Patent Publication Number: US-2021161671-A1

Title: Continuous compression fixation device for the fusion of an intercalary structural augment

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of, and claims priority to, U.S. patent application Ser. No. 15/919,829, filed Mar. 13, 2018, entitled “CONTINUOUS COMPRESSION FIXATION DEVICE FOR THE FUSION OF AN INTERCALARY STRUCTURAL AUGMENT”, which is incorporated herein by reference in its entirety. 
    
    
     FIELD 
     The present invention relates generally to a continuous compression fixation device for the fusion of an intercalary structural augment. More specifically, the present invention relates to a continuous compression fixation device, such as a surgical staple or the like, manufactured from a metallic or non-metallic shape memory material, such as nitinol (i.e. nickel-titanium) or the like, for the fusion of an intercalary structural augment, such as an intervertebral cage and/or bone graft in an intervertebral fusion, for example. The continuous compression fixation device of the present invention finds applicability in any bony structure fixation application in which restraint of rotational displacement and continuous compressive force are both desired, especially when an intercalary structural augment is present between the adjoined bony structures (e.g. foot, ankle, lower extremity, upper extremity, hand, craniomaxofacial, etc. applications) In the intervertebral fusion, for example, the continuous compression fixation device advantageously provides continuous compressive force over the middle column of the vertebral axis. Multiple levels of instrumentation are also contemplated herein. 
     BACKGROUND 
     In intervertebral fusion, for example, intervertebral structural augmentation after discectomy for spinal column decompression and subsequent fusion has long been a preferred procedure. Such intervertebral structural augments have varied from autologous free-fibular strut grafts to allografts to metallic cages to synthetic cages with spaces for bone grafts that increase the rate of fusion. Additional stabilizing instrumentation has also been found to increase the rate of fusion. The mainstays of such stabilizing instrumentation include anterior cervical plates coupled to the anterior or front column of the vertebral axis, lateral lumbar plates, and rod-screw constructs coupled to the posterior or back column of the vertebral axis, for example. Each of these modalities provides rigid fixation and minimizes motion and settling, however none of the modalities provides continuous compression, especially across the associated intervertebral structural augment over the middle column of the vertebral axis. Some of the modalities allow for a predetermined amount of compressive force to be applied initially via mechanical constructs, but this compressive force is diminished with time as settling and/or remodeling of the vertebral endplates occur. A similar situation exists in other anatomical applications. 
     Direct bony compression has long been identified as critical to achieving primary bone healing and arthrodesis for fusions. This direct bony compression allows for cutting cone bone formation in the absence of the micro-motion that occurs with non-rigid fixation. In foot and ankle surgery, for example, shape memory alloy staples have been utilized with marked success by providing direct bone-to-bone osteosynthesis. However, such shape memory alloy staples do not properly allow for intercalary structural augments and do not correspondingly apply continuous compressive force in the right place(s). The continuous compression fixation device of the present invention remedies these shortcomings. 
     In general, osseous fusion depends on three distinct physical conditions: bony apposition, strain/stability, and pressure. For primary bone-to-bone healing, these physical conditions allow for new osteon formation through cutting cones and Haversian remodeling. The spine presents a unique environment for iatrogenic fusion. Patients whose pathology dictates an intervertebral fusion mass in their treatment algorithm undergo preparation of the vertebral endplates to accept an intercalary structural augment, again typically consisting of an autologous free-fibular strut graft to a synthetic cage with a space for a bone graft that increases the rate of fusion. Once a graft is placed, for example, a surgeon has the option of instrumenting the fusion or leaving it as is in an in-situ fashion. Again, such instrumentation typically includes anterior cervical plates coupled to the anterior or front column of the vertebral axis, lateral lumbar plates, and rod-screw constructs coupled to the posterior or back column of the vertebral axis, for example. Each of these modalities provides rigid fixation and minimizes motion and settling, however none the modalities provides continuous compression, especially across the associated intervertebral structural augment over the middle column of the vertebral axis. Existing shape memory alloy staples designed for foot and ankle applications do not properly allow for intercalary structural augments and do not correspondingly apply continuous compressive force in the right place(s). Again, the continuous compression fixation device of the present invention remedies these shortcomings. 
     BRIEF SUMMARY 
     In various exemplary embodiments, the present invention provides a continuous compression fixation device, such as a surgical staple or the like, manufactured from a metallic or non-metallic shape memory material, such as nitinol (i.e. nickel-titanium) or the like for the fusion of an intercalary structural augment, such as an intervertebral cage and/or bone graft in an intervertebral fusion, for example. The continuous compression fixation device of the present invention finds applicability in any bony structure fixation application in which restraint of rotational displacement and continuous compressive force are both desired, especially when an intercalary structural augment is present between the bony structures. This includes, but is not limited to, opening wedge osteotomies with tricortical auto/allograft and/or deformity correction with intercalary structural augmentation. In intervertebral fusion, for example, the continuous compression fixation device advantageously provides continuous compressive force over the middle column of the vertebral axis. Multiple levels of instrumentation are also contemplated herein. 
