Patent Publication Number: US-2022233329-A1

Title: Multiple expansion stage interbody devices

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. provisional patent application No. 62/676,655, filed on May 25, 2018, and entitled “Ramp-Linkage Hybrid Expandable Interbody,” the disclosure of which is expressly incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     An interbody device is a prosthesis used during spinal surgery. An interbody device is inserted into the space between spinal disks to provide stability. For example, an interbody device can be introduced between vertebrae of a patient&#39;s spine (e.g., in the disk space between adjacent vertebrae) for fixation with bone to immobilize the joint as part of a surgical treatment such as Transforaminal Lumbar Interbody Fusion (TLIF). 
     SUMMARY 
     Expandable interbody devices are described herein. An example expandable interbody device includes a structural body having an upper endplate and a lower endplate, where the upper and lower endplates are shaped to nest tightly in a closed position. The device includes at least one wedge block arranged between the upper and lower endplates of the structural body, and at least one linkage block arranged between the upper and lower endplates of the structural body. The at least one linkage block includes a plurality of linkages and a shear pin disposed at a respective proximal end of each of the linkages. The device also includes a drive screw extending through the at least one wedge block and the at least one linkage block. The drive screw is configured to rotate and drive the at least one wedge block to expand the upper and lower endplates of the structural body from the closed position to an intermediate position. In addition, the drive screw is further configured to rotate and drive the at least one linkage block to expand the upper and lower endplates of the structural body from the intermediate position to an open position. 
     Additionally, the shear pin is configured to prevent rotation of the upper and lower endplates about an axis of the drive screw. 
     Alternatively or additionally, the shear pin extends from the at least one linkage block into a portion of the at least one wedge block. Optionally, the shear pin is attached to the portion of the at least one wedge block. 
     Alternatively or additionally, the shear pin extends from the at least one linkage block without extending into a portion of the at least one wedge block. 
     Alternatively or additionally, the upper and lower endplates include first oblique surfaces and the at least one wedge block comprises second oblique surfaces. The first oblique surfaces are configured to engage with the second oblique surfaces to expand the upper and lower endplates of the structural body from the closed position to the intermediate position. 
     Alternatively or additionally, displacement of the at least one wedge block is configured to exclusively control expansion between the closed and intermediate positions, and displacement of the at least one linkage block is configured to exclusively control expansion between the intermediate and open positions. The at least one wedge block is configured to bear load during expansion between the closed and intermediate positions, and the at least one linkage block is configured to bear load during expansion between the intermediate and open positions. Optionally, the at least one wedge block is configured to disengage with the structural body at the intermediate position. 
     Alternatively or additionally, the drive screw includes a first threaded portion and a second threaded portion spaced apart from the first threaded portion. The first threaded portion of the drive screw is configured to engage with corresponding threads of the at least one wedge block. The second threaded portion of the drive screw is configured to engage with corresponding threads of the at least one linkage block. 
     In some implementations, the device further includes a plurality of wedge blocks arranged between the upper and lower endplates and on opposite sides of the structural body, where each of the wedge blocks is threaded in an opposite-handed direction. The drive screw is configured to rotate and drive the wedge blocks in opposite directions. 
     In some implementations, the device further includes a plurality of linkage blocks arranged between the upper and lower endplates and on opposite sides of the structural body, where each of the linkage blocks includes a plurality of linkages and a shear pin, respectively. Each of the linkage blocks is threaded in an opposite-handed direction, and the drive screw is configured to rotate and drive the linkage blocks in opposite directions. 
     Alternatively or additionally, the drive screw includes at least one driver hole. 
     Alternatively or additionally, the device further includes an alignment block configured to prevent rotation of the upper and lower endplates about an axis of the drive screw. 
     Alternatively or additionally, the device is made of a molybdenum-rhenium (MoRe) alloy (e.g., Mo47.5Re), a titanium (Ti) alloy, a titanium-molybdenum (TiMo) alloy, or a cobalt-chromium (CoCr) alloy. 
