Abstract:
A bone fixation device for fixing a first bone to a second bone includes a self tapping screw having an aperture extending along a longitudinal axis of the screw, and a driver having an aperture extending from a proximal end to a distal end along a longitudinal axis of the driver, the distal end being configured to engage the screw such that the aperture of the driver and the aperture of the screw are coaxially aligned, thereby defining a lumen. A guide rod having a tapered tip for piercing bone tissue is shaped and dimensioned to extend through the lumen and configured to fasten to the driver. A blunt-ended rod advances a bioactive agent through the lumen, the blunt-ended rod being dimensioned to extend through the lumen to decrease the injury to vital structures as the screw is advanced into the second bone.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims priority from U.S. Patent Application No. 61/409,426 filed Nov. 2, 2010. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
       [0002]    Not Applicable. 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The field of the invention is medical devices and methods for their use. More particularly, the invention relates to medical devices for bone fixation and arthrodesis and methods for their use. 
         [0005]    2. Description of the Related Art 
         [0006]    Transarticular facet screw fixation is often used for treating instability between vertebrae, such as the atlas (C1 vertebra) and axis (C2 vertebra). This technique can also be used to fixate vertebrae inferior to the C2 vertebra and provides rigid internal fixation of the unstable vertebrae. In a typical C1-C2 fixation procedure, a midline incision is made on a patient from the occiput to the spinous process of, for example, the C5 vertebra, thereby exposing the C1 and C2 vertebrae, among others. Depending on the alignment of the C1 and C2 vertebrae, the fixation procedure can be performed in a human H directly through the incision or, as illustrated in  FIG. 1 , percutaneously along alignment line A. 
         [0007]    In a typical C1-C2 fixation procedure, a Kirschner wire (“K-wire”) is used to pierce the inferior facet of the C2 vertebra, run through the C2 vertebra, and pierce into the lateral mass of the C1 vertebra. Precise placement of the K-wire is necessary, or nearby vital structures, such as the vertebral artery and spinal nerves, can be damaged, resulting in injury to the patient. A cannulated drill is placed over the K-wire and used to drill a pilot hole, which is tapped, in the C1 and C2 vertebra. A cannulated screw is then placed over the K-wire and advanced through the C1 and C2 vertebra, guided by the pilot hole and the K-wire. After the screw is in place, the K-wire is removed. See, for example, Apostolides et al., “Technique of Posterior Atlantoaxial Arthrodesis With Transarticular Facet Screw Fixation and Interspinous Wiring”,  Operative Techniques in Neurosurgery , Vol. 1, No. 2 (June), pp. 67-71, 1998. 
         [0008]    Bone growth agents are typically administered during a bone fixation procedure to fuse the unstable bones. In some instances, a bone growth agent is administered through transverse openings in a cannulated bone fixation screw, so that the vertebrae being fixated can ultimately fuse together. See, for example, U.S. Pat. No. 7,354,442. 
         [0009]    To assist the surgeon in efficiently, safely, and effectively performing a bone fixation procedure, it would be desirable to provide a single device that performs the tasks of multiple individual tools, prevents the damage of vital structures, and administers a bone growth agent in a manner conducive to promoting the fixation of the unstable bones. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention overcomes the aforementioned drawbacks by providing a bone fixation device that utilizes a self tapping screw and sharp guide rod that is interchangeable with a blunt-ended rod that is configured to prevent damage to vital structures. Such a device includes a self tapping screw having an aperture extending along a longitudinal axis of the screw, and a driver having an aperture extending from a proximal end to a distal end along a longitudinal axis of the driver, the distal end being configured to engage the screw such that the aperture of the driver and the aperture of the screw are coaxially aligned, thereby defining a lumen. Also included is a guide rod having a tapered tip for piercing bone tissue, the guide rod being shaped and dimensioned to extend through the lumen and configured to fasten to the driver, and a blunt-ended rod for advancing a bioactive agent through the lumen, the blunt-ended rod also being shaped and dimensioned to extend through the lumen. 
