Abstract:
In an exemplary embodiment, the present invention provides an anchor assembly that can be used for the fixation or fastening of orthopedic devices or instruments to bone tissue. In particular, the present invention preferably provides a variable angle or fixed angle anchor assembly that is able to securely connect the orthopedic device to bone tissue even when there is a variance in the angle and position of the assembly with respect to the device. Furthermore, in an exemplary embodiment, the present invention provides an anchor assembly having a locking mechanism that will quickly and easily lock the anchor assembly with respect to the orthopedic device.

Description:
FIELD OF THE INVENTION 
     The present invention is directed to a bone fixation assembly and, in particular, to an anchor assembly for securing an orthopedic device to bone tissue. 
     BACKGROUND OF THE INVENTION 
     As is known in the field of orthopedic surgery, and more specifically spinal surgery, bone anchors may be used for fixation or for the fastening of orthopedic devices or instruments to bone tissue. An exemplary use of bone anchors may include using the bone anchors to fasten 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, bone anchors can be secured to a number of vertebral bodies and a bone plate can then be connected to the vertebral bodies via the bone anchors to fuse a segment of the spine. In another example, bone anchors can be used to fix the location of a spinal spacer once the spacer is implanted between adjacent vertebral bodies. In yet another example, bone anchors can be fastened to a number of vertebral bodies to anchor a spinal rod in place along a spinal column to treat a spinal deformity. 
     In each of these exemplary uses, a plurality of bone anchors are needed to fasten the orthopedic device to the area of treatment. In addition, depending on the extent of the disease or size of the defect to be treated, it is possible that several orthopedic devices each requiring a plurality of bone anchors may be required. Accordingly, the fastening of the orthopedic implants to the area of treatment can become a time consuming and even difficult task. 
     As such, there exists a need for bone anchors that can quickly and securely fasten an orthopedic device to the area of treatment. 
     SUMMARY OF THE INVENTION 
     In a preferred embodiment, the present invention provides an anchor assembly that can be used for the fixation or fastening of orthopedic devices or instruments to bone tissue. In particular, the present invention preferably provides a variable angle or fixed angle anchor assembly that is able to securely connect the orthopedic device to bone tissue even when there is a variance in the angle and position of the assembly with respect to the device. Furthermore, in a preferred embodiment, the present invention provides an anchor assembly having a locking mechanism that will quickly and easily lock the anchor assembly with respect to the orthopedic device. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description 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 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is an exploded partial perspective view of one embodiment of an anchor assembly; 
         FIG. 2  is a partial perspective view of the anchor assembly shown in  FIG. 1 ; 
         FIG. 3  is partial perspective view of the anchor assembly shown in  FIG. 1 ; 
         FIG. 4  is a partial cross-sectional view of the anchor assembly shown in  FIG. 1 ; and 
         FIG. 5  is a schematic view of another embodiment of an anchor assembly being seated and locked in an orthopedic device. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     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. 
     With reference to  FIGS. 1-4 , a preferred embodiment of an anchor assembly  10  is illustrated. The anchor assembly  10  preferably includes an anchor  11  and a locking mechanism  30 . Although the anchor  11  will be discussed in the context of an orthopedic screw, it is contemplated that the anchor  11  can be any type of anchoring element including, but not limited to, a hook, a pin, or a nail. In a preferred embodiment, the anchor  11  includes, concentric to a longitudinal axis  12 , a head portion  14 , a neck portion  18  and a shank portion  16 . The head portion  14  connects to the shank portion  16  through the neck portion  18 . The anchor assembly  10  is preferably constructed from any biocompatible material including, but not limited to, stainless steel alloys, titanium, titanium based alloys, or polymeric materials. 
     In a preferred embodiment, the head portion  14  of the anchor  11  has a generally spherical shape and includes at least one resilient finger element  20 . In another preferred embodiment, the head portion  14  includes four resilient finger elements  20 . Preferably, located on either side of the resilient finger element  20  is an elongated groove  22 . The grooves  22  may be configured and dimensioned to correspond with the end of a driving instrument (not shown) designed to engage the anchor  11 , and consequently the anchor assembly  10 . 
     As best shown in  FIG. 4 , the generally spherical shape of the head portion  14  is configured and dimensioned to be received within a correspondingly shaped cavity  52  in an orthopedic device  50  which may be part of a spinal fixation system. In an exemplary embodiment, the orthopedic device  50  is a bone plate, but the orthopedic device can be any device, such as a spinal rod “tulip” style holder or a spinal spacer. The shape of the head portion  14  and the correspondingly shaped cavity  52  allows the anchor assembly  10  to pivot, rotate and/or move with respect to the orthopedic device  50 . In another embodiment, instead of allowing the anchor assembly  10  to pivot, rotate and/or move with respect to the orthopedic device  50 , the head portion  14  and the correspondingly shaped cavity  52  may be configured and dimensioned to keep the anchor assembly  10  in a fixed position. In an exemplary use, the head portion  14  of the anchor  11  is received in the cavity  52  of the orthopedic device  50  and the anchor assembly  10  is pivoted, rotated or moved until the desired orientation with respect to the orthopedic device  50  is met. The anchor assembly  10  is then locked in place, which is discussed in detail below, in the cavity  52  of the orthopedic device  50 . In a preferred embodiment, the head portion  14  also includes texturing  24  that extends along at least a portion of the head portion  14 . The texturing  24  on the head portion  14  provides additional frictional surfaces which aid in locking the anchor assembly  10  in place with respect to the orthopedic device  50 . 
     Turning back to  FIGS. 1-3 , in a preferred embodiment, the neck portion  18  of the anchor  11  integrally connects the head portion  14  with the shank portion  16 . The diameter of the neck portion  18  is preferably dimensioned to match the minor diameter of the anchor  11 . By having the diameter of the neck portion  18  dimensioned at least as large as the minor diameter of the anchor  11 , the overall rigidity and strength of the anchor  11  is increased. 
     In a preferred embodiment, the shank portion  16  of the anchor  11  includes a shaft  26  surrounded at least in part by a thread portion  28 . The diameter of the shaft  26  is the minor diameter of the anchor assembly  10 . In a preferred embodiment, the diameter of the shaft  26  remains generally constant from a proximal end of the shaft  26  toward a distal end of the shaft  26 . The constant diameter of a majority portion of the shaft  26  allows for optimal anchor positioning when the anchor assembly  10  is inserted into a predetermined area in the bone tissue. The constant diameter also allows for varying the depth positioning of the anchor assembly  10  in the bone. For example, if a surgeon places the anchor assembly  10  into bone tissue at a first depth and decides the placement is more optimal at a second, shallower depth, the anchor assembly  10  can be backed out to the second depth and still remain fixed in the bone. In another embodiment, the diameter of the shaft  26  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. 
     With continued reference to  FIGS. 1-3 , the thread portion  28  surrounding the shaft  26  extends, in a preferred embodiment, from the distal end of the shaft  26  to the neck portion  18 . In another preferred embodiment, the thread portion  28  may extend along only a portion of shaft  26 . The thread portion  28  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. 
     In a preferred embodiment, the diameter of the thread portion  28  decreases towards the distal end of the anchor  11 . By having a decreased diameter thread portion  28  near the distal end of the anchor  11 , the anchor  11  can be self-starting. In another preferred embodiment, anchor  11  may also include at least one flute to clear any chips, dust, or debris generated when the anchor assembly  10  is implanted into bone tissue. 
     Looking again at  FIGS. 1-4 , the anchor assembly  10  preferably includes the locking mechanism  30 . In a preferred embodiment, the locking mechanism  30  will lock the anchor assembly  10  with respect to the orthopedic device  50  thereby preventing the anchor assembly  10  from disengaging from the orthopedic device  50 . The locking mechanism  30  preferably includes a locking member  32  which is configured and dimensioned to be received in an opening  34  in the anchor  11 . 
