Abstract:
A closure for an open ended medical implant with a pair of spaced arms to maintain a rod or the like in the implant. The closure including a top plate with depending side flanges forming a discontinuous ring that is received about the implant in comparatively low profile from side to side. The closure includes a threaded central cylindrical shaped boss depending from the plate to maintain spacing of the implant arms and secure the closure to the implant. The plate and boss have coaxial bores that receive a set screw. The flanges abut against an outer surface of the arms during use to prevent spreading of the arms.

Description:
BACKGROUND OF THE INVENTION 
     The present invention is directed to a closure for an open-ended medical implant that receives a rod or related rod-like structure in an open end of the implant and then the rod is captured within the end of the implant by the closure. 
     A wide range of medical implants are utilized within the human body. With respect to the spine these implants include bone screws that are implanted in vertebrae and various types of connectors and the like that are used to interconnect with bone screws and each other to form an overall support matrix or spinal implant system. Many of these implants, especially bone screws, but also hooks and connectors, are open-ended having a yoke with a pair of upstanding arms that receive rods or other structures in a channel formed between the arms. Typically, each yoke receives an elongate rod, but other elements of the system having cylindrical shaped nipples or the like may also be received in the yokes. Because such bone screws and the like are open-ended, some closure must be used in order to capture the rod or other structure received within the open end of the implant. 
     To insure that the closure remains secured to and on the bone screw or other implant and that the rod or other structure being held in the implant does not slip either axially or rotationally, in many systems a substantial amount of torque must be applied in installing the closure to both maintain the closure in position and urge the closure against the rod so as to lock the rod in position relative to the bone screw or other implant. The force required to torque the closure presents either a destabilizing force to the overall completed implant in that it may spread the arms or alternatively, if the closure has been made in such a way to counteract the destabilizing force of the torque, the closure and overall implant normally are too large to be used effectively within the system or the closure becomes very complex and difficult to manufacture and/or use. 
     In particular, the prior art has developed plug closures which are simply threaded cylinders that are screwed into threads on the inside of the arms in the open end of the implant to hold the rod or the like in place. High torque exerted on the plug tends to spread the arms during installation or the arms of the implant may later spread due to forces acting on the implant system, thereby loosening the closure and possibly allowing the rod to slip or the plug to work loose from the bone screw. 
     In addition, the rods are normally curved or non-linear at the location where they are placed in the implant. That is, typically, the spine is not straight and rods used for supporting the spine are bent to follow the curvature of the spine. Consequently, the rod often has a substantial amount of curvature where the closure plugs engage the rod. Because of this curvature, the rod often is somewhat arcuate underneath the plug even after the plug is fully installed. This presents substantial problems, if the rod is later subjected to forces in use in the body, such as where the patient encounters a fall or automobile accident, that cause the rod to bow somewhat against the desired curvature. This then spaces the rod from engagement with the plug or at least reduces the frictional engagement of the plug with the rod to a level that allows the rod to easily rotate or move axially and/or the plug to become loose and even work free of the bone screw over time. 
     Other types of prior art closure caps are not threadably received as a plug by the implant, but rather have a complex system of interlocking parts with the implant in order to bridge the gap between the arms. Such caps normally slide into place and then are locked by tightening a set screw or the like. Such closures are very difficult to manufacture and are comparatively very expensive. Closures of the slide-in type, in general, are often also difficult to install, because the parts are small and the working space provided to the surgeon during surgery is very limited. Further, the curvature of the rod may make it very difficult to slide the cap into place so that it may then interlock with mating elements in the bone screw. 
     Yet another type of closure of the prior art has been a closure that provides a ring that goes entirely about the outside of the arms of the implant. Such a ring may be threaded and received on mating threads on the outsides of the arms of the implant. The ring concept works well in preventing the arms of the implant from spreading due to forces. However, this type of system is subject to problems. One of the problems is that like the previous noted system, when the ring secures a curved rod, the rod may later flex so as to release pressure and reduce friction between the closure and rod, so that the rod becomes loose within the implant and can slip by rotation or axial movement therein. Such systems using a plug are usually not very effective in locking the rods in place, equally as the plug normally engages part of the ring and not the rod, so that direct friction of the plug on the rod does not occur. 
     Furthermore, the outside circumferential ring substantially increases the thickness of the implant along the axis of the rod. This presents a substantial problem, since there is often very limited space along the rod for all of the various connectors, bone screws and the like that are necessary for the overall implant system and such large closures take up too much space. Additionally, the large caps that are necessary for closing this type of implant leave very little room for the surgeons to work and block access of bender devices to the rod that are needed to shape the rod in some types of implant surgery which require that the curvature of the rod to be modified after connection to the bone screws. The large head of such caps is also contrary to the general desire to reduce size, weight and overall volume of such implants so as to reduce their physical impact on the patient. 
     It is noted that other problems with the prior art include that, while some types of caps prevent outward movement of the arms, such allow the tops of the arms to bend radially inward toward each other so the cap becomes loose. Further, where the cap is threaded and goes over the outside of the arms, it is often very difficult to line up the threads properly between opposite arms and the cap because of the tight working space, so the cap does not sit correctly and does not tighten correctly against the rod. 
     SUMMARY OF THE INVENTION 
     A closure cap for an open-ended implant wherein the implant has a pair of upstanding arms located on either side of a rod receiving channel and wherein the arms are interiorly or inwardly threaded to threadably receive the closure. The closure is an incomplete round cap having opposed and equally sized segments or sectors missing so that the cap does not form a complete circle. When positioned to act as a closure, the missing segments allow the closure cap to be comparatively thin in profile relative to a cap of the same radius that is complete. The cap includes an upper plate joined to opposed flanges. The flanges are snugly received around the arms of the implant in use. 
     The closure includes a central cylindrical member or boss that depends from the plate and is positioned between but in spaced relation to the flanges. The cylindrical boss is sized and shaped to maintain the spacing of the arms when installed on the implant by keeping the arms from bending inwardly. The boss is outwardly threaded to mate with the threads on the interior of the implant arms, so that the boss may be screwed in place between the arms and so that when the boss is fully screwed into the implant head, the flanges are positioned radially outward and in close relationship to the arms to prevent the arms from spreading outwardly. 
     The plate and the cylindrical boss also include a central top to bottom threaded bore which receives a set screw. In use the set screw engages and is urged under torque against a rod within the channel so as to fix in position and lock the rod against movement relative to the implant. 
     A set of tools is also provided for use with the invention. A cap installation tool is temporarily threadedly received in the threaded bore to allow the grasping and turning of the closure cap during installation. The installation tool is removed, when the cap is positioned such that the threads of the boss substantially engage and are threaded into the threads of the arms. Once the installation tool is removed and the surgeon is satisfied with the position of the rod relative to the implant, an anti-torque tool is placed over the cap to hold the cap in position and a set screw is positioned within the cap bore. A set screw installation tool is then utilized to torque the set screw which may be a break-off head type wherein the head breaks away at a preselected torque or a non-break-off head type set screw. Once the set screw has been properly torqued, the anti-torque tool and set screw installation tool are removed and the implant is thereafter complete. 
     A removal tool is also provided which comprises a T-shaped handle with a lower receptacle that receives the cap and allows the cap to be rotated. The cap in this manner can be rotated counterclockwise and removed, should it is necessary to do so for some reason after installation. 
     OBJECTS AND ADVANTAGES OF THE INVENTION 
     Therefore, the objects of the present invention are: to provide a closure for an open-ended medical implant that is comparatively thin in profile along an axis of a rod or other structure received in the implant, that resists movement of the upper ends of the implant arms either radially inward or outward subsequent to installation of the cap and that provides a set screw that secures the rod within the implant at the time of installation and at subsequent times when the normal curvature of the rod is bowed during use; to provide such a closure which comprises an upper plate joining a pair of depending flanges that are received around and in touching or abutting relation to the arms of the implant; to provide such a closure wherein the flanges are opposed and together extend approximately 180° about the implant; to provide such a closure having a central depending boss that is threaded to mate with threads on the interior sides of the arms; to provide such a closure in combination with the implant and with a set screw that is highly effective in locking the rod or the like in position relative to the implant and preventing subsequent movement of a rod or other structure either rotationally or axially relative to the implant; to provide such a closure utilizing a relatively small diameter set screw to secure the rod that is much less subject to loosening in comparison to the closure should the rod flex; to provide such a closure which is relatively easy to manufacture and inexpensive to produce; to provide such a closure which is relatively easy to install and may be installed with the rod substantially bent within a rod receiving channel of the implant; to provide such a closure which is relatively easy to remove, should removal be necessary; to provide a set of tools for installing such a closure including an installing tool to facilitate threading of the closure onto the implant; to provide such a set of tools including an anti-torque tool and a set screw installing tool to function in combination to install a set screw in the closure; and to provide a removal tool that captures the closure and allows rotation of the closure relative to the implant; and to provide an overall closure, implant system and set of tools that are especially easy to use and well adapted for the intended purpose thereof. 
     Other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. 
     The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded view of a medical implant, closure cap and set screw that are used cooperatively in accordance with the present invention. 
     FIG. 2 is a fragmentary front elevational view of the medical implant shown positioned within a vertebra with portions broken away to show placement of the implant and having a rod positioned within an open end of the implant prior to installation of the closure. 
     FIG. 3 is an exploded side elevational view of the medical implant, the closure cap and a closure installation tool in accordance with the present invention. 
     FIG. 4 is an enlarged and fragmentary side elevational view of the medical implant installed in the vertebra and with the closure cap in the process of being placed on the implant with the installation tool attached to the closure cap and with portions broken away to show detail thereof. 
     FIG. 5 is an exploded side elevational view of the bone screw with the cap positioned thereon and showing the set screw with an anti-torque tool and a set screw installation tool that are both used cooperatively to install the set screw. 
     FIG. 6 is an enlarged side elevational view of the implant with the cap positioned thereon and with the set screw being installed by the anti-torque tool and the set screw installation tool. 
     FIG. 7 illustrates the implant with the closure positioned thereon and with the set screw positioned so as to lock the rod within a yoke of the implant and with the anti-torque tool and the set screw installation tool just subsequent to being removed from the closure with a broken away head of the set screw still within the set screw installation tool. 
     FIG. 8 is a cross sectional view of the implant, closure and set screw, after completion of installation, taken along line  8 — 8  of FIG.  7 . 
     FIG. 9 is a side elevational view of the implant with the closure thereon and showing a closure cap removing tool positioned on the closure cap. 
     FIG. 10 is a side elevational view of an implant in accordance with the invention with a modified closure cap and a modified set screw. 
     FIG. 11 is a cross sectional view of the implant, modified closure cap and set screw, taken along line  11 - 11  of FIG.  10 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. 
     The reference numeral  1  generally indicates a closure in accordance with the present invention utilized in conjunction with an “open” type bone screw  2 . The closure  1  generally includes a closure cap  3  and a set screw  4 . The various elements including the bone screw  2 , closure cap  3  and set screw  4  are shown before installation in an exploded view in FIG.  1 . 
     The present invention is illustrated in conjunction with the bone screw  2 , although it is foreseen that the closure  1  could be used in conjunction with other types of medical implants that have an open end for receiving a rod or the like to allow connection between various implants of an overall implant system. 
     In the illustrated embodiment, the bone screw  2  has a shank  10  and a head  11 . The shank  10  is threaded and is received in a vertebral body  13  that is part of a vertebra in a patient&#39;s spinal column. The threaded shank  10  is inserted in the vertebral body  13 , as is shown in FIGS. 2 and 4 with the head  11  extending from the vertebral body  13 . The head  13  has a pair of upright branches or arms  16  and  17  that are generally equally spaced and form a channel  18  therebetween. In general the head  13  is shaped like a yoke for receiving a cylindrical and elongate rod  20  or other connectors associated with the medical implant system. The bottom of the channel  18  forms a seat  23  for receiving the rod  20  and may be grooved, knurled or otherwise surfaced so as to increase friction between the rod  20  and the seat  23 . 
     The rod  20  is laid into the seat  23  by passage through an open mouth  24  of the channel  18 . Each of the arms  16  and  17  have radially outward surfaces  26  and  27  and threaded radially inward surfaces  28  and  29 . The threaded surfaces  28  and  29  generally face each other and are not identically threaded. In particular, the threads on the surfaces  28  and  29  are designed to allow mating with a mateable threaded circular structure, and although the pitch of the threads on the threaded surfaces  28  and  29  are similar, the positioning of the threads will be slightly different on each side to adjust for mating with a normally threaded structure to allow the structure to rotate and threadedly advance along the threads of the surfaces  28  and  29 . 
     The rod  20  is normally not linear, but rather is curved to follow the curvature of the patient&#39;s spine, as is seen in FIG.  2 . FIG. 2 is a side view illustrating the rod as it is initially placed in the bone screw channel  18  and before placement of the closure  1  thereover to capture the rod  20  in the channel  18 . 
     The closure cap  3  includes a generally rectangular shaped body or plate  30 , a pair of side flanges  31  and  32  depending from opposite ends of the plate  30  and a central cylindrical shaped member or boss  33  also depending from the plate  30 . 
     The plate  30  is relatively thin from top to bottom and is illustrated as being substantially rectangular in shape (in horizontal cross-section) with a slight radius at the top to improve the strength thereof with opposite ends radiused. Although the plate  30  is illustrated as being generally rectangular in horizontal cross-section, such a shape is not required in accordance with the invention. The main criteria for the plate  30  is that it be longer from side to side where the side flanges  31  and  32  are attached than in width. This allows the closure cap  3  to have a comparatively thin profile relative to elements of the implant system that are located adjacent to the closure cap  3  when the entire system is fully installed. For example, the outermost edges of the side flanges  31  and  32  may in some instances be spaced twice as wide as the width of the closure cap  3  that is perpendicular thereto. The plate  30  has an upper surface  37  that is arcuate and a lower surface  38  that is flat. Near whereat the side flanges  31  and  32  attach to the plate  30  is a region  39  on the lower surface that may, but is not required to, abut or engage the upper ends of the arms  16  and  17 , when assembly is complete. The region  39  is on either side of the cylinder  33  spaced between the cylinder  33  and the side flanges  31  and  32 . 
     The side flanges  31  and  32  each have radially inward facing surfaces of  42  and  43  that each form a partial cylindrical surface in such a way as to mate with inner surfaces of the arms  28  and  29 . Consequently, the portion of the closure cap  3  that includes the plate  30  and side flanges  31  and  32  is very much like a full cylindrical or circular shaped closure cap that is placed about the outside of the arms  16  and  17 ,except that outer opposed segments have been removed to make the closure cap  3  thinner in profile. 
     The boss  33  is mounted in the center of the plate  30  and extends toward the seat  23  when the closure cap  3  is fully mounted on the bone screw  2 . The boss  33  has a cylindrical shaped outer surface  45  that is threaded and is carefully sized so as to allow the boss  33  to be screwed between the arms  16  and  17  during installation of the closure cap  3  on the bone screw  2 . In this manner the boss  33  prevents the arms  16  and  17  from bending inwardly toward one another during use of the bone screw  2 , while the flanges  31  and  32  prevent the arms  16  and  17  from bending outwardly relative to each other during usage. The boss  33  also has a lower surface  45  and an upper surface that is fixedly secured to the underside of the plate  30  and the boss lower surface  45  becomes closely spaced from or in touching engagement with the rod  20  during use. Because the set screw  4  is used to lock the position of the rod  20  relative to the bone screw  2 , the closure cap  3  does not have to be against the rod  20 , but only capture rod  20  in the head  11 . 
     A threaded bore  50  passes through the plate  30  and the boss  33  from top to bottom thereof and centrally with respect to the closure cap  3 . 
     The set screw  4  has a base  53  and a head  54 . The set screw base  53  has an outer cylindrical surface  56  that is threaded to be threadably received within the closure cap bore  50  during use. The base  53  also includes a lower tip or point  57 . The set screw head  54  includes a polyhedral shaped radially outward surface which in the illustrated embodiment is a hexagonal shaped surface  60  to allow a tool to have purchase or to grip of the set screw  4  during insertion. The head  54  is joined to the base  53  by a breakaway region  61 . 
     Installation of the set screw  4  into the closure cap  3  is illustrated in FIG.  6 . Illustrated in FIG. 7 is the set screw base  53  fully inserted into the cap  3  with the head  54  broken away. That is, as the set screw  4  is inserted into the closure cap  3  it is advanced in the bore  50  until the tip  57  engages the rod  20 , thereafter the set screw  4  is further rotated or torqued until sufficient torque is applied such that the head  54  breaks away from the base  53  at a preselected torque which may be on the order of 100 inch pounds. 
     The set screw  4  has a diameter that is substantially smaller than the space between the arms  16  and  17 . In this manner the set screw  4  sits and biases against a relatively short length of the rod  23  in comparison to the boss  33 . Therefore, even if the rod  23  is significantly bent, the set screw  4  engages such a small length of the rod  20  that it is less susceptible to loosening of either the rod  20  relative to the bone screw  2  or of the rod  20  relative to the set screw  4  when the rod  20  flexes during use. Preferably, the point  57  of the set screw  4  bites into the rod  20  directly opposite whereat the rod  20  abuttingly engages the seat  23 . 
     A set of tools is provided for both installing and removing the closure  1  from the bone screw  2 . The tools include a closure cap installing or holding tool  66 , a set screw torquing tool  68 , a closure cap anti-torque tool  69  and a removal tool  71 . 
     The closure cap installing or holding tool  66  includes an elongate shaft  88  ending in a threaded cylindrical mount  89  at a shoulder  90 . The threads on the mount  89  are sized and the tool  66  is also sized and shaped so that the mount  89  can be operably threaded into the closure cap bore  50 . 
     A gripable head  91  for operably rotating the tool  68  is positioned on the shaft  88  opposite the mount  89 . The mount  89  can be threaded into the closure cap bore  50  and snugged down thereagainst so as to temporarily secure the closure cap  3  to the closure cap holding tool  66 . The closure cap  3  is then threaded on the bone screw  2 , with the rod  20  received in the seat  23  of the bone screw  2 , by rotating the holding tool  66 . Once the closure cap  3  has been tightened onto the bone screw  2 , for example, to the position where the plate lower surface  38  engages the upper end of the bone screw arms  16  and  17 , the holding tool  66  is removed by rotating the tool  66  counterclockwise to release it from the closure cap  3 , leaving the closure  3  mounted on the bone screw  2  and configured so that the widest part of the closure  3  is generally perpendicular to the axis of the rod  20  at the seat  23 . 
     The second stage in the process of installing the closure cap  3  requires installation of the set screw  4 . This is accomplished by the combined usage of the set screw torquing tool  68  and the anti-torquing tool  69 . 
     The set screw torquing tool  68  is seen in FIG.  5  and includes an elongate shaft  93  ending at one end with a fixed torquing handle  94  and at the opposite end with a socket  95  that is sized and shaped to snugly receive the set screw head  54 . That is, the socket  95  will normally have the same polyhedral cross-section as the head  54  to allow it to firmly grip the head  54  and allow the torquing tool  68  to rotate the head. 
