Spinal cage

A spinal cage includes first and second spinal attachment members attachable to vertebrae, the first and second spinal attachment members articulating with one another by means of an articulation joint, and a wedge element arranged for wedging between the first and second spinal attachment members. An actuator is linked to the wedge element for moving the wedge element axially with respect to the first and second spinal attachment members. The actuator includes a threaded member adjacent the wedge element and a biasing device positioned between at least one of the first and second spinal attachment members and the wedge element. Upon turning of the threaded member, the wedge element is advanced with respect to the articulation joint so that the first and second spinal attachment members are tilted or parallel to each other. The biasing device applies a biasing force on the wedge element to move the wedge element axially.

FIELD OF THE INVENTION

The present invention relates generally to spinal implants and prostheses, and particularly to a rotatable spinal cage.

BACKGROUND OF THE INVENTION

Scoliosis is a spinal deformity affecting many people. Current surgical treatment involves affixing long fusion rods to the spine by pedicle screws. The rod system is intended to force the deformed spine into a more healthy position. Other spinal disorders which are often treated by fusion include hyperkyphosis and hyperlordosis.

PCT Patent Application PCT/US2013/020454 describes a spinal cage that has a rotational pivot and a mechanism to allow rotation in one direction while preventing rotation in the opposite direction.

SUMMARY OF THE INVENTION

The present invention also seeks to provide an improved way to correct spinal deformity by using a spinal cage inserted between adjacent vertebral bodies. The spinal cage is built in a way that it has a rotational pivot and a mechanism to allow rotation in one direction while preventing rotation in the opposite direction. The spinal cage may be used, for example, to correct lordosis of the spine or other disorders.

In one embodiment of the present invention, the spinal cage includes first and second spinal attachment members attachable to vertebrae, the first and second spinal attachment members articulating with one another by means of an articulation joint, and a wedge element arranged for wedging between the first and second spinal attachment members. An actuator is linked to the wedge element for moving the wedge element axially with respect to the first and second spinal attachment members. The actuator includes a threaded member attached to the wedge element and a biasing device positioned between at least one of the first and second spinal attachment members and the wedge element. Upon turning of the threaded member, the wedge element is either advanced or retracted with respect to the articulation joint so that the first and second spinal attachment members are either tilted or parallel to each other. The biasing device applies a biasing force on the wedge element to move the wedge element axially.

DETAILED DESCRIPTION OF EMBODIMENTS

Reference is now made toFIG. 1, which illustrates a rotatable spinal cage80of the prior art, PCT Patent Application PCT/US2013/020454.

Spinal cage80includes first and second spinal attachment members82and84, such as flat plates. First and second spinal attachment members82and84are attached to two adjacent vertebrae83and85, respectively. The plates may have coarse or roughened surfaces that interface with the vertebrae for enhanced binding to the vertebra bone or tissue (other adhesion enhancers may be used as well, such as coatings for binding with tissue and the like). For example, fixation of spinal cage80can be enhanced by means of spikes, screws or other means known to those skilled in the art.

First and second spinal attachment members82and84articulate with one another by means of an articulation joint. Accordingly, spinal cage80can pivot about the articulation joint in one rotational degree of freedom. In the illustrated embodiment, the articulation joint includes a male member86which is pivotally received in a female member88. In the illustrated embodiment, the male member86extends from first spinal attachment member82and the female member88is formed in second spinal attachment member84. The reverse can also be made.

A wedge element90is arranged for wedging between first and second spinal attachment members82and84. Wedge element90may have a generally conical or trapezoidal shape or any other shape that can be accommodated by first and second spinal attachment members82and84. An actuator92is linked to wedge element90for moving wedge element90in a direction that wedges wedge element90further in between members82and84(i.e., increases the wedging effect) or further away from members82and84(i.e., decreases the wedging effect). Actuator92can be, without limitation, a spring, motor, linear actuator, solenoid and the like. Actuator92can pull or push wedge element90directly or through a string, rod or any other connecting element.

The surfaces of first and second spinal attachment members82and84that contact wedge element90can be polished, roughened, grooved, etc., to increase the friction between the wedge and the members. In one embodiment, wedge element90can have a threaded hole, pin, groove and the like, for grasping with a tool to enable pulling the wedge and to release the uni-directional mechanism and allow some rotation of the attachment members82and84to another direction.

There are several features of the prior art wedge mechanism that should be noted.

First, the wedge element90and actuator92are positioned on opposite sides of the articulation joint.

