Patent Publication Number: US-2020297505-A1

Title: Internal Bone Fixation Device

Description:
BACKGROUND INFORMATION 
     Field of the Invention 
     The present invention relates generally to medical devices and, more specifically, to implants that aid bone fusion in the body. 
     Discussion of Prior Art 
     Internal bone fixation devices, or implants, are used in humans and animals to support and/or secure the subject&#39;s bones. For example, implants are used in the spine to support and/or replace damaged tissue between the vertebrae in the spine. Once implanted between two vertebrae, the implant provides support between the two vertebrae and bone growth takes place around and through the implant to at least partially fuse the two vertebrae for long-term support. 
     Implants often include relatively large rims comprised of solid material that may cover, for example, 50% of the area that interacts with the endplate. The rim may provide a contact area between the implant and the vertebral end plates. However, these large rims have several drawbacks. For example, large rims often impede bone growth and reduce the size of the bone column fusing the superior and inferior vertebral bodies. 
     Spinal implants typically include open channels through the center of the supporting rims in a superior/inferior direction. The open channel design requires members of the implant that separate the rims that interact with the vertebral endplates to absorb the compressive forces between the vertebral end plates. This often increases the pressure on smaller areas of the vertebral endplates and may potentially lead to stress risers in the vertebral endplates. Further, while bone graft material is often used in conjunction with implants to encourage bone growth, the open column design of implants may reduce the likelihood of bone graft material from securing itself to the implant which may result in a bio-mechanical cooperation that is not conducive to promoting good fusion. 
     Bone graft material may be packed into the implant in a high-pressure state to prevent bone graft material from exiting the implant while being placed between the vertebral endplates. The high-pressure state may also reduce the potential for the bone graft material loosening due to motion between the implant and the vertebral endplates or compressive forces experienced during settling of the implant. In addition, a high-pressure environment may allow the bone graft material to re-model and fuse at greater strength. High pressure states, however, may be difficult to create and maintain for the bone graft material in an implant. 
     What is needed, therefore, is an implant that has a rim that minimizes the effects of bone growth impediment while having the strength and flexibility to comfortably and safely absorb the compressive forces that occur as the subject moves about in the normal course of daily activities. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention is multi-layer implant device for interfacing with a bone structure that uses a number of off-setting struts to connect the layers, with a porous material filling the internal portion of the device structure between the layers. Each layer includes an inner rim and an outer rim that are connected to one another by horizontal struts, with the inner rims creating an open channel in the center of the device. More specifically, the device includes at least three, and possibly more, layers that are connected by non-continuous vertically oriented offsetting struts. 
     The non-continuous vertically oriented struts are offset from one another in that one pair of layers are connected by struts connecting the inner rim while a next pair of layers are connected by struts connecting the outer rims, i.e., if the first and second layers are connected at the inner rims the second and third layers are connected at the outer rims. The offsetting strut alignment allows for the use of a comparatively small rim and yet still provides the device with a strong frame but also provides the device with a degree of flexibility or elasticity that allows it to absorb the compressive forces that are exerted on it as the body in which it is implanted moves. 
     For example, the device may be used in the spine to support and/or replace damaged tissue between the vertebrae. Once implanted between two vertebrae, the implant may provide support between the two vertebrae and bone growth may take place around and through the implant to at least partially fuse the two vertebrae for long-term support. As a person moves about, for example walking or jogging, compressive forces act on the insert which the device is able to absorb. 
     The inner rims form an open channel in the center of the device, and collectively the layers of inner rims and outer rims define the structure that contains the porous materials. The combination of relatively small, e.g. narrow, rim members and the porous architecture create an ideal area for bone growth. 
     The device may be sized and shaped to fit into a number of areas of the body. For example, it may be shaped similar to a rounded rectangle or a trapezoid having rounded edges, which may be particularly well suited for a spinal implant. Or, alternatively, the device may be roughly cylindrical in shape in which case it may be used as a mid-shaft implant for a long bone such as the femur. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The present invention is described with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. The drawings are not drawn to scale. 
         FIG. 1  is a perspective view of the device according to the invention showing the top, front, and side. 
         FIG. 2  is a top plan view of the device. 
         FIG. 3  is a right side view of the device. 
         FIG. 4  is a left side view of the device. 
         FIG. 5  is an end view of the device. 
         FIG. 6  is a perspective view showing the top and end of the device. 
         FIG. 7  is a side view of the device inserted between two vertebras. 
         FIG. 8  is a perspective view of the device frame without the porous architecture showing the top, front, and side. 
         FIG. 9  is a top view of the frame. 
         FIG. 10  is a perspective cross-sectional along the line AA in  FIG. 9 . 
         FIG. 11  is a top view of the frame. 
         FIG. 12  is a perspective cross-sectional along the line BB in  FIG. 11 . 
         FIG. 13  is a top view of the porous architecture. 
         FIG. 14  is a side view of the porous architecture. 
         FIG. 15  is an end view of the porous architecture. 
         FIG. 16  is a perspective view of the porous architecture. 
         FIG. 17  is a close up view of a portion of the porous architecture. 
         FIG. 18  illustrate once example of a strand connection that may be used to create the porous architecture. 
         FIG. 19  illustrate where the strand shown in  FIG. 17  may fit into the largely porous material. 
         FIG. 20  illustrates a first example of a porous architecture. 
         FIG. 21  illustrates a second example of a porous architecture. 
         FIG. 22  illustrates a third example of a porous architecture. 
         FIG. 23  is a perspective view of the device having apertures for threaded fasteners. 
         FIG. 24  is a perspective view of the device having threaded fasteners. 
         FIG. 25  is an end view of the device with threaded fasteners. 
         FIG. 26  is a perspective view a second embodiment of the device showing the top, front, and side. 
         FIG. 27  is a cross-sectional view of the second embodiment. 
         FIG. 28  is a perspective view of a larger variant of the second embodiment having a porous architecture. 
         FIG. 29  illustrates the second embodiment in use a femur implant. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will now be described more fully in detail with reference to the accompanying drawings, in which the preferred embodiments of the invention are shown. This invention should not, however, be construed as limited to the embodiments set forth herein; rather, they are provided so that this disclosure will be complete and will fully convey the scope of the invention to those skilled in the art. 
       FIGS. 1-29  illustrate an internal bone fixation device  100  according to the invention. The device may be suitable for use with any number of implant situations, such as long bone reconstruction, knee replacements, both anterior lumbar inter-body fusion and posterior lumbar inter-body fusion, as well as with the foot and ankle. The following disclosure largely discusses the internal bone fixation device  100 , which may also simply be referred to as an “implant,” in terms of its use with lumbar inter-body fusion, however, it is understood that this is only one example of use and is not limiting in any way. The embodiment shown in  FIGS. 1-15  is particularly advantageous for use as a lumbar interbody fusion device, while the embodiment shown in  FIGS. 26-29  is particularly advantageous as a mid-shaft implant for a long bone. 
     The internal bone fixation device  100  according to the invention includes a support frame  10  that bounds and surrounds a porous architecture  50 . Generally, the frame is shaped to match the shape of the bone regions in which the device  100  is used for fusion, with approximate geometric shapes ranging from rounded and oval, rectangular or trapezoidal, or rounded rectangles and trapezoids having rounded edges. Generally, any corners are rounded so as to reduce the risk of harming other parts of the body during insertion. 
       FIGS. 1-16  illustrate the first embodiment of the device  100 , in which the frame  10 , best illustrated by  FIGS. 8-12 , includes three layers  12 . Each layer  12  includes an inner rim  14  and an outer rim  16 . The layers  12  are connected to one another by a first set of struts  18 , and the inner rims  14  and outer rims  16  are connected to one another by a second set of struts  22 . Additional layers  12  may be added in a similar manner to create a larger version of the device.  FIG. 7  illustrates one use of the first embodiment of the device  100 , with the device  100  inserted into the disc space between two vertebra V. 
     The outer rim  16  and inner rim  14  in this first embodiment generally have a shape that is approximately in the form of an oval or a rectangle or trapezoid with slightly rounded edges, which is generally intended to be the shape of device needed for lumbar interbody fusion. One side of each rim  14 ,  16 , is slightly narrower than the other. The layers are separated by approximately the same distance from one another, with the layers  12  on side of the device  100  tapered inward slightly. The angle and curvature of the device  100  is intended to match the Lordotic Angle of the area of the spine where the implant is intended to be inserted. The inner rim  14  bounds and defines an open channel through the center of the device. Again, as previously noted, the overall size and/or shape of the device  100  may vary to correspond to the size and/or shape of the cross section of the bones at the fusion or osteotomy site, thereby providing an optimal environment for bone ingrowth to occur. 
