Abstract:
A fastener assembly that can be used for the fixation or anchoring of orthopedic devices or instruments to bone tissue. In particular, a low profile variable angle or fixed angle fastener assembly is able to securely connect the orthopedic device to bone tissue. The fastener assembly may have a locking mechanism that will quickly and easily lock the fastener assembly with respect to the orthopedic device.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. Ser. No. 15/210,919, filed on Jul. 15, 2016, which is a continuation of U.S. patent application Ser. No. 14/877,177, filed on Oct. 7, 2015(now issued as U.S. Pat. No. 9,414,874), which is a continuation of U.S. patent application Ser. No. 14/645,466, filed Mar. 12, 2015 (now issued as U.S. Pat. No. 9,179,953), which is a divisional of U.S. patent application Ser. No. 14/103,556 filed on Dec. 11, 2013 (now issued as U.S. Pat. No. 9,005,258), which is a continuation of U.S. patent application Ser. No. 12/716,523 filed on Mar. 3, 2010 (now issued as U.S. Pat. No. 8,632,575). The contents of these prior applications are hereby incorporated by reference in their entities for all purposes. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention is directed to a bone fixation assembly and, in particular, to a low profile fastening assembly for securing an orthopedic device to bone tissue. 
       BACKGROUND OF THE INVENTION 
       [0003]    As is known in the field of orthopedic surgery, and more specifically spinal surgery, orthopedic fasteners may be used for fixation or for the anchoring of orthopedic devices or instruments to bone tissue. An exemplary use of fasteners may include using the fastener to anchor an orthopedic device, such as a bone plate, a spinal rod or a spinal spacer to a vertebral body for the treatment of a deformity or defect in a patient&#39;s spine. Focusing on the bone plate example, fasteners can be secured to a number of vertebral bodies and a bone plate can be connected to the vertebral bodies via the bone anchors to fuse a segment of the spine. In another example, orthopedic fasteners can be used to fix the location of a spinal spacer once the spacer is implanted between adjacent vertebral bodies. In yet another example, fasteners can be anchored to a number of vertebral bodies to fasten a spinal rod in place along a spinal column to treat a spinal deformity. 
         [0004]    However, the structure of spinal elements presents unique challenges to the use of orthopedic implants for supporting or immobilizing vertebral bodies. Among the challenges involved in supporting or fusing vertebral bodies is the effective installation of an orthopedic implant that will resist migration despite the rotational and translational forces placed upon the plate resulting from spinal loading and movement. Also, for certain implants, having low profile characteristics is beneficial in terms of patient comfort as well as anatomic compatibility. 
         [0005]    Furthermore, over time, it has been found that as a result of the forces placed upon the orthopedic implants and fasteners resulting from the movement of the spine and/or bone deterioration, the orthopedic fasteners can begin to “back out” from their installed position eventually resulting in the fasteners disconnecting from the implant and the implant migrating from the area of treatment. 
         [0006]    As such, there exists a need for a fastening system that provides for low profile placement of the bone anchor or screws and provides a mechanism where the fasteners are blocked to prevent the anchors from “backing out” of their installed position. 
       SUMMARY OF THE INVENTION 
       [0007]    In a preferred embodiment, the present invention provides an anchor assembly that can be used for the fixation or fastening of orthopedic implants to bone tissue. In particular, the present invention preferably provides a low profile variable angle or fixed angle fastener assembly that is able to securely connect the orthopedic device to bone tissue. Furthermore, in a preferred embodiment, the present invention further provides a fastener assembly having a locking mechanism that will quickly and easily lock the anchor assembly with respect to the orthopedic device. 
         [0008]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed desctiption and specific examples, while indicating the preferred or exemplary embodiments of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0010]      FIG. 1  is an exploded perspective view of one embodiment of a fastening assembly; 
           [0011]      FIG. 2  is a cross sectional side view of the fastening assembly shown in  FIG. 1 ; and 
           [0012]      FIG. 3  is schematic cross sectional side view of a prior art anchor system. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
         [0014]    With reference to  FIGS. 1 and 2 , a preferred embodiment of a fastening assembly  10  is illustrated. The fastening assembly  10  preferably includes a fastener  12 , a polyaxial locking head  24  and a locking mechanism  14 . The fastening assembly  10  is preferably constructed from any biocompatible material including, but not limited to, stainless steel alloys, titanium, titanium based alloys, or polymeric materials. Although the fastener  12  will be discussed in the context of an orthopedic screw, it is contemplated that the fastener  12  can be any type of fastening element including, but not limited to, a hook, a pin, or a nail. 
         [0015]    In a preferred embodiment, the fastener  12  includes, concentric to a longitudinal axis  16 , a head portion  18 , a neck portion  20  and a shank portion  22 . The head portion  18  connects to the shank portion  22  through the neck portion  20 . The neck portion  20  of the fastener  12 , preferably, integrally connects the head portion  18  with the shank portion  22 . The diameter of the neck portion  20  is preferably dimensioned to match a minor diameter of the fastener  12 . By having the diameter of the neck portion  20  dimensioned at least as large as the minor diameter of the fastener  12 , the overall rigidity and strength of the fastener  12  is increased. 
         [0016]    In a preferred embodiment, the shank portion  22  of the fastener  12  includes a shaft  23  surrounded at least in part by a thread portion  25 . The diameter of the shaft  23  is the minor diameter of the fastener  12 . In a preferred embodiment, the diameter of the shaft  23  remains generally constant from a proximal end of the shaft  23  toward a distal end of the shaft  23 . The constant diameter of a majority portion of the shaft  23  allows for optimal fastener positioning when the fastener  12  is inserted into a predetermined area in the bone tissue. The constant diameter also allows for varying the depth positioning of the fastener  12  in the bone. For example, if a surgeon places the fastener  12  into bone tissue at a first depth and decides the placement is more optimal at a second, shallower depth, the fastener  12  can be backed out to the second depth and still remain fixed in the bone. In another embodiment, the diameter of the shaft  23  may vary along its length, including increasing in diameter from the proximal end to the distal end or decreasing in diameter from the proximal end to the distal end. 
         [0017]    With continued reference to  FIGS. 1-2 , the thread portion  25  surrounding the shaft  23  extends, in a preferred embodiment, from the distal end of the shaft  23  to the neck portion  20 . In another preferred embodiment, the thread portion  25  may extend along only a portion of shaft  23 . The thread portion  25  is preferably a Modified Buttress thread but the thread can be any other type of threading that is anatomically conforming, including, but not limited to Buttress, Acme, Unified, Whitworth and B&amp;S Worm threads. 
         [0018]    In a preferred embodiment, the diameter of the thread portion  25  decreases towards the distal end of the fastener  12 . By having a decreased diameter thread portion  25  near the distal end of the fastener  12 , the fastener  12  can be self-starting. In another preferred embodiment, fastener  12  may also include at least one flute to clear any chips, dust, or debris generated when the fastener  12  is implanted into bone tissue. 
         [0019]    As best seen in  FIG. 1 , in a preferred embodiment, at least a portion of the head portion  18  of the fastener  12  has a generally spherical shape and is preferably surrounded by the polyaxial locking head  24 . In another preferred embodiment, the polyaxial locking head  24  includes at least one extension  26 , but, preferably includes two extensions  26 ; each extension  26  being located diametrically opposite to the other on the polyaxial locking head  24 . Preferably, also located on polyaxial locking head  24  is at least one, but preferably two, notches or openings  28 . The notches  28  are configured and dimensioned to correspond with the end of a driving instrument (not shown) designed to engage the polyaxial locking head  24 . This engagement allows a user to manipulate the polyaxial locking head  24  through the driving instrument. Similarly, the head portion  18  of the fastener  12  also preferably includes a cavity or opening  30  configured and dimensioned to correspond with the end of the same driving instrument or a separate driving instrument (not shown) designed to engage the fastener  12 . This engagement allows a user to drive the fastener  12  into bone tissue and otherwise manipulate the fastener  12 . 
         [0020]    Turning back to  FIGS. 1 and 2 , the generally spherical shape of the head portion  18  is configured and dimensioned to be received within a correspondingly shaped cavity  32  in the polyaxial locking head  24 . The shape of the head portion  18  and the correspondingly shaped cavity  32  allows the fastener  12  to pivot, rotate and/or move with respect to the polyaxial locking head  24 . It should be noted that the head portion  18  and the cavity  32  are dimensioned such that the head portion  18  cannot be removed or otherwise disengaged from the cavity  32  of the polyaxial locking head  24 . In another embodiment, instead of allowing the fastener  12  to pivot, rotate and/or move with respect to the polyaxial locking head  24 , the head portion  18  and the correspondingly shaped cavity  32  may be configured and dimensioned to keep the fastener  12  in a fixed position. In a preferred embodiment, the head portion  18  may include texturing  35  that extends along at least a portion of the head portion  18 . The texturing  35  on the head portion  18  provides additional frictional surfaces which aid in gripping the fastener  12  and holding the fastener  12  in place with respect to the polyaxial locking head  24 . 
         [0021]    In an exemplary use with an orthopedic device, the fastener  12  with the polyaxial locking head  24  is received in an opening  34  in an orthopedic device  36 . The opening is appropriately configured and dimensioned to receive the fastener  12  and the polyaxial locking head  24  such that the polyaxial locking head  24  can be rotated with respect to the device  36  and the fastener  12  can be pivoted, rotated or moved until the desired orientation is met with respect to the polyaxial locking head  24  and/or the device  36 . In a preferred embodiment, the opening  34  includes an upper opening  37  which receives the polyaxial locking head  24  and the head portion  18  of the fastener  12  and a lower opening  39  which receives the shank portion  22 . In a preferred embodiment, the upper opening  37  also includes extensions  38  which are configured and dimensioned to receive the extensions  26 . 
         [0022]    As mentioned above, in a preferred embodiment, the fastener assembly  10  includes the locking mechanism  14 . The locking mechanism  14  will lock the fastener assembly  10  with respect to the orthopedic device  36  thereby preventing the fastener assembly  10  from disengaging or “backing out” from the orthopedic device  36 . The locking mechanism  14  further assists in engaging the fastener  12  and the polyaxial locking head  24  with the opening  34  in the orthopedic device  36  in a low-profile arrangement. In a preferred embodiment, the locking mechanism  14  includes extensions  26  of the polyaxial locking head  24 , corresponding extensions  38  in the opening  34 , and grooves  40 . In a preferred embodiment, the grooves  40  extend from one extension  38  to the other extension  38  and are generally radial. Preferably, the grooves  40  are located between the upper surface  42  and a lower surface  46  of the device  36 . 
         [0023]    In an exemplary use of the fastener assembly  10  with the orthopedic device  36 , the orthopedic device  36  is first oriented and placed in the area of treatment. The orthopedic device  36  is then fastened to the bone tissue via at least one fastener assembly  10  which is received in at least one opening  34  of the orthopedic device  36 . More specifically, looking at  FIGS. 1-2 , in a preferred embodiment, the fastener  12  and the polyaxial locking head  24  are received in opening  34  such that the shank portion  22  passes through the lower opening  39  and the polyaxial locking head  24  and head portion  18  are receiving and seated in the upper opening  37 . The fastener  12  via notch  30  can then be driven into the bony tissue. As best seen in  FIG. 2 , when received in the opening  34 , the polyaxial locking head  24  and the fastener  12  are received in a low profile manner. In other words, regardless of the position of fastener  12 , even when the fastener  12  is rotated, pivoted, or otherwise moved, the head portion  18  of the fastener  12  will not breach the plane defined by an upper surface  42  of the device  36 . This is in contrast to prior art systems, one of which is shown in  FIG. 3 , where the head of a fastener will breach the plane defined by the upper surface of the orthopedic implant. This is particularly true when the fastener is installed at a steep or sharp angle. 
         [0024]    Once the fastener assembly  10  is seated in the cavity  34 , the fastener assembly  10  can be locked in the opening  34  by actuating the locking mechanism  14 . In a preferred embodiment, a user actuates locking mechanism  14  by rotating the polyaxial locking head  24  via notches  28  in a first direction. The rotational movement causes the extensions  26  which are seated in the extensions  38  to rotate into the grooves  40 . Although only one groove is shown in broken lines in  FIG. 1 , it should be understood that there are two sets of diametrically opposed grooves  40  which extend in an annular fashion between the extensions  38 . In a preferred embodiment, the grooves  40  include a stop to provide feedback to the user that the polyaxial locking head  24  has been fully rotated and the locking assembly  14  is engaged. In another preferred embodiment, the grooves  40  change in dimension so that the protrusions  26  can be captured in grooves  40  in an interference manner as the polyaxial locking head  24  is rotated. In yet another preferred embodiment, the grooves  40  include protrusions that provide audible and tactile feedback to the user as the user locks the fastening assembly  10 . 
         [0025]    With the polyaxial locking head  24  rotated, the fastener assembly  10  is locked in the opening  34  since the protrusion  26  in the grooves  40  prevents the polyaxial locking head  24  and fastener  12  from disengaging or “backing out” from the opening  34 . If a user wants to unlock the locking mechanism  14  and remove fastener assembly  10  from the opening  34  of device  36 , the user would simply rotate the polyaxial locking cap  24  via notches  28  in a second direction thereby rotating the protrusions  28  out of grooves  40  and into extensions  38 . At that point the locking mechanism  14  is disengaged and the fastener assembly  10  can be removed from the opening  34  of the orthopedic device  36 . 
         [0026]    The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.