FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to an expanding spacer or cage, particularly for spinal interbody applications.

Lumbar interbody fusion is a common procedure to treat degenerative disc disease as well as other spine diseases/conditions. Good clinical outcome depends (among other parameters) on sufficient restoration of disc height to reduce or remove pressure on the neural elements. For the promotion of fusion, good mechanical stability is desired, as well as sufficient packing of allograft/autograft with a large contact surface for endplate-to-endplate bridging.

Common surgical approaches to lumbar interbody fusion include transforaminal (TLIF), posterior (PLIF), oblique (OLIF), extraforaminal (ELIF) and lateral (LLIF). With TLIF, ELIF and OLIF (using a banana cage), there is typically a need to rotate the implant from the approach axis to be parallel to the coronal plate, at the anterior region of the endplate. Deployment of a cage at an oblique angle to the extensional direction of a delivery system to which the implant is connected complicates design of an expansion mechanism which can be operated by a tool inserted via the delivery system.

Restoration of intradiscal height in a gradual, continuous manner from within the disc space has many clinical benefits. SUMMARY OF THE INVENTION

The present invention is an expanding cage which can readily be adjusted after alignment of the cage at an oblique angle to the extensional direction of a delivery system.

According to the teachings of an embodiment of the present invention there is provided, an expanding cage comprising: (a) a first plate providing a first tissue contact surface and a second plate providing a second tissue contact surface, the first and second plates being deployed in overlapping relation with the first and second tissue contact surfaces facing outwards; (b) an actuator slide deployed at least partially between the first plate and the second plate, the actuator slide being in engagement with at least one of the first plate and the second plate so as to at least partially define a direction of travel of the actuator slide relative to the first plate, the actuator slide having a pressure surface; (c) a linkage interconnecting between the actuator slide and at least one of the first and second plates such that displacement of the actuator slide from a first position towards a second position along the direction of travel generates an increase in spacing between the first and second tissue contact surfaces; and (d) a threaded displacement mechanism comprising a threaded bolt having a central bolt axis, the threaded bolt being deployed such that rotation of the threaded bolt about the bolt axis causes the threaded bolt to advance so that a tip portion of the threaded bolt presses against the pressure surface, thereby displacing the actuator slide from the first position towards the second position, wherein the bolt axis is inclined by a deflection angle of between 15 degrees and 85 degrees to the direction of travel.

According to a further feature of an embodiment of the present invention, the linkage comprises lateral pins projecting from the actuator slide, the lateral pins being engaged with at least one inclined track of the second plate. In some cases, the lateral pins are engaged with oppositely- inclined tracks of both the first plate and the second plate.

According to an alternative feature of an embodiment of the present invention, the linkage comprises a plurality of rotatable cam elements mechanically engaged with the actuator slide so as to be rotated by displacement of the actuator slide along the direction of travel, wherein the rotating cam elements are deployed to increase a spacing between the first plate and the second plate as they rotate.

There is also provided according to the teachings of an embodiment of the present invention, an expanding cage comprising: (a) a first plate providing a first tissue contact surface and a second plate providing a second tissue contact surface, the first and second plates being deployed in overlapping relation with the first and second tissue contact surfaces facing outwards; (b) an actuator slide deployed at least partially between the first plate and the second plate, the actuator slide being in engagement with at least one of the first plate and the second plate so as to at least partially define a direction of travel of the actuator slide relative to the first plate; (c) a linkage interconnecting between the actuator slide and at least one of the first and second plates such that displacement of the actuator slide from a first position towards a second position along the direction of travel generates an increase in spacing between the first and second tissue contact surfaces; and (d) a threaded displacement mechanism comprising a threaded bolt and configured to displace the actuator slide from the first position towards the second position, wherein the linkage comprises a plurality of rotatable cam elements mechanically engaged with the actuator slide so as to be rotated by displacement of the actuator slide along the direction of travel, wherein the rotating cam elements are deployed to increase a spacing between the first plate and the second plate as they rotate.

According to a further feature of an embodiment of the present invention, the threaded bolt has a bolt axis inclined by a deflection angle of between 15 degrees and 85 degrees to the direction of travel, and in some cases, between 30 degrees and 80 degrees to the direction of travel.

According to a further feature of an embodiment of the present invention, the tissue contact surfaces are bounded along one side by a concave curve extending along a maj ority of a length of the expanding cage .

According to a further feature of an embodiment of the present invention, the first plate and the second plate are configured to engage with each other at complementary guide surfaces configured to define a direction of expansion of the expanding cage substantially perpendicular to the direction of travel.

