Abstract:
Pedicle screw assemblies and related bone screws. In some embodiments, the bone screw may comprise a head portion and an axial shaft. The axial shaft may comprise a threaded portion comprising a triple lead thread disposed about the axial shaft. The axial shaft may further comprise a tapering portion and a non-tapering portion. The tapering portion may comprise multiple tapering portions tapering at differing rates, and may be positioned adjacent to a tip of the axial shaft. Each of the three leads may extend coextensively along at least a majority of the length of the axial shaft, the threaded portion, the tapering portion, and/or the non-tapering portion.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a continuation application of U.S. patent application Ser. No. 12/818,749, filed on Jun. 18, 2010, and titled “TRIPLE LEAD BONE SCREW,” which claims the benefit of U.S. Provisional Patent Application No. 61/218,574, filed on Jun. 19, 2009, and also titled “TRIPLE LEAD BONE SCREW.” Both of the aforementioned applications are incorporated by reference herein in their entireties. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to a triple lead bone screw for use in surgical applications. More specifically, the present invention relates to a triple lead bone screw for use in spinal surgical applications, such as pedicle screw applications and the like. 
       BACKGROUND OF THE INVENTION 
       [0003]    Triple lead screws are used in a variety of applications, including bone screw applications. These screws utilize three thread starts/leads between the distal end (i.e. tip) of the screw and the proximal end (i.e. head) of the screw. The three thread starts are typically spaced apart by about 120 degrees. The screws may be used to engage bone, or, more often, the triple lead portion is used to engage an anatomical plate or other implant structure. The advantage of triple lead screws relative to single or double lead screws is that triple lead screws are advanced farther with fewer turns, i.e. they are placed more quickly and with less effort. The disadvantage of triple lead screws relative to single or double lead screws is that triple lead screws typically have a lower pullout or backout strength, i.e. they may become dislodged more easily and with less effort. 
         [0004]    What is still needed in the art is a triple lead pedicle screw or the like that overcomes the above mentioned disadvantage. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    In various exemplary embodiments, the present invention provides a triple lead pedicle screw or the like that is capable of being placed quickly with minimal effort and that resists pullout or backout at least as effectively as comparable single or double lead screws. This triple lead bone screw is ideally suited for the surgical correction of spinal deformities and other similar surgical procedures in which multiple screws must be placed. In such surgical procedures, a surgeon may be come fatigued and time is of the essence. 
         [0006]    In one exemplary embodiment, the present invention provides a pedicle screw assembly, including: a bone screw having a head portion and a thread portion, wherein the thread portion includes an axial shaft and a triple lead thread disposed about the axial shaft; and a rod retention member selectively coupled to the head portion of the bone screw. Optionally, the triple lead thread of the thread portion of the bone screw includes leads that start with about 120 degrees of separation. Optionally, the triple lead thread of the thread portion of the bone screw includes leads that originate at different points along the axial shaft of the thread portion of the bone screw. Optionally, the triple lead thread of the thread portion of the bone screw includes leads that terminate at different points along the axial shaft of the thread portion of the bone screw. Optionally, the axial shaft of the thread portion of the bone screw includes a first tapering portion proximate a tip of the axial shaft of the thread portion of the bone screw. Optionally, the axial shaft of the thread portion of the bone screw includes a second tapering portion proximate the tip of the axial shaft of the thread portion of the bone screw. Preferably, the second tapering portion tapers more steeply than the first tapering portion. Optionally, the axial shaft of the thread portion of the bone screw includes a reduced diameter portion proximate the head portion of the bone screw. Optionally, the axial shaft of the thread portion of the bone screw includes one or more tapering portions proximate the head portion of the bone screw. Preferably, the rod retention member is selectively pivotably coupled to the head portion of the bone screw. 
         [0007]    In another exemplary embodiment, the present invention provides a bone screw, including: a head portion; and a thread portion, wherein the thread portion includes an axial shaft and a triple lead thread disposed about the axial shaft. Optionally, the triple lead thread of the thread portion of the bone screw includes leads that start with about 120 degrees of separation. Optionally, the triple lead thread of the thread portion of the bone screw includes leads that originate at different points along the axial shaft of the thread portion of the bone screw. Optionally, the triple lead thread of the thread portion of the bone screw includes leads that terminate at different points along the axial shaft of the thread portion of the bone screw. Optionally, the axial shaft of the thread portion of the bone screw includes a first tapering portion proximate a tip of the axial shaft of the thread portion of the bone screw. Optionally, the axial shaft of the thread portion of the bone screw includes a second tapering portion proximate the tip of the axial shaft of the thread portion of the bone screw. Preferably, the second tapering portion tapers more steeply than the first tapering portion. Optionally, the axial shaft of the thread portion of the bone screw includes a reduced diameter portion proximate the head portion of the bone screw. Optionally, the axial shaft of the thread portion of the bone screw includes one or more tapering portions proximate the head portion of the bone screw. 
         [0008]    In a further exemplary embodiment, the present invention provides a bone screw, including: a head portion; and a thread portion, wherein the thread portion includes an axial shaft and a triple lead thread disposed about the axial shaft, wherein the axial shaft of the thread portion of the bone screw includes a first tapering portion proximate a tip of the axial shaft of the thread portion of the bone screw, and wherein the axial shaft of the thread portion of the bone screw includes a second tapering portion proximate the tip of the axial shaft of the thread portion of the bone screw, wherein the second tapering portion tapers more steeply than the first tapering portion. Optionally, the triple lead thread of the thread portion of the bone screw includes leads that originate at different points along the axial shaft of the thread portion of the bone screw. Optionally, the triple lead thread of the thread portion of the bone screw includes leads that terminate at different points along the axial shaft of the thread portion of the bone screw. Optionally, the axial shaft of the thread portion of the bone screw includes a reduced diameter portion proximate the head portion of the bone screw. Optionally, the axial shaft of the thread portion of the bone screw includes one or more tapering portions proximate the head portion of the bone screw. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The present invention is illustrated and described herein with reference to the various drawings, in which like reference numbers are used to denote like screw components, as appropriate, and in which: 
           [0010]      FIG. 1  is a planar side view of one exemplary embodiment of the triple lead pedicle screw assembly of the present invention, including the triple lead bone screw of the present invention and an associated rod retention member; 
           [0011]      FIG. 2  is a perspective view of the triple lead pedicle screw assembly of  FIG. 1 ; 
           [0012]      FIG. 3  is a perspective view of one exemplary embodiment of the bone screw of the present invention; 
           [0013]      FIG. 4  is a planar side view of the bone screw of  FIG. 3 ; 
           [0014]      FIG. 5  is another planar side view of the bone screw of  FIG. 3 ; 
           [0015]      FIG. 6  is a perspective view of another exemplary embodiment of the bone screw of the present invention; 
           [0016]      FIG. 7  is a planar side view of the bone screw of  FIG. 6 ; and 
           [0017]      FIG. 8  is another planar side view of the bone screw of  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    Again, in various exemplary embodiments, the present invention provides a triple lead pedicle screw or the like that is capable of being placed quickly with minimal effort and that resists pullout or backout at least as effectively as comparable single or double lead screws. This triple lead bone screw is ideally suited for the surgical correction of spinal deformities/anomalies/trauma and other similar surgical procedures in which multiple screws must be placed. In such surgical procedures, a surgeon may be come fatigued and operative time is of the essence. 
         [0019]    Referring to  FIGS. 1 and 2 , in one exemplary embodiment, the triple lead pedicle screw assembly  10  of the present invention includes a triple lead bone screw  12  and a rod retention member  14 . 
         [0020]    The triple lead bone screw  12  includes a head portion  16  and a threaded portion  18 . The head portion  16  of the triple lead bone screw  12  consists of an enlarged structure, such as a wholly or partially spherical structure, a wholly or partially cylindrical structure, or the like, having one or more tool receiving recesses  20  manufactured into the top surface thereof, by which the triple lead bone screw  12  is grasped and/or turned. Optionally, three such tool receiving recesses  20  are utilized and are spaced apart by about 120 degrees, although it will be readily apparent to those of ordinary skill in the art that other suitable configurations may be utilized. The threaded portion  18  of the triple lead bone screw  12  consists of three thread starts/leads between the distal end (i.e. tip)  22  of the screw  12  and the proximal end (i.e. head)  24  of the screw  12 . Optionally, the three thread starts are spaced apart by about 120 degrees, although it will be readily apparent to those of ordinary skill in the art that other suitable configurations may be utilized. Optionally, the three thread starts/leads also originate and/or terminate at different positions along the length of the screw  12 . In other words, the three thread starts/leads may or may not coincide along the length of the screw  12  and may be spaced apart by any desired constant or variable distance. Finally, one or more of the three thread starts/leads may be selectively broken or notched to create a biting surface, such as near the tip  22  of the screw  12  so that the screw will advance into bone from the first tum. Any suitable thickness, pitch, or other dimensions may be utilized, as well as any suitable materials (e.g. a biocompatible metal, ceramic, or plastic, bony material, etc.). 
         [0021]    The rod retention member  14  consists of a U-shaped member  26  having a hole in the bottom. The threaded portion  18  of the bone screw  12  is disposed through this hole, with the head portion  16  of the bone screw being pivotably seated in the interior bottom of the U-shaped member, prior to the screw  12  being driven into bone. The rod retention member  14  includes a plurality of internally threaded, concentrically arranged, vertically extending arm members  28  between which a stabilizing rod or other similar stabilizing structure (not illustrated) is selectively disposed. This stabilizing rod is then “locked” into place via the engagement of an externally threaded cap (not illustrated) into the internal threads of the arm members  28 , thereby “locking” the orientation of the rod retention member  14  with respect to the head portion  16  of the triple lead bone screw  12 , as the stabilizing rod is in direct or indirect contact with the head portion  16  of the triple lead bone screw  12 . It will be readily apparent to those of ordinary skill in the art that various other structures may also be disposed between the stabilizing rod and either or both of the externally threaded cap and the head portion  16  of the triple lead bone screw  12 . In this manner, screws  12  may be placed in different anatomical structures, or different parts of the same anatomical structure, and securely joined by stabilizing structures in a predetermined configuration and alignment. 
