Abstract:
A method for immobilizing a spine. The method includes the steps of implanting at least one low profile screw assembly into a first portion of the spine, implanting at least one bone screw assembly that is not a low profile screw into a second portion of the spine and connecting a rod to both the at least one low profile screw assembly to the at least one bone screw assembly which is not a low profile screw.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application is a divisional of U.S. application Ser. No. 12/470,874, filed May 22, 2009 which claims the benefit of, and priority to, U.S. Provisional Application Ser. No. 61/055,246, filed May 22, 2008, the contents of which are hereby incorporated by reference in their entirety. 
     
    
     BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present disclosure relates to orthopedic surgery. More particularly, the present disclosure relates to devices for stabilizing and fixing the bones and joints of the spine. 
         [0004]    2. Background Art 
         [0005]    The spinal column is a complex system of bones and connective tissues that provides support for the human body and protection for the spinal cord and nerves. The adult spine is comprised of 24 vertebral bodies, which are subdivided into three areas including seven (7) cervical vertebrae, twelve (12) thoracic vertebrae and five (5) lumbar vertebrae. Between each vertebral body is an intervertebral disc that cushions and dampens the various translational and rotational forces exerted on the spinal column. 
         [0006]    There are various disorders, diseases and types of injury which the spinal column may experience in a lifetime. The 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. 
         [0007]    One of the more common solutions to any of the above mentioned conditions involves a surgical procedure known as spinal fusion. A spinal fusion procedure involves fusing two or more vertebral bodies in order to eliminate motion at the intervertebral disc or joint. To achieve this, natural or artificial bone, along with a spacing device, replaces part or all of the intervertebral disc to form a rigid column of bone and mechanical hardware. In this way damaged or diseased vertebrae are connected to healthy adjacent vertebrae to stabilize the spine while the bone grows and fusion takes place. 
         [0008]    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 anteriorly, it is common practice to attach a thin metal plate directly to the vertebral bodies and secure it to each vertebral level using one or more bone screws. When the spine surgery is posteriorly performed, it is common practice to place bone screws into the vertebral bodies and then connect a metal rod between the bone screws, thereby creating a rigid structure between adjacent vertebral bodies. The remainder of this disclosure will relate to this second method of performing spinal fusion, wherein the vertebral bodies are connected using a series of bone screws connected by a metal rod. 
         [0009]    Traditional set screw assemblies include a screw that is implanted into a vertebral body and a locking nut that secures a metal rod to the screw. Traditional set screw assemblies are disclosed in U.S. Pat. Nos. 6,471,705, 6,296,642, 6,280,442, 6,074,391, 6,053,917, 5,885,286, 5,879,350, 5,797,911, 5,735,851, 5,733,286, 5,733,285, 5,716,356, 5,672,176, 5,549,608, 5,474,555, 5,466,237, and 5,207,678. 
         [0010]    Low profile screws, like those described in U.S. Patent Nos. 6,840,940, 6,827,719, 6,451,021, 5,683,392 and 7,090,674, and U.S. Patent Application Publication No. 2006/0276792 also are known. 
       SUMMARY 
       [0011]    A spinal fixation assembly includes at least one low profile bone screw assembly, a bone screw assembly, and a spinal rod. The spinal rod is operatively coupled to the bone screw assembly and the low profile bone screw assembly. Each of the disclosed bone screw assemblies are attachable to separate vertebral bodies. A rod and screw construct is formed when the spinal rod is coupled to two of the bone screw assemblies. A laminar hook may be attached to the spinal rod. A locking device may be used with one of the bone screw assemblies for securing the spinal rod with respect to the bone screw assemblies. The bone screw assemblies may be formed from titanium, titanium alloy, or another biocompatible material. The spinal rod may be formed from cobalt chrome, polyetheretherketone (“PEEK”), or another biocompatible material. 