     Another example expandable interbody device includes a structural body having an upper endplate and a lower endplate, where the upper and lower endplates are shaped to nest tightly in a closed position. The device includes at least one wedge block arranged between the upper and lower endplates of the structural body, and at least one linkage block arranged between the upper and lower endplates of the structural body. The at least one wedge block defines opposing lateral sides and includes a slot arranged in at least one of the lateral sides. The at least one linkage block includes a plurality of linkages and a shear pin disposed at a respective proximal end of each of the linkages. The device also includes a drive screw extending through the at least one wedge block and the at least one linkage block. The drive screw is configured to rotate and drive the at least one wedge block to expand the upper and lower endplates of the structural body from the closed position to an intermediate position. In addition, the drive screw is further configured to rotate and deploy the linkages to expand the upper and lower endplates of the structural body from the intermediate position to an open position. The shear pin of the at least one linkage block is configured to traverse within the slot of the at least one wedge block. 
     Other systems, methods, features and/or advantages will be or may become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features and/or advantages be included within this description and be protected by the accompanying claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The components in the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  illustrates a side view of an expandable interbody device in the closed position according to an implementation described herein. 
         FIG. 2  illustrates a side view of the expandable interbody device of  FIG. 1  in the open position. 
         FIG. 3  illustrates a transparent top view of the expandable interbody device of  FIG. 1  in the closed position. 
         FIG. 4  illustrates a transparent top view of the expandable interbody device of  FIG. 1  in the open position. 
         FIG. 5  illustrates a transparent side view of the expandable interbody device of  FIG. 1  in the open position. 
         FIGS. 6A and 6B  illustrate another example expandable interbody device according to an implementation described herein.  FIG. 6A  illustrates a cross-sectional view of the expandable interbody device in the closed position.  FIG. 6B  illustrates a cross-sectional view of the expandable interbody device in the open position. 
         FIGS. 7A-7D  illustrate another example expandable interbody device according to an implementation described herein.  FIG. 7A  illustrates a side view of the expandable interbody device in the closed position.  FIG. 7B  illustrates a transparent side view of the expandable interbody device during a first (e.g., initial) stage of expansion.  FIG. 7C  illustrates a side view of the expandable interbody device during a second stage of expansion.  FIG. 7D  illustrates a side view of the expandable interbody device in the open position. 
         FIG. 8  illustrates an alignment block of an expandable interbody device according to an implementation described herein. 
         FIG. 9  illustrates a rail system of an expandable interbody device according to an implementation described herein. 
         FIG. 10  illustrates a drive hole (e.g., insertion mechanism) of an expandable interbody device according to an implementation described herein. 
     
    
    
     DETAILED DESCRIPTION 
     Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. Methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present disclosure. As used in the specification, and in the appended claims, the singular forms “a,” “an,” “the” include plural referents unless the context clearly dictates otherwise. The term “comprising” and variations thereof as used herein is used synonymously with the term “including” and variations thereof and are open, non-limiting terms. The terms “optional” or “optionally” used herein mean that the subsequently described feature, event or circumstance may or may not occur, and that the description includes instances where said feature, event or circumstance occurs and instances where it does not. Ranges may be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, an aspect includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. 
     Multiple expansion stage interbody devices are described herein. An interbody device is a spine implant to position within an intervertebral space to facilitate bone fusion. More specifically, the interbody devices described herein are expandable to be used, for example, in a Transforaminal Lumbar Interbody Fusion (TLIF) approach. The interbody device can be inserted in the intervertebral space at an initial height profile, and through actuation of a control screw (e.g., turned clockwise), can cause the upper and lower bodies of the assembly to extend superiorly and inferiorly, respectively. The control screw can be turned in the counter-clockwise direction to cause the interbody to collapse to its initial height to reposition or remove the interbody device. The interbody device described herein has a two-stage expansion mechanism; where at lower heights, the expansion is controlled by the ramps on proximal and distal blocks, and at a certain height, the upper and lower bodies disengage from the ramps and the expansion is controlled by the linkages assembled within the interbody device. The use of linkages allows expansion to be controlled by the length of the linkages, which pivot around a point. Because of this, the linkages can fit within the insertion profile of the interbody device, but are also able to pivot, extending beyond the initial profile if the length of the profile is larger than the height of the profile. 