         [0022]    Referring to  FIGS. 3-5 , in one exemplary embodiment, the triple lead bone screw  12  of the present invention includes a head portion  16  and a threaded portion  18 . The head portion  16  of the triple lead bone screw  12  consists of an enlarged structure, such as a wholly or partially spherical structure, a wholly or partially cylindrical structure, or the like, having one or more tool receiving recesses  20  manufactured into the top surface thereof, by which the triple lead bone screw  12  is grasped and/or turned. Optionally, three such tool receiving recesses  20  are utilized and are spaced apart by about 120 degrees, although it will be readily apparent to those of ordinary skill in the art that other suitable configurations may be utilized. The threaded portion  18  of the triple lead bone screw  12  consists of three thread starts/leads between the distal end (i.e. tip)  22  of the screw  12  and the proximal end (i.e. head)  24  of the screw  12 . Optionally, the three thread starts are spaced apart by about  120  degrees, although it will be readily apparent to those of ordinary skill in the art that other suitable configurations may be utilized. Optionally, the three thread starts/leads also originate and/or terminate at different positions along the length of the screw  12 . In other words, the three thread starts/leads may or may not coincide along the length of the screw  12  and may be spaced apart by any desired constant or variable distance. Finally, one or more of the three thread starts/leads may be selectively broken or notched to create a biting surface, such as near the tip  22  of the screw  12  so that the screw will advance into bone from the first tum. Any suitable thickness, pitch, or other dimensions may be utilized, as well as any suitable materials (e.g. a biocompatible metal, ceramic, or plastic, bony material, etc.). 
         [0023]    Referring specifically to  FIG. 5 , the threaded portion  18  of the screw  12  includes an axial shaft  30  that may have a non-tapering portion  32 , a first tapering portion  34 , and a second tapering portion  36  disposed, in order, between the head portion  16  of the screw  12  and the rounded or pointed tip  38  of the screw  12 . Preferably, the taper of the second tapering portion  36  is greater than the taper of the first tapering portion  34 , with the second tapering portion sweeping a 45-degree arc, a 60-degree arc, etc. The threads are disposed about these various segments of the screw  12 . 
         [0024]    Referring to  FIGS. 6-8 , in another exemplary embodiment, the triple lead bone screw  12  of the present invention includes a head portion  16  and a threaded portion  18 . The head portion  16  of the triple lead bone screw  12  consists of an enlarged structure, such as a wholly or partially spherical structure, a wholly or partially cylindrical structure, or the like, having one or more tool receiving recesses  20  manufactured into the top surface thereof, by which the triple lead bone screw  12  is grasped and/or turned. Optionally, three such tool receiving recesses  20  are utilized and are spaced apart by about 120 degrees, although it will be readily apparent to those of ordinary skill in the art that other suitable configurations may be utilized. The threaded portion  18  of the triple lead bone screw  12  consists of three thread starts/leads between the distal end (i.e. tip)  22  of the screw  12  and the proximal end (i.e. head)  24  of the screw  12 . Optionally, the three thread starts are spaced apart by about 120 degrees, although it will be readily apparent to those of ordinary skill in the art that other suitable configurations may be utilized. Optionally, the three thread starts/leads also originate and/or terminate at different positions along the length of the screw  12 . In other words, the three thread starts/leads may or may not coincide along the length of the screw  12  and may be spaced apart by any desired constant or variable distance. Finally, one or more of the three thread starts/leads may be selectively broken or notched to create a biting surface, such as near the tip  22  of the screw  12  so that the screw will advance into bone from the first tum. Any suitable thickness, pitch, or other dimensions may be utilized, as well as any suitable materials (e.g. a biocompatible metal, ceramic, or plastic, bony material, etc.). 
         [0025]    Referring specifically to  FIG. 8 , the threaded portion  18  of the screw  12  includes an axial shaft  30  that may have a non-tapering portion  32 , a first tapering portion  34 , and a second tapering portion  36  disposed, in order, between the head portion  16  of the screw  12  and the rounded or pointed tip  38  of the screw  12 . Preferably, the taper of the second tapering portion  36  is greater than the taper of the first tapering portion  34 , with the second tapering portion sweeping a 45-degree arc, a 60-degree arc, etc. The threads are disposed about these various segments of the screw  12 . In this exemplary embodiment, a reduced diameter portion  40  and one or more tapering portions  42  are also disposed along the axial shaft  30  between the head portion  16  and the threaded portion  18  of the screw  12 . 
         [0026]    Axial pullout testing of the triple lead bone screw  12  of the present invention demonstrated performance comparable to that of a conventional single lead bone screw. 
         [0027]    Although the present invention has been 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, and are intended to be covered by the following claims.