fixing rods, and a connecting rod, which connects the pedicle screws with each other, to act as a supporting rod.

[6] Examples of the artificial device are disclosed in Korean Patent Application No.

10-2004-0076105, entitled "MULTIAXIAL SPINAL FIXATION DEVICE," and Korean Utility Model Registration Application No. 20-2004-0022470, entitled "PEDICLE SCREWS AND CONNECTING ROD."

[7] FIG. 20 shows a conventional multiaxial spinal fixation device. Described in more detail, pedicle screws 1 act as fixing rods for a damaged vertebra, and each of the pedicle screws 1 includes a head 11, which has a receiver having a predetermined depth in the top portion thereof and an axially-opened recess in the bottom of the receiver, and an anchor 12, which is stuck at a predetermined depth into the spine at a position above or under the damaged vertebra. A connecting rod 1 is seated in the recess of the receiver to connect the pedicle screws 1 with each other to adjust the angle or the interval of the vertebra. Locking members 3 are inserted into the receivers of the pedicle screws 1 to press the connecting rod 2, thereby preventing the connecting rod 2 from playing in the receiver.

[8] The connecting rod 2 is embodied by an elastic rod or a coil spring in Korean Patent

Application No. 10-2004-0076105, titled "MULTIAXIAL SPINAL FIXATION DEVICE." In Korean Utility Model Registration Application No. 20-2004-0022470, titled "PEDICLE SCREWS AND CONNECTING ROD," as shown in FIG. 20, a spring shaped layer is formed by a central piece, a first thin sheet having a rectangular cross section, which is wound several times on the central piece, and a second thin sheet having a rectangular cross section, which is wound several times on the first thin sheet.

[9] In this approach, the rod 2 has its own elasticity and, in an operation, is curved according to the shape of the spine of a patient. Thus, the rod 2 can bend along with the bending of the spine when the patient moves, and also has restoring force in order to improve the comfort of the patient and promote healing.

[10] In the case of the rod 2 having the shape of an elastic rod or coil spring, the single spring structure provides excellent elasticity. However, as a drawback, the rod 2 having the spring structure can shake. The rod is semi-permanently used once it is implanted in the body of the patient. The shaking may bend the rod beyond the range of the original shape of the spine, thereby deforming the spring, which is fastened to the spine for a long time. Therefore, it is difficult to maintain the curved shape matching the shape of the spine of the patient.

[11] In addition, for the latter case, using the sheets wound in opposite directions, it is possible to ensure rigidity for preventing the shaking as well as necessary elasticity. However, this is difficult to fabricate.

[12] Most importantly, when the spine is bent in one direction, respective regions of the spine are bent in different amounts. In the case of implantation in two or more vertebrae, the restraint of movement of each region is limited. Necessary elasticity should be determined precisely and differently with respect to forward/backward and lateral bending directions. However, according to the conventional approaches, the portions of the device having elasticity act independently from the directions. Disclosure of Invention Technical Problem

[13] The present invention has been made to solve the foregoing problems with the prior art, and therefore an object of the present invention is to provide a multiaxial spinal fixation device having a connecting rod, which can suitably adjust elastic restoring force in forward/backward and lateral directions.

[14] Another object of the invention is to provide a multiaxial spinal fixation device which can connect three or more vertebrae with each other, thereby facilitating operation performance.

[15] A further object of the invention is to provide a multiaxial spinal fixation device which has an elastic member interposed between a connecting rod and a pedicle screw to enhance the freedom of movement of the spine through the elastic deformation of the elastic member in response to the movement of the spine.

[16] Yet another object of the invention is to provide a multiaxial spinal fixation device which can be easily and separately fabricated when needed. Technical Solution

[17] According to an aspect of the invention, there is provided a multiaxial spinal fixation device, which includes a pedicle screw, acting as a stabilizing rod for a damaged spine, wherein each of the pedicle screws has a head in a top portion thereof and a threaded anchor extending downward from the head, the head having a receiver having a predetermined depth and having an axially-opened recess in a bottom thereof, and the anchor stuck into an upper or lower portion of the damaged spine; a connecting rod seated in the recess of the receiver to be connected to the pedicle screw, thereby correcting an angle or an interval of the spine; and locking members, each of which is inserted into each of the screw receivers to prevent the connecting rod from freely moving therein.

[18] The connecting rod is formed by cutting a single piece of material, and includes cylindrically-shaped rod portions and a leaf spring integrally connected to the rod portions, the leaf spring having an elastic portion, which is wider but thinner than the rod portions.

