Patent ID: 12213893

DETAILED DESCRIPTION

Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary sill in the art having the benefit of this disclosure. The expandable spinal fusion implant and related methods disclosed herein boasts a variety of inventive features and components that warrant patent protection, both individually and in combination.

In general, the expandable spinal fusion implants described in this document include a housing, upper and lower endplates, a translating wedge positioned between the upper and lower endplates and within the housing, and a drive mechanism to drive translation of the wedge. The expandable spinal fusion implant is designed to be inserted into the disc space between adjacent vertebral bodies from a posterior approach. The implant may be made of any suitable, biocompatible material or combination of materials. For example, the implant components may be metal, polyether ether ketone (PEEK), or a combination of the metal and PEEK. The implant is configured to be inserted into the disc space in a collapsed state and upon being seated in a desired location within the disc space the distal end of the implant is expanded in height to create an implant with a lordotic angle (i.e. the anterior height of the implant is greater than the posterior height of the implant, thereby restoring a more natural lordotic curvature of the particular segment of the lumbar spine). The expansion is accomplished by engaging the drive mechanism with a tool to activate the drive mechanism and cause the translating wedge to move between the implants in a distal direction.

FIGS.1-15illustrate an exemplary embodiment of the expandable spinal fusion implant10. The implant10includes a housing20. The housing20is comprised of first and second lateral walls22,23, a distal or leading end wall24and a proximal or trailing end wall25. The lateral walls22,23and distal24and proximal25walls define a hollow interior of housing20. According to this embodiment, the first and second lateral walls22,23are of equal length and the length of the lateral walls22,23spans the length of the implant10. The distal wall24is tapered, increasing in height from the distal most point to the point where it meets the lateral walls22,23to aid in insertion of the implant10into the disc space. As illustrated in the exemplary embodiment, the distal wall24may also include a slots26dimensioned to receive complementary projections49extending from the upper and lower endplates30,40. The slots comprise a first slot in the upper surface of the distal end24of the housing20for receiving a projection from the upper endplate30and a second slot in the lower surface of the distal end24of the housing20for receiving a projection49from the lower endplate40. The proximal wall25of the housing is best illustrated inFIGS.5and6. The proximal wall25includes two apertures. The first is a graft delivery port27and the second is a drive screw aperture28. The drive screw aperture28is offset from the mid longitudinal axis of the implant10to facilitate packing of graft into the hollow interior of the housing10through the graft delivery port27upon implantation of the implant10into the disc space. The housing20has a static height that remains unchanged when the implant10is in its collapsed configuration and in its expanded configuration. The maximum height of the housing20is less than the maximum height of the overall implant10.

According to the embodiment ofFIGS.1-15, the housing20is coupled to the upper and lower endplates30,40via pins29adjacent the proximal end15of the implant10. The upper and lower endplates30,40have identical features as described below. Each endplate30,40has a bone contacting surface32,42and an interior surface34,44. The endplates30,40have a width that is equal to the width of the overall implant and equal to the width of the housing20. The perimeter of the interior surfaces34,44of the endplates30,40rests adjacent the lateral walls22,23of the housing20when the implant10is in its collapsed configuration. The upper and lower endplates30,40according to this embodiment are generally rectangular and include a central fusion aperture35,45. The central fusion apertures35,45are in communication with the hollow interior of the housing20and the central fusion aperture55of the wedge50to allow for bone growth through the implant10after the implant10has been place within the disc space of a patient. The endplates further include anti-migration features31,41on their respective bone contacting surfaces32,42. The interior surface34,44of each endplate30,40includes an extension36,46coupled to the endplate30,40via a pin39. The extensions36,46include a projection39at the distal end and a ramp37,47at the proximal end. The ramps37,47engage the superior and inferior angled surfaces51,52on the wedge50to allow for expansion of the height of the implant10as the wedge50is driven distally within the implant10. As illustrated in the exemplary embodiment ofFIGS.1-15, the ramps37,47and angled surfaces51,52of the wedge may include mating features to couple the wedge50to the endplates30,40. In the exemplary embodiment, this mating feature is a dovetail connection, though other mating features may be employed in the alternative.

