Intervertebral spacer system with tilted integrated expansion mechanism and stepped locking mechanism

Abstract

An expandable intervertebral spacing system has a top plate and a bottom plate that form a cage. The top, bottom, and sides of the cage have openings to receive bone graft material. At least one ramp extends from the top plate or the bottom plate into the cage. The top plate and the bottom plate are hinged together at the proximal end of the cage. The cage is expanded by inserting a push rod into the proximal end of the cage against a ramp and forcing the top and bottom plates apart at a desired angle. A locking mechanism at the distal end of the cage locks the plates apart using a ratchet-like mechanism, where a torsion spring biases the movable post against the stationary post such that the serrations of the movable post and stationary post cooperate to lock the top and bottom plates apart.

Description

Technical Field

[0001] The present invention generally relates to intervertebral spacers for use in orthopedic surgery of the spine. In particular, the present invention relates to a spinal implant system in which the spacer has an angled, integral expansion mechanism and a stepped, ratchet-like locking mechanism. Background Art

[0002] Interbody fusion is a type of spinal surgery that removes all or part of a degenerated disc from between two adjacent vertebrae in a patient's back. Once the disc is removed, an expandable device is inserted into the disc space between the adjacent vertebrae to force the vertebrae apart and maintain separation. Bone graft material is packed in and around the spacers to provide a scaffold so that new bone can form. The spacers remain between the vertebrae and are anchored to the vertebrae above and below the spacers using anchors such as screws or barbs. The spacers help maintain spinal alignment and separation. During the healing process, additional surgical hardware (such as rods, plates, hooks, and wires) can be used to support the vertebral structure. During the healing period, the adjacent vertebrae fuse into a single, integral structure.

[0003] Typically, spacers are expanded using a removable mating tool that engages an expansion mechanism located within the body of the spacer. The user uses the tool to incrementally expand the spacer to the appropriate height to maintain the desired distance of vertebral separation. After the spacer is expanded to the appropriate height, the expansion tool is removed.

[0004] Lordosis refers to the curvature of the spine, which concaves posteriorly. A certain amount of curvature is desirable for spinal health and patient comfort, but too little or too much curvature can be problematic. When implanting a device between two vertebrae, the lordotic angle of the repaired disc space must be appropriately set, not only for the two surrounding vertebrae, but also for any adjacent vertebrae that may be affected. It would be desirable to have an expandable intervertebral implant to achieve the desired lordotic angle.

[0005] Once expanded, it's desirable to lock the spacer at the desired height and angle. The locking mechanism must be strong enough to withstand the compressive forces between the vertebrae, and the cage must be rigid enough to prevent it from collapsing or otherwise failing during the patient's lifetime. Strength and durability are crucial, but making the spacer unnecessarily strong can compromise the size of the cavity within the spacer for holding the bone graft material. There's a trade-off.

[0006] It is an object of the present invention to provide an expandable lordotic interbody spacer system having an integral expansion mechanism and ratchet locking mechanism that is expanded using a paired expansion tool. It is another object of the present invention to maximize the interface between the bone graft material and the patient's vertebrae and tissue. Summary of the Invention

[0007] An expandable intervertebral spacer system includes a spacer having an integral expansion mechanism and a ratchet locking mechanism and a mating insertion tool. The spacer includes top and bottom plates that form a cage surrounding a cavity. The top, bottom, and sides of the cage are open to receive bone graft material. A top ramp extends from the top plate into the cage, and optionally, a bottom ramp extends from the bottom plate into the cage. The top and bottom plates are hinged together at the proximal end of the cage, which allows the top plate to be forced apart from the bottom plate so that the plates are positioned at an angle relative to each other.

[0008] The cage is expanded using a mating insertion tool that inserts a push rod into an opening in the proximal end of the cage, against one or more ramps in the cage. As the push rod extends deeper into the cage, the end of the push rod cooperates with the one or more ramps to force the distal ends of the plates apart so that the top and bottom plates are no longer parallel.

