Vertebral Lock

This invention relates to a vertebral lock for separating and stabilizing vertebrae where a portion of the spine has been removed surgically.

It is sometimes necessary, by reason of injury or disease, to remove a portion of a vertebra from the spinal column. In such situations, a gap is left between adjacent vertebrae above and below the removed portion, which must be bridged or spanned structurally so that the vertical load on the spine can be transmitted safely across the gap. One technique used to accomplish this is bone fusion, which coheres the vertebrae as a monolithic element. A drawback of bone fusion, however, is that it requires a long period of recovery and rehabilitation. It is also known to use spinal stabilizing devices to separate the vertebra adjacent a damaged and/or partially removed vertebra. Some such devices, as shown, e.g., in U.S. Pat. Nos. 4,553,273 and 4,401,112, may be adjusted after insertion by means of a threaded shaft to provide a precise desired spacing. A drawback of spinal stabilizers has been the difficulty of placing and fixing them in the desired position, and the possibility that they might loosen or shift after they have been implanted in the body, by reasoning of turning of the threaded shaft.

The device of the present invention overcomes the shortcomings of the known devices and methods of spinal stabilization in that it is easily implantable and positionable and, once in place, is very much less susceptible to loosening.

Structurally, the vertebral lock of this invention includes a rigid, one piece load bearing body which is shaped to be insertable in the cavity formed when part of a vertebra has been removed from the spinal column. The body has a central slot which may extend through it in the direction perpendicular to the axis of the spine, i.e., the slot is horizontal when the lock is in use. Two pin guide holes or bores extend from opposite sides of the slot, parallel to the spine axis, i.e., vertically, through the upper and lower ends of the body. Retaining pins fit slidably within the respective guide holes and project out from each end of the body. The upper and lower ends of the body fit snugly between the vertebrae above and below the cavity to receive and carry the axial load on the spine. The pins are engageable with the adjacent vertebra directly above and below the body when so engaged to secure the body in place with respect to those vertebrae. Each retaining pin has a pointed tip at its outer end beyond the end of the body for engaging the adjacent vertebra, and also has means extending across its inner end for engaging a locking means that extends into the slot and locks the pins against vertical (axial) movement. The locking means is preferably in the form of a spline or bar that is insertable into the slot in the body of the device, to hold separate, engage and secure the inner ends of the pins and thereby hold the pins against both axial (vertical) and rotational movement.

In use, after the body has been inserted into the cavity in a vertebra and the retaining pins have been inserted in the guide holes and are in engagement with the adjacent vertebrae, the locking means is inserted into the slot wherein it engages the inner ends of the retaining pins, pushes the pins apart (outwardly) in the holes, and thereby locks the pins to the body and the body to the vertebrae. With the pins thus secured by the locking spline (which is transverse to them), there is no tendency for the pins to "back out" over time or to become unscrewed. The pins are oriented vertically, in line with the axis of the spine, and are loaded by the spine in compression against the locking spline. Because the spline is perpendicular to the pins, the locking spline is not cammed out of its engagement with them.

In a preferred form, the body has flanges that project from each end of the body (i.e., the upper and lower ends of the body) parallel to the guide holes but offset outwardly from them so as to overlap the inside faces of the adjacent vertebrae. Each flange has an aperture therein to permit additional securing of the device in place, as by screwing it to the adjacent vertebrae.

The vertebral locking device of the present invention will be further understood with reference to the accompanying drawings in which:

FIG. 1 is an exploded perspective view of a preferred embodiment of the invention, illustrating the device in juxtaposition to a cavity between adjacent vertebrae.

FIG. 2 is a vertical section, partially broken away, of a portion of a spinal column in which a vertebral lock of the type shown in FIG. 1 is being positioned, and also shows an instrument for inserting the retaining pins into the body of the device.

FIG. 3 is a vertical section similar to FIG. 2 but shows the vertebral lock secured in the spinal cavity.

FIG. 4 is a diagrammatic front elevation of a section of the spinal column with a portion of a vertebra removed to form the cavity for the lock, and adjacent vertebrae pre-drilled to receive the retaining pins.