     The interbody devices described herein facilitate a less invasive surgical procedure because the devices allow the implant to be inserted at a lower insertion profile and expanded to fit within the patient&#39;s intervertebral space. Additionally, the use of multiple expansion stages (e.g., ramps and linkages) allows for a greater range of expansion than conventional ramped devices, allowing the upper and lower bodies to extend beyond its initial height profile. The ramped portion also provides greater mechanical stability to mitigate the linkages&#39; inherent weakness at more acute angles. 
     Referring now to  FIGS. 1-5 , an expandable interbody device is described. The device can include a structural body having an upper endplate  1001   a  and a lower endplate  1001   b  (collectively “endplates  1001 ”), where the upper and lower endplates  1001  are shaped to nest tightly in a closed position. Optionally, porous and/or roughened surfaces can be used on the endplates  1001 , which can improve osseointegration. Example interbody devices that promote on-growth of bone are described in WO2018/053403, published Mar. 22, 2018, titled “INTERBODY FUSION DEVICES AND RELATED METHODS OF MANUFACTURE,” the disclosure of which is expressly incorporated herein by reference in its entirety. In the closed position, the device is at its minimum height. This disclosure contemplates that a range of initial, minimum heights can be implemented in the design of the devices, allowing a range of expansion possibilities. Expansion of the device is accomplished through multiple stages (e.g., two stages) as described below. For example, the device can be actuated using a control screw (e.g., drive screw  1004  in  FIGS. 1-5 ). During a first stage of expansion, actuation of the drive screw causes proximal and distal blocks (e.g., wedge blocks  1002  in  FIGS. 1-5 ) to translate simultaneously in opposing horizontal directions, which results in the distraction of the superior endplate (e.g., upper endplate  1001   a  in  FIGS. 1, 2, and 5 ) and the inferior endplate (e.g., lower endplate  1001   b  in  FIGS. 1, 2, and 5 ) in opposing vertical directions. In the first stage, the device is expanded from the closed position to an intermediate position. During a second stage of expansion, actuation of the drive screw causes linkages (e.g., linkages  1003   a - 1003   d  in  FIGS. 2, 4, and 5 ) to deploy, which results in the further distraction of the superior endplate (e.g., upper endplate  1001   a  in  FIGS. 1, 2, and 5 ) and the inferior endplate (e.g., lower endplate  1001   b  in  FIGS. 1, 2, and 5 ) in opposing vertical directions. In the second stage, the device is expanded from the intermediate position to an open position. 
     The endplates  1001  are configured to make direct contact with the patient&#39;s bone, e.g., with vertebral bodies in the section of the spine undergoing fixation/fusion. The endplates  1001  are designed to nest tightly with protrusions beyond center line to allow angled bosses to extend farther and thus allow more expansion of the structural body. Each of the endplates  1001  has faces oblique to the surfaces configured to contact the patient&#39;s bone (e.g., first oblique surfaces  1005  in  FIGS. 1 and 2 ). The device can also include at least one wedge block  1002  arranged between the upper and lower endplates  1001  of the structural body. As shown in  FIGS. 1-5 , the device includes a plurality of wedge blocks  1002  (e.g. proximal and distal wedge blocks). Each of the wedge blocks  1002  has faces oblique to the top and bottom surfaces of the wedge blocks  1002 , creating ramped surfaces (e.g., second oblique surfaces  1006  in  FIGS. 1 and 2 ). The wedge blocks  1002  are support structures with the second oblique surfaces  1006  designed to accommodate the first oblique surfaces  1005  of the endplates  1001 . As described below, when the wedge blocks  1002  travel, the second oblique surfaces  1006  interact with the corresponding first oblique surfaces  1005  of the endplates  1001  to cause expansion of the device. 
