Abstract:
A polyaxial bone fixation system minimizes the number of parts used to engage a bone bolt in various angular orientations relative to an elongated plate or rods, and also permits for nearly infinite positioning of two or more bone bolts relative to each other along the length of an elongated plate or rods.

Description:
PRIORITY CLAIM  
       [0001]     This application claims priority to U.S. Provisional Patent Application 60/652,570, filed Feb. 14, 2005, which is incorporated herein by reference, in its entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to surgical apparatuses, and more particularly to improved bone fixation apparatuses with improved positioning and locking capabilities. The apparatuses are particularly useful for spinal fixation.  
       BACKGROUND OF THE INVENTION  
       [0003]     A variety of clinical conditions require the use of fixation devices, such as apparatuses that include screws and connecting rods or plates, to achieve fixation of bones relative to each other. Numerous spinal fixation procedures involve the temporary and sometimes permanent use of such devices. Procedures for attaching fixation devices to the spine involve accessing the spine either from the back of the patient (posterior) or through the abdominal cavity (anterior). In a typical fixation procedure, bone bolts are used to affix and secure one or more rods or plates to adjacent vertebra within one or more of the cervical, thoracic, or lumbar regions of the spine, so as to achieve fixation of one or more vertebra relative to others. Fixation devices comprising bolts and plates or rods are well known in the art.  
         [0004]     It has been found desirable for bone fixation systems to accommodate angular orientation of a bolt or other anchor in multiple axes (“polyaxial”) relative to the fixation rod or plate and to other fixation components of the implant system. The capability of polyaxial fixation of one or more bone bolts in a fixation system is desirable such that each bolt can be placed in an optimal position for anchoring, enabling the surgeon to accommodate for uneven bone surfaces and any abnormalities that would influence bolt positioning. Polyaxial positioning is also deemed desirable because it should reduce the likelihood that the bone fixation system will loosen or pull out during use.  
         [0005]     Attempts in the art to provide for polyaxial positioning of bone bolts in bone fixation systems has led to devices that include a number of components that make attachment in the surgical field complicated and cumbersome. Such systems often require the surgeon to choose between several different component designs to configure a system appropriate to optimize fixation in a particular patient. The number and range of device components required in many polyaxial systems introduce undesirable time and complexity into the surgery. In addition, such systems also provide for only a finite number of positioning options for each of the bone bolts relative to each other along the length of the fixation rod or plate. This aspect of existing fixation systems imposes further limits on the surgeon&#39;s ability to achieve desired fixation.  
         [0006]     There is a need remaining in the art for a polyaxial bone fixation system that minimizes the number of parts used to engage a bone bolt in various angular orientations relative to an elongated plate or rods, and that also permits for nearly infinite positioning of two or more bone bolts relative to each other.  
       SUMMARY OF THE INVENTION  
       [0007]     In various embodiments, bone fixation locking systems and devices are provided that permit the relative fixation of two or more bone bolts. The bone fixation locking systems allow each bone bolt to be oriented in bone tissue at a wide range of axial positions relative to the plane of an elongated plate or rods, and the axes of other bone bolts. The bone fixation locking systems also allow each bone bolt to be positioned at an infinite number of positions along the length of an elongated plate or rod. According to the various embodiments, the bone fixation locking systems include a locking sleeve that has opposing upper and lower walls with interior and exterior faces, opposing first and second sidewalls, and opposing first and second opened ends that define an aperture through the locking sleeve. The upper and lower walls of the locking sleeve each have through holes that share a common axis, and the upper wall is defined on the exterior face of the upper wall by a spherical convex outer perimeter. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     For a further understanding of the nature and objects of the present invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings, in which like parts are given like reference numerals, and wherein:  
         [0009]      FIG. 1  is an exploded perspective view showing a compression washer with a threaded nut portion, a locking sleeve, an elongated plate, and a bone bolt, aligned but not engaged, according to one illustrated embodiment of the apparatus of the present invention;  
         [0010]      FIG. 2  is a perspective view of one embodiment of a bone bolt according to the present invention;  
         [0011]      FIG. 3  is a perspective view of one embodiment of an elongated plate according to the present invention;  
         [0012]      FIG. 4  is a perspective view of one embodiment of an elongated plate having a through-hole at one end according to the present invention;  