According to a further feature of an embodiment of the present invention, the complementary guide surfaces are provided at least in part by a plurality of guide posts, each engaging a corresponding one of a plurality of complementary channels.

According to a further feature of an embodiment of the present invention, the rotating cam elements are pivotally mounted to the first plate. BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein:

FIGS. 1A and IB are isometric views of an expanding cage, constructed and operative according to an embodiment of the present invention, shown in a fully collapsed and a fully expanded state, respectively;

FIG. 2 is an exploded isometric view of the expanding cage of FIG. 1A; FIG. 3 is a plan view of the expanding cage of FIG. 1A;

FIGS. 4A-4C are side views of the expanding cage of FIG. 1A, shown in a fully collapsed state, a partially expanded state, and a fully expanded state, respectively;

FIGS. 5A-5C are cross-sectional views taken along the lines A-A of FIGS. 4A- 4C, respectively;

FIG. 6 is an exploded isometric view of an expanding cage, constructed and operative according to a further embodiment of the present invention;

FIG. 7 is a plan view of the expanding cage of FIG. 6;

FIGS. 8 A and 8B are side views of the expanding cage of FIG. 6, shown in a collapsed state, and an expanded state, respectively;

FIGS. 9A-9C are cross-sectional views of the expanding cage of FIG. 6 taken along line B-B of FIG. 7, shown in a fully collapsed state, a partially expanded state, and a fully expanded state, respectively;

FIG. 10A is a schematic posterior isometric representation of the expanding cage of FIG. 1A or FIG. 6 during deployment in an intervertebral space, showing only the underlying vertebral body;

FIGS. 10B and IOC are schematic anterior isometric representations similar to FIG. 10A, showing the expanding cage in a collapsed state and in an expanded state after removal of a delivery system, respectively;

FIG. 11 is a schematic representation of a tool for adjusting the expansion of the expanding cages of the present invention;

FIGS. 12A and 12B are a schematic posterior isometric representations of a variant implementation of the expanding cage of FIG. 1 A or FIG. 6 during deployment in an intervertebral space, showing only the underlying vertebral body; and

FIGS. 12C and 12D are schematic anterior representations similar to FIGS. 12A and 12B, showing the expanding cage in a collapsed state and in an expanded state, respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is an expanding cage which can readily be adjusted after alignment of the cage at an oblique angle to the extensional direction of a delivery system. The principles and operation of expanding cages according to the present invention may be better understood with reference to the drawings and the accompanying description.

Referring now to the drawings, FIGS. 1A-5C illustrate a first embodiment of an expanding cage 100 according to the present invention, while FIGS. 6-9C illustrate a second embodiment of an expanding cage 200. Referring first to both exemplary embodiments generically, expanding cages 100, 200 each have a first plate 10 providing a first tissue contact surface 12 and a second plate 14 providing a second tissue contact surface 16. First and second plates 10 and 14 are deployed in overlapping relation, with first and second tissue contact surfaces 12 and 16 facing outwards. "Overlapping relation" in this context refers to the fact that the outlines of the tissue contact surfaces as viewed in plan view (e.g., FIGS. 3 and 7) are superimposed ("overlapping") over a majority of their area, and preferably over at least 80% of their area. Most preferably, first and second plates 10 and 14 are configured to engage with each other at complementary guide surfaces (discussed further below) configured to define a direction of expansion of the expanding cage substantially perpendicular to the direction of travel, thereby maintaining the overlap of the tissue contact surfaces as the cage is expanded. "Substantially perpendicular" in this context typically refers to a direction within 10-15 degrees of perpendicular. The expansion direction is typically also substantially perpendicular to a best-fit plane to the tissue contact surfaces.

An actuator slide 18 is deployed at least partially between the first plate and the second plate, and engages with at least one of the first and second plates 10 and 14 so as to at least partially define a direction of travel u of the actuator slide relative to the first plate. A linkage interconnects between actuator slide 18 and at least one of plates 10 and 14 such that displacement of the actuator slide from a first position towards a second position along the direction of travel u generates an increase in spacing between first and second tissue contact surfaces 12 and 16.

