Abstract:
An improved joint fusion screw for transiliac fixation has a screw head and extending therefrom an elongate hollow shaft. The hollow shaft has an externally threaded end portion extending to a tip end and a non-externally threaded shank portion having a plurality of window openings. At or near the tip end is a start of a thread with a bone cutting flute. The bone cutting flute has a cutting edge on a circumferential exterior of the threaded tip to cut bone and directs the cut bone internally into a bone receiving opening in the hollow shaft directly in front of the cutting flute. The cutting edge lies at the start of the thread extending radially above the bone receiving opening at least partially overhanging the opening configured to cut bone.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation in part of U.S. application Ser. No. 14/630,748 entitled “Improved Sacroiliac Screw” filed Feb. 25, 2015. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to an improved spinal fixation screw for transiliac fixation and a method of use. 
       BACKGROUND OF THE INVENTION 
       [0003]    Many complaints of lower back pain and leg pain have been attributed to herniated discs or other injuries to the spinal column. Extensive therapy and treatment has often been unsuccessful in alleviating such pain. It has been established that some of this lower back and leg pain can be attributed to symptomatic sacroiliac dysfunction or instability. Normally, the sacroiliac joint which spans between the sacrum bone and ilium bone has nutation of one to two degrees. “Nutation” is the medical term which describes the relative movement between the sacrum and ilium. A patient&#39;s sacroiliac joint can become damaged resulting in hypermobility of the joint. Because of the small range of motion in the sacroiliac joint, hypermobility is very difficult to diagnose. Therefore, lower back pain or leg pain caused by sacroiliac dysfunction often goes misdiagnosed or undiagnosed. 
         [0004]    Accordingly, it is an objective of this invention to provide a device for correcting symptomatic sacroiliac dysfunction or instability. It is another aspect of this invention to provide a device which enhances stability and compression for purposes of immobilizing a joint, and for fusing two opposed bone structures across the joint. 
       SUMMARY OF THE INVENTION 
       [0005]    An improved joint fusion screw for transiliac fixation has a screw head and extending therefrom an elongate hollow shaft. The hollow shaft has an externally threaded end portion extending to a tip end and a non-externally threaded shank portion having a plurality of window openings. At or near the tip end is a start of a thread with a bone cutting flute. The bone cutting flute has a cutting edge on a circumferential exterior of the threaded tip to cut bone and directs the cut bone internally into a bone receiving opening in the hollow shaft directly in front of the cutting flute. The cutting edge lies at the start of the thread extending radially above the bone receiving opening at least partially overhanging the opening configured to receive bone fragments. 
         [0006]    In each embodiment, the hollow shaft has a bone chamber for receiving the cut bone fragments. The bone chamber extends to at least the window openings of the shank portion. Autograft cut bone fragments are directed to the window openings to enhance new bone growth and rapid fusion of the fusion screw. Preferably, the window openings of the shank portion are elongated slots. 
         [0007]    The screw has an enlarged flat head with a convex rounded or hemispherical polyaxial bottom affixed or integral to an end of the shank. The end of the flat head has internal or female threads for receiving a threaded driver cap. The threaded driver cap has a cannulated opening or aperture for passing a guide wire and a torqueing tool receiving cavity to thread the screw into the bone. The drive cap is affixed into the threaded end of the shank. The driver cap can be removably attached to allow bone packing material to be packed into the hollow shaft after screw insertion into the bone. 
         [0008]    In one embodiment, the bone cutting flute has an ramp extending outwardly from the cutting edge forward of the thread at least partially overhanging the opening toward an inside diameter of the hollow shaft. The cut bone fragments are cut and re-directed internal along the ramps upon implantation of the screw into the bone receiving opening and into the hollow shaft. The cutting edge, instead of forming spiral cut autograft bone upon screw implantation, breaks the bone as it is redirected by the ramp. The spiral cut autograft bone fragments are pushed upwardly into the shaft toward the window openings. 
         [0009]    In a second embodiment, at least two cutting flutes extend starting from the tip end longitudinally through two thread starts. 
         [0010]    In a third embodiment, the tip end can have an annular ledge extending across the hollow shaft. The ledge has an aperture for receiving a guide wire. The aperture is coaxial with an axis of the screw and the aperture of the cap driver. 
         [0011]    A method of transiliac fixation using the improved screw comprises the steps of pre-drilling an opening in the sacrum and the ilium bones to be fixed with a pilot hole opening and inserting a joint fixation screw with a hollow shaft onto the pre-drilled opening while cutting autograft bone fragments directed into the hollow shaft. The hollow shaft has a bone receiving chamber extending to a plurality of window openings further in the hollow shaft and the step of threading of the screw directs the autograft bone fragments to an opening to enhance fusion. The screw can have apertures at the tip end and at the driver cap and the method may further comprise the steps of inserting a guide wire to create a drill path, inserting a cannulated drill over the guide wire to pre-drill the pilot hole, and then inserting the screw onto the guide wire to direct the path for insertion into the bone. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The invention will be described by way of example and with reference to the accompanying drawings in which: 
           [0013]      FIG. 1  is a plan view of a first embodiment of the present invention. 