         [0013]      FIG. 5  is a perspective view of one embodiment of an elongated plate having a through-hole at one end according to the present invention, wherein the through-hole is defined by a spherical convex outer perimeter on the upper surface;  
         [0014]      FIG. 6A  is a perspective view of a locking sleeve according to one embodiment of the present invention;  
         [0015]      FIG. 6B  is a perspective view of the exterior face of the upper wall of a locking sleeve showing a through-hole defined by a spherical convex outer perimeter on the exterior face of the upper wall according to one embodiment of the present invention;  
         [0016]      FIG. 6C  is a perspective view of the exterior face of the lower wall of a locking sleeve showing a through-hole defined by a spherical concave inner perimeter on the exterior face of the lower wall according to one embodiment of the present invention;  
         [0017]      FIG. 6D  is a perspective view of the exterior face of the upper wall of a locking sleeve showing a through-hole defined by a elliptical convex outer perimeter on the exterior face of the upper wall according to one embodiment of the present invention;  
         [0018]      FIG. 7  is a side view of one opened end side of a locking sleeve according to one embodiment of the present invention showing through-holes defined by a spherical convex outer perimeter on the exterior faces of the upper and lower walls;  
         [0019]      FIG. 8A  is a perspective view of a compression washer showing a spherical concave lower surface according to one embodiment of the present invention;  
         [0020]      FIG. 8B  is a perspective view of a compression washer showing a threaded nut portion according to one embodiment of the present invention;  
         [0021]      FIG. 8C  is a cut-away side view of one embodiment of a compression washer with a threaded nut portion according to one embodiment of the present invention;  
         [0022]      FIG. 9A  is a perspective view showing engagement between the spherical concave lower surface of a compression washer and the spherical convex outer perimeter on a locking sleeve through-hole according to an embodiment of the present invention;  
         [0023]      FIG. 9B  is a perspective view showing engagement between the spherical concave lower surface of a compression washer and a spherical convex outer perimeter on an elongated plate through-hole according to an embodiment of the present invention;  
         [0024]      FIG. 9C  is a side view of a locking sleeve sidewall showing engagement between the spherical concave lower surface of a first compression washer and the spherical convex outer perimeter on an upper through-hole, and engagement between the spherical concave lower surface of a second compression washer and a spherical convex outer perimeter on a lower through-hole according to an embodiment of the present invention;  
         [0025]      FIG. 10A  is a perspective view showing engagement between a compression washer with a threaded nut portion, a locking sleeve shown in  FIG. 6 , an elongated plate, and a bone bolt according to an embodiment of the present invention;  
         [0026]      FIG. 10B  is a perspective view of the bone fixation apparatus shown in  FIG. 10A  showing compression of the locking sleeve according to an embodiment of the present invention;  
         [0027]      FIG. 11A  is a perspective view showing engagement between a compression washer with a threaded nut portion, a second compression washer, a locking sleeve as shown in  FIG. 7 , an elongated plate, and a bone bolt according to an embodiment of the present invention;  
         [0028]      FIG. 11B  is a perspective view of the bone fixation apparatus shown in  FIG. 11A  showing compression of the locking sleeve according to an embodiment of the present invention;  
         [0029]      FIG. 12  is a cut-away side view showing three of the possible axial orientations of a bone bolt engaged with a compression washer with a threaded nut portion, locking sleeve, and elongated plate according to one embodiment of the apparatus of the present invention; and  
         [0030]      FIG. 13  is a schematic view illustrating one embodiment of the apparatus of the present invention in use as part of a spinal fixation system. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0031]     The present invention will now be described with occasional reference to the specific embodiments of the invention. Unless otherwise defined, all terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to that this invention belongs. The terminology used in the description of the invention herein is for describing particular embodiments only, and is not intended to be limiting of the invention. As used in the description of the invention and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.  
         [0032]     Unless otherwise indicated, all numbers expressing units of measure as used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless otherwise indicated, the numerical properties set forth in the following specification and claims are approximations that may vary depending on the desired properties sought to be obtained in embodiments of the present invention. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical values, however, inherently contain certain errors necessarily resulting from error found in their respective measurements.  
