Abstract:
A top-loading pedicle screw system for correcting a misalignment of the spinal column of a patient. The top-loading pedicle screw assembly comprises a screw having a threaded shaft for affixation the assembly to a vertebral pedicle. The screw has a shank top forming an internal curved socket. A head is positioned within the socket to move in a multi-axial relationship thereto. A through bore is formed in the head to receive a rod that joins two or more pedicle screw assemblies to the spinal column of a patient. A locking element is inserted into the head to lock the rod to the head while also locking the head to the shank top of the screw.

Description:
[0001]    This application claims priority to U.S. Provisional Patent Application No. 62/265,439, filed on Dec. 10, 2015. The entirety of the aforementioned application is incorporated herein by reference. The present disclosure relates to the field of orthopedic implements, and, more particularly, to a top-loading pedicle screw assembly adapted to be screwed into two or more vertebral pedicles for affixing a rod or other joining implement to the vertebral pedicles. 
     
    
     TECHNICAL FIELD 
     Background 
       [0002]    Pedicle screw assemblies are well known devices and are often used to fasten an orthopedic implement, such as a solid bar, to two or more vertebrae to hold the vertebrae into a desired orientation. 
         [0003]    A common design for a pedicle screw system is to have a screw shank top that is shaped as a spherical top and there is a head or socket that is attached to the spherical screw shank top to move poly-axially therewith. As such, the screw shank top is normally spherical with the head fitting over that spherical shaped shank top to allow movement there between. 
         [0004]    One problem, however, with such a design is that the rod that extends between two or more pedicle screw systems is displaced away from the spinal column whereas it would be preferable for the rod to be positioned as close to the spinal column as possible. In addition, with the prior art systems, there are insertional complications since the threaded shank portion can become misaligned during the insertion process. For example, the threaded shank portion may become misaligned from the head which is held by instrumentation during the insertion process. 
         [0005]    Accordingly, it would be advantageous to have a specially designed pedicle screw assembly where the rod joining two or more pedicle screw systems can be positioned close to the spinal column and also a system that can be readily installed to the spinal column in a positive and stable alignment manner. It would be further advantageous to have a pedicle screw assembly having the ability to allow poly-axial motion while having a direct connection to the alignment features that are necessary for screw insertion into the spinal column. 
       BRIEF SUMMARY OF THE DISCLOSURE 
       [0006]    The present disclosure therefore, improves upon the features of the existing pedicle screw systems and includes a screw having a distal end with a threaded shaft and a proximal screw shank top that forms a socket for a head that is interfitted into that socket. As such, the insertion cannot become misaligned since the screw shank, which is held for alignment during insertion, is integral with the threaded shaft and, therefore, there is no movement between the screw shank top and the threaded shaft of the screw, yet the poly-axial motion is maintained. In addition, with the present disclosure, the location of the rod, as finally installed, is positioned closer to the spinal column than with the prior art systems. In addition, the present disclosure positions the rod at the center of, or close to the center of, the socket head interface. 
         [0007]    As such, with the present disclosure, the distal or threaded end of the threaded shaft is pointed and is screwed into the vertebral pedicle. The proximal end is integral with the threaded shaft and can easily be manipulated to carry out the screwing of the screw into the vertebral pedicle. In one aspect, the screw shank top has two flat outer surfaces to facilitate the grasping and rotating of the screw in order to screw it into the vertebral pedicle of the patient. 
         [0008]    The interior surface of the shank top of the screw is a specially formed curved surface, such as a spherical configuration, to form a socket that receives the head that interfits into the interior socket of the shank top of the screw. The head has a lateral through bore to position and hold the rod as it passes through the head. The shape of the head is such as to conform to the interior surface of the shank top of the screw to allow the poly-axial movement between the head and the screw shank top. In one aspect, the exterior surface of the head and the interior surface of the shank top of the screw are both spherical. 
         [0009]    A locking element is introduced into the head so as to lock the head within the socket of the screw shank top. In one aspect, the locking element can be a set screw that is introduced into the head to expand the exterior surface of the head to firmly lock that head to the shank top of the screw so as to lock the rod in its desired position interconnecting to two or more vertebral pedicles. 
         [0010]    Other features of the present pedicle screw assembly will become more apparent in light of the following detailed description and as illustrated in the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a side view, partly in cross section, illustrating the pedicle screw assembly, according to one aspect of this disclosure. 
           [0012]      FIG. 2  is a front view of the pedicle screw assembly of  FIG. 1 , according to one aspect of this disclosure. 
           [0013]      FIG. 2A  is a side cross sectional view of the pedicle screw assembly of  FIG. 1  taken along the line  2 A- 2 A of  FIG. 2 , according to one aspect of this disclosure. 
           [0014]      FIG. 3  is as top view of the pedicle screw assembly of  FIG. 1 , according to one aspect of this disclosure. 
           [0015]      FIG. 4  is a perspective view of the pedicle screw assembly of  FIG. 1 , according to one aspect of this disclosure 
           [0016]      FIG. 5  shows a method for inserting the pedicle screw assembly into a vertebrae, according to one aspect of this disclosure. 
           [0017]      FIG. 6  shows a perspective view of two consecutive vertebrae and two pedicle screw assemblies, according to one aspect of this disclosure. 
           [0018]      FIG. 7A  shows another design of the head, according to one aspect of this disclosure. 
           [0019]      FIG. 7B  shows a side view of the head  70 , according to one aspect of this disclosure. 
           [0020]      FIG. 7C  shows a cross-sectional view of the head  70  taken along the A-A line in  FIG. 7B , according to one aspect of this disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    In  FIG. 1 , there is shown a side view illustrating the pedicle screw system  10  of the present disclosure. As can be seen in  FIG. 1 , the pedicle screw system  10  comprises a screw  12  having a threaded shaft  14  ending in a pointed distal end  16  that is adapted to be screwed into a pedicle of a patient&#39;s spine. The screw  12  is preferably made of titanium; however, other materials could be used, such as stainless steel or cobalt chrome. Alternatively, the screw  12  can be made by powder metallurgy methods using powder that is sintered to form the finished form. In such case, the material may be stainless steel. 
         [0022]    At the proximal end  18  of the screw  12 , there is a shank top  20  that is specially designed in accordance with the present disclosure. As can be seen, the shank top  20  has an interior socket  22  forming by its interior spherically shaped surface and an exterior surface  24  having oppositely disposed flat surfaces  26  to enable the physician to use a tool to grasp the shank top  20  to screw the screw  12  into the vertebral pedicle of the patient. The flat surfaces  26  are shown in  FIG. 1  in one location, however, it may be seen that the flat surfaces  26  may be moved 90 degrees or at some intermediate offset. 
         [0023]    There are lateral openings  28  (only one is shown in  FIG. 1 ) that pass through the shank top  20  and are provided to make space for the addition of a rod  30  that passes through the lateral openings  28  so that the rod can be poly-axially affixed to the pedicle screw assembly  10  and connect the pedicle screw assembly  10  in  FIG. 1  to at least another, adjacent pedicle screw assembly in creating some stability to the spinal column of the patient. In one aspect, the rod  30  may inserted into a through bore  40  (discussed in more detail below). In one aspect, the rod  30  may be lowered into the through bore  40  by passing the rod  30  through the threaded bore  42  (discussed in more detail below). Therefore, in one aspect of this disclosure, the pedicle screw system  10  may be a top-loaded pedicle screw. 
         [0024]    Interfitted into the shank top  20  is a head  32  that is comprised of a main body  34  that is generally arcuate and has an outer flange  36 . As can be seen, the outer surface  38  (shown in  FIG. 4 ) of the main body  34  is shaped to be compatible with the interior surface  22  of the shank top  20  so that the head  32  can move with a poly-axial motion with respect to the shank top  20  and, correspondingly, to the screw  12 . This is one aspect in which this disclosure differs from what is taught in the prior art. As discussed above, prior art systems have a screw that rotates about the shank top. However, in this aspect of this disclosure, the shank top  20  and the screw  12  are in a fixed relationship. Rather, it is the interfitted head  32  that enables poly-axial motion. Again, the head  32 , like the screw  12 , can be a sintered material such as cobalt/chrome. 
         [0025]    In one aspect as illustrated in the figures, the outer surface  38  of the main body  34  is spherical as is the interior surface of the shank top  20  so as to accommodate the poly-axial movement. One of ordinary skill in the art would readily recognize that shapes other than spherical may be used to accommodate the poly-axial movement. 
         [0026]    The head  32  has the through bore  40  to allow the rod  30  to pass therethrough for the purpose previously described. The through bore  40  is oriented about normal to the main longitudinal axis of the screw  12 . Head  32  also includes a threaded bore  42  having a main axis generally parallel to or even coaxial with the main longitudinal axis of the screw  12 . The threaded bore  42  includes threads  44  leading up to the outer flange  36 . In one aspect of this disclosure, the threads  44  may be dovetail threaded. When the threads  44  are dovetail threaded, it may mate with a locking element (described in more detail below) which may also be dovetail threaded. 
         [0027]    A locking element is thus used to lock the rod  30  to the head  32  such that the rod  30  moves along with the head  32  as the latter is poly-axially moved with respect to the shank top  20 . In one aspect of the present disclosure, the locking element is a set screw  46  (shown in  FIG. 4 ) having threads  48  that mesh with the threaded bore  42  so that the set screw  46  can be screwed into the threaded bore  42 . While a set screw  46  is certainly feasible as the locking element, it can be seen that other devices can be used in place of the set screw to lock the rod  30  to the head  32 . As alluded to above, in one aspect of this disclosure, the locking element may be dovetail threaded. When the locking element is dovetail threaded, it may mate with a dovetail threaded thread  44 . 
         [0028]    The pedicle screw system  10  may include a base  13 . In one aspect, the base  13  may have four flat surfaces such that a cross-section of the base  13  may be rectangular. In another aspect, the base  13  may be cylindrical such that the cross-section of the base  13  may be circular. One of ordinary skill in the art would readily recognize that other shapes of the base  13  may be used. 
         [0029]    Turning now to  FIG. 2 , there is shown a front view of the pedicle screw system  10  of the present disclosure.  FIG. 2  illustrates one of the flat surfaces  26  of the shank top  20  that facilitate the function of screwing the screw  12  into the vertebral pedicle of a patient and, again the flat surfaces  26  are oriented in one position in  FIG. 2 ; however, it can be seen that the flat surfaces may be in other orientations while maintaining their separation at 180 degrees. 
         [0030]      FIG. 2A  is a cross-sectional view of the present pedicle screw system  10  taken along the line  2 A- 2 A of  FIG. 2  and illustrates an optional feature of the present disclosure. That optional feature is a clip  50  that can be positioned within the interior of the head  32 . The clip  50  can be a relatively flexible member that allows the physician to simply snap the rod  30  into the head  32  to temporarily hold the rod  30  in position while other activities are being conducted during the surgery. 
         [0031]    In one aspect as illustrated in  FIG. 2A , the clip  50  can be seen to be U-shaped with a pair of ends  52  facing the set screw  46  forming an opening  54 . As such the insertion of the rod  30  (shown in  FIG. 1 ) flexes the ends  52  outwardly so that the rod  30  passes through the opening  54  in a snap-in manner to seat the rod  30  within the head  32 . Accordingly, the presence of the clip  50  is a convenience to the physician in carrying out the overall operation. The clip  50  may be designed so it also contacts the inner surface of the shank top  20  (shown spherically), thus causing a friction contact when the set screw  46  engages the rod  30 . In one aspect of this disclosure, an outer edge of the clip  50  may have a shape similar to gear teeth around the edge of the clip  50 . In this aspect, the gear teeth may be in contact with the shank top  20 . 
         [0032]    Turning then to  FIG. 3 , there is shown a top view of the pedicle screw system  10  of the present disclosure and illustrating, again, the flat surfaces  26  along with the upper surface of the set screw  46  with an indentation  54  that is shaped to receive a tool manipulated by a physician to screw the set screw  46  into the head  32 . 
         [0033]    Turning to  FIG. 4 , taken along with  FIG. 1 , there is a perspective view of the pedicle screw system  10  of the present disclosure and, as can be seen, the set screw  46  has been screwed into the head  32 . The progress of the set screw  46  and its insertion into the head  32  may serve two purposes. First, the insertion of the set screw  46  forcefully presses against the rod  30  to stabilize and hold the rod  30  firmly affixed to the head  32  and secondly, the insertion of the set screw  46  serves to expand the threaded bore  42  to, in turn, expand the outer surface  38  of the main body  34  of the head  32  so that the outer surface  38  forcefully engages the interior socket  22  of the shank top  20 , thus locking the head  32  into position within the shank top  20 . In addition, the force drives the rod  30  into the clip  50 , if present, causing additional locking between the head  32  and the shank top  20 . 
         [0034]    Accordingly, the dimensions of the set screw  46  and threaded bore  42  are predetermined so that the expansion of the main body  34  by the insertion of the set screw  46  into that threaded bore  42  is sufficient to engage and lock the head  32  within the shank top  20 . 
         [0035]    As such, the pedicle screw of the present disclosure is modular, that is, the head is readily and easily disconnected from the socket without damage to any of the components. As such, the connection is permanent enough to perform surgical expectations but simple enough to take apart wherein the pieces or components could be interchanged in the operating room. The head  32  cannot be disconnected with the rod  30  in place. 
         [0036]      FIG. 5  shows a method  500  for inserting the pedicle screw  10  into a vertebrae, according to one aspect of this disclosure. The method  500  may begin at block  502 . At block  502 , the pedicle screw  10  may be inserted into a desired vertebrae pedicle. For example, the desired vertebrae pedicle may be a vertebrae pedicle needing to be aligned. After block  502  is completed, the method  500  may proceed to block  504 . 
         [0037]    At block  504 , the rod  30  may be loaded into the through bore  40  of the pedicle screw  10 . The rod  30  may be inserted in any suitable manner. For example, in one aspect of this disclosure, the rod  30  may be top loaded into the pedicle screw  10 . In this aspect, the rod  30  may be lowered into the through bore through the threaded bore  42 . In another aspect, the rod  30  may be inserted directly into the through bore, skipping the open channel. After block  504  is completed, the method  500  may proceed to block  506 . 
         [0038]    At block  506 , the pedicle screw  10  may be adjusted to properly accept the rod  30 . For example, the curvature of the rod  30  may require that the head of the pedicle screw  10  be oriented in a certain manner to properly align the spine. One of ordinary skill in the art would readily recognize that other adjustments may be needed to properly accept the rod  30  to align the spine. After block  506  is complete, the method  500  may proceed to block  508 . 
         [0039]    At block  508 , the rod  30  may be locked to the pedicle screw  10 . For example, the set screw  46  may be inserted into the threaded bore  42 . The set screw  46  may apply a downward force to the rod  30 , which in turn may apply an outward force to the head  32 . The head  32  may then press against the shank top  20 , locking the head  32  in place. After block  508  is completed, the method  500  may end. 
         [0040]    One of ordinary skill in the art would readily recognize that method  500  may be used with any number of pedicle screws  10 . For example, a plurality of screws may be used to hold the  30  to properly align the spine. 
         [0041]      FIG. 6  shows a perspective view  60  of two consecutive vertebrae and two pedicle screw assemblies  10 , according to one aspect of this disclosure. As shown in  FIG. 6 , each of the vertebrae has a pedicle screw assembly  10  coupled to it. After each pedicle screw  10  is coupled to the respective vertebrae, the rod  30  may be inserted into the head  32  for each pedicle screw assembly  10 . The rod  30  may be inserted into the heads by lowering the rod through the opening. The rod  30  may serve to align the vertebrae. After the rod  30  has been inserted into the heads  32 , a locking element may be inserted into the threaded bore  42 , which may lock both pedicle screw assemblies  10 . 
         [0042]      FIG. 7A  shows another design of a head  70 , according to one aspect of this disclosure. In this aspect, the head  70  may include at least one angled surface  72 . In one aspect of this disclosure, the head  70  may include two angled surfaces  72  facing the through bore  40 . The head  70  may also include a slot  74 . The slot  74  may be formed in the inner surface of the head  70 . Therefore, when the set screw  46 , for example, is tightened, the set screw  46  not only spreads the outer surface  38  of the head  70 , via the rod  30 , to lock it, but the slot  74  may spread even further to assist in the locking. In this aspect, the head  70  may not include a clip  50 . 
         [0043]      FIG. 7B  shows a side view of the head  70 , according to one aspect of this disclosure. As shown in  FIG. 7A , the slot  74  is center aligned in the head  70 . One of ordinary skill in the art would readily recognize that the slot  74  may be located in other positions in the head  70 . 
         [0044]      FIG. 7C  shows a cross-sectional view of the head  70  taken along the A-A line in  FIG. 7B , according to one aspect of this disclosure. This cross-sectional view of the head  70  shows two angled surfaces  72 . In this aspect, the two angled surfaces  72  are opposite each other. However, one of ordinary skill in the art would readily recognize that other relative positions of the two angled surfaces  72  may be possible. Additionally, one of ordinary skill in the art would also recognize that any number of angled surfaces  72  may be used. 
         [0045]    While the present disclosure has been set forth in terms of a specific aspect or aspects, it will be understood that the pedicle screw assembly herein disclosed may be modified or altered by those skilled in the art to other configurations. Accordingly, the disclosure is to be broadly construed and limited only by the scope and spirit of the claims appended hereto.