Patent Application
20160270928
1. Field of the Invention
The invention is related to spinal spacers in general. More specifically, the invention relates to an implantable spinal spacer with a structure which promotes fusion of adjacent vertebral bodies while avoiding stress shielding.
2. Description of the Prior Art
The human spine is a column of stacked vertebrae that allow spinal nerves to exit the spinal cord and connect to the various regions of the body. The intervertebral disc lies between adjacent vertebrae, and acts as a shock-absorbing unit in the spine. However, pathological and age-related changes affecting the intervertebral disk may result in compression of the nerve, which causes pain and inconvenience of moving. In regard to the aforementioned dysfunction of intervertebral disc and many other problems resulted therefrom, common surgical treatment options include interbody fusion surgery, non-fusion surgery and/or implantation of artificial disc; wherein interbody fusion is associated with the accelerated degeneration of adjacent discs and an uncertain outcome. Moreover, an artificial disc does not mimic the typical biomechanical behaviors of a normal intervertebral disc.
In addition, there are a number of factors which influence bone growth, including nutrition, local blood supply, and mechanical environment. Furthermore, specific effects on the bone structure depend on the duration, magnitude and rate of loading. In particular, according to the principle of Wolff's law, when cyclic loading is applied to a bone, bone density increases in response to the load.
It is an object of the present invention to provide a spinal spacer which has deformability as well as the ability to act as a shock absorber.
It is another object of the present invention to provide a spinal spacer which is a compressible device for adapting to spine movements.
It is another object of the present invention to provide a spinal spacer which is capable of receiving higher compression and results in higherer bone density and bone growth.
The spinal spacer of the present invention includes a first plate, a second plate and a middle plate. The first and the second plates are stacked in one single piece and spaced from each other with a distance. The middle plate is located between the first plate and the second plate; wherein the middle plate connects with the first plate on one end to form the first gap, and connects with the second plate on the other end to form the second gap. Both the first and the second plates can move relative to the middle plate, which in turn leads to gap deformation.
The spinal spacer of the present invention is a spinal spacer with deformability as well as the ability to act as a shock absorber; on the other hand, the preferable structure of the spinal spacer of the present invention provides the spinal spacer the ability to move back and forth. In the embodiment shown in
As mentioned above, the middle plate 300 connects with the first plate 100 and the second plate 200; wherein between the middle plate 300 and the first plate 100, a first gap 310 is formed, and between the middle plate 300 and the second plate 200, a second gap 320 is formed. The opening of the first gap 310 and the opening of the second gap 320 are on opposite ends of the spinal spacer 10; in addition, the first gap 310 and the second gap 320 partially overlap in the direction in which the first plate 100, the middle plate 300 and the second plate 200 are stacked up. Alternatively, it may be regarded that the spinal spacer 10 has the first gap 310 and the second gap 320, which extend from opposite ends of the spinal spacer 10 toward the interior of the spinal spacer 10, wherein inside the spinal spacer 10 the first gap 310 and the second gap 320 are staggered. The first and the second gap 310 and 320 allow relative movement of the first plate 100 and the middle plate 300 and relative movement of the middle plate 300 and the second plate 200. Preferably, the above-mentioned back and forth movement accompanies the movements of the first plate 100 and the second plate 200, which leads to deformation of the first gap 310 and the second gap 320. When the first plate 100 and the second plate 200 have relative movements in the height direction of the spinal spacer in substance, the first plate 100 and the second plate 200 have a tendency of returning to the spacing distance “D” from each other as well as the initial height “H”. For example, if the range of restorative motion between the first plate 100 and the second plate 200 is at least 1.6 mm, the spacing D may have a range of approximately 0.8 mm in regard to the closing in of the first plate 100 and the second plate 200, which occurs when the spinal spacer 10 is pressed.
The spinal spacer of the present invention is preferably integrated. In the embodiment shown in
As the top view shown in
The spinal spacer of the present invention further has an indent formed on the first plate, the second plate or both, or has a through hole penetrating the spinal spacer substantially in the direction in which the first plate and the second plate are stacked up. In the embodiment of spinal spacer 10, a through hole 500 penetrates the central part of the spinal spacer 10 in the direction in which the first plate 100 and the second plate 200 are stacked up. The measured area of the opening of the through hole 500 on the outer surface of the first plate 100 or the outer surface of the second plate 200 takes up a range of proportions of the outer surface of the plate; for example, the opening may take up 50% of the measured area of the outer surface. The through hole 500 may be filled with materials such as artificial bone tissue or autologous bone tissue to enhance bone growth and/or bone fusion efficiency as well as increase the stability of the spinal spacer 10 between the vertebrae.
Preferably, the spinal spacer of the present invention has a first end and a second end opposite to the first end. In the embodiment of the spinal spacer 10, the first gap 310 has an opening on the first end 101 and the second gap 320 has an opening on the second end 102; in other words, the first gap 310 and the second gap 320 extend from the first end 101 and the second end 102 of the spinal spacer 10, respectively, toward the interior of the spinal spacer 10. In addition, the first end 101 may be regarded as the front-end with the second end 102 as the rear-end. The front-end and the rear-end are defined based on the direction of the spinal spacer during an operation of implantation, wherein the spinal spacer 10 enters first between the vertebrae by the first end 101 (the front-end). In the embodiment(s) of the present invention, it is preferred to insert the implant from the ventral surface of the human body. For example, the spinal spacer 10 may enter between the vertebrae by the first end 101 in a direction from the ventral surface to the dorsal surface. In this regard, the side of the spinal spacer 10 having the first end 101 is called the dorsal side, and the second end 102 is located on the ventral side.
The spinal spacer of the present invention further includes a lug disposed on the outer side of at least one plate for the disposition of a connecting element and for positioning the spinal spacer. Specifically, the connecting element is coupled with the vertebrae of the two sides of the intervertebral space for positioning the spinal spacer. As the embodiment shown in
The spinal spacer 10a further includes at least two lugs. For example, lugs 600a and 600b are disposed at two opposite sides of the spinal spacer 10a and are connected to the first plate 100 and the second plate 200, respectively. The lug 600a is further disposed on one end of the spinal spacer 10a and substantially stands on the first plate 100; the lug 600b is disposed on the one end of the spinal spacer 10a and stands on the second plate 200. For example, one may dispose the lugs 600a and 600b on the first end 101 and the second end 102 respectively. Further, as the front view shown in
The spinal spacer of the present invention further has a concave hole 700 formed on a surface of one end; wherein the one end is preferably the second end 102 of the spinal spacer 10. In addition, a first protrusion 710 extending toward the second plate 200 is formed from an edge of the first plate 100 of the one end, a second protrusion 720 extending toward the first plate 100 is formed from an edge of the second plate 200 of the one end, wherein the second protrusion 720 and the first protrusion 710 define an opening of the concave hole 700. The concave hole 700 and the protrusions around the opening provide the surgical instrument implanting the spinal spacer 10 between the vertebrae a holding place. The concave hole 700 may be formed from a surface of the second end 102.
When the spinal spacer of the present invention is implanted between the vertebrae, the outer surface of the first plate 100 and the outer surface of the second plate 200 are in contact with the adjacent vertebrae of the intervertebral space; furthermore, because of the deformability, the spinal spacer may auto-adjust finely to have a proper height such as H′/D′ when it is implanted in the intervertebral space; in addition, by means of the outside serration 400, the spinal spacer may be stably engaged between the adjacent vertebrae. On the other hand, hydroxyapatite may be applied to the outer surfaces of the plates so that the surfaces are in firm contact with the adjacent vertebrae by means of the hydroxyapatite applied and therefore have an effect of biologic fixation. In addition, as mentioned above, artificial bone tissue or autologous bone tissue from the operation may be filled into hole 500 to achieve better bone fusion as well as prevent the implanted spinal spacer from displacement, loosening or escaping out of the intervertebral space between two vertebrae, which may result in complications such as disc-height collapse and unstable spine.
In other embodiments, the spinal spacer of the present invention has tapered protrusion(s) formed on the outer side of at least one plate. In the embodiment shown in
In other embodiments, the spinal spacer includes a filling material filling the space among the first plate, the second plate and the middle plate. In the embodiment shown in
The filling material 900 is preferably a biomaterial such as polymeric biomaterial. The filling material 900 is preferably elastic; for example, an elastic material such as silicone is selected as the filling material 900 so that the spinal spacer's structure maintains its deformability and the ability to bounce back. In addition, the filling material 900 reduces the risk of damage to the spinal spacer 10c; for example, the use of filling material 900 avoids stress shielding and reduces damages.
According to the spinal condition of the patient which may vary in degree or kind, the spinal spacer of the present invention such as the spinal spacer 10, 10a, 10b, or 10c may be used. For example, the spinal spacer such as the spinal spacer 10, 10a, 10b, or 10c may be selected based on bone conditions of the end plate.
When the spinal spacer is implanted in the intervertebral space, a height before disc collapse is rebuilt. In addition, because of the deformability and an ability to change in the height direction, the spinal spacer between the vertebrae may auto-adjust in shape finely in accordance with the intervertebral space and the vertebrae; in other words, the spinal spacer is capable of being pressed and the height thereof is variable, and the artificial bone tissue/autologous bone tissue/bone substitute are therefore in firm contact with the vertebral end plates of the upside and underside vertebrae. In addition, the deformable spinal spacer applies force to the bone and therefore stimulates bone growth which acts in conjunction with the aforementioned effect of firm contact to promote bone growth; wherein according to the principle of Wolff's law, loading on the bone results in higher bone density. Since human body has its weight and the force resulted from the weight applied to the bone varies along with human activity, the spinal spacer of the present invention further applies dynamic stress which provides cyclic loading to the bone.
Furthermore, in addition to the whole spinal spacer's bouncing movement in the height direction, the spinal spacer further has a distinctive feature resulted from the first gap 310 and the second gap 320, i.e. the z-shaped structure, wherein the first gap 301 is formed from the first end 101 toward the interior, the second gap 302 is formed from the second end 102 toward the interior. For example, the circumstance may exist when the front-end is less pressed while the rear-end is more pressed, and vice versa. Accordingly, the springing of the spinal spacer of the present invention further caters to a relative movement between the frond side and the rear side of the spine; in other words, the z-shaped structure of the spinal spacer, and the orientation and deformability thereof allow a movement of the vertebrae, wherein the movement is higher in degree and moving angle, which is therefore helpful for avoiding stress shielding.
In view of the above mention, the spinal spacer of the present invention provides the bone a mechanical environment in which close contact with the vertebrae and dynamic pressure applied to the bone are possible. Further, the spinal spacer of the present invention provides a greater area for grafting due to the indent/through hole; the spinal spacer of the present invention promotes circulation of blood flow and nutrition therein by means of the grain/serration/protrusion/groove of the outer surface of the plates. Nutrition and proper mechanical environment which provides elements such as pressure and close contact are key factors for bone growth. In sum, the spinal spacer of the present invention not only maintains a disc height before a complete bone fusion and prevents deformation of the spine, it also shortens the time for bone fusion and increases bone density.
Accordingly, the spinal spacer 10 of the present invention rebuilds the (original) disc height after the implantation of such between the vertebrae; meanwhile, the spinal spacer of the present invention provides the treated area with the ability to move naturally and a range of motion, and eliminates pressure applied to the spinal cord or nerves; wherein with regard to spinal movement, the spinal spacer 10 may effectively share the forces applied to the spine in all directions by means of its deformability and the ability to absorb shock. For example, when a person jumps, falls from a high place, or when the shoulder, back or waist suddenly bear heavy weight, the spinal spacer 10 with its deformability and the ability to absorb shock and pressure, will provide a buffering effect to such shock.
The above is a detailed description of the particular embodiment of the invention which is not intended to limit the invention to the embodiment described. It is recognized that modifications within the scope of the invention will occur to a person skilled in the art. Such modifications and equivalents of the invention are intended for inclusion within the scope of this invention.
