Abstract:
An interspinous prosthetic device for insertion between adjacent spinous processes includes an inner/core member having upper and lower surfaces and a resiliently compressible cushion extending around at least the upper and lower surfaces of the inner member. The cushion includes at least one outwardly facing concave surface for engaging one of the spinous processes. The inner member is relatively stiff compared to the cushion.

Description:
[0001]    This application is a divisional of application Ser. No. 11/095,214, filed Mar. 31, 2005, the disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    The present invention relates to an intervertebral prosthetic device for stabilizing the human spine, and a method of manufacturing same. 
         [0003]    Spinal discs that extend between adjacent vertebrae in vertebral columns of the human body provide critical support between the adjacent vertebrae. These discs can rupture, degenerate, and/or protrude by injury, degradation, disease, or the like to such a degree that the intervertebral space between adjacent vertebrae collapses as the disc loses at least a part of its support function, which can cause impingement of the nerve roots and severe pain. 
         [0004]    In these cases, intervertebral prosthetic devices have been designed that can be implanted between the adjacent vertebrae, both anterior and posterior of the column to prevent the collapse of the intervertebral space between the adjacent vertebrae and thus stabilize the spine. 
         [0005]    However, many of these devices are less than optimum from a wear and strength standpoint. Also, since they are relatively stiff, they cannot flex to better accommodate the vertebrae, and do not provide a sufficient amount of shock absorption. 
       SUMMARY 
       [0006]    The intervertebral prosthetic device according to some embodiments of the invention overcomes the above deficiencies by providing increased wear, strength, and shock absorption, as well as a good fit with the anatomy. 
         [0007]    Various embodiments of the invention may possess one or more of the above features and advantages, or provide one or more solutions to the above problems existing in the prior art. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a side (lateral) elevational view of an adult human vertebral column. 
           [0009]      FIG. 2  is a posterior elevational view of the column of  FIG. 1 . 
           [0010]      FIG. 3  is an enlarged, front elevational view of one of the vertebrae of the column of  FIGS. 1 and 2 . 
           [0011]      FIG. 4  is an isometric view of a portion of the column of  FIGS. 1 and 2 , including the lower three vertebrae of the column, and depicting an intervertebral prosthetic device according to an embodiment of the invention implanted between two adjacent vertebrae. 
           [0012]      FIG. 5  is an enlarged isometric view of the prosthetic device of  FIG. 4 . 
           [0013]      FIG. 6A  is a view similar to that of  FIG. 5 , but depicting an alternate embodiment of the prosthetic device of  FIG. 5 . 
           [0014]      FIG. 6B  is an enlarged isometric view depicting an element of the device of  FIG. 6A . 
           [0015]      FIG. 7  is a view similar to that of  FIG. 5 , but depicting an alternate embodiment of the prosthetic device of  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    With reference to  FIGS. 1 and 2 , the reference numeral  10  refers, in general to a human vertebral column  10 . The lower portion of the vertebral column  10  is shown and includes the lumbar region  12 , the sacrum  14 , and the coccyx  16 . The flexible, soft portion of the vertebral column  10 , which includes the thoracic region and the cervical region, is not shown. 
         [0017]    The lumbar region  12  of the vertebral column  10  includes five vertebrae V 1 , V 2 , V 3 , V 4  and V 5  separated by intervertebral discs D 1 , D 2 , D 3 , and D 4 , with the disc D 1  extending between the vertebrae V 1  and V 2 , the disc D 2  extending between the vertebrae V 2  and V 3 , the disc D 3  extending between the vertebrae V 3  and V 4 , and the disc D 4  extending between the vertebrae V 4  and V 5 . 
         [0018]    The sacrum  14  includes five fused vertebrae, one of which is a superior vertebra V 6  separated from the vertebra V 5  by a disc D 5 . The other four fused vertebrae of the sacrum  14  are referred to collectively as V 7 . A disc D 6  separates the sacrum  14  from the coccyx  16  which includes four fused vertebrae (not referenced). 
         [0019]    With reference to  FIG. 3 , the vertebra V 5  includes two laminae  20   a  and  20   b  extending to either side (as viewed in  FIG. 2 ) of a spinous process  22  that extends posteriorly from the juncture of the two laminae. Two transverse processes  24   a  and  24   b  extend laterally from the laminae  20   a  and  20   b,  respectively. Two articular processes  26   a  and  26   b  extend superiorly from the laminae  20   a  and  20   b  respectively, and two articular processes  28   a  and  28   b  extend inferiorly from the laminae  20   a  and  20   b,  respectively. The inferior articular processes  28   a  and  28   b  rest in the superior articular process of the vertebra V 6  to form a facet joint. Since the other vertebrae V 1 -V 4  are similar to the vertebra V 5  they will not be described in detail. 
         [0020]    Referring again to  FIG. 2 , the vertebra V 6  of the sacrum  14  includes two laminae  30   a  and  30   b  extending to either side (as viewed in  FIG. 2 ) of a median sacral crest, or spinous process,  32   a  that extends posteriorly from the juncture of the two laminae. The vertebra V 6  also includes a pair of sacral wings  36   a  and  36   b  that extend laterally from the laminae  30   a  and  30   b,  respectively. Four additional axially-spaced sacral crests, or spinous processes,  32   b - 32   d,  are associated with the fused vertebrae V 7  of the sacrum  14  and extend inferiorly from the spinous process  32   a.    
         [0021]    Referring to  FIG. 4 , it will be assumed that, for one or more of the reasons set forth above, the vertebrae V 4  and V 5  are not being adequately supported by the disc D 4  and that it is therefore necessary to provide supplemental support and stabilization of these vertebrae. To this end, an intervertebral disc prosthetic device  40  according to an embodiment of the invention is implanted between the spinous processes  22  of the vertebrae V 4  and V 5 . 
         [0022]    The device  40  is shown in detail in  FIG. 5  and includes an inner, hollow, endoskeleton, or frame,  42  of a relatively stiff and hard material, such as metal. The frame  42  is formed by two spaced, parallel members  42   a  and  42   b,  and two additional spaced, parallel, members  42   c  and  42   d,  extending perpendicularly to the members  42   a  and  42   b  to form a closed polygon. Each member  42   c  and  42   d  is slightly curved inwardly towards the center of the frame  42 , and are either formed integrally with the members  42   a  and  42   b  or are connected to the latter members in any conventional manner. 
         [0023]    An outer layer  46  of a relatively flexible and soft material, such as silicone, is disposed around the outer surfaces of the frame  42 . The layer  46  has a substantially constant thickness so that the portions  46   a  and  46   b  of the layer  46  that extend over the curved members  42   c  and  42   d,  respectively, are also curved. The layer  46  can be molded in place around the frame, and since this molding technique is conventional, it will not be described in detail. 
         [0024]    When the device  40  is implanted between the spinous processes  22  of the vertebrae V 4  and V 5  as shown in  FIG. 4 , the processes extend in the corresponding curved portions  46   a  and  46   b  of the device. The relative stiff frame  42  adds compressive strength and durability to the device  40 , while the dimensions and shape of the members  42   a - 42   d  making up the frame  42  impart a resilience, or spring-like quality, to the frame thus providing excellent shock absorption. The relatively flexible and soft layer  46  readily conforms to the processes  22  and provides additional shock absorption. 
         [0025]    A prosthetic device according to an alternate embodiment is shown, in general, by the reference numeral  50  in  FIG. 6A . The device  50  includes an inner, hollow, endoskeleton, or frame,  52  of a relatively stiff and hard material, such as metal, disposed within an over mold  56  of a relatively flexible and soft material, such as silicone. 
         [0026]    The frame  52  is better shown in  FIG. 6B  and is formed by two parallel members  52   a  and  52   b  each of which is bent, or curved, in three places to form a substantially M-shaped cross section. Two spaced, parallel, cross-bars  52   c  and  52   d  extend perpendicular to, and between, the corresponding ends of the members  52   a  and  52   b,  and two spaced, parallel, cross-bars  52   e  and  52   f  also extend perpendicular to, and between, corresponding curved portions of the latter members. The cross-bars  52   c,    52   d,    52   e,  and  52   f  are either formed integrally with the members  52   a  and  52   b,  or are connected thereto in any conventional manner. 
         [0027]    The over mold  56  is formed separately from the frame  52  and has an internal space  56   a  that receives the frame  52 . The upper and lower portions  56   b  and  56   c  of the over mold  56  are curved and engage the corresponding spinous processes  22  ( FIG. 4 ) of the vertebrae V 4  and V 5  when the device  60  is inserted between the processes. 
         [0028]    When the device  50  is implanted between the spinous processes  22  ( FIG. 4 ) of the vertebrae V 4  and V 5 , the processes extend in the curved portions  56   b  and  56   c.  Also, the relatively stiff frame  52  adds compressive strength and durability to the device  50 , while providing excellent shock absorption. The relatively flexible and soft over mold  56  readily conforms to the processes  22  and also provides additional shock absorption. 
         [0029]    A prosthetic device according to another alternate embodiment is shown, in general, by the reference numeral  60  in  FIG. 7 . The device  60  includes an inner core  62  having a generally rectangular cross-section and formed of a relatively stiff material, such as hard rubber or plastic. 
         [0030]    An outer layer  66  of a relatively flexible and soft material, such as silicone, is molded around the core  62  in a conventional manner. The upper and lower portions  66   a  and  66   b  of the layer  66  are curved and engage the corresponding processes  22  ( FIG. 4 ) of the vertebrae V 4  and V 5  when the device  60  is inserted between the processes. 
         [0031]    The device  60  could be fabricated by a two-part molding process in which the inner core  62  is initially molded of a relatively stiff, hard rubber or hard plastic. The outer layer  66 , of the relatively flexible and soft material, would then be molded over the core  62 . 
         [0032]    When the device  60  is implanted between the processes  22  of die vertebrae V 4  and V 5  in the manner described above, the relatively stiff and hard material of the core  62  provides compressive strength and durability, while the flexible and soft layer  66  readily conforms to the processes  22  and also provides additional shock absorption. 
       Variations 
       [0033]    It is understood that variations may be made in the foregoing without departing from the invention and examples of some variations are as follows: 
         [0034]    A core, similar to the core  62  of the embodiment of  FIG. 7 , but of a different shape, can be provided in the frames  42  and/or  52 . 
         [0035]    The devices of the above embodiments can be implanted between body portions other than processes of vertebrae. 
         [0036]    The devices of the above embodiments can be inserted between two vertebrae following a corpectomy in which at least one vertebra has been removed. 
         [0037]    The frames  42  and  52 , and the core  62 , may vary in shape, size, composition, and physical properties. 
         [0038]    The outer layers  46 ,  56 , and  66  can be formed by any suitable flexible and soft material other than silicone, can take shapes that are different than those described above, and can be secured over the frames  42  and  52 , and the core  62  other than by molding. 
         [0039]    Any spatial references made above, such as “under”, “over”, “between”, “upper”, “lower”, “top”, “bottom”, etc. are for the purpose of illustration only and do not limit the specific orientation or location of the structure described above. 
         [0040]    The preceding specific embodiments are illustrative of the practice of the invention. It is to be understood, therefore, that other expedients known to those skilled in the art or disclosed herein, may be employed without departing from the invention or the scope of the appended claims, as detailed above. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a screw are equivalent structures.