Abstract:
A polyaxial fastener is secured within an implant with a retaining ring. The ring is assembled onto a circumferential groove formed in the fastener head. The groove and ring are positionable, when the fastener is installed into an implant, at a wide portion of the mating polyaxial aperture in the implant. The ring is compressible into the groove to form a narrowed diameter, which is passable into a narrow diameter of the aperture, near an entrance to the aperture. The ring is released to expand and increase an overall diameter of the head and ring assembly, thereby rending the assembly too wide to pass by the narrow entrance to the aperture, thereby securing the assembly within the implant.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 14/252,313 filed on Apr. 14, 2014, which is a continuation of U.S. Pat. No. 8,734,495, filed on Jan. 18, 2012, which is incorporated by reference in its entirety herein. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to securing fasteners within the body, and more particularly to securing a fastener head within an aperture in an implant. 
     BACKGROUND OF THE INVENTION 
     Bones and bony structures are susceptible to a variety of weaknesses that can affect their ability to provide support and structure. Weaknesses in bony structures may have many causes, including degenerative diseases, tumors, fractures, and dislocations. Advances in medicine and engineering have provided doctors with a plurality of devices and techniques for alleviating or curing these weaknesses. 
     The cervical spine has presented challenges for doctors, partially due to the small size of the vertebrae and the spacing between adjacent vertebrae. Typically, weaknesses in the cervical spine, for example, are corrected by using devices that fuse one or more vertebrae together. Common devices involve plate systems that align and maintain adjacent cervical vertebrae in a desired position, with a desired spacing. 
     These devices, commonly referred to as bone fixation plating systems, typically include one or more plates and screws for aligning and holding vertebrae in a fixed position with respect to one another. Initial devices used stainless steel plates and screws. In order to remain fixed in place, the screws were required to pass completely through the vertebrae and into the spinal canal. These devices caused many complications and involved significant risks. To allow a screw to pass, drilling and then tapping of the vertebrae was required. In the process, instruments came within close proximity of the spinal cord, which required extreme care on the part of the surgeon. 
     In addition to the risks of surgically applying bone fixation plates, other complications arose. Commonly, these problems involve loosening and failure of the hardware. Two common failures are the breakage of the plates, and the backing out of the screws into soft tissues of the patient&#39;s body. The backing out of the screws is typically a result of the screws failure to achieve a sufficient purchase in the bone, although the stripping of the screws has also been known to cause this problem. Regardless of the cause of the hardware failures, a surgeon must repair or replace the broken parts, which requires undesirable invasive procedures. 
     SUMMARY OF THE INVENTION 
     In accordance with the disclosure, a fastener is insertable within an implant in a body, where the implant has an aperture through which the fastener may be inserted, the aperture including a curved inner profile defining a larger dimension and a smaller dimension, the fastener comprising: an elongated body; a head connected to the body and defining a curved profile mateable with the curved inner profile of the implant, the head further including a circumferential groove disposable proximate the larger dimension of the curved inner profile of the implant when the head is mated with the implant; and an open ring sized to be positionable partly within the circumferential groove to extend from the circumferential groove to thereby increase a widest dimension of the head, the ring formed with a resilient material, the ring resiliently expandable from a first compressed configuration having a first dimension to a second relaxed configuration having a second dimension, the second dimension larger than the first dimension, the head passable into the aperture when the ring is assembled into the groove and the ring is in the first compressed configuration, and the head not passable out of the aperture when the ring is resiliently expanded to the second configuration, due to the ring interfering in the second configuration with the smaller dimension of the curved inner profile. 
     In embodiments, the ring further includes a first end and a second end, the first end fixable within the groove, the second end moveable to change the ring from the first configuration to the second configuration; the ring further includes a first end and a second end, the first end fixed within the circumferential groove, and the second end moveable to change a shape of the ring from the first compressed configuration to the second relaxed configuration, the second end including a notch releasably engageable to maintain the ring in the first compressed configuration; a pin is removably connectable with the head and insertable into the notch to engage the notch to maintain the ring in the first compressed configuration, or removed from the notch to disengage the notch and enable the ring to resiliently expand to the second dimension. 