     The device can also include at least one linkage block  1003  arranged between the upper and lower endplates  1001  of the structural body. As shown in  FIGS. 2-5 , the device includes a plurality of linkage blocks  1003  (e.g. proximal and distal linkage blocks). This disclosure contemplates that the wedge and linkage blocks can be integrated into a single block in some implementations, i.e., the linkage block can be a sub-portion of the wedge block. While in other implementations, this disclosure contemplates that the wedge and distal blocks can be separate and distinct blocks. The linkage blocks  1003  can include one or more linkages  1003   a - 1003   d  (e.g., levers). For example, the device shown in  FIGS. 1-5  can include eight linkages (i.e., four linkages per linkage block  1003 ). Each of the linkages  1003   a - 1003   d  extends between a shear pin  1010 , which is located at a proximal end of the linkage, and an endplate pin  1012 , which is located at a distal end of the linkage. The linkages  1003   a - 1003   d  can be coupled to the wedge and/or linkage blocks and the endplates with the shear pins  1010  and the endplate pins  1012 , respectively. The linkages  1003   a - 1003   d  rotate around a pivot point (e.g., the center of the shear pin) during actuation to expand the device. The device can optionally include four shear pins  1010   a - 1010   d  (i.e., two shear pins per linkage block, one on each opposing lateral side of the linkage block), which is shown in  FIG. 4 . Alternatively, the device can optionally include two shear pins  1010  (i.e., one shear pin per linkage block). Each of the shear pins  1010  can extend from a linkage block  1003  into a portion of a wedge block  1002 , which is also shown in  FIG. 4 . For example, the shear pin  1010  can extend into a lateral side or portion of the wedge block  1002 . Optionally, in some implementations, each of the shear pins  1010  is coupled with a portion of a wedge block  1002 . Optionally, in some implementations, each of the shear pins  1010  can extend from a linkage block  1003  without extending into a portion of the wedge block  1002  (e.g., the shear pins are only part of the linkage block  1003 ). Accordingly, each of the shear pins  1010  can support load during second stage expansion. Additionally, each of the shear pins  1010  can prevent rotation of the endplates  1001  about the axis of the drive screw  1004 . It should be understood that four shear pins (i.e., two per linkage block) is provided only as an example. This disclosure contemplates using one, two, or three shear pins with the device to prevent rotation of the endplates  1001 . 
     Additionally, as described herein, the device can further include a drive screw  1004  extending through the wedge blocks  1002  and the linkage blocks  1003 . The drive screw  1004  can include threads, and the wedge blocks  1002  and/or linkage blocks  1003  can include threads corresponding to the threads of the drive screw  1004 . In this way, the threads of the drive screw  1004  can engage corresponding threads of the wedge blocks  1002  and/or linkage blocks  1003 . In some implementations, only the wedge blocks  1002  include threads. In other implementations, both the wedge blocks  1002  and the linkage blocks  1003  include threads. Optionally, the pitches of the respective threads for controlling the wedge blocks  1002  and the linkage blocks  1003  are the same. Optionally, the pitches of the respective threads for controlling the wedge blocks  1002  and the linkage blocks  1003  are different. The drive screw  1004  can include a driver hole  1007  at one end of the drive screw  1004 . The driver hole  1007  can be configured to accept the bit of a driver instrument or tool. Optionally, this disclosure contemplates that the drive screw  1004  can be operated from either end by providing a driver hole  1007  at both ends.  FIG. 10  illustrates a close-up view of a driver hole  1007  (e.g., insertion mechanism) of an expandable interbody device. In  FIG. 10 , the drive screw  1004  extends through the wedge block  1002  of the device. 
     Referring again to  FIGS. 1-5 , the device can further include an alignment block  1008 . The alignment block  1008  can guide expansion of the structural body. The alignment block  1008  can also prevent rotation of the endplates  1001  about the axis of the drive screw  1004 . For example, the alignment block  1008  is located in the center of the device and prevents rotation of the endplates  1001 , further constraining the expansion to one direction (i.e., the vertical direction).  FIG. 8  illustrates a close-up view of an alignment block  1008  of an expandable interbody device. As shown in  FIG. 8 , the alignment block  1008  can include one or more notches that correspond to vertical grooves in the endplates  1001 . This keeps the expansion of the structural body in the vertical direction and/or prevents rotation of the endplates about the axis of the drive screw. 
     Referring again to  FIGS. 1-5 , the first oblique surfaces  1005  of the endplates  1001  engage with the second oblique surfaces  1006  of the wedge blocks  1002  during the first stage of expansion. Optionally, in some implementations, the device can include a rail system. For example, the first oblique surfaces  1005  of the endplates  1001  can be coupled to the second oblique surfaces  1006  of the wedge blocks  1002  by the rail system.  FIG. 9  illustrates a close-up view of a rail system of an expandable interbody device. As shown in  FIG. 9 , grooves  1113   a  located on oblique surfaces of the endplate  1001  can couple with bosses  1113   b  located on oblique surfaces of the wedge block  1002 . The rail system (e.g., grooves  1113   a,  bosses  1113   b ) can more effectively constrain the expansion of the device to one direction (i.e., the vertical direction). 
     Referring again to  FIGS. 1-5 , the device includes a plurality of wedge blocks  1002  arranged between the upper and lower endplates  1001  and on opposite sides of the structural body (e.g., proximal and distal wedge blocks). Each of the wedge blocks  1002  can be threaded in an opposite-handed direction such that the drive screw  1004  is configured to rotate and drive the wedge blocks  1002  in opposite directions and towards the center of the device (when expanding the device). Additionally, as shown in  FIGS. 2-5 , the device can further include a plurality of linkage blocks  1003  arranged between the upper and lower endplates  1001  and on opposite sides of the structural body. In some implementations, the device can include eight linkages. For example, the device can include two linkages per articular point, e.g., four linkages on each side of the device for a total of eight. It should be understood that the number of linkages is provided only as an example. In some implementations, each of the linkage blocks  1003  can be threaded in an opposite-handed direction such that the drive screw  1004  is configured to rotate and drive the linkage blocks  1003  in opposite directions and towards the center of the device (when expanding the device). 
     As described herein, the device has a dual stage mechanism (e.g., wedge blocks  1002  and linkage blocks  1003 ) controlled by rotation of the drive screw  1004 . In a first stage, the device expands between the closed and intermediate positions. Expansion in the first stage is controlled exclusively using the wedge blocks  1002 . To accomplish this, the threads of the drive screw  1004  are timed such that the wedge blocks  1002  are engaged by the drive screw  1004  during the first stage. The threads can be timed such that the wedge blocks  1002  move together and in opposite directions. The drive screw  1004  is therefore configured to rotate and drive the wedge blocks  1002 , which moves the upper and lower endplates  1001  of the structural body from a closed position to an intermediate position.  FIGS. 1 and 3  illustrate the device in the closed position, while  FIGS. 2, 4, and 5  illustrate the device in the open position. As shown in  FIGS. 1 and 2 , the first oblique surfaces  1005  are included on the upper and/or lower endplates  1001 , and the second oblique surfaces  1006  are included on the wedge blocks  1002 . The second oblique surfaces  1006  can be configured to interact with the first oblique surfaces  1005  to expand the upper and lower endplates  1001  of the structural body as the wedge blocks  1002  translate due to rotation of the drive screw  1004 . In other words, the wedge blocks  1002  control expansion in the first stage by physically forcing the endplates  1001  apart. Optionally, the first oblique surfaces  1005 /second oblique surfaces  1006  can function as a ratchet, e.g., such that the structural body expands (or contracts) in a step-wise manner as the drive screw  1004  is rotated. Optionally, the first oblique surfaces  1005 /second oblique surfaces  1006  can include a rail system to further constrain expansion. Once the device reaches the intermediate position, the wedge blocks  1002  can optionally disengage with the structural body (e.g., no more contact with the structural body). At this point, expansion control is transferred to the linkage blocks  1003  as described below. Additionally, during the first stage, the linkages  1003   a - 1003   d  are neither load supporting nor impacting/controlling expansion. 
     In a second stage, the device expands between the intermediate and open positions. Expansion in the second stage is controlled exclusively using the linkage blocks  1003 , for example, by deployment of the linkages  1003   a - 1003   d.  Horizontal translation of the proximal end of the linkages  1003   a - 1003   d  can be limited so that the endplates  1001  cannot re-engage with the wedge blocks  1002  during the second stage. This can be accomplished in different ways. For example, in some implementations, the linkage blocks  1003  are provided with threads corresponding to threads of the drive screw  1004  such that displacement of the linkage blocks  1003  is controlled directly by a pitch of the threads of the drive screw  1004 . This is described in detail with regard to  FIGS. 6A-6B . In other implementations, deployment of the linkages  1003   a - 1003   d  is controlled by interaction between slots in the wedge blocks  1002  and the shear pins  1010 . This is described in detail with regard to  FIGS. 7A-7D . 
