Abstract:
A surgical fixation system including a surgical fixation plate, a plurality of fasteners, and a retainer having an improved mechanism to prevent the back out of screws employed in securing a surgical fixation plate to an intended orthopedic location.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims the benefit of the filing date under 35 USC 119(e) of United States Provisional Application entitled “Anterior Cervical Plate,” Ser. No. 60/384,966 filed Jun. 4, 2002, the entire contents of which is fully incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   I. Field of the Invention 
   The present invention relates generally to the area of surgical fixation, and more particularly to a surgical fixation system having an improved mechanism to prevent the back out of screws employed in securing a surgical fixation plate to an intended orthopedic location. 
   II. Discussion of the Prior Art 
   The use of surgical fixation systems involving plates is accepted practice for a variety of orthopedic procedures. One procedure experiencing proliferated growth is that of spinal fusion, wherein a surgical fixation plate is secured along two or more vertebral bodies through the use of screws extending through bores formed in the plate. Secured in this fashion, the surgical fixation plates serve to immobilize the vertebral bodies. When employed with bone allograft or another fusion-effecting implant (such as a mesh cage, a threaded cage, etc. . . . ), this immobilization promotes fusion to occur between the adjacent vertebral bodies, which is intended to restore disk height between the vertebral bodies and reduce pain in the patient. 
   A challenge exists in the use of spinal fixation plates, however, in that the screws employed to fix the spinal fixation plate to the vertebral bodies have a tendency to back out from the plate over time. One application where this is particularly worrisome is with the use of a spinal fixation plate positioned over the anterior cervical spine. More specifically, such backing out may cause the screws to come into unwanted contact with the esophagus, which may lead to damage or impairment to that organ. Another problem is that, with the screws backed out (partially or fully), the mechanical properties of the overall construct will become compromised, which may lead to a loss in the height of the intervertebral space height and thereby cause pain to the patient. 
   Various efforts have been undertaken to prevent the back out of screws employed in prior art surgical fixation plates. Some include a plurality of elements or components to engage the head of the screw within the through bore. Others provide one or more elements or components to cover the through bore after the screw has been introduced into the intended orthopedic location (e.g. a vertebral body). Unfortunately, both types of prior art systems have various drawbacks or imperfections. The first type (with a plurality of parts to engage the head of the screw within the through bore) can be challenging due to the plurality of parts and associated instrumentation, which may disadvantageously increase surgical time. The second type (covering the head of the screw) can similarly be time consuming and challenging based on the need for additional instrumentation to place the cover. Both types of systems may be more costly based on the need for additional instrumentation above and beyond the screwdriver instrument. 
   The present invention is directed at overcoming, or at least reducing the effects of, one or more of the problems set forth above. 
   SUMMARY OF THE INVENTION 
   According to one broad aspect of the present invention, the present invention accomplishes this goal by providing a surgical fixation system including a plate, at least one fastener, and a retainer. The plate has at least one fastener-receiving aperture and at least one retainer-receiving aperture. The fastener-receiving aperture extends between an upper surface and a lower surface of the plate. The retainer-receiving aperture has a periphery defined by a plurality of tab members extending from the upper surface. The fastener has an anchor region and a head region. The anchor region is dimensioned to be passed through the fastener-receiving aperture for introduction into a surgical target site, and the head region is dimensioned to be received at least partially within the fastener-receiving aperture. The retainer is dimensioned to be introduced into the retainer-receiving aperture to overlap at least a portion of the head region of the fastener and thereby prevent the fastener from backing out of the fastener-receiving aperture. 
   According to another broad aspect of the present invention, the present invention accomplishes this goal by providing a method of surgical fixation is provided including the steps of: (a) positioning a plate over an intended surgical target site, the plate having at least one fastener-receiving aperture and at least one retainer-receiving aperture, the fastener-receiving aperture extending between an upper surface and a lower surface of the plate, and the retainer-receiving aperture having a periphery defined by a plurality of tab members extending from the upper surface; (b) introducing a fastener into the fastener-receiving aperture such that an anchor region of said fastener is introduced into the surgical target site and a head region of the fastener is received at least partially within the fastener-receiving aperture; and (c) introducing a retainer into the retainer-receiving aperture to overlap at least a portion of the head region of the fastener and thereby prevent the fastener from backing out of the fastener-receiving aperture. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Many advantages of the present invention will be apparent to those skilled in the art with a reading of this specification in conjunction with the attached drawings, wherein like reference numerals are applied to like elements and wherein: 
       FIG. 1  is a perspective view of a surgical fixation system according to a one aspect of the present invention; 
       FIG. 2  is a top view of the surgical fixation system shown in  FIG. 1 ; 
       FIG. 3  is a cross-sectional view of the surgical fixation system taken along lines  3 — 3  in  FIG. 2 ; 
       FIG. 4  is a perspective view of a surgical fixation system according to another broad aspect of the present invention; 
       FIG. 5  is a top view of the surgical fixation system shown in  FIG. 4 ; 
       FIG. 6  is a cross-sectional view of the surgical fixation system taken along lines  6 — 6  in  FIG. 5 ; 
       FIG. 7  is a cross-sectional view of the surgical fixation system shown in  FIG. 6  with the tab member closed over at least a portion of the retainer according to a still further aspect of the present invention; 
       FIG. 8  is a top view of a surgical fixation system according to another aspect of the present invention; 
       FIG. 9  is a top view of a surgical fixation system according to yet another aspect of the present invention; and 
       FIG. 10  is a top view of a surgical fixation system according to a still further aspect of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. The surgical fixation plate disclosed herein boasts a variety of inventive features and components that warrant patent protection, both individually and in combination. 