     In other embodiments, the fastener head is a polyaxial fastener head; the aperture is formed in an implant selected from the group consisting of bone plate, bone spacer, and prosthetic device; the fastener head further includes an access port through which an object may be inserted to maintain the ring in the first compressed configuration; the ring forming two ends, at least one of the ends forming a notch, the fastener further including a pin engageable with the head and the notch to maintain the ring in the compressed configuration when the pin is engaged with the head and the notch; the pin further including a pin head engageable with a tool to insert or remove the pin from the notch. 
     In yet further embodiments, the ring further includes moveable first end second ends, the first and second ends moveable towards each other to form the first configuration of the ring, and releasable to move away from each other to form the second configuration of the ring; and the ring forming first and second ends, the first end fastened within the groove by a method selected from welding, brazing, adhesive, interference fit, and mating hook. 
     Further in accordance with the disclosure, a fastener is insertable within an implant in a body, the implant having an aperture through which the fastener may be inserted, the aperture including a polyaxial curved inner profile defining a first diameter proximate an entrance to the aperture, and a second larger diameter further within the aperture, the fastener comprising: an elongated body; a polyaxial head connected to the body and defining a curved profile mateable with the curved inner profile of the implant, the head further including a circumferential groove disposable proximate the larger diameter of the curved inner profile of the implant when the head is mated with the implant; an open ring forming first and second ends, the ring sized to be positionable partly within the circumferential groove to extend from the circumferential groove to thereby increase a widest diameter of the head, the ring formed with a resilient material, the ring resiliently expandable from a first compressed configuration having a first dimension to a second relaxed configuration having a second dimension, the second dimension larger than the first dimension, the head passable into the aperture past the first diameter when the ring is assembled into the groove and the ring is in the first compressed configuration, and the head not passable back out of the aperture when the ring is resiliently expanded to the second configuration, due to the ring and assembled ring interfering in the second configuration with the smaller diameter of the curved inner profile, the first ring end fixed within the groove, the second ring end moveable to change the ring between the first and second configurations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present invention, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: 
         FIG. 1  depicts an implant including an installed fastener of the disclosure; 
         FIG. 2  depicts a top view of the fastener of  FIG. 1 ; 
         FIG. 3  depicts a perspective view of the fastener of  FIG. 1 ; 
         FIG. 4  depicts a section of the fastener of  FIG. 1 , taken through the longitudinal center of the fastener; 
         FIG. 5  depicts a perspective view of a retaining ring in accordance with the disclosure; 
         FIG. 5A  depicts an alternative hooked embodiment of the ring of  FIG. 5 ; 
         FIG. 6  depicts a top view of the ring of  FIG. 5 ; 
         FIG. 7  depicts a pin in accordance with the disclosure; 
         FIG. 8  depicts a perspective view of the pin of  FIG. 7 ; 
         FIG. 9  depicts a bottom view of the pin of  FIG. 7 ; 
         FIG. 10  depicts an assembly of the fastener of  FIG. 1  with the retaining ring of  FIG. 5  and pin of  FIG. 7 ; 
         FIG. 11  depicts a section of the assembly of  FIG. 10 ; 
         FIG. 12  depicts the assembly of  FIG. 10 , installed within an implant, in a compressed configuration; 
         FIG. 13  depicts the assembly of  FIG. 12 , having the pin removed, the ring in a relaxed configuration, the assembly secured within the implant; 
         FIGS. 14-16  depicts retaining rings usable to secure the fastener of  FIG. 1 , in accordance with the disclosure; 
         FIG. 17  depicts a cross section of the fastener of  FIG. 1 , assembled with the retaining ring of  FIG. 15 ; 
         FIG. 18  depicts an alternative retaining ring in accordance with the disclosure, including two moveable ends each having an engagement notch; and 
         FIG. 19  depicts a cross section of the fastener of  FIG. 1 , assembled with the retaining ring of  FIG. 18 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As required, detailed embodiments are disclosed herein; however, it is to be understood that the disclosed embodiments are merely examples and that the systems and methods described below can 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 subject matter in virtually any appropriately detailed structure and function. Further, the terms and phrases used herein are not intended to be limiting, but rather, to provide an understandable description of the concepts. 
