Abstract:
A surgical plate and process for preventing screw backout of repaired bones. At least one pawl is provided on a surgical plate adjacent to a screw hole. A screw having a ratchet wheel is inserted through the hole and screwed into the bone. The pawl engages the ratchet wheel to prevent rotational movement of the screw to prevent the screw from backing out. In a preferred embodiment, a pawl plate comprising a base portion is rigidly connected to the surgical plate and a torsion bar is pivotally connected to the base portion. The pawl is positioned at the end of the torsion bar. In the preferred embodiments, several of these special screw holes with pawls, and several screws (each with a ratchet wheel) are used in bone repair.

Description:
The present invention relates to surgical implants, and more specifically to surgical plates. 
     BACKGROUND OF THE INVENTION 
     Surgical plates, along with bone screws, are commonly used in the process of repairing broken bones in order to provide a distributed area of compression against the bones being clamped. Also, surgical plates are commonly used for spinal fusion or stabilization. Typically, a surgeon first places a surgical plate having screw holes onto a bone. He then drills screw holes into the bone with a drill. Then the surgeon will screw the plate onto the bone. 
     A problem that currently exists is that over time the screws may become loose and back out of the bone. This usually causes extreme discomfort to the patient and may lead to more serious health consequences. 
     What is needed is a surgical plate that is able to prevent screw backout. 
     SUMMARY OF THE INVENTION 
     The present invention provides a surgical plate and process for preventing screw backout of repaired bones. At least one pawl is provided on a surgical plate adjacent to a screw hole. A screw having a ratchet wheel is inserted through the hole and screwed into the bone. The pawl engages the ratchet wheel to prevent rotational movement of the screw to prevent the screw from backing out. In a preferred embodiment, a pawl plate comprising a base portion is rigidly connected to the surgical plate and a torsion bar is pivotally connected to the base portion. The pawl is positioned at the end of the torsion bar. In the preferred embodiments, several of these special screw holes with pawls, and several screws (each with a ratchet wheel) are used in bone repair. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a preferred embodiment of the present invention. 
     FIG. 2 shows a preferred plate. 
     FIG. 3 shows a cutout side view of the preferred plate of FIG.  2 . 
     FIG. 4 shows a perspective view of a preferred plate. 
     FIG. 5 shows a bottom view of a preferred plate. 
     FIG. 6 shows a top view of a preferred pawl plate. 
     FIG. 7 shows a side view of a preferred pawl plate. 
     FIG. 8 shows a preferred plate with a pawl plate attached. 
     FIGS. 9-11 show a preferred method for drilling a hole into a bone. 
     FIGS. 12-16 show the operation of a preferred embodiment of the present invention. 
     FIGS. 17-18 show the operation of a preferred embodiment of the present invention utilizing a preferred screw. 
     FIGS. 19-20 show the operation of a preferred embodiment of the present invention utilizing another preferred screw. 
     FIGS. 21-22 show another preferred embodiment of the present invention. 
     FIG. 23 shows another preferred embodiment of the present invention. 
     FIGS. 24-31 show other preferred embodiments of the present invention. 
     FIG. 32 shows a preferred embodiment of the present invention being used to repair a broken bone. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A top view of a first preferred embodiment of the present invention is shown in FIG.  1 . Bottom portion  4  of pawl plate  1  is rigidly connected to surgical plate  9 . Six hex screws  7 A- 7 F are inserted through holes  10  in surgical plate  9 . Each hex screw has a ratchet wheel  8 . Torsion bars  5 A- 5 F of pawl plates  1  engage the ratchets on ratchet wheels  8  to prevent counter-clockwise rotation of hex screws  7 A- 7 F after surgical plate  9  has been screwed into the bone of a patient. 
     Fabricating the First Preferred Embodiment 
     FIG. 2 shows a top view of surgical plate  9 . FIG. 3 shows a cutout side view of surgical plate  9  and FIG. 4 shows a perspective view of surgical plate  9 . FIG. 5 shows a bottom view of surgical plate  9 . In the first preferred embodiment, surgical plate  9  is stainless steel and is cast by sintered powder metallurgy. As shown in FIG. 2, surgical plate  9  is approximately 1.8 inches long and approximately 0.7 inches at its widest point. As shown in FIG. 3, surgical plate  9  is slightly curved and is approximately 0.1 inch thick. As shown in FIG.  1  and FIG. 4, surgical plate  9  has three recesses  11  cut into the top of the plate. Recesses  11  are preferably approximately 0.02 inches deep. 
     Six holes  10  are drilled through surgical plate  9 . Preferable, holes  10  are wider at the top of surgical plate  9  than they are at the bottom. In the preferred embodiment hole  10  is approximately 0.2 inches in diameter across the top of surgical plate  9  and approximately 0.14 inches in diameter across the bottom of surgical plate  9 . Preferably, the walls of hole  10  are slightly curved, as shown in FIG.  3 . 
     As shown in FIGS. 3 and 5, the bottom of surgical plate  9  preferably has seven “V” shaped compression ridges  13 . When surgical plate  9  is screwed onto a bone, compression ridges  13  are able penetrate soft tissue that may be covering the bone and grip solid bone underneath the soft tissue. 
     FIG. 6 shows a top view and FIG. 7 shows a side view of pawl plate  1 . Pawl plate  1  has bottom portion  4  and torsion bars  5 A and  5 B. A preferred pawl plate  1  is approximately 0.02 inches thick. As shown in FIG. 7, pawl plate  1  is slightly curved so that it fits appropriately into recess  11  (FIG.  4 ). 
     As shown in FIG. 8, each pawl plate  1  is fitted into each recess  11 . Bottom portions  4  are then rigidly bond to surgical plate  9 . In the preferred embodiment, bottom portions  4  are brazed to surgical plate  9 . 
     Utilization of the First Preferred Embodiment Drilling the Holes 
     FIGS. 9-10 illustrate a preferred method for drilling holes into the bone. FIG. 9 shows a cutout side view of surgical plate  9  positioned on top of bone  20 . Note that the curvature of plate  9  conforms to the curvature of bone  20 . Also “V” shaped compression ridges  13  assist in the gripping of bone  20 . 
     In the preferred embodiment, drill bushing  28  is connected to spring  30 . Spring  30  is connected to drill chuck  26 , which is connected to drill  22 . Drill bit  24  is inserted inside and rigidly held by drill chuck  26  and extends through spring  30 . 
     As shown in FIG. 9, drill bushing  28  is positioned over hole  10  of surgical plate  9 . As shown in FIG. 10, drill bushing  28  is lowered so that it mates with hole  10  of surgical plate  9 . Drill bushing  28  aligns drill bit  24  so that it is properly directed through the center of hole  10  and into bone  20 . 
     As shown in FIG. 11, drill bit  24  is pressed downward and into bone  20 . As the hole is drilled, spring force from spring  30  helps keep bushing  28  properly positioned in hole  10  and keeps the axis of the drilled hole centered. 
     Securing the Plate onto the Bone 
     After the holes have been drilled into the bone, surgical plate  9  is securely fastened to the bone via screws  7 A- 7 F. FIGS. 12-16 illustrate how pawl plate  1  prevents screws  7 A and  7 B from backing out after they have been screwed into the holes in the bone. In FIG. 12, torsion bar  5 A is engaged with ratchet wheel  8  of screw  7 A so as to prevent counterclockwise rotation of screw  7 A and torsion bar  5 B is engaged with ratchet wheel  8  of screw  7 B so as to prevent counterclockwise rotation of screw  7 B. 
     In FIG. 13, screw  7 A has been turned clockwise ½ of a notch so that pawl  80  of torsion bar  5 A has been moved downward as it has ridden along a ratchet of ratchet wheel  8 . 
     In FIG. 14, screw  7 A has been turned clockwise another ½ of a notch so that torsion bar  5 A has snapped back upward and is in a position to prevent counterclockwise rotation of screw  7 A. In this manner, screw  7 A is continually tightened until it is tightly pressing plate  9  against the bone. Screw  7 A is prevented from backing out through unwanted counterclockwise rotation by pawl  80  of torsion bar  5 A engaging ratchet wheel  8  of screw  7 A. 
     In FIG. 15, screw  7 B has been turned clockwise ½ of a notch so that pawl  82  of torsion bar  5 B has been moved downward as it has ridden along a ratchet of ratchet wheel  8 . 
     In FIG. 16, screw  7 B has been turned clockwise another ½ of a notch so that torsion bar  5 B has snapped back upward and is in a position to prevent counterclockwise rotation of screw  7 B. In this manner, screw  7 B is continually tightened until it is tightly pressing plate  9  against the bone. Screw  7 B is prevented from backing out through unwanted counterclockwise rotation by pawl  82  of torsion bar  5 B engaging ratchet wheel  8  of screw  7 B. 
     In a similar fashion, screws  7 C- 7 D (FIG. 1) are all tightened. As described above, all screws are prevented from accidental unwanted backout by pawl plates  1 . 
     However, it may be desirable to eventually purposely remove a screw after it has been tightly secured against surgical plate  9 . For example, to intentionally unscrew screw  7 A, a surgeon would move pawl  80  of torsion bar  5 A downward to a position shown in FIG. 13 with a scalpel (or other sharp instrument). The surgeon could then merely turn the screw counterclockwise to back it out. 
     FIG. 32 shows a side view of two surgical plates  9  screwed into broken bone  100 . 
     Screw Types 
     FIGS. 17 and 18 illustrate the utilization of conventional ratchet screws with the present invention. It should be noted that holes  10  of plate  9  allow for screw  30  to be inserted through plate  9  in a variety of angles. In this manner, the surgeon can screw conventional ratchet screw  30  into the bone at the optimum angle. 
     FIGS. 19 and 20 illustrate another preferred embodiment in which ratchet screw  32  has bottom hemisphere portion  33 . As with conventional ratchet screw  30  shown in FIGS. 17 and 18, ratchet screw  32  can be inserted through plate  9  in a variety of angles. However, hemisphere portion  33  of ratchet screw  32  enables it to also achieve a more secure fit against the curved walls of hole  10 . 
     Holes with Dimpled Walls 
     FIG. 21 shows a side view and FIG. 22 shows a top view of a preferred embodiment of the present invention in which holes  10  have dimples  40  protruding from their walls. In this preferred embodiment, screw  32  is seated against dimples  40  when tightened down. By seating against dimples  40 , unwanted debris  50  (such as skin tissue or bone chips) will not accidentally get squeezed between screw  32  and the surgical plate. 
     While the above description contains many specifications, the reader should not construe these as limitations on the scope of the invention, but merely as exemplifications of preferred embodiments thereof. Those skilled in the art will envision that many other possible variations are within its scope. For example, although approximate measurements were given for the first preferred embodiment, the size of the plate could be easily modified to accommodate various bone sizes. Also, although FIG. 3 shows that surgical plate  9  is only slightly curved, the degree of curvature could be increased to have a plate that is more curved or eliminated to have a flat plate. Also, although it was stated that pawl plate  1  was brazed to surgical plate  9 , pawl plate  1  could be rigidly attached to surgical plate  9  utilizing other known methods, such as welding. Also, although it was stated that surgical plate  9  was cast from of stainless steel, surgical plate  9  could be made from other materials, such as titanium. Also, although FIG. 1 shows surgical plate  9  having a specific shape, it would be easy to modify the shape of the plate. For example FIGS. 24-31 show surgical plates having a variety of shapes. Also, although pawl plate  1  was shown in discussed in the above preferred embodiments, it would also be possible to torsionally connect a pawl directly to the surgical plate. For example, as shown in FIG. 23, pawl  90  is connected to torsion bar  60 , which has been welded to recess  70  of surgical plate  9  at its base  62 . Likewise, pawl  92  is connected to torsion bar  64 , which has been welded to recess  70  of surgical plate  9  at its base  66 . Also, the present invention can not only be used for human bone repair, but it can also be used for bone repair for animals. Also, in addition to the repair of a broken bone, the present invention may be used for the repair of a fractured bone, unstable vertebra and for spinal fusion. Accordingly the reader is requested to determine the scope of the invention by the appended claims and their legal equivalents, and not by the examples which have been given.