Patent Publication Number: US-2009240291-A1

Title: Breached pedicle screw

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of, and priority to, U.S. Provisional Pat. Application Ser. No. 61/070,533 filed on Mar. 24, 2008, the entire contents of which are incorporated by reference herein. 
    
    
     BACKGROUND 
     The present disclosure relates generally to an apparatus for stabilizing the joints of the spine during orthopedic spine surgery and more specifically, to a multi-planar bone screw for securing a spinal rod to a vertebra. Particularly, the present disclosure relates to a bone screw apparatus having an eccentric unthreaded portion to allow the bone screw to be placed even after a pedicle has been breached. 
     The spinal column is a complex system of bones and connective tissues that provide support for the human body and protection for the spinal cord and nerves. The adult spine is comprised of twenty-four vertebral bodies, which are subdivided into three areas, including seven cervical vertebrae, twelve thoracic vertebrae and five lumbar vertebrae. Between each vertebral body is an intervertebral disc that cushions and dampens the various translational and rotational forces exerted upon the spinal column. 
     There are various disorders, diseases, and types of injury which the spinal column may experience in a lifetime. These problems may include, but are not limited to, scoliosis, kyphosis, excessive lordosis, spondylolisthesis, slipped or ruptured discs, degenerative disc disease, vertebral body fracture, and tumors. Persons suffering from any of the above conditions typically experience extreme or debilitating pain and often times diminished nerve function. 
     One of the more common solutions to any of the above-mentioned conditions involves a surgical procedure known as a spinal fusion. Spinal fusion involves fusing two or more vertebral bodies together to eliminate motion at the intervertebral disc or joint. To achieve spinal fusion, natural or artificial bone, along with a spacing device, replace part or the entire intervertebral disc to form a rigid column of bone. Mechanical hardware is connected to the adjacent vertebrae to stabilize the spine in that area while the bone grows and the fusion occurs. 
     The mechanical hardware used to immobilize the spinal column typically involves a series of bone screws and metal rods or plates. When the spine surgery is performed posteriorly, it is common practice to place pedicle bone screws into the vertebral bodies and then connect a metal rod between the screws, thus creating a rigid structure between adjacent vertebral bodies. In some cases, the use of these devices may be permanently implanted in the patient. In other cases, the devices may be implanted only as a temporary means of stabilizing or fixing the bones or bone fragments, with subsequent removal when no longer needed. It is also common that device implants that were intended to be permanent may require subsequent procedures or revisions as the dynamics of the subject&#39;s condition warrant. For these reasons, it is desirable that the implanted devices are easily implanted by the surgeon and are also configured to facilitate ease of removal, if required. 
     When using pedicle screws, the surgeon directs the screw through the pedicle into the vertebral body. Since different patients have different anatomies, there exists the potential for the pedicle to be breached. A pedicle is breached when the screw does not go directly through the pedicle channel and the screw protrudes through the bone on either the lateral or medial side. Often, if there is a lateral breach, the surgeon leaves the screw in place. If the breach occurs medially into the spinal canal, the spinal nerves can rub against the threads causing the patient pain and possibly requiring a revision surgery. Typically, when the surgeon recognizes the breach, he uses an instrument to displace the nerves to protect them from damage, removes the original screw and redirects it. Redirection removes more bone and can compromise fixation of the screw or completely damage the pedicle rendering it unusable as a point of device fixation. 
     To meet the problem of protecting the spinal nerves and preventing redirection, various types of bone fixation screws are available. One example is a device used for fixating fragments of bone together that is described in U.S. Pat. No. 5,019,079 issued to Ross. The proximal and distal portions have different thread pitches to allow for compression of the bone fragments together. Another design also used to fix bone fragments together is highlighted in U.S. Patent Application Publication No. 2005/0033300. In this design, the proximal and distal threads have the same pitch. 
     SUMMARY 
     The present disclosure is directed towards an apparatus for stabilizing the joints of the spine during orthopedic spine surgery and more specifically, to a multi-planar bone screw for securing a spinal rod to a vertebra. In particular, embodiments of the present disclosure include a bone screw having an eccentric unthreaded portion to allow the bone screw to be placed even after the pedicle has been breached. 
     A bone screw apparatus adapted to replace a breached pedicle is disclosed herein. The bone screw includes an unthreaded eccentric middle portion and has a proximal end and a distal end. In one embodiment, the bone screw apparatus includes a threaded proximal portion that extends from the proximal end to the unthreaded eccentric portion and a threaded distal portion that extends from the unthreaded eccentric portion to the distal end of the bone screw apparatus. In addition, the proximal portion and the distal portion each have a major diameter and a minor diameter. 
     According to one aspect of the disclosure, the bone screw apparatus includes a curved unthreaded eccentric portion. In this embodiment, the curvature of the unthreaded portion may not extend past the major diameter of the proximal portion and may not extend past the major diameter of the distal portion. 
     In another embodiment, the proximal portion and the distal portion may have threads with the same pitch. In addition, it is envisioned that the proximal portion may have a different diameter than the distal portion. It is contemplated that the proximal portion may have a larger diameter than the distal portion or a smaller diameter than the distal portion. 
     In another aspect of the present disclosure, the bone screw apparatus may include a polyaxial housing. According to this embodiment, the housing is located at the proximal end of the bone screw apparatus. Moreover, the bone screw apparatus may also include a proximal housing that is configured to accept a spine fixation rod. 
     According to another aspect of the disclosure, the bone screw apparatus may include a reference mark to be used in determining the orientation of the eccentric portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments of the presently disclosed breached pedicle screw are described hereinbelow with references to the drawings, wherein: 
         FIG. 1A  is a top view of a first embodiment of a breached pedicle screw; 
         FIG. 1B  is a front view of the breached pedicle screw of  FIG. 1A ; 
         FIG. 1C  is an isometric view of the breached pedicle screw of  FIG. 1A ; 
         FIG. 2A  is a side view of an additional embodiment of a breached pedicle screw with an eccentric unthreaded middle portion; 
         FIG. 2B  is a side view of a further embodiment of a breached pedicle screw with an unthreaded middle portion; 
         FIG. 2C  is a side view of another embodiment of a breached pedicle screw with an unthreaded top portion; 
         FIG. 2D  is a top view of a head of a breached pedicle screw in accordance with the present disclosure; 
         FIG. 3A  is a front view of a breached pedicle screw with a polyaxial head; 
         FIG. 3B  is an isometric view of the breached pedicle screw of  FIG. 3A ; 
         FIG. 3C  is an exploded view of the breached pedicle screw of  FIG. 3A ; 
         FIG. 4A  is a front view of a housing: 
         FIG. 4B  is a side view of the housing of  FIG. 4A ; 
         FIG. 5A  is a top view of a screw coupling; 
         FIG. 5B  is an isometric view of the screw coupling of  FIG. 5A ; 
         FIG. 5C  is a side view of the screw coupling of  FIG. 5A ; 
         FIG. 6A  is a side view of a screw insert; and 
         FIG. 6B  is an isometric view of the screw insert of  FIG. 6A . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Various embodiments of the presently disclosed bone screw apparatus will now be described in detail with reference to the drawings, wherein like reference numerals identify similar or identical elements. In the drawings and in the description that follows, the term “proximal,” will refer to the end of a device or system that is closest to the operator, while the term “distal” will refer to the end of the device or system that is farthest from the operator. In addition, the term “cephalad” is used in this application to indicate a direction toward a patient&#39;s head, whereas the term “caudad” indicates a direction toward the patient&#39;s feet. Further still, for the purposes of this application, the term “medial” indicates a direction toward the middle of the body of the patient, whilst the term “lateral” indicates a direction toward a side of the body of the patient (i.e., away from the middle of the body of the patient). The term “posterior” indicates a direction toward the patient&#39;s back, and the term “anterior” indicates a direction toward the patient&#39;s front. 
     With reference to  FIGS. 1A ,  1 B, and  1 C, a breached pedicle screw or bone screw  10  is depicted with an eccentric unthreaded middle portion  11 . The bone screw  10  further includes a proximal end and a distal end, where a distal tip  13  is located at the distal end of bone screw  10 .  FIG. 1A  depicts is a top view of the proximal end of bone screw  10 . A reference marker  15  is shown in  FIG. 1A  that can be used in determining the orientation of the eccentric unthreaded portion  11  with respect to the threaded portions of the bone screw  10 . 
