Patent Publication Number: US-2023157835-A1

Title: Artificial spinal disc and artificial disc insertion method using the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation application of U.S. patent application Ser. No. 17/424,883 filed on Jul. 21, 2021, which is a national-stage entry of international application No. PCT/IB2021/050930 filed on Feb. 5, 2021, and claims priority to Korean patent application No. 10-2020-0045107 filed on Apr. 14, 2020, and the entire contents of the mentioned applications are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to an artificial spinal disc and an artificial disc insertion method using the same, and more particularly, to an artificial spinal disc which is used to replace a damaged disc in the spine for the treatment of a spinal disc related disease and an artificial disc insertion method for inserting an artificial disc into the spine. 
     BACKGROUND ART 
     In general, discs serve as cushions between vertebrae to absorb loads and impacts of the body applied to the spinal column. Discs distribute impacts like springs, hold the vertebrae not to move out of place, separate two vertebrae to prevent nerve compression in the neuroforamina in motion, and help each vertebra to move smoothly. 
     Meanwhile, since discs frequently absorb and transmit vertically applied loads and impacts, a variety of diseases associated with disc trauma can occur, such as spinal stenosis, osteophyte formation, disc herniation, and nerve root compression. One treatment method for diseases associated with discs involves removal of a damaged intervertebral disc, and implanting an artificial disc in the space between two adjacent vertebrae to restore the function of the spine. 
     The artificial disc generally should have a proper thickness and anatomic restoration to restore the original height of the intervertebral disc. 
     Meanwhile, as an example of a conventional artificial disc, Korean Patent No. 10-1964862 discloses an artificial disc for cervical spine including an upper plate, a lower plate and an elastic member, a first groove formed in the shape of a dome on the bottom of the upper plate to receive the top of the elastic member, a circular second groove formed on the upper surface of the lower plate to receive the bottom of the elastic member, a concave portion formed in the shape of a dome recessed downward from the second groove of the lower plate to prevent contact with the bottom of the elastic member, a plurality of upper slots formed on the upper surface of the upper plate in the horizontal direction to prevent anterior movement of the artificial disc, and a plurality of lower slots formed on the bottom of the lower plate in the horizontal direction to prevent anterior movement of the artificial disc. 
     However, the conventional artificial discs require an intricate manufacturing process due to their complex shapes, and often fail to effectively ensure spinal mobility after surgery. 
     Additionally, the conventional artificial discs are implanted by the anterior approach to the spine through the abdomen, and since the anterior approach involves abdominal insertion and implantation, the artificial disc passes through the main arteries and the main veins. Thus, there is an increased risk of damage to the major blood vessels during surgery. Furthermore, the implantable artificial disc may migrate forward, causing a serious danger to the vital structures near the spine. 
     DISCLOSURE 
     Technical Problem 
     The present disclosure is directed to providing an artificial spinal disc which has a simple shape, is easy to manufacture, improves spinal mobility for a patient with a damaged disc and ensures stability after surgery, and an artificial disc insertion method using the same. 
     The present disclosure is further directed to providing an artificial spinal disc which is implanted by the lateral or anterolateral approach to the spine, not the anterior approach, and has an optimal shape for effective lateral implantation to reduce the risk of damage to the major vessels or other vital organs, which may be caused by surgery using the anterior approach, and an artificial disc insertion method using the same. 
     Technical Solution 
     The present disclosure provides an artificial spinal disc inserted between an upper vertebra and a lower vertebra, the artificial spinal disc including an upper disc formed in a plate shape, with top coupled to the upper vertebra, a protruding joint portion including a main joint portion protruding from a lower surface of the upper disc, and one or multiple auxiliary joint portions spaced apart from a side of the main joint portion and protruding from the lower surface of the upper disc, and a lower disc formed in a plate shape, with bottom coupled to the lower vertebra, the lower disc having, on an upper surface, a main joint groove in which the main joint portion is seated and an auxiliary joint groove in which the auxiliary joint portion is seated to allow the protruding joint portion to make multidirectional movements. 
     Here, the auxiliary joint portion may include a first auxiliary joint portion disposed at a distance on one horizontal side of the main joint portion, and a second auxiliary joint portion disposed at a distance on the other horizontal side of the main joint portion. 
     Preferably, the first auxiliary joint portion and the second auxiliary joint portion are symmetrically disposed with respect to the main joint portion on a plane. 
     Each of the first auxiliary joint portion and the second auxiliary joint portion may be formed in a hemispherical shape. 
     Alternatively, each of the first auxiliary joint portion and the second auxiliary joint portion may be formed in a semi-ellipsoidal shape. In this case, each of the first auxiliary joint portion and the second auxiliary joint portion may be formed such that a long axis connecting two points on a plane is disposed along a front-rear direction of a spine. 
     The main joint portion may be formed in a hemispherical shape. 
     Alternatively, the main joint portion may be formed in a semi-ellipsoidal shape. In this case, the main joint portion may be formed such that a long axis connecting two points on a plane is disposed along a left-right direction of a spine. 
     The main joint portion may protrude higher than a protrusion height of the auxiliary joint portion. 
     Further, the protruding joint portion may be integrally formed with the upper disc. 
     Preferably, the upper disc and the lower disc are spaced apart from each other at a distance between the lower surface of the upper disc and the upper surface of the lower disc in a range of 3 mm to 6 mm when the protruding joint portion is seated. 
     Preferably, the first auxiliary joint portion and the second auxiliary joint portion are formed with a smaller planar area than a planar area of the main joint portion. 
     The auxiliary joint portion may be formed such that a center of each of the first auxiliary joint portion and the second auxiliary joint portion is disposed at an anterior portion of a spine with respect to a center of the main joint portion on a plane. 
     The first auxiliary joint portion and the second auxiliary joint portion may be configured to have a same shape and planar area. 
     The upper disc and the lower disc may include a first side formed along one anterior side of the main joint portion and one anterior side of the first auxiliary joint portion, a second side having one side connected to one side of the first side and formed along the other anterior side of the main joint portion and one anterior side of the second auxiliary joint portion to form a set angle with the first side, and a third side having one side connected to the other side of the first side and the other side connected to the other side of the second side and formed along one posterior side of the first auxiliary joint portion and one posterior side of the second auxiliary joint portion. 
     The upper disc and the lower disc may have a plane shape of an approximate triangular shape formed by the first side, the second side and the third side. 
     Meanwhile, the upper disc and the lower disc may be formed in the shape of an isosceles triangle such that two insertion sides of the first auxiliary joint portion or the second auxiliary joint portion are narrow and the third side is long in the horizontal direction, when inserted through the lateral or anterolateral approach to the spine. In this instance, an angle between the first side and the second side with respect to the third side may be 18° to 22°, or an internal angle of intersection between a first imaginary line connecting the center of each of the first auxiliary joint portion and the second auxiliary joint portion and a second imaginary line connecting the center of each of the main joint portion, the first auxiliary joint portion and the second auxiliary joint portion may be 18° to 22°. 
     Each of the upper disc and the lower disc may be arranged with the third side facing an anterior side of a spine. 
     Each of the upper disc and the lower disc may be configured to have one or multiple concave portions on the third side. 
     The upper disc and the lower disc may include a first curved side formed along an anterior side of each of the first auxiliary joint portion, the main joint portion and the second auxiliary joint portion, and curved concavely on a plane, and a second curved side connected to the first curved side, formed along a posterior side of each of the first auxiliary joint portion, the main joint portion and the second auxiliary joint portion and curved convexly on the plane. 
     According to another aspect of the present disclosure, the present disclosure provides an artificial disc insertion method including inserting an artificial disc into an implantation space between an upper vertebra and a lower vertebra of a human body, the artificial disc including an upper disc formed in a plate shape, with top coupled to the upper vertebra, a protruding joint portion including a main joint portion protruding from a lower surface of the upper disc and one or multiple auxiliary joint portions spaced apart from a side of the main joint portion and protruding the lower surface of the upper disc, and a lower disc formed in a plate shape, with bottom coupled to the lower vertebra, the lower disc having, on an upper surface, a main joint groove in which the main joint portion is seated and an auxiliary joint groove in which the auxiliary joint portion is seated to allow the protruding joint portion to make multidirectional movements, wherein the artificial disc is inserted through a lateral or anterolateral approach to a spine and the auxiliary joint portion is first inserted into the implantation space, pushing the artificial disc into the implantation space such that the main joint portion is disposed at a center of the upper vertebra and the lower vertebra on a plane, and adjusting a location of the artificial disc. 
     Advantageous Effects 
     The artificial spinal disc according to the present disclosure and the artificial disc insertion method using the same may provide the following effects. 
     First, the artificial spinal disc according to the present disclosure is easy to manufacture due to its simple shape, and it is possible to improve the spinal mobility and ensure stability after surgery. 
     Second, it is possible to perform safer surgery without any risk of damage to blood vessels or other organs that may occur due to surgery using the anterior approach. This advantage is achieved by implanting the artificial disc with either the lateral or anterolateral approach to the spine, rather than the anterior approach, to avoid risking the vital structures in the human body, and by optimizing the shapes of the upper disc and the lower disc to make lateral or anterolateral implantation easier. 
     Third, the artificial spinal disc according to the present disclosure allows for broader and more free movements, as the location of the center of rotation and the slope of the spine through the main joint portion and the auxiliary joint portion are configured to closely mimic natural movements of the spine to the greatest extent, thereby preventing stress and fatigue with the surrounding tissues and improving a patient&#39;s joint mobility. 
     Fourth, the protruding joint portion includes the main joint portion as well as two auxiliary joint portions to increase the contact surface of the joint within the artificial disc, thereby greatly increasing the stability of spinal mobilization after surgery. Additionally, since the increased contact surface through the main joint portion and the two auxiliary joint portions ensures stability, it is possible to resolve issues concerning the reduced area of the center of rotation that may be involved in the lateral or anterolateral approach. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG.  1    is a plan view showing an artificial spinal disc according to an embodiment of the present disclosure inserted into the spine. 
         FIG.  2    is a plan view showing an artificial spinal disc insertion method according to an embodiment of the present disclosure. 
         FIG.  3    is an exploded perspective view of an artificial spinal disc according to an embodiment of the present disclosure. 
         FIG.  4    is plan and front views showing an upper disc of an artificial spinal disc according to an embodiment of the present disclosure. 
         FIG.  5    is plan and front views showing a lower disc of an artificial spinal disc according to an embodiment of the present disclosure. 
         FIG.  6    is a front view of an artificial spinal disc according to an embodiment of the present disclosure. 
         FIG.  7    is a side view of an artificial spinal disc according to an embodiment of the present disclosure. 
         FIG.  8    is a plan view showing another embodiment of an auxiliary joint portion of an artificial spinal disc according to an embodiment of the present disclosure. 
         FIG.  9    is a plan view showing another embodiment of concave portions formed on the sides of an upper disc and a lower disc of an artificial spinal disc according to an embodiment of the present disclosure. 
         FIG.  10    is a plan view showing another embodiment of an upper disc and a lower disc of an artificial spinal disc according to an embodiment of the present disclosure. 
         FIG.  11    is a plan view showing another embodiment of a main joint portion of an artificial spinal disc according to an embodiment of the present disclosure. 
         FIG.  12    is a plan view showing another embodiment of a main joint portion and an auxiliary joint portion having different shapes in an artificial spinal disc according to an embodiment of the present disclosure. 
         FIG.  13    is a plan view showing another embodiment of an upper disc and a lower disc having different side shapes in an artificial spinal disc according to an embodiment of the present disclosure. 
         FIG.  14    is a perspective view showing another embodiment of an auxiliary joint portion of an upper disc and an auxiliary joint groove of a lower disc in an artificial spinal disc according to an embodiment of the present disclosure. 
     
    
    
     BEST MODE 
     Hereinafter, the preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. 
     First, the present disclosure is inserted and implanted into an implantation space between an upper vertebra and a lower vertebra in place of a damaged disc after the damaged disc is removed, and  FIG.  1    is a plan view showing an artificial spinal disc  500  according to an embodiment of the present disclosure (hereinafter referred to as an ‘artificial disc’) implanted into the spine. In the drawing, the reference number  1  indicates the spinal cord, and the reference number  10  indicates the transverse process of the vertebra. 
     Meanwhile, as shown in  FIG.  2   , an artificial disc insertion method according to an embodiment of the present disclosure inserts the artificial disc  500  into the implantation space between the upper vertebra and the lower vertebra through the lateral or anterolateral approach to the spine, and as opposed to the conventional anterior approach of inserting the artificial disc  500  from the anterior of the spine, this approach avoids the major organs, blood vessels and so on, thereby minimizing the risk of injury associated with artificial disc replacement surgery. 
     Additionally, since the artificial disc  500  of the present disclosure is inserted through the lateral or anterolateral approach to the human body as opposed to the conventional anterior approach, when considering this, the artificial disc  500  may be formed in an anatomically optimal shape to ease the insertion and implantation through the lateral or anterolateral approach to the spine and minimize tissue damage. 
     Prior to description of the artificial disc  500 , the method for inserting the artificial spinal disc will be described with reference to  FIG.  2   . 
     First, the artificial disc  500  is coupled to an insertion instrument (not shown) and inserted into the implantation space between the upper vertebra and the lower vertebra in the human body through the insertion instrument to a set location on the lateral or anterolateral position of the spine. Describing the artificial disc insertion method in detail, first, the narrow side of the artificial disc  500  in which a first auxiliary joint portion  221  or a second auxiliary joint portion  222  is disposed as described below is inserted into the implantation space. In this instance, since the artificial disc  500  has two narrow sides and a wide center, the side of the artificial disc  500  formed in a narrow shape for an easy entry into the tissue in the human body is first inserted, in which the first auxiliary joint portion  221  or the second auxiliary joint portion  222  is disposed. 
     When the first auxiliary joint portion  221  or the second auxiliary joint portion  222  is first inserted, the artificial disc  500  is pushed into the implantation space to place a main joint portion  210  and the second auxiliary joint portion  222  or the first auxiliary joint portion  221  in the implantation space. In this instance, the main joint portion  210  may be disposed at the center of the upper vertebra and the lower vertebra on the plane in the implantation space, and this is a location taking the movement of the spine into account, and the location may be changed depending on the shape of the corresponding spine. 
     Meanwhile, since the artificial disc  500  is inserted by the lateral or anterolateral approach to the spine, when the artificial disc  500  is inserted into in the implantation space, the first auxiliary joint portion  221  and the second auxiliary joint portion  222  are not disposed on the same horizontal line and they are slanted at a set angle. Thus, when the insertion of the artificial disc  500  is completed, it is necessary to adjust the location of the artificial disc  500 . 
     Accordingly, the method ends with adjusting the location of the artificial disc  500  by axially rotating the artificial disc  500  so that the first auxiliary joint portion  221  and the second auxiliary joint portion  222  are disposed on the same horizontal line facing the anterior side of the spine, with the main joint portion  210  disposed at the installation location, i.e., at the center of the upper vertebra and the lower vertebra on the plane, as shown. 
     According to the foregoing description, due to the insertion through the lateral or anterolateral approach to the spine, the artificial disc insertion method of the present disclosure avoids the major organs, the main arteries, the main veins and so on, thereby preventing damage to the human body that may occur during the surgery, and reducing unnecessary dissection, which facilitates post-operative recovery. Additionally, due to the insertion through the lateral or anterolateral approach to the spine, the artificial disc insertion method of the present disclosure can preserve the anterior longitudinal ligament (ALL) in the insertion process, thereby avoiding potentially devastating complications that may occur with anterior extrusion of the artificial disc. 
     Meanwhile, since it is inserted through the lateral approach to the spine, not the anterior approach, the artificial disc  500  is formed with a small width and a large horizontal length for easy lateral insertion, and configured to be inserted using the narrow side as an insertion end. 
     In other words, the artificial disc  500  is formed in an optimal shape for easy lateral insertion into the spine, and hereinafter the details including the shape of the artificial disc  500  will be described. 
     Referring to  FIG.  3   , the artificial spinal disc  500  according to an embodiment of the present disclosure is inserted into the implantation space between the upper vertebra and the lower vertebra adjacent to each other, and may include an upper disc  100 , a protruding joint portion  200  and a lower disc  300 . 
