Abstract:
Systems, devices and methods for fusing both sacroiliac joints of a patient using a long implant are provided. The method can include inserting a guide pin through the first ilium and across the first SI-Joint, through the sacrum and above the S1 foramen, across the second SI-Joint, and through the second ilium; forming a first rectilinear cavity through the first ilium and the first SI-Joint; forming a second rectilinear cavity through the second ilium and the second SI-Joint, wherein the first rectilinear cavity and the second rectilinear cavity are aligned; and inserting an implant through the first cavity, across the first SI-Joint, through the sacrum, across the second SI-Joint, and through the second cavity.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 61/798,267 filed Mar. 15, 2013, and titled “LONG IMPLANT FOR SACROILIAC JOINT FUSION,” which is herein incorporated by reference in its entirety. 
     
    
     INCORPORATION BY REFERENCE 
       [0002]    All publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. For example, U.S. Publication No. 2011/0087294, filed Oct. 5, 2012, is hereby incorporated by reference in its entirety for all purposes. 
       FIELD 
       [0003]    Embodiments of the present invention relate generally to systems, devices and methods for fusing the sacroiliac joint. 
       BACKGROUND 
       [0004]    Many types of hardware are available both for the fixation of bones that are fractured and for the fixation of bones that are to be fused (arthrodesed). 
         [0005]    For example, the human hip girdle is made up of three large bones joined by three relatively immobile joints. One of the bones is called the sacrum and it lies at the bottom of the lumbar spine, where it connects with the L5 vertebra. The other two bones are commonly called “hip bones” and are technically referred to as the right ilium and-the left ilium. The sacrum connects with both hip bones at the sacroiliac joint (in shorthand, the SI-Joint). 
         [0006]    The SI-Joint functions in the transmission of forces from the spine to the lower extremities, and vice-versa. The SI-Joint has been described as a pain generator for up to 22% of lower back pain. 
         [0007]    To relieve pain generated from the SI Joint, sacroiliac joint fusion is typically indicated as surgical treatment, e.g., for degenerative sacroiliitis, inflammatory sacroiliitis, iatrogenic instability of the sacroiliac joint, osteitis condensans ilii, or traumatic fracture dislocation of the pelvis. Currently, screws and screws with plates are used for sacro-iliac fusion. At the same time the cartilage has to be removed from the “synovial joint” portion of the SI joint. This requires a large incision to approach the damaged, subluxed, dislocated, fractured, or degenerative joint. 
         [0008]    An alternative implant that is not based on the screw design can also be used to fuse the SI-Joint and/or the spine. Such an implant can have a triangular cross-section, for example, as further described below. To insert the implant, a cavity can be formed into the bone, and the implant can then be inserted into the cavity using a tool such as an impactor. The implants can then be stabilized together, if desired, by connected with implants with a crossbar or other connecting device. 
         [0009]    Therefore, it would be desirable to provide systems, devices and methods for SI-Joint and/or spinal fixation and/or fusion. 
       SUMMARY OF THE DISCLOSURE 
       [0010]    The present invention relates generally to an implant for SI-Joint fusion. 
         [0011]    In some embodiments, a system for the fusion of the sacroiliac joint is provided. The system includes a guide pin having a length greater than the width of a patient&#39;s pelvis, the guide pin having a proximal end with a first alignment feature and a distal end with a second alignment feature; a broach having a lumen for receiving the guide pin, the lumen having a complementary alignment feature that is configured to interact with the first alignment feature and the second alignment feature to register the broach with the guide pin in a predetermined orientation, the broach configured to form a rectilinear cavity in bone; and an implant having a rectilinear cross-section transverse to a longitudinal axis of the implant, the implant having a length greater than the width between a surface of the patient&#39;s right ilium and a surface of the patient&#39;s left ilium, the implant sized to fit through a cavity formed by the broach. 
         [0012]    In some embodiments, the implant has a rough surface. 
         [0013]    In some embodiments, the implant has a triangular cross-section transverse to the longitudinal axis of the implant. 
         [0014]    In some embodiments, the implant has a rectangular or square cross-section transverse to the longitudinal axis of the implant. 
         [0015]    In some embodiments, the first alignment feature and the second alignment feature are selected from the group consisting of lines, ridges, slots, and pins. 
         [0016]    In some embodiments, a system for the fusion of the sacroiliac joint is provided. The system can include a guide pin having a length greater than the width of a patient&#39;s pelvis; a broach having a lumen for receiving the guide pin, the broach configured to form a rectilinear cavity in bone; and an implant having a rectilinear cross-section transverse to a longitudinal axis of the implant, the implant having a length greater than the width between a surface of the patient&#39;s right ilium and a surface of the patient&#39;s left ilium, the implant sized to fit through the rectilinear cavity formed by the broach. 