Second, since the wedge element90is moved in the wedging direction only by the uni-directional mechanism (unless released and pulled by some grasping tool in a direction opposite to the wedging direction), it is desirable to increase the friction between the wedge element90and the spinal attachment members82and84, so that wedge element90does not slip.

Reference is now made toFIGS. 2-5, which illustrate a spinal cage10, constructed and operative in accordance with a non-limiting embodiment of the present invention.

Spinal cage10includes first and second spinal attachment members12and14, each of which has bone-interface surfaces13and15, respectively, attachable to vertebrae. The bone-interface surfaces13and15may be configured to promote osseointegration by increasing their surface area. For example, in the illustrated embodiment, bone-interface surfaces13and15are roughened, such as by means of a plurality of teeth. Additionally or alternatively, the surfaces13and15may be roughened in other manners, such as, by acid-etching, grit blasting, and/or machining. Additionally or alternatively, the surfaces13and15can be coated to promote osseointegration. Calcium phosphate ceramics, such as tricalcium phosphate (TCP) and hydroxyapatite (HA) are examples of materials that can enhance osseointegration of the surfaces13and15. Additionally or alternatively, the surfaces13and15can comprise macroscopic structures, such as, for example, threads, micro-threads, indentations, and/or grooves that are configured to promote osseointegration and can be used alone or combined with the roughening and/or the coatings described above.

First and second spinal attachment members12and14have inner surfaces3and5, respectively (opposite to bone-interface surfaces13and15). Distal and/or proximal portions of inner surfaces3and5may be curved to provide increased tilting between first and second spinal attachment members12and14. For example, the distal and/or proximal portion of inner surface3of first spinal attachment member12may be convex while the distal portion of inner surface5of second spinal attachment member14may be concave.

The bone-interface surfaces13and15of first and second spinal attachment members12and14may be flat. Alternatively, surfaces13and15may be curved or otherwise shaped to match the anatomical shape of the vertebra or other spinal structure to which they are designed to be attached. Additionally or alternatively, the geometrical shapes of first and second spinal attachment members12and14may be configured to accommodate the lordosis angle between adjacent vertebrae.

First and second spinal attachment members12and14articulate with one another by means of an articulation joint11. In the illustrated embodiment, the articulation joint11includes a male member16which is pivotally received in a female member18. In the illustrated embodiment, the male member16extends from second spinal attachment member14and the female member18is formed in first spinal attachment member12. Of course, the reverse can also be made.

A wedge element20(FIG. 4) is arranged for wedging between first and second spinal attachment members12and14. Wedge element20may have a generally conical or trapezoidal shape or any other shape that can be accommodated by first and second spinal attachment members12and14. In the illustrated embodiment, wedge element20has a generally flat surface20A that slides over the inner surface5of second spinal attachment member14and a chamfered surface20B that wedges against the inner surface3of first spinal attachment member12(FIG. 4). Wedge element20may be shaped such that at any position it is geometrically locked with respect to first and second spinal attachment members12and14.

An actuator24is linked to wedge element20for moving wedge element20axially between members12and14to change the tilt between members12and14. Actuator22includes a threaded member24(such as a screw) attached to wedge element20, and a biasing device26(such as a spring) positioned between the first or second spinal attachment members12and14and the wedge element20. By appropriate turning of threaded member24, the wedge element20is advanced with respect to articulation joint11so that first and second spinal attachment members12and14are tilted (FIGS. 2 and 4) or parallel to each other (FIGS. 3 and 5).

In one mode of operation, the surgeon installs spinal cage10, such as by means of a lateral access in the patient, and adjusts the threaded member24to place wedge element20at an initial configuration of first and second spinal attachment members12and14(e.g., a desired tilted configuration) to help correct curvature of the spine of the patient. After the operation, if the patient succeeds at some point to make a movement that tends to further correct the curvature of the spine (such as by means of post-operational lateral bending exercises and the like), the biasing device26will immediately apply a biasing force on wedge element20to further move wedge element20axially to a new position that maintains the current position of the spine at the newly corrected position. The wedge element20remains in the new position by being geometrically locked in the place to which it was pushed by the biasing device26. In this manner, over time and with gradual further corrective movements of the patient, the system gradually further corrects curvature of the spine.

Contrary to the prior art, in the present invention, both threaded member24and biasing device26are on the same side of the articulation joint11. In addition, contrary to the prior art, in the present invention, the wedge element20(particularly the chamfered surface20B) may be coated to reduce friction between the wedge element20and the inner surfaces of the first or second spinal attachment members12and14.