According to certain embodiments of the present invention, the expanding cage also has a threaded displacement mechanism which includes a threaded bolt 20 having a central bolt axis v engaged in a complementary bore 21, shown here as part of first plate 10. Threaded bolt 20 is deployed such that rotation of the threaded bolt about the bolt axis causes threaded bolt 20 to advance, so that a tip portion 22 of the bolt presses against a pressure surface 24 of actuator slide 18, thereby causing actuator slide 18 to advance from the first position towards the second position. The bolt axis v is inclined by a deflection angle of between 15 degrees and 85 degrees to the direction of travel u, and more preferably between about 30 degrees and about 80 degrees thereto. The angle is preferably chosen in order to correspond to the intended orientation of the final positioning of the implant in relation to the angle of the approach technique used, such that angles for TLIF approach are typically in the 50-70 degree range, while angles for a PLIF approach are typically in the 70-85 degree range. The appropriate choice of angle for various other approaches will be self-evident for a person familiar with the respective surgical techniques.

The effect of advancing bolt 20 is best seen in FIGS. 5A-5C. As bolt 20 advances, the region of contact between tip portion 22 and pressure surface 24 moves across surface 24, and the actuator slide 18 is simultaneously advanced in direction of travel u. This causes simultaneous increase in the height of the cage (FIGS. 4A-4C) according to the particular details of the linkage of each implementation, as further detailed below. Tip portion 22 of bolt 20 may advantageously be formed with a chamfer that is angled so as to spread pressure applied by the tip portion to the pressure surface. Specifically, the chamfer angle is most preferably inclined to the central axis of bolt 20 at an angle of 90° less the offset angle between directions u and v. Alternatively, in certain cases, a ball-end (e.g., with a surface corresponding to at least part of a hemispherical surface) may be used for tip portion 22.

The use of a bolt set at an oblique angle to the direction of travel, and bearing against a pressure surface, provides a particularly simple and reliable solution for actuating enlargement of the cage using a tool inserted along an extensional direction of a delivery system after reorientation of the cage to a desired position, oblique to the tool insertion direction. This functionality is illustrated in FIGS. 1 OA- IOC, where FIGS. 10A and 10B show the cage 100, 200, in this example, after insertion via a TLIF approach and deflection to assume a roughly central anterior position within the intervertebral space. For the purpose of introduction into the intervertebral space, the implant is preferably secured to a delivery system/holder 300 via engagement at a pivotal connection, such as at a clamping pin or hole 26. During insertion, the implant is generally aligned with the extensional direction of the delivery system and then, as the implant approaches its final position, it is deflected, typically by a suitable push-rod or drawstring, to assume its final orientation as shown. After deflection, an expansion instrument configured to engage the head of bolt 20 is inserted along a lumen 302 of the holder 300, and used to advance the bolt until a desired degree of expansion, and corresponding height restoration and/or lordosis correction is achieved. The expansion may be stopped at any point within the range of motion, according to the judgment of the surgeon performing the procedure. For a fusion procedure, bone material and/or bone growth promoting material are introduced into an internal volume of the implant/cage and/or adjacent areas, either via a lumen of the holder or via an adjacent or alternative insertion route. Engagement of holder 300 with the implant is then released, typically via operation of an engagement or release tool inserted via a second lumen 304 of holder 300, and the delivery system is removed, leaving the final state represented in FIG. IOC.

The expansion instrument is typically a screwdriver or Allen key driver. In one particularly preferred non-limiting option illustrated in FIG. 11, the expansion instrument is a ball-head hex key 306 or other driver arrangement which can accommodate some degree of offset angle between the extensional direction of the delivery system and the axis of the bolt, thereby rendering the assembly insensitive to variations in alignment.

Although referred to herein as "plates" 10 and 14, it will be noted that both plates have various associated structures which define the mechanical interrelation of the plates between each other and with sliding actuator 18, as detailed herein. Thus, the terminology of first and second "plates" may be used interchangeably with first and second "bodies", or plate 10 may be referred to as a "base" and plate 14 as a "cover". Similarly, with reference to the orientation as illustrated, reference may be made to a lower portion and an upper portion, or directions such as "up" and "down" etc., although the orientation in which the device is deployed is usually not critical, and all such terminology is used only for convenience of description. Although not limited to such embodiments, certain particularly preferred embodiments of the present invention are implemented as curved implants, i.e., where the tissue contact surfaces are bounded along one side by a concave curve extending along a majority of a length of the expanding cage (see FIGS. 3 and 7). Such devices are sometimes referred to as a "banana cage".