A preferred embodiment of the present invention is illustrated in FIGS. 1-3. The device, which is preferably made of molded plastic, has a body 10 which is preferably cylindrical with an elongated transverse central slot 12. Two opposed pin receiving guide holes 14, 14 extend perpendicularly to slot 12 through opposite ends of body 10. The holes may be and preferably are colinear. Two vertebra-engaging retaining pins 16, 16 fit slidingly within and are axially guided by the guide holes 14, 14. Each retaining pin 16 has a pointed end 20 which, when the pin is positioned in its guide hole 14, extends out from the upper or lower end of body 10, and is engageable with an adjacent vertebra as shown in FIGS. 2 and 3. Each retaining pin 16 is abutted and supported at its inner end 17, within slot 12, by slidable locking means designated generally by 22 which extends perpendicularly to each pin 16 and prevent it from being pushed axially into the body by the vertebra with which it is engaged. Locking means 22 is preferably in the form of a spline or flat bar, see FIG. 1. The inner end 17 of pin 16 preferably has a channel or socket 18 extending transversely to it. Locking means 22 has parallel ribs 24, 24 along its opposite upper and lower edges as seen in FIG. 1, and is sized to fit in slot 12 without play in the vertical direction. The ribs 24, 24 have angulated ramps 25 first at their inner ends to engage and cam outwardly the pins as they engage the respective channels 18, 18. Alternatively, the positions can be reversed: a rib can be formed on the inner end of each retaining pin to engage a channel in the respective edge of the locking bar.

For installation, each retaining pin 16 can be positioned within its guide hole 14 by insertion through slot 12, using a pin holder tool designated by 40 in FIG. 2. The pin holder has two parallel legs with tips which can be engaged in the channels 18, 18 of the pins. The legs can be moved and held apart by a threaded sleeve adjuster 44 so as to hold the pins axially apart against the vertebrae until the locking means is inserted. More specifically, tip 42 of device 40 engages channel 18 of retaining pin 16 and pin 16 is inserted into slot 12. The legs of device 40 are then spread using the adjuster 44 to push pin 16 into guide hole 14 so that pointed end 20 engages the adjacent vertebra in a pre-drilled or starter hole 32. (The hole 32 need only pierce the outer surface of the vertebra; the cancellous central bone, being softer, does not require drilling.) When the retaining pins 16, 16 are positioned in guide holes 14, 14, tool 40 is removed and locking means 22 is inserted in slot 12 to engage bar ribs 24 in channels 18 in retaining pins 16, thereby to lock the pins in place. Because locking means 22 extends into and engages pins 16, 16 perpendicularly to their axis, any compression or vertical thrust exerted by the spine on the pins acts as a compressive load on the locking means and there is no tendency for it to loosen or be cammed out of slot 12. (The ramps 25 at the leading or first end of the ribs do not extend along the length of the ribs; the ribs are parallel, excepting the ramps.)

As a means for providing additional spinal stabilization, body 10 has flanges 26, 26 which project from each end of the body parallel to guide holes 14, 14. Each flange 26 has an aperture 28 which allows the device to be secured in place for example by a screw 27, to the adjacent vertebrae as shown in FIG. 3. The screw 27 preferably has an inwardly flaring lip or shoulder 29 which, when the screw is tightened, engages the inner side of flange 26 and thereby prevents the screw from loosening.

The drawings show a portion of a human spinal column including vertebrae 34, 35 and 36. The middle vertebra 35 is depicted as having had a generally vertical cavity 38 on the front side, formed by surgical removal of a part of that vertebra. Pin locator holes 32, 32 are drilled diagonally upward and downward in vertebrae 34 and 36, above and below cavity 38, and body 10 is inserted into cavity 38. Retaining pins 16, 16 are positioned within guide holes 14, 14, which may be done as described above, to engage the starter holes in vertebrae 34 and 36. When in place, retaining pins 16, 16 project out from body 10 and into holes 32, 32 as shown in FIG. 3. At this point, the locking means 22 is inserted to push the pins into the cancellous bone and lock the device in place, and the device may be further secured with the screws 27, 27.

It will be appreciated by those skilled in the art that the vertebral lock of this invention may be made in varying sizes and body configurations for use in different vertebrae and in children as well as adults. In particular it is preferred that the distance between the upper and lower faces of body 10 correspond to the distance between vertebrae 34 and 36, so that these vertebrae will rest upon the end faces to transmit the spinal load directly through body 10.

Other variations and modifications in the structure of the device will be apparent to those skilled in the art, within the scope of the claims which follow: