|Publication number||WO2006022644 A1|
|Publication date||2 Mar 2006|
|Filing date||26 Jul 2004|
|Priority date||26 Jul 2004|
|Publication number||PCT/2004/24111, PCT/US/2004/024111, PCT/US/2004/24111, PCT/US/4/024111, PCT/US/4/24111, PCT/US2004/024111, PCT/US2004/24111, PCT/US2004024111, PCT/US200424111, PCT/US4/024111, PCT/US4/24111, PCT/US4024111, PCT/US424111, WO 2006/022644 A1, WO 2006022644 A1, WO 2006022644A1, WO-A1-2006022644, WO2006/022644A1, WO2006022644 A1, WO2006022644A1|
|Inventors||Brett O'neil Baynham, Clay G. Bynham, Matthew G. Baynham, David Cmpbell|
|Applicant||Innovative Spinal Design, Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (2), Referenced by (9), Classifications (8), Legal Events (5)|
|External Links: Patentscope, Espacenet|
BONE FIXATION PLATE
Field of the Invention This invention relates to the field of orthopedic surgery and, more particularly, to spinal fixation.
Background of the Invention The use of bone pins and plates for reducing fractures is well known in orthopedic medicine. The pins and plates extend across discontinuities in a bone to fix the broken ends in relation to each other to reduce pain and promote rapid healing without deformity. These devices are secured to the bone by bone screws or nails driven into the bone. More recently, pins, rods, plates and cages have been used to stabilize bone and joints that have deteriorated naturally or as a result of prior trauma. The bone plate of this invention is useful in all these situations. The interface between the bone screws and the bone presents problems of stability and long term usage that have been addressed in different ways. One of the major problems is usually termed as back-out. This defines the condition in which the screws attaching the plate to the bone loosen over time, either relative to the bone or the plate or both. Severe back-out results in the bone screw working itself out of the bone and/or plate resulting in instability of the bone or joint. This situation results in increasing pain and danger from the instability, as well as , the movement of the screw. There may be several reasons for the back-out but anatomical stresses from body movements contributes greatly to the problem. Prior art devices address the problem of back-out by use of secondary locking screws that hold the bone screws in the plate. The locking device engages the head of the bone screw and is tightened to fix the screw to the plate and, thus, the bone. Such devices are not particularly suited for deployment on the anterior aspect of the spine because of the close proximity of vital soft tissue organs which dictate a smooth, low profile, contoured surface. Michelson, U. S. Patent No. 6,454,771, discloses a bone plate for anterior cervical fixation. The plate has several holes for receiving bone screws. A locking screw mechanism is used to overlay the screw heads. An expandable insert for placement between vertebrae is disclosed by Paes et al, U. S. Patent No. 6,436,142. The device is in the nature of a lag screw and can expand with the insertion of an expansion screw. U. S. Patent No. 6,342,055 to Eisermann et al discloses a bone plate with bone screws having a snap-in retainer securing the heads to the plate. Geisler, U. S. Patent No. 6,231,610, discloses a bone plate with diverging bone screws and serrations on the plate to increase holding power. U. S. Patent No. 6,224,602 to Hayes discloses a bone plate with multiple bone screw holes which may be covered by a sliding locking plate. The bone plate has an undercut channel to hold the locking plate in contact with the screw heads. The locking plate is held to the plate by a locking screw once it is slid to the desired position. Aust et al, U. S. Patent No. 5,603,713, discloses an anterior lumbar plate attached by screws with various angular connections to the spine. What is needed in the art is a less complicated system with multiple locking components for added security.
SUMMARY OF THE PRESENT INVENTION It is an objective of this invention to provide a bone plate, suitable for anterior lumbar fixation, having countersunk screw holes, a low profile in cross section allowing the bone plate to be countersunk into the bone and a smooth distal surface to reduce the possibility of traumatizing adjacent soft tissue during use. A further objective of the invention is to provide threaded tubular bone anchors embedded in bone guided by the screw holes in the plate. The bone anchors being screwed into the bone by external threads. Another objective of the invention is to provide locking screws extending through the countersunk screw holes into the bone anchors with the leading ends of the screws expanding the ends of the bone anchors to fix the bone screws to the bone anchors and the anchors to the bone. Yet another objective of the invention is to provide a bone plate with a locking cap which extends over the area of the countersunk screw holes. The locking cap fits into a large countersunk area of the bone plate covering the countersunk screw holes allowing easy and positive assembly and preventing relative lateral movement between the locking cap and the plate. The locking cap has an aperture and the plate has a receptacle which align when the cap is placed in the countersunk area. A cap screw is threaded into the aligned aperture and receptacle to connect the plate and the cap. A still further objective of the invention is to provide a kit of several interchangeable components including plates, locking screws, anchors, caps and cap screws to permit the assembly of matching components to fit the anatomy of the patient. Another objective of the invention is to provide a bone plate system with double headed locking screws and a cam on the bone plate to wedge into the double headed screws. Other objectives and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof.
BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an exploded perspective view of the bone plate system of this invention; Fig. 2 is a perspective of assembled bone plate system of this invention; Fig. 2A is a perspective of another embodiment of Fig. 2; Fig. 3 is a cross section of Fig. 2 along line 3 - 3; Fig. 4 is a cross section of the bone plate counter sunk into the bone; Fig. 5 is a bottom view of the bone plate with the cam rotated into the double headed screws; Fig. 6 is a perspective of a double headed locking screw; and Fig. 7 is a cross section of a bone plate with a double headed screw in place.
DETAILED DESCRIPTION OF THE INVENTION The bone plate system 10 may be made from any materials having requisite strength and being suitable for use in the body. One complete bone plate system is shown in Fig. 1, Fig. 2 and Fig. 2A though it is understood that several different sizes of interchangeable components may be supplied together as a kit for mixing and matching components to size a system for a particular patient. A kit may have several different sized bone anchors 11 varying in diameter and length with complementary locking screws 12. The different sized locking screws may have the same sized heads 13 to be used in different sized bone plates 14 with screw holes 15' and countersunk depressions 15 of the same size. There may be several different sized locking caps 16, as shown in Fig.s 2 and 2A, to fit into the different complementary sized countersunk areas 19 of the plates while the aperture 17 and the threaded receptacle 18 are of the same size. The locking cap 16 is connected to the plate 14 by a cap screw 20. The kit merely refers to the dissembled components, shown in Fig. 1, that can be assembled to produce an integral whole which corresponds to the anatomical features of a particular patient. The bone plate system 10 addresses the problem of back- out by providing several locking features in the connection of the plate 14 with the bone. These locking features all resist the biomechanical loads placed on the implanted system and result in an aggregate resistance to movement of the components. The locking features are disposed over the length of the plate-bone connection such that the same biomechanical force may not act on all locks simultaneously. The tubular bone anchors 11 are initially inserted into the bone through pilot holes drilled in the bone or by the use of guide wires. The plate 14 may be used as a guide to align the longitudinal axis of the bone anchors with the longitudinal axis of the countersunk screw holes 15' in the plate. The bone anchors 11 are driven into the bone with a tool (not shown) that engages the slots 27 for rotation of the anchor. The exterior screw threads 21 of the anchor draw the anchor into its seated position in the bone. However, the screw threads 21 produce a mirror image of the toroidal ramp at the bone interface which is a path of least resistence in the opposite direction. The leading or proximal end of the anchor 11 has a number of radial slits 25 through the side wall dividing the proximal circumference into segments 26. Further, the leading end is tapered internally and externally toward a smaller end. This structure of the leading end of the bone anchors 11 creates a change in the bone-anchor interface by expanding, as the locking screws are inserted, to increase the resistence to reverse rotation. Once the bone anchors 11 are in place, the locking screws 12 are extended through the screw holes 15' of the bone plate 14 with the threads 22 and 23 threadably engaging the interior threads 24 of the bone anchors. The locking screws are rotated by a tool (not shown) fitted into the receptacle 28. As shown, the locking screw 12 has a smooth unthreaded shank near the head 13. An intermediate length of the locking screw has threads 22 to engage the interior threads of the bone anchor. The leading end of the locking screw has a tapered portion with threads 23 to engage the threaded tapered leading end of the bone anchor. The threaded engagement of the locking screws with the leading ends of the anchors and the resultant expansion of the anchors creates a difference in the threading along the interior length of the anchor which resists rotation in the opposite direction. The leading end of the locking screws may be un-threaded and act as a wedge. The locking screw heads 13 are completely enclosed by the depressions 15 and compressively disposed against the bottoms of the depressions. Therefore, the anchor 11 is locked in place by a new bone-anchor interface and the locking screw and anchor are locked together by compression and threading changes. Of course, other combinations of locking screws and anchor configurations may be used, such as, a constant taper of each. After the locking screws 12 have been seated in the bone anchors 11 and depressions 15, the locking cap 16 is placed in the complementary countersink 19 formed in the plate 14. The size and thickness of the locking cap and the size and depth of the countersunk area allow ease of assembly of these components and a resulting low profile with a smooth outer or distal surface. The vertebrae V is shaped to form a counter sunk area in which the plate is placed, as shown in Fig. 4. This is especially important in reducing the possibility of internal trauma to adjacent soft tissue, eg., in the anterior lumbar spinal fixation. The assembly of the locking plate 16 and the bone plate 14 automatically aligns the receptacle 16 and the aperture 17 for connection by the cap screw 20. The continuous side wall of the enlarged countersunk area and the periphery of the locking cap positively locate the components relative to each other. The cap screw 20 is tightened by a tool (not shown) that fits into receptacle 29. Once the locking cap is secured in place, the heads of the locking screws are prevented from retraction. Because the cap screw 20 is centrally located in the locking cap 16, any reverse rotation of the locking screws is opposed by a leveraging action between the locking cap and the cap screw. This action tends to jam the cap screw and locking cap tighter together. As an alternative or additional attachment system is shown in Fig.s 5, 6, and 7. To further secure the locking screws 12 to the plate 14 requires a slit 30 in the side of each of the depressions 15. The slit in each adjacent depression faces the other. A cam 31 is rotatably mounted in the plate 14 between the adjacent depressions and has a flange formed with a blade portion 32 and a brake portion 33. The blade portion 32 will register with the slit 30 in one position and be free of the slit in another position. The brake portion 33 will engage the curved plate when the blade portion is registered with the slit 30 to create a friction stop. In this embodiment, the locking screws have a double headed configuration 13, 13' with a circumferential groove 34 between the two heads. When the locking screws are securely in place in the anchors 11 and plate 14, the grooves 34 will register with the slits 30. The cam 31 extends through the plate 14 into the countersunk portion 19 and is turned by a tool (not shown) to register the blade portion 32 with the slits 30 and the grooves 34. In this position, the brake portion 33 of the flange engages the curved surface of the plate 14. The locking cap 16 may then be applied, as described above. The cams may extend through the locking cap to be tightened along with the cap screw. The implanted bone plate system results in a positive lock at the proximal ends of the bone anchors and locking screws and an additional lock at the distal end of the locking screws. A number of embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the invention is not to be limited by the specific illustrated embodiment but only by the scope of the appended claims.
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|Cooperative Classification||A61B17/863, A61B17/686, A61B17/7059, A61B17/8042|
|European Classification||A61B17/68P, A61B17/70K, A61B17/86B2, A61B17/80D4|
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