Patent Document

TECHNICAL FIELD OF THE INVENTION  
       [0001]     This invention relates in general to medical devices and, more particularly, to a bone anchor system.  
       BACKGROUND OF THE INVENTION  
       [0002]     In various surgical procedures, it is necessary to implant an anchor device in a bone for the installation and use of medical components. For example, an anchor device may be inserted into a bone to aid in the use of fiducial marker components, such as navigation landmarks in frameless stereotactic neurosurgical procedures. Such procedures may include tumor resections, deep brain stimulations, neuro-endoscopy and other deep brain access procedures. Some fiducial marker components may be screwed into the anchor device. In some cases, a separate device may be needed to hold the medical components in place. Moreover, when the anchor device is fully inserted into a bone using an installation tool, part of the device may extend beyond the surface of the bone.  
       SUMMARY OF THE INVENTION  
       [0003]     The present invention provides a bone anchor system that substantially eliminates or reduces at least some of the disadvantages and problems associated with previous medical devices.  
         [0004]     In accordance with a particular embodiment of the present invention, a bone anchor includes a screw portion configured to penetrate a bone. The screw portion includes a retention thread extending at least part of a length of the screw portion and a tip at a first end of the screw portion. The bone anchor includes a protrusion adjacent a second end of the screw portion. The second end is opposite the first end of the screw portion. The protrusion comprises a plurality of external sides forming a shape and a rounded interior surface enclosing a protrusion recess. The rounded interior surface includes a recess thread configured to retain a component at least partially in the protrusion recess. The protrusion has a maximum width that is less than a maximum diameter of the screw portion such that a shoulder is formed where the protrusion meets the second end of the screw portion.  
         [0005]     The screw portion may comprise a conical shape and at least one cutting flute extending at least part of the length of the screw portion through the retention thread. The shape may comprise a hexagonal shape, a cruciform shape or an approximate D-shape. The bone anchor may comprise a length of approximately 0.20 inch. The component may comprise a fiducial marker component.  
         [0006]     In accordance with another embodiment, a system for inserting a bone anchor into a bone includes a bone anchor comprising a screw portion configured to penetrate a bone. The screw portion comprises a retention thread extending at least part of a length of the screw portion and a tip at a first end of the screw portion. The bone anchor comprises a protrusion adjacent a second end of the screw portion. The second end is opposite the first end of the screw portion. The protrusion comprises a plurality of external sides forming a shape and a rounded interior surface enclosing a protrusion recess. The rounded interior surface includes a recess thread configured to retain a component at least partially in the protrusion recess when inserted into the bone. The protrusion has a maximum width that is less than a maximum diameter of the screw portion such that a shoulder is formed where the protrusion meets the second end of the screw portion. The system also includes a driver comprising a tip portion having a first diameter. The tip portion comprises a driver edge, an external surface and a plurality of internal surfaces enclosing a driver recess. The plurality of internal surfaces form the shape. The driver also comprises a second portion adjacent the tip portion and having a second diameter that is greater than the first diameter such that a rim is formed where the tip portion meets the second portion. The tip portion positions around the protrusion when the driver is used to insert the bone anchor into the bone. The driver edge contacts the shoulder during insertion. A distance between the driver edge and the rim of the driver is approximately equal to a distance between the shoulder and an end of the protrusion of the bone anchor such that when the rim contacts a surface of the bone during insertion the end of the protrusion will be approximately level with the surface of the bone.  
         [0007]     Technical advantages of particular embodiments of the present invention include a self-drilling, self-tapping bone anchor with a threaded protrusion recess to allow various surgical components to be secured within the anchor. The components may include fiducial marker components. Thus, the need for additional devices to hold the surgical components in place during operation is reduced.  
         [0008]     Another technical advantage of particular embodiments of the present invention includes a bone anchor insertion system with a driver that is configured to insert the anchor into a bone. The driver and the bone anchor may be frictionally coupled together. The driver and bone anchor may be configured such that after the bone anchor is fully inserted into the bone using the driver and the driver is uncoupled from the anchor, the anchor is flush-mounted within the bone. Accordingly, no part of the bone anchor extends beyond the bone&#39;s surface when the anchor is fully installed.  