   This invention improves upon the prior art by providing a surgical fixation system including a surgical fixation plate, a plurality of fasteners, and a retainer, wherein the retainer is configured and dimensioned to be received within a retainer-receiving aperture formed in the surgical fixation plate to prevent the fasteners from backing out over time. As will be described below, the retainer is capable of being easily introduced into the retainer-receiving aperture after the fasteners have been anchored into a given orthopedic target, which advantageously overcomes the drawbacks of the prior art. More specifically, back out prevention is accomplished in an easy to use and cost effective manner, in that simple off-the-shelf instrumentation may be used to deploy the retainer. Moreover, although particularly suited for use in anterior cervical spine fixation, it will be readily appreciated by those skilled in the art that the surgical fixation system of the present invention may be employed in any number of suitable orthopedic fixation procedures, including but not limited to lumbar spine fixation, thoracic spine fixation, as well as any non-spine fixation application such as bone fracture treatment. 
     FIGS. 1–3  illustrate a surgical fixation system  10  according to a first broad aspect of the present invention. The surgical fixation system  10  comprises a surgical fixation plate  12 , a plurality of fasteners  14 , and a retainer  16 . The surgical fixation plate  12  includes an upper surface  18 , a lower surface  20 , and an intermediate surface  22 . A plurality of fastener-receiving apertures  24  is provided extending between the upper and lower surfaces  18 ,  20 . A retainer-receiving aperture  26  is provided having a periphery defined by a plurality of tab members  28  extending from said upper surface  18 . A groove  30  is defined between each tab member  28  and a region of the intermediate surface  22  extending generally beneath the tab member  28 . In use as an anterior cervical plating system, the upper surface  18  would be the anterior-most (facing the esophagus of the patient) and the lower surface  20  would be the posterior-most (in general abutment with the anterior portion of the cervical spine). As best shown in  FIG. 3 , the plate  12  preferably has a curvature along both the upper and lower surfaces  18 ,  20 . In this fashion, the upper surface  18  has a generally reduced cross-sectional profile to avoid impinging upon or inadvertently contacting the esophagus of the patient, and the lower surface  20  can best accommodate the general curvature of the spine. Although shown having a generally rectangular outer periphery ( FIG. 2 ), the plate  12  may be provided having any number of suitable outer peripheral shapes, including but not limited to areas of reduced width between the fastener-receiving apertures  24 . The plate  12  may be provided in any number of suitable fashions and dimensions depending upon the particular surgical procedure. For cervical spine fixation, the plate  12  may be (by way of example only) 2 mm thick between the upper surface  18  and lower surface  20 , wherein the tab member  28  is preferably 0.2 mm thick, the groove  30  is preferably 0.9 mm thick, and the thickness between the intermediate surface  22  and the lower surface  20  is approximately 0.9 mm. 
   Each fastener  14  includes a shaft  32  and a head  34 . The shaft  32  is dimensioned and configured to be passed through a fastener-receiving aperture  24  and anchored (such as via threads  33 ) into a boney target (such as a vertebral body in the cervical spine). The head  34  is dimensioned and configured to be received within the fastener-receiving aperture  24 . In the embodiment shown, the concave curvature of the lower surface  20  causes the shaft  32  of the fasteners  14  to angle medially, generally towards one another. The head  34  of the fastener  14  may be equipped with any number of suitable mechanisms for engaging with a driving instrument, including but not limited to the hex-type female engagement portion  36 . Although shown with six fasteners  14 , it will be appreciated that the number of fasteners  14  (along with the number of fastener-receiving apertures  24 ) may be increased or decreased without departing from the scope of the invention. The fasteners  14  may be constructed from any number of biocompatible materials, and provided in any number of dimensions (including length, diameter, thread pitch), such that they are suitable for use as a bone screw. 
   The retainer  16  is dimensioned and configured to be introduced into the retainer-receiving aperture  26  and overlap at least a portion of the head  34  of each fastener  14  such that the retainer  16  prevents unwanted back out of fasteners  14  from the plate  12 . In the embodiment shown, this is accomplished by providing the retainer  16  as a generally U-shaped member including a first elongate region  40 , a second elongate region  42  disposed generally parallel to said first region  40 , and a third elongate region  44  extending generally perpendicularly between the first and second regions  40 ,  42 . The first and second regions  40 ,  42  are temporarily deformable relative to the third region  44  such that they may be forced towards one by applying force medially along a portion of the first and second regions  40 ,  42 . This may be accomplished in any number of suitable fashions, including but not limited to engaging a tool (such as a pliers-type instrument) within loops  46  provided at the free ends of the first and second regions  40 ,  42  and clamping together. The third region  44  should be engaged at least partially under the tab member  28  at one end of the plate  12  such that the first and second regions  40 ,  42  while in a contracted state (not shown) may be rotated about the third region  44 , introduced through the retainer-receiving aperture  26 , and thereafter released such that portions of the first and second regions  40 ,  42  are disposed at least partially under the respective tab members  28 . In this fashion, each fastener head  34  is covered by at least a portion of the retainer  16  to thereby prevent unwanted back out of fasteners  14  over time. 
   The surgical fixation system  10  may be provided having a variety of additional features and/or various modifications without departing from the scope of the invention. For example, as shown in  FIGS. 4–5 , the surgical fixation system  10  may be equipped with one or more viewing apertures  50 . This may be accomplished by removing portions of the plate  12  between the intermediate surface  22  and lower surface  20 , which may (by way of example only) result in one or more struts or cross bars  52  extending side to side (angularly or straight) across the plate  12 . In this fashion, the surgeon may visually inspect the surgical target site underneath portions of the plate  12  after placement on the spine. The viewing apertures  50  may be provided in any number of suitable geometries, including but not limited to the generally triangular shapes shown best in  FIG. 5 . 
   The tab members  28  may also be modified in any number of different fashions without departing from the scope of the present invention. For example, as shown in  FIGS. 6–7 , the tab members  28  may be deformed or otherwise moved such that the tab member  28  are brought to enclose a point or portions along the retainer  16  in an effort to prevent the retainer  16  from becoming dislodge or otherwise dissociated from the plate  12 . More specifically, the tab members  28  may be moved from a first position shown in  FIG. 6  (extending generally medially from the upper surface  18 ) into a second position shown in  FIG. 7  (extending generally downward toward the intermediate surface  22  to enclose some or all of the retainer  16  depending upon the width of the tab member  28 ). In one embodiment, this manner of engagement (as well as others) may be employed to provide a hinged coupling arrangement between the third region  44  of the retainer  16  and the respective tab member  28  at one end of the plate  12 . 
   The tab members  28  may also be dimensioned in any number of suitable fashions without departing from the scope of the present invention. For example, with reference to  FIG. 8 , the tab members  28  may extend a portion of the distance between adjacent fastener-receiving apertures  24  (as opposed to extending the entire distance as in the embodiment shown in  FIGS. 1–7 ). As shown in  FIG. 9 , the individual shapes of the various tab members  28  may also be different, such as (by way of example only) providing one or more of the tab members  28  angled medially. In this fashion, the retainer-receiving aperture  26  will be defined to include a flared region  54  towards one end of the plate  12 . The flared region  54  is suitable to accommodate the medial deformation of at least one of the first and second regions  40 ,  42  of the retainer  16  during introduction into the retainer-receiving aperture  26 . 
     FIG. 10  illustrates yet another manner of providing the tab members  28  according to a broad aspect of the present invention, wherein the tab members  28  are deformable in a generally medial direction to extend over at least a portion of the retainer  16 . In one embodiment, this is accomplished by providing tab-deployment apertures  56  (extending part or the entire distance between the upper surface  18  and the lower surface  20 ) immediately lateral to the tab members  28 . The tab members  28  may thus be selectively deformed to move from a first—undeployed—position (shown in the two-deployment apertures  56  closest to the third region  44  of the retainer  16 ) to a second—deployed—position (shown in the two tab-deployment apertures  56  closest to the loops  46  of the retainer  16 ). This may be accomplished in any number of suitable fashions, including but not limited to placing an instrument (such as a flat screwdriver) into the tab-deployment aperture  56  of an undeployed tab member  28  and actuating the instrument (such as via rotation in the case of a screwdriver) to thereby force the tab member  28  into position above at least a portion of the retainer  16 . 
   While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternative falling within the spirit and scope of the invention as described herein.