         [0012]    A method for using the presently disclosed spinal fixation system includes attaching at least one low profile bone screw assembly to a selected region of a patient&#39;s spine and attaching at least one bone screw assembly to a different region of the patient&#39;s spine. A spinal rod is attached to the at least one low profile bone screw assembly and the at least one bone screw assembly. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0013]    The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and, together with a general description of the disclosure given above, and the detailed description of the embodiment(s) given below, serve to explain the principles of the disclosure, wherein: 
           [0014]      FIG. 1A  is a side view of a spinal fixation system according to an embodiment of the present disclosure; 
           [0015]      FIG. 1B  is a perspective view of the spinal fixation system of  FIG. 1A ; 
           [0016]      FIG. 2A  is a perspective view of the base and coupling element of the set screw assembly of  FIGS. 1A and 1B ; 
           [0017]      FIG. 2B  is an enlarged top view of the base and coupling element of  FIG. 2A ; 
           [0018]      FIG. 3A  is a perspective view of a locking insert of the set screw assembly of  FIGS. 1A and 1B ; 
           [0019]      FIG. 3B  is a side view of the locking insert of  FIG. 3A ; 
           [0020]      FIG. 4A  is a perspective view of a low profile screw assembly of  FIGS. 1A and 1B ; 
           [0021]      FIG. 4B  is an enlarged top view of the low profile screw assembly of  FIG. 4A ; 
           [0022]      FIG. 5A  is top view of a spinal fixation system of the present disclosure affixed to a vertebral column; and 
           [0023]      FIG. 5B  is a perspective side view of the spinal fixation system of  FIG. 5A . 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    While the present disclosure will be described more fully hereinafter with reference to the accompanying drawings, in which particular embodiments and methods of spinal fixation are shown, it is to be understood at the outset that persons skilled in the art may modify the embodiments herein described while achieving the functions and results of this disclosure. Accordingly, the descriptions which follow are to be understood as illustrative and exemplary of specific structures, aspects and features within the broad scope of the present disclosure and not as limiting of such broad scope. 
         [0025]    Referring initially to  FIGS. 1A and 1B , a spinal fixation system according to aspects of the present disclosure is shown generally as spinal fixation system  10 . Spinal fixation system  10  includes at least one set screw assembly  100 , a low profile screw assembly  200 , and a connector rod  50  extending therebetween. While both set screw assemblies and low profile screw assemblies are known and have been used independently of each other, applicants believe they are the first to propose use of both a low profile design (such as a taper lock screw) in combination with a non-low profile screw such as a set screw or top locking nut design in the same construct. While it is envisioned that the aspects of the present disclosure may incorporate any traditional set screw assembly and any low profile screw assembly, for convenience the following discussion will relate to a low profile taper lock screw assembly  100  and a traditional set screw assembly  200 . The aspects of the present disclosure should not be read as limited to the low profile or traditional set screw assemblies  100 ,  200  described herein. 
         [0026]    Briefly, set screw assembly  100  includes a base  110 , a coupling element  120  operably connected to base  110 , and a locking insert  130  threadingly received within coupling element  120  for selectively securing connector rod  50 . 
         [0027]    With reference now to  FIGS. 2 , base  110  of set screw assembly  100  includes threaded shaft  112  configured for insertion into bone, and a curvate head (not shown) defining a slot, opening or recess  114  for receiving a driving device. By way of example only, slot  114  may engage a screw driver or more specifically a hex screw driver (not shown). Pivotably mounted on base  110  is coupling element  120 . Coupling element  120  is a substantially tubular member with a rod receiving channel  123  formed in the top thereof. Rod receiving channel  123  includes a threading  124  for receiving locking insert  130 . Alternatively, threading  124  may be provided on the outer upper surface of coupling element  120  to engage locking nut or combined nut/screw. 
         [0028]    With reference to  FIG. 3 , locking insert  130  includes a cylindrical body having a threading  132  thereon. Threading  132  is configured to mate with threading  124  formed in coupling member  120 . In an alternative embodiment, wherein threading  124  of the coupling element  130  is provided on the exterior surface thereof, locking insert  130  is replaced by a locking nut (not shown). Locking insert  130  further may include a flat, or ridged underside  134  which is ideally suited to gripping a rod surface. The upper portion of locking insert  130  includes a recess  136  into which a screw driving tool may be inserted to drive locking insert  130  into coupling element  120 . 
         [0029]    For a more detailed description of set screw type assembly  100  and the operation thereof, please refer to commonly owned U.S. Pat. No. 5,733,286, the contents of which are hereby incorporated by reference herein in its entirety. One suitable set screw locking pedicle screw is available under the brand name DENALI® (K2M, Inc., Leesburg Va.). 
         [0030]    Referring back to  FIGS. 1A and 1B , briefly, low profile screw assembly  200  includes a base  210  and a housing  220  operably connected to base  210  for selectively receiving connector rod  50 . 
         [0031]    With reference to now to  FIGS. 4A and 4B , base  210  of low profile screw assembly  200  includes a threaded shaft  212  configured for insertion into bone and a head portion (not shown) defining a slot, opening or recess  214  for receiving a driving device. By way of example only, slot  214  may engage a screw driver or more specifically a hex screw driver (not shown). Pivotably mounted on base  210  is housing  220 . Housing  220  includes an inner and outer housing  222 ,  224  and defines a rod receiving channel  223  therethrough. Inner and outer housings  222 ,  224  are configured to move relative to one another to selectively retain connector rod  50  ( FIG. 1A ). 
         [0032]    For a more detailed description of the preferred low profile screw and the operation thereof, please refer to commonly owned U.S. Patent Application Publication No. 2007/0093817 and commonly owned U.S. patent application Ser. No. 11/493,625, the contents of which are hereby incorporated herein in their entirety. The preferred low profile screw is available under the brand name MESA® (K2M, Inc., Leesburg, Va.). However, other designs of low profile screws also are contemplated, such as the design shown and described in published U.S. Patent applications 2006/0276792 and 2007/0225711. As used herein, the term “low profile screw” contemplates any screw design which presents little or no profile above the rod. The preferred low profile spinal screw is the MESA® taper lock screw. 
         [0033]    Turning now to  FIGS. 5A and 5B , spinal fixation system  10   a  is shown securely affixed to a portion of a vertebral column “V”. Vertebral column “V” includes thoracic vertebra T 1 , T 2  and lumbar vertebrae L 1 , L 2 . Although the aspects of the present disclosure may be utilized through the vertebral column, the following discussion will relate to the use of spinal fixation system  10  on thoracic vertebrae T 1 , T 2  and lumbar vertebrae L 1 , L 2 . 
         [0034]    Initially, bases  110  of set screw assemblies  100  are positioned and implanted within lumbar vertebra L 1 , L 2  and bases  210  of low profile screw assemblies  200  are positioned and implanted within thoracic vertebra T 1 , T 2 . As discussed above, each of bases  110 ,  210  ( FIG. 1A ) include a slot  114 ,  214  ( FIGS. 2B and 4B , respectively) for engaging a driving device. Once properly positioned and implanted within vertebral column “V”, as discussed in the above referenced documents, connecting rods  50  may be inserted within rod receiving channels  123 ,  223  ( FIGS. 2A and 4A , respectively) of screw assemblies  100 ,  200 , respectively. Coupling elements  120  of set screw assemblies  100  may be adjusted as necessary to permit the insertion of connector rods  50 . Housings  220  of low profile screw assemblies  200  may also be adjusted as necessary to accommodate the receipt of connector rods  50 . Set screw assemblies  100  and low profile screw assemblies  200  may be locked, unlocked, adjusted and relocked as necessary until proper alignment of vertebral column “V” is achieved. 
         [0035]    As discussed above, low profile screw assembly  200  presents little to no profile above connector rod  50 . This low profile is most important in the area of the spine where there is less soft tissue coverage, i.e. the thoracic region. The use of set screw assembly  100  in these regions may cause patient discomfort or undue scarring. Additionally, the thoracic region is where most deformity correction is required. The locking and partial locking features of low profile screw assembly  200  permits the adjustment of screw assembly  100  as a deformity is corrected. However, in a construct which extends from the thoracic region of the spine to the lumbar region of the spine, the rod usually curves in a posterior to anterior direction. As a result, there may be a perception that the forces on the rod after implantation might cause the rod to try to dislocate from a low profile screw, especially a low profile screw which appears open at the top thereof. Thus, it is believed that the combination of a low profile screw in the thoracic region, where its advantages may be more appreciated, with a set screw type locking pedicle screw in the lumbar region, may be perceived to provide advantages to the surgeon and patient. In addition, premium priced low profile screws may be perceived as unnecessary in portions of the construct where the advantages of such a structure are not realized, such as the lumbar region, and so a more economical approach can be achieved by utilizing low profile screws where warranted and set screw style pedicle screws where such screws will suffice. 
         [0036]    Maintenance and removal of spinal fixation system  10   a  is the same as would be for traditional set screw assemblies  100  and low profile screw assemblies  200  individually. Each of traditional set screw assemblies  100  and low profile screw assemblies  200  may be adjusted as necessary until the desired spinal alignment is achieved. 
         [0037]    It will be understood that various modifications may be made to the embodiments herein. For example, fixed angle screws, uniplanar screws, monomial rotating screws, hooks, wires and cables may be used in combination with traditional set screw assembly  100  and low profiles screw assembly  200 . 
         [0038]    The pedicle screws of the present construct may be fabricated from titanium, titanium alloys, stainless steel, nickel titanium, polyetheretherketone (PEEK) or any other suitable biocompatible material. The rods used in the present construct may be fabricated from the same or dissimilar materials to the screws. Thus, if the screws are fabricated from titanium, titanium alloy, stainless steel, cobalt chrome (CoCr) or PEEK, then so too can the rod be fabricated from the same material. On the other hand, the rod may also be fabricated from a dissimilar, compatible material. Thus, the rod may be fabricated from PEEK and used with screws fabricated from any of the foregoing materials. The rod also may be fabricated from CoCr with the screws fabricated from titanium, titanium alloy, cobalt chrome, stainless steel, nickel titanium, or PEEK.