     The outer surfaces of the device  100 , and in particular the outer surface of the outer rim  16 , may be substantially smooth and/or be polished so as to limit the risk of damaging internal body structures as the device is being inserted. Alternatively, or in addition, some portion of the outer surface may also be roughened to facilitate bone fusion and/or interactions with other materials. The device may be made of any suitable medical grade material such as, for example, titanium or a biocompatible polymer. 
     The first set of struts  18  are connected to the layers  12  in an offsetting manner, which to say that the first and second layers are connected to one another by struts  18  that are attached to the outer rims  16  while the second and third layers are connected to one another by struts  18  that are attached to the inner rims  14 . If viewed from the cross-sectional side view, as shown in  FIGS. 10 and 12 , this offsetting arraignment forms an approximate S-shape. When adding additional layers, it is preferred if the total number of layers is an odd number so that the same three-layer strut arrangement may be maintained throughout the additional layers. 
     The distance between the individual struts in the first set of struts  18  may vary. For example, an implant that is designed to be used with a human spine may measure approximately 50 millimeters (“mm”) wide, 25 mm deep and 12 mm in height. In this example, the individual struts in the first set of struts  18  may be spaced approximately 15 mm apart. Changing the spacing, or incorporating more or fewer struts, alters the strength and flexibility of the device at various points. As previously noted, the size and/or shape of the device may vary to correspond to the size and/or shape of the cross section of the bones at the fusion or osteotomy site. 
       FIGS. 13-22  illustrate the porous architecture  50 . The porous architecture  50  may be any architecture that includes a plurality of openings on an outer surface of the architecture such that these openings may contact a bone surface. It is advantageous if there are openings or spaces throughout the porous architecture so that bone is able to grow into and throughout the porous architecture. The porous architecture may be a lattice or matrix structure that is configured to allow, promote or encourage bone to grow into it and around it. The porous architecture may be mostly comprised of a uniform or mostly uniform non-variable arrangement. Conversely, the porous architecture may be comprised of any number of suitable patterns, such as a plurality of diamond or square shapes trusses or in the form of a honeycomb. It may also be a randomly generated or distributed architecture or lattice, or it may include a different architecture in differing portions. The only requirement of the porous architecture is that it has openings or spaces that contact a bone segment. 
     The device may be affixed to the bone using conventional attachment means such as a plate or fastening devices such as screws.  FIGS. 23-25  illustrate an embodiment of the device having apertures  24  for the insertion of screws S. 
       FIGS. 26-29  illustrate a second embodiment of the device  100 . This embodiment may be used with a number of different bone structures such as, for example, a mid-shaft for a long bone such as the femur or in the foot and/or ankle.  FIGS. 26 and 27  illustrate the same 3-level design shown in  FIGS. 1-15 , albeit in a relatively cylindrical arrangement rather than the approximately rectangular cuboid with rounded corners shown in the first embodiment. 
     The key structure of the second embodiment is the same as in the first embodiment. More specifically, the second embodiment includes a support frame  10  that bounds and surrounds a porous architecture  50 . The frame  10  includes a number of layers  12 . Each layer  12  includes an inner rim  14  and an outer rim  16 . The layers are connected to one another by a first set of struts  18 , and the inner rims  14  and outer rims  16  are connected to one another by a second set of struts  22 . The first set of struts  18  are connected to the layers  12  in an offsetting manner, which to say that the first and second layers are connected to one another by struts  18  that are attached to the outer rims  16  while the second and third layers are connected to one another by struts  18  that are attached to the inner rims  14 . If viewed from the cross-sectional side view, as best shown in  FIG. 27 , this offsetting arraignment forms an approximate S-shape. The porous architecture  50  is the same as with the first embodiment. 
       FIGS. 28 and 29  illustrate the use of this second embodiment as a mid-shaft insert for a long bone, such as the femur F. A longer insert is needed in this instance, and so a total of 13 layers  12  are provided. The off-setting strut arraignment is maintained throughout all 13 layers  12 . 
     It is understood that the embodiments described herein are merely illustrative of the present invention. Variations in the construction of the Internal bone fixation device may be contemplated by one skilled in the art without limiting the intended scope of the invention herein disclosed and as defined by the following claims.