Abstract:
A polyaxial bone anchor with a receiver, a shank, a pressure insert, a retainer for holding the shank in the receiver, and a closure. The receiver having at least one vertically aligned guide on a surface of an interior shank and insert receiving chamber. The insert having at least one shoulder that aligns with the guide and both properly positions the insert relative to the receiver during assembly and prevents the insert from axially rotating relative to the receiver.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 62/007,623 filed Jun. 4, 2014, which is incorporated by reference herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Polyaxial bone screws and related anchors of various types have been used for supporting rods and other elongate members in spinal surgery. Some of these bone screws utilize a lower pressure insert to transfer locking forces from a rod or other structure above the insert to a shank below the insert, so as to lock the shank in a fixed angular configuration with respect to a receiver. A problem encountered with the insert is that during assembly of the insert into the receiver and/or during transport and/or during implantation of the anchor into a patient, the insert may undesirably rotate from a preferred alignment and configuration relative to the receiver. 
       SUMMARY OF THE INVENTION  
       [0003]    A bone anchor assembly, especially a bone screw, includes a shank for implanting into a bone, a receiver for holding the shank and receiving an elongate connecting member such as a rod, a pressure insert with opposed upwardly extending arms and a closure. Preferably, the shank has a spherical head and polyaxially joins with the receiver and is held in the receiver by a retainer that may be joined to the receiver or the shank head. The receiver has upper arms that are spaced and form a channel for receiving the elongate member. The receiver arms include break-off extensions, although in some embodiments no extensions will be included. The closure is advancingly received between the arms and applies locking pressure to the elongate member which in turn applies the pressure to the insert that locks the position of the shank relative to the receiver. The closure can also be configured to apply locking pressure to the insert before independently applying locking pressure to the elongate member. 
         [0004]    The insert is preferably uploaded into the receiver, but may be downloaded through the channel in certain embodiments. The insert has a plurality of and particularly four opposed generally vertically aligned corners or shoulders. The receiver has a plurality of and particularly four alignment and positioning guides that form regions for receiving the insert shoulders and that snugly ‘slidingly mate with the shoulders on the insert as the insert is being axially or vertically loaded into the receiver. The insert shoulders and the receiver guides cooperate to properly position the insert in the receiver while preventing the insert from rotating axially relative to the receiver. The insert has upwardly extending arms form an insert channel that then aligns with a similar channel of the receiver to accept the elongate member. 
         [0005]    Preferably, the shank is cannulated and is polyaxially moveably in the receiver during positioning and thereafter locked in place. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is an exploded view of a bone screw including a shank, a receiver, a retainer, a pressure insert and a closure, shown in conjunction with a rod. 
           [0007]      FIG. 2  is a cross sectional view of the bone screw taken along line  2 - 2  of  FIG. 3 . 
           [0008]      FIG. 3  is a top plan view of the bone screw. 
           [0009]      FIG. 4  is a side elevational view of the receiver. 
           [0010]      FIG. 5  is a cross sectional view of the receiver, taken along line  5 - 5  of  FIG. 6 . 
           [0011]      FIG. 6  is a bottom plan view of the receiver. 
           [0012]      FIG. 7  is a top plan view of the receiver. 
           [0013]      FIG. 8  is a perspective view of the retainer. 
           [0014]      FIG. 9  is a top plan view of the retainer. 
           [0015]      FIG. 10  is a side elevational view of the retainer. 
           [0016]      FIG. 11  is a cross sectional view of the retainer, taken along line  11 - 11  of  FIG. 9 . 
           [0017]      FIG. 12  is a perspective view of the insert. 
           [0018]      FIG. 13  is a top plan view of the insert. 
           [0019]      FIG. 14  is a side elevational view of the insert. 
           [0020]      FIG. 15  is a bottom plan view of the insert. 
           [0021]      FIG. 16  is a perspective view of the receiver, insert and retainer with portions of the retainer cut away to show cooperation of the parts at a stage whereat the insert is being positioned in the receiver. 
           [0022]      FIG. 17  is a perspective view of the receiver, insert and retainer with portions of the retainer cut away to show cooperation of the parts at a stage whereat the insert is in an upper most position relative to the receiver. 
           [0023]      FIG. 18  is a partial top plan view of the combined receiver and insert with portions of the retainer broken away to illustrate mating of the insert and retainer. 
           [0024]      FIG. 19  is a cross section of a side elevational view of the receiver, taken along line  19 - 19  of  FIG. 7  showing the receiver before assembly of the bone anchor. 
           [0025]      FIG. 20  is a cross section of the receiver, as in  FIG. 19 , showing a first stage of the positioning of the insert in the receiver. 
           [0026]      FIG. 21  is a cross section of the receiver as in  FIG. 20  showing a second stage of the positioning of the retainer in the receiver. 
           [0027]      FIG. 22  is a cross section of the receiver as in  FIG. 20  showing a third stage of the positioning of the shank head in the receiver with the shank first entering the receiver. 
           [0028]      FIG. 23  is a cross section of the receiver as in  FIG. 19  showing a fourth stage of the positioning of the insert in the receiver with the shank head having passed through the retainer and being captured in the receiver. 
           [0029]      FIG. 24  is a cross section of the receiver as in  FIG. 19  showing view of a fifth stage of the positioning of the insert in the receiver with a rod and closure added and the closure applying pressure only to insert. 
           [0030]      FIG. 25  is a cross section of the receiver as in  FIG. 19  showing a sixth stage of the positioning of the insert in the receiver showing the closure pushing the rod downwardly into a locked position against the insert. 
           [0031]      FIG. 26  is a cross section of the receiver as in  FIG. 19  showing a ninth stage of the positioning of the insert in the receiver with the rod secured in place in a channel of the receiver and a head of the closure broken away. 
           [0032]      FIG. 27  is a side elevational view of the bone anchor with a rod shown in phantom and with the shank pivoted with respect to the retainer with portions removed to show detail thereof. 
           [0033]      FIG. 28  is a perspective view of a second embodiment of a closure usable with the present invention. 
           [0034]      FIG. 29  is a cross sectional view of the closure of  FIG. 28 , taken along line  29 - 29  of  FIG. 28 . 
           [0035]      FIG. 30  is a side elevational view of a bone anchor assembly with the closure of  FIG. 28  and a receiver, rod, pressure insert and retainer with the receiver partially broken away to show detail thereof. 
       
    
    
       [0036]    The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0037]    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. 
         [0038]    The reference numeral  1  generally indicates a bone anchor in accordance with the invention. While the illustrated anchor  1  is generally a polyaxial bone screw, it is foreseen that the invention could be utilized with other types of spinal implants that utilize pressure inserts, such as polyaxial bone hooks. 
         [0039]    The bone anchor  1  comprises a shank  5 , a retainer  6 , a pressure insert  7 , a receiver  8  and a closure  9  and is used with an elongate member  10 . 
         [0040]    The shank  5  as seen in  FIGS. 1 to 3  has a lower portion  15  and an upper portion  16  with an axial bore  17  throughout so as to cannulate the shank  5 . The lower portion  15  has a flighting or helical wound thread  20  which is doubled in the upper half for threading into a vertebra of a patient. 
         [0041]    The shank upper portion  16  includes a bulbous and partially spherical head  22  that radially extends outward from a neck  23  joining the head  22  to the lower portion  15 . Axially centered and extending downward from the top of the head  22  is a tool receiving structure  24  with radially inward extending alternating lobes  25  for receiving and gripping a tool (not shown) used to drive the shank  5  into a bone of a patient. An upper surface  26  of the head  22  has a series of concentric gripping ribs  27  for enhancing frictional contact with the insert  7  which can be made of a somewhat softer metal compared to that of the head. 
         [0042]    Illustrated in  FIGS. 4 to 7  is the receiver  8 . The receiver  8  has a lower body  30  and a pair of upstanding spaced arms  31  and  32  forming an elongate member receiving channel  33 . In the illustrated embodiment the channel  33  is generally U-shaped, but the shape can be varied to accommodate elongate members of different shapes. Attached by break off junctures  34  to the arms are extensions  35 . On facing inner surfaces of the arms are guide and advancement structure which in the illustrated embodiment are helical wound reverse angle thread forms  36 , but can be various types of threads, such as a conventional V thread, buttress or square threads or helical flanges. Tool grasping apertures  37  are located on the sides of each arm  31  and  32 . 
         [0043]    Located in the receiver body  30  is a chamber  40  formed by side walls  41  that opens both into the channel  33  above and to the exterior through a lower opening  42 . During assembly of the anchor  1 , the chamber  40  receives both the shank head  22  and the insert  7 . The lower end of the chamber has a first groove  44  and a larger second groove  45  that are axially aligned with a central Axis A of the receiver, the purpose of which will be discussed later. It is foreseen that the shank can be downloaded into the receiver and not require a retainer, and that the receiver does not have but one groove for the retainer. 
         [0044]    Located on the chamber side walls  41  near an upper side thereof are four spaced and radially inward projecting projections or guides  46 . The guides  46  cooperate with the insert  7  as discussed below. 
         [0045]    The retainer  6  is shown in  FIGS. 8 to 11 . The retainer  6  is an open resilient ring  49  with a gap or break  50  to allow contraction and expansion thereof. The ring  49  is compressed and loaded into the receiver. This can occur before or after loading the shank in some embodiments. In the embodiment shown, the ring is loaded first and passes over the shank head  22  during loading of the head  22  into the chamber  40  thereby capturing the shank. During expansion, the ring  49  is received in the larger receiver groove  45  after which the ring  49  is lowered into the smaller groove  44  which is about the same diameter as the ring  49  so that the ring  49  fits snugly therein to prevent repeated expansion. In this manner, the ring  49  holds the shank head  22  in the receiver  8  and allows the shank  5  to pivot relative to the receiver  8  during positioning and before locking. 
         [0046]    The insert  7  is best seen in  FIGS. 12 to 18 . The insert  7  includes a lower body  52  with a pair of spaced upstanding arms  53  and  54 . The arms  53  and  54  and body  52  have a continuous radially outer surface  55  on each side which are substantially smooth and vertically or axially aligned, but radially spaced from the Axis A. The arms  53  and  54  form a central U-shaped channel  57  therebetween and there is a central axially aligned and centered bore  58 . 
