Expandable intervertebral implant

1. An intervertebral implant configured for implantation in an intervertebral disc space defined by an upper vertebra and a lower vertebra, the intervertebral implant comprising:

an upper portion having an upwardly-facing vertebral engagement surface that is configured to abut the upper vertebra, upper teeth that project out from the upwardly-facing vertebral engagement surface and are configured to grip the upper vertebra, and an opposed inner surface opposite the upwardly-facing vertebral engagement surface;

a lower portion having a downwardly-facing vertebral engagement surface that is configured to abut the lower vertebra, lower teeth that project out from the downwardly-facing vertebral engagement surface and are configured to grip the lower vertebra, and an opposed inner surface opposite the downwardly-facing vertebral engagement surface;

an inner core movable along an expansion direction with respect to the upper and lower portions, the inner core including an upper sloped engagement surface configured to engage a respective engagement surface defined by the inner surface of the upper portion, and a lower sloped engagement surface configured to engage a respective engagement surface defined by the inner surface of the lower portion,

an actuation member that is engaged with the inner core and configured to urge the inner core to move along the expansion direction, which in turn causes the upper and lower sloped engagement surfaces of the inner core to ride along the engagement surfaces of the upper and lower portions, respectively, thereby causing the implant to lordotically expand from an initial position to an expanded position, wherein the inner core and the actuation member are sized and configured to remain in the intervertebral space after implantation of the intervertebral implant in the intervertebral disc space; and

a retention member that is coupled to each of the upper and lower portions prior to the expansion, during the expansion, and after the expansion, wherein the retention member expands during lordotic expansion of the implant,

wherein the implant is configured to prevent the inner core from moving a direction opposite the expansion direction while the implant is under compressive forces while 1) the upper sloped engagement surface engages the engagement surface defined by the inner surface of the upper portion, and 2) the lower sloped engagement surfaces engages the respective engagement surface defined by the inner surface of the lower portion.

2. The intervertebral implant of claim 1 , wherein the expansion of the implant increases a distance along a vertical direction between the upwardly-facing vertebral engagement surface and the downwardly-facing vertebral engagement surface.

3. The intervertebral implant of claim 2 , wherein the retention member extends along an external side surface of the upper portion and an external side surface of the lower portion.

4. The intervertebral implant of claim 3 , wherein the external side surfaces are aligned with each other.

5. The intervertebral implant of claim 2 , wherein the upper portion and the lower portion abut each other when the intervertebral implant is in the initial position.

6. The intervertebral implant of claim 2 , wherein the upper sloped engagement surface of the inner core and the lower sloped engagement surface of the inner core abut the engagement surfaces of the upper and lower portions, respectively, when the intervertebral implant is in the expanded position.

7. The intervertebral implant of claim 2 , wherein the actuation member extends between the upper portion and the lower portion with respect to the longitudinal direction.

8. The intervertebral implant of claim 2 , wherein the upper and lower portions define a leading end with respect to insertion into an intervertebral disc space and a trailing end opposite the leading end, and the actuator extends out from the leading end.

9. The intervertebral implant of claim 2 , wherein the expansion of the implant causes the retention member to expand along the vertical direction.

10. The intervertebral implant of claim 2 , wherein:

the upper sloped engagement surface is a first upper sloped engagement surface, the lower sloped engagement surface is a first lower sloped engagement surface,

the inner core defines a second upper sloped engagement surface spaced from the first upper sloped engagement surface along the longitudinal direction,

the inner core defines a second lower sloped engagement surface spaced from the first lower sloped engagement surface along the longitudinal direction, and

movement of the inner core along the longitudinal direction causes 1) the first and second upper engagement surfaces of the inner core to ride along respective first and second engagement surfaces of the upper portion, and 2) the first and second lower engagement surfaces of the inner core to ride along respective first and second engagement surfaces of the lower portion, thereby urging the upper and lower portions away from each other along the vertical direction.