           [0014]      FIG. 2  is an end view looking towards the distal end of the screw of the present invention. 
           [0015]      FIG. 3  is a top view of the screw of the first embodiment of the present invention. 
           [0016]      FIG. 4A  is a plan view of a first embodiment of the present invention showing the counterclockwise cutting edges of the slotted windows. 
           [0017]      FIG. 4B  is a cross-sectional view taken along lines  4 B- 4 B of  FIG. 4A . 
           [0018]      FIG. 5  is an isometric view of the first embodiment of the present invention. 
           [0019]      FIG. 6  is a second isometric or perspective view showing the bottom of the screw of the present invention. 
           [0020]      FIG. 7A  is a side view of the present invention. 
           [0021]      FIG. 7B  is a cross-sectional view taken along lines  7 B- 7 B of  FIG. 7A . 
           [0022]      FIG. 8A  is an exploded view of the first embodiment of the present invention showing the washer, the screw body and an end cap at the screw head portion. 
           [0023]      FIG. 8B  is a cross-sectional view taken along lines  8 B- 8 B of  FIG. 8A . 
           [0024]      FIG. 9  is a side view or plan view of a second embodiment of the present invention exhibiting a dual threaded shank. 
           [0025]      FIG. 10  is an end view showing the dual threaded shank of the present invention of the second embodiment of the present invention. 
           [0026]      FIG. 11  is a top view of the second embodiment of the present invention. 
           [0027]      FIG. 12A  is a side view of the second embodiment of the present invention. 
           [0028]      FIG. 12B  is a cross-sectional view taken along lines  12 B- 12 B showing the counterclockwise cutting edges on the slotted windows. 
           [0029]      FIG. 13  is an isometric view taken from the top end of the second embodiment of the present invention. 
           [0030]      FIG. 14  is a bottom view of the second embodiment of the present invention. 
           [0031]      FIG. 15A  is a side view of the second embodiment of the present invention. 
           [0032]      FIG. 15B  is a cross-sectional view taken along lines  15 B- 15 B of  FIG. 15A . 
           [0033]      FIG. 16A  is a side view of the second embodiment of the present invention. 
           [0034]      FIG. 16B  is a cross-sectional view taken along lines  16 B- 16 B of  FIG. 16A . 
           [0035]      FIG. 17  is a top view of the screw regardless of the embodiment where the end cap has been removed exposing the screw slot and cannulation for implanting the screw body. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0036]    With reference to  FIGS. 1-17 ; two versions or embodiments of an improved joint fixation screw  10 A and  10 B for a transiliac fixation are shown. Each embodiment has common features with variations on number of the cutting flutes and threads at or near the tip end.  FIG. 4  shows the proximal head end opposite to the bone cutting tip end. The head  30  at this end is a common feature to each embodiment. 
         [0037]    Each screw  10 A and  10 B has a hollow elongated shaft  20 . The shaft  20  has an externally threaded end portion  21  and a smooth shank portion  25 . The smooth shank portion  25  has a plurality of window openings  24  open to a chamber  12  inside the hollow shaft  20 . At a proximal end of the screws  10 A,  10 B is an enlarged head  30 . The center of the head  30  is a threaded opening  33  open to the chamber  12 . The threaded end portion  21  of the hollow shaft  20  has threads  28 ,  29 , these threads  28 ,  29  can be tapered with an increasing diameter towards the smooth portion of the shank, as shown in the figures. All these features are common to each screw  10 A and  10 B. 
         [0038]    In a first embodiment of  FIGS. 1-8B , the screw  10 A has one cutting flute  11 . As shown in  FIGS. 1, 4A and 5 , the cutting edge  13  lies in a plane almost or substantially parallel to the axis of the screw shaft and each had a ramp  14  for directing bone fragments to a bone receiving opening  15  into the hollow chamber  12  and is preferably oriented perpendicular to the helical thread start. The cut fragments spiral along the ramped surfaces  14  where they bend and break into bone fragments as they enter the opening  15 . 
         [0039]    With reference to  FIGS. 8A and 8B , an exploded view of the first embodiment shows a washer  50  with a concavity  52  in the form of a polyaxial shaped bowl to receive the bottom  32  of the head  30  which has a rounded or polyaxial hemispherical curvature. This feature allows the washer  50  to occupy a space between the screw head  30  and the bone on tightening and can accommodate any angulation so the washer  50  stays flush against the bone. In the absence of this feature, the screw head bottom  32  could be tilted and the washer  50  would not be flush to the bone surface. 
         [0040]    In a second embodiment of  FIGS. 9-16B , there are two cutting flutes  11 , one flute  11  at each start of the threads  28 ,  29  directly in front of and partially overhanging a bone receiving opening  15 . Each flute  11  is diametrically opposed from the other and each has a cutting edge  13  formed from a start or leading end of a thread  28 ,  29  at or near the tip end  21 . The cutting edges  13  are still circumferentially in a plane about parallel to the axis, but are positioned diametrically opposite at each thread start and overhanging the opening  15  ahead of the flutes  11 . Both flutes  11  capture the cut bone fragments and direct them into the chamber  12  in pieces that are broken on threading by having the ramp surfaces  14  pushing the bone fragments into the openings  15  during implantation. 
         [0041]    With reference to  FIGS. 2, 7A, 10 and 15B , a third embodiment, an annular ledge  23  extends across the hollow shaft  20  at the tip end  21 . The ledge  23  has an aperture  27  for receiving a guide wire. This third version screw has the same flutes  11  as shown in  FIG. 1 or 2 . 
         [0042]      FIGS. 7A-8B  and  FIGS. 15A-16B  show a threaded driver cap  40  with tool aperture  41  inserted and threaded into the threads  33  of the enlarged head  30 . This screw head  30  has a torque receiving cavity  41 A with projections  42  to receive a torqueing tool to implant the screw  10 A,  10 B. Centrally, there is an aperture  47  to allow the screw to pass over a guide wire along a directional pre-drilled path. 
         [0043]    As the screw  10 A,  10 B is torqued into the pre-drilled pilot hole, the cutting flutes  11  create autograft bone fragments that are delivered directly into the chamber  12 . In this way, the patient&#39;s bone fragments are made available to enhance new bone growth to fuse the screw  10 A,  10 B in place. 
         [0044]    One purpose of this invention is to direct bone that is cut by the self-tapping threads and cutting edge or edges  13  at or near the tip of the bone screw  10 A,  10 B or otherwise gathered by the flutes  11  and directed into the internal chamber  12  of the screw to serve as additional autograft material. Previously, this material would be compressed into the bone around the outside of the screw. The screw would be filled with previously harvested autograft material which could be packed into the screw from an opening in the head end of the screw. The screw is used to secure two bones together, in this case the sacrum and the ilium. When preparing the bone to accept the screw, a hole will be drilled and tapped to a size smaller than the actual screw. The screw can be packed with graft material prior to implantation. The self-tapping edge of the screw will cut additional autograft material as it is installed and the flute will direct this freshly cut autograft material to join the existing material in the inner chamber  12  of the screw. Some of this material will be pushed out of the plurality of window openings  24  or fenestrations in the shaft  20  of the screw as it is tightened to aid in fusion around and into the body of the screw. Many variations of similar flute shapes will produce a similar result. The screw material can be anything hard and strong enough to cut and direct bone chips and withstand the biomechanical loads of the application, preferably titanium, stainless steel or alloys of these materials or metals will work satisfactorily. 
         [0045]    The present invention SI (Sacro-iliac) screw described herein has shown several important features of this screw. These features include: the lagging where the head  30  is pulled down by the coarse threads  29  or  28 ,  29  and the lagged portion is within the smooth shank portion  25  and not engaged by threads  29 ; the screw has a large bore or chamber  12  for inserting bone graft with the option to cap this bore which communicates to the SI space after insertion with the driver cap  40 ; the shaft  20  has only the single or dual threaded end portion  21  to engage only the sacrum bone, the ilium bone is positioned on the smooth shank portion  25 ; an optional anti-back out feature of the washer  50  under the head  30  in the form of a series of wedge-shaped teeth  54  to engage the iliac bone surface can be used as shown in  FIG. 6 . Optionally, a wedge shaped washer  50  could be used under the screw head  30  to accommodate the surface angle of the ilium with respect to the screw axis and also employ an anti-back out feature shown in  FIG. 6 , but as a separate feature on the washer  50 . 
         [0046]    With reference to  FIGS. 4B and 12B , the window openings  24 , the longitudinal edges  24 C of at least one side or both sides of each window  24  can optionally be configured with sharp edges  24 C for cutting bone. The use of this feature is not needed during insertion of the screw, however, if the patient experiences any complications later or particularly after a few months, a surgeon may want to remove the screw  10 A,  10 B. With the cutting edges  24 C on the side of the window  24 , or facing the edges  24 C on a counterclockwise untightening position, facing the bone when the screw is untightened, when the counterclockwise rotation is made, the newly formed bone can easily be cut away to facilitate screw removal by the side having the bone cutting edge  24 C. Absent this feature, newly formed bone will make removal very difficult. 
         [0047]    With reference to  FIGS. 7A-8B and 15A-16B , particular attention is drawn to the end cap  40  which has a threaded male end  43  for engaging a female threaded portion  33  to fix the cap  40  to the screw body or shaft  20 . This removable threaded cap  40  allows the addition of autograft or allograft bone or other biocompatible and bioactive materials to be added to the screw  10 A or  10 B after implantation during the surgical procedure. The removed cap  40  exposes torque driving aperture  41 A in the screw head  30  for receiving a bit or end of an implantation tool. Once implanted, the screw  10 A or  10 B can be filled with material and the end cap  40  installed. 
         [0048]    Variations in the present invention are possible in light of the description of it provided herein. While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention. It is, therefore, to be understood that changes can be made in the particular embodiments described, which will be within the full intended scope of the invention as defined by the following appended claims.