     Further, as shown best in  FIGS. 1B and 1C , the bone screw  10  includes a proximal threaded portion  20  and a distal threaded portion  21 . Proximal threaded portion  20  has a specific major diameter  22  and minor diameter  23 . The distal threaded portion  21  has a specific major diameter  24  and minor diameter  25 . At the distal tip  13  of the bone screw  10 , there is a self-tapping feature  14 . It is also contemplated that the distal tip  13  of the bone screw  10  may have a self-starting feature. At the proximal end of the bone screw  10 , there is a saddle  12  which is configured and adapted for receiving a spine rod (not shown). Also at the proximal end, there is a lip  16 , a semicircular groove  19 , a keyway  18  and a lead in notch  17  which allow for the attachment of instruments used in surgery. Examples of these instruments can be found in U.S. patent application Ser. No. 12/104,653, filed on Apr. 17, 2008 and published as U.S. Patent Application Publication No. 2008/0262318. In this embodiment, the saddle  12  has a fixed orientation with respect to the threaded portions  20 ,  21  of the bone screw  10 . 
     The proximal threaded portion  20  and the distal threaded portion  21  have the same pitch, but the major diameter  22  of the proximal threaded portion  20  is larger than the major diameter  24  of the distal threaded portion  21 . The major diameter of the eccentric portion  11  is larger than the major diameter  24  of the distal threaded portion  21  but smaller than the major diameter  22  of the proximal threaded portion  20 . The reference marker  15  allows the surgeon to know where a middle unthreaded section  26  is even after the device has been inserted into bone. In particular, the reference marker  15  identifies a portion of the unthreaded section  26  that extends further from a central longitudinal axis of the bone screw  10  than the portion that is  1800  away ( FIG. 1B ). 
     With reference to  FIGS. 2A ,  2 B, and  2 C, low profile embodiments of bone screws  30 ,  40  and  50  are shown, while  FIG. 2D  shows a top view  32  of bone screws  30 ,  40 , and  50 .  FIG. 2A  depicts a curved bone screw  30  which includes a low profile head  132  that has a frusto-conical feature that allows for driving the bone screw  30  into vertebrae or other bones. Bone screw  30  further includes a middle curved unthreaded portion  131 , a proximal threaded portion  120  with a specific major diameter  122  and a minor diameter  123 , a distal threaded portion  121  with a specific major diameter  124  and a minor diameter  125 , and a distal tip  113  with self-tapping feature  114 . The curved unthreaded portion  131  has a curvature  133 . The major diameter  122  of the proximal threaded portion  120  is larger than the major diameter  124  of the distal threaded portion  121 . The curvature  133  of the middle portion  131  does not extend past the major diameter  122  of the proximal threaded portion  120 . 
       FIG. 2B  shows a bone screw  40  that includes a low profile head  232 , a middle unthreaded portion  241 , a proximal threaded portion  220  with a specific major  222  and a minor  223  diameters, a distal threaded portion  221  with a specific major diameter  224  and a minor diameter  225 , and a distal tip  213  with a self-tapping feature  214 . The low profile head  232  has a frusto-conical feature that allows for driving the screw  40  into vertebrae. The major diameter  222  and minor diameter  223  of the proximal threaded portion  220  are equal to the major diameter  224  and minor diameter  225  of the distal threaded portion  221 . The middle unthreaded portion  241  has the same diameter as the minor diameter  225  of the distal threaded portion  221 . 
       FIG. 2C  shows a bone screw  50  that includes a low profile head  332 , a proximal unthreaded portion  351  and a distal threaded portion  352 . Distal threaded portion  352  further includes distal threads with a specific major diameter  353  and a minor diameter  354 , and a distal tip  313  with a self-tapping feature  314 . The low profile head  332  has a frusto-conical feature that allows for driving bone screw  50  into vertebral bone. The proximal unthreaded portion  351  is on the same axis as the rest of the bone screw  50 . The proximal unthreaded portion  351  also has the same diameter as the minor diameter  354  of the distal threaded portion  352 . 
     With reference to  FIGS. 3A ,  3 B, and  3 C, a polyaxial embodiment of a bone screw  60  is depicted. Bone screw  60  includes a proximal threaded portion  420  with a specific major diameter  422  and a minor diameter  423 , a distal threaded portion  421  with a specific major diameter  424  and a minor diameter  425 , and a distal tip  413  with a self-tapping feature  414 . The bone screw  60  can be replaced by any of the low profile embodiments of bone screws  30 ,  40 , or  50  disclosed hereinabove. Further still, the bone screw  60  includes an unthreaded eccentric portion  411  similar to that previously discussed with respect to bone screws  10 ,  30 ,  40 , and  50 . 
     The polyaxial bone screw  60  further includes a polyaxial housing  462 , a screw-coupling  464 , and a threaded screw insert  465  with external threads  467 . The polyaxial housing  462  of bone screw  60  is depicted separate from bone screw  60  in  FIGS. 4A and 4B . As shown in  FIGS. 3A ,  3 B,  4 A, and  4 B, polyaxial housing  462  has a saddle  412  and an internal threaded portion  429  used to lock a rigid member such as a rod or plate (not shown) into the saddle  412 . Polyaxial housing  462  may also include a lip  416 , a semicircular groove  419 , a keyway  418  and a lead in notch  417  which would allow for the attachment of instruments used in surgery. Examples of these instruments can be found in U.S. patent application Ser. No. 12/104,653, filed on Apr. 17, 2008 and published as U.S. Patent Application Publication No. 2008/0262318, the entire contents of which are incorporated by reference herein. 
     The screw-coupling device  464  is depicted separate from bone screw  60  in  FIGS. 5A ,  5 B, and  5 C. As shown first in  FIG. 3C , screw-coupling device  464  has a frusto-conical distal end  466  that mates with a frusto-conical feature of the bone screw  60 . As shown in  FIGS. 5A ,  5 B, and  5 C, the screw-coupling device  464  also has a hexalobular cut out  463  that allows an instrument to drive the bone screw  60  into vertebrae. 
     The screw insert  465  is depicted separate from the bone screw  60  in  FIGS. 6A and 6B . As shown best in  FIG. 3C , screw insert  465  locks the screw-coupling device  464  into the screw head  462  by mating the internal threads  429  of the screw head  462  and the external threads  467  of the screw insert  465 . 
     In use, the bone screw  60  is inserted through the housing  462 . The inner portion of the housing  462  is configured and adapted to seat the head of the bone screw  60  while allowing the threaded portions  420 ,  421  and the unthreaded portion  411  of the bone screw  60  to extend distally beyond the housing  462 . As such, the bone screw  60  is rotatable and pivotable with respect to the housing  462 . The screw insert  465  is inserted over the threads of the bone screw  60  into the base of the housing  462  where the external threading of the screw insert  465  mates with internal thread of the housing  462 . Tightening the screw insert  465  with respect to the housing  462  secures the bone screw  60  in the housing  462  while permitting polyaxial movement of the bone screw  60  with respect to the housing  462 . The coupling  464  may be inserted into the head of the bone screw  60  where outer surfaces of the frusto-conical distal end  466  engage the surfaces of the recess in the bone screw  60 . This arrangement allows a driving tool to be used that may be off-axis from the central axis of the bone screw  60  while permitting the bone screw  60  to be driven into bone. In embodiments where the recess in the head of the bone screw  60  is not hexagonal, the coupling  464  has a complementary distal end suitable for engaging the recess. Other suitable bone screws may be used such as those disclosed in International Patent Application No. PCT/US2008/080668, filed on Oct. 22, 2008, the entire contents of which are hereby incorporated by reference. 
     During a procedure, if the pedicle is breached using a conventional bone screw, the physician removes the conventional bone screw and inserts the presently disclosed breached pedicle screw  10 . Depending on the geometry of the breach, the physician may select one of the other disclosed embodiments of the breached pedicle screw  60 . Since the outer thread diameter of the breached pedicle screw  10 ,  60  is greater than that of the conventional bone screw, the breached pedicle screw  10 ,  60  provides improved purchase when inserted into bone. The breached pedicle screw  10 ,  60  is inserted to a predetermined depth and the reference mark  15  indicates the orientation of the eccentric unthreaded portion of the respective breached pedicle screw  10 ,  60 . By using the reference mark  15  to adjust the position of the unthreaded eccentric portion, the physician orients the breached pedicle screw  10 ,  60  such that there is additional space for the nerve roots, thereby minimizing trauma to the patient. As such, the breached pedicle screw  10 ,  60  provides sufficient anchoring capabilities while still accepting a fixation device. 
     The bone screw disclosed hereinabove may be modified according to the present disclosure. For example, the bone screw may be cannulated. In addition, the bone screw may be have a number of different lengths and diameters. Moreover, the apparatus used in driving the bone screw into the vertebrae may be something other than a hex or square drive, such as Phillips or hexalobular. 
     It should be understood that the present disclosure is not limited to the precise embodiments discussed herein above, and that various other changes and modifications may be contemplated by one skilled in the art without departing from the scope or spirit of the present disclosure. For example, the bone screw described herein above may be formed from a variety of surgically acceptable materials including titanium, plastics, bio-absorbable materials, etc. Although the illustrative embodiments of the present disclosure have been described herein with reference to the accompanying drawings, the above description, disclosure, and figures should not be construed as limiting, but merely as exemplary of various embodiments.