         [0009]     Other technical advantages will be readily apparent to one skilled in the art from the following figures, descriptions and claims. Moreover, while specific advantages have been enumerated above, various embodiments may include all, some or none of the enumerated advantages.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     For a more complete understanding of particular embodiments of the invention and their advantages, reference is now made to the following descriptions, taken in conjunction with the accompanying drawings, in which:  
         [0011]      FIG. 1  illustrates a cross-sectional view of a bone anchor, in accordance with a particular embodiment of the present invention;  
         [0012]      FIG. 2  is a side view of the bone anchor of  FIG. 1 , taken along line  2 - 2  of  FIG. 1 ;  
         [0013]      FIG. 3  illustrates a driver used to insert the bone anchor of  FIGS. 1 and 2  into a bone, in accordance with a particular embodiment of the present invention;  
         [0014]      FIG. 4  is a side view of the driver of  FIG. 3  taken along line  4 - 4  of  FIG. 3 ;  
         [0015]      FIG. 5  is a side view of a bone anchor having a protrusion with a square configuration, in accordance with another embodiment of the present invention;  
         [0016]      FIG. 6  is a side view of a bone anchor having a protrusion with a triangular configuration, in accordance with another embodiment of the present invention;  
         [0017]      FIG. 7  is a side view of a bone anchor having a protrusion with an approximate D-shaped configuration, in accordance with another embodiment of the present invention; and  
         [0018]      FIG. 8  is a side view of a bone anchor having a protrusion with a cruciform configuration, in accordance with another embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]      FIG. 1  illustrates a bone anchor  10 , in accordance with a particular embodiment of the present invention. Bone anchor  10  is used to anchor, in a skull or other type of bone, accessories used in medical procedures involving the bone. In particular embodiments, bone anchor  10  may anchor accessories designed to establish fiducial markers, such as navigation landmarks in frameless stereotactic neurosurgical procedures. Such procedures may include tumor resections, deep brain stimulations, neuro-endoscopy and other deep brain access procedures. The accessories may be positioned in a recess partially enclosed by bone anchor  10  when anchor  10  is anchored in the bone. Bone anchor  10  includes an internal thread for securing accessories or other components within a recess of the anchor after insertion. Moreover, when inserted in a bone using a driver as discussed herein, bone anchor  10  may be flush-mounted in the bone such that its outermost end is approximately level with the bone&#39;s surface.  
         [0020]     In the illustrated embodiment, bone anchor  10  includes a self-drilling, self-tapping screw region  12  and a head region  14 . Because screw region  12  is self-drilling and self-tapping, it may be installed without the need to pre-drill an aperture to receive it and without the need to pre-tap threads in a hole formed in the bone. These characteristics also provide increased surface contact between the bone and screw region retention thread thus improving the holding power of the screw region. Bone anchors that require pre-drilling and/or pre-tapping may be used within the teachings of the present invention.  
         [0021]     In this embodiment, screw region  12  includes a conically-shaped portion with a tip  22  at one of its ends for penetrating the skull to initiate drilling. Other embodiments may include a screw region having other configurations, such as a cylindrically-shaped portion adjacent a conically-shaped portion with a tip. Screw region  12  includes a retention thread  18  that extends substantially through its length. One end of retention thread  18  is very near tip  22  thus aiding in the self-tapping characteristics of screw region  12 . Particular embodiments may include more than one retention thread. In some embodiments, retention thread  18  may have a lead angle β between approximately 48° and 52° (for example 50°) and a trailing angle γ between approximately 78° and 82° (for example 80°), each such angle as measured from a center line of bone anchor  10 . In some embodiments, both the lead and trail angles and the pitch of retention thread  18  may change across the length of screw region  12 .  
         [0022]     Bone anchor  10  has an included angle α proximate tip  22 . As illustrated, included angle α is defined by the angle between two imaginary lines  17   a  and  17   b  that each connect tangent points of an inside radii of retention thread  18 . In this embodiment, included angle α is approximately 46°. In particular embodiments this included angle α may vary from approximately 46° to 49° to provide a desirable combination of both penetrability and strength.  
         [0023]     Screw region  12  includes a cutting flute  20  extending over at least some portion of the length of screw region  12 . Cutting flute  20  is a cutting surface which will engage the bone as the screw region is rotated in a clockwise direction into the bone. In this embodiment, cutting flute  20  extends through screw region  12  to tip  22 . Cutting flute  20  cuts and removes bone fragments from the skull or other bone in which bone anchor  10  is being inserted in order to permit threads to be formed therein. Thus, cutting flute  20  provides self-tapping characteristics to screw region  12 . Cutting flute  20  may be formed by plunging a mill (not illustrated) proximate tip  22  and removing material towards a center line of screw region  12 . The configuration of screw region  12  proximate tip  22 , including included angle α and retention thread  18  extending to tip  22 , and the position of cutting flute  20  result in minimal amount of bone material being removed prior to thread engagement. This helps to maximize the amount of bone in contact with bone anchor  10  during insertion and when anchored. Particular embodiments may include more than one cutting flute. For example, some embodiments may include two cutting flutes 180° apart.  
         [0024]     The overall length of bone anchor  10  may be different in various embodiments; however, in particular embodiments such overall length may be approximately 0.12 to 0.24 inch, for example 0.20 inch. Bone anchor  10  may be composed of any suitable medical grade, biocompatible material. Examples of such material may include titanium, a titanium alloy, cobalt chrome, a high strength resinous polymer, implantable grade stainless steel, bioresorbable polymer or other material. This choice of material helps to provide the strength required to withstand the drive torque bone anchor  10  will experience during insertion into the bone.  
         [0025]     Head region  14  is proximate an end of screw region  12  opposite from tip  22 . Head region  14  includes a protrusion  24  having a recess  26  extending therethrough and into screw region  12 . In this embodiment, protrusion  24  has a hexagonal configuration as evident with respect to  FIG. 2  discussed below; however, head regions of bone anchors in accordance with other embodiments may include a protrusion having other configurations. The hexagonal configuration of protrusion  24  helps to maximize the torque that can be delivered to bone anchor  10  during insertion. Top edge  28  of protrusion  24  may have a rounded configuration for less obtrusiveness.  
         [0026]     Protrusion  24  includes rounded interior surface  30  surrounding recess  26 . A chamfered interior surface  29  may exist at the entrance to recess  26 . Interior surface  30  is threaded with thread  31  for receiving accessories or other components when bone anchor  10  is installed in a skull. Such accessories may include a fiducial marker component. Thread  31  of interior surface  30  may extend partially or substantially through the length of interior surface  30 . Other embodiments may include more than one thread  31 . Since a maximum width W of protrusion  24  is less than the diameter of the end of screw region  12  from which protrusion  24  extends, then a shoulder  32 , having a diameter M, is formed at such end. In particular embodiments, width W may be approximately 0.077 inch.  
         [0027]      FIG. 2  is a side view of bone anchor  10  of  FIG. 1  taken along line  2 - 2  of  FIG. 1 . As discussed above, protrusion  24  has a hexagonal configuration.  
         [0028]      FIGS. 3 and 4  illustrate a driver  40 , used to insert bone anchor  10  into a bone, in accordance with a particular embodiment of the present invention.  FIG. 4  is a cross-sectional view of driver  40  of  FIG. 3  taken along line  4 - 4  of  FIG. 3 . Driver  40  includes a tip portion  42  at its end that contacts the bone anchor during insertion. Tip portion  42  includes an edge  45  at such end of driver  40 . Tip portion  42  includes inside edges  44  which, in this embodiment, form a hex socket as illustrated in  FIG. 4  to provide a close fit with a bone anchor having a protrusion with a similar hexagonal configuration (such as bone anchor  10  of  FIGS. 1 and 2 ) for maximization of torque delivered to the anchor. Drivers of other embodiments may include a tip portion with inside edges forming a different configuration that may match a similar configuration of a bone anchor protrusion. Tip portion  42  has a diameter d slightly smaller than a diameter D of the portion of driver  40  adjacent tip portion  42 . Such change in diameter forms a rim  48  encircling driver  40 .  