     First, the upper disc  100  is formed in the shape of a plate having a set thickness, and is coupled and fixed to the bottom of the upper vertebra in the implantation space from which the disc has been removed. Although the drawing shows the upper disc  100  formed with an equal width (height), this is an example and the upper disc  100  may be formed with a tapered thickness or varying thickness of each location depending on the shape of the implantation space or the shape of the upper vertebra. 
     Although not shown, the upper disc  100  may be fixed with the upper vertebra through a fixing means. Here, for fixing with the upper vertebra, the fixing means may include a wedge type fixing protrusion (spike) protruding from the upper surface of the upper disc  100 , a porous surface to facilitate the bone growth or a fixing pin, and a variety of other configurations for fixing with the upper vertebra may be applied. The fixing means may be integrally formed with the upper disc  100  into a product in the manufacture of the upper disc  100 . 
     The plane of the upper disc  100  may have an approximate triangular shape as shown, to facilitate the lateral insertion into the spine. However, this is an example, and the upper disc  100  may be formed in various shapes including a streamlined or kidney bean shape, and various embodiments of the upper disc  100  will be described in  FIGS.  9 ,  10  and  12    below. 
     Meanwhile, when the upper disc  100  is formed in the shape of a triangle having a first side  110 , a second side  120  and a third side  130  on the plane, a concave portion  131  may be formed on the third side  130  as shown. To contribute to the material reduction and facilitate the insertion, the concave portion  131  may be formed in various shapes. 
     Referring to  FIG.  4   , the protruding joint portion  200  plays a role in allowing the upper disc  100  and the lower disc  300  to make multidirectional free movements, and through this, closely mimicking natural movements of the spine. 
     The protruding joint portion  200  protrudes downward from the lower surface of the upper disc  100  and comes into contact with the upper surface of the lower disc  300 . 
     The protruding joint portion  200  may be integrally formed with the upper disc  100  using the same material. 
     As shown in  FIG.  4   , the protruding joint portion  200  may include the main joint portion  210  and one or multiple auxiliary joint portions  220 . 
     The main joint portion  210  may be disposed at a location at which joint movements of the spine are made or at the center of the vertebrae on the plane after the implantation of the artificial disc  500 . 
     The main joint portion  210  may be formed in a hemispherical or semi-ellipsoidal shape according to the settings of the range of rotation and the center of mass. 
     Meanwhile, when the shape of the main joint portion ( 210   a  in  FIGS.  11 ,  12  and  13   ) is a semi-ellipsoidal shape, the main joint portion  210   a  is preferably formed such that the long axis connecting two points on the plane is disposed along the left-right direction of the spine. In general, the spine has a larger range of forward-backward movement (extension, flexion) than the range of leftward-rightward movement (lateral bending), and considering this, the long axis is disposed along the left-right direction of the spine to further increase the range of forward-backward movement. 
     The main joint portion  210 , 210   a  preferably protrudes to a larger height than the protrusion height of the auxiliary joint portion  220  (see  FIG.  6   ). The main joint portion  210 , 210   a  responsible for main joint movements has a large protrusion height for effective multidirectional movements. 
     The auxiliary joint portion  220  plays a role in maintaining the coronal and sagittal balance of the artificial disc  500 , and complements and supports the main joint portion  210 , 210   a  that inevitably has a smaller size than the joint of the conventional artificial disc due to the insertion through the lateral or anterolateral approach. 
     The auxiliary joint portion  220  is spaced apart from the side of the main joint portion  210 , and protrudes from the lower surface of the upper disc  100 . In the same way as the above-described main joint portion  210 , the auxiliary joint portion  220  may be integrally formed with the upper disc  100  using the same material. 
     Referring to  FIG.  4   , a pair of auxiliary joint portions  220  may be each disposed on two sides of the main joint portion  210 , spaced apart from each other, and may include the first auxiliary joint portion  221  and the second auxiliary joint portion  222 . 
     The first auxiliary joint portion  221  is disposed at a distance on one horizontal side of the main joint portion  210 . Additionally, the second auxiliary joint portion  222  is disposed at a distance on the other horizontal side of the main joint portion  210 . 
     Here, the first auxiliary joint portion  221  and the second auxiliary joint portion  222  may be configured with the same shape and planar area. 
     Additionally, each of the first auxiliary joint portion  221  and the second auxiliary joint portion  222  may be disposed symmetrically in the horizontal direction with respect to the main joint portion  210  on the plane. In detail, each of the first auxiliary joint portion  221  and the second auxiliary joint portion  222  is configured such that its center is disposed at the anterior portion of the spine with respect to the center of the main joint portion  210  on the plane. 
     Additionally, the first auxiliary joint portion  221  and the second auxiliary joint portion  222  may be formed with a smaller planar area than the planar area of the main joint portion  210 . 
     Here, the main joint portion  210 , the first auxiliary joint portion  221  and the second auxiliary joint portion  222  are preferably arranged in the shape of an isosceles triangle having a long base by connecting the center of each of the main joint portion  210 , the first auxiliary joint portion  221  and the second auxiliary joint portion  222  on the plane. In this instance, each of the main joint portion  210 , the first auxiliary joint portion  221  and the second auxiliary joint portion  222  is disposed adjacent to each vertex location of the triangular shape on the plane, and in this state, the base corresponds to a line connecting the center of each of the first auxiliary joint portion  221  and the second auxiliary joint portion  222 . 
     Meanwhile, referring to  FIG.  4   , the upper disc  100  has the plane shape which is narrow on two sides and long in the horizontal direction on the whole, to ease the lateral insertion into the spine, and this shape facilitates the lateral insertion into the spine. In other words, the upper disc  100  may be formed in the shape of an isosceles triangle having the long third side  130  in the horizontal direction and two insertion sides of the first auxiliary joint portion  221  or the second auxiliary joint portion  222  which are narrow when inserted in the lateral direction of the spine. 
     In detail, when it is assumed that the main joint portion  210  and the pair of auxiliary joint portions  220  are arranged in a triangular shape, an internal angle between two sides (the first side  110  and the second side  120 ) with respect to the base (the third side  130 ) of the triangle is preferably 18° to 22°. Alternatively, an internal angle of intersection between a first imaginary line connecting the center of each of the first auxiliary joint portion  221  and the second auxiliary joint portion  222  and a second imaginary line connecting the center of each of the main joint portion  210 , the first auxiliary joint portion  221  and the second auxiliary joint portion  222  is preferably 18° to 22°. 
     When the angle is less than 18°, the shape of the upper disc  100  increases in the horizontal direction, and a space for formation of the main joint portion  210  reduces, resulting in reduced range of motion of the artificial disc  500 . In contrast, when the angle is higher than 22°, the central width of the upper disc  100  increases and the lateral insertion into the spine may not be easy. 
     The auxiliary joint portion  220  may be formed in a hemispherical or semi-ellipsoidal shape. In this instance, when the auxiliary joint portion  220  is a semi-ellipsoidal shape, the auxiliary joint portion  220  is preferably formed such that the long axis connecting two points on the plane is disposed along the front-rear direction of the spine (see  FIG.  8   ). 
     Further, the main joint portion  210  may be spaced apart in the other direction with respect to one directional same tangent line of the first auxiliary joint portion  221  and the second auxiliary joint portion  222  on the plane, such that the upper side of the main joint portion  210  may be disposed at the lower position than the upper side of the first auxiliary joint portion  221  and the second auxiliary joint portion  222  on the plane. 
     Referring to  FIG.  5   , the lower disc  300  is disposed at a distance below the upper disc  100 , formed in the shape of a plate having a set thickness, and coupled and fixed onto the lower vertebra of the implantation space. 
     The lower disc  300  may be formed with the same width (height) and plane shape to match the upper disc  100 , and may be fixed with the lower vertebra through the above-described fixing means. In the drawing, the lower disc  300  may be formed in an approximate triangular shape having a first side  310 , a second side  320  and a third side  330  to match the plane shape of the upper disc  100 , and in the same way as the upper disc  100 , a concave portion  331  may be formed on the third side  330  as shown. 
     The lower disc  300  may have, on the upper surface, a joint groove in which the protruding joint portion  200  is seated to allow multidirectional movements. The joint groove may be configured to provide translational and rotational movements of the spine such as flexion, extension, side bending, and axial rotation (twisting), while maintaining slidable contact with the side of the protruding joint portion  200 . 
     The joint groove may include a main joint groove  311  in which the main joint portion  210  is seated, and an auxiliary joint groove  312  in which the auxiliary joint portion  220  is seated. 
     Here, the main joint groove  311  may be formed in the same hemispherical or semi-ellipsoidal shape to match the shape of the main joint portion  210 , and the auxiliary joint groove  312  may be formed in the same hemispherical or semi-ellipsoidal shape to match the shape of the auxiliary joint portion  220 , to bring that the main joint portion  210  and the auxiliary joint portion  220  into contact with the main joint groove  311  and the auxiliary joint groove  312 . 
     Meanwhile, an auxiliary joint groove  312   a  may be formed in a different shape from the corresponding auxiliary joint portion  220 , not in the same shape (see  FIG.  14   ). The auxiliary joint portion  220  may be formed in a hemispherical shape and the corresponding auxiliary joint groove  312   a  may be formed in a semi-ellipsoidal shape, and its detailed description will be provided in  FIG.  14    below. 
     The upper disc  100 , the lower disc  300  and the protruding joint portion  200  may be formed from metals such as titanium or carbon alloys or ceramics which are harmless to the human body and can withstand impacts and loads applied to the spine for a long time, but a variety of materials for achieving the above-described object may be applied. 
     Referring to  FIGS.  6  and  7   , when the protruding joint portion  200  is seated, the upper disc  100  and the lower disc  300  are spaced a set distance D apart from each other to allow the joint portion to move. The distance is a factor that affects the range of motion of the artificial disc  500 , and with the increasing distance, the thickness of the upper disc  100  and the lower disc  300  reduces and the stability reduces, and with the decreasing distance, the range of motion reduces. Accordingly, the artificial disc  500  preferably has the vertical distance between the lower surface of the upper disc  100  and the upper surface of the lower disc  300  in the range of 3 mm to 6 mm. As described above, when the distance is less than 3 mm, the side of the upper disc  100  and the side of the lower disc  300  interfere with each other during motion, which affects the motion of the artificial disc  500 , resulting in reduced range of motion. When the distance is more than 6 mm, since the total height from the upper surface of the upper disc  100  to the lower surface of the lower disc  300  is limited to a normal adult&#39;s disc insertion space (height), with the increasing distance between the upper disc  100  and the lower disc  300 , the height (thickness) of the upper disc  100  and the lower disc  300  reduces, causing a problem with durability and stable support. 
     Hereinafter, various embodiments of the upper disc  100 , the lower disc  300  and the protruding joint portion  200  will be described. Prior to description, since the upper disc  100 , the lower disc  300  and the protruding joint portion  200  have been hereinabove described in detail, the detailed description is omitted herein, and the shape and location of each element will be described in detail. 
     In a first embodiment, referring to  FIG.  8   , the plane shape of the upper disc  100  (the lower disc) has an approximate isosceles triangle shape. 
     In detail, the upper disc  100  and the lower disc  300  may have the plane shape of a triangular shape including the first side  110 , the second side  120  and the third side  130 . 
     The first side  110  is connected to one anterior side of the main joint portion  210  and one anterior side of the first auxiliary joint portion  221  with respect to the main joint portion  210 . 
     The second side  120  has one side connected to one side of the first side  110  to form a set angle with the first side  110 , and is connected to the other anterior side of the main joint portion  210  and one anterior side of the second auxiliary joint portion  222 . In this instance, the first side  110  and the second side  120  correspond to two sides of the triangle except the base. 
     The third side  130  has one side connected to the other end of the first side  110  and the other side connected to the other side of the second side  120 , is connected to one posterior side of the first auxiliary joint portion  221  and one posterior side of the second auxiliary joint portion  222 , and corresponds to the base of the triangle. 
     As such, the upper disc  100  and the lower disc  300  may be formed in an approximate triangular shape on the plane by the first side  110 , the second side  120  and the third side  130 . 
     Meanwhile, first, each of the upper disc  100  and the lower disc  300  is preferably positioned such that the third side  130  faces the anterior side of the spine, considering the insertion direction (see  FIG.  1   ). 
     In  FIG.  8   , the main joint portion  210  may be formed in a hemispherical shape, and the first auxiliary joint portion  221   a  and the second auxiliary joint portion  222   a  may be formed in a semi-ellipsoidal shape. In this instance, the auxiliary joint portion  220  is positioned in the up-down direction such that the long axis of the semi-ellipsoid faces the front-rear direction. 
     Additionally, the main joint portion  210  may be configured such that the horizontal tangent line to the uppermost surface is spaced apart in more downward direction than the uppermost horizontal tangent line of the auxiliary joint portion  220  so that the third side  130  may be concave. 
     Further, each of the upper disc  100  and the lower disc  300  may be configured to have one or multiple concave portions  131  on the third side  130 . The concave portion  131  may reduce unnecessary material consumption of the upper disc  100  and the lower disc  300 , and make the central width narrower so that the upper disc  100  and the lower disc  300  have a longer and thinner shape. Although the drawing shows two concave portions  131  each formed on two sides with respect to the main joint portion  210 , this is an example and the number and locations may change. Meanwhile, in addition to the third side  130 , the concave portions  111 , 121  may be respectively formed on a first side  110   a  and a second side  120   a  as shown in  FIG.  9   . 
     In a second embodiment, referring to  FIG.  10   , the upper disc  100  and the lower disc  300  have a third side  130   a  formed in a flat shape, and the main joint portion  210  and the auxiliary joint portion  220  are formed in a hemispherical shape. In this case, the artificial disc  500  is easy to form the shape, and has increased contact area of the upper disc  100  and the lower disc  300  with the upper vertebra and the lower vertebra, respectively, thereby achieving more stable support. 
     In a third embodiment, referring to  FIG.  11   , the upper disc  100  and the lower disc  300  have the third side  130   a  formed in a flat shape, the main joint portion  210   a  is formed in a semi-ellipsoidal shape, and the auxiliary joint portion  220  is formed in a hemispherical shape. In this instance, preferably, the main joint portion  210   a  is horizontally placed with the long axis of the ellipse facing the horizontal direction (the left-right direction of the spine) on the plane as shown. 
