Abstract:
An anterior instrumentation method of treating spinal deformities involves a combination of a spinal rod anterior system and one or two spinal plates fixed on the cephalad and caudal end vertebrae of the instrumented segment. Deformities are treated by the anterior rod system through compression, distraction and derotation. Two spinal plates are fixed to the cephalad and caudal end vertebrae respectively to prevent the end vertebrae from rotating into kyphosis. A number of cancellous screws are inserted into the cephalad and caudal end vertebrae and their adjacent vertebrae through the spinal plate to provide several points of fixation on the end vertebrae to prevent implant failure and loss of correction.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application is a continuation of International PCT Application No. PCT/US2004/028690, filed on Sep. 3, 2004 and published on Mar. 17, 2005 as International Publication No. WO 2005/023090, which claims the benefit of U.S. Provisional Application No. 60/500,187, filed on Sep. 4, 2003, the entire contents of each application hereby being incorporated by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention concerns an anterior spinal instrumentation system which allows two spinal plates at the cephalad and caudal end vertebrae to be combined with a rod-type anterior system. The rod-plate anterior system will be used for the surgical management of thoracolumbar and lumbar scoliosis and other situations requiring spinal stabilization.  
       BACKGROUND  
       [0003]     Dwyer first introduced spinal instrumentation for anterior spinal fusion in 1969. The Dwyer system used screws and a flexible cable. However, this system merely provided limited stability by the compressive effect of the one vertebral body against the other. The flexible cable resisted only tension forces, and the inability of the Dwyer system to provide a rigid connection between vertebrae often led to cable or screw failure with subsequent pseudarthrosis. In 1976 Zielke modified the Dwyer system by substituting a small diameter threaded rod and nuts for the cable and introduced a derotator designed to correct rotation and to prevent kyphosis. Over time, the Zielke instrumentation procedure for management of thoracolumbar and lumbar scoliosis was recognized to have significant advantages over the Dwyer system in terms of effective correctability of the coronal curvature, the ability to correct deformity by instrumenting shorter segments of the spine and also its derotation capability. However, the Zielke instrumentation has been reported to have high incidence of implant breakage, loss of correction, progression of the kyphosis, and pseudarthrosis caused primarily by lack of segmental stiffness in the relatively small diameter rod.  
         [0004]     With the introduction of a larger diameter solid rod system by TSRH in 1989, creation of lordosis in the instrumented segment was possible by the appropriate contouring and rotation of a larger diameter rod. The 300% to 400% increased stiffness of the 6.4 mm rod over that of the Dwyer or Zielke longitudinal members was expected to provide stiffness sufficient to increase fusion rates while maintaining correction without external immobilization. However, after review of cases performed with the instrumentation, the incidence of loss of correction in both frontal and sagittal planes remained unacceptable, though improved compared to Dwyer and Zielke.  
         [0005]     Some authors documented significantly high strains at the bone-screw interface of the cephalad and caudal end vertebral screws. Loss of correction and kyphosis in the single rod instrumented segment probably resulted from insufficient construct stiffness in the early postoperative period as a consequence of bone-screw interface loosening, especially at the cephalad and caudal interspaces. The single rigid rod may provide sufficient stability for the correction of the deformed spine during the early postoperative period. However, it may not prevent the vertebral rotation about each screw axis at the bone-screw interface during everyday activity. The possible reason is that the single solid rod system lacks two fixation points on each vertebra, particularly in the most cephalad and caudal end vertebrae of the instrumented segment.  
         [0006]     In 1996, Kaneda introduced a two-rod anterior system (KASS) with two fixation points on each vertebra for management of thoracolumbar and lumbar scoliosis. The KASS system seemed to address some of the problems associated with prior systems, preventing the end vertebrae from rotating into kyphosis. This technique has been performed with good results in the early follow-up period. However, this system has some limitations; namely, the system has a high prominent profile and is difficult to apply to a severely deformed spine.  
         [0007]     To combine the relative ease of implanting a single rigid rod structure with two fixation points on each end vertebra, the rod-plate anterior system of the present invention is an improvement over the single solid rod anterior system (TSRH), and also allows spinal plate fixation at the cephalad and caudal end vertebrae of the instrumentation segment.  
