Abstract:
The present invention relates to an internal anterior transpedicular fixation system and a method for rigidly fixing the spine anteriorly at the level above and below a thoracolumbar burst fracture or tumor. The internal anterior transpedicular fixation system has a support member defining a plurality of engaging portions thereon. At least two of the engaging portions are spaced longitudinally from each other and adapted to span at least one verteba. At least two of the engaging portions are spaced laterally from each other and adapted to span a lateral distance of the verteba. A plurality of fixation elements are provided to mount the engaging portions onto the verteba. Thereby, the support member is restrained from rotational or translational movement relative to the verteba.

Description:
This application claims the benefit of provisional application Ser. No. 60/165,971 filed Nov. 17, 1999. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to a system for correcting spinal deformities anteriorly. More specifically, the present invention relates to an improved anterior transpedicular fixation system and a method for maintaining vertebrae in a desired symmetrical spatial relationship. 
     BACKGROUND OF THE INVENTION 
     Various forms of instrumentation and procedures are known for surgical treatments of spinal disorders, burst fractures, or tumors. For example, Harrington posterior Spinal Instrumentation, Edwards Hooks and Rod Sleeves, Luque Segmental Spinal Instrumentation and Luque Rectangles, and Kostuik-Harrington Instrumentation are commonly used. U.S. Pat. Nos. 4,433,676; 4,653,481; 4,269,178; 4,409,968; and 4,648,388 disclose details of such instrumentations. Some of the above systems utilize hook-type members which are merely hooked over the laminae or on selected transverse processes of the spine. Other systems, such as the Luque Segmental Spinal Rectangles which is used to stabilize spinal fractures and low back fusions, use Luque wires to secure the rectangle to the spine. 
     In some of the prior posterior spinal fixation systems, screws are used to hold a single rod in place. In other systems, screws are used to hold a slotted plate in place. The screws and slots are located so that the plate can be adjusted in order to align the plate apertures or slots with the end of the screw. Typically, a nut is used to hold the plate to the screw. The latter arrangement is also referred to as a Steffee plate, which is a posterior fixation system with the cantilever arrangement. Such a arrangement has the large moments applied to the plate and screw junction, but has little purchase between the plate and the screw and nut since only a small portion of the plate is engaged adjacent to the slots. In addition, the rigid plates is not flexible in locating the fasteners in the vertebrae. The above posterior approaches, even to this level of advancement, do not solve the problem of treating thoracolumbar tumors or burst fractures. 
     In the early 1980&#39;s various anterior fixation devices were developed to allow visualization of bone fragments that were present with burst fractures, so that attention could then be directed toward complete decompression of the canal to provide the best environment for neurological recovery. However, the anterior approach has caused increased operative morbidity due to the very difficult nature of the procedure. Moreover, many of the anterior fixation approaches have problems of potential risk to the vascular network and in complete clearance of the spinal canal. The conventional anterior approaches are not true anterior fixation but anteo-lateral fixations. Most of the anterior systems rely on support from the vertebral body only and therefore cannot be used in the extremely osteoporotic spine because the vertebral body strength is not sufficient. 
     One such system is the Kanada device marketed by Acromed, Inc. of Cleveland, Ohio. The Kanada device utilizes vertebral body staples through which fixation screws are placed into the vertebral body. Rods are then engaged between the screws in the superior and inferior vertebral bodies. Normally two screws are placed in each body. Therefore two rods are needed between the vertebrae. The rods are threaded at their ends to allow compression and distraction. However, the loads are born solely by the vertebral bodies. The posterior column of the spine or pedicle do not share any loads. 
     U.S. Pat. No. 4,289,123 discloses another anterior spinal fixation system, marketed by Zimmer, for treating tumors or thoracolumbar burst fractures. This system is similar to the Kanada device in that it uses rods between the superior and inferior vertebrae. In addition, a pair of large plates are contoured in accordance with the vertebrae and engage with the same through, such as screws. 
     Several plating systems have been developed for anterior internal fixation of the spine. Among these plating systems, the Syracuse I-plate provides a number of differently sized I-shaped plates which are engaged across the burst fracture. However, the Syracuse I-plate does not allow for compression or distraction of a bone graft between the superior and inferior vertebrae. The Stafix plating system, provided by Duma International of Taipai, Taiwan, includes a plate that has a number of screw holes and a single screw slot. The Stafix plate permits quadrilateral placement of bone screws, but not compression or distraction. Moreover, the Stafix plate, as with the above-mentioned anterior plates, can not provide rigid or semi-rigid fixation using bone screws or bone bolts. Moreover, U.S. Pat. No. 5,324,290 discloses an internal anterior fixation systems for treating vertebral burst fractures. The internal anterior fixation system uses an elongated plate which includes integral superior, inferior and bridge portions. The superior and inferior portions are provided for fixation to corresponding vertebrae while the bridge portion spanning between the portions over the affected vertebra. 