         [0017]    In some embodiments, the implant has a length greater than the width between a surface of the patient&#39;s right ilium and a surface of the patient&#39;s left ilium by about 2 to 20 mm. 
         [0018]    In some embodiments, the implant has a length between about 100 mm to 300 mm. 
         [0019]    In some embodiments, the guide pin has an alignment feature that extends across the length of the guide pin. 
         [0020]    In some embodiments, a method for fusing both sacroiliac joints of a patient is provided. The method can include inserting a guide pin through the first ilium and across the first SI-Joint, through the sacrum and above the S1 foramen, across the second SI-Joint, and through the second ilium; forming a first rectilinear cavity through the first ilium and the first SI-Joint; forming a second rectilinear cavity through the second ilium and the second SI-Joint, wherein the first rectilinear cavity and the second rectilinear cavity are aligned; and inserting an implant through the first cavity, across the first SI-Joint, through the sacrum, across the second SI-Joint, and through the second cavity, wherein the implant has a rectilinear cross-section transverse to a longitudinal axis of the implant that corresponds to the first rectilinear cavity and the second rectilinear cavity. 
         [0021]    In some embodiments, the step of forming the first rectilinear cavity includes aligning a broach with an alignment feature on the guide pin. 
         [0022]    In some embodiments, the step of forming the second rectilinear cavity includes aligning the broach with the alignment feature of the guide pin. 
         [0023]    In some embodiments, the step of forming the second rectilinear cavity includes aligning the broach with a second alignment feature on the guide pin. 
         [0024]    In some embodiments, the step of forming the second rectilinear cavity includes aligning a broach with an image of the first rectilinear cavity under fluoroscopy. 
         [0025]    In some embodiments, the method further includes determining a length of the guide pin residing between the surface of the first ilium and the surface of the second ilium; and sizing the implant based on the determined length of the guide pin residing between the surface of the first ilium and the surface of the second ilium. 
         [0026]    In some embodiments, the step of determining the length of the guide pin residing between the surface of the first ilium and the surface of the second ilium includes measuring the length of the guide pin extending from the surface of the first ilium and the surface of the second ilium. 
         [0027]    In some embodiments, the implant has a length that is about 2 to 20 mm greater than the determined length of the guide pin residing between the surface of the first ilium and the surface of the second ilium. 
         [0028]    In some embodiments, the step of forming the first rectilinear cavity includes drilling a first bore over the guide pin in the first ilium; and shaping the first bore with a broach. 
         [0029]    In some embodiments, a method for fusing both sacroiliac joints of a patient is provided. The method includes inserting a guide pin through the first ilium and across the first SI-Joint, through the sacrum between the S1 and S2 foramen, across the second SI-Joint, and through the second ilium; forming a first rectilinear cavity through the first ilium and the first SI-Joint; forming a second rectilinear cavity through the second ilium and the second SI-Joint, wherein the first rectilinear cavity and the second rectilinear cavity are aligned; and inserting an implant through the first cavity, across the first SI-Joint, through the sacrum, across the second SI-Joint, and through the second cavity. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]    The novel features of the invention are set forth with particularity in the claims that follow. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which: 
           [0031]      FIG. 1  illustrates an embodiment of an implant structure. 
           [0032]      FIGS. 2A-2D  are side section views of the formation of a broached bore in bone according to one embodiment of the invention. 
           [0033]      FIGS. 2E and 2F  illustrate the assembly of a soft tissue protector system for placement over a guide wire. 
           [0034]      FIGS. 3 and 4  are, respectively, anterior and posterior anatomic views of the human hip girdle comprising the sacrum and the hip bones (the right ilium, and the left ilium), the sacrum being connected with both hip bones at the sacroiliac joint (in shorthand, the SI-Joint). 
           [0035]      FIGS. 5 to 7A  and  7 B are anatomic views showing, respectively, a pre-implanted perspective, implanted perspective, implanted anterior view, and implanted cranio-caudal section view, the implantation of three implant structures for the fixation of the SI-Joint using a lateral approach through the ilium, the SI-Joint, and into the sacrum. 
           [0036]      FIGS. 8A-8C  illustrate an embodiment of a long implant that has been implanted across the sacrum. The two ilia are not shown. 
           [0037]      FIGS. 9A-9C  illustrate an embodiment of the insertion of a guide pin through the SI-Joints and the formation of aligned cavities in the bone. 
           [0038]      FIGS. 10A and 10B  illustrate an embodiment of a guide pin and broach with alignment features. 
       
    
    
     DETAILED DESCRIPTION 
       [0039]    Elongated, stem-like implant structures  20  like that shown in  FIG. 1  make possible the fixation of the SI-Joint (shown in anterior and posterior views, respectively, in  FIGS. 3 and 4 ) in a minimally invasive manner. These implant structures  20  can be effectively implanted through the use a lateral surgical approach. The procedure is desirably aided by conventional lateral, inlet, and outlet visualization techniques, e.g., using X-ray image intensifiers such as a C-arms or fluoroscopes to produce a live image feed, which is displayed on a TV screen. 
         [0040]    In one embodiment of a lateral approach (see  FIGS. 5 ,  6 , and  7 A/B), one or more implant structures  20  are introduced laterally through the ilium, the SI-Joint, and into the sacrum. This path and resulting placement of the implant structures  20  are best shown in FIGS.  6  and  7 A/B. In the illustrated embodiment, three implant structures  20  are placed in this manner. Also in the illustrated embodiment, the implant structures  20  are rectilinear in cross section and triangular in this case, but it should be appreciated that implant structures  20  of other rectilinear cross sections can be used. 
         [0041]    Before undertaking a lateral implantation procedure, the physician identifies the SI-Joint segments that are to be fixated or fused (arthrodesed) using, e.g., the Fortin finger test; thigh thrust, FABER, Gaenslen&#39;s, compression, distraction, and diagnostic SI joint injection. 
         [0042]    Aided by lateral, inlet, and outlet C-arm views, and with the patient lying in a prone position, the physician aligns the greater sciatic notches and then the alae (using lateral visualization) to provide a true lateral position. A 3 cm incision is made starting aligned with the posterior cortex of the sacral canal, followed by blunt tissue separation to the ilium. From the lateral view, the guide pin  38  (with sleeve (not shown)) (e.g., a Steinmann Pin) is started resting on the ilium at a position inferior to the sacrum end plate and just anterior to the sacral canal. In the outlet view, the guide pin  38  should be parallel to the sacrum end plate at a shallow angle anterior (e.g., 15 degree to 20 degree off the floor, as  FIG. 7A  shows). In a lateral view, the guide pin  38  should be posterior to the sacrum anterior wall. In the outlet view, the guide pin  38  should be superior to the first sacral foramen and lateral of mid-line. This corresponds generally to the sequence shown diagrammatically in  FIGS. 2A and 2B . A soft tissue protector (not shown) is desirably slipped over the guide pin  38  and firmly against the ilium before removing the guide pin sleeve (not shown). 
         [0043]    Over the guide pin  38  (and through the soft tissue protector), the pilot bore  42  is drilled in the manner previously described, as is diagrammatically shown in  FIG. 2C . The pilot bore  42  extends through the ilium, through the SI-Joint, and into the sacrum. The drill bit  40  is removed. 
         [0044]    The shaped broach  44  is tapped into the pilot bore  42  over the guide pin  38  (and through the soft tissue protector) to create a broached bore  48  with the desired profile for the implant structure  20 , which, in the illustrated embodiment, is triangular. This generally corresponds to the sequence shown diagrammatically in  FIG. 2D . The triangular profile of the broached bore  48  is also shown in  FIG. 5 . 
         [0045]      FIGS. 2E and 2F  illustrate an embodiment of the assembly of a soft tissue protector or dilator or delivery sleeve  200  with a drill sleeve  202 , a guide pin sleeve  204  and a handle  206 . In some embodiments, the drill sleeve  202  and guide pin sleeve  204  can be inserted within the soft tissue protector  200  to form a soft tissue protector assembly  210  that can slide over the guide pin  208  until bony contact is achieved. The soft tissue protector  200  can be any one of the soft tissue protectors or dilators or delivery sleeves disclosed herein. In some embodiments, an expandable dilator or delivery sleeve  200  as disclosed herein can be used in place of a conventional soft tissue dilator. In the case of the expandable dilator, in some embodiments, the expandable dilator can be slid over the guide pin and then expanded before the drill sleeve  202  and/or guide pin sleeve  204  are inserted within the expandable dilator. In other embodiments, insertion of the drill sleeve  202  and/or guide pin sleeve  204  within the expandable dilator can be used to expand the expandable dilator. 
         [0046]    In some embodiments, a dilator can be used to open a channel though the tissue prior to sliding the soft tissue protector assembly  210  over the guide pin. The dilator(s) can be placed over the guide pin, using for example a plurality of sequentially larger dilators or using an expandable dilator. After the channel has been formed through the tissue, the dilator(s) can be removed and the soft tissue protector assembly can be slid over the guide pin. In some embodiments, the expandable dilator can serve as a soft tissue protector after being expanded. For example, after expansion the drill sleeve and guide pin sleeve can be inserted into the expandable dilator. 
