BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows perspective view of a bone plate with a plurality of holes and bone screws extending through the holes, wherein the holes include both compression features and locking features for the bone plate;
FIG. 2 shows a perspective view of an alternative embodiment of the bone plate and bone screws of FIG. 1;
FIG. 3 shows a perspective view of another alternative embodiment of the bone plate and bone screws of FIG. 1;
FIG. 4A shows a perspective view of an embodiment of a hole for the bone plate of FIG. 1;
FIG. 4B shows a cross-sectional view of the bone plate and hole of FIG. 4A;
FIG. 5A shows a perspective view of an alternative embodiment of a hole for the bone plate of FIG. 1;
FIG. 5B shows a cross-sectional view of the bone plate and hole of FIG. 5A;
FIGS. 6A-6C show three perspective views of a bone screw being inserted into the hole of FIG. 4A in a locking fashion;
FIGS. 7A-7B show alternative positions for engagement of a bone screw with the hole of FIG. 4A;
FIGS. 8A-8C show three perspective views of a bone screw being inserted into the hole of FIG. 4A in a compression fashion;
FIG. 9A shows an alternative embodiment of a bone screw having a detachable cam;
FIG. 9C shows the detachable cam positioned on the bone screw of FIG. 9A;
FIGS. 10A-10C show three perspective views of the bone screw of FIG. 9C being inserted into the hole of FIG. 5A using rotation of the detachable cam to lock the cam to the bone plate;
FIG. 11 shows a tool configured to rotate the detachable cam of FIG. 9A within a bone plate; and
FIGS. 12A-12C show three perspective views of the bone screw of FIG. 9C being inserted into the hole of FIG. 5A in a self-locking manner.
DESCRIPTION
With general reference to FIG. 1, a cam/compression bone plate 20 comprises an outward facing surface 22 and a bone facing surface 24 opposite the outward facing surface 22. The bone plate may be elongated in shape such that it defines a central longitudinal axis 21 extending across the length of the elongated plate. A plurality of holes 26 extend through the plate from the outward facing surface 22 to the bone facing surface 24. The holes 26 are generally provided along the longitudinal axis 21, but may also be positioned elsewhere on the plate 20. Each of the plurality of holes is configured to receive a bone screw 28. Both the bone plate 20 and the bone screws 28 are comprised of bio-compatible materials. Examples of such bio-compatible materials include titanium, nickel, cobalt chromium, and other bio-compatible materials as will be recognized by those of skill in the art.
The Bone Screw
As shown in FIGS. 1 and 2, each bone screw 28 generally comprises a head 30 with a threaded shaft 32 extending from the head 30. The screw head 30 includes a generally circular perimeter portion 31. A slot 34 is formed in the top of the screw head. The slot 34 is configured to receive the tip of a screw driving mechanism, thus allowing the screw 28 to be rotated and the threaded shaft 32 driven into the bone. The lower portion of the screw head 30 comprises a cupped surface 36. As will be recognized by those of skill in the art, the cupped surface 36 of the screw head 30 is configured to engage a compression surface on the bone plate.
In one embodiment of a bone screw 28 configured for use with the bone plate 20 described herein, at least one cam member 40 is provided on the screw head 30. The cam member 40 is generally provided as a crescent-shaped protrusion on the cupped lower surface 36 of the screw head, just below the perimeter 31 of the head 30. However, the cam member 40 may take any number of different forms and shapes. For example, the cam member 40 may comprise a small curved protrusion spanning less than thirty degrees around the cupped surface 36, as shown in FIG. 1.
Several other embodiments of a cam member positioned on the head of a bone screw are shown in FIGS. 2 and 3. In one embodiment shown in FIG. 2, the cam member 41 extends more than 90 degrees, but less than 360 degrees around the cupped surface of the bone screw. In another embodiment shown in FIG. 2, the cam member 42 is larger than the cam of FIG. 1, and protrudes farther from the lower cupped surface of the head. In addition, the cam member 42 extends between 45 degrees and 90 degrees around the head 30. In yet another embodiment shown in FIG. 2, the head 30 of the bone screw comprises two cam members 43, 44. The two cam members 43, 44 are directly opposed to one another on the cam head 30. In this embodiment, the two cam members 43, 44 each extend approximately forty-five to ninety degrees around the head 30.
Another embodiment where the head 30 includes two cams is shown in FIG. 3. In this embodiment, the cams 45, 46 are directly opposed to each other, with each cam extending between ninety and one hundred eighty degrees around the screw head 30. In this and other embodiments, each cam 45, 46 may extend around the head 30 in a helical fashion or may be level and parallel with perimeter 31 of the screw head. In any event, the exact shape, size, and configuration of the cam 40 will depend on the type of hole and associated cam slot that the bone screw 28 is configured for use with.
Bone Plate Holes
The configuration of holes in the bone plate 20 and associated cam slots are now described with reference to FIGS. 4A and 4B. Each hole 26 includes an upper edge 50 and a lower edge 54. The upper edge 50 begins an upper portion 52 of the hole 26, and the lower edge 54 ends a lower portion 56 of the hole 26. A compression surface 60 (also referred to herein as a “compression ramp”) is provided in the upper portion 52 of the hole and generally encircles the upper portion of the hole.
The compression surface 60 is cup-shaped, resulting in an arced compression surface. In other words, if a cross-section of the hole 26 is taken along the plane parallel to the axis of insertion for the bone screw, the compression surface will generally appear as a curved line along the side of the hole, and such line generally moves toward the center of the hole from top to bottom (see, e.g., FIG. 4B). Accordingly, the compression surface 60 is configured to engage a screw head 30, and particularly the cupped lower surface 36 of the screw head. As will be recognized by those of skill in the art, the engagement of the compression surface 60 of the bone plate 20 and the cupped surface 36 on the head of a bone screw 28 is operable to provide compression to a fractured bone. In addition, the compression surface 60 is provided on at least two directly opposite sides of the hole 26 along the central axis 21, or an axis parallel thereto. This allows the plate 20 to provide compression in one of at least two directly opposite directions. In the disclosed embodiment, the compression surface 60 substantially surrounds the hole 20, allowing the compression plate to provide compression in any of numerous directions parallel to the plane of the plate.
With continued reference to FIGS. 4A and 4B, it can be seen that at least one cam path 70 is formed in the hole 26. The at least one cam path 70 is cut into the compression surface 60, disrupting the continuity of the compression surface 60. The at least one cam path 70 includes a mouth 72 formed in or near the upper edge 50 of the hole 26. The mouth 72 of the cam path 70 feeds into a groove 74 that winds around the compression surface 60 in a helical fashion. The groove 72 generally extends less than one complete turn (i.e., less than 360 degrees) around the compression surface 60. The cam path 70 is configured to receive the cam provided on the head of the bone screw 28.
As shown in FIG. 4A, the hole 26 may include more than one cam path 70. Two cam paths 70 are provided in the embodiment of FIG. 4A. The mouths 72 of the two cam paths are provided directly opposite each other on the upper edge 50 of the hole 26. The grooves 74 extending from these mouths 72 do not intersect, but wrap around the compression surface 60 in a helical fashion. While the total span of the combined grooves may be more than 360° within the hole 26, no single groove 74 wraps around the compression surface more than 360°. In the embodiments providing more than one cam path 70, either cam path may be selected to lock the screw to the plate 20. Furthermore, in some embodiments where a screw 26 with multiple cams is used (e.g., see FIG. 3), each cam on the screw head may engage one of the cam paths 70 on the bone plate 20. In yet other embodiment, either cam on a screw head may engage one of the cam paths on the bone plate.
The hole 26 on the bone plate 20 may be provided in various sizes. In FIGS. 4A and 4B the hole 26 is generally elliptical in shape with two cam paths 70 provided within the hole 26. However, one of skill in the art will recognize that the hole itself may be configured in various shapes and sizes. For example, in FIG. 1 the holes 26 are elliptical in shape but include only a single cam path. In FIG. 2, holes 26 of differing sizes are shown, including a round hole with two cam paths. In another embodiment, a circular hole may be even larger in order to allow for compression by a screw in one of several directions, including laterally or longitudinally and/or increments in between.
Another alternative embodiment of a hole configured for use with the cam/compression plate 20 is shown in FIGS. 5A and 5B. In this embodiment, two opposing cam paths 70 are provided in the hole 26, but the cam paths 70 are flat instead of helical. Accordingly, the cam paths 70 are parallel with the upper surface 22 of the plate 20. The cam paths 70 are provided at the lower end of the compression surface 60, and do not otherwise cut into the compression surface 60. Each cam path includes a groove 74 of constant size that extends about 180° around the hole 26. A small mouth 72 that leads to the groove is provided where the opposing cam paths meet. Because the cam paths 70 of FIGS. 5A and 5B are flat, the cam paths are only configured to engage small cams or cams of parallel non-helical configuration provided on a screw head. In addition, the flat configuration of these cam paths may facilitate a cam being locked in place when the screw head moves a sufficient distance within the hole such that the cam snaps into the cam path. One of skill in the art will recognize that numerous other variations cam paths are possible in addition to those shown in FIGS. 4A-5B.
Locking Between Bone Screw and Bone Plate
FIGS. 6A-6C show a bone screw 28 being locked to a bone plate 20. In FIG. 6A, the cam 40 is shown resting at the mouth 72 of the cam path on the bone plate 20. After the cam 40 enters the mouth 72 of the cam path, the cam 40 follows the groove 74 as the bone screw 28 continues to rotate. In FIG. 6B, the bone screw 28 has been rotated such that the cam 40 is engaging the groove of the cam path and the rear portion of the cam 40 is entering the cam mouth 72. Then, in FIG. 6C, the bone screw 28 has been further rotated such that the cam 40 is fully engaging the cam path and has passed through the cam mouth 72. As the cam of the bone screw 28 reaches the end portion of the cam path 70, the head 30 of the bone screw is locked to the bone plate 20. Depending upon the size and shape of the cam, and the associated cam path, locking between the screw head 30 and the plate 20 may be achieved over a relatively short rotational distance or a longer rotational distance. For example, cam paths configured to engage a relatively thick cam that extends a relatively short distance across the head of the bone screw (e.g., 10°) will typically lock much faster than longer cams with a gradual taper that extend a relatively long distance across the head of the screw (e.g., 180°).
FIGS. 7A and 7B show an embodiment where the hole 26 includes two cam paths, 71A and 71B. Accordingly, two mouths 73A and 73B are shown at the start of the cam paths 71A, 71B. In FIG. 7A, the bone screw 28 has been placed in the hole 26 such that the cam 40 will enter the mouth 73A and travel along cam path 71A. Similarly, in FIG. 7B, the bone screw 28 has been placed in the hole 26 such that the cam 40 will enter the mouth 73B and travel along cam path 71B. Accordingly, the embodiment of FIGS. 7A and 7B provides the surgeon with two options for locking a bone screw 28 to a plate 20 on opposite sides of the hole.
Compression
Although a dual cam path elliptical hole 26 is shown in FIGS. 7A and 7B as used for a locking operation, the same hole 26 may also be used for a compression operation. FIGS. 8A-8C show such a compression operation using a dual cam path elliptical hole 26. In FIG. 8A, the bone screw 28 has been positioned along the right side of the hole with the cupped surface 36 of the screw head 30 positioned at the top of the compression ramp 60. As the bone screw 28 is driven into the bone, the cupped surface 36 of the screw head 30 is driven along the compression ramp into more complete engagement with the compression ramp 60. During this action, the bone plate 20 is pulled to the right as a result of the head being forced against the compression ramp. Movement of the bone plate 20 to the right can be seen by the position of the bone plate relative to screw centerline 66 and original hole line 68. The screw centerline 66 shows the center axis of the screw as it is driven into the bone. The original hole line 68 shows the original position of the right side of the hole before the screw is driven completely into the hole. As shown in FIGS. 8B and 8C, as the screw 28 is driven into the hole, the hole 26 and associated bone plate 20 moves further to the right relative to the screw 28.
In FIG. 8C, the screw head 30 has been driven further into the hole 26, and the cupped surface 36 fully engages the compression ramp 60. In this position, the action of the screw head against the compression ramp 60 has pulled the compression ramp and bone plate further to the right. Accordingly, this action may be used to compress a bone fracture where an opposite end of the plate 20 has been secured to the bone. For example, assuming a fracture is located to the left of the hole 26 shown in FIGS. 8A-8C, and the bone plate 20 is first secured to the bone portion to the left of the fracture, the action of FIGS. 8A-8C pulls the bone plate and bone to the right, thus compressing the bone at the location of the fracture.
Based on the foregoing description, it will be recognized that the bone plate described herein may be used as either a locking plate or a compression plate. In particular, a given hole 26 in the bone plate 20 includes both a compression ramp 60 configured to engage the head of a compression screw and a cam path 70 provided on the compression ramp, the cam path 70 configured to engage a cam on the head of a locking screw. With such an arrangement, a surgeon may use a single bone plate 20 as either a locking plate or a compression plate, depending upon the type of screw selected by the surgeon. One of skill in the art will also recognize that the bone plate described herein may also be used as a hybrid plate where some limited compression is offered as well as locking. For example, if a locking screw is used, but the locking screw is located on the edge portion of a hole during insertion, engagement of the cupped lower surface of the locking screw with the compression ramp of the hole will offer compression features before the cam on the locking screw enters the cam path and locks to the bone plate.
Detachable Cam
FIGS. 9A-12C show an embodiment where the bone screw 28 includes a detachable cam 80. As shown in FIG. 9A, the detachable cam 80 is C-shaped and includes an interior perimeter 82 and an exterior perimeter 84. The shape of the detachable cam 80 defines an opening 86 to the interior perimeter 82.
The bone screw 28 configured for use with the detachable cam 80 is shaped similar to other bone screws described herein, and includes a screw head 30 and a threaded screw shaft 32. The screw head includes a slot 34 formed in the top of the head 30 and a cupped lower surface 36. Unlike the other bone screws described herein, the bone screw of FIG. 9A includes a circular groove 90 provided in the cupped lower surface 36.
The circular groove 90 of the screw head 30 is configured to receive the detachable cam 80, as indicated by arrow 92 in FIG. 9A. In particular, the screw head 30 is inserted into the opening in the cam 80, causing the interior perimeter 82 of the cam to engage the circular groove 90 on the screw head. As the cam 80 is inserted onto the screw head 30, the cam slightly deforms as the ends of the C-shaped cam slide across the full diameter of the circular groove 90, and then the cam 80 snaps into place in the groove 90, thus securing the cam 80 within the groove 90, as shown in FIG. 9B. Although the cam 80 is held snugly within the groove 90, the cam 80 may still be rotated around the groove 90 when appropriate force is applied to the cam 80.
The bone screw of FIG. 9A including a detachable cam 80 is configured for use with a bone plate 20 having a hole 26 with a cam path 70 such as that shown in FIGS. 5A and 5B, where the cam path 70 formed in the hole 26 is parallel to the outward facing surface 22 of the bone plate 20.
FIGS. 10A-10C show the bone screw 28 of FIG. 9B being inserted into a hole 26 with a parallel cam path as shown in FIGS. 5A and 5B. Starting with FIG. 10A, the bone screw 28 is shown with the shaft 32 extending the through the hole 26 in the bone plate 20. As the bone screw 28 is rotated, the head 30 moves deeper into the hole, as shown in FIG. 10B. When the cam 80 is adjacent to the cam path 70, the cam 80 may be rotated within the groove 90 in the screw head 30 as shown in FIG. 10C. When the cam 80 is rotated in the screw head 30, the cam 80 fully engages the cam path 70 in the bone plate 20 such that the opening 86 is not positioned within the cam path 70, but is instead centrally located within the hole 26, as shown in FIG. 10C. Rotating the cam 80 in this fashion causes the cam 80 to fully engage the cam path 70 and locks the cam 80 and associated screw 26 in place upon the bone plate 20.
FIG. 11 shows a tool that may be used to rotate the detachable cam 80 within the cam path 70 of the bone plate 20. As shown in FIG. 11, the tool 100 includes a top handle 102 connected to one end of a shaft 104. The opposite end of the shaft 106 is connected to a foot 106. The foot 106 includes a slot finger (not shown) and a cam finger 108. The slot finger is a cylindrical post configured to rotate within the slot 34 on the top of the bone screw 28. The cam finger 108 is configured extend along the cup shaped surface 36 on the head of the bone screw 28 and be positioned within the opening 86 formed by the detachable cam 80. From this position, when the handle 102 of the tool 100 is rotated, the cam finger 108 contacts an end of the cam and forces the cam 80 to rotate within the groove 90 of the screw head and within the cam path 70 of the bone plate 20. Rotation of the cam 80 causes the cam to fully engage the cam path, thus locking the cam 80 and associated screw 26 in place within the bone plate 20.
FIGS. 12A-12C show an alternative embodiment where the detachable cam 80 is self-locking within the bone plate 20. In this embodiment, the cam 80 is comprised of a resilient compressible material, such as ultra high molecular weight polyethylene. Starting with FIG. 12A, the bone screw 28 is shown with the shaft 32 extending the through the hole 26 in the bone plate 20. As the bone screw 28 is rotated, the head 30 moves deeper into the hole, as shown in FIG. 10B. As the head 30 moves even deeper into the hole, the cam 80 is deformed as it is compressed along the compression surface 60 of the hole. When the head 30 becomes fully engage in the hole, the detachable cam 80 snaps into place within the cam path 70, thus locking the cam 80 and associated screw 26 in place within the bone plate 20. In this embodiment, the opening 86 is already properly positioned away from the cam path 70, and there is no need to further rotate the cam 80.
In yet another alternative embodiment, the detachable cam may be inserted into the groove on the head after the screw is fully engaged within the hole of the plate. In this embodiment, the screw may be used to provide compression with the plate, as described previously. After the screw is fully engaged in the hole, the groove 90 is aligned with the parallel cam path 70. The detachable cam is then inserted in the hole and slid into the groove. When the detachable cam is placed in the groove, the cam will also slide into engagement with the cam path. Thereafter, the detachable cam may be rotated to further secure the detachable cam within the cam path. In this and other embodiments as described above with a detachable cam, the bone plate may be used as a compression plate, a locking plate, or a combination thereof.
Although the present invention has been described with respect to certain preferred embodiments, it will be appreciated by those of skill in the art that other implementations and adaptations are possible. For example, one of skill in the art will recognize that cams and associated cam paths of different sizes and shapes from those disclosed herein may be used. Moreover, there are advantages to individual advancements described herein that may be obtained without incorporating other aspects described above. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred embodiments contained herein.
Patent Application
20080015592