     Referring again to  FIGS. 1-5 , expansion during the second stage is described.  FIGS. 1 and 3  illustrate the device in the closed position, while  FIGS. 2, 4, and 5  illustrate the device in the open position. As shown in  FIGS. 2, 4, and 5 , the linkage blocks  1003  include one or more linkages  1003   a - 1003   d  (e.g., levers) that are configured to displace the endplates  1001  when the linkage blocks  1003  are engaged by the drive screw  1004 . A linkage (e.g., one of linkages  1003   a - 1003   d ) is attached between a linkage block (e.g., one of linkage blocks  1003 ) with the shear pin (e.g., one of shear pins  1010 ) and an endplate  1001  (e.g., one of endplates  1001 ) with the endplate pin (e.g., one of endplate pins  1012 ). The linkage blocks  1003  control expansion in the second stage by moving the endplates  1001  with the linkages  1003   a - 1003   d.  The dual stage expansion described above (e.g., using both wedge and linkage blocks) allows the device to expand farther than conventional devices. For example, by using the linkage blocks  1003 , the device can expand double its initial height, which would be a limiting factor for devices that use only wedge blocks as a drive mechanism. Additionally, since the linkages  1003   a - 1003   d  experience higher stresses at the attachment to the device at more acute angles of the linkages, the wedge blocks  1002  are bearing the load during the first expansion stage (e.g., when the linkages  1003   a - 1003   d  are most acute). Once the expansion has reached its maximum height facilitated by the wedge blocks, the wedge blocks  1002  disengage and the linkage blocks  1003  provide for additional expansion of the device. 
     Referring now to  FIGS. 6A-6B , another example expandable interbody device is described.  FIG. 6A  illustrates a cross-sectional view of the expandable interbody device in the closed position.  FIG. 6B  illustrates a cross-sectional view of the expandable interbody device in the open position. The device includes endplates  1001   a  and  1001   b  (collectively “endplates  1001 ”), wedge blocks  1002 , and linkage blocks  1003  (and linkages  1003   a - 1003   d ). As shown in  FIGS. 6A-6B , the wedge blocks  1002  and linkage blocks  1003  are concentric with the drive screw  1004 . A drive screw  1004  extends through the wedge blocks  1002  and the linkage blocks  1003 , and a driver hole  1007  is provided at one end of the drive screw  1004 . An alignment block  1008  is also provided in the device. Except as provided below, the device shown in  FIGS. 6A and 6B  operates similarly as described above with regard to  FIGS. 1-5 . For example, during a first stage of expansion, the wedge blocks  1002  exclusively control expansion of the device. To accomplish this, the drive screw  1004  is actuated to drive the wedge blocks  1002 , which move together and in opposite directions. For example, when the device is expanded, the wedge blocks  1002  move towards one another (e.g., one wedge block moves to the left and the other wedge block moves to the right). It should be understood that when the device is collapsed, the wedge blocks  1002  move away from one another (e.g., one wedge block moves to the left and the other wedge block moves to the right). The drive screw  1004  includes a first threaded portion  1004   a  and a second threaded portion  1004   b.  The first threaded portion  1004   a  is spaced apart from the second threaded portion  1004   b.  As described herein, the first threaded portion  1004   a  engages with the wedge block  1002 , and the second threaded portion  1004   b  engages with the linkage block  1003 . The second oblique surfaces  1006  of the wedge blocks  1002  interact with the first oblique surfaces  1005  of the endplates  1001  to expand the upper and lower endplates  1001  of the structural body as the wedge blocks  1002  translate due to rotation of the drive screw  1004 . Thus, the wedge blocks  1002  control expansion in the first stage by physically forcing the endplates  1001  apart. 