       SUMMARY  
       [0008]     The present invention provides a rod-plate spinal anterior instrumented system having an improved single rigid rod anterior system to allow spinal plate fixation at the cephalad and caudal end vertebrae in the instrumented segment. Additionally, the present invention combines the relative advantages of a rod based anterior instrumentation with plates to increase bone implant strength and stability.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1   a  is a representation of the thoracolumbar spine with a rod-plate anterior system.  
         [0010]      FIG. 1   b  is a representation of the thoracolumbar spine with the rod-plate anterior system.  
         [0011]      FIG. 2   a  is a top view of an L-shaped spinal plate in accordance with one embodiment of the invention, as depicted in  FIG. 1   b.    
         [0012]      FIG. 2   b  is a bottom view of an L-shape spinal plate.  
         [0013]      FIG. 2   c  is a front view of an L-shape spinal plate.  
         [0014]      FIG. 2   d  is a lateral view of an L-shape spinal plate.  
         [0015]      FIG. 2   e  is a side cross-sectional view of the L-shape spinal plate illustrated in  FIG. 2   a,  as taken along line  2   e - 2   e  of  FIG. 2   a.    
         [0016]      FIG. 2   f  is a side cross-section view of the L-shape spinal plate illustrated in  FIG. 2   a,  as taken along line  2   f - 2   f  of  FIG. 2   a.    
         [0017]      FIG. 3   a  is a side view of an embodiment of a cancellous bone screw for use with present invention.  
         [0018]      FIG. 3   b  is a cross-sectional view of the bone screw illustrated in  FIG. 3   a,  as used in association with a spinal plate.  
         [0019]      FIG. 4  is a side cross-sectional view of the end vertebra fixation illustrated in  FIG. 1   b,  showing a stable triangular construct of the end vertebra between the two screws and the transverse portion of the spinal plate.  
         [0020]      FIG. 5  is a representation of the thoracolumbar spine and another embodiment of the rod-plate anterior system.  
         [0021]      FIG. 6   a  is a top view of a rectangular-shaped spinal plate in accordance with the embodiment of the invention illustrated in  FIG. 5 .  
         [0022]      FIG. 6   b  is a bottom view of a rectangular-shape spinal plate.  
         [0023]      FIG. 6   c  is a frontal view of a rectangular-shape spinal plate.  
         [0024]      FIG. 7   a  is a top view of a pair of vertebral staples in accordance with one embodiment of the invention, as illustrated in  FIG. 5 .  
         [0025]      FIG. 7   b  is a bottom view of vertebral staple.  
         [0026]      FIG. 7   c  is a top view of a pair of vertebral staples with a lower profile compared to those illustrated in  FIG. 7   a.    
         [0027]      FIG. 7   d  is a bottom view of a vertebral staple.  
         [0028]      FIG. 8   a  is a side view of an embodiment of a bone screw with a serration-wall junction in accordance with one embodiment of the invention, as illustrated in  FIG. 5 .  
         [0029]      FIG. 8   b  is a side view of an embodiment of a bone screw with a plain-wall junction in accordance with one embodiment of the invention, as illustrated in  FIG. 5 .  
         [0030]      FIG. 9   a  is a top view of a serration-washer in accordance with one embodiment of the invention, as illustrated in  FIG. 5 .  
         [0031]      FIG. 9   b  is a bottom view of a serration-washer in accordance with one embodiment of the invention, as illustrated in  FIG. 5 .  
         [0032]      FIG. 9   c  is a front view of a serration-washer in accordance with one embodiment of the invention, as illustrated in  FIG. 5 .  
         [0033]      FIG. 10  is a representation of spinal plate, bone screws, washer and nuts in accordance with one embodiment of the invention, as illustrated in  FIG. 5 , showing that the spinal plate can mount to a bone screw in varying angular orientations and with variable positions to match the adjacent bone screw.  
         [0034]      FIG. 11  is a representation of the thoracolumbar spine with another rod-plate anterior system similar to the system illustrated in  FIG. 5 .  
         [0035]      FIG. 12  is a representation of the thoracolumbar spine with another embodiment of a rod-plate anterior system that has a lower profile compared to the embodiment illustrated in  FIG. 5 .  
         [0036]      FIG. 13   a  is a top view of a rectangular spinal plate.  
         [0037]      FIG. 13   b  is a bottom view of a rectangular spinal plate.  
         [0038]      FIG. 13   c  a side cross-section view of the rectangular spinal plate illustrated in  FIG. 13   a,  as taken along line  13   c - 13   c  of  FIG. 13   a.    