     The terms “a” or “an”, as used herein, are defined as one or more than one. The term plurality, as used herein, is defined as two or more than two. The term another, as used herein, is defined as at least a second or more. The terms “including” and “having,” as used herein, are defined as comprising (i.e., open language). The term “coupled,” as used herein, is defined as “connected,” although not necessarily directly, and not necessarily mechanically. 
     Referring now to  FIG. 1 , a fastener  100  of the disclosure is connected to an implant  300  within a patient&#39;s body  400  (not shown), by being passed through an implant aperture  302 . In the example shown in  FIG. 1 , implant  300  is joining three portions of body tissue  402 ,  404 ,  406 , schematically represented as dashed outlines. Body tissue may be bony or soft tissue, and may be a single bone which is strengthened or aligned until healed, or may be multiple bones, for example vertebrae, which are maintained in relative spaced alignment by implant  300 . While in the example shown in  FIG. 1 , implant  300  is a plate, it should be understood that implant  300  may be any object placed into the body for a therapeutic purpose, including for example a body tissue replacement or prosthetic, an instrument or tool, or an autograft, allograft, or xenograft. An example of a stabilizing plate may be found in commonly assigned U.S. Pat. No. 7,963,981, to Binder, et al. While a plate is shown, the disclosure contemplates any implant capable of including an aperture  302  into which fastener  100  may be inserted, including bone spacers, for example an intervertebral spacer, and a prosthetic device, for example an articulating joint surface replacement, or a joint stabilizer, including for example a rod holder. 
     Additionally referring to  FIGS. 12 and 13 , implant  300 , in accordance with the disclosure includes one or more implant apertures  302  each having an entry  304  that is wider than an exit  306 . A tapering or curved profile  308  is defined between entry  304  and exit  306 . 
     With reference to  FIGS. 2-4 , fastener  100  includes a fastener head  104  having a width wider than exit  306 , but which may pass, in a first configuration, through entry  304 , as explained further below. Fastener head  104  is advantageously formed with an outer tapering or curved profile  108  that is complementary to inner curved profile  308  of aperture  302 . In this manner, fastener extension  106  may be passed through exit  306 , and outer and inner curved profiles  108 ,  308  may be positioned in mating conformity. Provided exit  306  is wider than a width of fastener extension  106 , fastener  100  may be swiveled within aperture  302  while maintaining a substantial extent of mutual contact between outer and inner curved profiles  108 ,  308 . Either or both of curved profiles  108 ,  308  may be provided with a roughened or textured surface to promote maintaining a particular conforming configuration once fastener  100  is tightened. As such, aperture  302  and fastener head  104  form a polyaxial mating surface, wherein fastener  100  may be secured at any of a wide range of angles with respect to implant  300 . In one embodiment, fastener  100  forms a polyaxial screw. 
     Fastener  100  includes threads  110  operative to retain fastener  100  in a desired position. While threads  110  are illustrated, it should be understood that fastener  100  may advantageously include, in accordance with the disclosure, an extension of any known or hereinafter developed type, including as examples circumferential rings, barbs, expanding elements, pivotable elements, cammed elements, tapered threads, self tapping threads, and machine threads. Additionally included is a tool engaging surface  112  which may be internally disposed, as illustrated, or which may be externally formed as an extension of head  104 . In the example shown, tool engaging surface is a hex socket; however, any known or hereinafter developed tool engagement may advantageously be used in accordance with the disclosure. 