     In a preferred embodiment, the locking member  32  has a head member  36  and a shaft member  38 . The head member  36  preferably includes an opening  40  for receiving a driving instrument (not shown). The opening  40  may also include threading  42  that is capable of threadingly engaging a driving instrument for reasons explained below. In a preferred embodiment, the shaft member  38  includes at least one protrusion  44  extending along at least a portion of the circumference of the shaft member  38 . Focusing on  FIG. 4 , at least a portion of the shaft member  38 , in a preferred embodiment, also includes a hollow portion  46  which allows at least a portion of the shaft member  38  surrounding the hollow portion  46  to flex inwardly. 
     Turning back to  FIGS. 1 and 4 , the opening  34 , preferably, is generally annular and extends coaxially with the longitudinal axis  12  from the head portion  14  through the neck portion  18  into the shank portion  16 . The opening  34  preferably also includes at least two recesses  47 ,  48 , each recess  47 ,  48  extending along at least a portion of the circumference of the opening  34 . Each recess  47 ,  48  is configured and dimensioned to accommodate the protrusion  44 . 
     In an exemplary use of the anchor assembly  10  with the orthopedic device  50 , the orthopedic device  50  is first oriented and placed in the area of treatment. The orthopedic device  50  is then fastened to the bone tissue via at least one anchor assembly  10  which is received in at least one cavity  52  of the orthopedic device  50 . Looking at  FIG. 4 , in a preferred embodiment, the cavity  52  has a generally spherical shape with a first diameter y at an upper portion  54 . When viewed from the upper portion  54  to a lower portion  56 , the diameter of the cavity  52  generally increases until approximately the middle portion of the cavity  52 . The diameter of the approximately middle portion of the cavity  52  is a second diameter x. The diameter of the cavity  52  then decreases from the approximately middle portion of the cavity  52  to the lower portion  56 , where the diameter of the cavity near the lower portion  56  is the same as or smaller than the first diameter y. 
     In a preferred embodiment, the anchor assembly  10  passes through the cavity  52  until the head portion  14  of the anchor  11  abuts the top portion  54  of the cavity  52 . As can be seen in  FIG. 4 , in a preferred embodiment, the diameter of the head portion  14  of the anchor  11  is generally the same width as diameter x. Since the top portion  54  of the cavity  52  has a diameter y, which is smaller than the diameter x, as the head portion  14  is brought into the cavity  52 , the finger elements  20  of the head portion  14  resiliently bias inwardly reducing the diameter of the head portion  14  until the head portion  14  fits through top portion  54  of the cavity  52 . Once the head portion  14  passes through the top portion  54 , the resilient finger elements  20  return back to their original position as the head portion  14  is seated in the cavity  52 . 
     As best seen in  FIGS. 3 and 4 , in a preferred embodiment, once the anchor assembly  10  is seated in the cavity  52 , the anchor assembly  10  can be locked in the cavity  52  by actuating the locking mechanism  30 . In a preferred embodiment, a user actuates locking mechanism  30  by pushing on the head member  36  of the locking member  32 . The downward force moves the locking member  32  further into the opening  34 . As the locking member  32  moves into the opening  34 , the protrusion  44  will disengage from the recess  47 . Since, in a preferred embodiment, the diameter of the shaft member  38  of the locking member  32  is generally equivalent to the diameter of the opening  34  near the neck portion  18  and the shaft portion  16 , the shaft member  38  will flex inwardly, aided by the hollow portion  46 , to accommodate the protrusion  44  once it disengages from the recess  47 . The locking member  32  will continue to move further into opening  34  until the protrusion  44  engages the recess  48  at which point the head member  36  will be seated between the resilient finger elements  20  of the head portion  14 . The anchor assembly  10  is now locked in the cavity  52  since the head member  36 , once seated between the resilient finger elements  20 , prevents the resilient finger elements  20  from flexing inwardly. It is important to note that the disengagement of protrusion  44  from recess  47  and the engagement of the protrusion  44  with the recess  48  (and vice versa) provides the user with audible and/or tactile feedback allowing the user to quickly and easily confirm the locked or unlocked status of the anchor assembly  10 . 
     As mentioned earlier, the head portion  36  includes the opening  40  which may include threading  42 . The threading  42  in opening  40  engages a driving instrument (not shown) allowing a user to pull on the locking mechanism  30  thereby unlocking the anchor assembly  10  in the event a user wants to disengage the anchor assembly  10  from the orthopedic device  50 . 