         [0033]     As used throughout this disclosure, the term “substantially” means significantly, considerably, or for the most part, and when used with reference to the shape terms “conical,” “spherical,” “elliptical,” “square,” “rectangular,” and the like, is intended to contemplate shapes that may deviate slightly, or comprise minor variations or interruptions. For example, when the term “substantially spherical” is used, it is intended to encompass a shape according to a common definition of spherical that refers to a feature having the form of a sphere or of one of its segments (e.g., hemisphere, arc), wherein a sphere or a portion of a sphere is defined by a three-dimensional surface wherein every point on the surface is equidistant from the center, including shapes that are generally dome-like but not perfectly spherical such that most but not every point on the surface is equidistant from the center.  
         [0034]     Turning now to description of the bone fixation apparatuses of the invention,  FIG. 1  illustrates an embodiment of the apparatus of the present invention designated generally by the reference numeral “ 10 .” Referring to  FIG. 1 , there can be seen bone bolt  20 , an elongated plate  40 , a locking sleeve  60 , and a compression washer  80 , aligned for engagement according to the invention. Each of these components, including their various embodiments, as more fully described herein, comprise materials that are satisfactory for use in achieving bone fixation, and more particularly for implantation into patients in need of such devices. Of course it will be understood that the materials useful for providing the bone fixation system and its components according to the invention are not limited, and can vary according to the materials known or developed within the art.  
         [0035]     Referring to  FIG. 2 , a first component of the bone fixation apparatus  10  is a bone bolt  20  having an axis AA′ and comprising a first end portion  21 , a central portion  22 , and a second end portion  25 , wherein the diameter of the central portion  22  is greater than the diameters of the first end portion  21  and the second end portion  25 . In some embodiments, as illustrated in  FIG. 2 , the first end portion  21  has a diameter that is less than the diameter of the second end portion  25 . Of course, in alternate embodiments, the first end portion  21  has a diameter that is equal to or greater than the diameter of the second end portion  25 . According to the illustrated embodiment, the bone bolt  20  also comprises a hexagonal tool socket  26  for receiving an allen wrench or like tool to aid in manipulation of the bone bolt  20  for surgical installation into bone. The illustrated bone bolt  20  also comprises an optional void  27  visible at the terminus of the second end portion  25  which passes partially or completely through the length of at least the second end portion  25 . According to alternate embodiments of the invention, the bone bolt  20  may lack one or both of the features including the hexagonal tool socket  29 , and the void  27 . Further, the bone bolt  20  may comprise additional features that are known in the art to be useful or satisfactory for facilitating the manipulation of the bone bolt  20  or its surgical installation into bone.  
         [0036]     Referring again to  FIG. 2 , the first end portion  21  of the illustrated embodiment of the bone bolt  20  comprises along at least a portion of its length a fine thread  28 . According to various embodiments of the bone bolt  20  of the present invention, a fine thread  28  on the first end portion  21  is useful for engagement with a nut (not shown) to facilitate locked engagement between the bone bolt  20  and other components of the fixation apparatus  10 . The second end portion  25  of the illustrated embodiment of the bone bolt  20  comprises along at least a portion of its length a coarse thread  29 . According to various embodiments of the bone bolt  20  of the present invention, a coarse thread  29  on the second end portion  21  is useful for insertion into and engagement with a bone (not shown), such as the pedicle or other portion of a vertebra. A variety of fine and course threads are well known in the art, more particularly with respect to the bone bolt art, and even more particularly with respect to bone bolts for spinal fixation. Applicant&#39;s disclosure is not intended to limit the possible thread configurations that may be employed with respect to embodiments of the bone bolt  20  of the present invention.  
         [0037]     Again referring to  FIG. 2 , the middle portion  22  of the bone bolt  20  has a portion that comprises flat faces  23 , wherein according to the illustrated embodiment the flat faces  23  are arranged around the periphery of the central portion  22  to form a hexagonal shape. The central portion  22  of the illustrated embodiment of the bone bolt  20  also comprises an upper surface  24  which is substantially spherical convex in shape. As will be further described herein, this spherical convex upper surface  24  of the central portion  22  of the bone bolt  20  is adapted for engagement with other portions of the bone fixation apparatus  10  to enable the desired orientation and locking of the apparatus within bone tissue of a patient in need of the same.  
         [0038]     Alternate embodiments of the bone bolt  20  comprise a central portion  22  that lacks one or both of the features that include the spherical convex upper surface  24  and the flat faces  23 . For example, in alternate embodiments, the central portion  22  may lack flat faces  23  around its periphery, or the number of flat faces  23  may vary, and may number from 1, to  2 , to  3 , to  4 , to 5, to 7, to 8 or more, arranged around the periphery of the central portion  22 . Likewise, in alternate embodiments, the upper surface  24  of the central portion  22  of the bone bolt  20  may be substantially flat, or may be convex elliptical.  
         [0039]     Turning now to a second component of the bone fixation apparatus  10 ,  FIG. 3 ,  FIG. 4  and  FIG. 5  show various illustrated embodiments of an elongated plate  40 .  FIG. 3  shows an elongated plate  40  having a longitudinal axis X, and comprising an upper surface  41 , a lower surface  42 , first and second outer edges  43  and  44 , first and second ends  45  and  46 , and an opening  47  bounded by said first and second outer edges  43  and  44 , and said first and second ends  45  and  46 . According to the illustrated embodiment, the opening  47  has a length that is less than the length of the elongated plate  40 , and is generally centered within the outer boundaries of the elongated plate  40 . According to the illustrated embodiments of  FIGS. 3, 4  and  5 , the opening  47  is slot-like in shape, extends longitudinally through the center-line of the elongated plate  40 , and comprises semicircular ends. In alternate embodiments, the opening  47  may have a length that extends along a greater or lesser length of the longitudinal axis X of the elongated plate  40 , and the opening  47  may be positioned parallel to the longitudinal axis X but not centered between the first and second outer edges  43  and  44 . The illustrated embodiment of the elongated plate  40  also comprises a bevel or concavity on one or both of interior edges  49  of the opening  47 . In various embodiments, this concavity on the interior edge  49  of the opening  47  may be conical, spherical, or of some other shape. According to some embodiments of the elongated plate  40 , neither of the interior edges  49  comprises a bevel or concavity.  
         [0040]     In the illustrated embodiment, the elongated plate  40  is a single piece in which the corners where the first and second outer edges  43  and  44 , and the first and second ends  46  and  47  converge, are curved. Likewise, in the illustrated embodiment, the first and second outer edges  43  and  44 , and the first and second ends  45  and  46  are rounded to form a convex domed shape around the periphery of the elongated plate  40 . As will be appreciated, alternate embodiments according to the invention may lack one or both of the curved corners and rounded peripheral edges, and may embody alternate forms. For example, according to some alternate embodiments, the corners of the elongated plate  40  may be squared. In yet other embodiments, the peripheral edges of the elongated plate  40  are substantially flat, or are concave and comprise a groove along all or a portion of one or more of the first and second outer edges  43  and  44 , and the first and second ends  45  and  46  of the elongated plate  40 . In yet other alternate embodiments, the elongated plate  40  may comprise more than a single piece; for example, the plate may comprise two or more rod-like members (not shown) that can be engaged with one another at one or both ends of each rod to form a plate that has first and second outer edges  43  and  44 , first and second ends  45  and  46  that may be opened or closed, wherein the outer edges and ends bound an opening between the two rod-like members that is parallel to the rods. According to such embodiments, the inner and outer edges of the rod-like members comprise one or more individual or combinations of features described herein in connection with the elongated plate  40  embodiments illustrated in  FIG. 3 ,  FIG. 4  and  FIG. 5 .  
         [0041]     In some embodiments, the elongated plate  40 , as illustrated in  FIG. 3 , comprises on at least a portion of at least one of its upper and lower surfaces  41  and  42  an optional locking enhancement means  48 , which is shown as a granular or rough surface texture. It will be appreciated that the locking enhancement means  48  is intended to provide additional friction between one or more of the upper and lower surfaces  41  and  42  of the elongated plate  40 , and objects that come into contact with such upper and lower surfaces  41  and  42 , such as the locking sleeve  60 , described herein, as well as bone and other structures in a patient into whom the bone fixation apparatus  10  of the invention is introduced. The locking enhancement means  48  may take alternative forms, such as cuts or grooves arranged in patterns such as in parallel or cross hatches, bumps, ridges, or any of a number of other textural features, on all or a portion of one or both of the upper and lower surfaces  41  and  42  of the elongated plate  40 . The locking enhancement means  48  may be integral with the surface of the elongated plate  40 , or may comprise material that is applied to the surface of the elongated plate  40  by spray or other application means. In some embodiments, the elongated plate  40  lacks locking enhancement means  48 .  
         [0042]     Referring to  FIG. 4  and  FIG. 5 , the illustrated embodiments of the elongated plate  40  comprise a through-hole  50  having an axis BB at one of the first and second ends  45 ,  46  of the elongated plate  40 . The embodiment illustrated in  FIG. 4  comprises within the inner perimeter of the through-hole  50  on the upper surface  41  of the elongated plate  40  a bevel or concavity  52 , which may be conical, spherical or have some other shape. According to some embodiments of the elongated plate  40 , as described more fully herein, the concave inner perimeter  52  on at least one of the upper and lower surfaces  41  and  42  of the through-hole  50  of the elongated plate  40  has a substantially spherical shape that is particularly adapted for engagement with the convex upper surface  24  of the central portion  22  of an embodiment of the bone bolt  20  according to the invention. The concave inner perimeter  52  of the through-hole  50 , and more particularly a spherical concave inner perimeter  52 , is adapted for permitting engagement of the bone bolt  20  within the through-hole  50  at one of a wide range of positions, wherein the axis of the bone bolt  20  may be aligned in parallel with the axis BB of the through-hole, or may be oriented so as to transect the axis BB of the through-hole, depending on the angle at which the bone bolt  20  is inserted into the through-hole  50  and engages at its spherical convex upper surface  24  with the concave inner perimeter  52  of the through-hole  50 .  
         [0043]     The embodiment illustrated in  FIG. 5  comprises at the outer perimeter of the through-hole  50  on the upper surface  41  of the elongated plate  40  a substantially spherical convex outer perimeter  51 . According to other embodiments of the elongated plate  40  illustrated in  FIG. 5 , the elongated plate  40  further comprises a concave inner perimeter  52  on the lower surface  42  of the through-hole  50 . In one such embodiment, the concave inner perimeter  52  has a substantially spherical shape that is particularly adapted for engagement with the convex upper surface  24  of the central portion  22  of an embodiment of the bone bolt  20  according to the invention.  
         [0044]     Turning now to a third component of the bone fixation apparatus  10 ,  FIGS. 6A  through D show various embodiments of a locking sleeve  60  according to the invention. Referring to  FIG. 6A , the locking sleeve  60  comprises an upper wall  61  and a lower wall  64 , each of which comprise an exterior surface  62  and  65 , and an interior surface  63  and  66 . The locking sleeve  60  also comprises first and second sidewalls  67  and  68 , and first and second opened ends  69  and  70  that provide an aperture  71  having a central axis Z through the locking sleeve  60 . As depicted in  FIGS. 6A  through D, the locking sleeve  60  has a generally rectangular shape, with a first width defined as the distance between the first and second sidewalls  67  and  68 , and a second width defined as the distance between the first and second opened ends  69  and  70 . According to the embodiment illustrated in  FIGS. 6A  through D, the first width is greater than the second width. It will be appreciated that in alternate embodiments, the locking sleeve  60  may have a substantially square shape, such that the first and second widths are essentially equal. In yet other embodiments, the dimensions of the first and second widths may further vary to provide a rectangular device wherein the second width is greater than the first width. As can be seen in  FIG. 6A , the upper and lower walls  61 ,  62  and the sidewalls  67 ,  68  have an essentially uniform thickness, and each of the sidewalls  67  and  68  intersects with the adjacent portions of the upper and lower walls  61  and  62  to form rounded corner edges. In alternate embodiments, the corner edges may be more or less rounded, or may form a right angle. Likewise, the thickness of each of the walls of the locking sleeve  60  may vary from one another.  
         [0045]     Referring to  FIG. 6B , the illustrated locking sleeve  60  comprises a through-hole  72  in its upper wall  62  comprising a substantially convex outer perimeter  73  and a conical concave interior perimeter  74 , wherein the diameter of the through-hole  72  on the exterior surface  62  of the upper wall  61  is greater than the diameter on the interior surface  63  of the upper wall  61 . In alternate embodiments, the interior perimeter  74  of the upper wall through-hole  72  is cylindrical, having substantially straight walls, such that the diameter of the through-hole  72  on the exterior surface  62  of the upper wall  61  is approximately equal to the diameter on the interior surface of the upper wall  61 . Generally, the upper wall through-hole  72  has a maximum diameter on the exterior face  62 , and a minimum diameter on the interior face  63 , wherein the diameter of the interior face  63  does not exceed the diameter on the exterior face  62 .  
         [0046]     Referring to  FIG. 6C , the illustrated locking sleeve  60  comprises a through-hole  76  in its lower wall  65  having a substantially spherical concave interior perimeter  77 , wherein the diameter of the through-hole  76  on the exterior surface  65  of the lower wall  64  is greater than the diameter on the interior surface  66  of the lower wall  64 . Generally, according to the embodiments of the locking sleeve  60  as illustrated in  FIGS. 6   a -D, the lower wall through-hole  76  has a maximum diameter on the exterior surface  65 , and a minimum diameter on the interior face  66 , wherein the diameter of the lower wall through-hole  76  on the interior surface  66  is always less than the diameter on the exterior surface  65 . As previously described in connection with an embodiment of an elongated plate  40  comprising a through-hole  50 , the spherical concave inner perimeter  77  of the through-hole  76  is adapted for permitting engagement of the bone bolt  20  within the through-hole  76  at one of a wide range of positions, wherein the axis AA′ of the bone bolt  20  may be aligned in parallel with the axis Y of the through-hole  76 , or may be oriented so as to transect the axis Y of the through-hole  76 , depending on the angle at which the bone bolt  20  is inserted into the through-hole  76  and engages at its spherical convex upper surface  24  with the concave inner perimeter  77  of the through-hole  76 .  
         [0047]      FIG. 7  shows an illustration of one alternate embodiment of a locking sleeve  60 , wherein the lower wall through-hole  76  comprises a substantially convex outer perimeter  75  and a conical concave interior perimeter  78 , wherein the exterior diameter of the through-hole  76  on the exterior surface  65  of the lower wall  64  is greater than the diameter on the interior surface  66  of the lower wall  64 . In alternate embodiments, the interior perimeter  77  of the lower wall through-hole  76  is cylindrical, having substantially straight walls, such that the diameter of the through-hole  76  on the exterior surface  65  of the lower wall  64  is approximately equal to the diameter on the interior surface  66  of the lower wall  64 . Generally, according to the embodiments as illustrated in  FIG. 7 , the lower wall through-hole  76  has a maximum diameter on the exterior surface  65 , and a minimum diameter on the interior surface  66 , wherein the diameter of the interior surface  66  does not exceed the diameter on the exterior surface  65 .  
         [0048]     The upper and lower wall through-holes  72  and  76  are generally spherical according to various embodiments of the invention, and share a common central axis Y. In various embodiments of the locking sleeve  60 , one or both of the minimum and maximum diameters the upper and lower wall through-holes  72  and  76  are approximately equal. In yet another embodiment, the upper wall through-hole  72  is elliptical in shape, as illustrated in  FIG. 6D , wherein the long axis of the elliptical through-hole  72  is aligned with the axis Z of the aperture  71 . According to the embodiments shown in FIGS.  6 A-D, the through holes are generally centered between the first and second sidewalls  67  and  68 , and the first and second opened ends  69  and  70 . In alternate embodiments, the through-holes are not centered on the upper and lower surfaces  62  and  65  of the locking sleeve  60 .  
         [0049]     Turning now to a fourth component of the bone fixation apparatus  10 , FIGS.  8 A-C show compression washers  80  according to the invention.  FIG. 8A  shows a compression washer having a substantially disc-like shape comprising a flat upper surface  81  and comprising on its lower surface  82  a substantially spherical concavity, and having a central hole  83  with a central axis AA for receiving therethrough a first end portion  21  of a bone bolt  20  according to one or more of the embodiments described herein. The lower surface concavity  82  of the compression washer  80  is configured to contact and engage with one or more of the substantially spherical convex outer perimeters on one of the embodiments of the locking sleeve  60  and elongated plate  40 . In some embodiments, the compression washer  80  has a central hole  83  having a diameter sufficient to receive therethrough the first end portion  21  of a bone bolt  20 . In yet other embodiments, the compression washer  80  has a central hole  83  having a different diameter, for example, a diameter sufficient to receive therethrough the second end portion  25  of a bone bolt  20 .  FIG. 8B  shows one alternate embodiment of a compression washer  80  comprising a nut portion  84  that comprises a threaded interior  85 . A cross sectional view of the compression washer of  FIG. 8B  is shown in  FIG. 8C . The nut portion  84  is configured to receive the first end portion  21  of a bone bolt  20  and reversibly engage with the same by cooperation between the threaded interior  85  of the nut portion  84  of the compression washer  80  and threads on the first end portion  21  of the bone bolt  20 .  
         [0050]     Turning now to description of the use of the components of the bone fixation apparatus  10 ,  FIGS. 10A and 11A  illustrate various components of the system engaged for use according to the instant invention. Referring to  FIG. 10A , one of the first and second ends  45  and  46  of the elongated plate  40  is passed through the aperture  71  in a locking sleeve  60  such that the central axis Y of the locking sleeve  60  through-holes  72  and  76  is aligned with the center of the opening  47  in the elongated plate  40 . Once the elongated plate  40  and the locking sleeve  60  are engaged, the first end portion  21  of a bone bolt  20  comprising a convex spherical upper surface  24  on its central portion  22  can be passed through the aligned through-holes  72  and  76  and opening  47 .  
         [0051]     Prior to locking of the fixation apparatus  10 , the position of the bone bolt  20  and locking sleeve  60  can be slidably adjusted along the length of the elongated plate  40  to occupy any position between the ends of the opening  47 . Likewise, the position of the bone bolt  20  can be adjusted such that the bone bolt  20  axis AA′ can be aligned with the locking sleeve through-hole axis Y, or the bone bolt  20  can be rotated at its engagement locus between the convex spherical upper surface  24  on its central portion  22  and the spherical concavity within the lower wall  64  through-hole  76  to assume a position wherein the bone bolt  20  axis AA′ transects the locking sleeve through-hole axis Y. According to the various embodiments of the bone fixation apparatus  10 , the range of degrees of angulation (i.e., the angle, in degrees, between the axes Y and AA) is from 0.2, 0.4, 0.6, 0.8, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 or more. In some embodiments wherein the locking sleeve  60  comprises an elliptical upper though-hole  72  (as described and illustrated in connection with  FIG. 6D ), the range of degrees of angulation may be greater than with a locking sleeve  60  that comprises a circular upper though-hole  72 . According to the embodiment of the fixation device shown in  FIG. 10A , good results have been obtained wherein the range of angulation between the axes Y and AA is 10°.  
         [0052]     Once the desired position of the locking sleeve  60  and bone bolt  20  combination has been selected on the elongated plate  40 , and the position of the bone bolt  20  relative to the through-hole axis Y has been achieved, the device is reading for locking, as shown in  FIG. 10 B . Using appropriate tools known in the art for manipulation and installation of bone bolts and related parts, a compression washer  80  having a threaded nut portion  82  is engaged with the first end portion  21  of the bone bolt  20  by cooperation between the nut threads  85  and the bone bolt  20  threads  28 . The fixation apparatus  10  is locked when the concave spherical lower surface  82  of the compression washer  80  engages with the spherical convex outer perimeter  73  of the upper wall through-hole  72 . The interaction between these two surfaces, in cooperation with the interaction between the convex spherical upper surface  24  on the central portion  22  of the bone bolt  20  and the spherical concavity  77  within the lower wall through-hole  76 , allow for a high-degree of rotational freedom of the bone bolt  20  within the aligned elongated plate  40  and locking sleeve  60 .  
         [0053]     When the components are engaged, the concave spherical lower surface  82  of the compression washer  80  interfits with the spherical convex outer perimeter  73  of the upper wall through-hole  72  and delivers a compressive force to the upper surface  62  of the locking sleeve  60  to achieve locking. When the fixation apparatus  10  is locked, the upper surface  62  of the locking sleeve  60  can be observed to bow along the aperture  71  axis Z such that the locking sleeve  60  assumes a figure-8-like, or generally lemniscate shape. In some embodiments, the assembly of a bone fixation apparatus  10  as described above will involve the use of an elongated plate  40  that has a through-hole as described in connection with one of  FIG. 4  or  FIG. 5 .  
         [0054]     As previously described herein, in some embodiments according to the invention the interior perimeter of the upper wall though-hole  74  has a concave shape that such as would be defined by an inverted cone. This concavity aids in providing maximal rotational freedom of the bone bolt  20  relative to the upper wall through-hole  72 . In alternate embodiments, the interior perimeter of the upper wall though-hole  74  is not concave, and has a straight shape such as would be defined by cylinder, with walls that are parallel to the through-hole axis Y.  
         [0055]     In yet another alternate embodiment, a bone fixation apparatus  10  is shown in  FIG. 11 A , wherein an elongated plate  40  and a locking sleeve  60  are engaged. A bone bolt  20  comprising a flat upper surface  24  on its central portion  22 , is first passed through the central hole  83  in a compression washer  80 , oriented with its lower surface concavity  82  facing upwards; thereafter, the bone bolt  20  can be passed through the aligned through-holes  72  and  76  and opening  47  of the elongated plate and locking sleeve combination. The apparatus is further combined as described above in connection with the embodiments illustrated in  FIG. 10A and 10B  wherein the desired position of the locking sleeve  60  along the elongated plate  40  is chosen, and the axial orientation of the bone bolt  20  is selected, the opposing upper compression washer  80  is engaged with the first end portion  21  of the bone bolt  20 , and the components are locked. In this configuration, tightening of the nut portion  84  of the upper compression washer  80  is expected to result in the application of opposing forces on each of the upper and lower surfaces  62  and  65  of the locking sleeve  60 , such that both the upper and lower surfaces  62  and  65  of the locking sleeve  60  can be observed to bow along the aperture axis Z such that the locking sleeve  60  assumes a figure-8-like, or generally lemniscate shape.  
         [0056]     When the fixation apparatus  10  is used in a patient, as depicted in  FIG. 12 , the components according to the various embodiments of the invention are installed into a patient, wherein at least two bone bolts  20  are used. In use, the bone bolts  20  are first threaded into appropriate structures of selected bones, usually spinal vertebra, which are usually adjacent. A key advantage to the apparatuses of the present invention is that each bone bolt can be installed in an optimal position to best ensure stability. Once installed, an appropriate length elongated plate  40  is selected, and a number of locking sleeves equal to the number of bone bolts is selected. The appropriate number of locking sleeves are engaged in series on the elongated plate, either at the same time or one at a time, the combination of plate and one or more locking sleeves is aligned with a first installed bone bolt, a locking sleeve being placed over said bone bolt, and positioning of the sleeve and bone bolt determined. The process is repeated for each bone bolt, followed by engagement with compression washers and locking.  
         [0057]     In alternate embodiments, a locking sleeve having a hole at one end, as described herein, is used for attachment to one of the installed bone bolts. In yet other embodiments, bone fixation apparatuses according to the embodiment described in connection with FIG.  11 A and  FIG. 11B  may be employed, wherein a different embodiment of bone bolt  20  is used with an additional compression washer.  
         [0058]     The embodiments described above are examples of preferred embodiments and are not intended to limit the scope of the claims set forth below. Variations to the inventions described herein, including alternate embodiments not specifically described, are quiet possible and are encompassed by the claims as understood by one of ordinary skill in the art. Indeed, the claimed inventions have their broad and ordinary meaning as set forth below in the claims.