Abstract:
Provided is a surgical rod fixation assembly having a pedicle screw for insertion into spinal bone of a subject, the pedicle screw having a polyaxial mounted coupling member for driving the pedicle screw into bone on or off axis and coupling the pedicle screw to an orthopaedic device such as a spinal rod by means of a slidable coupling action.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a surgical rod fixation assembly having a screw configured to provide a polyaxial rod coupling capability for use with orthopaedic fixation systems. More particularly, the present invention relates to a surgical rod fixation assembly having a pedicle screw for insertion into the spinal bone of a subject, the pedicle screw having a polyaxial mounted coupling member for coupling the pedicle screw to an orthopaedic device such as a surgical rod, or more particularly a spinal rod. 
     2. Background of the Technology 
     The fixation of surgical devices and appliances to bone is often difficult and time consuming, thus adding to the potential for trauma and complications in such surgical procedures. This is particularly true in spinal surgery procedures. Conventional locking mechanisms used to secure spinal rods to bone connectors such as pedicle screws have typically failed to provide the configurational versatility needed to make a secure attachment when individual bone configurations do not lend themselves to easy attachment. 
     Typically, conventional fixation systems, which attempt to provide the necessary versatility in quickly changing the configuration of the devices, employ too many small parts that serve only to complicate and prolong the surgical process and worse, can present hazards to the patient. Such conventional systems have attempted to avoid these problems but in doing so have had to sacrifice some of the configurational options that are needed for a best fit of the appliance. 
     Thus a need exists for a fixation assembly that can be easily and quickly used to provide the maximum flexibility in selecting a configuration for attachment of an appliance or surgical rod, such as a spinal rod, to the spine of a subject. 
     SUMMARY OF THE INVENTION 
     The present invention provides a novel polyaxial surgical rod fixation assembly having a surgical screw with a rotatable head securely held by an inner housing that is easily and slidably engaged with a complementary outer housing such that upon such engagement, the surgical screw is fixedly held in a relative position to the housing while the housing simultaneously securely holds the surgical rod. 
     Also provided is a method of using the assembly of the present invention such that minimal time and effort is required to set the assembly in the desired position relative to the anatomy of the subject. 
     Also provided is a kit that includes the assembly of the present invention in combination with at least one surgical rod to be placed in a subject. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other features of the present invention will become apparent to one skilled in the art to which the present invention relates upon consideration of the following description of the invention with reference to the accompanying drawings, wherein: 
         FIG. 1A  provides a side view of the screw member of the present invention showing a bowl-shaped curvate head, 
         FIG. 1B  is a top view of the screw member shown in  FIG. 1A , the top view showing the spherical hexagonal configuration of the interior surface of the bowl-shaped curvate head, 
         FIG. 2A  is a cross sectional side view of the polyaxial surgical rod fixation assembly in an unlocked configuration, 
         FIG. 2B  is a top view of the polyaxial surgical rod fixation assembly shown in  FIG. 2A , 
         FIG. 2C  is a cross sectional side view of the polyaxial surgical rod fixation assembly fully assembled in a locked configuration with a spinal rod securely held therein. 
         FIG. 3A  provides a side view of a hemispherical insert member configured to be removably positioned within the polyaxial surgical rod fixation assembly shown in  FIG. 2A , and 
         FIG. 3B  is a top view of the hemispherical insert member shown in  FIG. 3A , showing the drive receiving recess. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Detailed embodiments of the present invention are disclosed herein; however, it is understood that the following description is provided as being exemplary of the invention, which may be embodied in various forms without departing from the scope of the claimed invention. Thus, the specific structural and functional details provided in the description are non-limiting, but serve merely as a basis for the invention defined by the claims provided herewith. 
     A novel polyaxial surgical rod fixation assembly, generally shown at  10 , is illustrated in  FIGS. 2A-2C . The assembly  10  of the present invention includes a screw member  12  configured to be inserted into and releasably retained within an inner housing  14  of the assembly  10 . As best shown in  FIGS. 3A-3B , a hemispherical insert  16  is provided to be positioned directly above and in engaging contact with the screw member  12 , the insert  16  having position retention members  17  and drive supports  19  to facilitate positioning and retention of the insert within the inner housing  14 . As best shown in  FIGS. 2A-2C , an outer housing  18  is sized and configured to have an inner surface taper complementary to the outer lateral surface taper of the inner housing  14  and to be in slidable contact with and to circumscribe at least a portion of the outer lateral surface of the inner housing  14 . 
     As best shown in  FIG. 1A-1B , the screw member  12  includes a threaded shaft  20 , which is configured to penetrate and engage bone material so as to be removably fixed to the bone. The screw member  12  also includes a screw head  22  integrally formed with the screw shaft  20 . As best shown in  FIG. 1A , the screw head  22  is curvate in shape having a convex undersurface  24 , preferably of a constant radius of curvature so as to be a section of a sphere. The screw head  22  has an interior surface  26 , which is concave and also preferably of a constant radius of curvature so as to be capable of receiving the hemispherical insert  16 . The interior surface  26  can have a configuration that can be complementary to the configuration of the corresponding contacting or under surface of the hemispherical insert  16 . That is, the retention members  17  of the hemispherical insert  16  can be configured so as to interact with the configuration of the interior surface  26  of the screw head  22  such that a rotational movement of the hemispherical insert  16  will cause a similar rotational movement of the screw head  22 . The retention members  17  of the insert  16  can preferably be configured as a hexagonal convex surface that conforms to a hexagonal concavity configuration of the interior surface  26  of the screw head  22 . Other alternative configurations for the retention members such as, for example, square, triangular, octagonal, or raised-ribs or the like can be used so long as the configuration of the retention members on the under surface of the hemispherical insert  16  provide a gripping interaction with the configuration of the interior surface  26  of the screw head  22 . As best shown in  FIG. 1B , the interior surface  26  of the concavity of the screw head  22  can alternatively have an additional or secondary screw head concavity  28  defined in the lower portion of the interior surface  26  of the screw head  22 . This alternative secondary concavity  28  can be configured in similar fashion to that described above for the interior surface  26  of the screw head  22 . That is, the alternative secondary concavity can have a complementary configuration to a convex surface such as hexagonal, octagonal, square, ribbed or the like so long as the interaction between the secondary concavity  28  and the under surface of the hemispherical insert  16  results in sufficient gripping action to allow transfer of rotational motion of the hemispherical insert  16  to rotational motion of the screw head  22 . 
     As best shown in  FIGS. 3A-3B  and discussed above, the hemispherical insert  16  has a convex undersurface with position retention members  17 , which contact the gripping interior surface  26  or alternative the secondary concavity  28  This gripping interaction between the hemispherical insert  16  and the interior surface  26  of the screw member  12  allows a tightening or loosening tool to be inserted into contact with the drive support  19  of the hemispherical insert  16  with good effect even when the longitudinal axis of the screw member  12  is not aligned with the longitudinal axis of the hemispherical insert  16 . Thus, screw member  12  tightening or loosening can be accomplished off-axis providing a significant improvement in flexibility for the surgeon. In operation, the gripping action of the retention members  17  of hemispherical insert  16  with the complementary configured interior surface  26  or secondary concavity  28  of the screw head  22  serves to transfer the rotational motion from the hemispherical insert  16  to the screw member  12 . Thus, when a tightening or loosening tool is inserted into contact with drive support  19  of the hemispherical insert  16  and rotational forces are applied by an operator the rotational force is transferred to the screw head  22 . This transfer of rotational motion from the insert  16  to the screw head  22  by the interaction of the retention members  17  permits the screw member  12  to be rotated to a tightened or loosened position without regard for whether the axis of the insert  16  is in alignment with the axis of the screw member  12 . By this mechanism, the polyaxial tightening or loosening capacity of the invention is realized. While the preferred configuration of the retention members  17  on the under surface of the insert  16  is of a hexagonal convex shape and the interior surface  26  of the screw head  22  has the shape of a hexagonal concavity, the particular configurations of the interacting surfaces can be quite varied as indicated above without departing from the concept of the invention. 
     The inner housing  14 , into which the screw member  12  can be inserted, defines an axial bore  30 , which extends from the upper surface  32  along the longitudinal axis of the inner housing  14  to a screw shaft exit portal  34 , which is sized and configured to permit the threaded shaft  20  of the screw member  12  to extend below and outside of the inner housing  14  but is also sized so as to not permit the screw head  22  to pass through the exit portal  34 . The outer surface  36  of the inner housing  14  is provided with a taper between an inner housing first end  38  and an inner housing second end  40 , the diameter of the inner housing  14  decreasing from the inner housing first end  38  to the inner housing second end  40 . The inner housing from first end  38  to second end  40  defines an inner housing slit  42 , which is sized to permit limited inward compression of the inner housing when an external force is applied to the outer surface  36  of the inner housing  14 . The inner housing  14  proximate to the first end  38  defines a surgical rod receiving portal  44 , which is sized and configured to moveably receive a surgical rod  46 . While it is preferable that the surgical rod receiving portal  44  does not extend so far toward the first end  38  of the inner housing  14  so as to open out beyond the upper limit of the inner housing; that is to form a slot instead of a portal, it is still within the concept of the invention that a surgical rod could be placed and securely held in such a slot by the present invention. 
     The outer housing  18  of the assembly  10  defines an inner passageway  48 , which is sized and configured with an inner surface  50  having a taper that is complementary to that of the outer surface  36  of the inner housing  14 . The inner passageway  48  of the outer housing  18  is sized and tapered so as to slidably fit circumferentially about the outer surface  36  of the inner housing  14  in such a manner so as to exert a compressing force against the outer surface  36  of the inner housing  14  when the outer housing  18  is fully in place around the circumference of the inner housing  14 . 
     In operation, as the inner housing  14  and the outer housing  18  are slidably joined along their coincidental longitudinal axis and contacting the complementary tapered outer surface  36  and inner surface  50  limited inward compression of the inner housing  14  results. This inward compression of the inner housing  14  is sufficient to force the axial bore  30  of the inner housing  14  into a locking compressive engagement against the surgical rod  46 , which is resident in the surgical rod receiving portal  44 . Further, compression of the inner housing  14 , as caused by the circumferential engagement of the outer housing  18  with the inner housing  14  causes sufficient compression to force the axial bore  30  of the inner housing  14  into a locking compressive engagement against the screw head  22  thus securely holding the screw member  12  in a fixed position relative to the inner housing  14  when an external force is applied to the outer surface  36  of the inner housing  14 . Alternatively, the inner housing  14  and the outer housing  18  can be configured such that when the outer housing  18  is moved into a locking position in relation to the inner housing  14 , the compression of the inner housing  14  is sufficient to lock a surgical rod  46  into a fixed position relative to the inner housing  14  but does not enter into a compressive engagement against the screw head  22 ; thus, leaving the screw head  22  free to move relative to the inner housing  14 . 
     Thus, the present invention provides a polyaxial surgical rod fixation assembly that enables a user to securely but releasably connect a surgical rod to bone with a device having fewer parts and greater simplicity of use than that conventionally provided. 
     It is within the concept of the present invention to provide the polyaxial surgical rod fixation assembly described above in a kit including at least one surgical rod that can be positioned and secured within a subject in need thereof. Such a kit can be provided in sterile packaging for opening and immediate use in the operating room. 
     The components of the present invention can be manufactured using methods and materials as known in the art such as for example, implant grade metallic materials, such as titanium, cobalt chromium alloys, stainless steel, and the like. It is also within the concept of the present invention that the components can be manufactured from any bio-compatible materials such as composite materials or plastics. Non-limiting examples of such materials include polyetheretherketone (PEEK) or polyaryletherketone (PAEK), or composites thereof, which can incorporate carbon fibers or similar materials. The materials used in the manufacture of the device and components of a kit can be radiopaque or radiolucent. The components of the present invention can be manufactured by any of a variety of known methods to include, for example, molding, casting, forming, machining, and extruding. 
     The method of the present invention provides for the implantation of the system of the present invention in a subject in need of the same. Variations of standard method steps in such surgical procedures can be made to adapt to the specific needs of the subject without departing from the concept of the invention. Normal operative techniques and tools for implantation of the device can be employed as necessary in accordance with safe surgical practices. A particular convenience of the present invention is the ease by which the device with a surgical or spinal rod in place can be releasably locked by simply sliding the outer housing  18  upward along the outer surface of the inner housing. By this method the slit of the inner housing is compressed together so as to decrease the size of the upper portion of the axial bore  30  of the inner housing thus holding the surgical or spinal rod in place. 
     Each of the embodiments described above are provided for illustrative purposes only and it is within the concept of the present invention to include modifications and varying configurations without departing from the scope of the invention that is limited only by the claims included herewith. While the descriptive example of the present invention is primarily directed to securing of a spinal rod, it is within the concept of the present invention to employ assembly to releasably secure any surgical rod in place. 
     Each of the embodiments described above are provided for illustrative purposes only and it is within the concept of the present invention to include modifications and varying configurations without departing from the scope of the invention that is limited only by the claims included herewith.