Turning now specifically to the non- limiting exemplary embodiment of FIGS. 1A-5C, this illustrates an expanding cage 100 in which the linkage between actuator slide 18 and plate 14 is implemented using at least one inclined track, which may be in the form of a slot or rail. Specifically, in the example illustrated here, lateral pins 102 project from actuator slide 18. Lateral pins 102 are engaged with at least one inclined track, in this case inclined slots 104, of second plate 14. As a result of this inclination, displacement of actuator slide 18 forces second plate 14 "upwards" (in the arbitrary orientation as illustrated in FIGS. 1A-1B and 4A-4C). In the particularly preferred implementation shown here, lateral pins 102 are also engaged in contrarily- inclined tracks or slots 106 of first plate 10 so that displacement of actuator slide from its first position towards its second position effects simultaneous outwards displacement of both first and second plates 10 and 14 relative to actuator slide 18. Parallel motion of the two plates is preferably ensured by complementary guide surfaces in the form of a vertical ridge-and-slot configuration (not shown) between the two bodies and/or abutment of the ends of the side walls of the upper body with inwardly-projecting shoulders of the lower body, or vice versa, all as will be clear to a person ordinarily skilled in the art.

In contrast, in the non-limiting exemplary embodiment of FIGS. 6-9C, expanding cage 200 employs a linkage in which a plurality of rotatable cam elements 202 are mechanically engaged with actuator slide 18 so as to be rotated by displacement of the actuator slide along the direction of travel. In the example illustrated here, each rotatable cam element 202 is formed with a projecting tooth 204 which engages a corresponding recess 206 formed in actuator slide 18, forming a partial rack-and-gear engagement. Each rotatable cam element 202 is formed with, or mounted on, a hinge pin projection 214 engaged in a corresponding bore in first plate 10. Depending on the forces to be transmitted, the strength of the materials and the range of angular motion required, a series of teeth and corresponding recesses may be provided. Rotating cam elements 202 are deployed to increase a spacing between the first plate and the second plate as they rotate. To this end, cam elements 202 are eccentric or have a variable radius, having at least one projecting region 208 which presses outwards on at least one of first and second plates 10 and 14. In the case illustrated here, projecting region 208 is a relatively long extension, corresponding to an increase in excess of 100% from the minimum radius to the maximum radius measured from the axis of rotation. In alternative implementations (not shown), cam elements 202 may be implemented with two diametrically opposed projecting regions which bear outwards against both first and second plates, thereby expanding the cage bidirectionally from actuator slide 18 in a manner similar to expanding cage 100. In such an implementation, the first plate is preferably implemented as a separate structure from the side walls which support the pivotal mounting of cam elements 202 so as to allow displacement of first plate 10 away from the axes of cam elements 202, resulting in a symmetrical opening of the device functionally similar to that of device 100 illustrated above.

Where two or more cams are employed, the dimensions of the projection(s) may differ. This may be useful in applications where non-parallel expansion is desired, for example, for restoration of lordosis or correction of scoliosis.

In this example, in order to maintain alignment between the first and second plates 10 and 14 during expansion, complementary guide surfaces are provided at least in part by a plurality of guide posts 210, each engaging a corresponding one of a plurality of complementary channels 212, as best seen in FIG. 6 and FIGS. 9A-9C. In the example illustrated here, two guide posts 210 are integrated with second plate 14, and two complementary channels 212 are formed in first plate 10. Optionally, posts 210 may have enlarged tips which are retained by restrictions at the openings of channels 212, thereby preventing complete separation of the two plates.

It should be noted that the expansion mechanism described herein based on rotating cam elements deployed between the two plates is believed to be advantageous in a wide range of applications, and is not limited to obliquely-deployed cages. Thus, for example, for lateral approach directions, a cage of this type may be implemented with zero, or near-zero deflection angle between a bolt axis and the direction of motion. Furthermore, actuation mechanisms other than the specific bolt arrangement illustrated herein may be used.

Turning finally to FIGS. 12A-12D, both expanding cages 100 and 200 were illustrated above in examples where threaded bolt 20 is accessed from an angle deflected towards the concave side of a banana cage form. Such implementations are particularly suited to PLIF and TLIF approaches. It should be noted however that the invention can readily be implemented in variant forms suited to different approach directions. By way of a further non-limiting example, FIGS. 12A-12D illustrate a sequence of insertion, deflection and expansion as part of an OLIF procedure. In this case, after insertion of the implant as illustrated in FIG. 12 A, deflection is performed so that the delivery system access is at an oblique angle along the convex outer wall of the banana cage form. In this case, the adjustment mechanism is configured with bolt 20 aligned along an axis 50 (FIGS. 12C and 12D) so that it can be actuated by a tool inserted along a lumen of the holder 300 in the orientation as illustrated in FIG. 12B. As before, bolt 20 is rotated until the desired degree of expansion is achieved, and then, after introduction of whatever filling material is required (not shown), the delivery system is disconnected and removed, leaving the expanding cage in place.

