Patent Application
20060149253
This invention relates to the field of orthopedic surgery and to bone plates which are affixed to bone by screws, including spinal plates for the cervical, thoracic and lumbar regions.
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 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.
Spinal bone plates are usually attached to adjacent vertebrae to reduce pain due to injury or deterioration of the intermediate disk. The plate spans the intervertebral space to stabilize the vertebrae. Pedicle screws or bone screws are inserted through apertures in the opposite ends of the plate into the respective vertebrae or on opposite sides of a break. Due to anatomical forces on the skeleton, the screws sometimes back out of the bones and plates.
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. Pat. 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. Pat. 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. Pat. 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. Pat. No. 6,231,610, discloses a bone plate with diverging bone screws and serrations on the plate to increase holding power.
U.S. Pat. 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. Pat. No. 5,603,713, discloses an anterior lumbar plate attached by screws with various angular connections to the spine.
Published application, US 2004/0102773 A1, to Morrison et al, uses the ends of the bone plate to cover the heads of the bone screws.
U.S. Pat. No. 6,740,088 B1, to Kozak et al uses extra set screws to interfere with the heads of the bone screws.
U.S. Pat. No. 6,730,127 B2 to Michelson attaches an overlay to the plate to partially cover the heads of the screws.
What is needed in the art is a bone plate with an internal sliding screw lock that rotates to wedge the bone screws to the plate.
Disclosed is a bone plate for stabilizing adjacent vertebrae. The plate is formed from a span of rigid material for bridging intervertebral space, the span having a bone engaging surface and a distal surface. A first bracket is located at one end of the span and a second bracket is located on the other end of the span. The first bracket includes a first bone fastener aperture and a second bone fastener aperture therethrough with a cam bore between the first bone fastener aperture and the second fastener aperture. A slot in the first bracket extends from the first bone fastener aperture to the second bone fastener aperture with an eccentric cam rotatably mounted in the cam bore, the cam includes a cam surfaces. A first wedge shoe is slidably disposed in the slot between the cam and the first bone fastener aperture for contacting the cam surface. A second wedge shoe is slidably disposed in the slot between the cam and the second bone fastener aperture for contacting the cam surfaces. A cam cover plate can be used to close the slot whereby rotating the cam slides te first and second wedge shoe partially into the first and second bone fastener aperture.
Therefore, it is an objective of this invention to provide a bone plate with an integral internal screw lock.
It is another objective of this invention to provide a spinal plate with sliding wedge shoes.
It is yet another objective of this invention to provide a low profile bone plate with countersunk bone screw apertures therethrough having wedge shoe openings.
It is a further objective of this invention to provide a bone plate to span a plurality of discontinuaties in the bone.
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.
and
The bone plate 10, shown in
The second bracket 13 has the same components as the first bracket 12. An aperture 50 is located in the span 11 to facilitate boney ingrowth to increase stability. In
The bone plate has two major surfaces, a bone engaging surface 18 and a distal surface 19. The bone screw apertures and the cam bores extend through the bone plate from the bone engaging surface to the distal surface. The cam bore 16, in the distal surface 19, is circular and serves as a guide and bearing surface for the distal end of the actuator 20 of the eccentric cam 17. The actuator has a receptacle 21 for a tool (not shown) used to rotate the cam. The actuator 20 terminates on the distal surface to preserve the smooth surface.
Eccentric cam surfaces 22 and 23 are formed 180° apart on the shaft of the cam 17. In the unlocked position, the cam surfaces are aligned with the longitudinal axis of the span 11. By turning the actuator 90°, the cam surfaces 22 and 23 are aligned transverse to the axis of the span.
As shown in
A cam cover plate 27, as shown in
One end 32 of the wedge grip shoes 25 is shaped to conform generally with the head of the screw 101 or pin 200 but including contact points 33 and 34 near the sides of the shoes to insure more than one positive pressure point about the circumference of the head. The other end 35 of the shoes is shaped with an indentation 36 to act as a lock to prevent the eccentric cam surfaces from reverse rotation.
The heads of the bone screws have a spherical shape, as do the countersunk portions of the brackets. This allows for some flexibility in placement of the plate and pedicle screws to compensate for anatomical considerations or to gain better purchase in the bone. When the bone screws or pins have been fully tightened, the eccentric cam is rotated by the actuator. The cam surfaces engage the wedge grip shoes and slide each toward the countersunk apertures. At 90° the cam surfaces are disposed in the indentations of the shoes and cannot freely return to the original position. The other ends of the shoes have moved into the countersunk portion of the apertures and engage the circumference of the spherical heads at least at two points. The surface of the countersunk bores opposite the wedge shoes serves as a reaction surface to secure the screws from backing out of the bone.
The bone plate and screws may be fabricated from surgical steel, titanium, other suitable alloys, ceramics alone or as coatings, and polymers or combinations thereof with the requisite strength and nontoxicity in the body.
The bone plates and screws may be supplied in kit form with different sized screws and plates for selection due to anatomical necessities.
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.