     A circumferential groove  114  extends at least partially around head  104 , exposed by an access port  116 . Groove  114  is sized and dimensioned to receive a retaining ring  118 , illustrated in  FIGS. 5-6 . As explained more fully below, retaining ring  118 , when disposed within groove  114  in an expanded configuration, functions to increase a dimension of fastener head  104 . When the assembled retaining ring  118  and head  104  are disposed within aperture  302 , the assembly  118 ,  104  is too large to pass out of aperture  302 , and fastener  100  is thereby secured within implant  300 . 
     With further reference to  FIGS. 5 and 6 , retaining ring  118  is formed to have a first, relaxed configuration having a resting diameter, and a second, compressed configuration having a reduced diameter with respect to the relaxed configuration. One or more weakened, narrowed, or more flexible portions  120  formed along an interior periphery of ring  118  facilitate an over-expansion to a dimension greater than the relaxed configuration, for assembly of ring  118  onto fastener head  104 , or a contraction from the relaxed to the compressed configuration, without damage or excessive distortion to retaining ring  118 . Retaining ring  118  is formed from, or includes, a resilient material, whereby ring  118  expands from the compressed configuration to the relaxed configuration due to this resiliency. 
     Retaining ring  118  further includes a fixed ring end  122  and a movable ring end  124 , which become closer together in the compressed configuration. Fixed ring end  122  may be tethered or affixed within groove  114  by any known means, including welding, brazing, or adhesive. Alternatively, fixed end  122  may be have a larger dimension than a remainder of ring  118 , whereby an interference fit is formed with groove  114 . In another embodiment, shown in  FIG. 5A , fixed ring end  122  may be formed with a hook, mateable with a projection within groove  114  (not shown). In yet another embodiment, retaining ring is machined from the material of fastener head  104 . 
     When fixed ring end  122  is affixed within groove  114 , ring  118  may be compressed or relaxed by controlling a position of moveable ring end  124 . In one embodiment of the disclosure, ring  118  is placed within groove  114 , and is squeezed or coiled inwards about fastener  104  into the compressed configuration by applying pressure to different portions of ring  118 . In such configuration, an engagement notch  126  may be aligned with access port  116  of fastener head  104 . Once aligned, retaining pin  130  may be inserted through access port  116  and engagement notch  126 , to thereby retain ring  118  in the compressed configuration. The assembled fastener  100 , ring  118 , and pin  130 , shown in  FIGS. 10-12 , may then be fastened to implant  300 . 
     Once fastener head  104  is seated within aperture  302 , for example after having been driven into body tissue, pin  130  may be removed by grasping pin head  132  with a tool, for example forceps, or a forked instrument (not shown) operable to engage pin neck  134 . Once pin  130  is removed, moveable ring end  124  is free to move in a direction away from fixed ring end  122 , and ring  118  is may then expand to the relaxed configuration, as shown in  FIG. 13 . As the assembled fastener head  104  and ring  118  are disposed within aperture  302 , ring  118  expands so that portions of ring  118  become closer to, or engages with, curved profile  308  of aperture  302 . 
     Curved profile  308  forms a progressively smaller diameter towards entry  304 . The diameter of fastener head  104  and assembled compressed ring  118  is sufficiently small to pass through entry  304 , or is further compressible to pass through entry  304 . However, assembled diameter of fastener head  104  and relaxed ring  118  is greater than the narrow diameter proximate entry  304 , and therefore when ring  118  is in the relaxed configuration, the assembled fastener head  104  and ring  118  cannot pass back through entry  304 , and fastener  100  is thus prevented from separating from implant  300 , for example by a backing-out of threads of a threaded fastener  100 . It is accordingly advantageous for groove  114  to be formed upon fastener head  104  to correspond to a widest diameter of aperture  302 . 
     As may be seen in  FIGS. 7-9 , pin  130  may be provided with a cam  136  operative to contact engagement notch  126  to retain ring  118  in the compressed configuration. Pin  130  may further be provided with a curved profile  138  mateable with a surface of fastener head  104 , whereby pin  130  may be rotated to either release or contact engagement notch  126 . A flattened profile  140  is advantageously provided to avoid interference with aperture  302  during installation of fastener  100  into implant  300 . Engagement notch is sized and dimensioned to admit a portion of pin  130 , for example cam  136 , when pin  130  is assembled onto fastener  100 . 
