Patent Publication Number: US-2011071636-A1

Title: Displacement Leaf Spring and Artificial Intervertebral Disc Containing the Same

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the displacement leaf spring and the artificial intervertebral disc containing the same, particularly about the artificial intervertebral disc using the displacement leaf spring to cushion axial compression. 
     2. Prior Art Introduction 
     With the growth of the human body age, the organs of the body will slowly degenerate over time. In terms of spine, the intervertebral disc is one of the structures which is the easiest to degenerate over time. The intervertebral disc is between the upper vertebral body and the lower vertebral body to be the main connecting support structure and also the main cushion structure to sustain the axial compression of the spine. When the intervertebral disc degenerates, the lower water content often results in the decreasing of the intervertebral joint&#39;s height and the loss of flexibility simultaneously, which brings about compression of nerve roots or spinal cord, and then causes pathological changes. The condition includes pain in partial body of the patient, weakness of extremities, neuralgia, paraesthesia or function disturbance, and the foregoing makes the patient extremely indisposed. 
     When intervertebral disc of the patient degenerates or with pathological changes, the common surgery is spinal interbody fusion. The principle of spinal interbody fusion is to transplant the cage to the place between the two vertebrae of a patient. The cage is used to restore or maintain intervertebral spacing and avoid the compression of nerve roots, which may cause other diseases to complicate at the same time. Eventually, combine the vertebral body with the artificial intervertebral disc just as the real one to make the structure of vertebral body much firmer. However, spinal interbody fusion will increase the stress around the vertebral body, which leads to compensatory degeneration also known as secondary degeneration and increases the activity of forward tilting, backward tilting, and rotating motility of adjacent joint. Above mention will accelerate the degeneration and pathological changes of adjacent joint, therefore the development of keeping the primary range of movement of the real intervertebral disc is important to retrieve the defect of the spinal interbody fusion. 
     There are a variety of products of artificial intervertebral discs nowadays; even so, most of the conventional artificial interverbral discs can only provide moderate angular displacement for the upper vertebral body and the lower vertebral body to simulate the structure of the human body, but not like the real interverbral discs having elasticity to cushion the axial compression between two vertebrae. The axial compression between two vertebrae is unavoidable, for example, going upstairs and downstairs, walking, and so forth. The biggest shortcoming of the current artificial intervertebral disc is that most of them do not have axial cushion structure so that the artificial intervertebral discs have to absorb the compression directly and will be damaged early. 
     In view of the above, several artificial intervertebral discs having axial cushion structure such as U.S. Pat. No. 5,893,889 using an annular shock absorbing member  68  composed of flexible material and a shock absorbing plug  69  to absorb axial shock energy. 
     Further, as shown in US publication number US2002/0130112A1, U.S. Pat. No. 6,520,996, and U.S. Pat. No. 6,802,867, these patents use the axial support  200  composed of flexible material and plurality of torsional supports  300 A,  300 B to connect the first plate  100  and the second plate  102 , wherein the torsional supports  300 A,  300 B are used to provide sufficient resistance to bending and torsion to allow the artificial intervertebral disc to support surrounding tissue and prevent injury due to excessive bending or torsion, and the axial support  200  is used to cushion the axial compression between vertebral bodies. 
     In addition, as shown in US publication number US2004/0073310A1, this patent uses the articulating core member  51  to cushion the axial compression between two vertebrae, and flexible polymer installed around the articulating core member  51  to cushion the torsion between two vertebrae. 
     Further, as shown in US publication number US2005/0197702A1, this patent is about an artificial intervertebral disc composed of flexible polymer material and shaped into a hollow ring, wherein the artificial intervertebral disc comprising a valve  20 , the valve  20  providing access to the interior  19  of the artificial intervertebral disc so that fluid  22  may be injected into, or removed from, the interior  19  of the artificial intervertebral disc to cushion all sorts of compression between two vertebrae. 
     Furthermore, as shown in US publication number US2005/0228500A1 and US2007/0168033A1, these patents use the fibrous compressible element  17  composed of the fiber  16  to simulate the displacement capability of the real intervertebral disc under the condition of being compressed by placing the fibrous compressible element  17  between two vertebrae. 