[19] According to a desirable feature of the invention, the elastic portion and the rod portions are connected by connecting portions, which are smoothly curved without edges.

[20] According to a further desirable feature of the invention, the elastic portion is substantially quadrangular and includes vertical slits, which are vertically cut from above and below and are formed at positions at which they do not interfere with each other, and lateral slits, which are laterally cut from left and right edges without interfering with the vertical slits.

[21] According to another desirable feature of the invention, the elastic portion has: at least one first slit cut from a first edge toward an opposite second edge of the elastic portion, and having a closed inner end, which is spaced apart at a predetermined interval from the second edge of the elastic portion, the closed inner end of the first slit being expanded in a form of a circle that is larger than the width of the cut first slit; and at least one second slit, cut from the second edge toward the first edge of the elastic portion, wherein the first and second slits alternate with each other at a predetermined interval.

[22] According to another desirable feature of the invention, the elastic portion has a plurality of third slits, which extend in lateral or longitudinal directions and vertically extend through the elastic portion.

[23] According to another desirable feature of the invention, the elastic portion has a rectangular through hole, which vertically extends through the elastic portion, and a plurality of protrusions, which extend from one inner edge toward an opposite edge of the through hole in alternating directions.

[24] According to another desirable feature of the invention, the connecting rod has the rod portions, which are defined by straight portions of a hollow pipe, adjacent to both ends thereof, the elastic portion defined by an intermediate portion of the hollow pipe between the rod portions, and an elastic cable inserted into and stored in the hollow pipe, wherein the elastic portion has a spiral slit in the outer circumferential portion thereof.

[25] According to a further desirable feature of the invention, the elastic portion is prepared separately from the rod portions and is then connected thereto by welding, or the rod portions and the elastic portion are integrally formed by cutting a single piece of material.

[26] According to another desirable feature of the invention, the connecting rod is eccentrically connected to the elastic portion.

[27] According to another desirable feature of the invention, the pedicle screw has an elastic member placed in the receiver of the head, in which one end of the connecting rod is inserted, wherein the elastic member has a shape of a ring or a plate having a predetermined thickness and elastically supports one end of the connecting rod.

[28] The above objects and other features and advantages of the present invention will become more apparent after a reading of the following detailed description when taken in conjunction with the drawings. While the present invention will be described with reference to particular illustrative embodiments and the accompanying drawings, it is not to be limited thereto, but will be defined by the appended claims. It is to be appreciated that those skilled in the art can substitute, change or modify the embodiments in various forms without departing from the scope and spirit of the present invention.

Advantageous Effects

[29] In the multiaxial spinal fixation device of the invention, the connecting rod can suitably adjust the elastic restoring force in forward/backward and lateral directions and is thus optimally adopted to alleviate the symptoms of a patient and is optimally applied to a connecting region. It is also possible to connect three or more vertebrae to reduce the number and the structure of restorative elements, thereby minimizing the burden on the patient's body. [30] The connecting rod can be easily and separately fabricated as needed, and can thus be easily applied to the patient in various states. [31] The pedicle screw connected to one end of the connecting rod can enhance the freedom of movement of the connecting rod through the elastic deformation of the elastic member in the head, which has excellent expansion and restorability, thereby enhancing the effect of the operation on the patient.

Brief Description of the Drawings [32] FIG. 1 is a perspective view illustrating a connecting rod of a multiaxial spinal fixation device according to a first embodiment of the invention; [33] FIG. 2 is a view illustrating the usage of FIG. 1;

[34] FIG. 3 is a perspective view illustrating a connecting rod of a multiaxial spinal fixation device according to a second embodiment of the invention; [35] FIG. 4 is a perspective view illustrating a connecting rod of a multiaxial spinal fixation device according to a third embodiment of the invention; [36] FIG. 5 is a plan view of FIG. 4;

[37] FIG. 6 is a side elevation view of FIG. 4;

[38] FIGS. 7 to 11 are perspective views illustrating connecting rods of a multiaxial spinal fixation device according to a fourth embodiment of the invention; [39] FIG. 12 is a perspective view illustrating a connecting rod of a multiaxial spinal fixation device according to a fifth embodiment of the invention;

[40] FIG. 13 is an assembled perspective view of FIG. 12, which is partially cut away;

[41] FIG. 14 is a perspective view illustrating a pedicle screw of a spinal fixation device according to the invention; [42] FIGS. 15 to 17 are views illustrating a pedicle screw and a connecting rod of a multiaxial spinal fixation device according to the invention, in which the pedicle screw is coupled with the connecting rod; [43] FIGS. 18 and 19 are views illustrating a variation of the pedicle screw of the multiaxial spinal fixation device according to the invention; and [44] FIG. 20 is a view illustrating the usage of a conventional multiaxial spinal fixation device.

[45] <Major Reference Numerals of Drawings>

[46] 1 : pedicle screw 11 : head

[47] 12: anchor 2: connecting rod [48] 21 : rod portion 22: leaf spring

[49] 22a: elastic portion 22b: connecting portion

[50] 22c: first slit 22d: second slit

[51 ] 22e: third slit 22f : through hole

[52] 22g: protrusion 3: locking member

Mode for the Invention

[53] The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description.

[54] Hereinafter the present invention will be described more fully with reference to the accompanying drawings, in which exemplary embodiments thereof are shown.

[55] It should be appreciated that the same reference numerals and symbols are used throughout the different drawings to designate the same or similar components. In the following description of the present invention, a detailed description of known functions and components incorporated herein will be omitted when it may make the subject matter of the present invention unclear.

[56] FIG. 1 is a perspective view illustrating a first embodiment of the invention, and

FIG. 2 is a view illustrating the usage of the first embodiment of the invention.

[57] As shown in the drawings, a spinal fixation device of the invention generally includes pedicle screws 1, a connecting rod 2 and locking members 3.

[58] First, each of the pedicle screws 1 acts as a stabilizing rod for damaged spinal vertebrae, and has a head 11 in the top portion thereof and a threaded anchor 12 extending downward from the head 11. The head 11 has a receiver 11a having a predetermined depth and having an axially-opened recess in the bottom thereof, and the anchor 12 is stuck into an upper or lower one of the damaged spinal vertebrae.

[59] The connecting rod 2 is seated in the bottom recess of the receiver 1 Ia to connect the screws 1 with each other, thereby correcting the angle or the interval of the spinal vertebrae.

[60] Each of the locking members 3 is inserted into the receiver 1 Ia of a respective pedicle screw 1 to lock the connecting rod 2 so that the rod 2 cannot move freely.

[61] The connecting rod 2 is formed by cutting a single piece of material, and includes cylindrically-shaped rod portions 21 and a leaf spring 22, which is integrally connected to the rod portions 21. The rod portions 21 have an elastic restoring force and are formed in both end portions of the connecting rods. The leaf spring 22 includes an elastic portion 22a, which is wider but thinner than the rod portions 21, and connecting portions 22b, which are smoothly curved without an edge to connect the elastic portion 22a to the rod portions 21.

[62] This type of rod is generally manufactured by Numerical Control (NC) machining, and can be heat-treated to adjust the elasticity of the leaf spring 22.

[63] However, in order to obtain a desired level of elastic force, the length, thickness and width of the elastic portion 22a can be suitably adjusted to set the desired level of elastic force and the maximum refraction angle. Since the raw material has elasticity, the rod portions 21 are also elastic.

[64] In the prior art, the connecting rod and the spring were separately fabricated and then bonded by welding. In that case, the joint was vulnerable to damage or oxidation due to changes in the properties thereof. However, the invention can fundamentally prevent this problem.

[65] While the leaf spring has elasticity in a predetermined direction even with a simple structure, the connecting rod 21 has elasticity with respect to bending in all directions. Accordingly, elasticity when bending in forward/backward directions is different from elasticity when bending in lateral directions, and bending angles in response to pressure are also variable.

[66] In the case of precision fabrication in consideration of the properties of the parts of the leaf spring 22, the forward/backward and lateral bending angles necessary for respective spinal regions can be obtained differently. Thus, an optimal connecting rod, which is easily returned to its original shape by restoring force and minimizes the burden on the movement of the patient, is realized.

[67] FIG. 3 is a perspective view illustrating a connecting rod for pedicle screws according to a second embodiment of the invention.

[68] As shown in FIG. 3, the connecting rod of this embodiment includes at least three rod portions 21 and leaf springs 22, each of which connects one rod portion 21 with an adjacent one.

[69] The connecting rod of this embodiment is preferably applied to connect three or more vertebrae. Here, as described hereinbefore, the leaf springs 22 can be variously shaped to provide an optimum function, which is suitable to a user.

[70] According to this embodiment, fabrication can be facilitated. In addition, a rod can be designed according to optimal rod conditions, which are set in consideration of the statuses of the patient and necessary dimensions. Thus, treatment can be applied according to individual symptoms rather than in an indiscriminate manner. Accordingly, an advanced method of treatment can be performed, which runs counter to the mass production of spinal restorative elements.

[71] Together with the development of a suitable program, when data such as the body size of the patient, necessary elasticity values in respective directions and bending angle for a predetermined force are inputted, a connecting rod can be differently and automatically fabricated in suitable dimensions through NC. This will greatly contribute to the development of spinal fixation technology. [72] FIG. 4 is a perspective view a connecting rod for pedicle screws according to a third embodiment of the invention, FIG. 5 is a plan view of FIG. 4, and FIG. 6 is a side elevation view of FIG. 4.

[73] As a characteristic feature, the connecting rod 2 of this embodiment has an elastic portion 22a placed between rod portions 21, as in the foregoing embodiments. The elastic portion 22a is designed to induce elastic deformation in vertical and horizontal directions, impart restriction against torsion, and have a restoring force.

[74] That is, the elastic portion 22a is substantially rectangular shaped, and as shown in

FIG. 4, includes vertical slits 22'a, which are vertically cut from above and below and are formed at positions at which they do not interfere with each other, and lateral slits 22'b, which are laterally cut from left and right edges without interfering with the vertical slits 22'a.

[75] The vertical slits 22'a and the lateral slits 22'b are formed with a predetermined interval from each other. The vertical slits 22'a are configured to vertically adjust the elastic force and the refraction angle, and the lateral slits 22'b are configured to laterally adjust the elastic force and the refraction angle.

[76] As shown in FIG. 6, the rod portions 21 are eccentric with respect to the elastic portion 22a, so that the rod portions 21 are placed coplanar with one surface of the elastic portion 22a. This functions to minimize location interference with respect to a joint after operation as one coplanar side is arranged opposite the spine.

[77] As shown in FIG. 4, the connecting rod 2 may be integrally formed by cutting or by separately forming the rod portions 21 and the elastic portions 22a followed by welding into one body.

[78] FIGS. 7 to 11 are perspective views illustrating connecting rods for pedicle screws according to a fourth embodiment of the invention.

[79] First, FIG. 7 shows an embodiment having an elastic portion 22a in which one or more first slits 22c alternate with one or more second slits 22d. Each of the first slits 22c is cut from one edge toward the opposite edge of the elastic portion 22a, and has a closed inner end, which is spaced apart at a predetermined interval from the opposite edge of the elastic portion 22a. The inner end of the first slit 22c is expanded in the form of a circle that is larger than the width of the cutting. Each of the second slits 22d is cut from the opposite edge toward the first edge. The first and second slits 22c and 22d alternate with each other at a predetermined interval.

[80] This embodiment makes it possible to adjust the lateral elastic force and the refraction angle in the elastic portion 22a, so that elastic restoring force can be variably applied in forward/backward and left/right directions when the rod portions have little or no elasticity.

[81] This embodiment, illustrated in FIG. 7, can be integrally formed by cutting or welding to provide elastic force, which can be varied in forward/backward and left/ right directions, and can also provide elastic restoring force against torsion. Accordingly, welding can be applied to achieve the effects presented as the major object of the invention.

[82] FIGS. 8 and 9 show variations to the connecting rod for pedicle screws, in which each elastic portion 22a has a plurality of third slits 22e, which extend in the lateral or longitudinal direction and vertically extend through the respective elastic portion 22a.

[83] These variations in the configuration also allow the elasticity of the elastic portion

22a to be easily adjusted.

[84] FIGS. 10 and 11 illustrate variations to the connecting rod for pedicle screws, in which a respective elastic portion 22a has a rectangular through hole 22f , which vertically extends through the elastic portion 22a, and a plurality of protrusions 22g, which extend from one inner edge toward the opposite edge of the through hole 22f in an alternating direction.

[85] These variations have an excellent effect of enhancing the elastic restoring force against torsion.

[86] FIG. 12 is a perspective view illustrating a connecting rod according to a fifth embodiment of the invention, and FIG. 13 is an assembled perspective view of FIG. 12, which is partially cut away.

[87] As shown in FIGS. 12 and 13, the connecting rod 2 of this embodiment includes a single hollow pipe, which is divided into rod portions 21 and an elastic portion 22a, and an elastic body of cable 22t stored inside the hollow pipe.

[88] The rod portions 21 are defined by straight portions of the hollow pipe, and the elastic portion 22a is defined by a portion of the hollow pipe in which a spiral slit 22s is formed. Circular holes 22sh are formed at starting and terminating ends of the spiral slit 22s. Since the rod portions 21 and the elastic portion 22a are vulnerable to deflection, the cable 22t is inserted thereinto. The cable 22t may be implemented with a strand of steel wire having predetermined elasticity, and desirably, with several strands of twisted steel wire.

[89] This embodiment can be elastically deformed irrespective of the direction of torsion, and provides a simple structure, which facilitates an operation. The overall elasticity of this structure can be adjusted by the elastic force of the cable 22t.

[90] FIG. 14 is a perspective view illustrating the pedicle screw of the invention.

[91] As shown in FIG. 14, the pedicle screw 1 includes an anchor 12 having threads formed in the outer circumference thereof and a head 11 attached to one end of the anchor 12. The head 11 is expanded in diameter with respect to the anchor 12, and has a receiver 11a having a predetermined depth having at least one axially-opened recess in the bottom thereof. [92] The pedicle screw 1 of this construction is substantially the same as known pedicle screws. As the characteristic feature of the invention, an elastic member 15 is added into the receiver 11a. The elastic member 15 is in the form of a ring or a plate having a predetermined thickness, and is made of a predetermined material, such as rubber, urethane or silicone, which has excellent elasticity and restorability and does not have any effect on the human body.

[93] The elastic member 15 is interposed between the pedicel screw 1 and the connection rod 2 and, through elastic deformation, compensates for movement transmitted to the pedicle screw 1 and the connecting rod 2.

[94] The elastic member 15 of this construction can be provided in various forms and ways, some of which are proposed as exemplary embodiments of the invention in FIGS. 15 to 17.

[95] Referring to FIG. 15, the elastic member 15 is placed on the bottom of the receiver

I Ia of the head 11 of the pedicle screw 1, the connecting rod 2 is placed on top of the elastic member 15, and the receiver 1 Ia is closed by a locking member 3.

[96] FIG. 16 shows an embodiment in which the elastic members 15 are placed on top and bottom of the connecting rod 2, which is placed in the receiver 1 Ia of the head 11 of the pedicle screw 1. Referring to FIG. 17, the elastic member 15 is interposed between the connecting rod 2 and the locking member 3.

[97] As explained above, the elastic member 15, provided in the receiver 1 Ia of the head

I 1 of the pedicle screw 1, elastically supports the connecting rod 2 to induce elastic deformation in response to the external force acting on the pedicel screw 1 or the connecting rod 2, so that the connecting rod 2 can have freedom of movement in response to the movement of the spine.

[98] FIGS. 18 and 19 illustrate an alternative embodiment of the pedicle screw in a multiaxial spinal fixation device according to the invention. FIG. 18 is a perspective view of the pedicle screw, and FIG. 19 is a longitudinal cross-sectional view of FIG. 18.

[99] As shown in FIGS. 18 and 19, the pedicle screw 1 has an anchor 12 with threads formed in the outer circumference thereof and a head 11, which is attached to one end of the anchor 12 and is expanded in diameter with respect to the anchor 12. The head 11 has a receiver 11a having a predetermined depth in the upper portion thereof, the receiver 11a having at least one axially-opened recess in the bottom thereof.

[100] The anchor 12 is inserted, at the top portion, into the head 11 as shown in the drawing. The top portion of the anchor 12 does not have threads, but is expanded in diameter.

[101] This construction is substantially the same as that of known pedicle screws. As a characteristic feature of the invention, two or more pins p are provided in upper positions, where the top portion (not shown) of the anchor 12 is located, so that the anchor 12, which is vertically inserted into the head 11, is not detached therefrom, and does not play therein.

[102] For this purpose, pin holes h are formed in side portions of the head 11 of the pedicle screw 1, and are spaced apart from each other at a predetermined interval. The pin holes h have threads in the inner circumferences thereof. Each of the rod-shaped pins p, which has threads in the outer circumference, is screwed into and fixed to a respective pin hole h. The interval of the two or more pins p is set to be smaller than the diameter of the anchor 12, and the pins p act to prevent the anchor 12 from being detached from or playing in the head 11.

[103] While the present invention has been described with reference to the particular illustrative embodiments and the accompanying drawings, it is not to be limited thereto, but will be defined by the appended claims. It is to be appreciated that those skilled in the art can substitute, change or modify the embodiments in various forms without departing from the scope and spirit of the present invention.

Claims

[1] A multiaxial spinal fixation device, comprising: a pedicle screw (1), acting as a stabilizing rod for a damaged spine, wherein each of the pedicle screws (1) has a head (11) in a top portion thereof and a threaded anchor (12) extending downward from the head (11), the head (11) having a receiver (1 Ia) having a predetermined depth having an axially-opened recess in a bottom thereof, and the anchor (12) stuck into an upper or lower portion of the damaged spine; a connecting rod (2) seated in the recess of the receiver (1 Ia) to be connected to the pedicle screw (1), thereby correcting an angle or an interval of the spine; and locking members (3), each of which is inserted into each of the screw (1) receivers (1 Ia) to lock the connecting rod (2) from freely moving therein, wherein the connecting rod (2) is formed by cutting a single piece of material, and includes cylindrically-shaped rod portions (21) and a leaf spring (22) integrally connected to the rod portions (21), the leaf spring (22) having an elastic portion (22a), which is wider but thinner than the rod portions (21).

[2] The multiaxial spinal fixation device according to claim 1, wherein the elastic portion (22a) and the rod portions (21) are connected by connecting portions (22b), which are smoothly curved without edges.

[3] The multiaxial spinal fixation device according to claim 1, wherein the elastic portion (22a) is substantially quadrangular and includes vertical slits (22'a), which are vertically cut from above and below and are formed in positions at which they do not interfere with each other, and lateral slits (22'b), which are laterally cut from left and right edges without interfering with the vertical slits (22'a).

[4] The multiaxial spinal fixation device according to claim 1, wherein the elastic portion (22a) has: at least one first slit (22c) cut from a first edge toward an opposite second edge of the elastic portion (22a), and having a closed inner end, which is spaced apart at a predetermined interval from the second edge of the elastic portion (22a), the closed inner end of the first slit (22c) being expanded in a form of a circle that is larger than a width of the cut first slit (22c); and at least one second slit (22d) cut from the second edge toward the first edge of the elastic portion (22a), wherein the first and second slits (22c, 22d) alternate with each other at a predetermined interval.

[5] The multiaxial spinal fixation device according to claim 1, wherein the elastic portion (22a) has a plurality of third slits (22e), which extend in lateral or longitudinal directions and vertically extend through the elastic portion (22a).

[6] The multiaxial spinal fixation device according to claim 1, wherein the elastic portion (22a) has a rectangular through hole (22f), which vertically extends through the elastic portion (22a), and a plurality of protrusions (22g), which extend from one inner edge toward an opposite edge of the through hole (22f) in an alternating direction.

[7] The multiaxial spinal fixation device according to claim 1, wherein the connecting rod (2) has the rod portions (21), which are defined by straight portions of a hollow pipe, adjacent to both ends thereof, the elastic portion (22a) defined by an intermediate portion of the hollow pipe between the rod portions (21), and an elastic cable (22t) inserted into and stored in the hollow pipe, wherein the elastic portion (22a) has a spiral slit (22s) in an outer circumferential portion thereof.

[8] The multiaxial spinal fixation device according to any of the preceding claims 3 to 7, wherein the elastic portion (22) is prepared separately from the rod portions (21) and is then connected thereto by welding, or the rod portions (21) and the elastic portion (22) are integrally formed by cutting a single piece of material.

[9] The multiaxial spinal fixation device according to claim 1 or 3, wherein the connecting rod (2) is eccentrically connected to the elastic portion (22a).

[10] The multiaxial spinal fixation device according to claim 1, wherein the pedicle screw (1) has an elastic member (15) placed in the receiver (1 Ia) of the head (11), in which one end of the connecting rod (2) is inserted, and wherein the elastic member (15) has a shape of a ring or a plate having a predetermined thickness and elastically supports one end of the connecting rod (2).

[11] The multiaxial spinal fixation device according to claim 1, wherein the pedicle screw (1) has pin holes (h) in side portions thereof, which are spaced apart from each other, each of the pin holes (h) having threads in an inner circumference thereof, and pins (p) screwed into the pin holes (h) and crossing the receiver of the pedicle screw (1), whereby a bottom of the connecting rod placed in the receiver of the pedicle screw (1) and a top portion of the anchor are supported.