     Meanwhile, the foregoing description shows the upper disc  100  and the lower disc  300  configured with an approximate triangular shape as an embodiment. However, the upper disc  100  and the lower disc  300  may have curved sides, and the sides may be formed in a streamlined shape in the insertion direction. 
     A fourth embodiment will be described with reference to  FIG.  12   . The upper disc  100  and the lower disc  300  may be formed with the plane shape in a kidney bean shape including a first curved side  140  and a second curved side  150 . 
     In detail, the first curved side  140  is formed along the anterior side of each of the first auxiliary joint portion  221   a , the main joint portion  210  and the second auxiliary joint portion  222   a  and curves on the plane. The second curved side  150  is connected to the first curved side  140 , and is formed along the posterior side of each of the first auxiliary joint portion  221   a , the main joint portion  210   a  and the second auxiliary joint portion  222   a  and curves on the plane. 
     In the drawing, the first curved side  140  curves convexly, and the second curved side  150  curves concavely. However, this is an example, and both the first curved side  140  and the second curved side  150  may curve concavely to form a streamlined shape. 
     Here, the main joint portion  210   a  may be formed in a semi-ellipsoidal shape, and the first auxiliary joint portion  221   a  and the second auxiliary joint portion  222   a  may be also formed in a semi-ellipsoidal shape. In this instance, when the main joint portion  210   a  is formed in a semi-ellipsoidal shape, the main joint portion  210   a  is preferably positioned with the long axis of the ellipse facing the left-right direction on the plane, and the first auxiliary joint portion  221   a  and the second auxiliary joint portion  222   a  is preferably positioned with the long axis of the ellipse facing the front-rear direction on the plane. 
     In a fifth embodiment, referring to  FIG.  13   , compared to  FIG.  12   , the first auxiliary joint portion  221  and the second auxiliary joint portion  222  may be formed in a hemispherical shape. As described above, the main joint portion  210   a , the first auxiliary joint portion  221  and the second auxiliary joint portion  222  may be formed in various shapes according to the surgery condition and the patient&#39;s condition. 
     Meanwhile, the present disclosure may have the same shape of the first auxiliary joint portion  221  and the second auxiliary joint portion  222  as the shape of the corresponding auxiliary joint groove  312  as described above, but as a different embodiment, the shape of the first auxiliary joint portion  221  and the second auxiliary joint portion  222  and the shape of the auxiliary joint groove  312   a  in contact with them may be different from each other. Describing with reference to  FIG.  14   , the first auxiliary joint portion  221  and the second auxiliary joint portion  222  may be formed in a hemispherical shape, and the corresponding auxiliary joint groove  312   a  may be formed in a semi-ellipsoidal shape. 
     Accordingly, the first auxiliary joint portion  221  and the second auxiliary joint portion  222  of a hemispherical shape may have the increased rotational movement in the auxiliary joint groove  312   a  of a semi-ellipsoidal shape, and through this, rotation between the upper disc  100  and the lower disc  300  increases, thereby allowing rotation in all the front-rear direction (x-axis rotation), left-right direction (y-axis rotation) and up-down direction (Z-axis rotation), and allowing for more diverse and flexible movements of the spine. 
     While the present disclosure has been hereinabove described with reference to the embodiments shown in the drawings, this is provided for illustration purposes only and it will be appreciated by those skilled in the art that various modifications and equivalents may be made thereto. Therefore, the true technical protection scope of the present disclosure should be defined by the technical spirit of the appended claims. 
     
       
         
           
               
             
               
                   
               
               
                 [Detailed Description of Main Elements] 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   100: 
                 Upper disc 
                 110, 110a, 310:       
                 First side 
               
               
                 111, 121, 131, 331:           
                 Concave portion 
                 120, 120a, 320:       
                 Second side 
               
               
                 130, 130a, 330:       
                 Third side 
                 140: 
                 First curved side 
               
               
                 150: 
                 Second curved side 
                 200: 
                 Protruding joint portion 
               
               
                 210: 
                 Main joint portion 
                 220: 
                 Auxiliary joint portion 
               
               
                 221: 
                 First auxiliary joint portion 
                 222: 
                 Second auxiliary joint portion 
               
               
                 300: 
                 Lower disc 
                 311: 
                 Main joint groove 
               
               
                 312: 
                 Auxiliary joint groove 
                 500: 
                 Artificial disc