As illustrated by the exemplary embodiment ofFIGS.1-15, the implant10includes a wedge50housed between the upper and lower endplates30,40and within the hollow interior of the housing20. The wedge50includes first and second opposing angled surfaces51,52at its distal end and a drive block53at its proximal end. The opposing angled surfaces51,52and drive block53are connected via a pair of lateral arms54extending therebetween. The opposing angled surfaces51,52, lateral arms54and drive block53reside inside the hollow interior of the housing20and define a central aperture55that is in communication with the central apertures35,45of the upper and lower endplates30,40. Optionally, the lateral arms54of the wedge50may engage rails70that rest in between a recess in the exterior surface of the lateral arms54and the interior surface of the lateral walls22,23of the housing20. The drive block53includes a graft aperture57extending through its thickness. The graft aperture57of the drive block53is in communication with the graft delivery port27in the proximal wall25of the housing20to allow graft material to be pass through the housing20and wedge50into the interior of the implant10. The drive block53also includes a receptacle56dimensioned to house the distal end64of the drive mechanism60.

According to the exemplary embodiment ofFIGS.1-15, the drive mechanism60is a screw. The drive screw60has a proximal end64and a distal end65and a threaded shaft62extending between the proximal end64and the distal end65. The proximal end64includes a mating feature63for engaging a driving tool (not shown). The distal end65is configured to complement the shape of the receptacle56of the drive block53. The threaded shaft of62of the drive screw is configured to be received in a complementary threaded drive screw aperture28in the housing20, such that as the drive screw60is rotated, it translates distally through the drive screw aperture28and consequently pushes the wedge50distally. When the wedge50is urged distally, the opposing angled surfaces51,52engage the ramps37,47on the endplates30,40thereby increasing the distance between the distal ends of the endplates30,40and increasing the distal height of the implant10.

In use according to this exemplary embodiment, the implant10implant is inserted into the disc space between adjacent vertebral bodies in its collapsed position as illustrated inFIG.12. The collapsed configuration of the implant is illustrated inFIGS.1,3,5,7and9. Once the implant10has been placed in the desired position within the disc space, the drive screw60is engaged with a driving tool and rotated to advance the drive screw60distally within the implant, thereby advancing the wedge50distally and causing the upper and lower endplates30,40to separate at the distal end14of the implant10. When the drive screw has been fully advanced, the implant10is in its fully expanded configuration as illustrated inFIG.13. Upon desired expansion of the implant, graft material is inserted into the interior of the implant through the graft delivery port27and graft aperture57of the wedge in the proximal end of the implant.

FIGS.16-27illustrate an alternative embodiment of the expandable spinal fusion implant110. The implant110according to this alternative embodiment has many of the same features as described for the implant10inFIGS.1-15which are not necessarily repeated in detail here. The implant110according to the alternative embodiment shown inFIGS.16-27is an oblique implant, meaning it is dimensioned to be inserted into the disc space at an angle that is oblique to the midline of the disc space. For example, this implant insertion trajectory is common in a transforaminal lumbar interbody fusion (TLIF) surgical procedure. The implant110according to the alternative embodiment is similar in structure to the one described inFIGS.1-15in that it includes a housing120, upper and lower endplates130,140, a wedge150and a drive mechanism160which are described in further detail below.

According to the embodiment ofFIGS.16-27, the implant110has a housing120. The housing has the same structure as previously described, including a distal wall124, a proximal wall125and first and second lateral walls122,123extending between the distal and proximal walls124,125. The four walls define a hollow interior of the housing120. However, the housing120according to the alternative embodiment is different in that the first lateral wall122, the anterolateral wall when the implant120is positioned in the disc space, is greater in length than the second lateral wall123(the posterolateral wall). The distal wall124is tapered to aid in insertion of the implant110into the disc space. The proximal wall125includes a threaded drive screw aperture127and a graft delivery port128. The drive screw aperture127is offset from the midline of the implant110and configured to receive the drive mechanism160therethrough. The height of the housing120is static, remaining unchanged when the implant110is in its collapsed configuration and its expanded configuration. The maximum height of the housing120is less than the maximum height of the overall implant110.

The upper and lower endplates130,140according to this alternative embodiment are identical, mirror images of each other. The endplates130,140of the alternative embodiment differ from the endplates30,40of the previously described embodiment in that they increase in height across the endplate130,140from the proximal end133,143to the distal end131,141of the endplate130,140and from the posterolateral side136,146to the anterolateral side138,148of the endplate130,140. As a result, when the implant120is in its fully expanded configuration, the anterolateral height h1of the implant110is greater than the posterolateral height h2of the implant, as best shown inFIGS.23and25. Each endplate130,140further comprises a bone contacting surface132,142and an interior surface134,144. Although not illustrated inFIGS.16-27, it is contemplated that the bone contacting surfaces132,142could include antimigration features. The interior surfaces134,144of the endplates130,140include a ramped surface137,147at the distal end of the endplate131,141that engage opposing angled surfaces151,152on the wedge150. According to the embodiment shown inFIGS.16-27, the interior side surfaces of the endplates include slots139,149for receiving projections126on the sides of the wedge150.

According to the alternative embodiment, the wedge150is similar in structure to the wedge50as previously described. The wedge150has opposing angled surfaces151,152at its distal end and a drive block153at its proximal end. The opposing angled surfaces151,152and drive block153are coupled via a pair of lateral arms154defining a central aperture155therebetween. The drive block153similarly includes a graft aperture157through its thickness and a drive screw receptacle158dimensioned to house the distal end164of the drive screw160.

The drive mechanism160of this alternative embodiment is similar in form and in function to the drive screw mechanism60described for the previous embodiment. The drive mechanism160is a drive screw. The drive screw160has a distal end164dimensioned to be received within the receptacle158of the drive block153and a proximal end165equipped with a mating feature for engaging a drive tool (not shown) and a threaded shaft162extending between the proximal end and distal end. As the drive screw162is rotated, the threads on the shaft162engage the complementary threads on the drive screw aperture128of the housing120allowing the drive screw to translate distally into the implant110thereby urging the wedge150distally within the implant and causing the endplates130,140to separate.

FIGS.28-36illustrate yet another alternative embodiment of an expandable spinal fusion implant210in a partially expanded state. As with the embodiment illustrated inFIGS.16-27, the current embodiment is designed to be an oblique implant for use in a TLIF procedure. The embodiment illustrated inFIGS.28-36includes the same basic structures as the two previous embodiments, including a housing220, upper and lower endplates230,240, a wedge250and a drive mechanism260. These structures are described in further detail in the following paragraphs.

According to the third embodiment ofFIGS.28-36, the implant210includes a housing220. The housing220has a distal wall224, a proximal wall225and first and second lateral walls222,223defining a hollow interior. The distal wall224of the housing220is tapered from where it meets the lateral walls222,223to the distal most point of the distal wall to aid in insertion of the implant210into the disc space. The distal wall224includes a drive mechanism aperture228configured to receive the distal end of the drive mechanism260. The proximal wall225has first and second bone contacting surfaces229and a graft delivery port227extending through its thickness. The proximal wall225may also include channels290for receiving arms of an insertion tool (not shown) As illustrated inFIGS.28-36, it is contemplated that the bone contacting surfaces229of the proximal wall225include anti-migration features231,241. The height of the housing220is static, remaining unchanged when the implant210is in its collapsed configuration and in its expanded configuration. The first lateral wall222, the anterolateral wall of the implant when the implant is positioned within the disc space, has a length that is greater than the length of the second lateral wall223(the posterolateral wall). It is contemplated that the housing220can be manufactured of metal or PEEK.

According to the embodiment shown inFIGS.28-36, the housing is coupled to the upper and lower endplates230,240via pins239. The upper and lower endplates230,240are identical, mirror images of each other. Each endplate230,240has a bone contacting surface232,242and an interior surface234,244. The bone contacting surfaces232,242may include anti-migration features239. The endplates230,240include a central fusion aperture235,245in communication with the hollow interior of the housing220to allow bone growth through the implant210after the implant has been placed within the disc space of patient. Each endplate230,240further includes an interior side walls272,273having a recess282and a projection283for engaging proximal projections259on the wedge260. When the projections283on the interior side walls272,273of the endplates are engaged with the proximal projections259on the wedge250, the upper and lower endplates230,240are locked in the collapsed configuration until such time as the wedge260is translated distally and the projections283,259are disengaged. The interior surfaces234,244of the endplates230,240include a ramp237,247adjacent the distal end of the endplates230,240that engage the opposing angled surfaces251,252on the wedge250to facilitate the expansion of the distal end214of the implant210. As best illustrated inFIG.36, the ramp237,247is slightly radiused. While illustrated here as having a radiused ramp237and a generally planar angled surface251,252on the wedge, it is contemplated that the ramp237,247could be planar and the opposing angled surfaces251,252on the wedge could be radiused. Alternatively, it is contemplated that both the ramp237,247and the opposing angled surfaces251,252could be planar or both could be radiused. As best seen inFIGS.33and34, the endplates230,240have a greater height on the anterolateral sides232,242of the distal ends234,244of the end plates such that when the implant is in its fully expanded state, the overall height of the implant is both greater at the distal end of the implant than at the proximal end of the implant but also the height h1on the anterolateral side of the implant is greater than the height h2on the posterolateral side of the implant.

The wedge250according to the third embodiment is housed in the hollow interior of the housing220and between the interior surfaces234,244of the upper and lower endplates230,240. The wedge250has a distal face defined by opposing angled surfaces251,252and a proximal face293. The wedge has a threaded drive mechanism aperture258extending throughout the wedge from the proximal face243through the distal face dimensioned to receive a threaded shaft262of the drive mechanism260. As previously mentioned, the wedge has projections259extending from the proximal face293for engaging projections283on the interior side walls272,273of the endplates230,240. The wedge250is positioned in the interior of the implant210such that when the implant210is in its collapsed configuration the wedge250is sitting in the hollow interior and blocking the distal portion of the central fusion apertures235,245of the endplates230,240. When the implant210is in its fully expanded configuration, the wedge has been urged distally and thus is blocking less of the central fusion apertures235,245effectively increasing the size of the aperture extending through the implant210.

According to the embodiment shown inFIGS.28-36, the drive mechanism260includes a threaded shaft262having a proximal end265including an engagement feature267for mating with a drive tool (not shown). The distal portion264of the drive mechanism260extends distally from the threaded shaft262and is configured to be anchored in the distal wall224of the housing220. The distal portion of the drive mechanism260is non-threaded, and is allowed to rotate within the drive mechanism aperture227in the distal wall224of the housing without translating. As the drive mechanism260is rotated by a drive tool, the threaded shaft engages complementary threads inside the threaded aperture258extending through the wedge250and causes the wedge250to translate distally until the implant210is fully expanded.

In use, the expandable spinal fusion implant210is inserted into a disc space between adjacent vertebral bodies in its collapsed configuration. Although not shown, it is contemplated that an insertion tool having two arms extending from the distal end will engage the insertion tool channels290on the proximal wall225of the housing220. The insertion tool has a hollow shaft to allow the drive mechanism driver to be inserted therethrough. The distal end of the drive mechanism driver is inserted through the graft delivery port227in the housing220and engaged with the mating feature267of the drive mechanism267. The drive mechanism driver is used to rotate the drive mechanism thereby causing the wedge260to translate distally between the upper and lower endplates230,240. Then the driver is disengaged from the drive mechanism and withdrawn from the hollow shaft of the insertion tool. Subsequently, graft material is inserted through the hollow shaft of the insertion tool, through the graft delivery port227in the proximal wall224of the housing220and into the hollow interior of the implant210. In an exemplary embodiment, a sufficient amount of graft is inserted to fill the interior of the implant, through the central apertures235,245in the endplates such that there is graft in compact contact with the endplates of each of the adjacent vertebral bodies.

A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.