[0009] The strut locks the plates at a desired distance apart and, therefore, at a desired angle. The strut is made of a top, rotatable post and a bottom, stationary post that work together to lock the top plate at the desired angle from the bottom plate using a ratchet-like locking mechanism. The posts have intermeshing serrations and are biased against each other by a torsion spring. Optionally, the strut is surrounded by a sheath to prevent bone particles and other debris from interfering with the mating of the serrations.

[0010] In some embodiments, the insertion tool is configured to cooperate with the movable post to unlock the serrations and allow the spacer to return to its unexpanded state. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a top perspective view from the distal end of a first embodiment of a spacer in an unexpanded configuration.

[0012] Figure 2 It is from Figure 1 A top perspective view of the proximal end of the spacer.

[0013] Figure 3 yes Figure 1 Side view of the spacer.

[0014] Figure 4 yes Figure 1 Side view of the spacer without the sheath shown.

[0015] Figure 5 yes Figure 1 A top view of the spacer.

[0016] Figure 6 It is along Figure 3 The line AA intercepts Figure 1 A top view of the spacer.

[0017] Figure 7 yes Figure 1 End view of the distal end of the spacer.

[0018] Figure 8 is from the expanded configuration Figure 1 A top perspective view of the distal end of the spacer is shown without the sheath.

[0019] Figure 9 It is from Figure 8 A top perspective view of the proximal end of the spacer.

[0020] Figure 10 yes Figure 9 Side view of the spacer.

[0021] Figure 11 yes Figure 9 Side view of the spacer without the sheath shown.

[0022] Figure 12 yes Figure 8 A top view of the spacer.

[0023] Figure 13 It is along Figure 10 The line BB intercepts Figure 1 A top view of the spacer.

[0024] Figure 14 yes Figure 9 End view of the distal end of the spacer.

[0025] Figure 15 is a top perspective view of the distal end of the second embodiment of the spacer in an unexpanded configuration.

[0026] Figure 16 It is from Figure 15 A top perspective view of the proximal end of the spacer.

[0027] Figure 17 yes Figure 15 Side view of the spacer.

[0028] Figure 18 yes Figure 15 Side view of the spacer without the sheath shown.

[0029] Figure 19 yes Figure 15 A top view of the spacer.

[0030] Figure 20 It is along Figure 17 The line CC intercepts Figure 15 A top view of the spacer.

[0031] Figure 21 yes Figure 15 End view of the distal end of the spacer.

[0032] Figure 22 is from the expanded configuration Figure 15 A top perspective view of the distal end of the spacer.

[0033] Figure 23 It is from Figure 22 A top perspective view of the proximal end of the spacer.

[0034] Figure 24 yes Figure 22 Side view of the spacer.

[0035] Figure 25 yes Figure 22 Side view of the spacer without the sheath shown.

[0036] Figure 26 yes Figure 22 A top view of the spacer.

[0037] Figure 27 It is along Figure 24 The line DD intercepts Figure 22 A top view of the spacer.

[0038] Figure 28 yes Figure 22 End view of the distal end of the spacer.

[0039] Figure 29 is a perspective view of the insertion tool.

[0040] Figure 30 is a side view of the insert's shaft assembly and retaining collar.

[0041] Figure 31 is a perspective view of a threaded clamping nut.

[0042] Figure 32 is a top cross-sectional view of the clamping arm before the tab is clamped to the cage.

[0043] Figure 33 is a top cross-sectional view of the clamping arm after the tab has been clamped to the cage.

[0044] Figure 34 is a top perspective view of the open clamping arms approaching the cage.

[0045] Figure 35is a top perspective view of the clamping arm in position to clamp the cage.

[0046] Figure 36 is a top perspective view of the clamping arm clamped to the cage.

[0047] Figure 37 is a top perspective view from the proximal end of the insert and spacer of the first embodiment.

[0048] Figure 38 is a cut-away side view of an insert showing the push rod and spacer of the first embodiment.

[0049] Figure 39 There are no spacers Figure 37 Cross-sectional view of the insertion device.

[0050] Figure 40 is a side view of a push rod partially extending into the spacer of the first embodiment.

[0051] Figure 41 is a side view of a push rod extending far enough into the spacer of the first embodiment to expand the spacer to a desired height.

[0052] Figure 42 is a side view of a push rod and bone graft material withdrawn from the spacer of the first embodiment, leaving the push rod at a locked, expanded desired height.

[0053] Figure 43 is a side view of the push rod and spacer of the second embodiment.

[0054] Figure 44 is a cross-sectional view of an insertion tool and a spacer of a second embodiment.

[0055] Figure 45 is a cross-sectional view of a push rod for use with a second embodiment of a spacer.

[0056] Figure 46 is a side view of a push rod partially extending into a spacer of a second embodiment.

[0057] Figure 47 is a side view of a push rod extending far enough into the spacer of the second embodiment to expand the spacer to a desired height.

[0058] Figure 48 is a side view of a push rod and bone graft material withdrawn from a spacer of a second embodiment, leaving the push rod at a locked, expanded desired height.

[0059] Figure 49 is a side view of an unlocking cable attached to the ratchet locking mechanism in the spacer of the second embodiment.

[0060] Figure 50 yes Figure 49 An enlarged view of the circled portion showing the cable attached to the ratchet locking mechanism.

[0061] Figure 51 is a side view of an unlocking cable attached to the ratchet locking mechanism in the spacer of the second embodiment.

[0062] Figure 52 is a side view of the insert and spacer showing the unlocking cable attached to the ratchet locking mechanism in the spacer of the second embodiment.

[0063] Figure 53 is a diagram showing the unlocking cable being disconnected and withdrawn from the ratchet locking mechanism Figure 52 .

[0064] Figure 54 It is a schematic illustration of parts of a pillar.

[0065] Figures 55A to 55D is a side view of the locking mechanisms, each engaging a different number of serrations.

[0066] Figure 56 The diagram shows the effect of sawtooth patterns that are not 90 degrees to the column.

[0067] Figure 57 is a perspective view of a torsion spring.

[0068] Figure 58 is a schematic illustration of an unexpanded spacer between two vertebrae.

[0069] Figure 59 is in a state of expansion Figure 58 Schematic illustration of a spacer.

[0070] Figure 60 is a top view of a third embodiment of a spacer.

[0071] Figure 61 yes Figure 60 Side view of the spacer. DETAILED DESCRIPTION

[0072] The expandable intervertebral spacer system includes a spacer 10 having an integral expansion mechanism and an integral ratchet locking mechanism and a mating insertion tool. The spacer 10 is inserted into the patient's body in an unexpanded form using a mating removable insertion tool 50 that also includes a push rod 51 and an optional unlocking mechanism.

[0073] The spacer includes a top plate 11 and a bottom plate 12 that form a cage 13 that surrounds a cavity. The top, bottom, and sides of the cage 13 have openings, referred to herein as cutouts 18, to allow bone graft material 44 to be more easily loaded into the cavity between the plates and thereby increase the surface contact of the graft material with the patient's vertebrae. In some embodiments, the cage is substantially rectangular, such as Figure 1 and Figure 15 In other embodiments, cage 13 is barbell-shaped, wherein top plate 11 and bottom plate 12 include a central ridge connecting a proximal hinge region with a distal ratchet region. Figures 60 to 61 .

[0074] The proximal end 15 of the cage 13 has a clamping slot 16 that is grasped by an insertion tool, as explained in more detail below. The distal end 14 of the spacer 10 is the front end when the device is inserted between the vertebrae and is typically rounded to ease insertion. The distal end 14 is typically solid so that no debris from the patient's body enters the cavity during insertion, but optionally, the distal end 14 can also have a cutout. The proximal end 15 of the spacer 10 is open to accommodate the insertion tool. This opening is considered the cutout 18 of the device. The bone graft material packed in and around the spacer provides a scaffold so that new bone can form. The bone graft material can be cancellous bone or compact bone or both, and is preferably autograft or allograft tissue.

[0075] Cage 13 comprises one or more inclined members. In one embodiment, each inclined member has a first portion connected to a second portion, forming a V-shaped or solid wedge-shaped member extending from the plate to which the inclined member is attached. The first portion of the inclined member angles into the cage from the proximal end toward the distal end. The second portion of the inclined member angles away from the plate. In yet other embodiments, the inclined member has a single leg angled from the proximal end toward the distal end of the cage.

[0076] The inclined members are preferably V-shaped, with no material below the apex of the V to minimize weight and maximize the volume of the cage for bone graft material. In other embodiments, the inclined members are solid wedge-shaped members, with material filling the V to form a solid triangle. Instead of a sharp point at the apex of the inclined member, the apex can be rounded to be more like a U-shape. Wherein, each inclined member extends into the cage from the top plate or the bottom plate or both, rather than extending from either side of the cage, the top, bottom and sides of the cage have cutouts 18, rather than being solid. The cutouts 18 in the top, bottom and all sides of the cage 13 allow bone graft material to be loaded through each surface and contact the material with the patient's vertebrae. The cutouts in the top, bottom and all sides of the cage maximize the contact of the bone graft material with the patient's tissue.

[0077] The inclined members extend from the top and bottom of the cage into the cage, rather than from the sides of the cage into the cage. In the first embodiment, the top inclined member 31 extends from the top plate 11 into the cavity, and the bottom inclined member 32 extends from the bottom plate 12 into the cavity. See Figures 1 to 14 Each inclined member may be as long as the entire length of the cage from the proximal end to the distal end, or the inclined member may be shorter than the entire length of the cage 13, such as Figures 1 to 13 The tilting members are preferably equidistant from the longitudinal centerline of the cage, whether near the centerline or at the periphery of the cage.

[0078] Top and bottom panels 11, 12 are connected at a hinge 40 at the proximal end of cage 13, which allows top panel 11 to be forced apart from bottom panel 12 at an angle, as explained in more detail below. As shown in the figures, hinge 40 is typically a pin hinge that fits into cylindrical slots in the top and bottom panels to hold the panels together and allow them to swing away from each other. Alternatively, the panels can be hinged together using two pivot hinges on either side of the proximal end of the cage.

[0079] In a second embodiment, only one ramp extends from either the top or bottom plate into the cavity. Figures 15 to 28 In the preferred embodiment shown in FIG, a top sloped member 31 extends from the top plate 11 into the cavity. The top sloped member 31 can be as long as the entire length of the cage from the proximal end to the distal end, or the sloped member can be shorter than the entire length of the cage 13, as shown in FIG. Figures 15 to 27 A single ramp is located on the longitudinal centerline of the cage to promote uniform lifting and limited side-to-side rolling of the top panel during expansion.

[0080] In another embodiment, two inclined members extend from the top plate or the bottom plate into the cavity.The inclined members are equidistant from the longitudinal centerline of the cage, either near the centerline or at the periphery of the cage.

[0081] The top and bottom panels 11, 12 are separated and held apart by a ratchet locking mechanism 19. The locking mechanism 19 uses at least one post 20 to provide a strong and balanced support between the panels. Each post 20 includes two serrated posts 21, 22 that move relative to each other and cooperate to lock the top panel 11 at a desired angle to the bottom panel 12. Figure 54 to Figure 5 5. One serrated post 21 is movable, rotating toward and away from the other serrated post 22. The serrated post 22 is stationary. Preferably, the movable post 21 protrudes from the top plate 11 into the cage 13, and the stationary post 22 protrudes from the bottom plate 12 into the cage 13.

[0082] The posts 21, 22 are biased against each other by a helical torsion compression spring 25 which exerts a torque or rotational force on the movable post 21 about the axis of the torsion spring. Figure 57 . When the torsion spring is at rest, the torsion spring 25 forces the movable post 21 against the stationary post 22 in the support column 20. When the top and bottom plates are forced apart, the torsion spring is compressed, and the posts 21, 22 are forced apart and unlocked. When the top and bottom plates are separated to the desired distance, the torsion spring relaxes, forcing the serrations of the posts to reengage, which locks the top and bottom plates to the desired distance apart. Certain figures illustrate embodiments in which the coils of the torsion spring 25 extend slightly above the top plate 11, thereby maximizing the open volume of the cage 13. In other embodiments, the torsion spring 25 is positioned lower in the cage 13, such that the spring coils are flush with or even below the top surface of the top plate 11.

[0083] In an alternative embodiment, instead of torsion springs biasing the posts 21, 22 against each other, linear springs disposed vertically between the top and bottom plates 11, 12 bias the plates 11, 12 apart. This in turn forces the teeth of the posts 21, 22 against each other, locking them in place.

[0084] Each tooth is generally triangular in shape, with one side of the triangle extending away from the post at an angle of approximately 90-106 degrees. This portion of the tooth is referred to herein as the horizontal edge 35. In one embodiment, the horizontal edge is at right angles to its post, parallel to the top plate 11 and the bottom plate 12. See Figure 54 In another embodiment, the horizontal edge is greater than 90 degrees from the column, and the angle θ shows the difference from the vertical. Figure 56 Angle θ represents the angular offset between the center-to-root line and the root-to-tip line, where the root is the point where the step attaches to the post. The other edge of the serrations is at a complementary angle to its post, referred to herein as the angled edge 36. The teeth of one post intermesh with the teeth of the adjacent post. When the serrations engage, the horizontal edge 35 of each tooth rests against the horizontal edge 35 of one or more teeth on the opposing post. This holds the top and bottom plates stationary relative to each other, locking the plates together. The greater the angle θ between the horizontal edge 35 and the post, the greater the force required to separate the posts 21 and 22. When the cage is expanded and the horizontal edges are at an angle exceeding 90 degrees, the ramp must be forced open further than when the horizontal edges are at 90 degrees to clear the edge of the step. The post then slides downward, causing the teeth to intermesh. The posts intermeshing at an angle θ greater than zero creates an interlocking force on the step that pushes them together and increases the security of the locking mechanism.

[0085] The asymmetrical shape of the teeth enables the plates to be incrementally forced apart, one tooth at a time, in a ratchet-like motion. Due to the cooperating shape of the teeth, as the top and bottom plates are forced away from each other by the expansion mechanism, the posts 21, 22 are forced apart from each other. As the top plate is forced away from the bottom plate, as explained in more detail below, the angled edges of the teeth of the top post slide against the angled edges of the teeth of the bottom post, forcing the top post to rotate away from the bottom post by an amount sufficient to release the horizontal edges of the teeth that were previously engaged.

[0086] The height of the teeth determines the distance of each incremental separation between the plates: the smaller the tooth height, the finer the separation at each increment. The number of teeth and their height determine the maximum distance the plates can be separated. At maximum expansion, preferably a minimum of two teeth engage each strut.

[0087] The width of the struts 20 varies depending on the size of the spacer, with the struts ranging in width from about 2 mm to 6 mm. In one example, the horizontal edge 35 of each serration is 1.5 mm deep and 4 mm wide. Assuming each strut engages two teeth, this provides a 6 mm 2 The minimum total contact area (2 teeth x 1.5 mm deep x 4 mm wide) is 10,200 N. Given that the compressive strength of titanium alloy is 850 MPa, the failure load is 10,200 N. Therefore, the locking mechanism can withstand the compressive forces between the vertebrae and the cage so that the spacer will not collapse or otherwise fail during the patient's lifetime.

[0088] Preferably, a single strut is used at the distal end to lock the plates apart to minimize the number of moving parts and maximize the size of the teeth and therefore the compressive strength. In some embodiments, two struts may be used, such as one at each corner of the distal end of the cage.

[0089] Optionally, a sheath 24 surrounds each strut or the entire locking mechanism to prevent bone particles and other debris from interfering with the mating of the serrations. The sidewall thickness of the sheath 24 is preferably less than 1 mm.

[0090] The spacer 10 is inserted into the patient's body in an unexpanded form using a removable insertion tool 50. Figure 29 and Figure 37 The insertion tool 50 includes clamping arms 55 and 56, a push rod 51, and optionally an unlocking cable 53 within a hollow shaft 52, which serves as a lumen through which the insertion tool components pass to operate on the septum. In a preferred embodiment, the push rod 51 sits within the hollow shaft between the clamping arms and concentrically inside the clamping arms. The unlocking cable can sit alongside or between the clamping arms within the hollow shaft, but preferably, it passes through the central lumen of the insertion tool.

[0091] Clamping arms 55 and 56 are Figures 29 to 36 . The ends of the clamping arms are protrusions that fit into the clamping slots 16 on the ends of the proximal cage 13, allowing the insertion tool to be securely held to the cage during insertion and released once inserted. The clamping arm protrusions are inserted into the clamping slots and closed toward each other by moving the clamping collar 57 toward the ends of the clamping arms. The clamping collar 57 is moved over the clamping arms by rotating a threaded cylinder 58. Rotation of the cylinder 58 in a first direction moves the collar 57 toward the cage, thereby tightening the protrusions in the cage's clamping slots. Rotation of the cylinder 58 in the reverse direction moves the collar 57 away from the cage, thereby releasing the protrusions from the cage's slots.

[0092] Once the cage is clamped to the insertion tool, the cage is inserted between two vertebrae of the patient. The cage is movable between a collapsed configuration, in which the top and bottom plates are parallel, and an expanded configuration, in which the top and bottom plates are not parallel. When expanded, the plates 11, 12 separate at the distal ends, forming an opening, which is herein referred to as the incision 18. Expansion is achieved by extending the push rod 51 into the cage 13 by turning the threaded handle 54. The push rod moves toward the cage through the hollow shaft 52 without rotation. The distal end of the push rod is wide enough to cooperate with one or more inclined members in the cage, but narrow enough to fit into the aperture in the proximal end of the cage. The distal end of the push rod is preferably rounded, but can also be pointed or flat.

[0093] A push rod 51 is paired with each embodiment. For the first embodiment of the spacer with two inclined pieces, the push rod 51 is hinged at the end, most easily Figure 38 and Figure 39 As the push rod 51 extends into the cage 13, the hinged top end moves upwardly along the bottom slope 32 between the top and bottom slopes, forcing the top and bottom panels apart. Figures 40 to 41 Once the top and bottom plates are positioned at the desired angles, the push rods 51 are withdrawn. Figure 42 The bone graft material 44 is then loaded into the spacer.

[0094] For the second embodiment of the spacer with a single inclined member, the push rod 51 is preferably not hinged at the end, as Figures 43 to 45 As the push rod 51 extends into the cage 13, it slides along the bottom plate 12 beneath the top ramp 31, forcing the top and bottom plates apart as the push rod penetrates deeper into the cage. Figures 46 to 47 Once the top and bottom plates are positioned at the desired angles, the push rod 51 is withdrawn. Figure 48 The bone graft material 44 is then loaded into the spacer.

[0095] Optionally, the unlocking cable 53 resides in a cannulated push rod 51. Figures 49 to 52 The cable 53 is attached to the movable post 21 by a connector 61. Preferably, the connector is threaded, but other fastening means may be used. When the cable is pulled proximally, it rotates the movable post 21 away from the stationary post 22, disengaging the serrations and allowing the top plate to drop back to a lower position relative to the bottom plate, thereby reducing the angle between the plates. To disconnect the cable from the post, the cable is unwound and withdrawn from the cage. See Figure 53 .

[0096] Once the spacer is in its desired position, the clamping arms are released from the cage by turning the threaded cylinder and the insertion tool is removed from the patient.

[0097] Spacers are made of biocompatible materials (usually titanium or titanium alloys) and can be made in several sizes. They are typically between 26-30 mm long and 10-11 mm wide. Table 1 shows an exemplary size range, where the height h, width w, and length l of the spacer are in Figure 4 and Figure 5 Shown in.

[0098] Table 1 <![CDATA[Unexpanded height h1 (mm)]]> <![CDATA[Full expansion height h2 (mm) at the distal end]]> The angle formed Width w (mm) Length l (mm) 7 10 0-16 10 28 8 12 0-16 10 28 9 14 0-16 10 28 10 16 0-16 10 28 While the general shape of the vertebrae 9 is common between patients, the specific size, shape, lordosis, and condition of the cancellous bone are unique to each patient. These biological factors influence the size, shape, and placement of the spacers. Each plate can be flat, concave, or convex, depending on the shape required to most closely match the curvature of the patient's vertebral surface.

[0099] Figure 58 A single unexpanded spacer 10 is shown inserted between two vertebrae 9 separated by a distance d1 . Figure 59 A single spacer 10 is shown expanded between two vertebrae 9, forcing the vertebrae 9 apart by a distance d2 and an angle al.

[0100] While there has been illustrated and described what are presently considered to be the preferred embodiments of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made and equivalents may be substituted for elements thereof without departing from the true scope of the invention. It is therefore intended that the present invention not be limited to the particular embodiments disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

1. An expandable intervertebral spacer system, comprising: a) top and bottom panels forming a cage having a proximal end, a distal end, a top, a bottom, and four sides; b) a first inclined member extending from the top or bottom of the cage into the cage; c) a hinge connecting the top panel and the bottom panel at the proximal end; d) a strut at the distal end, the strut comprising a movable post having serrations and a stationary post having serrations; and e) a torsion spring configured to bias the movable post against the stationary post such that the movable post and the stationary post cooperate to lock the top and bottom plates a desired distance apart.

2. The system according to claim 1, wherein: The top, bottom, and at least three of the four sides of the cage have cutouts.

3. The system according to claim 1, wherein: The torsion spring exerts a rotational force on the movable post about a longitudinal axis of the torsion spring.

4. The system according to claim 1, wherein: The cage has a longitudinal centerline, and the first angled member is disposed at the centerline.

5. The system of claim 1 , further comprising a second inclined member extending into the cage from the same plate as the first inclined member, wherein the cage has a longitudinal centerline, and the first and second inclined members are disposed on opposite sides of the centerline and at equal distances from the centerline.

6. The system of claim 1 further comprising a removable insertion tool comprising an extendable push rod insertable from the proximal end between the top and bottom plates, the extendable push rod cooperating with the first ramp to force the top and bottom plates apart.

7. The system according to claim 6, wherein: The insertion tool also includes an unlocking cable removably mated to the movable post.

8. The system according to claim 1, wherein: The cage is movable between a collapsed configuration and an expanded configuration, and wherein in the expanded configuration the top and bottom plates are non-parallel.

9. An expandable intervertebral spacer system, comprising: a) a top plate and a bottom plate forming a cage having a proximal end and a distal end; b) a first inclined member extending from the top plate or the bottom plate into the cage; c) a second inclined member extending into the cage from one of the top or bottom panels, which is different from the panel from which the first inclined member extends, wherein the cage has a longitudinal centerline and the first and second inclined members are arranged parallel to the centerline; d) a hinge connecting the top panel and the bottom panel at the proximal end; e) a strut at the distal end, the strut comprising a movable post having serrations and a stationary post having serrations; f) a torsion spring configured to bias the movable post against the stationary post such that the movable post and the stationary post cooperate to lock the top and bottom plates a desired distance apart.

10. An expandable intervertebral spacer system, the spacer system comprising: A spacer, comprising: a) top and bottom panels forming a cage having a proximal end, a distal end, a top, a bottom, and four sides; b) a first inclined member and a second inclined member, wherein the first inclined member extends from the top of the cage into the cage, and the second inclined member extends from the bottom of the cage into the cage; c) a hinge connecting the top panel and the bottom panel at the proximal end; d) a strut at the distal end, the strut comprising a movable post having serrations and a stationary post having serrations; and e) a torsion spring configured to bias the movable post against the stationary post such that the movable post and the stationary post cooperate to lock the top and bottom plates a desired distance apart.

11. The system according to claim 10, wherein: The top, bottom, and at least three of the four sides of the cage have cutouts.

12. The system according to claim 10, wherein: The torsion spring exerts a rotational force on the movable post about a longitudinal axis of the torsion spring.

13. The system of claim 10 further comprising a removable insertion tool comprising an extendable push rod having a top end, wherein the push rod is insertable between the top plate and the bottom plate from a proximal end, the push rod cooperating with the first ramp to force the top plate and the bottom plate apart.

14. The system according to claim 13, wherein: The insertion tool also includes an unlocking cable that removably mates with the movable post.

15. The system according to claim 10, wherein: The spacer is movable between a collapsed configuration and an expanded configuration, and wherein in the expanded configuration the top plate and the bottom plate are non-parallel.

16. An expandable intervertebral spacer system, the spacer system comprising: a) a top panel having a top sloped member extending toward the bottom panel; b) a bottom plate having a bottom sloped member extending toward the top plate; The top plate and the bottom plate form a cage having a proximal end and a distal end; c) a hinge connecting the top panel and the bottom panel at the proximal end; d) a strut at the distal end, the strut comprising a movable post having serrations and a stationary post having serrations; and e) a torsion spring configured to bias the movable post against the stationary post such that the movable post and the stationary post cooperate to lock the top and bottom plates a desired distance apart; as well as a removable insertion tool comprising an extendable push rod having a tip, wherein the push rod is insertable between the top plate and the bottom plate from a proximal end, the push rod cooperating with the first ramp to force the top plate and the bottom plate apart, The push rod is hinged at its top end.

17. An expandable intervertebral spacer system, the spacer system comprising: a) top and bottom panels forming a cage having a proximal end, a distal end, a top, a bottom, and four sides; b) an inclined member extending from the top or bottom of the cage into the cage; c) a hinge connecting the top panel and the bottom panel at the proximal end; d) a strut at the distal end, the strut comprising a movable post having serrations and a stationary post having serrations; and e) a torsion spring configured to bias the movable post against the stationary post such that the movable post and the stationary post cooperate to lock the top and bottom plates a desired distance apart; and f) a removable insertion tool comprising an extendable push rod insertable between the top and bottom panels from the proximal end, the extendable push rod cooperating with the first ramp to force the top and bottom panels apart.

18. The system according to claim 17, wherein: The top, bottom, and at least three of the four sides of the cage have cutouts.

19. The system according to claim 17, wherein: The insertion tool also includes an unlocking cable that removably mates with the movable post.

20. The system of claim 17, wherein: The cage is movable between a collapsed configuration and an expanded configuration, and wherein in the expanded configuration the top and bottom plates are non-parallel.

21. An expandable intervertebral spacer system, the spacer system comprising: a) top and bottom panels forming a cage having a proximal end, a distal end, a top, a bottom, and four sides; b) an inclined member extending from the top or bottom of the cage into the cage; c) a hinge connecting the top panel and the bottom panel at the proximal end; d) a strut at the distal end, the strut comprising a movable post having serrations and a stationary post having serrations, wherein i) each of the teeth has a horizontal edge; ii) the horizontal edges of the serrations on the stationary post are angled at an angle greater than 90 degrees relative to the stationary post; and iii) the horizontal edges of the serrations on the movable post are angled relative to the movable post at angles complementary to those of the serrations on the stationary post; and e) a torsion spring configured to bias the movable post against the stationary post such that the movable post and the stationary post cooperate to lock the top and bottom plates a desired distance apart.

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