         [0039]      FIG. 13   d  is a cross-sectional view of a bone screw with the spinal plate connection, as illustrated in  FIG. 12 .  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0040]     For the purposes of promoting an understanding of the principles of the invention, reference will now be made to certain embodiments thereof and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations, further modifications and further applications of the principles of the invention as described herein being contemplated as would normally occur to one skilled in the art to which the invention relates.  
         [0041]     The present invention provides numerous advantages over a dual rod system, including fewer parts and a lower profile, accommodation of spinal deformity, ease in applying implants to a severely deformed spine, ease in adjusting the end vertebrae to avoid wedging and/or degeneration of disc caudal of the last screw, usable from the thoracic spine to the lumbar spine, reduced operation times and simplification of the operational steps.  
         [0042]     In preferred embodiments, the invention includes an anterior spinal instrumented method of treating spinal deformities, the spine having a convex side and a concave side, the method comprising the following steps: on the convex side of the deformity, attaching two spinal plates to cephalad and caudal end vertebrae respectively; fixing a rod anterior system on the posterior portion of the convex side; attaching two spinal plates on the most cephalad and caudal end vertebrae through the vertebral screws of the single-rod anterior system; and the deformity of the spine is corrected through compression, distraction and derotation of the rod anterior system. The method may further include inserting several cancellous screws into the cephalad and caudal end vertebrae and their adjacent vertebrae at the anterior portion of the convex side through the spinal plate which is connected to the rod spinal instrumentation.  
         [0043]     This preferred method may also include a spinal plate which has an “L” shape that connects at least two vertebrae, and which comprises: a first end and a second end, where the first end has a longitudinal portion and a length sufficient to span between two vertebrae. The longitudinal portion has an elongated slot which has a series of openings for receiving screws such that the plate can be attached to the vertebrae. The openings allow the force transmitting members to be positioned on the vertebra where desired and enables the spinal plate to be used with different sized vertebrae.  
         [0044]     The second end of the spinal plate has a transverse portion that is vertical with the longitudinal portion. The transverse portion fits together with the lateral side of the vertebra in an anterior-posterior direction. In the superior-inferior direction, the plate&#39;s thickness is narrowed to avoid endplate prominence and so that the plate fits closely to the bone. The transverse portion has a first aperture in the anterior region and a second aperture in the posterior region. The second aperture is located in the middle point of the superior inferior direction, which indicates that the spinal screw is safely in the middle position. The first aperture is angled towards the center allowing the screw to be inserted in the posterior direction to avoid damaging the aorta and disrupting the front edge of the vertebral body. The two-hole design provides a stable triangular screw construct in the vertebrae between the two screws and the transverse portion of the spinal plate. Different angles are designed from 80° to 100° between the longitudinal portion and the transverse portion of the spinal plate so that the spinal plate can accommodate different spinal deformities. Different lengths are designed for the longitudinal portion of the spinal plate so the spinal plate can span at least two vertebrae.  
         [0045]     On the bottom side surface and top side surface, the spinal plate has a bottom side surface for facing the vertebrae. In the longitudinal portion, pluralities of serrations are formed along the slot. The serrations prevent sliding of the spinal plate relative to the vertebrae. In the transverse direction, the spinal plate is slightly concave in shape so that it matches the vertebral anatomy for optimum anatomic fit and to minimize the construct profile in the anterior-posterior direction. On the top surface, in the longitudinal portion, the slot is provided with a beveled upper or outer edge portion, which slopes at the same angle as the lower rounded surface of the head portion of cancellous screw. A plurality of recesses is provided in the beveled edge portions to engage the lower rounded surface of the cancellous screw. The recesses hold the screw against sidewise movement relative to the spinal plate. The recesses are defined by surfaces, which form a portion of a cone having the same included angle as the lower round surface of the screw head. In the transverse portion, an anterior hole is provided with a beveled upper edge portion, which slopes at the same angle as the lower rounded surface of the screw head. The topside surface of the transverse portion is slightly convex in anterior-posterior direction so that it matches the vertebral anatomy.  
         [0046]     The cancellous screw may also include a bone engaging portion having cancellous threads thereon, and may include a head portion. The head portion includes a lower rounded surface and an upper rounded surface. A generally cylindrical portion separates the lower rounded surface and the upper rounded surface. The screw head also includes a tool-engaging recess. The tool-engaging recess may be of any suitable configuration, including hexagonal, hexalobed, or any other appropriate configuration. The rod anterior system may be any suitable single-rod anterior system including, for example, TSRH, CDH, Miami, or any others.  