     On the other hand, during a second stage of expansion, the linkage blocks  1003  exclusively control expansion of the device. The drive screw  1004  is actuated to drive the linkage blocks  1003 , which move together and in opposite directions. For example, when the device is expanded, the linkage blocks  1003  move towards one another (e.g., one linkage block moves to the left and the other linkage block moves to the right). It should be understood that when the device is collapsed, the linkage blocks  1003  move away from one another (e.g., one linkage block moves to the left and the other linkage block moves to the right). To accomplish this, both the wedge blocks  1002  and the linkage blocks  1003  are provided with threads corresponding to those of the drive screw  1004 . For example, the drive screw  1004  includes the first threaded portion  1004   a  and the second threaded portion  1004   b,  which is spaced apart from the first threaded portion  1004   a.  The portion of the drive screw  1004  between the first threaded portion  1004   a  and the second threaded portion  1004   b  (i.e., the unthreaded portion) does not have any threads. The first threaded portion  1004   a  engages with the wedge block  1002  during the first stage (see  FIG. 6A ), and the second threaded portion  1004   b  engages with the linkage block  1003  during the second stage (see  FIG. 6B ). The unthreaded portion of the drive screw  1004  is aligned with the linkage blocks  1003  and the wedge blocks during the first and second stages, respectively. In other words, the respective first and second threaded portions are used to drive the wedge and linkage blocks, respectively. The threads of the second threaded portion  1004   b  of the drive screw  1004  are timed such that the linkage blocks  1003  are engaged by the drive screw  1004  during the second stage. The threads can be timed such that the linkage blocks  1003  move together and only after initial expansion by the wedge blocks  1002 . The drive screw  1004  can therefore be configured to engage the linkage blocks  1003  at the intermediate position, and at this point, the shear pins (not shown in  FIGS. 6A and 6B ) take on load as the linkages deploy. As described above, a shear pin (e.g., shear pins  1010  in  FIGS. 4 and 5 ) can extend through the proximal end of each of the linkages  1003   a - 1003   d  to a portion of the wedge block  1002  (e.g., to a lateral side of the wedge block  1002 ). The device in  FIGS. 6A-6B  includes two shear pins, each of which extends through the proximal end of four linkages (e.g., two on each lateral side of a linkage block). The shear pin can be anchored or attached to the wedge block  1002 . For example, the shear pin can be coupled with or within the lateral side of the wedge block  1002 . Then, as the drive screw  1004  is further actuated, it rotates and drives the linkage blocks  1003 , which further expands the upper and lower endplates  1001  of the structural body from the intermediate position to an open position. In this way, the linkage blocks  1003  are directly controlled by the pitch of the second threaded portion  1004   b  of the drive screw  1004 . Additionally, the unthreaded portion of the drive screw  1004  allows the drive screw  1004  to travel without resistance, which prevents loading of the linkages  1003   a - 1003   d  during the first stage of expansion. In some implementations, the first threaded portion  1004   a  has the same pitch as the second threaded portion  1004   b,  while in other implementations, the first threaded portion  1004   a  has a different pitch than the second threaded portion  1004   b.    
     Referring now to  FIGS. 7A-7D , another example expandable interbody device is described.  FIG. 7A  illustrates a side view of the expandable interbody device in the closed position.  FIG. 7B  illustrates a transparent side view of the expandable interbody device during a first (e.g., initial) stage of expansion.  FIG. 7C  illustrates a side view of the expandable interbody device during a second stage of expansion.  FIG. 7D  illustrates a side view of the expandable interbody device in the open position. The device includes endplates  1001   a  and  1001   b  (collectively “endplates  1001 ”), wedge blocks  1002 , and linkage blocks  1003  (and linkages  1003   a - 1003   d ). A drive screw  1004  extends through the wedge blocks  1002  and the linkage blocks  1003 , and a driver hole  1007  is provided at one end of the drive screw  1004 . As shown in  FIGS. 7A-7D , the wedge blocks  1002  and linkage blocks  1003  are concentric with the drive screw  1004 . An alignment block  1008  is also provided in the device. Except as provided below, the device shown in  FIGS. 7A-7D  operates similarly as described above with regard to  FIGS. 1-5 . For example, during a first stage of expansion, the wedge blocks  1002  exclusively control expansion of the device. To accomplish this, the drive screw  1004  is actuated to drive the wedge blocks  1002 , which move together and in opposite directions. For example, when the device is expanded, the wedge blocks  1002  move towards one another (e.g., one wedge block moves to the left and the other wedge block moves to the right). It should be understood that when the device is collapsed, the wedge blocks  1002  move away from one another (e.g., one wedge block moves to the left and the other wedge block moves to the right). The second oblique surfaces  1006  of the wedge blocks  1002  interact with the first oblique surfaces  1005  of the endplates  1001  to expand the upper and lower endplates  1001  of the structural body as the wedge blocks  1002  translate due to rotation of the drive screw  1004 . Thus, the wedge blocks  1002  control expansion in the first stage by physically forcing the endplates  1001  apart. 
     On the other hand, during a second stage of expansion, the linkage blocks  1003  exclusively control expansion of the device. The drive screw  1004  is actuated to deploy the linkages  1003   a - 1003   d,  which are attached to the endplates  1001  by endplate pins  1012  and to the linkage blocks  1003  by shear pins  1010  as described above. To accomplish this, a shear pin  1010  can extend through the proximal end of each of the linkages  1003   a - 1003   d  and through a portion of the wedge block  1002 . One shear pin  1010  can extend through the proximal end of each of the linkages of each linkage block  1003 . For example, the device in  FIGS. 7A-7D  includes two shear pins, each of which extends through the proximal end of four linkages (e.g., two linkages on each lateral side of a linkage block). Additionally, a slot  1011  is arranged in the lateral side of the wedge block  1002 . The device in  FIGS. 7A-7D  includes four slots  1011  (e.g., two on each lateral side of a wedge block and/or one slot for each end of the shear pin). The size and/or shape of the slot  1011  (e.g., outer diameter of the slot  1011 ) is designed such that the shear pin  1010  can traverse within the slot  1011 . For example, in the closed position shown in  FIG. 7A , the shear pins  1010  are located within the slots  1011  and centrally with respect to the device. During the first stage of expansion shown in  FIG. 7B , the shear pins  1010  traverse within the slots  1011  outwardly with respect to the device as the drive screw  1004  is actuated. Eventually as shown in  FIGS. 7C and 7D , the shear pins  1010  reach the outermost edge of the slots  1011  near the intermediate position. As a result, further actuation of the drive screw  1004  drives the shear pins  1010  causing the linkages  1003   a - 1003   d  to deploy. As described herein, the shear pins  1010  take on load as they deploy and expand the device between the intermediate and open positions. Optionally, in some implementations, the drive screw  1004  can include a first threaded portion and a second threaded portion as described with regard to  FIGS. 6A and 6B . As described herein, the first threaded portion can engage with the wedge block  1002 , and the second threaded portion can engage with the linkage block  1003 . 
     Although examples are provided for expanding the device, it should be understood that the drive screw can be rotated in the opposite direction to contract or collapse the device. For example, the linkage blocks can be used to collapse the device from the open position to the intermediate position, and the wedge blocks can be used to collapse the devices from the intermediate position to the closed position. Additionally, it should be understood that the device can be expanded to a desired height and stay at this desired height during and after implantation. The desired height is independent of the intermediate and/or fully open positions. For example, some patients may require the device to be expanded to a height less than the intermediate position, while some patients may require the device to be expanded to a height greater than the intermediate position. In other words, the device does not need to be expanded to the fully open position (or even the intermediate position) in every case. The dual stage expansion mechanism facilitates the ability of the device to expand to a larger range of heights. 
     This disclosure contemplates that the devices (e.g., components of the devices such as the structural body, wedge blocks, linkage blocks, linkages, drive screw, etc.) described herein can be made using alternative medical grade materials. This disclosure contemplates that some or all of the components can be made of the same material in some implementations, while in other implementations some or all of the components can be made of different materials. In some implementations, the device can be made of a molybdenum-rhenium (MoRe) alloy. Optionally, the MoRe alloy is Mo47.5Re. Alternatively, the alloy is optionally 99.99% pure with at least 40 weight percent (wt %) rhenium. Optionally, the alloy is optionally 99.99% pure with between 40 wt % and 99.9 wt % rhenium (e.g., 40.0 wt %, 40.01 wt %, 40.02 wt % . . . 99.88 wt %, 99.89 wt %, 99.9 wt %) and any value or range therebetween. In other implementations, the device can be made of titanium (Ti). In other implementations, the device can be made of a titanium-molybdenum (TiMo) alloy including, but not limited to, Ti-15Mo. In other implementations, the device can be made of a titanium (Ti) alloy. In other implementations, the device can be made of a cobalt-chromium (CoCr) alloy. Other example alloys that can be used are described, for example, in U.S. 2019/0008995, published Jan. 10, 2019, titled “Molybdenum Alloys for Medical Devices,” the disclosure of which is expressly incorporated herein by reference in its entirety. 
     Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.