     In another exemplary use of the anchor assembly  10  with the orthopedic device  50 , the orthopedic device  50  is first oriented and placed in the area of treatment. The orthopedic device  50  is then fastened to the bone tissue via at least one anchor assembly  10  which is received in at least one cavity  52  of the orthopedic device  50 . In this exemplary use, after the anchor assembly  10  is seated in the cavity  52 , but before the anchor assembly  10  is locked in the cavity  52 , the anchor assembly  10  is pivoted, rotated or otherwise moved until the desired orientation with respect to the orthopedic device  50  is met. The anchor assembly  10  is then locked in place at that desired orientation by actuating the locking mechanism  30  as discussed above. 
     In this exemplary use, to lock the anchor assembly  10  at the desired orientation another preferred embodiment of the anchor assembly  10 , and more specifically, another preferred embodiment of the locking mechanism  30  is necessary. In this preferred embodiment, the locking mechanism  30  is configured and dimensioned to resiliently bias the resilient finger elements  20  of head portion  14  outwardly when the locking mechanism  30  is pushed from the first, unlocked position, to the second, locked position. By resiliently biasing the finger elements  20  outwardly, the finger elements  20  will push against the walls of the cavity  52  thereby locking the anchor assembly  10  in place in the desired orientation. To resiliently bias the finger elements  20  outwardly, the head member  36  of the locking mechanism  30 , preferably, is configured and dimensioned to include tapering surfaces and a diameter larger than the diameter of the opening  34  near the head portion  14 . 
     Turning to  FIG. 5 , a preferred embodiment of the anchor assembly  100  is shown. The anchor assembly  100  is similar to anchor assembly  10 , as such, only the differences between the two embodiments are addressed herein. The anchor assembly  100  preferably includes an anchor  110  and a locking mechanism  130 . In a preferred embodiment, the anchor  110  includes, concentric to a longitudinal axis  112 , a head portion  114 , a neck portion  118  and a shank portion  116 . The head portion  114  connects to the shank portion  116  through the neck portion  118 . In a preferred embodiment, the head portion  114  of the anchor  110  has a generally spherical shape and includes a resilient ring element  120  captured between an upper and lower end of the head portion  114 . 
     With continued reference to  FIG. 5 , in a preferred embodiment, the locking mechanism  130  will lock the anchor assembly  100  with respect to the orthopedic device  150  thereby preventing the anchor assembly  100  from disengaging from the orthopedic device  150 . The locking mechanism  130  preferably includes a locking member  132  which is configured and dimensioned to be received in an opening  134  in the anchor  110 . 
     In an exemplary use of the anchor assembly  100  with the orthopedic device  150 , the orthopedic device  150  is first oriented and placed in the area of treatment. The orthopedic device  150  is then fastened to the bone tissue via at least one anchor assembly  100  which is received in at least one cavity  152  of the orthopedic device  150 . In a preferred embodiment, the anchor assembly  100  passes through the cavity  152  until the head portion  114  of the anchor  110  abuts a top portion of the cavity  152 . Since the top portion of the cavity  152  has a diameter that is smaller than the diameter of the head portion  114 , to fit the head portion  114  into the cavity  152 , the resilient ring  120  is resiliently bias inwardly, reducing the diameter of the head portion  114 , until the head portion  14  fits through top portion of the cavity  152 . Once the head portion  114  passes through the top portion of the cavity  152 , the ring  120  returns back to its original position as the head portion  114  is seated in the cavity  152 . 
     With continued reference to  FIG. 5 , in a preferred embodiment, once the anchor assembly  100  is seated in the cavity  152 , the anchor assembly  100  can be locked in the cavity  152  by actuating the locking mechanism  130 . In a preferred embodiment, a user actuates locking mechanism  130  by pushing on the locking member  132 . The downward force moves at least a portion of the locking member  132  into opening  134 . The anchor assembly  100  is now locked in the cavity  152  since the locking member  132 , once seated in the opening  134 , prevents the ring  120  from flexing inwardly. 
     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.