Abstract:
Spinal apparatus is disclosed that includes reference structure spatially fixed relative to a plurality of pedicle screws that are mounted in adjacent vertebrae of a patient, and a device connected to the reference structure which is adapted to install an anterior spinal prosthesis, wherein the reference structure defines a spatial relationship between the anterior spinal prosthesis and a posterior spinal prosthesis attached to the pedicle screws.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims priority under 35 USC §119 to U.S. Provisional Patent Application Ser. No. 60/669,902, filed Apr. 11, 2005, and U.S. Provisional Patent Application Ser. No. 60/757,467, filed Jan. 10, 2006, which are incorporated herein by reference. 

   FIELD OF THE INVENTION 
   The present invention relates to human prostheses, and more particularly to spinal column vertebral disc prosthesis in conjunction with posterior spinal prostheses and methods for the insertion and harmonious coordination between the prostheses. 
   BACKGROUND OF THE INVENTION 
   A common procedure used for stabilizing the vertebral column is bracing adjacent vertebrae by connecting rigid or resilient connecting implants to anchor members such as pedicle screws. Rigid stabilization (fusion) of the spinal column can be disadvantageous due to migration of the problems to adjacent level in the spinal column. Dynamic stabilization provided by resilient implant on the other hand offer a possibility of reduced damage to the adjacent level. This is because it allows for motion preservation, near normal distribution of stress along the spine. 
   A common approach is an anterior approach which involves going through a patient&#39;s abdomen. This is a complex procedure often involving extensive vessel retraction among other difficulties. A posterior approach can alleviate some of these problems. The placement of implants in the disc space from a posterior lateral approach has been described that allows unilateral or bilateral disc space preparation and implant insertion to provide stability to the subject disc space. 
   However when a disc prosthesis is to be inserted either in conjunction with or subsequent to a procedure involving a spinal posterior prosthesis, involving the use of pedicular screws, there is a need to take into account the relative positioning of the disc prosthesis in relation to the posterior prosthesis in particular when at least one of them involves articulation and also in relationship to the vertebrae and disc morphology. 
   SUMMARY OF THE INVENTION 
   The present invention seeks to provide a spinal column vertebral disc prosthesis in conjunction with posterior spinal prostheses and methods for the insertion and harmonious coordination between the prostheses, as described more in detail hereinbelow. 
   According to some embodiments of the present invention, a plurality (such as, but not limited to, at least three) of pedicle screws are placed in position in preferably adjacent vertebra of a patient who is a suitable candidate for receiving a posterior implant and a disc prosthesis. The methods of introducing pedicular screws are known in the art. Once the pedicle screws are in place, the vertebral disc insertion device is connected to the pedicle screws that are inserted in two vertebrae. Following the connection of the disc insertion device to the pedicle screws, distractors may be used to distract the two vertebrae by means that are also known to those skilled in the art. 
   The device may define a trajectory or path or reference point, for the insertion of the disc prosthesis. This trajectory or path or reference point ensures that the implanted disc will be placed in a predetermined position in relation to the pre-inserted screws. Since the screws are in a known position in relation to the vertebra and to a posterior implant to be subsequently placed onto the pedicle screws, this device will aid in the placement of the disc prosthesis preferably via a transforaminal approach (such a disc insertion approach being known in the art) in an accurate position in relation to both the vertebrae and to the posterior implant, thus minimizing human error. The positioning of the pedicle screws defines the positioning of the posterior prosthesis. 
   The device according to embodiments of this invention combines the functions of attachment to pedicle screws, distraction of two vertebrae and the insertion of a disc prosthesis using a predetermined trajectory or reference point. 
   There is thus provided in accordance with an embodiment of the present invention a method for inserting spinal prostheses including providing reference structure spatially fixed relative to a plurality of pedicle screws that are mounted in adjacent vertebrae of a patient, installing an anterior spinal prosthesis with a device that is connected to the reference structure, and installing a posterior spinal prosthesis to the pedicle screws, wherein the reference structure defines a spatial relationship between the anterior and posterior spinal prostheses. The adjacent vertebrae may be distracted before installing the anterior spinal prosthesis. The reference structure defines a path for insertion of the anterior spinal prosthesis in relation to the pedicle screws. 
   There is also provided in accordance with an embodiment of the present invention a spinal apparatus including reference structure spatially fixed relative to a plurality of pedicle screws that are mounted in adjacent vertebrae of a patient, and a device connected to the reference structure which is adapted to install an anterior spinal prosthesis, wherein the reference structure defines a spatial relationship between the anterior spinal prosthesis and a posterior spinal prosthesis attached to the pedicle screws. 
   The spinal apparatus may further include a positioning adapter attachable to a plurality of (e.g., at least three) pedicle screws, the positioning adapter including a pair of connecting devices, each connecting device including a pair of arms that extend outwards corresponding to a spacing of a pair of pedicle screws mounted on a particular vertebra, the arms being attachable to that pair of pedicle screws, wherein the connecting devices are formed with the reference structure, wherein the device includes a disc implant holder adapted to hold an anterior spinal prosthesis, and further including a connecting element adapted to fix the disc implant holder to the positioning adapter with respect to the reference structure. 
   The positioning adapter may be attached to a distraction device adapted to distract two vertebrae to which the pedicle screws are attached. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice. 
     In the drawings: 
       FIG. 1  is an isometric view of two vertebrae with pedicle screws in place and positioning adapter fixed to the pedicle screws; 
       FIG. 2  is an isometric view of the positioning adapter and two distraction devices; 
       FIGS. 3A-D  are isometric and top views of a disc implant holder; 
       FIG. 4  is a top view of a vertebra with the disc implant holder connected to the positioning adapter; 
       FIG. 5  is a top view of a vertebra with the disc implant holder connected to the positioning adapter and the distraction device in place; and 
       FIG. 6  is a side view of two vertebrae with an anterior disc prosthesis and a posterior prosthesis in place. 
   

   DESCRIPTION OF EMBODIMENTS 
   Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting. 
   Reference is now made to  FIG. 1 , which illustrates a positioning adapter  10  attached to four pedicle screws  22  which are anchored into two adjacent vertebrae, for example, L4  24  and L5  26 . The screws  22  were initially placed into the pedicle of the vertebrae as is known to those skilled in the art. The pedicle screws  22  may be used, for example, to anchor a posterior spinal prosthesis to the pedicles. 
   Although four pedicle screws are shown here in this non-limiting example of the application of positioning adapter  10 , a minimum of three anchoring elements such as pedicle screws are sufficient for the successful implementation of positioning adapter  10 . The attachment points from two vertebrae define a plane and connect two adjacent vertebrae. 
   Positioning adapter  10  may include a pair of connecting devices  12  and  14 . Each connecting device may be shaped as a planar flange with a pair of arms  28  that extend outwards corresponding to the spacing of the pedicle screws  22 . Arms  28  are preferably sufficiently long to accommodate most any spacing of the screws  22 . Alternatively, a set of positioning adapters  10  may be provided to span any range of spacing of the screws  22 . The arms  28  of positioning adapter  10  may be attached to the vertebrae by inserting the arms into the heads  30  of screws  22 . As the screws are positioned in their correct place, so positioning adapter  10  is now positioned in place for the next stage of the procedure which is the distraction of the two vertebrae. 
   Each vertebra has its own connecting device as illustrated in  FIG. 1 . The connecting devices  12  and  14  may be formed with reference structure  16 , such as but not limited to, points, pivots or apertures, for example, holes. In summary, positioning adapter  10  is configured to be connected to pedicle screws  22  and has reference structure  16  (also referred to as reference positioning points  16 ) for proper placement and registration of an anterior disc prosthesis with respect to a posterior spine prosthesis, as is described hereinbelow. 
   Reference is now made to  FIG. 2 , which is a side view of a distraction device  32  in place attached to screws  22 . Distraction devices are known in the art and are commercially available, such as the Distraction Forceps with hinged handle for pedicle screws, manufactured by Synthes Spine, 1302 Wrights Line East, West Chester, Pa. 19380. The purpose of distraction is to temporarily expose the posterior disc space in order to ease discectomy and the delivery of the disc implant.  FIG. 2  illustrates distraction device  32  assembled on the pedicle screws  22 . It is noted that positioning adapter  10  does not interfere with the positioning or functionality of distraction device  32 . 
   Following discectomy and endplate preparation, the next function of positioning adapter  10  can be implemented. Reference is now made to  FIGS. 3A-3B , which illustrate a disc implant holder  46  which is used for inserting an artificial disc into the intervertebral disc space, while providing the surgeon with freedom of movement in the workspace of the spinal operation. The disc implant holder  46  may include a handle  50  from which extends a proximal shaft  51 . A distal shaft  55  may be pivotally attached to proximal shaft  51  at a pivot  52 . The pivot  52  may be, for example, a pinned connection that allows free movement of the proximal shaft  51  relative to distal shaft  55 . Alternatively, pivot  52  may be, for example, a ratcheted connection that allows ratcheted movement of the proximal shaft  51  relative to distal shaft  55 . More than one pivoted connection may be provided to allow other degrees of movement of the shafts. The distal shaft  55  may include a pair of clamping jaws  53 . Jaws  53  may be spring-baised to be normally closed and may be opened by pressing or squeezing them to spread them apart, or by means of some opening handle or cam, as is well known in the art of clamps, pliers and the like. Jaws  53  may clamp tightly on an artificial disc prosthesis or implant  48  (also referred to as anterior prosthesis  48 ). 
   The anterior prosthesis  48  may be, without limitation, an articulating prosthesis. A suitable articulating anterior prosthesis is described in U.S. patent application Ser. No. 10/898,229 (corresponding to PCT Application WO 2005/084590) to Arnin, et al., the disclosure of which is incorporated herein by reference. PCT Application WO 2005/084590 describes an endoprosthesis including a first articulating member formed with a generally concave articulating surface, and a second articulating member formed with a generally convex articulating surface which articulates with the concave articulating surface, the first and second articulating members each having a generally planar attachment surface for attachment to spine structure. 
   Reference is now made to  FIGS. 3B-3D , which illustrate the disc implant holder  46  in the spinal procedure workspace. The spinal disc prosthesis or implant  48  may be attached to one end of disc implant holder  46  and handle  50  may be used for placing, guiding and pushing the implant  48  into workspace.  FIG. 3B  illustrates the first step of the insertion of the artificial disc into the intervertebral disc space using for example a TLIF (Transforaminal Lumbar Interbody Fusion) procedure known in the art. Pivot  52  provides the surgeon the ability to swing proximal shaft about an angle  54  relative to distal shaft  55  to facilitate the initial placement of the implant  48 . Handle  46  may be used by the surgeon to vary the angle  54  about pivot  52  ( FIGS. 3B ,  3 C and  3 D). 
   Reference is now made to  FIG. 4 . After initial placement of the implant  48 , positioning adapter  10  may be connected to disc implant holder  46  with a connecting element  56  ( FIG. 4 ). Connecting element  56  fixes disc implant holder  46  to positioning adapter  10 . For example, without limitation, connecting element  56  may include a tubular portion  71  through which the proximal shaft of disc implant holder  46  passes and a flange portion  73  that is fixedly attached to positioning adapter  10  at the reference positioning points  16  ( FIG. 1 ), such as by means of mechanical fasteners (e.g., pins, screws). Connecting element  56  defines the final positioning of implant  48  in relation to the pedicle screws  22 . Reference positioning points  16  define the ideal relative positioning between implant  48  and screws  22 . A correct positioning of implant  48  in relation to screws  22  will provide a merging of the centers of rotation of implant  48  and spinal posterior implant that is to be attached to screws  22 . It may also provide a correct load sharing between the anterior and posterior inserts. This will facilitate a close to natural range of motion and load sharing of the functional spinal unit. 
     FIG. 5  illustrates the workspace of the operation once again with only L5 visible from a top view for a clarified depiction of the devices. Distraction device  32 , positioning adapter  10 , and disc implant holder  46  are seen together with positioning adapter  10  and disc implant holder  46  being connected at connecting point  56 . 
   Reference is now made to  FIG. 6 . After installation of anterior prosthesis  48 , a posterior prosthesis  60  may be attached to the pedicle screws  22 .  FIG. 6  illustrates two adjacent vertebrae with an anterior prosthesis  48  and posterior prosthesis  60  each in their respective correct position in relation to each other according to the embodiments of the present invention. In essence, according to the embodiments of this invention, an artificial disc, will work more efficiently if it articulates around same center of rotation with a posterior implant (e.g., facet replacement). 
   A suitable posterior prosthesis is described in U.S. Pat. No. 7,011,685 to Arnin, et al., the disclosure of which is incorporated herein by reference. U.S. Pat. No. 7,011,685 describes a spinal prosthesis having a unitary body with at least three attachment points attachable to spinal structure, the unitary body including a flexure assembly positioned between first and second attachment members, wherein flexure of the flexure assembly permits movement of the first attachment member relative to the second attachment member. 
   It is appreciated that various features of the invention which are, for clarity, described in the contexts of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination.