This application claims the benefit of U.S. Provisional Application Serial No.

60/681,879, filed May 17, 2005 titled "Axial Compressing Screw," and U.S. Provisional Application Serial No. 60/716,575, filed September 13, 2005 titled "Axial Bone Plate

Compressing Screw," the entire contents of each of which are hereby incorporated by reference.

BACKGROUND Fractures across the head, neck or intertrochanter regions of the femur, as well as fractures of other bones, such as the humerus, are fairly common. These fractures result in two portions of bone that need to be compressed and held together during the healing process. The bone fragments may be secured using a bone plate and/or a compression system.

There are many orthopedic fasteners designed to compress a fracture axially through rotation of the fastener into bone. As the fastener is rotated into the bone, a threaded portion at the distal tip or end of the fastener grips the far fragment of the bone. This tends to rotate the far fragment of bone as the fastener continues to advance until final compression is achieved. For example, a screw that is inserted into the head of a femur is typically advanced until the head of the screw contacts the near cortex. The continued turning of the screw in this example advances the screw and compresses the fracture. However, because the head of the screw should be tightened until it is flush with the bone it is entering, the distal tip of the screw often ends up past the most appropriate stopping point, and the fragment ends up slightly rotated. Another problem caused by rotating the distal screw tip past the optimal stopping point (the optimal stopping point is usually in about the middle of the bone) is that the screw tip can advance through the bone and protrude into the surface of the joint. Li this case, although the fracture may be reduced, the screw tip protrudes past the bone, potentially causing a myriad of other problems.

Some have attempted to solve this problem by inserting a screw to the proper depth in the far fragment and then placing a nut over the back end of the threaded shank and advancing the nut until the screw/nut construct compresses the fracture. This eliminates both the potential for twisting the far fragment out of place and for placing the tip of the screw in the wrong place. One problem with this approach, however, is that the nut is bulky, and when the remaining shank of the screw is cut, there is a sharp edge remaining which may

irritate soft tissue. This approach may also be difficult to use with a bone plate, if the use of one is desired.

Other attempts at solving this problem have been to provide an intramedullary nail, a threaded shank, a sleeve with internal threads that can move longitudinally along the threaded shank (so that the sleeve receives the shank in a threaded bore such that the threads of the shank cooperate with the threads of the internal bore), and a connector that connects the sleeve to the threaded shank. This design provides a maximum and a minimum implant screw length because the shank can be screwed into the sleeve (e.g., when almost all of the threads are engaged) or the shank can be extended almost completely from the sleeve (e.g., when very few threads are engaged). One problem with these types of designs, however, is that the rotation of the shank to the proper location and then the rotation of the sleeve onto the shank to the achieve the desired length of the overall screw can still cause the screw to extend past the optimal stopping point and/or over-rotate the far fragment. In other words, after the first rotation step (to place the screw) occurs, there is a second rotation step in which the sleeve is rotated down the screw shank. This second rotation step can cause the tip of the screw to continue to rotate deeper into bone and extend past the desired location. Even if the second rotation problem is solved (e.g., by turning the screw in one direction (clockwise) and the sleeve in the opposite direction (counter-clockwise)), there is still not provided a way to secure the sleeve to a bone plate. Thus, another problem that is not solved by the prior art is how to both compress a fracture and lock the compression screw through a locking plate. Typically, compression screws cooperate with an intramedullary nail. There may be instances, however, when using a bone plate is more desirable that using a rod or nail. Attempts at using bone plates to date have not been effective. Accordingly, it is desirable to provide a fastener for use in compressing fractures of bone that can advanced to the desired position and secured at the desired stopping point. It is also desirable to provide a fastener that can be used in combination with a bone plate.

SUMMARY Embodiments of the present invention provide an axial compression fastener system, comprising a fastener with a distal end with bone-engaging elements and a shank with collar- engaging threads, a collar adapted to cooperate with the fastener, the collar having a bore with internal threads that correspond to cooperate with the collar-engaging threads of the shank, wherein the bone-engaging elements are oriented in one direction and the collar-

engaging threads on the shank are orientated in an opposite direction. The collar of the fastener system also a threaded external portion, wherein the external threads of the collar are oriented in the same direction as the bone-engaging elements.

Methods for placing an axial compression fastener system are also provided. They include:

(a) providing a fastener having (i) a distal end with bone-engaging elements and (ii) a shank with collar-engaging threads;

(b) providing a collar adapted to cooperate with the fastener, the collar having (i) a bore with internal threads that correspond to cooperate with the collar-engaging threads of the shank and (ii) external threads;

(c) providing a structure to support the axial compression system;

(d) advancing the fastener through the structure to a desired position using a first directional turning motion;

(e) securing the collar onto the fastener using a second directional turning motion that is opposite the first directional turning motion; and

(f) securing the collar to the structure via the external threads using a third directional turning motion that is in the same direction as the first directional turning motion.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. IA shows a side view of an axial compression fastener system according to one embodiment of the present invention.

FIG. IB shows the system of FIG. IA in exploded perspective cross-sectional view. FIG. 2 shows an alternate embodiment of an axial compression fastener system. FIG. 3 shows a further embodiment of an axial compression fastener system having a floating retainer.

FIG. 4 shows a dual driver according to one embodiment of the present invention. FIG. 5 shows a spring loaded driver according to another embodiment of the present invention.

FIG. 6A shows a side view of a locking washer according one embodiment of the present invention.

FIG. 6B shows a top view of the locking washer of FIG. 6 A.

FIG. 7 shows a threaded collet according to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

FIGS. IA and IB show one embodiment of an axial compression fastener system according to certain embodiments of the invention. FIG. IA shows that system in an assembled position and FIG. IB shows the system in exploded perspective cross-sectional view. The system 10 of FIG. 1 includes fastener 12 with a distal end 14 and a proximal head 16. The distal end 14 has bone-engaging elements 18, which are typically threads, but may also be any other appropriate element that can secure fastener into bone. Elements 18 may be typical cortical or cancellous bone threads. They may be any appropriate size, shape, pitch or diameter, as long as they are able to secure fastener 12 into bone. Particularly preferred dimensions are 2.5 - 8 mm in diameter, with a threaded portion that extends about 10 to about 80 mm up the fastener 12, and even more preferably, about 16-48 mm up the length of fastener 12. The threads 18 are preferably right-handed threads, which means that as the fastener 12 is being inserted into bone, the fastener is turned to the right as the threads 18 advance into bone. It is possible, however, for threads 18 to be provided as left-handed threads if desired.

Fastener 12 also has a shank portion 20. Shank portion 20 typically begins where the bone-engaging elements 18 end, although in some embodiments, shank portion may include types of bone-engaging elements as well, hi a preferred embodiment, at least a portion of shank portion 20 has collar-engaging threads 22. It should be understood that shank portion 20 may also have one or more smooth portions, for example, located either before or after the collar-engaging threads 22. Threads 22 may be any appropriate size, shape, pitch or diameter, as long as they are adapted to cooperate with internal threads on collar, described below. It is particularly preferred that threads 22 be fine threads that are closer together and of a smaller diameter than the bone-engaging elements 18, although that is not essential to the invention. It is important, however, that the threads 22 be formed in the opposite direction than the direction of threads 18. In other words, if bone-engaging elements 18 are right- handed directional threads, then collar-engaging threads 22 should be left-handed directional threads, and vice versa. This is shown by arrows A and B of FIG. IA. The importance of the directional difference between threads 18 and 22 will be described in more detail below. The proximal head 16 may have an upper end with an internal receiver 24. Receiver

24 may be any size and shape that corresponds to the driver intended to be used to secure fastener at the desired depth in bone, for example a slot, a hex, or any other appropriate shape. It is preferred that proximal head (and preferably, the entire fastener 12) have an outer

diameter that is slightly less than the inner diameter of the collar 30 (described below) so that fastener 12 can be received by the collar.

Collar 30 is shown as having a distal end 32, a proximal end 34, and an internal bore 36. Bore 36 begins at distal end 32 and may or may not extend the entire length of collar to proximal end 34. Bore 36 has internal threads 38 that preferably begin at the distal end 32 and again, may or may not extend the entire length of internal bore 36. Internal threads 38 are designed to mate with collar-engaging threads 22 of shank 20. (If shank threads 22 are left-handed threads, then internal threads 36 will be left-handed receiving threads. If shank threads 22 are right-handed threads, then internal threads 36 will be right-handed receiving threads.)

Proximal end 34 of collar 30 has a head 40 that may have threads 42 adapted to cooperate and lock with a bone plate or an intramedullary nail or both. Threads 42 should preferably have a directional orientation that is the opposite orientation to that of the internal threads 38. For example, if internal threads 38 are left-handed threads, the head threads 42 of head should be right-handed threads.

Alternate embodiments of collar 30 have a head 40 that is non-locking, e.g., a spherical or non-threaded head. Proximal end 34 may also feature an internal receiver 44. Receiver 44 may be any size and shape that corresponds to the driver intended to be used to place collar 30. By providing fastener 12 having bone-engaging elements 18 that rotate in one direction and collar-engaging threads 22 that rotate in the opposite direction, the surgeon is able to rotate the fastener in a first direction (e.g., if the threads are right-handed threads, the fastener is rotated with a right-handed twist) in order to engage bone with the bone-engaging elements 18. Once the fastener is positioned where desired, the surgeon can then rotate the collar 30 in the opposite direction (e.g., if a right-handed twist was used to place the fastener, the collar can rotated down the fastener shank 20 using a left-handed twist) in order to seat the fastener 12 within the collar 30 at the desired length. This directional difference in the threads of the fastener allows the system 10 to be placed through a bone plate or intramedullary nail and inserted using turns in one direction to place bone-engaging elements 18, and then the collar 30 can be secured without forcing the distal tip of the fastener deeper into the bone. Additionally, it is believed that because the bone-engaging elements 18 achieve such a good purchase on bone, they are not loosened or twisted back out by the pressure in the other direction as the collar is being placed.

The following method will describe the placement and use of the axial compression fastener system to reduce a fracture of the femoral head. It should be understood, however, that the systems described herein may be used to reduce any appropriate bone fracture, and this description is not intended to be limiting. During surgery, the axial compression fastener system 10 may be placed through a locking plate. (It should be understood that the fastener may be used with an intramedullary nail, but for convenience and because it is preferred embodiment, use with a bone plate will be described, although this description is in no way intended to be limiting.) The bone plate is positioned on the patient's bone, and a step drill is used to bore a hole through the near and far cortex of the bone, or alternatively, the sub- chondral bone. The far cortex is bored to the minor diameter of the fastener (which is typically defined by the shank portion 20) and the near cortex is bored to accept the collar 30. The fastener is then inserted according to methods that are well known in the art until the distal tip 14 is at the appropriate position in the far cortex. In the preferred embodiment, the bone-engaging elements 18 are right-handed directional threads, so the fastener is preferably inserted using a right-hand turning motion.

Next, the collar 30 portion of the system 10 is then rotated so that it "seats" itself on the fastener. If the bone-engaging elements 18 are right-handed threads, then the collar- receiving threads 22 of the shank 20 will be left-handed threads, and thus, the collar will be turned using a left-handed turning motion. The collar 30 is turned until it is at the desired position, which is preferably the point at which the proximal end 34 of the collar contacts the bone plate. This turning will cause the collar 30 to rotate down the shank 20 of the fastener 12. Once in place, continued left hand turning of the collar will compress the fragments to the desired state. Finally, a right-hand turn of approximately ¹ A turn will lock the head of the collar to the bone plate using tapered right hand threads. In this example, if the bone-engaging elements are left-handed, then the collar- receiving threads 22 and internal threads of the collar 30 should be right-handed, and the threads 42 at the head of the collar should be left-handed.

Embodiments of the invention also includes a dual screw driver that has a larger portion for engaging the internal receiver 44 of the collar 30 and a smaller portion (perhaps running through the center of the large portion) that engages the internal receiver 24 of the fastener 12. The driver may have a latch that allows the two portions of the driver to be driven as one, or when disengaged, driven separately. The driver can drive the fastener 12 in one direction and the collar 30 in the opposite direction. If desired, driver may feature an

optional member that secures and holds the fastener 12 in place as the collar 30 is driven in the opposite direction.

FIG. 2 shows an alternate collar assembly 50 for use in axial compression. The collar 50 of FIG. 2 is a two-piece system that has a tapered head 52 and a threaded head 80. Once the fastener 12 is in place, the tapered head 52 is inserted over the proximal end 16 of fastener 12. The tapered head 52 has tapered or angled sides 54, a threaded through bore 58, an upper portion 60, and shoulders 62. hi use, the tapered sides 54 of collar 50 are intended to cooperate with a bone plate 70 that has an opening 72 with corresponding tapered or angled sides 74. The opening 72 also preferably has threading 76 at or near an upper area 78 of opening 72. Accordingly, when tapered head 52 is inserted into opening 72 of bone plate 70, the corresponding tapered sides 54 and 74 press together. The cooperating tapered or angled sides 54, 74 prevent the fastener 12 from rotating or being inserted at an angle; instead, the fastener may be rigidly affixed in place. They also help to draw the bone plate 70 tightly against the bone. If the plate is standing proud of the bone (e.g., there is a gap between the bottom of plate and the bone), the use of a tapered head 52 can help cinch the plate against bone.

Next, threaded head 80 is placed over tapered head 52 to provide the securing function. Threaded head 80 has a series of threads 82 on its outer periphery. Although the entire periphery is shown as threaded in FIG. 2, it is only necessary that there be provided enough threads 82 that will allow threaded head 80 to cooperate with the threading 76 of bone plate 70. Head 80 also has a through bore 84 that receives upper area 60 of tapered head 52. This allows the collar assembly 50 to be seated in the opening 72 of bone plate 70 (such that head 80 sits on shoulders 62), preferably to a depth that prevents fastener 12 and collar 50 from extending past the upper surface 71 of bone plate 70. According to the general concepts of the invention described above, the bone-engaging elements 18 of fastener rotate in one direction, and the threaded through bore 58 of the collar 50 should have threads that rotate in the opposite direction. This will allow the fastener to be seated in bone (and extend through the bone plate 70), while also allowing compression by rotation of the tapered head 52. Providing an embodiment that separates the collar 50 into two pieces helps to draw the bone plate to the bone, helps to secure the plate 70 tightly against bone, and helps to hold the fastener in the desired angular position.

FIG. 3 shows an alternate embodiment of collar 50 that has a retaining ring 90. In this embodiment, tapered head 52 has a horizontal groove 92 on its outer surface 94 and threaded head 80 has a vertical groove 96 on its inner surface 98. (It should be understood, however, that either groove 92, 96 may be provided on either head 52, 80.) A retaining ring 90 is secured in place between the grooves 92, 96. Vertical groove 96 is preferably a tall groove (meaning that is has a height that is greater than that of ring 90 so that ring 90 can slide and be accommodated in multiple positions in the space 91 formed by grooves 92, 96). By providing a vertical groove 96 that can accommodate this "sliding" of retaining ring 90, independent movement of heads 52 and 80 is allowed, hi use, the taper 54 of head 52 can be inserted into a bone plate until it bottoms out or reaches the furthest distance into opening of the plate that it can extend. Then, because retaining ring 90 holds heads 52, 80 together but allows their independent movement due to its location in the space 91 formed by grooves, threaded head 80 can then be positioned so that it can engage the first of the threads of opening. By allowing the heads to be secured to one another, but yet "float" independently relative to one another, the threads of threaded head 80 can engage the threads of opening without head 80 being perfectly positioned because it can float to "find" the threads. In short, the threads of head 80 and plate do not have be lined up as perfectly as they would otherwise likely need to be. It should be understood that threaded head may have any desired shape, and that, although it shown as cylindrical, it could be tapered, or any other appropriate shape to cooperate with plate.

Although the collars 50 in FIGS. 2 and 3 are shown as two-piece structures, it should be understood that the tapered sides 54 (and threaded head 80) could be provided on a one- piece collar , such as that shown in FIG. 1. It should also be understood that more than two pieces may also be used to design collar 50. FIG. 4 shows a dual driver 100 that may be used with any of the collar embodiments described, although it is particularly useful for use with the embodiments of FIGS 2 and 3. Dual driver 100 is intended to drive the tapered head 52 independently from the threaded head 80. (It should be understood, however, that dual driver 100 may also be configured to drive fastener 12, as well as collars 30 or 50). Dual driver 100 has a first driver portion 102 and a second driver portion 104. As shown in FIG. 4, first driver portion 102 may be used to seat tapered head 52 and second driver portion 104 may be used to seat threaded head 80. Each of driver portions 102, 104 may have a member 106 that engages one of heads 52, 80.

Driver portions 102, 104 may be activated separately from one another so that the heads 52, 80 may be pre-secured onto driver 100 so that only one loading step needs to take place.

FIG. 5 shows an alternate driver - a spring loaded driver 110. Spring loaded driver

110 is particularly useful in connection with the collar embodiment shown in FIG. 3 because it allows independent rotation of head 80. It has a driver portion 112 that is used to secure both heads in place. Portion 112 has a torsion spring 114 that is spring loaded. Torsion spring 114 acts to rotate head 80 until its threads 82 align with threading 76 of bone plate opening 72. In use, as the tapered head 52 is being advanced, the spring loaded portion

"drags" and rotates the threaded head 80 to the proper position so that its threads will engage threads of opening. The spring creates a torque that makes it easier to advance head 80 into place.

Drivers 110 and 100 may also have a quick release feature that allows the driver to release the collar portions once they are in place.

FIGS. 6 A and 6B shows side and top views of a U- washer 120 that may be useful with various embodiments of this invention, particularly the embodiment having a collar 30 with a threaded head 40. U-washer 120 is intended to be used below the threads 42 of head

40 as collar 30 is being advanced over fastener 12. One use of U-washer 120 is to prevent the threads 42 from engaging with the threads of plate until desired. Once collar 30 is positioned as desired, U-washer 120 can be removed and the threads 42 are tightened against threading of the bone plate 70.

FIG. 7 shows a double-threaded collet 140. Collet 140 has external threads 142 and internal threads 144. As the collet 140 descends into the plate opening (which is shown as tapered), the opening forces the collet 140 to lock onto the threaded fastener 12. The collet 140 may have separate lobes that are separated by small spaces that, when compressed by the plate, force the lobes together to hold collet 140 and fastener 12 in place in the bone plate. As discussed above, the bone-engaging elements 18 face one direction and the collar- engaging threads 22 face the opposite direction. The external threads 142 face the same direction as the bone-engaging elements 18. During use, the fastener 12 is positioned as described, and the collet 140 is then rotated in the opposite direction to compress bone fragments. To seat the collet 140 in plate, it is then turned in the first direction (the direction used to place fastener) to lock external threads 142 in place in bone plate 70. In this embodiment, if part of proximal head 16 of shank 20 extends above plate 70, it may need to be cut off or otherwise removed.

The axial compression fastener systems described herein may be manufactured using traditional machining operations. The system can be provided in its unassembled configuration, or the fastener and collar may be screwed or pre-threaded into one another. The system is preferably sold in it extended length. The length of the system may be any appropriate length in order to provide a compression function. Particularly preferred lengths may be anywhere from 20-150 mm. In a preferred embodiment, the system can telescope from 40-60 mm, although greater and/or lesser lengths are considered within the scope of this invention.

Changes and modifications, additions and deletions may be made to the structures and methods recited above and shown in the drawings without departing from the scope or spirit of the invention and the following claims.