     In one exemplary embodiment, the present invention provides a continuous compression fixation device for coupling a first bony structure to a second bony structure, including: a body structure; and a plurality of arm structures coupled to and extending from the body structure, wherein at least one of the plurality of arm structures is configured to be coupled to the first bony structure and at least one opposed one of the plurality of arm structures is configured to be coupled to the second bony structure; wherein the body structure and the plurality of arm structures are manufactured from a shape memory material; and wherein tips (and other portions) of the at least one of the plurality of arm structures and the at least one opposed one of the plurality of arm structures are biased towards one another relative to a perpendicular orientation with respect to the body structure thereby providing a compressive force between the first bony structure and the second bony structure. Preferably, the tips (and other portions) of the at least one of the plurality of arm structures and the at least one opposed one of the plurality of arm structures are biased towards one another relative to the perpendicular orientation with respect to the body structure such that a desired compressive force is applied to an intercalary structural augment disposed between the first bony structure and the second bony structure. The tips of the at least one of the plurality of arm structures and the at least one opposed one of the plurality of arm structures are configured to be deflected away from one another prior to being coupled to the first bony structure and the second bony structure, respectively. Optionally, the continuous compression fixation device further includes an additional arm structure and an additional opposed arm structure coupled to and extending from the body structure, wherein tips of the additional arm structure and the additional opposed arm structure are biased towards one another relative to the perpendicular orientation with respect to the body structure thereby also providing the compressive force between the first bony structure and the second bony structure. The tips of the at least one of the plurality of arm structures and the at least one opposed one of the plurality of arm structures are biased towards one another relative to the perpendicular orientation with respect to the body structure by a compressive force generated in a proximity of where each of the arm structures and the body structure are coupled. Optionally, the shape memory material includes a shape memory alloy. Optionally, the shape memory alloy includes nitinol. Each of the plurality of arm structures includes a tapered tip such that it may be disposed in a hole drilled into the associated bony structure. Each of the plurality of arm structures further includes one or more friction structures such that it is securely retained in the hole drilled into the associated bony structure. Optionally, the body structure is coupled to the intercalary structural augment disposed between the first bony structure and the second bony structure. 
     In another exemplary embodiment, the present invention provides a method for providing a continuous compression fixation device for coupling a first bony structure to a second bony structure, including: providing a body structure; providing a plurality of arm structures coupled to and extending from the body structure, wherein at least one of the plurality of arm structures is configured to be coupled to the first bony structure and at least one opposed one of the plurality of arm structures is configured to be coupled to the second bony structure; wherein the body structure and the plurality of arm structures are manufactured from a shape memory material; and wherein tips (and other portions) of the at least one of the plurality of arm structures and the at least one opposed one of the plurality of arm structures are biased towards one another relative to a perpendicular orientation with respect to the body structure thereby providing a compressive force between the first bony structure and the second bony structure deflecting the tips of the at least one of the plurality of arm structures and the at least one opposed one of the plurality of arm structures away from one another; coupling the at least one of the plurality of arm structures to the first bony structure and the at least one opposed one of the plurality of arm structures to the second bony structure; and releasing the tips of the at least one of the plurality of arm structures and the at least one opposed one of the plurality of arm structures to provide the compressive force between the first bony structure and the second bony structure. Preferably, the tips (and other portions) of the at least one of the plurality of arm structures and the at least one opposed one of the plurality of arm structures are biased towards one another relative to the perpendicular orientation with respect to the body structure such that a desired compressive force is applied to an intercalary structural augment disposed between the first bony structure and the second bony structure. Optionally, the method further includes providing an additional arm structure and an additional opposed arm structure coupled to and extending from the body structure, wherein tips of the additional arm structure and the additional opposed arm structure are biased towards one another relative to the perpendicular orientation with respect to the body structure thereby also providing the compressive force between the first bony structure and the second bony structure. The tips of the at least one of the plurality of arm structures and the at least one opposed one of the plurality of arm structures are biased towards one another relative to the perpendicular orientation with respect to the body structure by a compressive force generated in a proximity of where each of the arm structures and the body structure are coupled. Optionally, the shape memory material includes a shape memory alloy. Optionally, the shape memory alloy includes nitinol. Each of the plurality of arm structures includes a tapered tip such that it may be disposed in a hole drilled into the associated bony structure. Each of the plurality of arm structures further includes one or more friction structures such that it is securely retained in the hole drilled into the associated bony structure. Optionally, the body structure is coupled to the intercalary structural augment disposed between the first bony structure and the second bony structure. 
     In a further exemplary embodiment, a continuous compression fixation device is provided in which some or all of the plurality of arm structures are replaced with conventional locking or non-locking fixed or variable angle bone screws. The remaining arm structures, if any, operate as before. In the case where all of the arm structures  18  are replaced by bone screws, compressive force is provided solely by the shape memory material body structure itself, which acts on the coupled bony structures through the bone screws. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is illustrated and described herein with reference to the various drawings, in which like reference numbers are used to denote like device components/method steps, as appropriate, and in which: 
         FIG. 1  is a perspective view of one exemplary embodiment of the continuous compression fixation device of the present invention in a deployed configuration, 
         FIG. 2  is a perspective view of one exemplary embodiment of the continuous compression fixation device of the present invention in an expanded configuration, 
         FIG. 3  is a front planar view of one exemplary embodiment of the continuous compression fixation device of the present invention in an implanted and deployed configuration, 
         FIG. 4  is a side planar view of one exemplary embodiment of the continuous compression fixation device of the present invention in an implanted and deployed configuration; 
         FIG. 5  is a perspective view of one exemplary embodiment of the continuous compression fixation device of the present invention in an expanded configuration; 
         FIG. 6  is a perspective view of one exemplary embodiment of the continuous compression fixation device of the present invention in an expanded configuration being implanted with an intervertebral cage; 
         FIG. 7  is a perspective view of one exemplary embodiment of the continuous compression fixation device of the present invention in a deployed configuration implanted with an intervertebral cage; 
         FIG. 8  is a front planar view of one exemplary embodiment of the continuous compression fixation device of the present invention in a deployed configuration implanted with an intervertebral cage; 
         FIG. 9  is a side planar view of one exemplary embodiment of the continuous compression fixation device of the present invention in a deployed configuration implanted with an intervertebral cage; and 
         FIG. 10  is a side planar view of another exemplary embodiment of the continuous compression fixation device of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now specifically to  FIGS. 1-4 , in one exemplary embodiment, the present invention provides a continuous compression fixation device  10  for coupling a first bony structure  12  to a second bony structure  14 . The continuous compression fixation device  10  includes a body structure  16  and a plurality of arm structures  18  coupled to and extending from the body structure  16  towards the first bony structure  12  and the second bony structure  14 . Accordingly, one or more of the plurality of arm structures  18  are configured to be coupled to the first bony structure  12  and one or more of the plurality of arm structures  18  are configured to be coupled to the second bony structure  14 . In the exemplary embodiment illustrated, two of the arm structures  18  are associated with each of the bony structures  12  and  14 , although other desired numbers of the arms structures  18  could be associated with each of the bony structures  12  and  14  equally. 
     The body structure  16  and the plurality of arm structures  18  are manufactured from a shape memory material, such as a shape memory polymer or a shape memory alloy like nitinol. It will be readily apparent to those of ordinary skill in the art that any suitable shape memory material may be utilized provided that it continuously biases the structure(s) at issue to an original intended shape after deflection, thereby resisting such deflection with a reactionary force. By design, the tips  20  of the plurality of arm structures  18  are biased towards one another relative to a perpendicular orientation with respect to the body structure  16 , thereby providing a compressive force between the first bony structure  12  and the second bony structure  14  when the plurality of arm structures  18  are deflected and coupled to their respective bony structures  12  and  14 . In other words, each of the plurality of arm structures  18  is intentionally angled inwards in at least one plane as illustrated and persistently seeks to return to such configuration despite its state of deflection and what it is coupled to. Preferably, by design, the tips  20  of the plurality of arm structures  18  are biased towards one another relative to the perpendicular orientation with respect to the body structure  16  such that a desired compressive force is applied to an intercalary structural augment  22  ( FIGS. 6, 7, and 9 ) disposed between the first bony structure  12  and the second bony structure  14 . Again, the tips  20  of the plurality of arm structures  18  are configured to be deflected away from one another prior to being coupled to the first bony structure  12  and the second bony structure  14 , respectively. Thus, the plurality of arm structures  18  are opened up prior to implantation into appropriate holes drilled into the first bony structure  12  and the second bony structure  14 , for example, and then released subsequent to implantation. This provides a desired compressive force between the first bony structure  12  and the second bony structure  14 . This compressive force is applied (and in fact tailored) to the intercalary augment structure  22  disposed between the first bony structure  12  and the second bony structure  14 , promoting both fixation and fusion, when appropriate. 
     The tips  20  (and other portions) of the plurality of arm structures  18  are preferably biased towards one another relative to the perpendicular orientation with respect to the body structure  16  by a compressive force generated primarily in the proximity of where each of the arm structures  18  and the body structure  16  are coupled, at the shoulders  24  of the continuous compression fixation device  10 . In general, it is desirable that the body structure  16  and the plurality of arm structures  18  are integrally formed to minimize areas in which failure and corrosion can be initiated and propagate. 
     Each of the plurality of arm structures  18  includes a tapered and/or sharpened tip  20  such that it may be more easily disposed in the hole drilled into the associated bony structure  12  or  14 . Each of the plurality of arm structures  18  further includes one or more friction structures  26  (e.g. protrusions, barbs, or threads) such that it is securely retained in the hole drilled into the associated bony structure  12  or  14 . 
     Referring now specifically to  FIG. 5 , one exemplary embodiment of the continuous compression fixation device  10  of the present invention is illustrated. In this exemplary embodiment, the body structure  16  is a substantially planar structure  28  with a generally rectangular shape that terminates in a raised central ridge  30  to minimize its anatomical protrusion when the continuous compression fixation device  10  is implanted in a spinal column or the like. The body structure  16  may define any number of recesses, holes, or other openings as desired in a given application. In general, the plurality of arms structures extend away from the body structure  16  at an angle of between greater than about 0 degrees and less than about 45 degrees from perpendicular in a natural or resting state, with a few degrees past zero degrees preferred. This natural or resting angular displacement of the plurality of arm structures  18  is illustrated in one plane along each side of the continuous compression fixation device  10  and not in the perpendicular planes along the ends of the continuous compression fixation device, although such multidimensional angular displacement of the plurality of arm structures  18  is possible. In this exemplary embodiment, each of the plurality of arm structures  18  includes a generally tapered tip  20  for insertion purposes and a plurality of raised barbs  26  for retention purposes. The plurality of arm structures  18  meet the body structure  16  to form a plurality of arcs  32  that are designed to enhance conformal anatomical fit in a given application. As described above, the body structure  16  and the plurality of arm structures  18  are manufactured from a shape memory material, such as a shape memory polymer or a shape memory alloy like nitinol. It will be readily apparent to those of ordinary skill in the art that any suitable shape memory material may be utilized provided that it continuously biases the structure(s) at issue to an original intended shape after deflection, thereby resisting such deflection with a reactionary force. Again, in general, it is desirable that the body structure  16  and the plurality of arm structures  18  are integrally formed to minimize areas in which failure and corrosion can be initiated and propagate. 
       FIGS. 6-9  illustrate the continuous compression fixation device  10  of the present invention being implanted in a spine  34  of a patient after an intercalary structural augment  22 , such as an intervertebral cage and/or bone graft, has been implanted into the prepared intervertebral space  36 .  FIG. 9  illustrates the low-profile nature of this installation. Although not specifically illustrated, the continuous compression fixation device  10  can be coupled directly to the intercalary structural augment  22 , if desired. 
     Thus, the present invention provides continuous compression across a single-level, or multi-level, osseous segment, with or without the use of an intercalary cage/graft, with fixation using staple arms incorporating, in whole or in part, a shape memory material. The staple is manufactured in a deployed configuration with acute angles between the staple arms. These are heated/expanded and placed into a carrying mechanism, and subsequently deployed into bony structures across the intercalary structural augment. Once deployed, the staple will reconfigure to its original shape, providing continuous compression across the anterior and middle columns of the spine, for example, with most of the compressive force being directed through the middle column through the tips of the staple arms. Compression across the middle column, rather than through an anterior plate, minimizes the concern for iatrogenic kyphosis in the cervical and lumbar spine, for example, and focuses the compression more linearly across the intercalary structural augment. 
     It is additionally important to consider rotational strain across a fusion mass, just as one would consider resistance to flexion and extension. In that regard, the present invention incorporates a variety of angular connections to resist torsional stresses and provide a lower-strain, higher-stability construct than would typically be seen in existing routine spinal instrumentation after cyclic loading, for example. 
     Because of the conceptual similarity among all iatrogenic bony fusions, the continuous compression provided by the osseous staple design of the present invention would work for all bony fusions with intercalary structural augments. Other exemplary applications include opening wedge osteotomies with tri-cortical auto/allograft or other material/device osteotomy filling and deformity correction with structural augmentation. 
     Referring now specifically to  FIG. 10 , in another exemplary embodiment, the present invention provides a continuous compression fixation device  110  in which some or all of the plurality of arm structures  18  are replaced with conventional locking or nonlocking fixed or variable angle bone screws  112 . The remaining arm structures  18 , if any, operate as before. In the case where all of the arm structures  18  are replaced by bone screws  1   12 , compressive force is provided solely by the shape memory material body structure  16  itself, which acts on the coupled bony structures through the bone screws  112 . 
     Although the present invention is illustrated and described herein with reference to preferred embodiments and specific examples thereof, it will be readily apparent to those of ordinary skill in the art that other embodiments and examples may perform similar functions and/or achieve like results. All such equivalent embodiments and examples are within the spirit and scope of the present invention, are contemplated thereby for all purposes, and are intended to be covered by the following non-limiting claims.