     In another embodiment, curved profile  308  may be provided with a ramped profile  310  at entry  304 , whereby ring  118  may engage ramped profile  310  as fastener  100  is inserted into aperture  302 . During engagement, ring  118  may be urged into the compressed configuration by engagement with ramped profile  310 , and fastener  100  and assembled ring  118  may thereby form a sufficiently small diameter to pass into aperture  302 . As curved profile  308  widens, ring  118  resiliently expands to form a wider diameter, thereby preventing undesired exit of fastener  100  from aperture  302 . A bevel (not shown) on a lower ramp engaging surface of ring  118  may advantageously be provided, independent of, or cooperative with ramped profile  310 , to facilitate compression of ring  118  during insertion of fastener  100 . 
     With reference to  FIGS. 14-17 , in a further embodiment, retaining ring  150 , shown in various forms  150 A- 150 C, in  FIGS. 14-16 , has the form of an internal retaining ring or snap ring with apertures for engagement by retaining ring pliers. Retaining ring  150  is inserted into groove  114 , and engages curved profile  308  in the manner described for retaining ring  118 . Fastener head  104  and or implant  300  may advantageously be provided with removed material in order to admit access to retaining ring pliers. 
     In accordance with the disclosure, the extent of interference, or cling, between ring  118  or  150  and groove  114 , does not prevent ring  118 ,  150  from returning to a relaxed configuration when not engaged by pin  130  or retaining ring pliers. 
     With reference to  FIGS. 18-19 , in accordance with a further embodiment of the disclosure, retaining ring  118  may be provided with two moveable ring ends, including moveable ring end  124 A, which is provided with an engagement notch  126 A. In this embodiment, engagement notches  126 ,  126 A are overlapped, and pin  130  is positioned within the overlapped notches to maintain ring  118  in a compressed configuration until fastener head  104  is positioned within aperture  302 . 
     All components of fastener  100 , including ring  118 ,  150 , pin  130 , and implant  300  are advantageously formed from biocompatible materials of suitable strength and wear resistance to perform an intended therapeutic function within the body. Examples of such materials include, but are not limited to, polymers, for example ultra high molecular weight polyethylene or polyoxymethylene copolymer, metals, for example titanium or nitinol, natural materials, bone, autograft, allograft, or xenograft tissue, or composite materials. 
     Ring  118  may be removed by an instrument (not shown) which is shaped to enter access port  116  and pull engagement notch  126  towards alignment with access port  116 , whereby pin  130  or other object may be inserted to prevent uncoiling or relaxing of ring  118 . Alternatively, fastener  100  may be pressed against tapered profile  308  while rotated, to coil ring  118  to form the compressed configuration. Ring  150  may be removed with retaining ring pliers. 
     In accordance with the foregoing, the disclosure provides a device and method for retaining a fastener within an implant. For example, when using certain implants, specifically anterior cervical plates, the utilization of a bone screw locking mechanism of the disclosure provides screw retention that greatly increased the safety of the implanted device. Medical practitioners may have much greater certainty that an implanted device and fastener are locked together. The locking mechanism including fastener  100  and ring  118 ,  150  of the disclosure provides a visual and tactile confirmation that the screw is locked to the plate. Visible confirmations include the absence of pin  130 , as well as the presence of ring  118 ,  150  occupying the free space between fastener head  104  and curved profile  308 , as may be observed through access port  116 . An audible and or tactile confirmation is provided when pin  130  is removed, as ring  118  snaps against curved profile  308 , or as retaining pliers release retainer  150 . 
     To use fastener  100 , retaining ring  118  is assembled into groove  114  in head  104 , for example by resiliently bending ring  118 , possibly using a tool which engages ring ends  122 ,  124 . Ring  118  is compressed by applying pressure to the ring, possibly using a tool, and pin  130  is assembled into head  104  to pass through retaining ring engagement notch  126  to secure moveable ring end  124 . An implant  300  is positioned at a desired location with respect to body tissue  400 . Fastener extension  106  is passed into aperture  302 , passing through aperture entry  304  and contacting body tissue at aperture exit  306 . For threaded fasteners, fastener  100  is rotated, for example through a tool engaged with tool engaging surface  112 , or by pushing a barbed or toggling fastener, or by any other means appropriate to the type of fastener extension  106  used. For the retaining rings of  FIGS. 14-17 , retaining ring pliers may be used to maintain a compressed configuration of ring  118 . For ramped or beveled embodiments, insertion force of fastener  100  may be sufficient to compress ring  118  into groove  114  at aperture entry  304 . When fastener  100  is seated, outer curved profile  108  of head  104  will be positioned in mating contact with inner curved profile  308  of aperture  302 . Where pin  130  is used, pin  130  is removed once head  104  is seated within aperture  302 , thereby releasing ring  118  to resiliently expand against aperture inner curved profile  308 , to secure head  104  from backing out of a position within aperture  302 . 
     To remove fastener  100 , a tool may be passed through fastener access port  116  to draw engagement notch  126  into alignment with access port  116 , whereby pin  130  may be reassembled onto head  104  to maintain a compressed configuration of ring  118 . Fastener  100  may then be withdrawn using a tool or other means appropriate to the type of fastener extension  106  employed. Retaining ring pliers may be employed for the embodiments of  FIGS. 14-17 . It should be understood that other embodiments of retaining rings  118  may be provided with apertures similar to those of  FIGS. 14-17 , whereby retaining ring pliers may be used to compress ring  118 . In other embodiments, a sufficient force of unscrewing or withdrawing may be applied operative to break ring  118 , particularly for thin, non-metallic, or polymeric retaining rings. Once retaining ring is compressed or broken, fastener  100  may be withdrawn in a like manner as inserted. 
     In another embodiment, fastener  100  is not connected to body tissue, but connects portions of implant  300 . Otherwise, use is correspondingly similar to the foregoing description. 
     Additional fasteners, and or longer fasteners, have been employed in the prior art to reduce a likelihood that a fastened implant will come loose. The instant disclosure provides an alternative to these methods, because a medical practitioner can be certain that the fasteners implanted will not back out of engagement with the implant. A drawback to longer screws is that long screws do not allow for sufficient movement of the vertebrae to accommodate the compression of a bone graft, because the purchase of the screws is too great. Thus, the vertebrae cannot move and are unable to adjust to the compression of the bone graft. The instant disclosure provides a way to reliably use shorter screws which permit sufficient, but not excessive, movement of the vertebrae to maintain compression of a bone graft. A drawback to additional fasteners is increased time in surgery, increased cost in materials, and further trauma to the body. The instant disclosure therefore provides for reducing these drawbacks. 
     The instant disclosure further provides an alternative to placing a second plate or structure on top of a fastener. This avoids the additional bulk and undesirable interference with and irritation to overlying body tissue, as well as the additional installation time required for assembly during surgery. Examples of undesirable consequence of a bulky implant include dysphasia, and wear to neighboring tissue, which may include the aorta, or vena cava. 
     The instant disclosure further prevents backing out of fasteners due to tiny vibrations, or micromotions, through the resilient and continual engagement of ring  115 ,  150  with curved profile  308 . 
     It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings without departing from the scope and spirit of the invention. 
     All references cited herein are expressly incorporated by reference in their entirety. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. There are many different features to the present invention and it is contemplated that these features may be used together or separately. Thus, the invention should not be limited to any particular combination of features or to a particular application of the invention. Further, it should be understood that variations and modifications within the spirit and scope of the invention might occur to those skilled in the art to which the invention pertains. Accordingly, all expedient modifications readily attainable by one versed in the art from the disclosure set forth herein that are within the scope and spirit of the present invention are to be included as further embodiments of the present invention.