         [0047]    As shown in  FIGS. 5 and 6 , a triangular implant structure  20  can be now tapped through the soft tissue protector over the guide pin  38  through the ilium, across the SI-Joint, and into the sacrum, until the proximal end of the implant structure  20  is flush against the lateral wall of the ilium (see also  FIGS. 7A and 7B ). The guide pin  38  and soft tissue protector are withdrawn, leaving the implant structure  20  residing in the broached passageway, flush with the lateral wall of the ilium (see  FIGS. 7A and 7B ). In the illustrated embodiment, two additional implant structures  20  are implanted in this manner, as  FIG. 6  best shows. In other embodiments, the proximal ends of the implant structures  20  are left proud of the lateral wall of the ilium, such that they extend 1, 2, 3 or 4 mm outside of the ilium. This ensures that the implants  20  engage the hard cortical portion of the ilium rather than just the softer cancellous portion, through which they might migrate if there was no structural support from hard cortical bone. The hard cortical bone can also bear the loads or forces typically exerted on the bone by the implant  20 . 
         [0048]    The implant structures  20  are sized according to the local anatomy. For the SI-Joint, representative implant structures  20  can range in size, depending upon the local anatomy, from about 35 mm to about 60 mm in length, and about a 7 mm inscribed diameter (i.e. a triangle having a height of about 10.5 mm and a base of about 12 mm). The morphology of the local structures can be generally understood by medical professionals using textbooks of human skeletal anatomy along with their knowledge of the site and its disease or injury. The physician is also able to ascertain the dimensions of the implant structure  20  based upon prior analysis of the morphology of the targeted bone using, for example, plain film x-ray, fluoroscopic x-ray, or MRI or CT scanning. 
         [0049]    Using a lateral approach, one or more implant structures  20  can be individually inserted in a minimally invasive fashion across the SI-Joint, as has been described. Conventional tissue access tools, obturators, cannulas, and/or drills can be used for this purpose. Alternatively, the novel tissue access tools described above and in U.S. Provisional Patent Application No. 61/609,043, titled “TISSUE DILATOR AND PROTECTER” and filed Mar. 9, 2012, which is hereby incorporated by reference in its entirety, can also be used. No joint preparation, removal of cartilage, or scraping are required before formation of the insertion path or insertion of the implant structures  20 , so a minimally invasive insertion path sized approximately at or about the maximum outer diameter of the implant structures  20  can be foimed. 
         [0050]    The implant structures  20  can obviate the need for autologous bone graft material, additional pedicle screws and/or rods, hollow modular anchorage screws, cannulated compression screws, threaded cages within the joint, or fracture fixation screws. Still, in the physician&#39;s discretion, bone graft material and other fixation instrumentation can be used in combination with the implant structures  20 . 
         [0051]    In a representative procedure, one to six, or perhaps up to eight, implant structures  20  can be used, depending on the size of the patient and the size of the implant structures  20 . After installation, the patient would be advised to prevent or reduce loading of the SI-Joint while fusion occurs. This could be about a six to twelve week period or more, depending on the health of the patient and his or her adherence to post-op protocol. 
         [0052]    The implant structures  20  make possible surgical techniques that are less invasive than traditional open surgery with no extensive soft tissue stripping. The lateral approach to the SI-Joint provides a straightforward surgical approach that complements the minimally invasive surgical techniques. The profile and design of the implant structures  20  minimize or reduce rotation and micromotion. Rigid implant structures  20  made from titanium provide immediate post-op SI Joint stability. A bony in-growth region  24  comprising a porous plasma spray coating with irregular surface supports stable bone fixation/fusion. The implant structures  20  and surgical approaches make possible the placement of larger fusion surface areas designed to maximize post-surgical weight bearing capacity and provide a biomechanically rigorous implant designed specifically to stabilize the heavily loaded SI-Joint. 
         [0053]    To improve the stability and weight bearing capacity of the implant, the implant can be inserted across three or more cortical walls. For example, after insertion the implant can traverse two cortical walls of the ilium and at least one cortical wall of the sacrum. The cortical bone is much denser and stronger than cancellous bone and can better withstand the large stresses found in the SI-Joint. By crossing three or more cortical walls, the implant can spread the load across more load bearing structures, thereby reducing the amount of load borne by each structure. In addition, movement of the implant within the bone after implantation is reduced by providing structural support in three locations around the implant versus two locations. 