     As shown in US publication number US2005/0251260A1, the characteristic of this patent is using the spring element  30 , the elastomeric strut  54 , or the recess  362  to form a flexible space which is similar to a leaf spring in order to cushion the axial compression between two vertebrae. 
     Further, as shown in U.S. Pat. No. 7,001,433, this patent uses the combination of the ball bearing body  13  which is flexible and the bearing body  17  to cushion the axial compression between two vertebrae. 
     As shown in US publication number US2006/0064169A1, this patent reveals the diversified use of combination or application mode of the spring  112  and piston assembly  110  which is used to be the structure to cushion the compression. 
     As shown in U.S. Pat. No. 7,001,433 and US publication number US2006/0293753A1, these patents use polymeric material to wrap all kinds of cushion elements such as spring, damping spring, and structure beam to make the artificial intervertebral disc have a more powerful cushion structure. 
     Furthermore, as shown in US publication number US2006/0178744A1, this patent uses the core  216  to achieve the purpose of torsion activity, wherein this patent uses the elastic element of inner sandwich structure of the plate  230  and  232  to cushion the axial compression between two vertebrae. 
     Finally, as shown in US publication number US2006/0282165A1, this patent uses structure which is similar to a leaf spring only to cushion the axial compression between two vertebrae but not to provide the function of torsion activity between two vertebrae. 
     The above prior arts all have the function to cushion the axial compression between two vertebrae, but fewer of them can simulate the displacement capability of the real intervertebral disc under the condition of being compressed, wherein only the elastomer knitted by fiber can achieve forgoing goal; however, the elastomer knitted by fiber can not provide a wide range of torsion activity angle as the other artificial intervertebral disc shown above. The conventional artificial intervertebral disc can not provide both the displacement capability of the real intervertebral disc under the condition of being compressed and a wide range of torsion activity angle at the same time, which is a defect that all current techniques extremely want to improve. 
     Furthermore, the majority of the aforementioned technologies are only conceptual designs used to describe the function of how to cushion the compression; when it comes to product-oriented structure, it may be totally different from the conventional structure so that the cost of aforementioned artificial intervertebral disc will be too high and then result in economic stress of the patient. If disregarding the compatibility between aforementioned artificial intervertebral disc and the modern surgical instrument, the conceptual design may easily lead to a technical gaps and difficulties during practical surgical operation. The above is a tough question that the design of the artificial intervertebral disc has to overcome. 
     SUMMARY OF THE INVENTION 
     Due to the defect of foregoing artificial intervertebral discs, the present invention provides a displacement leaf spring and an artificial intervertebral disc containing the same. When using the displacement leaf spring, the artificial intervertebral disc can have a wide range of torsion activity angle and capability to cushion the axial compression, just like the real one. 
     In order to achieve above purpose, the present invention comprising the displacement leaf spring, and the displacement leaf spring comprising an upper plate, an inclined plate, and a lower plate, wherein the upper plate having a first breach, and the inclined plate having a first connecting side which connects to one side of the first breach. There is an angle between the inclined plate and the upper plate. The inclined plate further having a second breach, and the lower plate having a second connecting side which connects to one side of the second breach. There is an angle between the lower plate and the inclined plate, and the lower plate parallels the upper plate. In addition to the displacement leaf spring, the artificial intervertebral disc further comprising a top plate, a bottom plate, a core structure, and a socket structure, wherein the top plate and the bottom plate connect to the bottom of the upper vertebral body and the top of the lower vertebral body respectively; the form of the core structure fits in the socket structure, and the core structure and the socket structure are installed between the top and the bottom plate. Above shall be the basic structure of the present invention. 
     By the above-mentioned technical solution, the present invention compared to known technology has at least the following advantages:
         1. The use of the conventional artificial intervertebral discs composed of elastic buffer makes the activity angle of the upper and the lower vertebral body restricted. The core structure and the socket structure of the present invention are installed between the top plate and the bottom plate, and then the top plate and the bottom plate connect to the bottom of the upper vertebral body and the top of the lower vertebral body respectively, which makes the artificial intervertebral disc have a wide range of activity angle.   2. The conventional artificial intervertebral disc composed of elastomer which can be compressed in irregular or vertical direction such as spring, piston, and elastic buffer to cushion the axial compression. The use of the displacement leaf spring in the present invention is to cushion the axial compression of the artificial intervertebral disc. When the displacement leaf spring is compressed in the vertical direction, it absorbs the compression, which is just like the same function as the real intervertebral disc absorbing the compression; after that, said function results in lateral displacement.   3. The use of the displacement leaf spring and the artificial intervertebral disc in the present invention make the present invention have a wide range of activity angle and simulate the function of the real intervertebral disc to absorb the compression and then result in displacement.   4. Considering the compatibility between the artificial intervertebral disc of the present invention and the conventional artificial intervertebral disc, the present invention is made to fit the structure of conventional artificial intervertebral disc as far as possible, so that the present invention can make use of the known surgical instruments and procedures to avoid the trouble and risk of surgical operations, which provides patients with significant usage security and improves the effect of operations.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an external appearance schematic drawing of the displacement leaf spring of the present invention. 
         FIG. 2  is a cross-sectional view of the present invention of  FIG. 1  taken along line A-A. 
         FIG. 3-1  is the first schematic side view of the displacement leaf spring of the present invention. 
         FIG. 3-2  is the second schematic side view of the displacement leaf spring of the present invention. 
         FIG. 4-1  is the first decomposition chart of the artificial intervertebral disc equipped with the displacement leaf spring of the present invention. 
         FIG. 4-2  is the second decomposition chart of the artificial intervertebral disc equipped with the displacement leaf spring of the present invention. 
         FIG. 5-1  is the first side view of the artificial intervertebral disc equipped with the displacement leaf spring of the present invention. 
         FIG. 5-2  is the second side view of the artificial intervertebral disc equipped with the displacement leaf spring of the present invention. 
         FIG. 5-3  is the first front view of the artificial intervertebral disc equipped with the displacement leaf spring of the present invention. 
         FIG. 5-4  is the second front view of the artificial intervertebral disc equipped with the displacement leaf spring of the present invention. 
         FIG. 6  is another decomposition chart of the artificial intervertebral disc equipped with the displacement leaf spring of the present invention. 
         FIG. 7  is another cross-sectional view of the artificial intervertebral disc equipped with the displacement leaf spring of the present invention. 
         FIG. 8  is another decomposition chart of the artificial intervertebral disc equipped with the displacement leaf spring of the present invention. 
         FIG. 9  is another cross-sectional view of the artificial intervertebral disc equipped with the displacement leaf spring of the present invention. 
         FIG. 10  is another external appearance schematic drawing of the displacement leaf spring of the present invention. 
         FIG. 11  is a cross-sectional view of the present invention of  FIG. 10  taken along line B-B. 
         FIG. 12  is another external appearance schematic drawing of the displacement leaf spring of the present invention. 
         FIG. 13  is a cross-sectional view of the present invention of  FIG. 12  taken along line C-C. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     These and other aspects and embodiments will be described in further detail below, with reference to the drawing figures. 
     In the first place, there is a structure of the displacement leaf spring  10  of the present invention with reference to  FIG. 1  and  FIG. 2 , the thing which shown in the figure is only a better embodiment of the present invention and is not intended to be limited to one or the other of above embodiment, wherein the displacement leaf spring  10  comprises an upper plate  11 , an inclined plate  12 , and a lower plate  13 ; the upper plate has a first breach  111 , the inclined plate  12  has a first connecting side  101  which connects to one side of the first breach  111 , and there is an angle between the inclined plate  12  and the upper plate  11 ; the inclined plate  12  further has a second breach  121 , the lower plate  13  has a second connecting side  102  which connects to one side of the second breach  121 , and there is an angle between the lower plate  13  and the inclined plate  12  to make the lower plate  13  parallel the upper plate  11 . Above shall be the basic structure of the displacement leaf spring  10  in the present invention, wherein the upper plate  11 , the inclined plate  12 , and the lower plate  13  are formed integrally and composed of restoring resilient material so that the displacement leaf spring  10  can cushion and absorb the compression by resilient capability between the upper plate  11  and the lower plate  13 . 
     In order to illustrate the displacement capability of the displacement leaf spring  10  under the condition of being compressed, please refer to  FIG. 3-1  and  FIG. 3-2 ;  FIG. 3-1  and  FIG. 3-2  show the schematic side view of the displacement leaf spring  10 , as shown in the figure, the displacement leaf spring  10  has a Z-shaped appearance. As shown in  FIG. 3-1 , the relative vertical length between the upper plate  11  and the lower plate  13  is marked as H, and the relative horizontal length between the upper plate  11  and the lower plate  13  is marked as W. When there is axial force imposed on the upper plate  11  and the lower plate  13 , the displacement leaf spring  10  will be compressed and then deformed as shown in  FIG. 3-2 ; in this condition, the relative vertical length between the upper plate  11  and the lower plate  13  is marked as H 1 , and the relative horizontal length between the upper plate  11  and the lower plate  13  is marked as W 1 . As shown in  FIG. 3-1  and  FIG. 3-2 , the vertical length H is longer than the vertical length H 1 , and the horizontal length W 1  is longer than the horizontal length W. It can be saw clearly that the vertical length between the upper plate  11  and the lower plate  13  will be reduced, and the horizontal length between the upper plate  11  and the lower plate  13  will be changed as well when the displacement leaf spring  10  under the condition of being compressed; that is to say, besides the vertical displacement capability of the displacement leaf spring  10  under the condition of being compressed, there will be a kind of horizontal displacement (from horizontal length W to horizontal length W 1 ) capability provided. 
     The use of said displacement leaf spring  10  can cushion the compression and provide a kind of horizontal displacement property; moreover, the use of said displacement leaf spring  10  can apply to an artificial intervertebral disc  100 .  FIG. 4-1  shows a decomposition chart of the artificial intervertebral disc  100  equipped with displacement leaf spring  10 , wherein said decomposition chart of artificial intervertebral disc comprises a top plate  31  and a bottom plate  32 , the top plate  31  and the bottom plate  32  connect to the bottom of the upper vertebral body  41  (shown in  FIG. 5-3 ) and the top of the lower vertebral body  42  respectively; the artificial intervertebral disc  100  further comprises a core structure  21  and a socket structure  22 , wherein the form of the core structure  21  fits in the socket structure  22 , and the core structure  21  and the socket structure  22  are installed between the top plate  31  and the bottom plate  32 . 
     The core structure  21  and the socket structure  22  of the present invention are installed between the top plate  31  and the bottom plate  32 , and then the top plate  31  and the bottom plate  32  connect to the bottom of the upper vertebral body  41  and the top of the lower vertebral body  42  respectively, which makes the artificial intervertebral disc  100  have a wide range of activity angle. The displacement leaf spring  10  provides a characteristic to cushion and absorb the axial compression. The artificial intervertebral disc  100  further comprises at least one mounting component  33  which is between the top plate  31  and the bottom of the upper vertebral body  41  and between the bottom plate  32  and the top of the lower vertebral body  42 ; the artificial intervertebral disc  100  can be firmly fixed to the upper vertebral body  41  and the lower vertebral body  42  by the use of the mounting component  33  with reference to the embodiment side view  1  and  2  of artificial intervertebral disc  100  equipped with the displacement leaf spring  10  as shown in  FIG. 5-1  and  FIG. 5-2 . 
     The condition of the displacement leaf spring  10  between the upper vertebral body  41  and the lower vertebral body  42  which changes from not under compression to under compression provides a buffer force for the artificial intervertebral disc  100  to cushion the axial compression. As the embodiment front view  1  and  2  of artificial intervertebral disc  100  equipped with the displacement leaf spring  10  as shown in  FIG. 5-3  and  FIG. 5-4 , the condition of relative movement swing between the upper vertebral body  41  and the lower vertebral body  42  by relative movement between the core structure  21  and the socket structure  22  is used to simulate the displacement characteristic and the torsion angle as the real intervertebral disc under compression, which makes the present invention much closer to the primary intervertebral disc and increases the safety and comfort of the patient. 
     The displacement leaf spring  10  may be installed between the core structure  21  and the top plate  31  as shown in  FIG. 4-1  or between the core structure  21  and the bottom plate  32  as shown in  FIG. 4-2 ,  FIG. 6 ,  FIG. 7 , wherein the artificial intervertebral disc  100  equipped with the displacement leaf spring  10  can be not only composed of independent components separated from each other but composed of a variety of assembly selecting from each component, such as when the displacement leaf spring  10  is installed between the core structure  21  and the top plate  31 , the socket structure  22  and the bottom plate  32  are formed integrally; when the displacement leaf spring  10  is installed between the core structure  21  and the bottom plate  32 , the socket structure  22  and the top plate  31  are formed integrally. 
     In addition, besides the method of forming integrally between the socket structure  22  and the top plate  31  or between the socket structure  22  and the bottom plate  32 , and the connection method between the socket structure  22  and the top plate  31  or between the socket structure  22  and the bottom plate  32  can make use of tenon as shown in  FIG. 4-1 , wherein when the displacement leaf spring  10  is installed between the core structure  21  and the top plate  31 , the bottom plate  32  has two fixed chutes  321 ; the socket structure  22  has two fixed convex portions  221  corresponding to the fixed chute  321  so that the socket structure  22  slides into the fixed chute  321  and then combines with the bottom plate  32  by the fixed convex portion  221 . As shown in  FIG. 4-2 , when the displacement leaf spring  10  is installed between the core structure  21  and the bottom plate  32 , the top plate  31  has two fixed chutes  311 ; the socket structure  22  has two fixed convex portions  221  corresponding to the fixed chute  311  so that the socket structure  22  slides into the fixed chute  311  and then combines with the top plate  31  by the fixed convex portion  221 . The above shall be another condition of connection method between the socket structure  22  and the top plate  31  or between the socket structure  22  and the bottom plate  32 . 
     Another component disposition mode of the artificial intervertebral disc  100  as shown in  FIG. 8  and  FIG. 9 , the displacement leaf spring  10  may be installed between the socket structure  22  and the bottom plate  32  but not limit to the displacement leaf spring  10 , the displacement leaf spring  10  may also be installed between the socket structure  22  and the top plate  31 , and the artificial intervertebral disc  100  equipped with the displacement leaf spring  10  can be not only composed of independent components separated from each other but composed of a variety of assembly selecting from each component, such as when the displacement leaf spring  10  is installed between the socket structure  22  and the top plate  31 , the core structure  21  and the bottom plate  32  are formed integrally; when the displacement leaf spring  10  is installed between the socket structure  22  and the bottom plate  32 , the core structure  21  and the top plate  31  are formed integrally. 
     The best embodiment of the displacement leaf spring  10  of the present invention has been shown above, but there is another embodiment of the displacement leaf spring  10  which can cushion the compression and provide a kind of horizontal displacement with reference to  FIG. 10  and  FIG. 11 , wherein the displacement leaf spring  10  comprises an upper plate  11  and a lower plate  13 ; the upper plate  11  has a bending portion  112 , and the lower plate  13  is able to connect with the bending portion  112  of the upper plate  11 , which makes the lower plate  13  parallel the upper plate  11 . The above is another basic structure of the displacement leaf spring  10 , wherein the displacement leaf spring  10  is formed integrally and composed of restoring resilient material so that the displacement leaf spring  10  can cushion and absorb the compression by resilient capability between the upper plate  11  and the lower plate  13 ; Another embodiment of the displacement leaf spring  10 , please refer to  FIG. 12  and  FIG. 13 , wherein the displacement leaf spring  10  comprising an upper plate  11 , a lower plate  13 , and a third bending portion  14 ; the upper plate  11  has a first bending portion  113  shaped by extending from the edge of the upper plate  11  and then bending inward, the lower plate  13  has a second bending portion  131  shaped by extending from the edge of the lower plate  13  and then bending inward, and the third bending portion  14  extending from two extremities of itself and then connecting to the first bending portion  113  and second bending portion  131  respectively, which makes the upper plate  11  parallel the lower plate  13 . The above is another basic structure of the displacement leaf spring  10 , wherein the displacement leaf spring  10  is formed integrally and composed of restoring resilient material so that the displacement leaf spring  10  can cushion and absorb the compression by resilient capability between the upper plate  11  and the lower plate  13 . The displacement capability of the displacement leaf spring  10  under the condition of being compressed in above-mentioned two embodiments are equal to the best embodiment, which does not have to give unnecessary details. 
     While there have been illustrated and described particular embodiments of the present invention, it will be appreciated that numerous changes and modifications will occur to those skilled in the art, and it is intended in the appended claims to cover all those changes and modifications which fall within the true spirit and scope of the present invention.