Patent Publication Number: US-11648129-B2

Title: Distally expanding facet joint implant and delivery device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. application Ser. No. 16/653,010 filed on Oct. 15, 2019 which issues on May 11, 2021 as U.S. Pat. No. 11,000,384. Each of the aforementioned patent applications is herein incorporated by reference in their entirety. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable to this application. 
     BACKGROUND 
     Field 
     Example embodiments in general relate to a distally expanding facet joint implant and delivery device for distracting the joint between facets of adjacent vertebrae of the spine, including cervical vertebrae, to provide nerve root decompression, maintain or improve vertebral alignment, and enhance spinal stability. 
     Related Art 
     Any discussion of the related art throughout the specification should in no way be considered as an admission that such related art is widely known or forms part of common general knowledge in the field. 
     Spine degeneration is a major burden to society. The current growth of the aging population is linked to a rise in cases of age-related spine joint degenerative change or arthropathy, which is a leading cause of chronic neck and back pain. The socioeconomic costs of degenerative spine disease are large. Such costs include both direct costs, such as payments for treatment of pain and neurologic disorders, and indirect costs from loss of work and frequent sick leaves. 
     The spinal column is composed of 33 vertebrae, separated by intervertebral discs and held together with ligaments and muscles. The spinal column provides an axial support for the human body in addition to its function as a protector to the spinal cord and its emerging nerve roots. Movement within each spine segment (adjacent superior and inferior vertebrae) is facilitated by the anteriorly located intervertebral discs and two posterior facet joints. The series of these joints between adjacent vertebrae of the spinal column permit the complex flexible movements of the spinal column. 
     The aging process often leads to degenerative changes that impact the structure of the spine joints. The process involves dehydration of the intervertebral discs resulting in reduction of disc height. Subsequently, friction between the joint surfaces occurs and a process of degeneration and local inflammation begins. The joints then become stiffer and the ligaments become thickened and less elastic. The overall process is collectively named spondylosis. Spondylosis leads to reduction in the size of the neural foramens (the space where the nerves emerge from the spinal cord), disc herniation, and spinal stenosis resulting in axial neck and/or back pain and neurological compromise. As the degenerative changes advance and the intervertebral foramen narrowing progresses, compression of the nerve roots can occur leading to nerve damage. Such damage often manifests itself as numbness and weakness due to motor and sensory function loss in addition to persistent pain in what is called radiculopathy. Radiculopathy resulting from damage to the cervical nerve roots is referred to more particularly as cervical radiculopathy. 
     The main goal in treating radiculopathy is to decompress the affected nerve. This goal can be accomplished by direct nerve decompression and removal of the compressing element, or by distracting the inter-facet joints between adjacent superior and inferior vertebrae compressing the nerve. The two approaches are frequently combined. Typically, either an anterior procedure is performed that involves the removal of the collapsed intervertebral disc and replacement with a bone or synthetic cage, or a posterior procedure that involves laminectomy with or without facetectomy (facet removal). In either case, the procedure is often coupled with the addition of instrumentation between the involved vertebrae to stabilize them and facilitate their fusion together. 
     With respect to the cervical spine in particular, evidence has highlighted the importance of maintaining the natural cervical spine alignment during surgical treatment of cervical radiculopathy as maintaining the natural alignment is often associated with better neurological functional outcomes. Thus, surgical treatment of the cervical spine to counteract the effects of the degenerative process must incorporate cervical alignment to achieve the most beneficial outcome. 
     At the same time, the current trend is to employ minimally invasive surgical approaches to treat various spinal diseases because such approaches have been demonstrated to lead to less post-operative pain, less surgical blood loss, and earlier recovery from surgery. For treatment of cervical radiculopathy, the commonly performed minimally invasive technique utilizes the posterior approach and specially designed devices to distract the facet joint by inserting an implant inside the facet joint and, consequently, relieving the nerve root compression. 
     A number of different facet joint implants and delivery devices have been proposed. However, to date nearly all such implants have limited success in providing optimal distraction of a facet joint and, when used in a cervical facet joint, maintaining the natural lordosis and preventing excessive kyphosis of the cervical spine. 
     There thus remains a need for a facet joint implant that is distally expandable to distract the facet joints of affected adjacent superior and inferior vertebrae to decompress the neural foramens and relieve the symptoms of cervical radiculopathy and, when used with a cervical facet joint, to also maintain or improve proper cervical alignment. A device that expands more anteriorly when inserted in the facet joint is more likely to achieve anterior facet joint distraction, intervertebral space distraction, and widening of the intervertebral foramen in addition to correcting existing spondylolisthesis. There also remains a need for such an implant and a delivery device that are readily usable with minimally invasive, posterior surgical techniques, and that can be used and deployed while minimizing undesirable damage to the soft tissue around the facet joint. There also remains a need for such an implant and delivery device that are less complex, easier to manipulate and use, and more readily result in the implant being properly positioned and oriented in the facet joints of affected vertebrae. There further remains a need for such an implant that is more reliable in achieving its intended function despite having a smaller size that facilitates insertion inside the relatively limited facet joint space. There further remains a need for such an implant and delivery device wherein the placement and expansion of the implant is more readily and easily reversible. There still further remains a need for such an implant that adheres effectively to the facet bones of affected vertebrae, that facilitates post-operative bone fusion, and that effectively stabilizes the spine and prevents undesirable inter-facet movement. There still further remains a need for such an implant and delivery tool that are relatively simple, easy, and inexpensive to manufacture and assemble. 
     The example embodiments of a distally expanding facet joint implant and delivery device described herein seek to address these needs with respect mainly for cervical facet joints. 
     SUMMARY 
     An example embodiment is directed to a distally expanding facet joint implant and delivery device. The distally expanding facet joint implant includes an outer part and an inner part. The outer part includes a first facet plate, a second facet plate, and a hinge. The first facet plate has a first distal end portion, a first proximal end portion, and a first opening between the first distal end portion and the first proximal end portion. The second facet plate has a second distal end portion, a second proximal end portion, and a second opening between the second distal end portion and the second proximal end portion. The hinge connects the first proximal end portion of the first facet plate and the second proximal end portion of the second facet plate. 
     The inner part is at least partially exposed in the first opening and the second opening and includes a wedge-shaped engagement structure with a third distal end portion and a third proximal end portion. The inner part is movable relative to the outer part. 
     When the inner part is moved toward the first distal end portion of the first facet plate and the second distal end portion of the second facet plate, the distal end portion of the wedge engages the first facet plate and the second facet plate, the first distal end portion of the first facet plate and the second distal end portion of the second facet plate move apart, and the first proximal end portion of the first facet plate and the second proximal end portion of the second facet plate rotate on the hinge in a first direction until the facet joint implant assumes a distally expanded open state. 
     When the inner part is moved toward the first proximal end portion of the first facet plate and the second proximal end portion of the second facet plate, the first distal end portion of the first facet plate and the second distal end portion of the second facet plate move toward each other, and the first proximal end portion of the first facet plate and the second proximal end portion of the second facet plate rotate on the hinge in a second direction until the facet joint implant assumes a distally contracted closed state. 
     According to one aspect of the example embodiments, the outer and inner parts comprise first and second monolithic structures and are formed in a pre-assembled arrangement. 
     According to another aspect of the example embodiments, the first facet plate has a first exterior surface with a first plurality of serrations or spikes and the second facet plate has a second exterior surface with a second plurality of serrations or spikes. The serrations or spikes facilitate the facet joint implant adhering to the bony surfaces of the facets adjacent to a facet joint in which it is implanted when it is in the open state. 
     According to another aspect of the example embodiments, the first facet plate has a first interior surface with a first sloped portion, the second facet plate has a second interior surface with a second sloped portion, and the wedge has a third exterior surface with a third sloped portion and a fourth exterior surface with a fourth sloped portion. When the inner part of the facet joint implant is moved toward the first distal end portion of the first facet plate and the second distal end portion of the second facet plate, the third sloped portion of the third exterior surface of the wedge engages the first sloped portion of the first interior surface of the first facet plate, and the fourth sloped portion of the fourth exterior surface of the wedge engages the second sloped portion of the second interior surface of the second facet plate to cause the first distal end of the first facet plate and the second distal end of the second facet plate to expand apart until the facet joint implant assumes the distally expanded open state. 
     According to another aspect of the example embodiments, the outer part of the facet joint implant includes a first set of teeth and the inner part of the facet joint implant includes at least a first set of indents and a second set of indents. When the facet joint implant is in the closed state, the first set of teeth engage the first set of indents and when the facet joint implant assumes the distally contracted closed state, the first set of teeth engage the second set of indents. This helps hold the facet joint implant in the open or closed position and can provide physical feedback when the facet joint implant assumes the open and closed positions. 
     According to yet another aspect of the example embodiments, the outer part of the facet joint implant includes a first delivery device interface and the inner part includes a second delivery device interface. The first delivery device interface includes a first connector that is configured to selectively receive, be brought into engagement with, and be brought into locked engagement with a corresponding first connector of a delivery device. When the first connector is in locked engagement with the corresponding first connector, the facet joint implant is held in a fixed position and orientation relative to the delivery device. The second delivery device interface comprises a second connector that is configured to selectively receive, be brought into engagement with, and be brought into locked engagement with a corresponding second connector of a delivery device. When the second connector is in locked engagement with the corresponding second connector, motion can be selectively imparted to the inner part of the facet joint implant relative to the outer part of the facet joint implant to distally expand and contract the facet joint implant. 
     The delivery device adapted for use with the distally expanding facet joint implant has a distal end portion and a proximal end portion. The delivery device includes a corresponding first connector at the distal end portion that is configured to be brought into engagement with, be inserted in, and be brought into locked engagement with the first connector of the facet joint implant and when in locked engagement to hold the facet joint implant in a fixed position and orientation relative to the delivery device. The delivery device includes a corresponding second connector at the distal end portion that is configured to be brought into engagement with, be inserted in, and be brought into locked engagement with the second connector of the facet joint implant. When the corresponding second connector is in locked engagement with the second connector of the facet joint implant, the delivery device is operable to selectively impart motion to the inner part of the facet joint implant relative to the outer part of the facet joint implant to distally expand and contract the facet joint implant. 
     According to another aspect of the example embodiments, the delivery device includes an outer tube control knob that is coupled to an outer tube of the delivery device. The outer tube control knob is configured and is operable to advance the outer tube relative to the corresponding first connector of the delivery device and the first connector of the facet joint implant to ensure that the corresponding first connector and the first connector are brought into engagement and locked engagement only in proper alignment, and with surfaces of the first connector in secure engagement with support surfaces on the outer tube. 
     According to another aspect of the example embodiments, the delivery device includes a control handle located at the proximal end portion of the delivery device. The control handle is coupled with the corresponding first connector of the delivery device and is configured and operable to selectively bring the corresponding first connector into locked engagement with the first connector of the facet joint implant. 
     According to another aspect of the example embodiments, the delivery device includes an inner shaft control knob located at the proximal end portion of the delivery device. The inner shaft control knob is coupled with the corresponding second connector of the delivery device and is operable to selectively bring the corresponding second connector into and out of engagement with the second connector of the facet joint implant. 
     According to another aspect of the example embodiments, the delivery device includes a lock switch and a lock located at the proximal end portion of the delivery device. The lock switch is coupled with the corresponding second connector of the delivery device, and is configured and operable to selectively rotate the corresponding second connector between a first position wherein the corresponding second connector is not in locked engagement with the second connector of the facet joint implant, and a second position wherein the corresponding second connector is in locked engagement with the second connector. The lock is responsive to operation of the lock switch to hold or maintain the corresponding second connector in the second position wherein the corresponding second connector is in locked engagement. 
     There has thus been outlined, rather broadly, some of the embodiments of the distally expanding facet joint implant and delivery device in order that the detailed description thereof may be better understood, and in order that the present contribution to the art may be better appreciated. There are additional embodiments of the distally expanding facet joint implant and delivery device that will be described hereinafter and that will form the subject matter of the claims appended hereto. In this respect, before explaining at least one embodiment of the distally expanding facet joint implant and delivery device in detail, it is to be understood that the distally expanding facet joint implant and delivery device are not limited in their application to the details of construction or to the arrangements of the components set forth in the following description or illustrated in the drawings. The distally expanding facet joint implant and delivery device are capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of the description and should not be regarded as limiting. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Example embodiments will become more fully understood from the detailed description given herein below and the accompanying drawings, wherein like elements are represented by like reference characters, which are given by way of illustration only and thus are not limitative of the example embodiments herein. 
         FIG.  1 A  is a perspective view of a distally expanding facet joint implant in a closed state in accordance with an example embodiment. 
         FIG.  1 B  is a perspective view of a distally expanding facet joint implant in an open state in accordance with an example embodiment. 
         FIG.  2 A  is a side view of a distally expanding facet joint implant in a closed state in accordance with an example embodiment. 
         FIG.  2 B  is a side view of a distally expanding facet joint implant in an open state in accordance with an example embodiment. 
         FIG.  3 A  is a top view of a distally expanding facet joint implant in a closed state in accordance with an example embodiment. 
         FIG.  3 B  is a top view of a distally expanding facet joint implant in an open state in accordance with an example embodiment. 
         FIG.  4 A  is a bottom view of a distally expanding facet joint implant in a closed state in accordance with an example embodiment. 
         FIG.  4 B  is a bottom view of a distally expanding facet joint implant in an open state in accordance with an example embodiment. 
         FIG.  5 A  is a distal end view of a distally expanding facet joint implant in a closed state in accordance with an example embodiment. 
         FIG.  5 B  is a distal end view of a distally expanding facet joint implant in an open state in accordance with an example embodiment. 
         FIG.  6 A  is a proximal end view of a distally expanding facet joint implant in a closed state in accordance with an example embodiment. 
         FIG.  6 B  is a proximal end view of a distally expanding facet joint implant in an open state in accordance with an example embodiment. 
         FIG.  7 A  is a top cross-sectional view of a distally expanding facet joint implant in a closed state in accordance with an example embodiment. 
         FIG.  7 B  is a top cross-sectional view of a distally expanding facet joint implant in an open state in accordance with an example embodiment. 
         FIG.  8 A  is a side cross-sectional view of a distally expanding facet joint implant in a closed state in accordance with an example embodiment. 
         FIG.  8 B  is a side cross-sectional view of a distally expanding facet joint implant in an open state in accordance with an example embodiment. 
         FIG.  9 A  is an exploded first perspective view of a distally expanding facet joint implant in a closed state showing a distally expanding outer part and an inner part with wedge-shaped engagement structure of the implant in accordance with an example embodiment. 
         FIG.  9 B  is an exploded second perspective view of a distally expanding facet joint implant in a closed state showing a distally expanding outer part and an inner part with wedge-shaped engagement structure of the implant in accordance with an example embodiment. 
         FIG.  9 C  is an exploded perspective view of the inner part of a distally expanding facet joint implant in accordance with an alternative example embodiment. 
         FIG.  9 D  is a perspective view of a second or inner connector of the inner part of a distally expanding facet joint implant in accordance with an alternative example embodiment. 
         FIG.  9 E  is a perspective view of a second or inner connector of an inner part and a first or outer connector of an outer part of a distally expanding facet joint showing threaded engagement between the second connector and first connector in accordance with an alternative example embodiment. 
         FIG.  10    is a perspective view of a delivery device for use with a distally expanding facet joint implant in accordance with an example embodiment. 
         FIG.  11    is a side view of a delivery device for use with a distally expanding facet joint implant in accordance with an example embodiment. 
         FIG.  12    is a top view of a delivery device for use with a distally expanding facet joint implant in accordance with an example embodiment. 
         FIG.  13    is a side cross-sectional view of a delivery device for use with a distally expanding facet joint implant in accordance with an example embodiment. 
         FIG.  14    is a top cross-sectional view of a delivery device for use with a distally expanding facet joint implant in accordance with an example embodiment. 
         FIG.  15    is an enlarged detail side view of the distal end portion of a delivery device for use with a distally expanding facet joint implant in accordance with an example embodiment. 
         FIG.  16    is a distal end view of a delivery device for use with a distally expanding facet joint implant in accordance with an example embodiment. 
         FIG.  17    is a proximal end portion cross-sectional view of a delivery device for use with a distally expanding facet joint implant in accordance with an example embodiment. 
         FIG.  18    is a proximal end view of a delivery device for use with a distally expanding facet joint implant in accordance with an example embodiment. 
         FIG.  19    is a distal end portion cross-sectional view of a delivery device for use with a distally expanding facet joint implant in accordance with an example embodiment. 