         [0054]    Long Implant 
         [0055]      FIGS. 8A-8C  illustrate an embodiment of a long implant  800  for SI-Joint fusion or fixation that has been implanted through both SI-Joints of the patient. The length of the long implant  800  can be selected to enter one side of the first ilium, cross the first SI-Joint, traverse the sacrum, cross the second SI-Joint, and exit the second ilium. In some embodiments, the length of the long implant  800  can additionally include extra length to leave a predetermined length of implant proud of both surfaces of the ilium. For example, the long implant  800  can have a length such that the implant is proud of each surface of the ilium by between about 1 to 10 mm, or between about 2 to 8 mm, or about 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 mm, or less than about 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 mm. In some embodiments, the long implant  800  can be generally between about 100 mm to about 300 mm, or about 150 mm to about 250 mm. 
         [0056]    Besides the length, the long implant  800  can share many of the same features as described above for the regular sized implant. For example, the transverse cross-sectional profile of the long implant  800  can be rectilinear, such as triangular or rectangular. The long implant  800  can be made of a metal or metal alloy, such as titanium. In some embodiments, the surface of the long implant  800  can be roughened and/or provided with a texture that promotes bone tissue ingrowth and integration. For example, a porous and/or irregular surface texture can be provided by titanium plasma spray coating the surface of the long implant. The long implant  800  can also have a lumen for receiving a guidewire, and one or both ends of the lumen can have internal screw threads. In some embodiments, the distal end of the long implant can be slightly tapered to facilitate insertion into a bone cavity and to provide a visual identification of the distal end of the implant. 
         [0057]    In some embodiments, as illustrated in  FIGS. 8A-8C , the long implant  800  can be implanted through the first ilium (not shown) and across first SI-Joint, through the sacrum and above the Si foramen, across the second SI-Joint, and through the second ilium (not shown). In some embodiments, the long implant  800  can be implanted between the S1 and S2 vertebrae. 
         [0058]    As shown in  FIGS. 9A and 9B , to implant the long implant  800 , a guide pin  900  can be inserted, by for example drilling, through the first ilium and across first SI-Joint, through the sacrum and above the Si foramen and/or between the S1 and S2 vertebrae, across the second SI-Joint, and through the second ilium. An incision can be made through the skin and tissue to the ilium to facilitate passage of the guide pin  900 . Since the length of the guide pin  900  is known, the operator can measure the lengths of the guide pin  900  extending from both sides of the ilium and determine the length of guide pin  900  residing within bone by subtracting the length outside the body from the total length of the guide pin  900 . Once the length of guide pin  900  within the bone is known, the size of the long implant  900  that should be used can be selected by taking that length and adding the length of implant that is desired to be left proud from each surface of the bone. In some embodiments, the length of the implant  800  to be used can be estimated before surgery by imaging the pelvis region of the patient including the sacrum and the ilium. For example, an X-ray or CAT scan can be taken of the pelvis region, allowing the distance between the illium surfaces to be determined. 
         [0059]    After the guide pin  900  is inserted, a cavity  902  can be formed through the ilium and SI-Joint and into the sacrum on both sides to receive the implant. The cavity can be formed as described above by drilling a bore and then shaping the bore using a broach. In some embodiments, the cavity can have a rectilinear transverse cross-section. As shown in  FIG. 9C , the two cavities  902  should be aligned together so that the long implant  900  can be inserted through both cavities  902 . In one embodiment, the guide pin  900  can have alignment features at both the distal end and the proximal end to facilitate alignment of the instrumentation such as the dilators and/or broach used to form the cavity. For example, as illustrated in  FIGS. 10A and 10B , the alignment feature  904  can be a line, ridge, or slot that runs across the length of the guide pin  900  or at least runs across both ends of the guide pin. Alternatively, the alignment feature  904  can be a pin, such as a triangular pin or flat edge pin, that is located at each end of the guide pin. The broach  906  can have a complementary alignment feature  908  along its guide pin lumen  910 , such as a slot or ridge, that registers the broach with the guide pin in the proper alignment. In some embodiments, once a first cavity has been formed, the second cavity can be aligned with the first cavity using fluoroscopy. The first cavity is readily visible under fluoroscopy and allows the operator to determine or confirm the proper orientation of the broach used to form the second cavity. 
         [0060]    After the cavities are formed, the long implant  900  can be inserted into the first cavity and impacted through the sacrum and out the second cavity. Some advantages of using a long implant  900  over separate shorter implants is that the long implant may provide enhanced stability, particularly in the sacrum. Use of the long implant may allow a more medial implant location relative to the implant location of separate implants, and generally the bone quality is better as the implant location moves medially. 
         [0061]    The foregoing is considered as illustrative only of the principles of the invention. Furthermore, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims.