Dual-action expandable intervertebral implants
A two-stage intervertebral implant comprises an expandable cage comprising a pivot connecting upper and lower bodies, a first expansion mechanism, such as a wedge, configured to pivot the upper body and the lower body at the pivot point in a first stage, and a second expansion mechanism, such as a toggle joint, configured to pivot the upper body and the lower body at the pivot point in a second stage beyond the first stage. A method of implanting an implant comprises inserting the implant into anatomy, the implant comprising a first component rotatably coupled to a second component at a pivot point, operating a first expansion mechanism to rotate the implant at the pivot point to expand the implant to a first level, and operating a second expansion mechanism to rotate the implant at the pivot point from the first level to a second level.
1 . An intervertebral implant comprising:
a first cage comprising a first angled surface;
a second cage comprising a second angled surface opposing the first angled surface;
a drive shaft comprising a first shaft and a second shaft, the second shaft being threaded into the first shaft;
a hinge connecting the first cage and the second cage at a first side of the intervertebral implant;
a toggle joint connecting the first cage and the second cage at a second side of the intervertebral implant; and
a wedge having opposing surfaces and positioned between the first cage and the second cage and configured to translate from proximate the first side toward the second side,
wherein the wedge is positioned on the first shaft such that rotation of the first shaft causes the wedge to move closer to the second shaft and opposing surfaces of the wedge are pushed into the angled surfaces of the first and second cages to force the first cage and the second cage away from each other to cause rotation about the hinge and initial expansion of the toggle joint.
2 . The intervertebral implant of claim 1 , wherein:
the first shaft threadably engages the wedge such that the first shaft has an outer threaded surface along which the wedge translates and a threaded bore to engage a threaded exterior surface of the second shaft.
3 . The intervertebral implant of claim 2 , wherein the first cage comprises a first angled surface; and the second cage comprises a second angled surface opposing the first angled surface; wherein the wedge translates along the first and second angled surfaces to push the first and second cages away from each other and further comprising:
a first stop surface extending inward from the first angled surface; and
a second stop surface extending inward from the second angled surface;
wherein in a first stage expansion, the first and second stop surfaces are configured to inhibit further translation of the wedge along the first and second angled surfaces and the first and second shafts are configured to be disengaged from the toggle joint; and
wherein in a second stage expansion, the first and second shafts are configured to engage and rotate the toggle joint while being disengaged from further translation of the wedge along the first and second angled surfaces.
4 . The intervertebral implant of claim 1 , wherein:
the intervertebral implant is configured to rotate from a collapsed position to an expanded position;
in the collapsed position the first cage and the second cage are within ten degrees of parallel; and
in the expanded position the first cage and the second cage are angled relative to each other in a range of twenty-five to thirty-five degrees.
5 . The intervertebral implant of claim 1 , wherein the wedge is accessible between the first cage and the second cage from the first side via a portal in the hinge that is configured to receive a driver to enable the driver to engage the first shaft.
6 . The intervertebral implant of claim 5 , wherein the first shaft has an outer threaded surface along which the wedge translates; the first shaft further comprising a socket located at a first end of the first shaft; and the second shaft threaded into the first shaft and including a pivot connected to the toggle joint at a second end.
7 . The intervertebral implant of claim 6 , wherein:
the wedge is provided with stops to engage stop surfaces of the first and second cages.
8 . The intervertebral implant of claim 1 , wherein the toggle joint comprises:
a first linkage extending from the first cage; and
a second linkage extending from the second cage; and
a pin coupling the first and second linkages.
9 . The intervertebral implant of claim 8 , wherein the first and second linkages are curved.
10 . The intervertebral implant of claim 9 , wherein:
the toggle joint forms a rounded tip at the second side of the intervertebral implant in an expanded configuration; and
the toggle joint forms a pointed tip at the second side of the intervertebral implant in a collapsed position.
11 . The intervertebral implant of claim 1 , further comprising a plurality of arcuate slots located proximate the first side configured to couple to an inserter in a collapsed configuration and an expanded configuration.
12 . The intervertebral implant of claim 1 , wherein a first expansion mechanism comprises the wedge to rotate the intervertebral implant at a pivot point to expand the intervertebral implant to a first level, wherein a second expansion mechanism comprises the toggle joint to rotate the intervertebral implant at the pivot point from the first level to a second level, and wherein the first and second expansion mechanisms are sequentially operated by a compound threading action between the second shaft threadably engaging an interior of the first shaft, an exterior of the first shaft threadably engaging the wedge.
13 . The intervertebral implant of claim 12 , wherein the pivot point connects proximal portions of the first and second cages, the first expansion mechanism rotates distal portions of the first and second cages of the intervertebral implant at the pivot point, and the second expansion mechanism rotates the distal portions of the first and second cages of the intervertebral implant at the pivot point from the first level to a second level, wherein, in the first level, the first expansion mechanism pivots the distal portions of the first and second cages at the pivot point without engagement of the second expansion mechanism, wherein, in the second level, the second expansion mechanism pivots the distal portions of the first and second cages at the pivot point without engagement of the first expansion mechanism, and wherein operating the first expansion mechanism and operating the second expansion mechanism comprise rotating a driver engaging the first shaft.
14 . A two-stage intervertebral implant comprising:
an expandable cage comprising:
an upper body;
a lower body; and
a pivot connecting the upper body and the lower body;
a first expansion mechanism configured to pivot the upper body and the lower body at the pivot in a first stage;
a second expansion mechanism configured to pivot the upper body and the lower body at the pivot in a second stage beyond the first stage, and an actuation mechanism configured to sequentially operate the first expansion mechanism and the second expansion mechanism,
wherein the first expansion mechanism comprises a wedge configured to slide against the upper body and the lower body to push apart the upper body and the lower body;
wherein the second expansion mechanism comprises a toggle joint configured to expand between the upper body and the lower body to push apart the upper body and the lower body; and
wherein the actuation mechanism comprises a first shaft configured to engage a driver and a second shaft configured to threadably engage the first shaft, wherein the wedge engages the first shaft such that displacement of the first shaft relative to the second shaft causes displacement of the wedge, whereby opposing surfaces of the wedge engage corresponding first and second angled surfaces of the upper and lower bodies, respectively, to cause rotation and initial expansion of the toggle joint, and wherein engagement of the first shaft by the driver causes the first and second stages through sequential engagement of the first and second expansion mechanisms.
15 . The two-stage intervertebral implant of claim 14 , wherein the first expansion mechanism has a greater opening strength than the second expansion mechanism and is used to initiate expansion while the second expansion mechanism has a greater expansion height than the first expansion mechanism and is used to provide further expansion; and wherein:
the first and second expansion mechanisms comprise:
a binding post fastener connected to the toggle joint; and
the wedge threaded onto the binding post fastener and engaged with the upper and lower bodies.
16 . The two-stage intervertebral implant of claim 14 , wherein:
the first shaft threadably engages the wedge such that the first shaft has an outer threaded surface along which the wedge translates and a threaded bore to engage a threaded exterior surface of the second shaft; and
wherein the wedge translates along the first and second angled surfaces to push the upper and lower bodies away from each other.
17 . The two-stage intervertebral implant of claim 16 , further comprising:
a first stop surface extending inward from and transverse to the first angled surface; and
a second stop surface extending inward from and transverse to the second angled surface;
wherein, in the first stage, the first and second stop surfaces are configured to inhibit further translation of the wedge along the first and second angled surfaces and the first and second shafts are configured to inhibit rotation of the toggle joint; and
wherein, in the second stage, the first and second shafts are configured to rotate the toggle joint without further translation of the wedge along the first and second angled surfaces.
18 . The two-stage intervertebral implant of claim 17 , wherein the wedge is accessible between the upper and lower bodies from a proximal end via a portal in a hinge that is configured to receive the driver to enable the driver to engage the first shaft.
19 . The two-stage intervertebral implant of claim 18 , further comprising:
a screw mechanism configured to transition the implant between an expanded position and a collapsed position, the screw mechanism comprising the first shaft and the second shaft, the first shaft comprising a socket located at a first end of the first shaft to receive the driver, and the pivot connected to the toggle joint at a second end.
20 . The two-stage intervertebral implant of claim 19 , wherein opposing surfaces of the wedge each comprises an angled edge portion engaging a corresponding one of the first and second angled surfaces and a front portion engaging a corresponding one of the first and second stop surfaces, and wherein, in each of the opposing surfaces, the corresponding one of the first and second angled surfaces is transverse to the front portion.