         [0011]    It is an aspect of the invention to provide a method for fixing a first bone to a second bone, such as two cervical or other vertebrae using a bone fixation device. Such a method includes the steps of providing the device to a surgeon, the device generally including a cannulated self tapping screw, a cannulated driver configured to coaxially engage the cannulated screw; a guide rod shaped and dimensioned to engage the cannulated screw and cannulated driver, and having a tapered end for piercing a bone tissue; and a blunt-ended rod shaped and dimensioned to engage the cannulated screw and cannulated driver, and having a blunt end for advancing a bioactive agent through a lumen formed when the cannulated driver engages the cannulated screw. The cannulated driver engages the cannulated screw, thereby defining a lumen running through both the screw and the driver. The guide rod is advanced through the lumen so that the guide rod pierces a surface of the first bone, and the guide rod is fastened to the cannulated driver. The cannulated driver is operated to collectively advance the cannulated screw and the guide rod through the first bone until the guide rod pierces a surface of the second bone, forming a pilot hole in that bone. The guide rod is then removed from the lumen of the device and a bioactive agent is provided to the lumen. Then, the blunt-ended rod is advanced through the lumen of the device, thereby dispersing the bioactive agent into a joint space between the first and second bones. The blunt-ended rod is then fastened to the cannulated driver and the cannulated driver is operated to collectively advance the cannulated screw and blunt-ended rod through the second bone, thereby fixing the first and second bones together. The cannulated driver and blunt-ended rod are then disengaged from the cannulated screw. The device can also be used to fixate fractures within a single bone. 
         [0012]    The foregoing and other aspects and advantages of the invention will appear from the following description. In the description, reference is made to the accompanying drawings which form a part hereof, and in which there is shown by way of illustration an example embodiment of the invention. Such embodiment does not necessarily represent the full scope of the invention, however, and reference is made therefore to the claims and herein for interpreting the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  illustrates an exemplary surgical trajectory used during the percutaneous fixation of a C1 and C2 vertebra; 
           [0014]      FIG. 2  is an elevation view of an exemplary bone fixation device in accordance with embodiments of the present invention; 
           [0015]      FIG. 2A  is a cross-sectional view of the exemplary bone fixation device of  FIG. 2  viewed along line  2 A- 2 A of  FIG. 2 ; 
           [0016]      FIG. 3  is an elevation view of an exemplary cannulated screw, cannulated driver, and guide rod that form a part of the exemplary bone fixation device of  FIG. 2 ; 
           [0017]      FIG. 4  is a perspective view showing the engagement of a distal end of the cannulated driver and the head of the cannulated driver of  FIG. 2 ; 
           [0018]      FIG. 5  is a pictorial view of the bone fixation device of  FIG. 2  with a guide rod being operated to advance a screw through a first bone; 
           [0019]      FIG. 5A  is a partial cross-sectional view of  FIG. 5  viewed along line  5 A- 5 A of  FIG. 5 ; 
           [0020]      FIG. 6  is a pictorial view of the bone fixation device of  FIG. 2  with a blunt-ended rod being operated to advance a bioactive agent through the lumen of the device and out the distal aspect of the screw into a joint space between the first bone and a second bone; 
           [0021]      FIG. 6A  is a partial cross-sectional view of  FIG. 6  viewed along line  6 A- 6 A of  FIG. 6 ; 
           [0022]      FIG. 7  is a pictorial view of the bone fixation device of  FIG. 2  with a blunt-ended rod being operated to advance a screw through a second bone; 
           [0023]      FIG. 7A  is a partial cross-sectional view of  FIG. 7  viewed along line  7 A- 7 A of  FIG. 7 ; and 
           [0024]      FIG. 8  is a pictorial representation of the fixation of a C1 and C2 vertebra with a cannulated screw. 
       
    
    
       [0025]    Like reference numerals will be used to refer to like parts from Figure to Figure in the following description of the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0026]      FIGS. 2 ,  2 A, and  3  illustrate an exemplary bone fixation device  200  in accordance with the present invention. The bone fixation device  200  generally includes a cannulated screw  202 , a cannulated driver  204 , a guide rod  206 , and a blunt-ended rod (not shown in  FIGS. 2 ,  2 A, and  3 ). As used herein, the term “cannulated” refers to an object having a hollow shaft, aperture, or lumen, running through it. Thus, a “cannulated screw” includes a screw having a hollow shaft, aperture, or lumen, running, for example, through the length of the screw. The cannulated screw  202 , cannulated driver  204 , guide rod  206 , and blunt-ended rod are preferably composed of a material suitable for surgical use, such as stainless steel or titanium. 
         [0027]    The head  208  of the cannulated screw  202  is configured to engage the distal end  210  of the cannulated driver  204 , as illustrated in  FIG. 4 . The head  208  of the cannulated screw  202  may include any number of suitable drive types that allow for a centrally positioned lumen to run therethrough while still providing a portion that can be engaged by the distal end  210  of the cannulated driver  204 . When the tip of the guide rod  218  is positioned through the axial distal tip  212  of the cannulated screw  202 , the resulting configurations is for a self-drilling screw, so that it can be advanced through bone tissue without the need for a pilot hole to be drilled first. A self-tapping screw is a screw that can advance through a pilot hole without the need to tap the pilot hole first. 
         [0028]    As illustrated in  FIG. 4 , the cannulated screw  202  has a lumen  214  running therethrough that is substantially coaxial with a lumen  216  running through the cannulated driver  204 . As illustrated in  FIGS. 2 and 2A , when the cannulated driver  204  engages the cannulated screw  202 , a single lumen configured to receive the guide rod  206  is formed by the alignment of the lumens  214 ,  216 . This single lumen is similarly configured to receive a blunt-ended rod, as will be described below. 
         [0029]    The guide rod  206  has a sharp, tapered tip  218  at its distal end that is configured to pierce bone tissue. The proximal end of the guide rod  206  includes a locking mechanism  220  that is configured to securely engage the proximal end  222  of the cannulated driver  204  so that when the cannulated driver  204  is operated, the guide rod  206  moves in unison with the cannulated driver  204 . For example, the locking mechanism  220  may include a series of threads disposed on a proximal portion of the shaft of the guide rod  206 , and a series of similarly cut threads in the proximal portion of the lumen  216  in the cannulated driver  204  thereby provides the secure engagement of the guide rod  206  with the cannulated driver  204 . 
         [0030]    To prevent inadvertent damage to vital structures, such as the vertebral artery, the guide rod  206  is fastened to the cannulated driver  204 , thereby effectively forming the tip of the cannulated screw  202  when it is engaged by the cannulated driver  204 . Because the guide rod  206  is securely fastened to the cannulated driver  204 , the guide rod  206  remains in a stationary position relative to the cannulated screw  202  during advancement of the cannulated screw  202 . As the cannulated screw is advanced near vital structures, such as the vertebral artery, the guide rod  206  can be retracted and replaced with a blunt-ended rod. As will be described below, this blunt-ended rod may also serve the purpose of advancing a bioactive agent through the single lumen formed by lumens  214 ,  216 . The blunt-ended rod is similar in construction to that of the guide rod  206 , except that the tip of the blunt-ended rod is blunt so that it cannot pierce bone tissue or vital structures. Alternatively, the guide rod  206  can also have a blunt end as in rod  232  instead of the sharp end  218  shown in  FIG. 3 . Otherwise, the blunt-ended rod is composed of a similar material and includes a similarly configured locking mechanism. 
         [0031]    Having generally described the features of the bone fixation device  200 , a discussion of its general operation is now provided. The bone fixation device  200  is provided to a surgeon, who engages the cannulated screw  202  with the cannulated driver  204 , thereby forming a single lumen by coaxially aligning the lumens  214 ,  216  of the cannulated screw  202  and cannulated driver  204 . The guide rod  206  is then passed through the single lumen and secured to the cannulated driver  204  by way of the locking mechanism  220 . For example, the guide rod  206  is threaded into a threaded portion of the cannulated driver  204  lumen  216 . 
         [0032]    Referring now to  FIGS. 5 and 5A , the assembled device  200  is positioned over the surface of a first bone  224  so that the exposed tip  218  of the guide rod  206  pierces the surface of the first bone  224 . The cannulated driver  204  is then operated so as to advance the cannulated screw  202  through the first bone  224 . Because the guide rod  206  is securely fastened to the cannulated driver  204 , the cannulated screw  202  and the guide rod  206  are collectively advanced through the bone tissue. As illustrated in  FIGS. 5 and 5A , the cannulated driver  204  is operated until the tip  218  of the guide rod  206  pierces through the first bone  224 , crosses a joint space  226  between the first bone  224  and an adjacent second bone  228 , and pierces the surface of the second bone  228 . At this point, the guide rod  206  is removed from the lumen of the bone fixation device  200 . 
         [0033]    After the guide rod  206  has been removed from the bone fixation device  200 , a bioactive agent  230  is provided to the lumen of the device. A “bioactive agent” as used herein includes, without limitation, physiologically or pharmacologically active substances that act locally or systemically in the body. A bioactive agent is a substance used for the treatment, prevention, diagnosis, cure or mitigation of disease or illness, or a substance which affects the structure or function of the body or which becomes biologically active or more active after it has been placed in a predetermined physiological environment. Bioactive agents include, without limitation, enzymes, organic catalysts, ribozymes, organometallics, proteins, glycoproteins, peptides, polyamino acids, antibodies, nucleic acids, steroidal molecules, antibiotics, antimycotics, cytokines, growth factors, carbohydrates, oleophobics, lipids, extracellular matrix and/or its individual components, pharmaceuticals, allograft bone, and therapeutics. Exemplary bioactive agents for use with the present invention include bone morphogenetic proteins (“BMPs”) and demineralized bone matrix (“DBM”) as these agents promote the growth of bone, thereby aiding the fixation process. 
         [0034]    As illustrated in  FIGS. 6 and 6A , after the bioactive agent  230  is provided to the lumen of the device  200 , the blunt-ended rod  232  is advanced through the lumen of the device  200  so that the bioactive agent  230  is dispersed out of the tip  212  of the cannulated screw  202  and into the joint space  226 . Because the guide rod  206  was allowed to pierce the surface of the second bone  228 , a pilot hole  234  is provided in the second bone  228  for the advancement of the cannulated screw  202  into the bone tissue. Because the cannulated screw  202  is self tapping, its advancement into the bone tissue without a guide wire is similarly improved. The blunt-ended rod  232  is securely fastened to the cannulated driver  204  by way of a similar locking mechanism to the locking mechanism  220  on the guide rod  206  and the cannulated driver  204  operated to advance the cannulated screw  202  across the joint space  226  and into the second bone  228 , as illustrated in  FIGS. 7 and 7A . Thus, the screw  202  goes through the facet joint. In this manner, the first bone  224  and the second bone  228  are fixed together by way of the cannulated screw  202 , and this fixation is made more structurally sound as a result of the bioactive agent provided to the joint space  226  between the first bone  224  and the second bone  228 . The cannulated driver  204  is then disengaged from the cannulated screw  202  and the cannulated driver  204  and blunt-ended rod  232 , which are still fastened together, are collectively removed from the patient. 
         [0035]    While reference was previously made to the fixation of the C1 and C2 vertebrae, it should be appreciated by those skilled in the art that that bone fixation device  200  can be used during the fixation any number of different bones or bone fragments together. For example, the bone fixation device  200  can be used to fix two different cervical vertebrae together, as well as different thoracic and lumbar vertebrae. In general, the bone fixation device  200  can be used to fix together two bones that share an articulated joint, or a bone and a bone fragment. 
         [0036]    Although the present invention has been described in detail with reference to certain embodiments, one skilled in the art will appreciate that the present invention can be practiced by other than the described embodiments, which have been presented for purposes of illustration and not of limitation. Therefore, the scope of the appended claims should not be limited to the description of the embodiments contained herein.