         [0047]    On either side of the arms  53  and  54  are flat surfaces  60  and  61 . At the intersection of the surfaces  60  and  61  with the surfaces  55  and  56  are formed four corners or shoulders  65 . The shoulders  65  extend along a length of the insert  7  and are vertically or axially aligned. Each of the shoulders  65  are sized and shaped to vertically slide, but snugly mate with the receiver guides  46 . This allows the insert  7  to move vertically during loading into the receiver  8  and during certain positioning required during assembly and implantation of the anchor  1 , but prevents the insert  7  from rotating about the axis A relative to the receiver  8 . This relationship is perhaps best seen in  FIG. 16  wherein the left rear shoulder  65  is seen sliding vertically along the receiver surface  66  and guide  46 , but is constrained from axial rotation by the abutment of the shoulder  65  with the guide  46 . 
         [0048]    The closure  9  is best seen in  FIG. 1 . The closure  9  has a body  70  with a head  71  that has a tool engagement surface  72  and that breaks from the body  70  at a predetermined torque. Helically wound about the body  70  is a guide and advancement structure  73  which operably mates with the guide and advancement structure  36  on the receiver arms  31  and  32 . 
         [0049]    The elongate member  10  is for extending between various implants (not shown) in an overall system. The illustrated elongate member  10  is a circular rod, although members of various construction and shape may be utilized. 
         [0050]      FIGS. 19 to 27  show various stages in the assembly and utilization of the anchor  1  in a snap-on screw embodiment. 
         [0051]    The receiver  8  is shown by itself in  FIG. 19 . In  FIG. 20  the pressure insert  7  is uploaded through the opening  42  into the chamber  40 . In  FIG. 21 , the retainer ring  49  is placed in the chamber  40 . In  FIG. 22 , the top of the shank  5  is partially inserted into the chamber  40  and abuts against the retainer  6 . 
         [0052]    In  FIG. 23 , the ring  6  has captured the shank head after moving up into the larger receiver groove  45  and coming back down into the smaller groove, while the insert moved upward being aligned and guided by the guides  46 . In  FIG. 24 , the shank head is, again, shown fully captured and the ring  49 , which is located around the lower half of the head  22 , is shown fully seated in the lower and smaller groove  44 . The closure is seen compressing the insert to lock the shank with respect to the receiver before locking the rod. 
         [0053]    Shown in  FIG. 25 , the closure is now also independently locking the rod  10 . In  FIG. 26 , the closure  9  is fully advanced against both the insert and the rod  10  and the head  71  is broken away. The arm extensions  35  can then be broken away (not shown). At this point, the closure  9  applies pressure to the rod  10  and/or pressure insert  7  which applies pressure to the shank  5  thereby locking the shank  5  in a fixed rotational position relative to the axis A of the receiver with the shank implanted in a bone (not shown). Prior to locking the shank  5  is polyaxially rotatable relative to the receiver  8  meaning that the angle of the shank  5  may be varied with respect to the receiver  8  and the axis A. 
         [0054]      FIG. 27  shows an alternative locked configuration for the polyaxial positioning of the shank  5  relative to the receiver  8 . 
         [0055]    Once the insert  7  enters the receiver chamber  40 , the guides  46  cooperate with the insert shoulder  65  to guide the insert  7  up and down in the receiver  8  while preventing rotation of the insert relative to the receiver  8 . 
         [0056]    Shown in  FIGS. 28 to 30  is an alternative closure for use with the present invention generally identified by the reference numeral  109 . It is shown in use in an implant assembly  101  shown in  FIG. 30 . The closure  109  differs in several aspects from the closure  9 . In particular, the closure  9  has an outer ring with a central screw sometimes referred to as a dual innie. The present closure has a unitary body  170  and includes a break off head  171 . The body  170  includes outer helical wound reverse angle threads  173  and an internal tool receiving structure  172  for driving the closure  109 . The head  171  is attached to the body  170  at a break off neck  175 . The head  171  is shown attached to the body  170  in  FIG. 30  just prior to breaking away. Importantly, depending from the bottom of the body  170  is a solid circular ring  180  that provides a reduced radius or step down  181 . 
         [0057]    Seen in  FIG. 30  is the closure  109  in a receiver  108  along with a shank  105 , a shank retainer  106 , a pressure insert  107  and a rod  110 . The present insert  107  has two upstanding arms  180  and  181  each with a top surface  182 . The arms  180  and  181  are spaced such that the ring  180  on the bottom of the closure  109  passes therebetween on assembly with a slight clearance on each side. A lower surface  185  of the closure body  170  that is radially outward of the ring  180  remains spaced from the insert arms upper surface  182  during assembly and locking. The parts of the assembly  1  and  101  and especially the receiver  8  and  108  and the insert  7  and  107  are preferably constructed of metal that is strong and resists bending or splaying of the arms of either the insert  107  or receiver  108 . Preferred material of construction is any grade of titanium and most preferably, cobalt chrome. 
         [0058]    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.