     The anti-torquing tool  69  also includes a shaft  97  attached at one end to a handle  98  for gripping and having a head  99  at an opposite end. A bore  100  extends through the shaft  97  to receive the tool  68 . The anti-torquing tool head  99  is sized and shaped to fit over both the closure cap  3  and about the tops of the bone screw arms  16  and  17 , so as to hold the cap  3  in place relative to the screw  2  and to operably prevent rotation of the closure cap  3  relative to the arms  16  and  17 , when the anti-torquing tool  69  is installed thereover. A central arch  103  allows the head  99  to be positioned over the rod  20 , as is shown in FIG.  6 . 
     Also as is shown in FIG. 6, the set screw torquing tool  68  is positioned through the bore  100  of the anti-torquing tool  69  with the anti-torquing tool  69  positioned over the combined closure cap  3  and on top of the bone screw  2 . The torquing tool  68  is specifically positioned on and operatively engages the set screw head  54  and is rotated clockwise, so as to drive the set screw  4  into the bore  50 . The anti-torquing tool  69  is simultaneously held by the installer so that the closure cap  3  does not rotate relative to the bone screw  2  during installation of the set screw  4 . The set screw  4  eventually engages the rod  20  and torque is continuously applied and increased to the set screw  4  until a predetermined torque is achieved at which time the set screw head  54  breaks from the base  52 , such as is illustrated in FIG.  7 . The set screw base  53  is then positively set against the rod  20  and secures and locks the rod  20  in place. The set screw tip or point  57  is preferably positioned opposite a location  104  where the rod  20  touches the seat  23 . In this manner, the set screw base  53  securely and tightly holds the rod  20  relative to the bone screw  2  even when ends of the rod  20  flex. 
     It is sometimes necessary for a closure device  1  to be removed from a bone screw  2  for various reasons. The removal tool  71  is provided for this purpose. 
     The removal tool  71  includes an elongate shaft  108  terminating at one end in a handle that can be rotated by a user and at an opposite end in a head  110 . The head  110  includes an internal cavity  112  that is substantially sized and shaped to snugly receive the closure cap  3 . The removal tool  71  is placed such that the closure cap  3  is received in the cavity  112  And rotated counterclockwise until free of the bone screw  2 . 
     Shown in FIGS. 10 and 11 is a second embodiment of a closure according to the present invention which is generally identified by the reference numeral  150 . The second closure  150  is in many ways similar to the closure  1  of the previous embodiment and is installed and generally removed by the same tools, as described for the previous embodiment. Further, many of the parts of the closure  150  are the same as the parts for closure  1  and, therefore, great detail will not be utilized to describe the similar parts. Further, the closure  150  is installed on a bone screw  151  that is very similar to the bone screw  2  and only dissimilar parts will be described in detail herein. 
     In particular, the bone screw  151  is essentially the same as bone screw  2 . The closure cap  150  has a plate  159  and side flanges  160  and  161 . The closure  150  includes a cylinder or boss  164  that depends from the plate  159  in a similar fashion, as described with respect to the previous embodiment. 
     The second closure  150  differs from the first embodiment primarily in that it includes a set screw  167  that is a non-break-off type of set screw. That is, the set screw  167  includes a threaded body  168  and head  169  that remains attached to the body  168  once the set screw has been fully installed and torqued to a desired torque against a rod  171 . 
     It is foreseen that the flange facing surfaces  42  and  43  and the bone screw arm outer surfaces  26  and  27  could also be matingly threaded so that not only the boss  33  screws into the threads of the interior surfaces  28  and  29  but the flanges  31  and  32  would also threadedly screw onto the exterior of the arms  16  and  17 . 
     It is to be understood that while certain forms of the present invention have been illustrated and described herein, it is not to be limited to the specific forms or arrangement of parts described and shown.