Patent Publication Number: US-2013231708-A1

Title: Bone Screw

Description:
TECHNICAL FIELD 
     The present invention relates generally to bone screws, and more particularly to a bone screw that does not require preparation of a bone or bone segment prior to insertion into the bone. 
     BACKGROUND 
     Bone screws have been used in spinal instrumentation since at least as early as the 1960s. A bone screw is a screw that is usually made of titanium and perhaps finished with inert titanium nitride (gold colored finish). If a bone screw is used in a pedicle of the spine, then it is called a pedicle screw. Pedicle screws are most often used as part of a system of screws, plates and rods that immobilize part of the spine. During anterior fixation or plating of cervical vertebral bodies, the spine is approached from an anterior or anterlo-lateral direction and bone screws are typically used to solidly mount a spinal plate to the affected vertebrae. This helps spinal fusion wherein two or more vertebrae are encouraged to grow together after damage to the intervening disks or spinal fracture makes the original structure unstable. 
     Current pedicle screws require multiple steps in order to implant the screw in the pedicle. Typically, these steps include creating a starting hole with a very small drill bit, pedicle or bone probe, or awl. Once the starter hole is created, a bigger drill bit or pedicle probe may be used to create a pilot hole. After the pilot hole has been created, the pilot hole may then be tapped in a size compatible with the threads of the pedicle screw using a tap. Some pedicle screws are self-tapping thereby eliminating the step of tapping the pilot hole. Some bone screws, not pedicle screws, include a drill-bit feature associated with a thread and shaft. Each additional step required during a surgical procedure requiring the use of bone screws creates a greater potential for the patient to experience complications from the procedure as well as the chances for a physician to make a mistake due to fatigue during long constructs requiring numerous bone screws. 
     Thus, there remains a need for improved, inexpensive, and easy to use bone screws and methods for inserting bone screws in bone that minimize the need for preparatory steps prior to insertion of the bone screws into the bone. 
     SUMMARY 
     A bone screw is disclosed that is capable of directly being inserted into a bone without the requirement of separately creating a starter hole, a pilot hole and tapping the pilot hole. In one embodiment, the bone screw includes a distal tip segment, an intermediate pilot segment, an intermediate threaded segment, and a proximal head or fixation segment. The distal tip segment is used to create a starter hole in the bone. The intermediate pilot segment is used to create a pilot hole in the bone and the intermediate threaded segment is used to fixedly secure the bone screw into the bone. In alternative embodiments, the distal tip segment and the intermediate pilot segment may be combined into a pilot segment which, in essence, eliminates the starter hole segment. This embodiment may be useful for procedures in which a starter hole is not necessary, is being placed in the bone by another instrument, or where paddle probes are used as the tip segment. 
     The fixation segment is used as an anchor for a rod or the like that is utilized as part of an immobilization system for a spine. In one embodiment, the fixation segment comprises a head that has a U-shaped format. In other embodiments, the fixation segment may comprise a straight shaft that is clamped onto by other devices. It is envisioned that the bone screw disclosed herein may be used for other types of surgical procedures beyond spinal procedures such as, implant or replacement procedures for example, and as such, may include other head configurations. 
     The tip segment of the bone screw comprises a conical shaped portion that includes a cutout that forms a cutting edge in the tip segment. In another embodiment, the tip segment comprises an awl or a probe. As set forth above, the tip segment is used to create a starter or small hole in the bone prior to creation of a pilot hole. The pilot segment comprises an elongate shaft that includes a flute running up the elongate shaft. The flute may be a straight flute or a spiral flute. The elongate shaft may be tapered such that it increases in size as the pilot segment enters the bone, but in other embodiments it may not be tapered. The flute includes a cutting edge for removing bone to create the pilot hole for the bone screw. The pilot segment may be formed like a drill bit for the purposes of removing bone. 
     The threaded segment is used to fixedly secure the bone screw in place in the bone. The threaded segment includes a thread that is used to secure the bone screw in the bone. In one embodiment, the thread is formed as a self-tapping thread so that the pilot hole does not need to be tapped. In another embodiment, the threaded segment includes a self-tapping feature as well as threads. The self-tapping features taps the pilot hole prior to the threads of the threaded segment being inserted into the threads created in the bone by the self-tapping feature. The head of the bone screw may be a conventional type screw head, but in one embodiment, comprises a U-shaped head designed to receive a rod of an implant. As such, the bone screw disclosed herein is capable of providing three functions that include creating a starter hole, creating a pilot hole, and creating a threaded connection that fixedly secures the bone screw in the bone. This eliminates the need for a surgeon to perform three separate steps in order to insert a bone screw into a bone. 
     In another embodiment, a bone screw is disclosed that includes a drill bit segment located at a distal end of the bone screw. The drill bit segment is used to create a pilot hole in the bone. A threaded segment is located proximate the drill bit segment for fixedly securing the bone screw in the bone. The threaded segment may include a self-tapping feature that taps the pilot hole created by the drill bit segment prior to entry of the threads of the threaded segment. A head may be located proximate the threaded segment which may comprise a conventional head or a U-shaped head designed to receive a rod. 
     In yet another embodiment, a bone screw is disclosed that includes a probe segment located at a distal end of the bone screw. The probe segment is used to create a pilot hole in the bone. A threaded segment is located proximate the drill bit segment for fixedly securing the bone screw in the bone. The threaded segment may include a self-tapping feature that taps the pilot hole created by the drill bit segment prior to entry of the threads of the threaded segment. A head located proximate the threaded segment may comprise a conventional head or a U-shaped head designed to receive a rod. 
     Another aspect includes a method of inserting a bone screw into a bone. In this embodiment, a starter hole is formed in the bone with a tip segment of the bone screw. Once the starter hole is formed, a pilot hole is formed in the bone with a pilot segment of the bone screw. Finally, a threaded connection in the bone is formed with a threaded segment of the bone screw proximate the pilot segment such that the bone screw is fixedly secured in the bone. 
     Another method for inserting a bone screw in a bone involves the use of a drill bit segment or a probe segment. The drill bit or probe segment, depending on which embodiment is used, is used to form a pilot hole in the bone. The bone screw includes a threaded segment that is used to create a threaded connection between the bone and the bone screw once the pilot hole is formed. 
     Other systems, methods, features and advantages of the invention will be, or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the following claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like reference numerals designate corresponding parts throughout the different views. 
         FIG. 1  is a perspective view of a representative bone screw. 
         FIG. 2  illustrates the bone screw of  FIG. 1  making a starter hole in a pedicle of a spine. 
         FIG. 3  illustrates the bone screw of  FIG. 1  making a pilot hole in the pedicle. 
         FIG. 4  illustrates the bone screw of  FIG. 1  being threaded in to the pedicle. 
         FIG. 5  illustrates a bone screw having a polyaxial head assembly. 
         FIG. 6  illustrates a bone screw having a drill bit type segment. 
         FIG. 7  illustrates a bone screw having a probe segment. 
         FIG. 8  illustrates a portion of a bone screw having an awl tip and a probe portion. 
         FIG. 9  illustrates a portion of a bone screw having a square-shaped tip segment. 
         FIG. 10  illustrates a portion of a bone screw having a Lenke style tip segment. 
         FIG. 11   a  illustrates a portion of a bone screw having a curved paddle probe tip segment. 
         FIG. 11   b  is a side view of a portion of the curved paddle probe tip segment illustrated in  FIG. 11   a.    
         FIG. 12  illustrates a portion of a bone screw having another curved paddle probe tip segment. 
         FIG. 13  illustrates a portion of a bone screw having a acorn tip segment. 
         FIG. 14  illustrates a portion of a bone screw having a cup curette tip segment. 
     
    
    
     DETAILED DESCRIPTION 
     Referring collectively to  FIGS. 1-4 , a representative bone screw  10  is illustrated that extends along a longitudinal axis and includes a distal tip segment  12 , an intermediate pilot segment  14 , an intermediate threaded segment  16 , and a proximal fixation segment  18 . As used herein, distal refers to the direction toward which the bone screw  10  is advanced as the bone screw  10  is engaged to bone and proximal refers to the direction opposite the distal direction. The tip segment  12  is used to create a small starter hole  20  or to enlarge an existing starter hole  20  in a bone  22 , which in one example comprises a pedicle, in which the bone screw  10  is to be inserted. In this embodiment, the tip segment  12  includes a blunt tip  24  and a conical portion  26  that includes a cutout  28  defining a cutting edge  30  that gradually increases in size or diameter as it runs up the conical portion  26  toward the pilot segment  14 . As such, using the bone screw  10  disclosed herein eliminates the need to create a starter hole with a separate instrument and as a separate step during a surgical procedure. 
     As set forth in greater detail below, in one embodiment of the present invention, the bone screw  10  is operable to create a starter hole, to create a pilot hole, and to fixedly secure the bone screw  10  in a bone of a patient with threads. This saves the surgeon time and shortens the length of surgical procedures involving placement of multiple bone screws  10 . As a result, the patient does not have to spend as much time undergoing a surgical procedure and the stress experienced by physicians during long procedures is reduced. In other embodiments, creation of a starter hole may not be necessary and as such, only a pilot segment  14  may be included in these embodiments of the bone screw  10 . In these embodiments, the tip segment  12  and the pilot segment  14  may be viewed as one and the same. 
     The tip segment  12  transitions into a pilot segment  14  that is located proximate to the tip segment  12 . The pilot segment  12  is used to create a pilot hole  32  in the bone  22  after the starter hole  20  has been formed by the tip segment  12  or by a separate instrument. The pilot segment  12  includes an elongate cylindrical portion  34  that includes a straight flute  36  traversing upwardly a predetermined distance of the elongate cylindrical portion  34 . The straight flute  36  includes a cutting edge  38  for cutting the pilot hole  32  in the bone  22 . The cylindrical portion  34  may slightly increase in diameter or be tapered as it approaches the threaded segment  16 . As such, the pilot segment  14  is operable to form a pilot hole  32  in the bone  22 . This eliminates the need for a surgeon to utilize a second instrument to create a pilot hole  32  after the starter hole  20  has been created in the bone  22 , which eliminates a surgical step. 
     The pilot segment  14  transitions into a threaded segment  16  that is located proximate to the pilot segment  14 . The threaded segment  16  is used to fixedly secure the bone screw  10  in the bone  22 . The threaded segment  16  has a helically wound, radially outwardly extending bone implantable thread  40  axially extending from the end of the pilot segment  14  to approximately the fixation segment  18 . The threaded segment  16  may also include a self-tapping feature  42  located at the transition point between the pilot segment  14  and the threaded segment  16 . The self-tapping feature  42  cuts a thread in the inside surface of the pilot hole  32  so that the threads  40  of the threaded segment  16  engage or mate with the threads cut in the pilot hole  32 . In alternative embodiments, the threads  40  may comprise self-tapping threads  40  thereby eliminating the need for the self-tapping feature  42  to be included in the threaded segment  16 . 
     As set forth above, the threaded segment  16  transitions into a fixation segment  18  that is located proximate to the pilot segment  14 . In one embodiment, the fixation segment  18  comprises a U-shaped head that includes a pair of opposed upwardly standing arms  44  that extend upwardly from a cylindrical base  46  to a top surface  48 . The arms  44  form a U-shaped cradle  50  and define a U-shaped channel  52  between the arms  44 . The U-shaped cradle  50  has substantially the same radius of rods used in spinal procedures for operably snugly receiving the rod, such as rod  11  shown in dashed lines in  FIG. 4 . 
     Each of the arms  44  has an interior surface  54  that defines a cylindrical profile. The interior surface  54  of each of the arms  44  includes an inner threaded member  56  located distally of the top surface  48  and running about half way down the arms  44 . Although the inner threaded member  56  is illustrated as a helical thread, it is also envisioned that a buttress thread, a square thread, a reverse angle thread or other thread-like structures could be used. A locking member or set screw  58  is included for securing the rod in the U-shaped cradle  50 . The locking member  58  screws into the inner threaded member  56  to apply pressure or force to the rod  11  thereby ensuring that the rod  11  is fixed in place. 
     Although the fixation segment  18  is illustrated as a U-shaped head throughout the figures, it should be appreciated that the term fixation segment should be broadly construed to include other types of fixation mechanisms. For example, the fixation segment  18  may comprise an elongate shaft (e.g. shaft  102  of  FIG. 7 ) in some embodiments of the present invention. A clamping device of another surgical device or simply a clamping device may be used to clamp onto the elongate shaft. In other embodiments of the present invention, the bone screw  10  may take the form of a cannulated screw. 
     Referring to  FIG. 5 , in yet another embodiment, the bone screw  10  includes a polyaxial head assembly  60 . In this embodiment, a U-shaped head  62  is included whereby the threaded segment  16 , the pilot segment  14 , and the starter segment  12  are provided with free angular and pivoting movement with respect to the U-shaped head  62 . A female socket portion  64  may be formed in a spherical head  66  of the bone screw  10  for applying torque to the threaded segment  16 , the pilot segment  14 , and the starter segment  12  to position them in the bone  22 . The spherical head  66  is positioned proximate the threaded segment  16 . 
     The U-shaped head  62  is generally configured the same as in the previous embodiment of the present invention except that it includes an axial opening  68  to permit passage of a shank portion  70  of the bone screw  10  there through while maintaining the spherical head  66  therein. A compression cap  72 , which is adapted to be positioned within the U-shaped head  62 , has a generally cylindrical shape and includes a rod-receiving surface  74 . The bone screw  10  disclosed herein is provided in one embodiment with a polyaxial head assembly  60  that allows the shank portion  70  of the bone screw  10  to have free or selective angular movement with respect to the U-shaped head  62 . The polyaxial head assembly  60  set forth in  FIG. 5  should be viewed in an illustrative sense as several different types of polyaxial head assemblies exist that may be utilized in the present invention. 
     Referring to  FIG. 6 , in another embodiment, the bone screw  10  may include a starter segment  12  that transitions into a drill bit segment  80 . The drill bit segment  80  includes an elongate cylindrical portion  82  that includes a spiral flute  84  that runs in a spiral configuration up the elongate cylindrical portion  82  a predetermined distance to approximately the beginning of the threaded segment  16 . The spiral flute  84  includes a cutting edge  86  for removing bone when the bone screw  10  is installed in a bone  22 . The drill bit segment  80  is used to create a pilot hole for the threaded segment  16 . The starter segment  12  includes a conical shaped portion  88  that terminates at a sharp point  90 . Those skilled in the art should recognize that the style, shape and size of the flutes may vary in alternative embodiments of the present invention. 
     Referring to  FIG. 7 , in this embodiment, the bone screw  10  includes a pedicle probe segment  100  that transitions into the threaded segment  16 . The pedicle probe segment  100  includes an elongate shaft portion  102  and a probe portion  104 . The probe portion  104  illustrated in  FIG. 7  is a paddle probe having a tip  106  and a paddle portion  108 . The probe portion  104  may be selected from several different types of probes such as a Lenke style probe, a paddle style probe, and a curette style probe to name a few. As illustrated in  FIG. 5 , the starter segment  12  may also be shaped in the form of an awl having a sharp tip. 
     Referring to  FIG. 8 , a portion of a bone screw  10  is illustrated that includes an awl tip  110  that transitions into a probe segment  112 . The awl tip  110  is used to create a starter hole in the bone  22  and the probe segment  112  is used to create a pilot hole in the bone  22 . The awl tip  110  comprises a spike sharpened to a fine point that is capable of cutting through bone  22 . The probe segment  112  is similar to the probes described with respect to the previous embodiments of the present invention and may comprise, for example, a paddle probe. The bone screw  10  illustrated in  FIG. 8  includes a threaded segment  16  and a head  18  as set forth in  FIGS. 1-4 . 
     Referring to  FIGS. 2-4 , another aspect of the present invention relates to a method of inserting a bone screw  10  into a bone  22 . In one embodiment, the method comprises the steps of (a) forming a starter hole  20  with a tip segment  12  of the bone screw  10 ; (b) forming a pilot hole  32  with a pilot segment  14  of the bone screw  10  proximate the tip segment  12 ; and (c) forming a threaded connection  41  in the bone  22  with a threaded segment  16  of the bone screw  10  proximate the pilot segment  14  such that the bone screw  10  is fixedly secured in the bone  22 . 
     Yet another embodiment includes a method of inserting a bone screw  10  in a bone  22 , comprising the steps of (a) forming a pilot hole  32  with a drill bit segment  80  (see  FIG. 6 ) of the bone screw  10 ; and (b) forming a threaded connection  41  in the bone  22  with a threaded segment  16  of the bone screw  10  proximate the drill bit segment  80  such that the bone screw  10  is fixedly secured in the bone  22 . 
     In yet another embodiment, a third method of inserting a bone screw  10  in a bone  22  comprises the steps of (a) forming a pilot hole  32  with a probe segment  100  (see  FIG. 7 ) of the bone screw  10 ; and (b) forming a threaded connection  41  in the bone with a threaded segment  16  of the bone screw  10  proximate the probe segment  100  such that the bone screw  10  is fixedly secured in the bone  22 . The surgical methods also include engaging an implant to the bone screw  10 . In one embodiment, a spinal rod  11  is positioned in and engaged in the head  18  with a locking member, such as set screw  58 . 
     Referring to  FIG. 9 , yet another embodiment of the present invention discloses a bone screw  10  that includes a square-shaped awl tip segment  120 . The square-shaped awl tip segment  120  transitions into a drill bit segment  122 . The drill bit segment  122  transitions into a threaded segment  124  that is connected with a head segment  126 . The square-shaped awl tip segment  120  is used to create a starter hole. The drill bit segment  122  is used to create a pilot hole and includes at least one flute  128 . Although illustrated as a spiral flute, the flute  128  may also comprise a straight flute. In addition, the threaded segment  124  may also include a self-tapping feature as previously set forth. 
     Referring to  FIG. 10 , a representative Lenke style tip segment  130  is illustrated that may be utilized on the tip segment  12  of the bone screw  10 . Referring to  FIGS. 11   a  and  11   b,  a curved paddle probe  132 , also known as a “Steffe Style probe,” that may be utilized on the tip segment  12  of the bone screw is illustrated. The curved paddle probe  132  includes a curved section that is connected with the intermediate pilot segment  14 .  FIG. 12  illustrates another version of a curved paddle probe  132 . As illustrated in  FIG. 13 , an acorn style tip segment  134  may also be utilized to start the starter hole.  FIG. 14  illustrates a cup curette style tip segment  136  that includes a cup  138  located at the very end of the tip segment  12 . 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character.