In all of the above embodiments, the various expansion mechanisms (pins on rails, cams) may be used to advantage in devices deployed by any of the various surgical approaches to the spine (TLIF, PLIF, OLIF, LLIF, etc.), regardless of whether the device shape is straight, curved (banana shaped) or other. The lengths, heights and widths of the embodiments may be implemented in different sizes and proportions to accommodate different dimensions of the anatomy. There may be teeth, ridges, or any other sort of protrusions on the upper and/or lower tissue contact surfaces to enhance the interface with adjacent tissue. The materials used to implement the implant may be titanium, titanium alloy, stainless steel, polymer or other biocompatible materials, or any combination thereof.

The thread of bolt 20 and the corresponding threaded bore 21 may be a standard thread, a double helix or any other desired type of thread. Openings or "windows" are preferably provided in the upper and lower tissue contact surfaces to as to create a continuous, unobstructed path from one side to the other.

An arrangement for interfacing between the implant and an implant holder/delivery device may include one or more pin or other protrusion, such as a pair of oppositely-projecting pins, an indentation, a tooth of any shape, and may be permanent or removable (including break-away).

At least one hole is preferably provided on the side of the device embodiments for inserting bone (or other bone-growth enhancing material) into the inner volume of implant via a bone delivery system, after expansion of the device, and ensures bridging between bone formations inside and outside the implant. The lateral hole may include openings formed in one or more of the first plate 10, second plate 14 and actuator slide 18, and the openings are preferably shaped so as to maintain overlapping openings across the entire range of adjustment of the cage.

It should be noted that the edges of the device may be rounded, and the upper and/or lower tissue contact surfaces may have an "anatomical" contour. The distal end may have a "bullet nose" shape for easier insertion into the disc space.

The implant/device may be used in conjunction with a delivery system, including (but not limited to) an instrument for opening/closing the height between the upper and lower surface, an access tube, a bone delivery system (for bone graft and/or any other biological material).

The mechanism of action can be implemented in a "straight" cage or in a "banana" cage, for types of surgical procedures (such as LLIF, ALIF, etc.).

There may be one, two, three or more pin-and-track arrangements (for device 100) or cams (for device 200) that enable the separation of the top and bottom plates.

The footprint of the device is preferably constant throughout expansion. The expansion may be continuous/analog or may have discrete steps, for example, defined by teeth or steps in the rail or slot. Whether continuous or in steps, the device is typically "self-locking" in an expanded configuration due to frictional locking of the threaded engagement of bolt 20 in threaded bore 21, so that applying vertical load at any point of expansion will not collapse the device back to its "flat" configuration. In one particularly preferred subset of applications, the device is a curved "banana" shaped device for insertion between (preferably adjacent) vertebrae. After insertion into the disc space, the device is positioned toward the anterior side of the vertebral body and then expanded in the cranial-caudal direction, while maintaining a curved shape.

For minimally invasive insertion, the implant inserter handle 300 preferably has an articulating feature (not shown) to allow streamlined insertion of the device into the disc space and then rotation of the device to enable optimal positioning in the central, anterior region of the endplate.

It should be noted that the expansion of the devices of the present invention is generally reversible, in that, when the screw is rotated in the opposite direction, anatomical loading on the device causes the device to revert towards its collapsed state. Optionally, bolt 20 may be tethered to sliding actuator 18 so that turning the bolt in a reverse direction positively displaces the sliding actuator in the reverse direction to ensure collapsing of the device.

Although illustrated herein in the context of a device with a single bolt and a single sliding actuator, it should be noted that alternative implementations may employ two or more such mechanisms side-by-side. This allows selective adjustment of the separation between the tissue contact surfaces on each side of the implant, which may be used to advantage for controlled simultaneous correction of intervertebral height restoration and lordotic angle and/or correction of scoliosis. For such applications, a larger footprint device, spanning a majority of each dimension of the intervertebral space, is preferably used. Alternatively, two independent devices similar to those described above may be deployed side-by-side and each adjusted independently, according to the requirements of the particular application, for lordotic correction or for correction of scoliosis.

The implant inserter handle 300 may include an interface for a bone delivery system.

It will be appreciated that the above descriptions are intended only to serve as examples, and that many other embodiments are possible within the scope of the present invention as defined in the appended claims.