     Therefore, it is an object of the present invention to provide a fixation system that is capable of efficient management of thoracolumbar burst fractures and tumors and of easy implantation, to thereby reduce operative morbidity. Another object is to provide a system which permits anterior load sharing by the fixation system, posterior load sharing by posterior vertebral structure. Yet another object is to provide a fixation system that has compression and/or distraction function. 
     SUMMARY OF THE INVENTION 
     The present invention relates to an anterior transpedicular fixation system having longitudinal and transverse support members. The support members are connected to each other and mounted onto one or more vertebrae to support the spine and to prevent rotational or translational movement of the support members. The anterior transpedicular spinal fixation system allows a surgeon the full access to the disc area, captures two cortical surfaces via transpedicular screws or rods insertion, and pulls the two vertebral bodies closer to each other insuring a tight fusion. Therefore, the anterior transpedicular spinal fixation system is capable of distributing compressive loads to the support members, the vertebral body, and the posterior column of the spine, restraining the support members from rotational and translational movement, and preventing displacement of the graft material. 
     In one embodiment, the anterior transpedicular fixation system comprises a pair of supporting plates each having a first engaging portion, a second engaging portion, and a bridge portion integrally spanning between the first and second engaging portions. The first and second engaging portions each define a receiving portion, such as an opening. Moreover, a plurality of fixation elements are provided each adapted to extend through one the openings and be mounted onto a vertebra. Further, the anterior transpedicular spinal fixation system comprises a joining member adapted to connect the bridge portions of the supporting plates. It is preferred that the components of the anterior transpedicular spinal fixation system are made of rigid materials. As a result, the supporting plates are restrained from rotational or translational movement. In an alternative embodiment, the bridge portions of the supporting plates and the clamping member are merged into one unitary member to provide both longitudinal and transverse support to the spine. 
     The present invention also relates to a method for maintaining vertebrae in a desired relationship. The surgical process according to the present invention includes removing the patient&#39;s intervertebral disc or vertebral body, inserting the bone graft material to replace the extracted anterior column, pre-drilling pilot screw holes on both cordices of the pedicle and the vertebral body, and mounting a support member to the vertebral body to increase its mechanical stability and to distribute rotational and translational loads to the support members, the vertebral body, and the posterior column of the spine. 
     These and other features and advantages of the present invention will be readily apparent from the following detailed description of the invention, the scope of the invention being set out in the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The detailed description of the present invention will be better understood in conjunction with the accompanying drawings, wherein like reference characters represent like elements, as follows: 
     FIG. 1 is a lateral diagrammatic view of one embodiment of the spinal anterior fixation system of the present invention, mounted on a portion of a spinal column. 
     FIG. 2 is a top view of the spinal fixation system of the present invention of FIG. 1, which conforms to the transpedicular of the spine; 
     FIG. 3 is an anterior diagrammatic view of the spinal fixation system as illustrated in FIGS. 1 and 2, which is held in a desired position; 
     FIG. 4 is an elevational view of the supporting plates of the spinal fixation system of FIGS. 1 to  3 , which supporting plates are joined by a clamping member; 
     FIG. 5 is an elevational view showing one embodiment of a supporting plate of FIG. 4; 
     FIG. 6 is an elevational view of one embodiment of a transpedicular screw of FIGS. 1 to  3 ; 
     FIGS. 7 a  and  7   b  are transverse cross-sectional and elevational views of a fastener member of FIGS. 3 and 4; 
     FIGS. 8 a  and  8   b  are longitudinal partial cross-sectional and elevational views of a clamping member of the fixation system of FIG. 4; and 
     FIG. 9 is an anterior diagrammatic view of an alternative embodiment of the anterior spinal fixation system of the present invention, in which the supporting plates and the clamping member are integrated into a unitary member. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Exemplary anterior transpedicular fixation systems embodying the principles of the present invention are shown throughout the drawings. The anterior transpedicular fixation system of the present invention is adapted to be mounted onto one or more vertebrae to support the spine and to prevent the same from rotational or translational movement. In the following description of various embodiments of anterior transpedicular fixation systems, similar elements or components thereof are designated with reference numbers that have the same last two digits and redundant description is omitted. 
     FIGS. 1 to  8  illustrate a first embodiment of the anterior transpedicular fixation system  1  formed according to the present invention. The anterior transpedicular fixation system  1  has a support member  10  adapted to span at least one vertebra and to be mounted thereonto. In an exemplary embodiment as shown in FIG. 1, the fixation system  1  includes a pair of supporting plates  10   a  and  10   b  adapted to span one or more vertebrae. For example, the supporting plates  10   a  and  10   b  can span a vertebra S 2  that can have a burst fracture or tumors and can have been subjected to a vertebral body corpectomy. Additionally or alternatively, the fixation system  1  can apply to situations where a vertebral bone graft is inserted between first and second vertebrae, such as superior and inferior vertebrae S 1  and S 3  (see FIG.  1 ). The supporting plates  10   a  and  10   b  can be joined to each other through a joining member  80  and be mounted onto first and second vertebrae, respectively, through fixation elements  24  and  34 . Preferably, the various components of the present invention are made of rigid material. As a result, the anterior transpedicular fixation system  1  of the present invention is capable of providing support for the spine. As the supporting plates  10   a  and  10   b  can be formed similarly, only one of which will be described in great detail as follows. 
     The supporting plate  10   a  can comprise first and second engaging portions  20  and  30  provided at opposite ends of the supporting plate  10   a  and a bridge portion  40  joining the first and second engaging portions  20  and  30 . The first engaging portion  20 , such as a superior engaging portion, can include a first receiving portion  22  for receiving a first fixation element  24 . The first receiving portion  22  can be formed in various ways as will be described below. The first fixation element  24  can be adapted to engage with a first vertebra S 1  to thus mount the first engaging portion  20  of the supporting plate  10   a  onto the first vertebra S 1  as will be described below. Similarly, the second engaging portion  30 , such as an inferior engaging portion, can include a second receiving portion  32  for receiving a second fixation element  34 . The second receiving portion  32  can be formed in various ways as will be described below. The second fixation element  34  can be adapted to engage with the second vertebra S 3  to thus mount the second engaging portion  30  of the supporting plate  30  onto the second vertebra S 3  as will be described below. 
     The first and second receiving portions  22  and  32  can be formed in various ways to facilitate their engagement with the fixation elements  24  and  34 , respectively. For instance, the receiving portions  22  and  32  can be threaded openings adapted to engage with plate thread portions  28  on the fixation elements  24  and  34 . It will be appreciated that other embodiments for engaging the receiving portions  22  and  32  with the fixation elements  24  and  34  are also within the scope of the present invention. 
     The supporting plate  10   a  can be formed so that it can be applied to various spinal anatomy situations and/or span different numbers of vertebrae. In an embodiment as shown in FIGS. 4 and 5, the second receiving portion  32  of the supporting plate  10   a  can be formed as an elongated slot. The second fixation element  34  can extend through and move along the second receiving portion  32  to a desired position depending on the spinal anatomy situations and/or the number of vertebrae that the supporting plate  10   a  spans. The second fixation element  34  can then be fixed to the second receiving portion  32  at the desired position through the mechanism discussed below. As a result, the elongated slot  32  is capable of allowing the supporting plate  10   a  to span a desired number of vertebrae and thus to fit for various spinal anatomy situations. 
     The elongated slot  32  of the supporting plate  10   a  can be formed in various ways. In one embodiment as shown in FIGS. 3 to  5 , the longitudinal axis of the elongated slot  32  extends parallelly to that of the supporting plate  10   a.    
     In one embodiment, the elongated slot  32  can further include a scalloped structure  60  provided thereon. Preferably, the scalloped structure  60  is provided at the interface of the elongated slot  32  and the fastener member  50 , which can include a complementary scalloped structure  54  as will be described below. In a preferred embodiment, the scalloped structure  60  may be curved to engage a curved scalloped surface  56  on the fastener member  50  as will be described below. The elongated slot  32  and/or the scalloped structures  54  and  60  are capable of assisting the application of compression and/or distraction to the vertebrae after the fixation system  1  is partially mounted onto the vertebrae. In an exemplary embodiment, the scalloped slots  32  can allow the fixation elements  34  to be adjusted, oriented, and/or repositioned therein as desired to maintain an appropriate degree of compression or distraction at the fracture or graft site. It will be appreciated that minimizing the distance between the fixed vertebrae is essential to create compression on a bone graft G inserted between the vertebrae as shown in FIG.  1 . 
     The supporting plate  10   a  of the anterior transpedicular fixation system  1  can have any suitable length. Among other factors, the length of the supporting plate  10   a  can be determined according to the spinal anatomy situations and/or the number of vertebrae that the supporting plate  10   a  spans. For example, the length of the supporting plate  10   a  can be between 6 cm and 12 cm. In one embodiment, a plurality of supporting plates  10   a  are formed which are in 1 cm increments. 
     The first and second engaging portions  20  and  30  can be joined to each other through a bridge portion  40 . The bridge portion  40  can be configured to span a burst fracture vertebra S 2 . In a preferred embodiment, the bridge portion  40  can be so formed that its length can be adjusted as desired depending upon the particular vertebral anatomy. As shown in FIGS. 3 and 4, the distance between the first and second engaging portions  20  and  30  can be adjusted by changing the length of the bridge portion  40 . It will be appreciated that various embodiments of bridge portion  40  arc within the scope of the present invention. 
     In a preferred embodiment, the transverse width of the bridge portion  40  is smaller than the width of the first and second engaging portions  20  and  30  of the supporting plate  10   a . Unlike conventional anterior plates, the supporting plate  10   a  of the present invention is capable of limiting its wider portions to the areas that directly interface the vertebrae. The reduced profile of the bridge portion  40  can facilitate the insertion of the supporting plate  10   a  and thus minimize possible trauma to surrounding tissue without affecting the stability of the supporting plate  10   a  in maintaining the fixation of the region. 
     The anterior transpedicular fixation system  1  of the present invention further comprises first and second fixation elements  24  and  34  adapted to mount the supporting plates  10   a  and  10   b  onto the vertebrae, respectively. As the fixation elements  24  and  34  can be formed similarly, only one of which will be described in great detail as follows. 
     The fixation element  24  can be formed in various ways. In one embodiment, the fixation element  24  can be a transpedicular screw element. The transpedicular screw element  24  can be adapted to extend through the first and second thread openings  22  and  32  on the supporting plates  10   a  and  10   b  and further engage with the vertebrae. In an exemplary embodiment as shown in FIGS. 1,  2 , and  6 , the transpedicular screw element  24  can have the dual-threading design and include a bone screw thread  26  and a plate screw thread  28 . The bone screw thread  26  can be used to purchase of bone and therefore can have a wider pitch and a deeper thread than those of the plate screw thread  28 . The plate screw thread  28  can be adapted to engage with a thread opening  22  (see FIGS. 4 and 5) in the supporting plate  10   a . In an alternative embodiment, the plate screw thread  28  can be adapted to engage with a threaded opening  32  in the fastener member  50 . It will be appreciated that other embodiments of fixation elements  24  and  34  are within the scope of the present invention. 
     In the above embodiment, the transpedicular screw element  24  can have a drill bit end  36  as shown in FIG.  6 . The drill bit end  36  can guide the transpedicular screw element  24  through the verteba and can be removed after the transpedicular screw element  24  is threaded into the supporting plate  10   a . At the other end of the transpedicular screw element  24 , a locking member  38 , such as a locking nut (see FIG.  6 ), or similar locking devices is provided. The locking member  38  can engage with the posterior surface of the vertebrae column after the transpedicular screw element  24  is inserted into vertebra and mounted to one of the first and second engaging portions  20  and  30  as shown in FIGS. 1 and 2. Because the pedicle is the strongest vertebral structure, the anterior transpedicular fixation system  1  of the present invention allows loads to be distributed between and shared by the pedicles P and the supporting plates  10   a  and  10   b.    
     In another embodiment, the fixation element  24  can further comprise a fastener member  50 . The fastener member  50  can be adapted to mount the fixation element  24  onto the second receiving portion  32 . In an exemplary embodiment, the fastener member  50  can have a threaded opening  52  for engaging with plate thread portions  28  on the fixation elements  24  and  34 . 
     Additionally or alternatively, the fastener member  50  can have a scalloped structure  54  (see FIGS. 7 a  and  7   b ) for engaging with a complementary scalloped structure  60  on the second receiving portion  32  of the supporting plate  10   a . In an exemplary embodiment, the scalloped structure  54  can be curved, such as that shown in FIGS. 7 a  and  7   b . In a preferred embodiment, the curved scalloped structure  54  is a semi-circular surface. The scalloped structures  54  and  60  allow the fastener member  50  to be adjusted and oriented in the second receiving portion  32  as desired when applying compression and/or distraction to the vertebrae. It will be appreciated that other embodiments of the fastener member  50  are also within the scope of the present invention. 
     The anterior transpedicular fixation system  1  of the present invention further comprises a joining member  80  adapted to join the supporting plates  10   a  and  10   b . The length of the clamping member  80  can be varied to accommodate different width of the vertebrae of patients. The joining member  80  can be formed in various ways. In an exemplary embodiment, the joining member  80  can be a two-piece clamping member include two half members  82 , as illustrated in FIGS. 3,  4 ,  8   a , and  8   b . The two-piece joining member  80  can be adapted to join each other by various conventional clamping mechanism, such as clamping screws  84 . 
     As shown in FIG. 4, the two half members  82  are adapted to sandwich the bridge portions  40  of the supporting plates  10   a  and  10   b . Each half member  82  can have at least one screw opening  86  thereon for receiving the clamping screws  84 . By tightening the clamping screws  84 , the supporting plates  10   a  and  10   b  can be clamped and fixed in relation to each other and thus restrained from rotational and translational movement. Accordingly, the joining member  80  can form a stable, firm, and symmetrical structure, which allows optimum anterior load distribution between the joined vertebrae and the supporting plates  10   a  and  10   b . It will be appreciated that other embodiments of the joining member  80  are also within the scope of the present invention. 
     The anterior transpedicular system  1  of the present invention can be made of any suitable material. Preferably, the material forming the anterior transpedicular system  1  is a material that is bio-compatible. Additionally or alternatively, the material can have the required stiffness for anterior fixation of the spine. Exemplary materials can be FDA approved human implant metals (e.g., 316L stainless steel), titanium, and titanium alloy (e.g., titanium-vanadium-aluminum). It will be appreciated that other applicable materials are also within the scope of the present invention. 
     In a typical surgical procedure, the fixation elements  24  and  34  are inserted into and through a patient&#39;s vertebae. Then the fixation elements  24  and  34  are made to extend through and partially engage with the receiving portions  22  and  32  of the supporting plates  10   a  and  10   b . After applying compression and/or distraction to the supporting plates  10   a  and  10   b , the fixation elements  24  and  34  can be completely joined with the receiving portions  22  and  32  to fix the supporting plates  10   a  and  10   b  to the patient&#39;s vertebrae, thereby forming a solid fixation. In the embodiment where transpedicular screws are used as the fixation elements  24  and  34 , such transpedicular screws are inserted into a patients vertebae and the threaded holes  22  and  32  in the supporting plates  10   a  and  10   b . Before the transpedicular screws  24  and  34  are to be firmly tightened, compression and/or distraction is applied to the supporting plates  10   a  and  10   b.    
     FIG. 9 shows an alternative embodiment of the anterior transpedicular system of the present invention. In the following description, elements or components similar to those in the embodiment of FIGS. 1 to  8 , are designated with the same reference numbers increased by  100  and redundant description is omitted. 
     According to the anterior transpedicular fixation system  101 , the supporting plates  110   a  and  110   b  are integrated with the joining member  180  to form a unitary member. As a result, the anterior transpedicular fixation system  101  comprises longitudinal and transverse support members  110  and  180  that are integrally formed. The longitudinal support member  110  is adapted to span at least one vertebra. The transverse support member  180  is adapted to accommodate different width of the vertebrae of patients. The anterior transpedicular fixation system  101  also comprises a plurality of fixation elements  124  and  134  adapted to mount the anterior transpedicular fixation system  101  onto a patient&#39;s vertebac. It is preferred that the various components of the anterior transpedicular fixation system  101  are made of rigid materials. Accordingly, the anterior transpedicular fixation system  101  of the present invention is capable of supporting the spine and preventing vertebrae from rotational or translational movement. 
     It will be appreciated that the various features described herein can be used singly or in any combination thereof. Therefore, the present invention is not limited to only the embodiments specifically described herein. While the foregoing description and drawings represent a preferred embodiment of the present invention, it will be understood that various additions, modifications and substitutions can be made therein without departing from the spirit and scope of the present invention as defined in the accompanying claims. The presently disclosed embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, and not limited to the foregoing description.