         [0047]     In practice of the preferred method, the spinal plate may also be of a rectangle-shape that connects at least two vertebrae through a pair of similar upper and lower vertebral staples. The staples comprise a first end and a second end. The first end has a first hole and the second end has an elongated u-shaped slot. The plate also includes a bottom side surface (the screw-facing side) and top side surface (the washer-facing side). On the bottom side surface, the first hole defines a plurality of serrations extending radially about the hole so that the spinal plate can mount to a cancellous screw in varying angular orientations. On the top side surface, the elongated u-shaped slot defines a plurality of parallel serrations so that the spinal plate may be placed in a variable position to match the adjacent bone screw through a rectangle-serrated washer. Using this plate, a pair of similar upper and lower vertebral staples may be attached to both end vertebrae of the instrumentation segment.  
         [0048]     The vertebral staples also include a posterior hole and an anterior hole. The posterior hole receives the screws of the anterior rod system, and the anterior hole receives a cancellous screw for the spinal plate fixation. The vertebral staple is wedge-shaped and is capable of securing a pair of metal tensioning cables to a vertebra via spinal screws. The staple preferably comprises three prongs, a pair of substantially parallel and perpendicularly offset laminar posterior legs which are inserted into the vertebral endplates, the parallel distance between the posterior legs being such as to fit snugly over either side of a vertebra. The third prong is located in central position of the staple to avoid damaging the aorta and thoracic-abdominal organs.  
         [0049]     The staple may further include a pair of spinal screw receiving apertures. The posterior hole is located in the middle portion between the two posterior staple prongs, which positions the spinal screw safely in the middle position. The anterior hole is inclined towards the center of the anterior portion of the staple. The anterior hole geometrically allows the anterior screw to be directed posterior to avoid damaging the aorta and disrupting the front edge of the vertebral body for good purchase. The posterior hole allows the posterior vertebral screw to be directed anteriorly to avoid injury of the spinal cord. The two-hole design provides a stable triangular screw construct in the vertebra between the two screws and the staple.  
         [0050]     The staple further comprises an integral substantially solid and wedge-shaped laminal bridge portion which is slightly convex in shape so that it matches the vertebral anatomy for optimum anatomic fit to minimize the construct profile in the anterior-posterior direction. The portion of the superior-inferior direction is narrower than the two posterior prongs to avoid endplate prominences and to allow the plate to fit closely to the bone.  
         [0051]     As a template to start a hole for screw insertion, the vertebral staple increases the screw pullout force and has been shown to be very effective in preventing screw migration and screw pullout. Different sizes and shapes accommodate a variety of anatomical shapes of vertebra so as to allow the lateral plates to be fixed to either lumbar or thoracic vertebrae.  
         [0052]     In the preferred method, the cancellous screw may receive the rectangle-shaped spinal plate via the anterior hole of the staple, which comprises a first end and a second end. The first end has an insertion tip with cancellous thread extending from the insertion tip along a substantial portion of the first end. The second end is defined as a protruding shaft extending outwardly from said first end with at least a portion of said protruding shaft threaded. The protruding shaft has the same diameter as the first end. The second end also includes a tool-engaging recess. The tool-engaging recess may be of any suitable configuration, including hexagonal, hexalobed, or any other suitable configuration. A wall junction is formed between the first end and second end. There are radial serrations on the top surface of the wall junction in the most end cancellous screw, but a plain top surface of the wall junction in the adjacent most end cancellous screw. The radial serrations allow the spinal plate to match the adjacent vertebral screw.  
         [0053]     The preferred method may also include embodiments in which the rectangle-serrated washer is a rectangle-shaped washer. The washer comprises a bottom side surface defined by a plurality of parallel serrations so that the washer can mount to the lateral plate to lock the anterior screw. The topside surface may be plain to receive the nut, and the washer may further include an aperture in the central position. The rectangle-shaped spinal plate may also have a sufficient length to cover more vertebrae, even from cephalad to caudal vertebrae of the instrumented segment.  
         [0054]     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected. In addition, all publications cited herein are indicative of the abilities of those of ordinary skill in the art and are hereby incorporated by reference in their entirety as if individually incorporated by reference and fully set fourth.