         [0029]     Disposed within driver  40  proximate end  45  is an insert  49  comprising a rubber-like material. In particular embodiments, insert  49  may comprise silicon. When inserting bone anchor  10  into a skull or other bone using driver  40 , bone anchor  10  is positioned such that its protrusion  24  is inside gap  50  formed between inside edges  44  and insert  49 . Insert  49  is positioned at least partially within recess  26  of anchor  10 . The rubber-like material of insert  49  helps to form a friction fit with thread  31  of interior surface  30  so that anchor  10  does not easily separate from driver  40  during insertion into a bone.  
         [0030]     During insertion of the bone anchor, edge  45  of tip portion  42  contacts shoulder  32  of bone anchor  10 . Diameter d of tip portion  42  is approximately equal to diameter M of bone anchor  10  at shoulder  32 . Thus, when bone anchor  10  is inserted in a bone using driver  40 , tip portion  42  of driver  40  enters the hole in the bone formed by screw region  12  until rim  48  (having a larger diameter D than diameter d of tip portion  42 ) contacts the surface of the bone. Driver  40  is then withdrawn from the bone as retention thread  18  secures bone anchor  10  in place within the bone. Thus, top edge  28  of protrusion  24  of bone anchor  10  is approximately level with the surface of the bone such that bone anchor  10  is flush mounted within the bone.  
         [0031]     The length of protrusion  24  from its edge  28  to shoulder  32  may be different in various embodiments; however, in particular embodiments such length may be approximately 0.05 inches. In some embodiments, such length of protrusion  24  may be altered relative to the length of tip portion  42  of driver  40  such that bone anchor  10  may not be flush mounted within the skull when inserted. For example, if the length of protrusion  24  was greater than the length of tip portion  42  then protrusion  24  would extend partially out of the skull when inserted using the driver, because rim  48  would contact the surface of the skull before top edge  28  of protrusion  24  had reached the level of the skull surface. Likewise, if protrusion  24  had a length less than the length of tip portion  42  then when completely inserted using driver  40 , bone anchor  10  would rest entirely below the surface of the skull.  
         [0032]     One or more detents  54  provide a manner to engage the rounded surfaces of handle portion  43  and to provide torque during use of driver  40 . In particular embodiments, a grip handle may be cast over handle portion  43  for insertion of the bone anchor. The grip handle may include a plurality of grooves longitudinally disposed on the exterior of the handle to provide a surface for a surgeon to grip. Other gripping features may also be used in lieu of or in addition to the longitudinal grooves. For example, knurled surfaces and/or other indentations may be provided. Moreover, driver  40  may be configured to cooperate with a power instrument to rotate the driver for insertion of the bone anchor. Such a power instrument may include a torque limiting device. Furthermore, a grip portion of the driver may be constructed of a number of surgical grade materials, such as metal, plastic, alloys or a combination thereof.  
         [0033]      FIGS. 5-8  illustrate cross-sections of bone anchors, in accordance with other embodiments of the present invention. In  FIG. 5 , a protrusion  82  of a bone anchor  80  has a square configuration. In  FIG. 6 , a protrusion  88  of a bone anchor  86  has a triangular configuration. In  FIG. 7 , a protrusion  92  of a bone anchor  90  has an approximate D-shaped configuration. In  FIG. 8 , a protrusion  98  of a bone anchor  96  has a cruciform configuration. As indicated above, protrusions of bone anchors in other embodiments may include other configurations or shapes. As is the case with driver  40  and bone anchor  10  discussed above, drivers used to insert such bone anchors may include inside edges at their tip regions that form configurations that match the configurations of the particular bone anchors being inserted by the drivers.  
         [0034]     Although the present invention has been described in detail, various changes and modifications may be suggested to one skilled in the art. It is intended that the present invention encompass such changes and modifications as falling within the scope of the appended claims.

Technology Category: 1