Abstract:
A medical device adapted to facilitate pedicle screw fusion surgery is disclosed herein. The medical device includes a proximal end and a sharp distal end opposite the proximal end. The distal end is configured to allow the medical device to function as an awl. The medical device also includes a body portion defined between the proximal end and the distal end, and a threaded section defined by the body portion near the distal end. The threaded section is configured to allow the medical device to function as a tap. Accordingly, the medical device provides a single tool adapted to function as both an awl and a tap. A corresponding method for securing a pedicle screw to a vertebra is also provided.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention pertains generally to a method and apparatus for performing pedicle screw fusion surgery. 
       BACKGROUND OF THE INVENTION 
       [0002]    Pedicle screw fusion surgery generally involves the insertion of pedicle screws into a short tubular structure connecting the vertebral body with the lamina and represents the strongest portion of the vertebra found on each side of the vertebra. This allows the pedicle screws to grab into the bone of the vertebral body, giving them a solid hold on the vertebra. Once the pedicle screws are placed, they are attached to metal rods that connect the screws together. This creates a stiff metal frame that holds the vertebrae still and thereby facilitates decompression for pain relief and healing. Bone graft is typically placed around the back of the vertebra to help the vertebrae heal together, or fuse. 
         [0003]    Pedicle screw fusion procedures can incorporate surgical navigation technology wherein the location of a medical device is measured and virtually superimposed on a patient image. The patient image may be pre-recorded, near real-time, or real-time, and is preferably obtained using known imaging technology such as X-ray, computed tomography (CT), magnetic resonance imaging (MRI), or ultrasound (US). Conventional navigation technology measures the location of a remote unit attached to the medical device relative to a reference unit. Patient motion can be taken into account by rigidly mounting the reference unit directly onto the patient. A reference unit attached in this manner is also referred to as a dynamic reference because it moves along with the patient. 
         [0004]    A number of medical instruments including an awl, a blunt probe, a ball tip probe-feeler, and a tap are commonly implemented during pedicle screw fusion surgery. Awls have a sharp pointed end that is used to create a shallow pilot hole opening through the bone surface. The pointed end of the awl is particularly well adapted to pedicle screw fusion surgery as blunt instruments would be prone to sliding off the pedicle&#39;s dome shaped surface. The blunt probe is used to carve the hole from the pedicle cortex into the vertebal body at an appropriate angle and depth. The ball tip probe-feeler is implemented to verify pedicle integrity via a process of palpation and thereby ensure no violation of the pedicels walls occurred prior to implantation. If a non-significant violation is detected, the pedicle screw is either redirected or the site is abandoned. A tap includes a cutting edge adapted to form internal threads in the cancellous bone of the pedicle canal. The internal treads formed by the tap engage complementary external pedicle screw threads to retain and secure the pedicle screws. These taps that are specifically matched to implant screw counterparts, are commonly used after the pedicle hole is created and prior to implant screw placement. 
         [0005]    Conventional awls, blunt probes and taps are individual medical instruments adapted to perform a specialized function as previously described. These individual instruments must be switched back and forth many times during the course of a single pedicle screw fusion procedure. Though these instruments are necessary for the conventional technique, the intra-operative steps associated with switching the instruments are a potential source of inefficiency and can prolong the overall duration of a procedure. 
       SUMMARY OF THE INVENTION 
       [0006]    The above-mentioned shortcomings, disadvantages and problems are addressed herein which will be understood by reading and understanding the following specification. 
         [0007]    In an embodiment, a medical device adapted to facilitate pedicle screw fusion surgery includes a proximal end and a sharp distal end opposite the proximal end. The distal end is configured to allow the medical device to function as an awl. The medical device also includes a body portion defined between the proximal end and the distal end, and a threaded section defined by the body portion near the distal end. The threaded section is configured to allow the medical device to function as a tap. Accordingly, the medical device provides a single tool adapted to function as both an awl and a tap. 
         [0008]    In another embodiment, a system adapted to facilitate pedicle screw fusion surgery includes a position detection process in communication with a remote unit and a reference unit. The position detection process is configured to estimate the location of the remote unit relative to the reference unit. The system also includes a medical device attached to the remote unit. The medical device includes a proximal end, a distal end, and a body portion defined therebetween. The medical device also includes a generally pointed tip defined at the distal end. The pointed tip is configured to allow the medical device to function as an awl. The medical device also includes a threaded section defined by the body portion near the distal end. The threaded section is configured to allow the medical device to function as a tap. The system also includes a display operatively connected to the position detection device. The display is adapted to convey the location of the medical device relative to the reference unit. 
         [0009]    In yet another embodiment, a method for securing a pedicle screw to a vertebra includes creating a pilot hole in a pedicle with a medical device, forming a screw hole in the vertebra at the location of the pilot hole with the medical device, forming an internal thread disposed about the periphery of the screw hole with the medical device, and inserting an externally threaded pedicle screw into the internally threaded screw hole. Wherein creating a pilot hole, forming a screw hole, and forming an internal thread are all performed with a single medical device. 
         [0010]    Various other features, objects, and advantages of the invention will be made apparent to those skilled in the art from the accompanying drawings and detailed description thereof. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a schematic diagram of a navigation system; 
           [0012]      FIG. 2  is a detailed perspective illustration of a medical device in accordance with an embodiment; 
           [0013]      FIG. 2   a  is a detailed perspective illustration of the distal end of the medical device of  FIG. 2  in accordance with an embodiment; 
           [0014]      FIG. 2   b  is a detailed perspective illustration of the distal end of the medical device of  FIG. 2  in accordance with an embodiment; 
           [0015]      FIG. 3   a  is a cross sectional view of a vertebra having a pilot hole formed in each pedicle; 
           [0016]      FIG. 3   b  is a cross sectional view of a vertebra having a screw hole formed in each pedicle; 
           [0017]      FIG. 3   c  is a cross sectional view of a vertebra having an internally threaded hole formed in each pedicle; 
           [0018]      FIG. 3   d  is a cross sectional view of a vertebra having a pedicle screw inserted into each pedicle; and 
           [0019]      FIG. 4  is a block diagram illustrating a method in accordance with an embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific embodiments that may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments, and it is to be understood that other embodiments may be utilized and that logical, mechanical, electrical and other changes may be made without departing from the scope of the embodiments. The following detailed description is, therefore, not to be taken as limiting the scope of the invention. 
         [0021]    Referring to  FIG. 1 , a medical device or instrument  10  in accordance with an embodiment is shown. The medical device  10  may be implemented with a variety of different navigation systems such as, for example, the surgical navigation system  12 . The navigation system  12  includes a reference unit  14 , a remote unit  16 , a display  18 , a position detection process  20 , an imaging device  22  and a computer  24 . 
         [0022]    The reference unit  14  is preferably rigidly attached to a patient  28  near the target operation site  30  (e.g., a portion of the spine) in a conventional manner. A reference unit attached in this manner is also referred to as a “dynamic reference” because it moves along with the patient. The remote unit  16  is attached to the medical device  10 . The present invention will hereinafter be described in accordance with an embodiment wherein the reference unit  14  includes a field generator  38 , and the remote unit  16  includes one or more field sensors  40 . It should, however, be appreciated that according to alternate embodiments the reference unit may include the field sensors and the remote unit may include the field generator. 
         [0023]    The field generator  38  in the reference unit  14  generates a position characteristic field  44  in an area that includes the target operation site  30 . The field sensors  40  in the remote unit  16  produce sensor signals (not shown) in response to the sensed position characteristic field  44 . The sensor signals are transmitted or input into the position detection process  20 . The sensor signals may be transmitted via communication line  46 , or may be wirelessly transmitted. The position detection process  20  is adapted to estimate the location of the remote unit  16  relative to the reference unit  14 . A known calibration procedure can be implemented to estimate the location of the distal end or tip  36  of the medical device  10 . 
         [0024]    The location of the medical device  10  may be conveyed via the display  18 . According to one embodiment, a graphical representation  48  of the distal end  36  is virtually superimposed onto a patient image  50 . More precisely, the graphical representation  48  of the distal end  36  is virtually superimposed onto the portion of the image  50  that corresponds to the actual location of the distal end  36  within the patient  28 . The graphical representation  48  may include a dot or cross hairs identifying just the distal end  36 , or may include a more complete rendering showing the medical device  10  in detail. 
         [0025]    According to one embodiment, the patient image  50  is obtained prior to the medical procedure using known imaging technology such as X-ray, computed tomography (CT), magnetic resonance imaging (MRI), or ultrasound (US). Additionally, during the course of the medical procedure, the imaging device  22  may be implemented to observe the patient  28  in real-time or near real-time. Therefore, the pre-recorded patient image  50  can be replaced with a real-time patient image or a near real-time image as desired. According to an exemplary embodiment, the imaging device  22  may include a fluoroscopic X-ray device mounted to a C-arm, however, other imaging devices may also be implemented. 
         [0026]    Referring to  FIG. 2 , the medical device  10  is shown in more detail. The medical device  10  is preferably comprised of a material compatible with electro-magnetic tracking technology such a non-metallic material or a minimally conductive metal so that position characteristic field  44  (shown in  FIG. 1 ) is not distorted. The medical device  10  includes a proximal end  34 , the distal end  36 , and a generally cylindrical body portion  52  defined therebetween. The generally cylindrical body portion  52  defines an axis  53 . The proximal end  34  of the medical device  10  is adapted to receive the remote unit  16  and/or a driver such as, for example, the power drill  54 . The body portion  52  tapers to a sharp point  56 . The point  56  is similar to the tip of a conventional awl (not shown). The point  56  is configured to pierce through cortical bone and into cancellous bone in order to produce a pilot hole  74  (shown in  FIG. 3   a ). 
         [0027]    The body portion  52  of the medical device  10  defines a threaded section  58  near the distal end  36 . The threaded section  58  is similar to that of a conventional tap (not shown), and includes one or more external threads  60  defining a cutting edge  62 . The cutting edge  62  is configured to cut both cortical bone and cancellous bone, and thereby form an internally threaded hole  78  (shown in  FIG. 3   c ) adapted to accommodate a pedicle screw  80  (shown in  FIG. 3   d ). 
         [0028]    Referring to  FIG. 2   a , a distal end  36   a  configuration is shown in accordance with one embodiment. The distal end  36   a  of the medical device  10  defines a plurality of generally flat sections  64   a  disposed axially between the point  56   a  and the threaded section  58   a . For purposes of this disclosure, the terms “flat section” and “blunt section” may be used interchangeably. An edge  66   a  is defined at the intersection of adjacent blunt sections  64   a . The blunt sections  64   a  and the edges  66   a  are adapted to allow the medical device  10  to function similarly to a conventional blunt probe (not shown). More precisely, by rotating the body portion  52  (shown in  FIG. 2 ) back and forth about its axis  53  (shown in  FIG. 2 ), the edges  66   a  can carve a screw hole  77  (shown in  FIG. 3   b ) through the pedicle  76  (shown in  FIGS. 3   a - 3   d ) into the vertebra  68  (shown in  FIGS. 3   a - 3   d ). 
         [0029]    Referring to  FIG. 2   b , a distal end  36   b  configuration is shown in accordance with another embodiment. In this embodiment, the body portion  52  (shown in  FIG. 2 ) tapers to a sharp edge  56   b  rather than the previously described sharp point  56   a  (shown in  FIG. 2   a ). The distal end  36   b  of the medical device  10  defines a plurality of blunt sections  64   b  disposed axially between the edge  56   b  and the threaded section  58   b . An edge  66   b  is defined at the intersection of adjacent blunt sections  64   b . The blunt sections  64   b  and the edges  66   b  are adapted to allow the medical device  10  to function similarly to a conventional blunt probe (not shown). More precisely, by rotating the body portion  52  back and forth about its axis  53  (shown in  FIG. 2 ), the edges  66   b  can carve a screw hole  77  (shown in  FIG. 3   b ) through the pedicle  76  (shown in  FIGS. 3   a - 3   d ) into the vertebra  68  (shown in  FIGS. 3   a - 3   d ). 
         [0030]      FIGS. 3   a - 3   d , illustrate a sequence of procedures that may be performed by the medical device  10  during pedicle screw fusion surgery. Referring to  FIG. 3   a , a cross sectional view of a vertebra  68  is shown. The vertebra  68  includes an outer layer of cortical bone  70  surrounding a core of porous cancellous bone  72 . A pilot hole  74  is preferably pierced into each pedicle  76  by the point  56  of the medical device  10  (shown in  FIG. 2 ). Referring to  FIG. 3   b , a screw hole  77  is carved into the vertebra  68  at the location of the pilot holes  74 . The screw holes  77  can be formed with the edges  66   a  (shown in  FIG. 2   a ) as the body portion  52  (shown in  FIG. 2 ) is rotated back and forth about its axis  53  (shown in  FIG. 2 ). 
         [0031]    Referring to  FIG. 3   c , an internal thread  79  is formed in the portion of the vertebra  68  defining the screw hole  77  (shown in  FIG. 3   b ). The internal thread  79  is therefore disposed about the periphery of the screw hole  77  such that an internally threaded hole  78  is produced. The internal thread  79  can be formed by the threaded section  58  of the medical device  10 . Referring to  FIG. 3   d , a pedicle screw  80  is driven into each of the internally threaded holes  78 . Metal rods (not shown) connect the pedicle screws  80  of adjacent vertebra together such that the vertebrae are held still. Bone graft (not shown) may be placed around the back of the vertebra to help the vertebrae heal together, or fuse. 
         [0032]    Referring to  FIG. 4 , a block diagram illustrates a method  100 . The individual blocks  102 - 114  represent steps that may be performed in accordance with the method  100 . It should be appreciated that the steps of the method  100  described in detail hereinafter are preferably performed in combination with a navigation system such as the surgical navigation system  12  (shown in  FIG. 1 ). 
         [0033]    At step  102 , the target operation site  30  (shown in  FIG. 1 ) is examined to select an optimal pedicle screw diameter, length, entry point and trajectory. The imaging device  22  (shown in  FIG. 1 ) is preferably implemented during this step to directly observe the pedicle  76  (shown in  FIGS. 3   a - 3   d ) and thereby provide a more accurate estimate. An imaging device  22  implementing fluoroscopic imaging technology is particularly well adapted for use during step  102 . 
         [0034]    At step  104 , an optimal configuration for the threaded section  58  of the medical device  10  (shown in  FIG. 2 ) is selected. More precisely, the threaded section  58  configuration is selected to produce an internally threaded hole  78  (shown in  FIG. 3   c ) that is sized to receive a pedicle screw  80  (shown in  FIG. 3   d ) having predetermined selectable features such as screw diameter, length, thread density, etc. The diameter of the internally threaded hole  78  may be formed to approximately match that of the pedicle screw  80 , or may be somewhat undersized to produce an interference fit or crush fit technique. For purposes of the present invention, an “nterference fit technique” is one wherein a pedicle screw is forcibly driven into an undersized or relatively smaller pedicle hole such that, during insertion, the screw is compressed by the pedicle bone. The compressive force applied by the pedicle bone to the pedicle screw is intended to improve screw retention. 
         [0035]    At step  106 , the medical device point  56  is implemented to pierce the pedicle  76  (shown in  FIGS. 3   a - 3   d ) at the pre-selected entry point such that a pilot hole  74  (shown in  FIG. 3   a ) is created. The navigation system  12  (shown in  FIG. 1 ) is preferably implemented to guide the medical device  10  (shown in  FIG. 2 ) and thereby ensure that the pilot hole  74  is precisely located at the pre-selected entry point. Advantageously, implementing the navigation system  12  to guide the medical device  10  obviates the need for a guide-wire (not shown) that would otherwise be required for locating the pedicle entry point. Therefore, the method  100  expedites the entire medical procedure by eliminating the time associated with inserting and placing a guide-wire. Conventional targeting software may also be implemented at this step to help guide the medical device  10  toward the pre-selected entry point. 
         [0036]    At step  108 , the screw holes  77  (shown in  FIG. 3   b ) are formed. More precisely, while the distal end  36  (shown in  FIG. 2 ) remains disposed within the pilot hole  74  (shown in  FIG. 3   a ), the body portion  52  (shown in  FIG. 2 ) is rotated back and forth about its axis  53  (shown in  FIG. 2 ). During this step, the axis  53  should remain aligned with the pre-selected pedicle screw trajectory in order to properly form the screw holes  77 . 
         [0037]    At step  110 , the threaded section  58  of the medical device  10  (shown in  FIG. 2 ) is introduced into the screw hole  77  (shown in  FIG. 3   b ) in alignment with the pre-selected pedicle screw trajectory, and thereafter the medical device  10  is translated toward the pedicle  76  (shown in  FIGS. 3   a - 3   d ) and generally simultaneously rotated in order to cut the internal threads  79  (shown in  FIG. 3   c ). The medical device  10  may be manually rotated or may be attached to the power drill  54  (shown in  FIG. 2 ) configured to drive the medical device rotation. 
         [0038]    At step  114 , a pedicle screw  80  (shown in  FIG. 3   d ) is driven into the internally threaded hole  78  (shown in  FIG. 3   c ). The pedicle screw  80  is driven in a conventional manner, such as with a screwdriver. According to an alternate embodiment, the pedicle screw  80  may be a self tapping screw driven directly into the pilot hole  74  (shown in  FIG. 3   a ) or into the screw hole  79  (shown in  FIG. 3   b ) such that step  110  is not required. 
         [0039]    Steps  102 - 114  are repeatable at other sights to place additional pedicle screws  80 . Advantageously, step  102 - 110  can all be performed with a single device (i.e., the medical device  10 ). Performing these steps in a more conventional manner would require at least three separate tools (i.e., an awl; a probe; and a tap), and the surgeon would have to switch back and forth between these separate tools throughout the procedure. It can therefore be seen that the method  100  which implements a single medical device  10  to perform a variety of different procedures saves the time otherwise required for switching and positioning new instruments during the course of the procedure. 
         [0040]    While the invention has been described with reference to preferred embodiments, those skilled in the art will appreciate that certain substitutions, alterations and omissions may be made to the embodiments without departing from the spirit of the invention. Accordingly, the foregoing description is meant to be exemplary only, and should not limit the scope of the invention as set forth in the following claims.