         FIG.  20    is an exploded perspective view of a delivery device for use with a distally expanding facet joint implant showing the components of the delivery device in accordance with an example embodiment. 
         FIG.  21    is a perspective view of a distally expanding facet joint implant and the distal end of a delivery device for use with the implant showing the implant and delivery device aligned for connection in accordance with an example embodiment. 
         FIG.  22 A  is a perspective view of a distally expanding facet joint implant and a delivery device for use with the implant showing the delivery device and an outer part of the implant being brought into locked engagement in accordance with an example embodiment. 
         FIG.  22 B  is a partially transparent enlarged detail perspective view of a distally expanding facet joint implant and the distal end of a delivery device for use with the implant showing the delivery device and an outer part of the implant being brought into locked engagement in accordance with an example embodiment. 
         FIG.  23 A  is a perspective view of a distally expanding facet joint implant and a delivery device for use with the implant showing the delivery device and an inner part of the implant being brought into engagement in accordance with an example embodiment. 
         FIG.  23 B  is a partially transparent enlarged detail perspective view of a distally expanding facet joint implant and the distal end of a delivery device for use with the implant showing the delivery device and an inner part of the implant being brought into engagement in accordance with an example embodiment. 
         FIG.  23 C  is a partially transparent enlarged detail perspective view of a distally expanding facet joint implant and the distal end of a delivery device for use with the implant showing the delivery device and an inner part of the implant being brought into engagement in accordance with an example embodiment. 
         FIG.  23 D  is a perspective view of a distally expanding facet joint implant and a delivery device for use with the implant showing the delivery device and an inner part of the implant being brought into locked engagement in accordance with an example embodiment. 
         FIG.  23 E  is a partially transparent enlarged detail partial perspective view of a distally expanding facet joint implant and the distal end of a delivery device for use with the implant showing the delivery device and an inner part of the implant in locked engagement in accordance with an example embodiment. 
         FIG.  24 A  is a side view of a distally expanding facet joint implant and a delivery device for use with the implant showing the delivery device and an inner part of the implant in locked engagement in accordance with an example embodiment. 
         FIG.  24 B  is a top cross-sectional view of a distally expanding facet joint implant and a delivery device for use with the implant showing the delivery device and an inner part of the implant in locked engagement in accordance with an example embodiment. 
         FIG.  24 C  is an enlarged detail view of a proximal end portion of the distally expanding facet joint implant and a distal end portion of the delivery device for use with the implant as shown in  FIG.  24 B  showing the delivery device and the inner part of the implant in locked engagement in accordance with an example embodiment. 
         FIG.  24 D  is a cross-sectional view of a proximal end portion of the distally expanding facet joint implant and a distal end portion of the delivery device for use with the implant as shown in  FIG.  24 A  showing the delivery device and the inner part of the implant in locked engagement in accordance with an example embodiment. 
         FIG.  25 A  is a perspective view of a distally expanding facet joint implant and a delivery device for use with the implant showing the delivery device in locked engagement with an inner part of the implant and the inner part being translated into a distally expanding outer part of the implant in accordance with an example embodiment. 
         FIG.  25 B  is a partially transparent enlarged detail partial perspective view of a distally expanding facet joint implant and the distal end of a delivery device for use with the implant showing the delivery device in locked engagement with an inner part of the implant and the inner part being translated into a distally expanding outer part of the implant in accordance with an example embodiment. 
         FIG.  26 A  is a side view of a distally expanding facet joint implant and a delivery device for use with the implant showing the delivery device in locked engagement with an inner part of the implant, the inner part translated into a distally expanding outer part of the implant, and the implant in an open state in accordance with an example embodiment. 
         FIG.  26 B  is a top cross-sectional view of a distally expanding facet joint implant and a delivery device for use with the implant showing the delivery device in locked engagement with an inner part of the implant, the inner part translated into a distally expanding outer part of the implant, and the implant in an open state in accordance with an example embodiment. 
         FIG.  26 C  is an enlarged detail view of a proximal end portion of the distally expanding facet joint implant and a distal end portion of the delivery device as shown in  FIG.  26 B  showing the delivery device in locked engagement with the inner part of the implant, the inner part translated into the distally expanding outer part of the implant, and the implant in the open state in accordance with an example embodiment. 
         FIG.  26 D  is a cross-sectional view of a proximal end portion of the distally expanding facet joint implant and a distal end portion of the delivery device for use with the implant as shown in  FIG.  26 A  showing the delivery device in locked engagement with the inner part of the implant, the inner part translated into the outer distally expanding part of the implant, and the implant in the open state in accordance with an example embodiment. 
         FIG.  27 A  is a perspective view of an inter-facet connection plate for use with a distally expanding facet joint implant in accordance with an example embodiment. 
         FIG.  27 B  is a top view of an inter-facet connection plate for use with a distally expanding facet joint implant in accordance with an example embodiment. 
         FIG.  27 C  is a side view of an inter-facet connection plate for use with a distally expanding facet joint implant in accordance with an example embodiment. 
         FIG.  28 A  is a perspective view of a distally expanding facet joint implant and an inter-facet connection plate in accordance with an example embodiment showing the implant in a closed state positioned in a facet joint between adjacent cervical facets. 
         FIG.  28 B  is a perspective view of a distally expanding facet joint implant and an inter-facet connection plate in accordance with an example embodiment showing the implant in an open state positioned in a facet joint between adjacent cervical facets. 
         FIG.  29 A  is a partial perspective view of a distally expanding facet joint implant with an inter-facet connection plate and a delivery device in accordance with an example embodiment showing a step in a process of implanting the implant in a facet joint between adjacent cervical facets. 
         FIG.  29 B  is a partial perspective view of a distally expanding facet joint implant with an inter-facet connection plate in accordance with an example embodiment showing another step in a process of implanting the implant in a facet joint between adjacent cervical facets. 
         FIG.  29 C  is a side view of a distally expanding facet joint implant with an inter-facet connection plate in accordance with an example embodiment showing still another step in a process of implanting the implant in a facet joint between adjacent cervical facets. 
         FIG.  29 D  is a perspective view of a distally expanding facet joint implant with an inter-facet connection plate in accordance with an example embodiment showing still another step in a process of implanting the implant in a facet joint between adjacent cervical facets. 
         FIG.  29 E  is a partial perspective view of a distally expanding facet joint implant with an inter-facet connection plate and a delivery device in accordance with an example embodiment showing yet another step in a process of implanting the implant in a facet joint between adjacent cervical facets. 
     
    
    
     DETAILED DESCRIPTION 
     Example embodiments of a distally expanding facet joint implant and delivery device embodying the concepts of the present invention are described below with reference to the foregoing figures. 
     A. Overview. 
     Example embodiments of a distally expanding facet joint implant generally include a facet joint implant  10  having an outer part  12  and an inner part  14 . The facet joint implant  10  has an open state in which it is distally expanded and a closed state in which it is distally contracted. The inner part  14  is movable relative to the outer part  12  to cause the facet joint implant  10  to distally expand to the open state and to distally contract to the closed state. 
     The outer part  12  includes a first facet plate  20 , a second facet plate  30 , a hinge  38 , a first set of teeth  40 , and a first or outer connector  51 . The first facet plate  20  has a first distal end portion  21 , a first proximal end portion  22 , and a first opening  23  between the first distal end portion  21  and the first proximal end portion  22 . The second facet plate  30  has a second distal end portion  31 , a second proximal end portion  32 , and a second opening  33  between the second distal end portion  31  and the second proximal end portion  32 . The hinge  38  connects the first proximal end portion  22  of the first facet plate  20  and the second proximal end portion of the second facet plate  30 . 
     The first facet plate  20  has a first exterior surface  24  with a first plurality of serrations  25  and the second facet plate  30  has a second exterior surface with a second plurality of serrations  35 . Alternatively, the serrations can be replaced by projections or spikes. When the facet joint implant  10  is implanted in a facet joint and in the distally expanded open state, the first plurality of serrations  25  and the second plurality of serrations  35  help adhere the facet joint implant to the bony surfaces of the facets adjacent to the facet joint so that the facet joint implant  10  does not move in the facet joint and the facet joint and adjacent facets are strengthened and stabilized. The bone of the facets also can grow into the first plurality of serrations  25  and the second plurality of serrations  35  and through the first opening  23  in the first facet plate  20  and the second opening  33  in the second facet plate to help fuse the facets adjacent to the facet joint and further improve the strength and stability of the facet joint and the surrounding facets. 
     The inner part  14  includes a wedge  61  with a third distal end portion  62  and a third proximal end portion  63 , a second or inner connector  81 , an elongated connector  70  connecting the second connector  81  and the wedge  61 , and a first set of indents  73  and a second set of indents  74  formed on the elongated connector  70 . The inner part  14  is movable relative to the outer part  12  and is at least partially exposed in the first opening  23  of the first facet plate  20  and the second opening  33  of the second facet plate  30 . 
     When the inner part  12  is caused to move toward the first distal end portion  21  of the first facet plate  20  and the second distal end portion  31  of the second facet plate  30 , the third distal end portion  62  of the wedge  61  engages the first facet plate  20  and the second facet plate  30 . This in turn causes the first distal end portion  21  of the first facet plate  20  and the second distal end portion  31  of the second facet plate  30  to move apart until the facet joint implant  10  reaches the distally expanded open state. As the first distal end portion  21  of the first facet plate  20  and the second distal end portion  31  of the second facet plate  30  move apart, the first proximal end portion  22  of the first facet plate  20  and the second proximal end portion  32  of the second facet plate  30  rotate on the hinge  38  in a first direction. 
     In the distally expanded open state, the first set of teeth  40  on the outer part  12  of the facet joint implant  10  engage the second set of indents  74  on the elongated connector  70  of the inner part  14  of the facet joint implant  10 , provide physical feedback, and help maintain the facet joint implant  10  in the open position. 
     When the inner part  12  is moved toward the first proximal end portion  22  of the first facet plate  20  and the second proximal end portion  32  of the second facet plate  30 , the first distal end portion  21  of the first facet plate  20  and the second distal end portion  31  of the second facet plate  30  move toward each other until the facet joint implant  10  reaches the distally contracted closed state. As the first distal end portion  21  of the first facet plate  20  and the second distal end portion  31  of the second facet plate  30  move toward each other, the first proximal end portion  22  of the first facet plate  20  and the second proximal end portion  32  of the second facet plate  30  rotate on the hinge  38  in a second direction opposite to the first direction. 
     In the distally contracted closed state, the first set of teeth  40  on the outer part  12  of the facet joint implant  10  engage the first set of indents  74  on the elongated connector  70  of the inner part  14  of the facet joint implant  10 , provide physical feedback, and help maintain the facet joint implant  10  in the closed position. 
     The first or outer connector  51  of the outer part  12  is configured to be selectively engaged by and brought into locked engagement with a corresponding first or outer connector  100  of a delivery device  90  to hold the facet joint implant  10  in a fixed orientation relative to the delivery device for introduction into the body of a patient, delivery to a facet joint in which the facet joint implant  10  is to be implanted, and insertion and positioning in the facet joint. The second or inner connector  81  of the inner part  14  of the facet joint implant  10  is configured to be selectively engaged by and brought into locked engagement with a corresponding second or inner connector  110  of the delivery device  90  to impart motion to the inner part  14  of the facet joint implant  10 , and more specifically the wedge  61 , relative to the outer part  12  of the facet joint implant  10 , and more specifically the first facet plate  20  and the second facet plate  30 . The first or outer connector  51  and the second or inner connector  81  are arranged concentrically with the first connector  51  extending around the second connector  81 . 
     Example embodiments of the delivery device  90  for use with the distally expanding facet joint implant  10  generally include a distal end portion  92  and a proximal end portion  93 , an elongated hollow outer tube  91 , the corresponding first or outer connector  100 , and the corresponding second or inner connector  110 . The corresponding first connector  100  and the corresponding second connector  110  are located at the distal end portion  92  of the delivery device  90 . 
     The delivery device  90  also includes an elongated hollow inner tube  105  that extends from the corresponding first connector  100  to the proximal end portion  93  and an elongated inner shaft  115  that extends from the corresponding second connector  110  to the proximal end portion of the delivery device  90 . 
     The delivery device  90  also includes an outer tube control knob  116 , a control handle  120 , an inner shaft control knob  121 , and a lock switch  124  and lock  126 . The outer tube control knob  116 , control handle  120 , inner shaft control knob  121 , and lock switch  124  and lock  126  are located at the proximal end portion  93  of the delivery device  90 . 
     The corresponding first connector  100  and the corresponding second connector  110  are arranged concentrically with the corresponding first connector  100  extending around the corresponding second connector  110 . The corresponding first connector  100  and the corresponding second connector  110  are at least partially contained within the hollow outer tube  91 . The inner tube  105  and the inner shaft  115  are at least partially contained within the hollow outer tube  91  and are arranged concentrically with the inner shaft  115  being contained at least partially in the inner tube  105 . 
     The outer tube control knob  116  is coupled with the hollow outer tube  91  and is configured and operable to advance the outer tube  91  relative to the corresponding first connector of the delivery device and the first connector of the facet joint implant so that when the corresponding first connector and the first connector are brought into locked engagement, surfaces of the first connector are brought into secure engagement with support surfaces on the outer tube. 
     The control handle  120  is coupled with the corresponding first connector  100  and is operable to bring the corresponding first connector  100  into engagement with the first connector  51  of the facet joint implant  10  by inserting the corresponding first connector  100  into the first connector  51 . The control handle  120  is also configured and operable to bring the corresponding first connector  100  into locked engagement with the first connector  51  by rotating the corresponding first connector  100  relative to the first connector  51 . 
     The inner shaft control knob  121  is rotatably connected to the control handle  120  and is coupled with the corresponding second connector  110  by a threaded coupling  122  with the inner shaft  115 . The inner shaft control knob  121  rotates on the threaded coupling  122  relative to the inner shaft  115 . The inner shaft control knob  121  is configured and is operable to be selectively rotated to cause the corresponding second connector  110  to move toward the distal end portion  92  and the proximal end portion  93  of the delivery device  90 , depending on the direction in which it is rotated. When the inner shaft control knob  121  is rotated in a first direction the corresponding second connector  110  moves toward the distal end portion  92  and into engagement with the second connector  81  of the facet joint implant  10 . When the inner shaft control knob  121  is rotated in a second opposite direction the corresponding second connector  110  moves toward the proximal end portion  93  and out of engagement with the second connector  81 . 
     The lock switch  124  is coupled with the inner shaft  115  and via the inner shaft  115  with the corresponding second connector  110 . The lock switch  124  includes a lever  125  that is rotatable between a first (unlocked) position and a second (locked) position on the control handle  120 . Rotation of the lever  125  between the first (unlocked) position and the second (locked) position correspondingly rotates the corresponding second connector  110 . When the corresponding second connector  110  is in engagement with the second connector  81  of the facet joint implant  10 , rotating the lever  125  from the first (unlocked) position to the second (locked) position brings the corresponding second connector  110  into locked engagement with the second connector  81 . The lock  126  is responsive to rotation of the lever  125  to the second (locked) position to temporarily hold or lock the corresponding second connector  110  in locked engagement with the second connector  81 . 
     With the first connector  51  of the facet joint implant  10  in locked engagement with the corresponding first connector  100  of the delivery device  90  and the second connector  81  of the facet joint implant  10  in locked engagement with the corresponding second connector  110  of the delivery device  90 , the delivery device  90  can be manipulated to introduce the facet joint implant  10  into the body of a patient, guide it to a facet joint  140  in which it is to be implanted, and insert and position it within the facet joint  140 . 
     Once the facet joint implant  10  is positioned in the facet joint  140 , rotating the inner shaft control knob  121  further in the first direction causes the inner part  14  of the facet joint implant  10 , and more specifically the wedge  61 , to move distally relative to the outer part  12 , and more specifically the first facet plate  20  and the second facet plate  30 , and causes the facet joint implant  10  to distally expand to its open position. Rotating the inner shaft control knob  121  in the second opposite direction causes the inner part  14  to move proximally relative to the outer part  12  and causes the facet joint implant  10  to distally contract to its closed position. 
     B. Outer Part. 
     Illustrated primarily in  FIGS.  1 A through  9 B , the outer part  12  of the distally expanding facet joint implant  10  comprises a first facet plate  20 , a second facet plate  30 , a hinge  38 , a first set of teeth  40 , a connecting shoulder  41 , and a first delivery device interface  50 . 
     Preferably, the outer part  12  comprises a first monolithic structure in which all of the components are formed or fabricated together as a single structure. For example, the outer part  12  may be formed or fabricated using a suitable 3D printing method such as selective laser melting (SLM). Alternatively, suitable molding techniques can be employed. Also alternatively, one or more of the components of the outer part  12  can be fabricated separately via SLM, other 3D printing techniques, and/or suitable molding or machining processes, and can then be interconnected with the other components of the outer part  12  in any suitable manner. 
     Also preferably, the outer part  12  and the inner part  14  described below are formed at the same time, for example using a suitable 3D printing method such as SLM, and also are formed pre-assembled as illustrated in  FIGS.  1 A,  1 B , and others. Alternatively, the outer part  12  and the inner part  14  may be separately fabricated and assembled as illustrated in the figures. 
     1. First and Second Facet Plates. 
     The first facet plate  20  and the second facet plate  30  of the distally expanding facet joint implant  10  are configured and are operable to engage the bony surfaces of the superior and inferior facets  143 ,  145  of a facet joint  140  and to distally expand and distally distract the facet joint  140  when the facet joint implant  10  is distally expanded. 
     The first facet plate  20  of the outer part  12  has a first distal end portion  21 , a first proximal end portion  22 , and a first opening  23  between the first distal end portion  21  and the first proximal end portion  22 . The first facet plate  20  has a first exterior surface  24  with a first plurality of serrations  25  and a first interior surface  26 . 
     The first interior surface  26  is generally opposed to a second interior surface  36  of second facet plate  30  described below. Preferably, at least a portion of the first interior surface  26  comprises a first sloped portion  27 . Preferably, the first sloped portion  27  extends upwardly from the direction of the first distal end portion  21  of the first facet plate  20  toward the first proximal end portion  22  of the first facet plate  20 . The first sloped portion  27  is adapted to be engaged by a third sloped portion  65  of a third exterior surface  64  of the wedge  61  of the inner part  14  of the facet joint implant  10  as described below. 
     The second facet plate  30  of the outer part  12  has a second distal end portion  31 , a second proximal end portion  32 , and a second opening  33  between the second distal end portion  31  and the second proximal end portion  32 . The second facet plate  30  has a second exterior surface  34  with a second plurality of serrations  35  and a second interior surface  36 . 
     The second interior surface  36  is generally opposed to the first interior surface  26  of the first facet plate  20  described above. Preferably, at least a portion of the second interior surface  36  comprises a second sloped portion  37 . Preferably, the second sloped portion  37  extends upwardly from the direction of the second distal end portion  31  of the second facet plate  30  toward the second proximal end portion  32  of the second facet plate  30 . The second sloped portion  37  is adapted to be engaged by a fourth sloped surface  67  of a fourth exterior surface  66  of the wedge  61  of the inner part  14  of the facet joint implant  10  as described below. 
     The first opening  23  of the first facet plate  20  and/or the second opening  33  of the second facet plate  30  at least partially expose the inner part  14 . As will become apparent, this facilitates bone growth through and around the facet joint implant  10  to help fuse the superior and inferior facets  143 ,  145  adjacent to the facet joint  140  in which the facet joint implant  10  is implanted, and to thus strengthen and stabilize the facet joint  140  and the adjacent facets  143 ,  145 . It also facilitates observation of the movement of the inner part  14  of the facet joint implant  10  relative to the outer part  12  of the facet joint implant  10 , for example to confirm proper operation of the facet joint implant  10  prior to insertion and deployment. 
     The facet joint implant  10  has a closed position or state and an open position or state. Throughout the description herein, the terms “position” and “state” are employed interchangeably in this regard. 
     In the closed state, the first distal end portion  21  of the first facet plate  20  and the second distal end portion  31  of the second facet plate  30  are in close proximity, and the first interior surface  26  of the first facet plate  20  and the second interior surface  36  of the second facet plate  30  are in close proximity and approximately parallel.  FIGS.  1 A,  2 A,  3 A,  4 A,  5 A,  6 A,  7 A, and  8 A  among others illustrate the facet joint implant  10  in the closed state. 
     In the open state, the first distal end portion  21  of the first facet plate  20  and the second distal end portion  31  of the second facet plate  30  are spaced apart, and the first interior surface  26  of the first facet plate  20  and the second interior surface  36  of the second facet plate  30  are also spaced apart distally and at an acute angle.  FIGS.  1 B,  2 B,  3 B,  4 B,  5 B,  6 B,  7 B, and  8 B  among others illustrate the facet joint implant  10  in the open state. 
     The first plurality of serrations  25  on the first exterior surface  24  of the first facet plate  20  and the second plurality of serrations  35  on the second exterior surface  34  of the second facet plate  30  are configured and operable to engage the bony surfaces of the superior and inferior facets  143 ,  145  facing the facet joint  140  respectively when the facet joint implant  10  is positioned in the facet joint  140  and distally expanded in the open state or position. Alternatively or in addition to the first plurality of serrations  25  and the second plurality of serrations  35 , spikes or other protrusions may be employed. The first plurality of serrations  25  and the second plurality of serrations  35  help the facet joint implant  10  to adhere to the bony surfaces of the superior and inferior facets  143 ,  145 , to prevent movement of the facet joint implant  10  within the facet joint  140 , and to stabilize and strengthen the facet joint  140  and the adjacent superior and inferior vertebrae. These effects are further enhanced as bone from the adjacent facets  143 ,  145  grows into the first and second pluralities of serrations  25 ,  35 . 
     The first facet plate  20  and the second facet plate  30  of the example embodiments are illustrated as being approximately rectangular in shape and as having the same shape and dimensions. However, persons skilled in the art will appreciate that the first facet plate  20  and the second facet plate  30  may be formed with various shapes and dimensions, and that the shapes and dimensions of the first facet plate  20  and the second facet plate  30  may be different, provided the shapes and dimensions are suitable to achieve the objectives identified herein. Similarly, in the example embodiments the first opening  23  in the first facet plate  20  and the second opening  33  in the second facet plate  30  have the same shape and dimensions and extend to the first proximal end portion  22  of the first facet plate  20  and to the second proximal end portion  32  of the second facet plate  30  respectively as illustrated in  FIGS.  1 A,  1 B,  3 A,  3 B,  4 A,  4 B , and others. However, persons skilled in the art will appreciate that the first opening  23  and the second opening  33  may have various shapes and dimensions provided the shapes and dimensions are suitable to achieve the objectives identified herein. Persons skilled in the art also will appreciate that the first opening  23  need not necessarily extend to the first proximal end portion  22  of the first facet plate  20  but may be completely enclosed by the first exterior surface  24  of the first facet plate  20 , and that the second opening  33  need not necessarily extend to the second proximal end portion  32  of the second facet plate  30  but may be completely enclosed by the second exterior surface  34  of the second facet plate  30 . 
     2. Hinge. 
     The hinge  38  connects the first proximal end portion  22  of the first facet plate  20  and the second proximal end portion  32  of the second facet plate  30 . The hinge  38  is preferably positioned between the first proximal end portion  22  of the first facet plate  20  and the second proximal end portion  32  of the second facet plate  30 . Preferably the hinge  38  is formed as a single monolithic structure with the first facet plate  20  and the second facet plate  30 . Preferably the hinge  38  comprises a living hinge. Alternatively, the hinge  38  can be formed as a separate structure and attached or connected to and between the first proximal end portion  22  of the first facet plate  20  and the second proximal end portion  32  of the second facet plate  30  in any suitable manner. 
     In the example embodiments, the hinge  38  extends across substantially the entire width of the first proximal end portion  22  of the first facet plate  20  and the second proximal end portion  32  of the second facet plate  30  except where it is interrupted by the first opening  23  in the first facet plate  20  and the second opening  33  in the second facet plate  30 . Persons skilled in the art will appreciate that the hinge  38  need not necessarily extend across substantially the entire width of the first proximal end portion  22  of the first facet plate  20  and the second proximal end portion  32  of the second facet plate  30  in all applications, however, and that it may be provided at select points between the first proximal end portion  22  of the first facet plate  20  and the second proximal end portion  32  of the second facet plate  30  as desired for various applications. 
     The hinge  38  has a third opening  39 . The third opening  39  is shaped and configured to allow an elongated connector  70  of the inner part  14  to extend through the third opening  39  and to move distally and proximally relative to the first facet plate  20  and the second facet plate  30  of the outer part  12  as described below. 
     When the first distal end portion  21  of the first facet plate  20  and the second distal end portion  31  of the second facet plate  30  expand apart, the first proximal end portion  22  of the first facet plate  20  and the second proximal end portion  32  of the second facet plate  30  rotate in opposite directions around the axis of the hinge  38 . In the example embodiments, the first proximal end portion  22  of the first facet plate  20  rotates clockwise about the axis while the second proximal end portion  32  of the second facet plate  30  rotates counter-clockwise about the axis. 
     Accordingly, the first proximal end portion  22  of the first facet plate  20  and the second proximal end portion  32  of the second facet plate  30  remain in close proximity as the first distal end portion  21  of the first facet plate  20  and the second distal end portion  31  of the second facet plate  30  expand apart. The first proximal end portion  22  of the first facet plate  20  and the second proximal end portion  32  of the second facet plate  30  remain in close proximity even when the facet joint implant  10  is in the open state. 
     3. First Set of Teeth. 
     In the example embodiments, the first set of teeth  40  are adapted and configured to selectively engage a first set of indents  73  and a second set of indents  74  on the inner part  14  of the facet joint implant  10  to securely hold the facet joint implant  10  in a selected position of distal expansion as further described below. More specifically, the first set of teeth  40 , the first set of indents  73 , and the second set of indents  74  are configured, are relatively positioned, and are operable to function like a ratchet to help hold the inner part  14  of the facet joint implant  10  in one of two selected positions relative to the outer part  12  of the facet joint implant  10 , and hence the facet joint implant  10  in one of two selected states or positions of distal expansion. 
     For example, the first set of teeth  40 , the first set of indents  73 , and the second set of indents  74  are preferably positioned relative to one another so that when the facet joint implant  10  is in the closed state, the first set of teeth  40  is engaged with the first set of indents  73  to help hold the facet joint implant  10  in the closed state. When the facet joint implant  10  is in the distally expanded open state, the first set of teeth  40  is engaged with the second set of indents  74  to help hold the facet joint implant  10  in the open state. 
     In the example embodiments, the first set of teeth  40  is formed as part of a first set of elongated fingers  44  having distal end portions  45  and proximal end portions  46 . The first set of teeth  40  is formed at the distal end portions  45  of the first set of elongated fingers  44  with one tooth of the first set of teeth  40  formed on the distal end portion  45  of each elongated finger of the first set of elongated fingers  44 . The proximal end portions  46  of the first set of elongated fingers  44  are attached or connected to a distal end portion  42  of the connecting shoulder  41  of the outer part  12  of the facet joint implant  10 . In the example embodiments, the distal end portion  42  of the connecting shoulder  41  abuts and is attached or connected to the hinge  38  of the outer part  12 . The connecting shoulder  41 , the first set of elongated fingers  44 , and the first set of teeth  40  are stationary relative to movement of the inner part  14  of the facet joint implant  10 . 
     The elongated fingers of the first set of elongated fingers  44  extend distally from the distal end portion  42  of the connecting shoulder  41  preferably along the surfaces of opposite lateral sides  75  of the elongated connector  70  of the inner part  14  of the facet joint implant  10 . The first set of teeth  40 , and more specifically each tooth of the first set of teeth  40 , faces inwardly toward and extends into contact with the surfaces of the opposite lateral sides  75  of the elongated connector  70 , including the first set of indents  73  and the second set of indents  74 , which are formed in the surfaces of the elongated connector  70 . 
     The elongated fingers of the first set of elongated fingers  44  are formed and configured to be deformable and elastic so that the teeth of the first set of teeth  40  apply a force against the surfaces of the elongated connector  70  with which they are in contact. Preferably the force is insufficient to substantially impede movement of the inner part  14  of the facet joint implant  10  relative to the outer part  12  of the implant when the first set of teeth  40  are not engaged with either the first set of indents  73  or the second set of indents  74  on the elongated connector  70 . At the same time, the force preferably is sufficient so that when the teeth of the first set of teeth  40  encounter the indents of either the first set of indents  73  or the second set of indents  74 , the teeth are caused to securely engage and seat in the indents and to securely (but not irreversibly) hold the inner part  14  of the facet joint implant  10  in position relative to the outer part  12  of the facet joint implant  10 . It is also preferred that the force be sufficient to produce a physical feedback, such as a clicking feel or sound, when the teeth engage and seat in the indents. 
     This in turn securely (but not irreversibly) holds the facet joint implant  10 , and more specifically the first facet plate  20  and the second facet plate  30  of the outer part  12  of the facet joint implant  10 , in one of two selected positions of distal expansion, which as described above may correspond to the closed state and the open state of the facet joint implant  10 . The secure holding provided by the first set of teeth  40  and second set of indents  74  is particularly beneficial when the facet joint implant  10  is deployed in a facet joint  140  in the distally expanded open state. In that circumstance, the facet joint implant  10  can be subjected to substantial forces from the vertebrae adjacent the joint. The secure holding provided by the first set of teeth  40  and second set of indents  74  helps prevent the facet joint implant  10  from possibly inadvertently distally contracting and perhaps moving within the joint  140  or even being ejected, especially if an inter-facet connection plate, such as described below, is not used. 
     At the same time, and as also described below, the holding force provided by the first set of teeth  40  and at least the second set of indents  74  may or may not be so great as to prevent manually disengaging the first set of teeth  40  from the second set of indents  74 , and manually causing the facet joint implant  10  to distally contract. For example, if it is deemed desirable or necessary to be able to reposition the facet joint implant  10  in the facet joint  140  or to remove it from the facet joint  140  once it has been distally expanded, the second set of indents  74  can be configured to permit the first set of teeth  140  to be manually disengaged from the second set of indents  74  by the application of a degree of force so that the facet joint implant  10  can be manually distally contracted. Alternatively, however, the indents  74  and teeth  40  can be made deeper or can be otherwise configured to substantially prevent the first set of teeth  40  from being disengaged, and thus substantially prevent the facet joint implant  10  from being distally contracted once it has been distally expanded. 
     It is preferred that the first set of teeth  40  of the outer part  12 , and the first set of indents  73  and second set of indents  74  of the inner part  14  be at least partially visible through the first opening  23  in the first facet plate  20  and/or the second opening  33  in the second facet plate  30 . This facilitates observation of the movement of the first set of teeth  40  relative to the lateral sides  75  of the elongated connector  75 , the first set of indents  73 , and the second set of indents, for example to confirm proper operation of the facet joint implant  10  prior to insertion and deployment. 
     Preferably the first set of teeth  40 , the first set of elongated fingers  44 , and the connecting shoulder  41  are formed as a single monolithic structure with the other components of the outer part  12  of the facet joint implant  10 . Alternatively, one or more of the first set of teeth  40 , the first set of elongated fingers  44 , and the connecting shoulder  41  be formed as a separate structure or structures, and can be attached or connected with the other components of the outer part  12  in any suitable manner. 
     In the specific example embodiments illustrated, the first set of teeth  40  comprises a first set of two teeth and the first set of elongated fingers  44  comprises a first set of two elongated fingers with one tooth formed on each elongated finger. In addition, in the specific example embodiments illustrated, two sets of indents  77 ,  78  are provided on opposite lateral sides of the elongated connector  70 . However, persons skilled in the art will appreciate that depending on particular circumstances and intended applications of the facet joint implant  10 , more or fewer teeth, elongated fingers, and indents may be used. In addition, the arrangements of the teeth, elongated fingers, and indents may be altered. For example, the teeth and indents may be arranged to engage on adjacent sides of the elongated connector  70  rather than or in addition to opposite lateral sides  75 . Further, additional sets of indents may be provided at additional locations to engage the teeth when the facet joint implant is in states of partial distal expansion rather than or in addition to the closed and open states described. The shapes of the teeth and indents may be varied. Still further, the teeth may be formed on other structures of the outer part  12  and the indents may be formed on other structures of the inner part  14 . All of these variations can be made without deviating from the concepts of the invention provided they are consistent with achieving the objectives described herein. 
     4. First Delivery Device Interface and First (Outer) Connector. 
     The first delivery device interface  50  provides a connection interface to the outer part  12  of the facet joint implant  10  for a delivery device  90  described below. 
     The first delivery device interface  50  is connected to the outer part  12  of the facet joint implant  10 . More specifically, the first delivery device interface  50  is connected to the first proximal end portion  22  of the first facet plate  20  and to the second proximal end portion  32  of the second facet plate  30 . Still more specifically, the first delivery device interface  50  is connected to the proximal end portion  43  of the connecting shoulder  41  and is connected via the connecting shoulder  41  to the first proximal end portion  22  of the first facet plate  20  and to the second proximal end portion  32  of the second facet plate  30 . 
     Preferably, the connection of the first delivery device interface  50  to the outer part  12  of the facet joint implant  10  is a substantially fixed or similar connection or attachment that does not allow the first delivery device interface  50  to substantially rotate or otherwise move relative to the outer part  12 . Rather, it is preferred that as the first delivery device interface  50  is moved, whether rotationally or otherwise, the outer part  12  of the facet joint implant  10  moves with it. 
     The first delivery device interface  50  of the facet joint implant  10  comprises a first or outer connector  51 . The first connector  51  is configured to be selectively engaged by a corresponding first connector  100  of the delivery device  90  and to be brought into locking engagement with the corresponding first connector  100  to hold the facet joint implant  10  in a fixed orientation relative to the delivery device  90 . In the example embodiments, the first connector  51  comprises a first bayonet connector  52 . The first bayonet connector  52  is adapted and configured to receive, engage, and be in locked engagement with a first bayonet  101  of the corresponding first or outer connector  100  of the delivery device  90  as described below. 
     The first or outer connector  51  comprises a substantially cylindrical body  53  that defines an open interior space  54  with an open face  55 . The body  53  has an exterior surface  56 . The exterior surface  56  contains one or more flats  57  adapted and configured to engage corresponding structures of the delivery device  90  as described below. 
     The third opening  39  through the hinge  38  described previously also extends through the body of the connecting shoulder  41  and into the open interior space  54  of the first connector  51 . The third opening  39  is dimensioned and configured to allow the elongated connector  70  of the inner part  14  of the facet joint implant  10  to extend through the third opening  39  and to move distally and proximally relative to the hinge  38 , connecting shoulder  41 , and first connector  51  of the outer part  12  of the facet joint implant  10 . 
     As described further below, a second or inner connector  81  of a second delivery device interface  80  connected to the inner part  14  of the facet joint implant  10  is fixedly connected or attached to a proximal end of the elongated connector  70 . As the second or inner connector  81  is moved in a distal direction toward the first facet plate  20  and the second facet plate  30  it enters the open interior space  54  of the first or outer connector  51  through the open face  55  and the first or outer connector  51  extends around the second or inner connector  81 . In the example embodiments, the first or outer connector  51  and the second or inner connector  81  are arranged to be substantially concentric, although that is a preference and not always necessary. As the second or inner connector  81  is moved in a proximal direction away from the first facet plate  20  and the second facet plate  30 , it exits the open interior space  54  of the first or outer connector  51  through the open face  55  and is exposed outside the first or outer connector  51 . 
     When the first connector  51  of the outer part  12  of the facet joint implant  10  is in locked engagement with the corresponding first connector  100  of the delivery device  90 , the facet joint implant  10  is securely held in a fixed position and orientation relative to the delivery device  90  and the position and orientation of the facet joint implant  10  can be manipulated using the delivery device  90 . This facilitates the positioning and orientation of the facet joint implant  10  for insertion into the body of a patient, delivery to a facet joint  140  in which it is to be implanted, and implantation in the facet joint  140 . 
     Preferably, the first delivery device interface  50 , more specifically the first or outer connector  51 , and even more specifically the first bayonet connector  52  is configured to have an outer dimension greater than the expected or intended dimension of the posterior space between the superior and inferior facets  143 ,  145  of the facet joint  140  in which the facet joint implant  10  is to be implanted, i.e., the dimension of the expected or intended posterior opening  141  of the facet joint  140 . This facilitates the ability to achieve proper positioning of the facet joint implant  10  in the facet joint  140  by allowing only the components of the outer part  12  and the inner part  14  necessary to distally distract the facet joint  140  to be inserted and preventing over-insertion of the facet joint implant  10  in the joint. In addition, the distance or dimension between the first delivery device interface  50 , more specifically the first connector  51 , and the distal end of the facet joint implant  10  can vary based on the facet size and the intended position of the maximum expansion of the distal end of the facet joint implant  10 . 
     Preferably, the first delivery device interface  50 , more specifically the first or outer connector  51 , and even more specifically the first bayonet connector  52  is formed as a single monolithic structure with the other components of the outer part  12  of the facet joint implant  10 . Alternatively, however, the first delivery device interface  50 , more specifically the first or outer connector  51 , and even more specifically the first bayonet connector  52  may be formed as a separate structure or structures, and may be fixedly attached or connected with the other components of the outer part  12  as described herein in any suitable manner. 
     C. Inner Part. 
     Illustrated primarily in  FIGS.  1 A through  9 E , the inner part  14  of the distally expanding facet joint implant  10  comprises a wedge  61 , a first set of indents  73 , a second set of indents  74 , a second delivery interface  80  comprising a second or inner connector  81 , and an elongated connector  70  between the wedge  61  and the second connector  81 . 
     Preferably, the inner part  14  comprises a second monolithic structure, separate from the first monolithic structure of the outer part  12 , in which all of the components of the inner part  14  are formed or fabricated together as a single structure. For example, the inner part  14  may be formed or fabricated using a suitable 3D printing method such as selective laser melting (SLM). Alternatively, suitable molding techniques can be employed. Also alternatively, one or more of the components of the inner part  14  can be fabricated separately via SLM, other 3D printing techniques, and/or suitable molding or machining processes, and can then be interconnected with the other components of the inner part  14  in any suitable manner. 
     Also preferably, the inner part  14  is formed at the same time as the outer part  12  described above, for example using a suitable 3D printing method such as SLM, and also is formed pre-assembled with the outer part  12  as illustrated in  FIGS.  1 A through  8 B  for example. Alternatively, the inner part  14  may be fabricated separately from the outer part  12  and assembled with the outer part  12  as illustrated in the figures. 
     As described further below, the inner part  14  of the facet joint implant  10  is moveable relative to the outer part  12 . More specifically, the inner part  14  is movable in a distal direction toward the first facet plate  20  and the second facet plate  30 , and in an opposite proximal direction away from the first facet plate  20  and the second facet plate  30 . The movement of the inner part  14  relative to the outer part  12  causes the facet joint implant  10  to distally expand and contract between the open and closed states depending on the direction of motion of the inner part  14 . As previously mentioned, the inner part  14  is at least partially exposed in the first opening  23  of the first facet plate  20  and/or the second opening  33  of the second facet plate  30  to facilitate controlling the movement of the inner part  14  relative to the outer part  12 . 
     1. Wedge. 
     The inner part  14  includes an engagement structure  60  that is configured and operable to be selectively moved relative to the outer part  12  and to engage the outer part  12  to selectively cause the facet joint implant  10  to distally expand into the open state and distally contract into the closed state. More specifically, the engagement structure is configured and operable to be selectively moved in a distal direction toward and into engagement with the first facet plate  20  and the second facet plate  30  of the outer part  12  to selectively cause the first distal end portion  21  of the first facet plate  20  and the second distal end portion  31  of the second facet plate  30  to expand apart to place the facet joint implant  10  in the open state, and to be selectively moved in an opposite proximal direction away from and out of engagement with the first facet plate  20  and the second facet plate  30  of the outer part  12  to selectively cause the first distal end portion  21  of the first facet plate  20  and the second distal end portion  31  of the second facet plate  30  to contract toward each other and place the facet joint implant  10  in the closed state. 
     Although the engagement structure  60  may take any shape suitable to accomplish the above description, in the example embodiments, the inner part  14  comprises a wedge  61  as the engagement structure  60 . The wedge  61  has a third distal end portion  62  and a third proximal end portion  63 . The third distal end portion  62  is adjacent to and faces the first sloped portion  27  on the first interior surface  26  of the first facet plate  20  of the outer part  12  of the facet joint implant  10  and the second sloped portion  37  on the second interior surface  36  of the second facet plate  30  of the outer part  12  of the facet joint implant  10  when the facet joint implant  10  is in the closed state. The third proximal end portion  63  is connected to a distal end portion  71  of the elongated connector  70  of the inner part  14  and via the elongated connector  70  to the second delivery device interface  80  of the inner part  14  described below. 
     The wedge  61  also has a third exterior surface  64  and a fourth exterior surface  66 . At least a portion of the third exterior surface  64  and a portion of the fourth exterior surface  66  are sloped. The sloped portion of the third exterior surface  64  comprises a third sloped portion  65  and the sloped portion of the fourth exterior surface  66  comprises a fourth sloped portion  65 . 
     Preferably, the third sloped portion  65  of the third exterior surface  64  of the wedge  61  extends downwardly from the direction of the third proximal end portion  63  of the wedge  61  toward the third distal end portion  62  of the wedge  61 . Preferably the fourth sloped portion  65  of the fourth exterior surface  66  of the wedge  61  extends downwardly from the direction of the third proximal end portion  63  of the wedge  61  toward the third distal end portion  62  of the wedge  61 . As a result, the third distal end portion  62  of the wedge  61  has a first thickness and the third proximal end portion  63  of the wedge  61  has a second thickness greater than the first thickness. 
     The third sloped portion  65  of the third exterior surface  64  of the wedge  61  is adapted to engage and to move relative to the first sloped portion  27  of the first interior surface  26  of the first facet plate  20  of the outer part  12 . The fourth sloped portion  65  of the fourth exterior surface  66  of the wedge  61  is adapted to engage and to move relative to the second sloped portion  37  of the second interior surface  36  of the second facet plate  30  of the outer part  12 . 
     When the inner part  14  of the facet joint implant  10  is manipulated using the delivery device  90  and caused to move distally in the direction of the first facet plate  20  and the second facet plate  30  of the outer part  12  of the facet joint implant  10  as described below, the distally downward sloping third sloped portion  65  on the third exterior surface  64  of the wedge  61  engages and moves relative to the proximally upward sloping first sloped portion  27  of the first interior surface  26  of the first facet plate  20  of the outer part  12 . Similarly, the distally downward sloping fourth sloped portion  65  on the fourth exterior surface  66  of the wedge  61  engages and moves relative to the proximally upward sloping second sloped portion  37  of the second interior surface  36  of the second facet plate  30  of the outer part  12 . 
     As the wedge  61  continues to move distally between the first facet plate  20  and the second facet plate, the increasing thickness of the wedge between the first interior surface  26  of the first facet plate  20  and the second interior surface  36  of the second facet plate  30  causes the first distal end portion  21  of the first facet plate  20  and the second distal end portion  31  of the second facet plate  30  to move and apart until the facet joint implant  10  reaches the distally expanded open position. The first proximal end portion  22  of the first facet plate  20  and the second proximal end portion  32  of the second facet plate  30  rotate in a first set of opposite directions about the axis of the hinge  38  and remain in close proximity as the facet joint implant  10  is distally expanded, even when the facet joint implant  10  reaches the open position. 
     Similarly, when the inner part  14  of the facet joint implant  10  is manipulated using the delivery device  90  and caused to move proximally in the opposite direction away from the first facet plate  20  and the second facet plate  30  of the outer part  12  of the facet joint implant  10 , the distally downward sloping third sloped portion  65  on the third exterior surface  64  of the wedge  61  moves relative to and in engagement with the proximally upward sloping first sloped portion  27  of the first interior surface  26  of the first facet plate  20  of the outer part  12 , and the distally downward sloping fourth sloped portion  65  on the fourth exterior surface  66  of the wedge  61  moves relative to and in engagement with the proximally upward sloping second sloped portion  37  of the second interior surface  36  of the second facet plate  30  of the outer part  12 . 
     As the wedge  61  continues to move proximally between the first facet plate  20  and the second facet plate, the decreasing thickness of the wedge between the first interior surface  26  of the first facet plate  20  and the second interior surface  36  of the second facet plate  30  causes the first distal end portion  21  of the first facet plate  20  and the second distal end portion  31  of the second facet plate  30  to move together or toward each other until the facet joint implant  10  reaches the distally contracted closed position. The first proximal end portion  22  of the first facet plate  20  and the second proximal end portion  32  of the second facet plate  30  rotate in a second set of opposite directions about the axis of the hinge  38  and remain in close proximity as the facet joint implant  10  is distally contracted and reaches the closed position. 
     Preferably the wedge  61  also has substantially flat surfaces  68  on the third exterior surface  64  between the third sloped portion  65  and the third proximal end portion  63  of the wedge  61  and on the fourth exterior surface  66  between the fourth sloped portion  67  and the third proximal end portion  63  of the wedge  61 . The flat surfaces  68  are configured to help distribute the pressure or weight exerted on the facet joint implant  10  by the facet joint  140  over a wider surface area when the facet joint implant  10  is positioned in the facet joint  140  with the exterior surfaces  24 ,  34  of the first and second facet plates  20 ,  30  in contact with the interior facet surfaces  150 ,  152 . 
     Preferably, the engagement structure  60  and more specifically the wedge  61  is formed as a single monolithic structure with the other components of the inner part  14  of the facet joint implant  10 . Alternatively, however, the engagement structure  60  and more specifically the wedge  61  may be formed as a separate structure or structures, and may be fixedly attached or connected with the other components of the inner part  14  as described herein in any suitable manner. 
     2. Indents. 
     As described above, the inner part  14  of the facet joint implant  10  comprises a first set of indents  73 , wherein the first set of indents  73  is located on the inner part  14  so that when the facet joint implant  10  is in the closed state, the first set of teeth  40  of the outer part  12  of the facet joint implant  10  is engaged with the first set of indents  73 . Similarly, the inner part  14  of the facet joint implant  10  comprises a second set of indents  74 , wherein the second set of indents  74  is located on the inner part  14  so that when the facet joint implant  10  is in the open state, the first set of teeth of the outer part  12  is engaged with the second set of indents  74 . 
     More specifically, and as described above, in the example embodiments the first set of indents  73  and the second set of indents  74  are formed in the surfaces of opposite lateral sides  75  of the elongated connector  70  of the inner part  14  of the facet joint implant  10  with the opposite lateral sides  75  facing corresponding teeth of a first set of teeth  40  formed on the outer part  12  of the facet joint implant  10 . The first set of indents  73  and the second set of indents  74  are configured, are relatively positioned, and are operable to function like a ratchet with the first set of teeth  40  to help hold the inner part  14  of the facet joint implant  10  in one of two selected positions relative to the outer part  12  of the facet joint implant  10 , and hence the facet joint implant  10  in one of two selected states or positions of distal expansion. 
     In the example embodiments, these two selected positions correspond to the closed state and the open state of the facet joint implant  10  respectively. Thus, the first set of indents  73  is formed on opposite lateral sides  75  of the elongated connector  70  at the distal end portion  71  of the elongated connector  70  at a first position that is just proximal to the third proximal end portion  63  of the wedge  61 . At this first position, the first set of indents  73  align with the first set of teeth  40  of the outer part  12  of the facet joint implant  10  when the elongated connector  70  is positioned such that the third distal end portion  62  of the wedge  61  is adjacent to but not substantially engaged with the first interior surface  26  of the first facet plate  20  of the outer part  12  and the second interior surface  36  of the second facet plate  30  of the outer part  12 . This corresponds to the distally contracted closed state of the facet joint implant  10 . 
     Similarly, the second set of indents  74  is formed on the same opposite lateral sides  75  of the elongated connector  70  as the first set of indents  73  but at a second position that is spaced apart from the first position and is closer to the proximal end of the elongated connector  70  to which the second delivery device interface  80  is connected. At this second position, the second set of indents  74  aligns with the first set of teeth  40  of the outer part  12  when the wedge  61  is fully inserted between the first facet plate  20  and the second facet plate  30  with the third exterior surface  64  of the wedge  61  and the fourth interior surface  65  of the wedge engaged with the first interior surface  26  of the first facet plate  20  and the second interior surface  36  of the second facet plate  30  respectively. This corresponds to the distally expanded open state of the facet joint implant  10 . 
     As described previously, the first set of indents  73  and the second set of indents  74  are preferably configured and dimensioned to facilitate the first set of teeth  40  securely engaging and seating in the indents to securely (but not irreversibly) hold the inner part  14  of the facet joint implant  10  in position relative to the outer part  12  of the facet joint implant  10 . As mentioned above, it also is preferred that the indents be configured to provide a physical feedback, such as a clicking feel or sound, when the first set of teeth  40  engage and seat in the first set of indents  73  and the second set of indents  74 . 
     The secure engagement and seating of the first set of teeth  40  in the indents is particularly beneficial when the facet joint implant  10  is deployed in a facet joint  140  in the distally expanded open state for the reasons explained above. As also described above, it is preferred that at least the second set of indents  74  are configured and dimensioned so that the force with which they engage and hold the first set of teeth  40  is sufficient to reliably keep the facet joint  140  distracted anteriorly. At the same time, the holding force may or may not be so great as to prevent an operator from manually disengaging the first set of teeth  40  from the second set of indents  74 , and manually causing the facet joint implant  10  to distally contract. For example, if it is deemed desirable or necessary to be able to reposition the facet joint implant  10  in the facet joint  140  or to remove it from the facet joint  140  once it has been distally expanded, the second set of indents  74  can be configured to permit the first set of teeth  140  to be manually disengaged from the second set of indents  74  by the application of a degree of force so that the facet joint implant  10  can be manually distally contracted. Alternatively, however, the indents  74  and teeth  40  can be made deeper or can be otherwise configured to substantially prevent the first set of teeth  40  from being disengaged, and thus substantially prevent the facet joint implant  10  from being distally contracted once it has been distally expanded to the open state. 
     It is preferred that the first set of indents  73  and second set of indents  74  be at least partially visible through the first opening  23  in the first facet plate  20  and/or the second opening  33  in the second facet plate  30 . This facilitates observation of the movement of the inner part  14  of the facet joint implant  10  relative to the outer part  12  of the facet joint implant  10 , for example to confirm proper operation of the facet joint implant  10  prior to insertion and deployment. 
     It is also preferred that the first set of indents  73 , the second set of indents  74 , and the elongated connector  70  be formed as a single monolithic structure with each other and with the other components of the inner part  14  of the facet joint implant  10 . Alternatively, however, the components may be formed as one or more separate structures, and can be attached or connected together and with the other components of the inner part  14  in any suitable manner. 
     In the specific example embodiments illustrated, the first set of indents  73  and the second set of indents  74  each comprise two indents located on opposite lateral sides of the elongated connector  70 . However, persons skilled in the art will appreciate that depending on particular circumstances and intended applications of the facet joint implant  10 , more or fewer indents may be used in each set and total. In addition, the arrangements of the indents may be altered. For example, indents may be arranged on adjacent sides of the elongated connector  70  rather than or in addition to opposite lateral sides  75 . Further, additional sets of indents may be provided at additional locations to engage teeth of the outer part  12  when the facet joint implant is in states of partial distal expansion rather than or in addition to the closed and open states as described. The corresponding shapes of the indents and teeth may be varied. Still further, the indents may be formed on other structures of the inner part  14  rather than or in addition to the elongated connector  70 . All of these variations can be made without deviating from the concepts of the invention provided they are consistent with achieving the objectives described herein. 
     3. Second Delivery Device Interface and Second (Inner) Connector. 
     The second delivery device interface  80  provides a connection interface to the inner part  14  of the facet joint implant  10  for the delivery device  90  described below. 
     The second delivery device interface  80  is connected to the inner part  14  of the facet joint implant  10 . More specifically, the second delivery device interface  80  is connected to the wedge  61 . Still more specifically, the second delivery device interface is connected to the third proximal end portion  63  of the wedge  61 . Even more specifically, the second delivery device interface  80  is connected to the proximal end portion  72  of the elongated connector  70  and is connected via the elongated connector  70  to the third proximal end portion  63  of the wedge  61 . 
     Preferably, the connection of the second delivery device interface  80  to the inner part  14  of the facet joint implant  10  is a substantially fixed or similar connection or attachment that does not allow the second delivery device interface  80  to substantially move relative to the inner part  14 . Rather, it is preferred that as the second delivery device interface  80  is moved, the inner part  14  of the facet joint implant  10  moves with it relative to the outer part  12  of the facet joint implant  10 . 
     The second delivery device interface  80  of the facet joint implant  10  comprises a second or inner connector  81 . The second connector  81  is configured to be selectively engaged by and to be brought into locked engagement with a corresponding second connector  110  of the delivery device  90  to impart motion to the inner part  14  of the facet joint implant  10  relative to the outer part  12  of the facet joint implant  10 . The second connector  81  is configured to be engaged by the corresponding second connector  110  by receiving the corresponding second connector  110  at least partially in the second connector  81 . The second connector  81  is configured to be brought into locked engagement with the corresponding second connector  110  by permitting the corresponding second connector  110  to rotate within and relative to the second connector  81 , for example by approximately 90 degrees. 
     In the example embodiments, the second connector  81  comprises a second bayonet connector  82 . The second bayonet connector  82  is adapted and configured to receive, be engaged by, and be brought into locked engagement with a second bayonet  111  of the corresponding second connector  110  of the delivery device  90 , which is described further below. The second bayonet connector  82  comprises a substantially cylindrical body  83  that defines an open interior space  84  with an open face  85  for receiving a second bayonet  111  of the corresponding second connector  110  of the delivery device  90 . The open face  85  is shaped and adapted to permit the second bayonet  111  to be inserted into the open interior space  84  of the second bayonet connector  82  and to be brought into engagement with the second bayonet connector  82 . The second bayonet connector  82  is further adapted and configured to be brought into locked engagement with the second bayonet  111  of the delivery device  90  by permitting the second bayonet  111  to rotate within and relative to the second bayonet connector  82 , for example by approximately 90 degrees. 
     The shape of the open face  85  is adapted both to act as a key opening for a second key  113  of the delivery device  90  as described further below, and more importantly to prevent the second bayonet  111  from inadvertently exiting the second bayonet connector  82  once it is in locked engagement. Thus, the open face  85  is shaped to only allow the second bayonet  111  to be inserted in or to be withdrawn from the second bayonet connector  82  when the second bayonet  111  is in a particular orientation relative to the second bayonet connector  82 . Conversely, the open face  85  is shaped and adapted to block the second bayonet  111  from being inserted into or withdrawn from the open interior space  84  of the second bayonet connector  82  when the second bayonet  111  is not in the particular orientation relative to the second bayonet connector  82 . 
     As described above, as the second or inner connector  81  is moved in a distal direction toward the first facet plate  20  and the second facet plate  30  of the outer part  12  of the facet joint implant  10 , the second connector  81  enters the open interior space  54  of the first or outer connector  51  of the outer part  12  through the open face  55  and the first or outer connector  51  extends around the second or inner connector  81 . In the example embodiments, the first or outer connector  51  and the second or inner connector  81  are arranged to be substantially concentric, although that is a preference and is not always necessary. As the second or inner connector  81  is moved in a proximal direction away from the first facet plate  20  and the second facet plate  30 , it exits the open interior space  54  of the first or outer connector  51  through the open face  55  and is exposed outside the first or outer connector  51 . 
     As described previously, the third opening  39  through the hinge  38  of the outer part  12  of the facet joint implant  10  also extends through the body of the connecting shoulder  41  of the outer part  12  and into the open interior space  54  of the first connector  51  of the outer part  12 . The elongated connector  70  of the inner part  14  extends through the third opening  39  and is movable within the third opening  39  in distal and proximal directions relative to the outer part  12  of the facet joint implant  10 . Preferably, the second or inner connector  81 , more specifically the second bayonet connector  82 , and even more specifically the body  83  of the second bayonet connector  82 , is configured and dimensioned relative to the third opening  39  so that the second connector  81  cannot enter the third opening  39  through the first or outer connector  51 . 
     Because the second or inner connector  81  is fixedly connected to the elongated connector  70 , when the second connector  81  is moved in a distal direction toward the first facet plate  20  and the second facet plate  30  of the outer part  12 , so is the elongated connector  70 . Similarly, when the second or inner connector  81  is moved in an opposite proximal direction away from the first facet plate  20  and the second facet plate  30  of the outer part  12 , so is the elongated connector  70 . Thus, moving the second or inner connector  81  also moves the inner part  14  of the facet joint implant  10  relative to the outer part  12  of the facet joint implant  10 . 
     Accordingly, because the wedge  61  is connected at the distal end portion  71  of the elongated connector  70 , moving the second or inner connector  81  in the distal direction toward the first facet plate  20  and the second facet plate  30  of the outer part  12  causes the wedge  61  to engage and move relative to the first facet plate  20  and the second facet plate  30 , which in turn causes the facet joint implant  10  to distally expand to the open state in the manner previously described. Similarly, moving the second or inner connector  81  in the opposite proximal direction away from the first facet plate  20  and the second facet plate  30  of the outer part  12  causes the wedge  61  to move relative to and to disengage from the first facet plate  20  and the second facet plate  30 , which in turn causes the facet joint implant  10  to distally contract to the closed state in the manner previously described. 
     When the second connector  81  of the inner part  14  of the facet joint implant  10  is in engagement with but not necessarily in locked engagement with the corresponding second connector  110  of the delivery device  90 , the delivery device  90  can be manipulated as described below to selectively cause the second connector  81  and the inner part  14  of the facet joint implant  10 , including the wedge  61 , to move distally relative to the outer part  12 , including the first facet plate  20  and the second facet plate  30 . Thus, the delivery device  90  can be manipulated to selectively cause the facet joint implant  10  to distally expand from its closed state to its open state. This is possible because the wedge  61  is pushed in a distal direction, rather than pulled in a proximal direction, to cause the facet joint implant  10  to distally expand to the open state. When the second connector  81  is in locked engagement with the corresponding second connector  110 , the delivery device  90  also can be manipulated as described below to selectively cause the second connector  81  and the wedge  61  to move proximally relative to the first facet plate  20  and the second facet plate  30 . Thus, the delivery device  90  also can be manipulated to selectively cause the facet joint implant  10  to distally contract from the open state to the closed state in the manner described herein. 
     In the example embodiments illustrated in  FIGS.  1 A through  9 B , the second delivery device interface  80 , more specifically the second or inner connector  81 , and even more specifically the second bayonet connector  82  is preferably formed as a single monolithic structure with the other components of the inner part  14  of the facet joint implant  10 . Alternatively, however, the second delivery device interface  80 , more specifically the second or inner connector  81 , and even more specifically the second bayonet connector  82  may be formed as a separate structure or structures, and may be fixedly and rigidly attached or connected with the other components of the inner part  14  as described herein in any suitable manner. 
     In an alternative example embodiment illustrated in  FIGS.  9 C- 9 E , the second delivery device interface  80 , more specifically the second or inner connector  81 , and even more specifically the second bayonet connector  82  is formed as a separate structure from the remaining components of the inner part  14  of the facet joint implant  10 . In the alternative embodiment, the second delivery device interface  80 , more specifically the second or inner connector  81 , and even more specifically the second bayonet connector  82  is connected to the elongated connector  70  of the inner part  14  by a ball-socket connector  86 . 
     As described further below, the ball-socket connector  86  enables the second bayonet connector  82  to be rotated relative to and without rotating the elongated connector  70  or the wedge  61  of the inner part  14  of the facet joint implant  10  and to cause the inner part  14  to translate in distal and proximal directions relative to the outer part  12  of the facet joint implant  10  without rotating. The ball-socket connector  86  can also be replaced by a disc-in-socket connector or any other connector that permits the second connector  81  to be rotated at the proximal end portion of the facet joint implant  10  and to cause the inner part  14  to be pushed in the direction of the distal end portion of the facet joint implant  10  or to be pulled in the direction of the proximal end portion relative to the outer part  12  without rotating the other components of the inner part  14  nearer the distal end portion of the facet joint implant  10 . 
     The ball-socket connector  86  comprises a ball  87 . The ball  87  is seated in a socket  88  formed in the body  83  of the second connector  81 . The socket  88  and hence the body  83  of the second connector  81  is able to rotate on and relative to the ball  87 . 
     The ball-socket connector  86  and hence the second connector  81  is preferably rigidly but removably coupled to the elongated connector  70  of the inner part  14  of the facet joint implant  10 . This coupling may be accomplished in many suitable ways. In one preferred way, the ball-socket connector  86  comprises a threaded shaft  89  having outside threads. The threaded shaft  89  is fixedly connected or attached to the ball  87  and extends outwardly from the socket  88 . 
     The proximal end  72  of the elongated connector  70  of the inner part  14  of the facet joint implant  10  comprises a threaded passage  76  having inner threads. The threaded shaft  89  of the ball-socket connector  86  extends within the threaded passage  76  of the elongated connector  70  with the outer threads of the threaded shaft  89  in threaded engagement with the inner threads of the threaded passage  76 . With the ball-socket  86  coupled to the elongated connector  70 , the socket  88  and hence the second connector  81  is free to rotate on the ball  87  relative to the elongated connector  70 . The second connector  81  is also free to rotate relative to the first or outer connector  51  of the outer part  12  of the facet joint implant. 
     The body  83  of the second or inner connector  81  is provided with a set of outer threads  83 A. The body  53  of the first or outer connector  51  is provided with a corresponding set of inner threads  53 A. The body  83  of the second or inner connector  81  and the body  53  of the first or outer connector  51  are dimensioned and configured so that when the second or inner connector  81  is positioned within the first or outer connector  51 , for example as illustrated in  FIG.  1 B , the outer threads  83 A on the body  83  of the second or inner connector  81  engage with the inner threads  53 A on the body  53  of the first or outer connector  51 . 
     When the first connector  51  is in locked engagement with the corresponding first connector  100  of the delivery device  90  as described herein, the outer part  12  of the facet joint implant  10  is held in position by the delivery device  90  and the inner part  14  of the facet joint implant  10  is free to move relative to the outer part  12 . Accordingly, rotation of the second connector  81  within the first connector  51  causes the second connector  81  to translate within the first connector  51  on the inner and outer threads  53 A,  83 A. This in turn causes the inner part  14 , including the wedge  61 , to advance distally or retract proximally relative to the outer part  12 , including the first facet plate  20  and the second facet plate  30 , depending on which direction the second connector  81  is rotated. In turn, this causes the facet joint implant  10  to distally expand or to distally contract in the manner described herein, again depending on the direction the second connector  81  is rotated. 
     As an additional alternative, the entire inner part  14  could simply be replaced by a threaded screw with outer threads, and the entire outer part  12  could simply be replaced by a structure with a thicker distal end than proximal end and a passage with inner threads. In this alternative, the threaded screw would extend into the passage with the outer threads of the screw engaged with the inner threads of the passage. Rotation of the screw relative to passage would cause the thicker distal end of the structure to translate distally creating a wedge-like expansion of the facet joint implant. 
     D. Delivery Device. 
     Illustrated primarily in  FIGS.  10  through  26 D , the delivery device  90  for use with the distally expanding facet joint implant  10  is an elongated device with a distal end portion  92  and a proximal end portion  93 . The delivery device  90  generally comprises a hollow outer tube  91  that extends between the distal end portion  92  and the proximal end portion  93 . The delivery device  90  also comprises a hollow inner tube  105  that extends between the distal end portion  92  and the proximal end portion  93  and that has a corresponding first or outer connector  100  at the distal end portion  92 . The corresponding first or outer connector  100  is configured to be brought into engagement and into locked engagement with the first or outer connector  51  of the first delivery device interface  50  of the facet joint implant  10 . The delivery device  90  also comprises an inner shaft  115  that extends between the distal end portion  92  and the proximal end portion  93  and that has a corresponding second or inner connector  110  at the distal end portion  92 . The corresponding second or inner connector  110  is configured to be brought into engagement and into locked engagement with the second or inner connector  81  of the second delivery device interface  80  of the facet joint implant  10 . 
     The delivery device  90  also comprises an outer tube control knob  116  that is located at the proximal end portion  93  and that is coupled with the outer tube  91  and with the inner tube  105 . The delivery device  90  also comprises a control handle  120  that is located at the proximal end portion  93  and that is coupled with the corresponding first connector  100  via the inner tube  105 . The delivery device  90  further comprises an inner shaft control knob  121  that is located at the proximal end portion  93  and that is coupled with the corresponding second connector  110  of the delivery device  90  via the inner shaft  115 . The delivery device  90  further comprises a lock switch  124  and lock  162  that are located at the proximal end portion  93  and that are coupled with the corresponding second connector  110  of the delivery device  90  via the inner shaft  115 . 
     The delivery device  90  is used to introduce the facet joint implant  10  into the body of a patient posteriorly through a posterior incision and to deliver the facet joint implant  10  through a preferably dilated passageway to a facet joint  140  in which the facet joint implant  10  is to be implanted. Once the facet joint implant  10  is at the facet joint  140 , the delivery device  90  is used to position and orient the facet joint implant  10  relative to a posterior opening  141  of the facet joint  140  as desired, and then to insert the facet joint implant  10  into the facet joint  140 , position the facet joint implant  10  in the facet joint  140  as desired, and deploy the facet joint implant  10  by causing it to distally expand to its open position to distally distract the facet joint  140 . The delivery device  90  may also be used to cause the facet joint implant  10  to distally contract to its closed position for repositioning within the facet joint  140  or even removal from the facet joint  140 . 
     1. Corresponding First (Outer) Connector. 
     The corresponding first or outer connector  100  is located at the distal end of the hollow inner tube  105  at the distal end portion  92  of the delivery device  90 . The corresponding first or outer connector  100  is configured to selectively be brought into engagement with the first or outer connector  51  of the first delivery device interface  50  of the facet joint implant  10  and to selectively be inserted into the first or outer connector  51 . The corresponding first or outer connector  100  is also configured to selectively be brought into locked engagement with the first or outer connector  51  to hold the facet joint implant  10  in a fixed position and orientation relative to the delivery device  90 . This enables the delivery device  90  to be manipulated to insert the facet joint implant  10  into the body of a patient, deliver it to a facet joint  140  in which it is to be implanted, insert it in the facet joint  140 , and position it within the facet joint  140 . 
     The hollow inner tube  105  and the corresponding first connector  100  are at least partially contained within the hollow outer tube  91  and are movable relative to the hollow outer tube  91  for the corresponding first connector  100  to be selectively brought into engagement with and inserted into the first connector  51  of the first delivery device interface  50  of the facet joint implant  10 , and for the corresponding first connector  100  to be selectively brought into locked engagement with the first connector  51 . More specifically, the hollow inner tube  105  and the corresponding first connector  100  are at least rotationally movable within and relative to the hollow outer tube  91 . At least a portion of the corresponding first connector  100  extends beyond the distal end portion  92  of the hollow outer tube  91  and is exposed outside of the hollow outer tube  91  for being brought into engagement, being inserted in, and being brought into locked engagement with the first connector  51  of the first delivery device interface  50  of the facet joint implant  10 . In the example embodiments, the corresponding first or outer connector  100  of the delivery device  90  and the first or outer connector  51  of the facet joint implant  10  are brought into engagement by manipulating the delivery device  90  to bring the corresponding first connector  100  into contact with the first connector  51  in the proper alignment. When the corresponding first connector  100  is in proper alignment with the first connector, the delivery device  90  is manipulated to insert the corresponding first connector  100  at least partially in the first connector  51 . Once the corresponding first connector  100  is inserted in the first connector  51 , the corresponding first connector  100  is brought into locked engagement with the first connector  51  by rotating the corresponding first connector  100  within the first connector  51 , for example by approximately 90 degrees. This is accomplished in a manner described further below. 
     Although the corresponding first connector  100  can take many suitable forms, in the example embodiments where the first or outer connector  51  of the facet joint implant  10  comprises a first bayonet connector  52 , the corresponding first connector  100  of the delivery device  90  comprises a first bayonet  101 . Preferably, the first bayonet  101  has a substantially cylindrical shape and is configured and dimensioned to be at least partially insertable into the interior space  54  of the body  53  of the first bayonet connector  52  through the open face  55 . Preferably, the first bayonet  101  is configured and dimensioned so that rotating it relative to the body  53  of the first bayonet connector  52  by 90 degrees, for example, locks it in engagement with first bayonet connector  52 . 
     The hollow outer tube  91  of the delivery device  90  is provided with a first key  94  to ensure the corresponding first or outer connector  100  of the delivery device  90  can only be brought into engagement with and inserted in the first or outer connector  51  of the outer part  12  of the facet joint implant  10  in proper alignment. The first key  94  also prevents the facet joint implant  10  from inadvertently rotating relative to the delivery device  90  when it is connected to the delivery device  90 . 
     The first key  94  comprises a set of holding arms  95 . The holding arms  95  extend outwardly from the distal end portion  92  of the hollow outer tube  91  of the delivery device  90  around the exterior of the corresponding first connector  100 . In the example embodiments, two holding arms  95  extend from the distal end portion  92  of the hollow outer tube  91  on opposite sides of the corresponding first connector  100 . Each holding arm  95  has a flat portion  96  that faces the corresponding first connector  100 . 
     The holding arms  95  and flat portions  96  are configured so that the corresponding first connector  100  of the delivery device  90  can only be brought into engagement with and inserted into the first connector  51  of the facet joint implant  10  when the flat portions  96  on the holding arms  95  are aligned with the flats  57  on the exterior surface  56  of the body  53  of the first connector  51 . When the flat portions  96  on the holding arms  95  are aligned with the flats  57  on the exterior surface  56  of the body  53  of the first connector  51  and it is attempted to insert the corresponding first connector  100  in the first connector  51 , the flat portions  96  of the holding arms  95  pass outside of and over the flats  109  on the exterior surface  56  of the body  53  of the first connector  51  permitting the corresponding first connector  100  to be inserted in the first connector  51 . If the flat portions  96  on the holding arms  95  are not aligned with the flats  57  on the exterior surface  56  of the body  53  of the first connector  51  when it is attempted to bring the corresponding first connector  100  into engagement with first connector  51  and to insert the corresponding first connector  100  in the first connector  51 , the flat portions  96  on the holding arms  95  make contact with the body  53  of the first connector  51  and the corresponding first connector  100  is blocked from being inserted. 
     When the corresponding first connector  100  is brought into engagement with the first connector  51  and is inserted in the first connector  51  with the proper alignment, i.e., with the flat portions  96  on the holding arms  95  aligned with the flats  57  on the exterior surface  56  of the body  53  of the first connector  51 , the holding arms  95  also prevent the body  53  of the first connector  51  from rotating relative to the holding arms  95 . Hence, the first connector  51  is prevented from rotating relative to the corresponding first connector  100  and the outer part  12  of the facet joint implant  10  is prevented from rotating relative to the delivery device  90 . 
     Each of the holding arms  95  also includes a support surface  97 . The support surfaces  97  are located adjacent to the flat portions  96 , are substantially flat, and are approximately perpendicular to the flat portions  96 . The support surfaces  97  are configured to be engaged by surfaces of the body  53  of the first connector  51  when the corresponding first connector  100  is inserted in the first connector  51 , the corresponding first connector  100  and the first connector  51  are brought into locked engagement, and the flat portions  96  of the holding arms  95  are advanced over the flats  57  on the body  53  of the first connector  51 . The engagement of the body  53  of the first connector  51  with the support surfaces  97  further stabilizes the connection between the facet joint implant  10  and the delivery device  90 . The holding arms  95 , including the flat portions  96  and support surfaces  97 , are configured to be advanced and withdrawn relative to the corresponding first connector  100  and the first connector  51  using the outer tube control knob  116  of the delivery device  90  in a manner described further below. 
     When it is desired to connect the facet joint implant  10  to the distal end portion  92  of the delivery device  90  for introduction into the body of a patient, for example, the corresponding first or outer connector  100  of the delivery device  90 , and more specifically the first bayonet  101 , is aligned with the first or outer connector  51  of the facet joint implant  10 , and more specifically the first bayonet connector  52 . The corresponding first or outer connector  100  of the delivery device  90 , and more specifically the first bayonet  101 , is then brought into engagement with the first or outer connector  51 , and more specifically the first bayonet connector  52 , of the outer part  12  of the facet joint implant  10 , and the corresponding first connector  100 , and more specifically the first bayonet  101 , is inserted into the first connector  51  and more specifically the first bayonet connector  52 . 
     The corresponding first or outer connector  100  of the delivery device  90 , and more specifically the first bayonet  101 , is then rotated relative to the first or outer connector  51  of the outer part  12  of the facet joint implant  10 , and more specifically the first bayonet connector  52 , to bring the corresponding first connector  100  and the first connector  51  into locked engagement. The corresponding first connector  100  of the delivery device  90  is rotated relative to the first connector  51  of the facet joint implant  10  using the control handle  120  as described below. 
     The flat portions  96  on the holding arms  95  of the delivery device are aligned with the flats  57  on the body  53  of the first connector  51  by manipulating the outer tube  91  of the delivery device  90 , which is described further below. The connection between the facet joint implant  10  and the delivery device  90  is further stabilized by using the outer tube control knob  116  of the delivery device  90  to advance the holding arms  95  of the delivery device  90  around the body  53  of the first connector  51  so that the body  53  of the first connector  51  is brought into engagement with the support surfaces  97  of the holding arms  95 , also as described below. 
     With the corresponding first or outer connector  100  of the delivery device  90  and the first or outer connector  51  of the facet joint implant  10  in locked engagement, the facet joint implant  10  is securely held in a fixed position and orientation relative to the delivery device  90 . The delivery device  90  can then be manipulated to introduce the facet joint implant  10  into the body of a patient and to deliver it to and insert it in the facet joint  140  in which it is to be implanted. When it is desired to disconnect the delivery device  90  from the facet joint implant  10 , the process is simply reversed. The holding arms  95  of the delivery device  90  are retracted relative to the first corresponding connector  100  of the delivery device  90  and the first connector  51  of the facet joint implant  10 . Then the corresponding first connector  100 , and more specifically the first bayonet  101 , is rotated in the opposite direction and is withdrawn from the first connector  51 , and more specifically the first bayonet connector  52 , of the facet joint implant  10 . 
     In the example embodiments, the corresponding first connector  100  of the delivery device  90  is preferably substantially cylindrical in shape. In addition, the corresponding first connector  100  is preferably at least partially hollow with an interior space  102  and the corresponding second or inner connector  110  of the delivery device  90  is at least partially contained within the interior space  102  of corresponding first connector  100 . The corresponding second or inner connector  110  of the delivery device  90  is described further below. In the example embodiments, the corresponding second or inner connector  110  is also substantially cylindrical in shape, and the corresponding first connector  100  and the corresponding second connector  110  are arranged to be substantially concentric. However, that arrangement is a matter of preference and is not always necessary. 
     The corresponding first connector  100  also has an open face  103  at the distal end portion  92  of the delivery device  90  and the open face  103  provides access to the interior space  102  within the corresponding first connector  100 . The corresponding first connector  100  is configured and dimensioned so that when it is properly inserted in the first or outer connector  51  of the facet joint implant  10 , the second or inner connector  81  of the facet joint implant  10  extends at least partially through the open face  103  and into the interior space  102  of the corresponding first connector  100  where it can be brought into engagement with, inserted in, and brought into locked engagement with the corresponding second connector  110  of the delivery device  90  as described below. 
     The inner tube  105  of the delivery device  90  has an opening comprising a window  104 . The window  104  is located at the distal end portion  92  of the delivery device  90  and is spaced just proximally from the corresponding first connector  100 . The window  104  is located so that when the corresponding first connector  100  is brought into engagement with and is inserted in the first connector  51  of the facet joint implant  10 , the second or inner connector  82  of the facet joint implant  10  is at least partially visible through the window  104 . In addition, the corresponding second connector  110  of the delivery device  90  also is at least partially visible through the window  104  when it is brought into engagement with the second connector  81 . This facilitates checking the orientation of the corresponding second connector  110  relative to the second connector  81  and if necessary adjusting the alignment so that the corresponding second connector  110  can be brought into engagement with, inserted into, and brought into locked engagement with the second connector  81  as described further below. 
     The corresponding first connector  100  is formed or connected at the distal end of the inner tube  105 . The inner tube  105  extends within the hollow outer tube  91  from the distal end portion  92  of the delivery device  90  to the proximal end portion  93  of the delivery device  90 . The inner tube  105  is moveable within and relative to the hollow outer tube  91 , and more specifically is rotationally moveable within and relative to the hollow outer tube  91 . 
     In the example embodiments, the inner tube  105  is substantially cylindrical shaped and is at least partially hollow. The corresponding second connector  110  of the delivery device is formed or connected to the distal end of the inner shaft  115 , which extends within the hollow outer tube  91 , and more specifically within the hollow inner tube  105  within the hollow outer tube  91 , from the corresponding second connector  110  at the distal end portion  92  of the delivery device  90  to the proximal end portion  93  of the delivery device  90 . Preferably but not necessarily, the hollow inner tube  105  and the inner shaft  115  are arranged to be substantially concentric. The corresponding second connector  110  and the inner shaft  115  are described further below. 
     At the proximal end portion  93  of the delivery device  90 , the outer tube  91  is fixedly connected or attached to the outer tube control knob  116 , which is in turn rotatably connected to the inner tube  105  in a manner described further below. The inner tube  105  also is fixedly connected or attached to the control handle  120  of the delivery device  90 . The outer tube  91  is configured and adapted to be controlled by the outer tube control knob  116 . More specifically, movement of the outer tube  91  to advance and withdraw relative to the inner tube  105  and the corresponding first connector  100  is controllable via manipulation of the outer tube control knob  116 . The inner tube  105  and the corresponding first connector  100  are configured and adapted to be controlled by the control handle  120 . More specifically, the movement of the inner tube  105  and the movement of the corresponding first connector  100  are controllable via manipulation of the control handle  120 . The operation of the outer tube control knob  116  and the control handle  120  are described further below. 
     It is preferred that the corresponding first connector  100  and the inner tube  105  comprise a single monolithic structure. However, the inner tube  105  can comprise a separate structure from the corresponding first connector  100 . In that case, the corresponding first connector  100  is preferably fixedly connected or attached to the inner tube  105  at the distal end of the delivery device  90  so that the inner tube  105  and the corresponding first connector  100  move together, e.g., when the inner tube  105  is rotated within the hollow outer tube  91 , the corresponding first connector  100  rotates the same. 
     2. Corresponding Second (Inner) Connector. 
     The corresponding second or inner connector  110  is located at the distal end of the inner shaft  115  at the distal end portion  92  of the delivery device  90 . The corresponding second connector  110  is configured and operable to selectively be brought into engagement with the second or inner connector  81  of the first delivery interface  80  of the facet joint implant  10  and to be selectively inserted into the second or inner connector  81 . The corresponding second connector  100  also is configured and operable to selectively be brought into locked engagement with the second or inner connector  81 . The corresponding second connector  110  also is configured and operable to impart motion to the inner part  14  of the facet joint implant  10  relative to the outer part  12  of the facet joint implant  10 . The delivery device  90  is thus able to be manipulated to cause the facet joint implant  10  to distally expand to its open position in a facet joint  140  in which it is implanted so as to distally distract the facet joint  140 , and to cause the facet joint implant  10  to distally retract in order to reposition or remove the facet joint implant  10  from the facet joint  140 . 
     More specifically, the inner shaft  115  and the corresponding second connector  110  are at least partially contained within the hollow outer tube  91  and are movable relative to the hollow outer tube  91  to selectively be brought into engagement with, inserted into, and brought into locked engagement with the second connector  81  to impart motion to the wedge  61  of the inner part  14  of the facet joint implant  10  relative to the first facet plate  20  and the second facet plate  30  of the outer part  12  of the facet joint implant  10 . Still more specifically, the inner shaft  115  and the corresponding second connector  110  are selectively moveable at least in the direction of the distal end portion  92  and the proximal end portion  93  of the delivery device  90 , rotationally within and relative to the hollow outer tube  91 , and relative to the corresponding first connector  100 . Even more specifically, the inner shaft  115  and the corresponding second connector  110  are at least partially contained within the hollow inner tube  105  within the hollow outer tube  91  of the delivery device  90 , and are selectively movable at least in the direction of the distal end portion  92  and the proximal end portion  93  of the delivery device  90  and rotationally within and relative to the hollow inner tube  105  within the hollow outer tube  91 , and relative to the corresponding first connector  100 . 
     As mentioned previously, in the example embodiments the inner shaft  115  and the corresponding second connector  110  are substantially cylindrical in shape and are at least partially contained within the substantially cylindrical shaped and at least partially hollow inner tube  105 . In addition, the hollow inner tube  105  and the corresponding first connector  100 , and the inner shaft  115  and the corresponding second connector  110  preferably are arranged to be substantially concentric. However, this arrangement is a matter of preference and not necessity. 
     In the example embodiments, the corresponding second or inner connector  110  of the delivery device  90  and the second or inner connector  81  of the facet joint implant  10  are brought into engagement by manipulating the delivery device  90  to bring the corresponding second connector  110  into contact with the second connector  81  with the proper alignment. When the corresponding second connector  110  is in proper alignment with the second connector  81 , the delivery device  90  is manipulated to insert the corresponding second connector  110  at least partially in the second connector  81 . Once the corresponding second connector  110  is inserted in the second connector  81 , the corresponding second connector  110  is brought into locked engagement with the second connector  81  by rotating the corresponding second connector  110  within and relative to the second connector  82 , for example by approximately 90 degrees. 
     Although the corresponding second connector  110  can take many suitable forms, in the example embodiments where the second or inner connector  81  of the inner part  14  of the facet joint implant  10  comprises a second bayonet connector  82 , the corresponding second connector  110  of the delivery device  90  comprises a second bayonet  111 . The second bayonet  111  is adapted and configured to be brought into engagement with and to be inserted in the second bayonet connector  82 . The second bayonet  111  is inserted into the second bayonet connector  82  by inserting the bayonet into the open interior space  84  in the body  83  of the second bayonet connector  82  through the open face  85  of the second bayonet connector  82 . The second bayonet  111  is adapted and configured to be brought into locked engagement with the second bayonet connector  82  by rotating the second bayonet  111  relative to the second bayonet connector  82 , for example by approximately 90 degrees. 
     In the example embodiments, the corresponding second connector  110  of the delivery device  90  comprises a second key  113 . The second key  113  is configured and operable to allow the corresponding second connector  110  to be inserted in and withdrawn from the second connector  81  only when the corresponding second connector  110  and the second connector  81  are in a particular alignment, and not otherwise. In the example embodiments where the corresponding second connector  110  comprises the second bayonet  111 , the second bayonet comprises a t-shaped pin  112  as the second key  113 . The t-shaped pin  112  is configured to correspond to the shape of the open face  85  of the second bayonet connector  82  of the second or inner connector  81  of the facet joint implant  10 . That shape can be, for example, a vertical slot shape. Accordingly, the t-shaped pin  112  allows the second bayonet  111  to be inserted into and withdrawn from the open interior space  84  in the body  83  of the second bayonet connector  82  only when the t-shaped pin  112  is aligned in a particular orientation relative to the shape of the open face  85 , e.g., the vertical slot, and otherwise blocks the second bayonet  111  from being inserted or withdrawn. Accordingly, once the t-shaped pin  112  of the second bayonet  111  is inserted into the second bayonet connector  82  and rotated to bring the corresponding second connector  110  into locked engagement with the second connector  81 , the t-shaped pin  112  prevents the corresponding second connector  110  from inadvertently being withdrawn from the second connector  81 . 
     It will be appreciated that while in the example embodiments, the second key  113  comprises a t-shaped pin  112  of a second bayonet  111 , the second key may take many other forms consistent suitable to achieve the objective described. It will also be appreciated that the t-shaped pin  112  and the corresponding shape of the open face  85  of the second bayonet connector  82  may have many variations suitable to achieve the objective described. For example, other letter shapes, e.g. “H,” and other geometric shapes, e.g., a star shape, may be used. 
     To facilitate the proper alignment of the corresponding second connector  110  of the delivery device  90  and the second connector  81  of the inner part  14  of the facet joint implant  10 , and as mentioned previously, the inner tube  105  of the delivery device  90  has an opening comprising a window  104 . The window  104  is located at the distal end portion  92  of the delivery device  90  and is spaced just proximally from the corresponding first connector  100  of the delivery device  90 . With the corresponding first connector  100  of the delivery device  90  in engagement with and inserted in the first connector  51  of the outer part  12  of the facet joint implant  10 , the corresponding second connector  110  of the delivery device  90  and the second connector  81  of the inner part  14  of the facet joint implant  10  are at least partially visible through the window  104  as the corresponding second connector  110  is brought into engagement with and inserted into the second connector  81 . The window  104  thus provides for the orientation of the corresponding second connector  110  relative to the second connector  81  to be checked visually and, if necessary, to be adjusted so that the corresponding second connector  110  can be brought into engagement with, inserted into, and brought into locked engagement with the second connector  81  as described above. 
     When the corresponding second connector  110  of the delivery device  90  is in engagement with and inserted in the second connector  81  of the inner part  14  of the facet joint implant  10 , the delivery device  90  can be manipulated as further described below to selectively impart motion to the inner part  14  of the facet joint implant  10 , including the wedge  61 , to move distally relative to the outer part  12  of the facet joint implant  10 , including the first facet plate  20  and the second facet plate  30 . Thus, the delivery device  90  can be manipulated to selectively cause the facet joint implant  10  to distally expand from its closed state to its open state in the manner described herein. It will be appreciated that because the wedge  61  is pushed in a distal direction, rather than pulled in a proximal direction, to cause the facet joint implant  10  to distally expand to the open state, it is only necessary for the corresponding second connector  110  to be in engagement with and inserted in the second connector  81  of the facet joint implant  10  to achieve this effect. It is not necessary that the corresponding second connector  110  be in locked engagement with the second connector  81 . Nevertheless, it is preferred for the corresponding second connector  110  and the second connector  81  to be in locked engagement to avoid potential inadvertent disengagement during a procedure. In addition, if it is desired to pull the wedge  61  in the proximal direction to cause the facet joint implant  10  to distally retract to the closed state, for example for removal or repositioning, the corresponding second connector  110  and the second connector  81  must be in locked engagement. 
     When it is desired to unlock and disengage the delivery device  90  from the inner part  14  of the facet joint implant  10 , the process described above is simply reversed. The corresponding second connector  110  of the delivery device  90 , and more specifically the second bayonet  111 , is rotated in the opposite direction and then withdrawn from the second connector  81  of the facet joint implant  10 , and more specifically the second bayonet connector  82 . 
     As mentioned previously, the corresponding second connector  110  is fixedly connected or attached to the distal end of the inner shaft  115 , which extends within the hollow outer tube  91 , and more specifically within the hollow inner tube  105  within the hollow outer tube  91 , from the corresponding second connector  110  at the distal end portion  92  of the delivery device  90  to the proximal end portion  93  of the delivery device  90 . Preferably but not necessarily, the inner tube  105  and the inner shaft  115  are arranged to be substantially concentric. 
     The inner shaft  115  is selectively moveable within and relative to the hollow outer tube  91 . More specifically, the inner shaft  115  is selectively movable at least in the direction of the distal end portion  92  and the proximal end portion  93  of the delivery device  90  and rotationally within and relative to the hollow outer tube  91 . Still more specifically, the inner shaft  115  is selectively moveable within and relative to the hollow inner tube  105  within the hollow outer tube  91 . Still more specifically the inner shaft  115  is selectively movable at least in the direction of the distal end portion  92  and the proximal end portion  93  of the delivery device  90  and rotationally within and relative to the hollow inner tube  105  within the hollow outer tube  91 . 
     At the proximal end portion  93  of the delivery device  90 , the inner shaft  115  is movably connected or attached to the inner shaft control knob  121  and to a lock switch  124  and a lock  162 . The inner shaft  115  and the corresponding second connector  110  are configured and adapted to be controlled by the inner shaft control knob  121  and the lock switch  124 . More specifically, the movement of the inner shaft  115  and the corresponding second connector  110  are controllable via manipulation of the inner shaft control knob  121  and the lock switch  124 . Still more specifically, the movement of the inner shaft  115  and the corresponding second connector  110  in the directions of the distal end portion  92  and the proximal end portion  93  of the delivery device  90  and relative to the outer tube  91 , inner tube  105 , and corresponding first connector  100  are controllable via manipulation of the inner shaft control knob  121 . The movement of the inner shaft  115  and the corresponding second connector  110  rotationally within and relative to the hollow outer tube  91 , the hollow inner tube  105 , and the corresponding first connector  100  is controllable via manipulation of the lock switch  124 . The inner shaft control knob  121  and the lock switch  124  are described further below. 
     It is preferred that the corresponding second connector  110  and the inner shaft  115  comprise a single monolithic structure. However, the inner shaft  115  can comprise a separate structure from the corresponding second connector  110 . In that case, the corresponding second connector  110  is preferably fixedly connected or attached to the inner shaft  115  at the distal end of the delivery device  90  so that the inner shaft  115  and the corresponding second connector  110  move together, e.g., when the inner shaft  115  is rotated within and relative to the hollow inner tube  105  within the hollow outer tube  91 , the corresponding second connector  110  rotates the same, and when the inner shaft  115  is moved within and relative to the hollow inner tube  105  within the hollow outer tube  91  toward the distal end portion  92  or the proximal end portion  93  of the delivery device  90 , the corresponding second connector  110  moves the same. 
     3. Outer Tube Control Knob. 
     The outer tube control knob  116  is located at the proximal end portion  93  of the delivery device  90 . The outer tube control knob  116  is fixedly coupled with the hollow outer tube  91  via a fixed coupling  117 . The outer tube control knob  116  has a passageway  118  through which the inner tube  105  extends. The outer tube control knob  116  is movably coupled to the inner tube  105  via a threaded coupling  119  within the passageway  118 . 
     The outer tube control knob  116  is configured and is selectively operable to control the outer tube  91  and to cause it to move toward the distal end portion  92  and the proximal end portion  93  of the delivery device  90  relative to the inner tube  105  and the first corresponding connector  100 . Accordingly, the outer tube control knob  116  is configured and is selectively operable to cause the holding arms  95 , including the flat portions  96  and support surfaces  97 , to move toward the distal end portion  92  and the proximal end portion  93  of the delivery device  90 . 
     The outer tube control knob  116  is configured and is selectively operable to cause the outer tube  91  and the holding arms  95 , including the flat portions  96 , and the support surfaces  97 , to move toward the distal end portion  92  of the delivery device  90  by rotating the outer tube control knob  116  in a first direction. This causes the outer tube control knob  116  to translate on the threaded coupling  119  with the inner tube  105  in the direction of the distal end portion  92  and thus causes the outer tube  91  and the holding arms  95  to move in the direction of the distal end portion  92  relative to the inner tube  105  and the first corresponding connector  100  of the delivery device  90 . 
     Similarly, the outer tube control knob  116  is configured and is selectively operable to cause the outer tube  91  and the holding arms  95 , including the flat portions  96  and the support surfaces  97 , to move toward the proximal end portion  93  of the delivery device  90  by rotating the outer tube control knob  116  in a second direction opposite to the first direction. This causes the outer tube control knob  116  to translate on the threaded coupling  119  with the inner tube  105  in the direction of the proximal end portion  93  and thus causes the outer tube  91  and the holding arms  95  to move in the direction of the proximal end portion  92  relative to the inner tube  105  and the first corresponding connector  100  of the delivery device  90 . 
     When the first corresponding connector  100  is in engagement with and inserted in the first connector  51  of the facet joint implant  10 , the outer tube control knob  116  is configured and is selectively operable to be rotated in the first direction to cause the outer tube  91  to move toward the distal end portion  92  of the delivery device  90 , the flat portions  96  of the holding arms  95  to advance over the flats  57  on the body  53  of the first connector  51  of the facet joint implant  10 , and the support surfaces  97  of the holding arms  95  to advance toward the surfaces surrounding the open face  55  of the body  53  of the first connector  51 . When the corresponding first connector  100  is brought into locked engagement with the first connector  51 , the body  53  of the first connector  51  is urged into engagement with the support surfaces  97 . Similarly, the outer tube control knob  116  is configured and is selectively operable to be rotated in the second direction opposite to the first direction to cause the outer tube  91  to move toward the proximal end portion  93  of the delivery device  90 , the flat portions  96  of the holding arms  95  to withdraw with respect to the flats  57  on the body  53  of the first connector  51 , and the support surfaces  97  of the holding arms  95  to withdraw from the body  53  of the first connector  51 . 
     4. Control Handle. 
     The control handle  120  is located at the proximal end portion  93  of the delivery device  90 . The control handle  120  is fixedly coupled with the hollow inner tube  105  and hence with the corresponding first or outer connector  100  of the delivery device  90 . The control handle  120  is configured and selectively operable to bring the corresponding first connector  100  of the delivery device  90  into locked engagement with the first connector  51  of the first delivery device interface  50  of the outer part  12  of facet joint implant  10  in the manner described above. 
     The control handle  120  is fixedly connected to the inner tube  105  at the proximal end portion  93  of delivery device  90  and is configured and selectively operable to control the inner tube  105  and the corresponding first connector  100 . More specifically, by manipulating the control handle  120 , the movement of the inner tube  105  and the corresponding first connector  100  are controllable at least to an extent. Still more specifically, at least when the corresponding second or inner connector  110  of the delivery device  90  is not in locked engagement with the second or inner connector  81  of the facet joint implant  10 , the control handle  120  can be rotated to cause the corresponding first connector  100  to rotate relative to the hollow outer tube  91  of the delivery device  90 . 
     The delivery device  90  and control handle  120  can be manipulated to bring the corresponding first connector  100  of the delivery device  90  into engagement and into locked engagement with the first connector  51  of the first delivery device interface  50  of the facet joint implant  10  in the following manner. The delivery device  90  is moved distally relative to the facet joint implant  10 , or vice versa, to cause the corresponding first connector  100  of the delivery device to be brought into engagement with and inserted in the first connector  51  of the facet joint implant  10  in the manner described herein. The control handle  120  is then rotated, for example by about 90 degrees to cause the corresponding first connector  100  to rotate in and relative to the first connector  51  and bring the corresponding first connector  100  into locked engagement with the first connector  51 . The outer tube  91  of the delivery device  90  is manipulated to align the flat portions  96  on the holding arms  95  at the distal end portion  92  of the delivery device  90  with the flats  57  on the exterior surface  56  of the first connector  51  of the facet joint implant  10 . The outer tube control knob  116  is rotated to advance the holding arms  95  over the flats  57 . To unlock and disengage the corresponding first connector  100  from the first connector  51 , the delivery device  90  and control handle  120  are manipulated to simply reverse the process described. 
     5. Inner Shaft Control Knob. 
     The inner shaft control knob  121  is located at the proximal end portion  93  of the delivery device  90  and is movably coupled with the control handle  120 , with the inner shaft  115 , and via the inner shaft  115  with the corresponding second or inner connector  110  of the delivery device  90 . 
     More specifically, the inner shaft control knob  121  is rotatably connected to the control handle  120  at the proximal end portion  93  of the delivery device  100  and is free to rotate relative to the control handle  120  but is not free to move toward the distal end portion  92  or the proximal end portion  93  of the delivery device  90 . The inner shaft control knob  121  is also movably connected to the inner shaft  115  and via the inner shaft  115  to the corresponding second connector  110  at the proximal end portion  93  of the delivery device  90 . Still more specifically, in the example embodiments the inner shaft has a threaded proximal end portion  114  and the inner shaft control knob  121  has a threaded passageway  122 . The threaded proximal end portion  114  of the inner shaft  115  extends through the control handle  120  and into the threaded passageway  122 , which comprises a threaded coupling  122  to the inner shaft  115 . The inner shaft control knob  121  is free to rotate on the inner shaft  115  via the threaded coupling. 
     The inner shaft control knob  121  is configured and is selectively operable to control the inner shaft  115  and the corresponding second connector  110 . More specifically, the inner shaft control knob  121  is configured and is selectively operable to control the movement of the inner shaft  115  and the corresponding second connector  110  in the directions of the distal end portion  92  and the proximal end portion  93  of the delivery device  90 . Even more specifically, the inner shaft control knob  121  is selectively rotatable relative to the inner shaft  115  and is selectively operable by being rotated to cause the inner shaft  115  and the corresponding second connector  110  to move toward the distal end portion  92  and the proximal end portion  93  of the delivery device  90  relative to the control handle  120 , the hollow outer tube  91 , and the inner tube  105  and the corresponding first connector  100  of the delivery device  90 . Rotation of the inner shaft control knob  121  on the inner shaft  115  via the threaded coupling causes the inner shaft  115  and the corresponding second or inner connector  110  of the delivery device  90  to translate in the direction of the distal end portion  92  and the proximal end portion  93  depending on the direction the inner shaft control knob  121  is rotated. 
     The inner shaft control knob  121  is thus configured and operable when rotated in a first direction to selectively cause the corresponding second connector  110  to move toward the distal end portion  92  of the delivery device  90  and to be brought into engagement with and inserted in the corresponding second connector  110  in the second connector  81  of the facet joint implant  10  in the manner described herein. The inner shaft control knob  121  also is configured and operable when rotated in a second direction opposite to the first direction to selectively cause the corresponding second connector  110  to move toward the proximal end portion  93  of the delivery device  90  and to be brought out of engagement with and withdraw from the second connector  81  of the facet joint implant  10  in the manner described herein. 
     The inner shaft control knob  121  is also configured and operable when rotated in a first direction to selectively cause the facet joint implant  10  to distally expand into its open position. Thus, the inner shaft control knob  121  is configured and operable when rotated in the first direction to selectively cause the corresponding second connector  110  of the delivery device  90  to move toward the distal end portion  92  of the delivery device  90 , in turn causing the inner part  14  of the facet joint implant  10 , and more specifically the wedge  61 , to move distally relative to the outer part  12  of the facet joint implant  10 , and more specifically the first facet plate  20  and the second facet plate  30 , and the facet joint implant  10  to distally expand to its open state in the manner described previously. 
     Similarly, the inner shaft control knob  121  is configured and operable when rotated in a second direction opposite to the first direction to selectively cause the corresponding second connector  110  of the delivery device  90  to move toward the proximal end portion  93  of the delivery device  90 , in turn causing the inner part  14  of the facet joint implant  10 , and more specifically the wedge  61 , to move proximally relative to the outer part  12  of the facet joint implant  10 , and more specifically the first facet plate  20  and the second facet plate  30 , and the facet joint implant  10  to distally contract to its closed state in the manner described previously. 
     As mentioned previously, because rotating the inner shaft control knob  121  in the first direction effectively pushes the corresponding second connector  110  of the delivery device  90  in the distal direction, the corresponding second connector  110  need only be in engagement with and inserted in the second connector  81  of the facet joint implant  10  while the inner shaft control knob  121  is rotated in the first direction to cause the facet joint implant  10  to distally expand to the open position. The corresponding second connector  110  need not be in locked engagement with the second connector  81 . However, the corresponding second connector  110  must be in locked engagement with the second connector  81  when the inner shaft control knob  121  is rotated in the second direction in order to cause the facet joint implant  10  to distally contract to the closed position. If the corresponding second connector  110  is not in locked engagement with the second connector  81 , rotation of the inner shaft control knob  121  in the second direction simply moves the corresponding second connector  110  toward the proximal end portion  93  of the delivery device  90  and brings the corresponding second connector  110  out of engagement with the second connector  81 . 
     6. Lock Switch and Lock. 
     The lock switch  124  and lock  126  of the delivery device  90  are located at the proximal end portion  93  of the delivery device  90 . The lock switch  124  and lock  126  are coupled with the inner shaft  115  and via the inner shaft  115  with the corresponding second connector  110  of the delivery device  90 . 
     The lock switch  124  is configured and operable to selectively rotate the corresponding second connector  110  of the delivery device  90  relative to the second connector  81  of the facet joint implant  10  in order to bring the corresponding second connector  110  into and out of locked engagement with the second connector  81 , depending on the direction the lock switch  124  is rotated. The lock  126  is responsive to the operation of the lock switch  124  and is configured and operable to hold or lock the corresponding second connector  110  in the locked engagement position to prevent the inadvertent rotation of the corresponding second connector  110  from the locked engagement position and potential unlocking and disengagement from the second connector  81 . 
     More specifically, the lock switch  124  is configured and operable to be manipulated to rotate approximately 90 degrees between a first position and a second position relative to the control handle  120 , the hollow outer tube  91 , and the inner tube  105  and corresponding first connector  100  of the delivery device  90 . Rotation of the lock switch  124  approximately 90 degrees between the first position and the second position also rotates the inner shaft  115  and the corresponding second connector  110  by approximately 90 degrees relative to the control handle  120 , the hollow outer tube  91 , and the inner tube  105  and corresponding first connector  100 . 
     Most importantly, however, when the corresponding second connector  110  of the delivery device  90  is in engagement with and inserted in the second connector  81  of the facet joint implant  10  in the manner described above, rotation of the lock switch  124  approximately 90 degrees from the first position to the second position rotates the corresponding second connector  110  approximately 90 degrees relative to and within the second connector  81  and brings the corresponding second connector  110  into locked engagement with the second connector  81 . Similarly, when the lock switch  124  is rotated from the second position to the first position, the corresponding second connector  110  rotates approximately 90 degrees relative to and within the second connector  81  and brings the corresponding second connector  110  and second connector  81  out of locked engagement. Thus, when the corresponding second connector  110  is in engagement with and inserted in the second connector  81 , the first position of the lock switch  124  corresponds to an unlocked engagement position, and the second position corresponds to a locked engagement position. 
     In response to the lock switch  124  being rotated approximately 90 degrees from the first position (unlocked) to the second position (locked), the lock  126  is configured and operable to temporarily hold or lock the corresponding second connector  110  in the approximately 90 degree rotated second position relative to the control handle  120 , the hollow outer tube  91 , and the inner tube  105  and corresponding first connector  100 . More importantly, when the corresponding second connector  110  of the delivery device  90  is in engagement with and inserted in the second connector  81  of the facet joint implant  10  in the manner described above, the lock  126  is configured and operable to temporarily hold or lock the corresponding second connector  110  in the approximately 90 degree rotated second (locked) position relative to the second connector  81 , i.e., in the locked engagement position. 
     Still more specifically, in the example embodiments the lock switch  124  comprises a rotatable lever  125  that is seated and is rotatable in a slot  123  of the control handle  120 . Also, as best seen in  FIG.  17   , and as also seen at least partially in  FIGS.  22 A,  23 D, and  24 B , the lock  126  comprises a detent mechanism  127  that is coupled to the lock switch  124 , and that more specifically is coupled to the rotatable lever  125  and to the control handle  120 . Even more specifically, the detent mechanism  127  comprises a spring-loaded ball plunger  128  that is connected or attached to the lock switch  124 , and more specifically to the rotatable lever  125 , and a ball detent  129  that is located on the control handle  120  and more specifically in the slot  123  of the control handle  120 . 
     The slot  123  extends approximately 90 degrees around the control handle  120  with one end of the slot  123  corresponding to the first (unlocked) position of the lock switch  124  and the other end corresponding to the second (locked) position of the lock switch  124 . The lock switch  124 , and more specifically the rotatable lever  125 , is configured and operable to be rotated approximately 90 degrees in the slot  123  between the first (unlocked) and second (locked) positions. 
     The inner shaft  115  passes through and is engaged by the lock switch  124 , and more specifically the lever  125 . The inner shaft  115  is engaged by the lock switch  124 , and more specifically the lever  125 , in such a way that it is free to move toward the distal end portion  92  and the proximal end portion  93  of the delivery device  90  relative to the lock switch  124 , and more specifically the lever  125 , but rotates with the lock switch  124 , and more specifically the lever  125 . 
     Thus, when the lock switch  124 , and more specifically the lever  125 , is rotated approximately 90 degrees in the slot  123  from the first (unlocked) to the second (locked position), the inner shaft  115  and the corresponding second connector  110  are rotated approximately 90 degrees as described above. More importantly, when the corresponding second connector  110  of the delivery device  90  is in engagement with and inserted in the second connector  81  of the facet joint implant  10 , rotation of the lock switch  124 , and more specifically the lever  125 , approximately 90 degrees in the slot  123  from the first (unlocked) to the second (locked) position rotates the corresponding second connector  110  within and relative to the second connector  81  and brings corresponding second connector  110  into locked engagement with the second connector  51 . 
     The lock  126 , and more specifically the ball plunger  128  of the detent mechanism  127 , rotates with the lock switch  124 , and more specifically the rotatable lever  125 . When the lock switch  124 , and more specifically the lever  125 , is rotated approximately 90 degrees in the slot  123  from the first (unlocked) to the second (locked) position, the ball of the ball plunger  128  is pushed into engagement with the ball detent  129  in the slot  123  under the pressure of the spring of the ball plunger  128 . This holds or locks the lock switch  124  in the approximately 90 degree rotated second position, which holds or locks the inner shaft  115  and corresponding second connector  110  in the approximately 90 degree rotated second (locked) position relative to the control handle  120 , the hollow outer tube  91 , and the inner tube  105  and corresponding first connector  100  of the delivery device  90 . Most importantly however, when the corresponding second connector  110  of the delivery device  90  is in engagement with and inserted in the second connector  81  of the facet joint implant  10  in the manner described above, it holds or locks the corresponding second connector  110  in the approximately 90 degree rotated second (locked) position relative to and within the second connector  81 , i.e., in the locked engagement position. 
     In order to bring the corresponding second connector  110  out of locked engagement with the second connector  81 , the process described above is simply reversed. That is, sufficient force is applied to the lever  125  of the lock switch  124  to overcome the force of the ball detent  129  mechanism and rotate the lock switch  124  in the opposite direction in the slot  123  approximately 90 degrees from the second (locked) to the first (unlocked) position. This rotates the corresponding second connector  110  approximately 90 degrees in the opposite direction and brings it out of locked engagement with the second connector  81  of the facet joint implant  10 . The inner shaft control knob  121  can then be manipulated as described above to withdraw the corresponding second connector  110  from engagement with the second connector  81 . 
     E. Operation of Preferred Embodiment. 
     In use of the distally expanding facet joint implant  10  and delivery device  90 , a facet joint  140  in which the facet joint implant  10  is to be implanted is first prepared to receive the facet joint implant  10 . It is noted that while facet joint  140  and facet joint implant  10  are referred to here in the singular, such reference is for ease of discussion only and is not meant to be limiting. Persons skilled in the art will realize that each cervical vertebra includes a pair of laterally spaced facet joints. Accordingly, it is likely, although not necessarily always the case, that multiple facet joints must be prepared and multiple facet joint implants implanted in a given procedure. Thus, reference to facet joint and facet joint implant in the singular is not meant to exclude, but rather to encompass multiple facet joints, facet joint implants, and the procedures used to prepare multiple facet joints and implant multiple facet joint implants. 
     The manner and tools for preparing an intervertebral joint to receive an implant are well known to those skilled in the art and need not be described in detail. Briefly, various known joint preparation tools may be used to prepare an affected facet joint and these may be delivered to the joint posteriorly through a small incision using a suitable guide wire or pin. The tools may be delivered percutaneously under X-ray guidance, under direct vision, under endoscopic guidance, or through a previously inserted hollow needle, for example. 
     Commonly employed tools include one or more chisels for cutting the joint capsule and other tissues as necessary or desired to facilitate subsequent insertion of the facet implant in the joint. A rasp may be used to roughen the external boney surfaces of the facets facing the facet joint  140  as necessary or desired to facilitate the implant adhering to the bony surfaces. One or more dilators may be used to dilate the facet joint  140  to facilitate delivery of the facet joint implant  10  to the affected facet joint  140 . Dilators of successively larger sizes in all three dimensions can be used sequentially until the necessary or desired dilation is achieved. 
     In preparation for implanting the facet joint implant  10 , the facet joint implant  10  is connected to the distal end portion  92  of the delivery device  90  with the facet joint implant  10  in its closed state. With reference to  FIGS.  21  through  22 B  among others, the delivery device  90  is manipulated to bring the corresponding first connector  100  of the delivery device  90  into engagement with the first connector  51  of the facet joint implant  10  and insert the corresponding first connector  100  into the first connector  51  of the facet joint implant  10 . The control handle  120  of the delivery device  90  is rotated by approximately 90 degrees to bring the corresponding first connector  100  into locked engagement with the first connector  51 . The outer tube  91  of the delivery device  90  is then manipulated to align the flat portions  96  of the holding arms  95  of the delivery device  90  with the flats  57  on the body  53  of the first connector  51  and the outer tube control knob  116  is rotated to advance the holding arms  95  toward the distal end portion  92  of the delivery device  90  and push the support surfaces  97  of the holding arms  95  into secure engagement with the first connector  51 . 
     Next, with reference to  FIGS.  23 A through  23 E  among others, the corresponding second or inner connector  110  of the delivery device  90  is brought into locked engagement with the second or inner connector  81  of the facet joint implant  10 . With the lock switch  124  of the delivery device  90  in the first (unlocked) position, the inner shaft control knob  121  of the delivery device  90  is rotated as to advance the corresponding second or inner connector  110  of the delivery device  90  distally into engagement with the second connector  81  of the facet joint implant  10  and to insert the t-shaped pin  112  of the second bayonet  111  into the open interior space  84  in the body  83  of the second bayonet connector  82  of the second or inner connector  81  of the facet joint implant  10 . Proper alignment of the corresponding second or inner connector  110  and the second or inner connector  81  can be visually confirmed in the window  104  of the inner tube  105  of the delivery device  90 . 
     With the corresponding second connector  110  in engagement with and inserted in the second connector  81 , the lock switch  124  on the delivery device  90  is rotated approximately 90 degrees from the first (unlocked) position to the second (locked) position. This brings the corresponding second connector  110  into locked engagement with the second connector  81 . The inner shaft control knob  121  can then be rotated in a first direction to cause the corresponding second connector  110  and the second connector  81  to advance distally, push the wedge  61  of the inner part  14  of the facet joint implant  10  forward distally relative to the first facet plate  20  and the second facet plate  30  of the outer part  12  of the facet joint implant  10 , and thus cause the facet joint implant  10  to distally expand to its open position. 
     Optionally, an inter-facet connection plate  130  can be used with the facet joint implant  10  if desired. As illustrated in  FIGS.  27 A through  29 E , a suitable inter-facet connection plate  130  may comprise a thin elongated plate  131  with a first opening  132 , one or more second openings  133 , and one or more third openings  134 . 
     The first opening  132  is preferably located approximately centrally on the plate  131 , but may be offset from a central location as desired. The first opening  132  is dimensioned and configured to permit at least the outer part  12  and the inner part  14  of the facet joint implant  10  to pass through the first opening  132  and into an adjacent facet joint  140  when the first opening  132  is aligned with a posterior opening  141  of the facet joint  140 . The first opening  132  is also dimensioned and configured to block at least the first or outer connector  51  of the facet joint implant  10  from passing through the first opening  132  and entering the facet joint  140 . This helps provide suitable positioning of the facet joint implant  10  in the facet joint  140  by helping to prevent the facet joint implant  10  from being over-inserted into the facet joint  140 . 
     The one or more second openings  133  are located on the plate  131  relative to the first opening  132  so that when the first opening  132  is aligned with the posterior opening  141  of the facet joint  140 , the one or more second openings  133  are positioned adjacent to the bony external surface  142  of the facet  143  superior to the facet joint  140 . Similarly, the one or more third openings  134  are located on the plate  131  relative to the first opening  132  so that when the first opening  132  is aligned with the posterior opening  141  of the facet joint  140 , the one or more third openings  134  are positioned adjacent the bony external surface  144  of the facet  145  inferior to the facet joint  140 . Accordingly, the lengthwise dimension of the inter-facet connection plate  130  is preferably selected to be sufficient to span the posterior opening  141  of the facet joint  140  with the second and third openings  133 ,  134  located adjacent to the bony external surfaces  142 ,  144  of the superior and inferior facets  143 ,  145  when the first opening  132  is aligned with the posterior opening  141  of the facet joint  140 . 
     The one or more second openings  133  and the one or more third openings  134  are dimensioned and configured to accept suitable screws  146  or other suitable fasteners so that the inter-facet connection plate  130  can be fixedly attached to and between the superior and inferior facets  143 ,  145  above and below the facet joint  140  with the facet joint implant  10  positioned in the facet joint  140  as illustrated in  FIGS.  28 A through  29 E  for example. To accommodate different vertebral physiologies, and for ease of adjustability during an implant procedure, the second and third openings  133 ,  134  can comprise a plurality of slightly overlapping openings. This permits the inter-facet connection plate  130  to be attached to the adjacent upper and lower facets  143 ,  145  at slightly different locations, and also provides a degree of adjustability to the entry angle and position of the facet joint implant  10  relative to the posterior opening  141  of the facet joint  140 . 
     The inter-facet connection plate  130 , if used, functions together with the distal expansion of the facet joint implant  10  to help stabilize the facet joint  140 , help return or maintain the cervical spine in the locality of the facet joint  140  to proper alignment, and help in enhancing facet fusion by fixing the adjacent facets together. The inter-facet connection plate  130  may be constructed of any material that is suitable for long-term implantation in the body of a patient, and that is relatively strong and rigid, but also malleable enough to be shaped as necessary or desired to achieve the objectives noted above. One example of an inter-facet connection plate  130  shaped for use in connection with implantation of a facet joint implant in the facet joint between cervical vertebrae C4-C5 is illustrated in  FIG.  28 B . Another example is shown in  FIGS.  29 C- 29 D . 
     Once the facet joint implant  10  is connected at the distal end portion  92  of the delivery device  90  as described above, the delivery device is manipulated to introduce the facet joint implant  10  through the incision and to direct it through the dilated passage to the facet joint  140  in which it is to be implanted. As is known to persons skilled in the art, various means are available for visually or otherwise tracking the facet joint implant  10  as it is directed to the facet joint  140 , including various means identified above. 
     If an inter-facet connection plate  130  is used, the outer part  12  of the facet joint implant  10  is passed through the first opening  132  in the inter-facet connection plate  130  before being introduced through the incision. In that case, the delivery device  90  is manipulated to introduce the facet joint implant  10  and the inter-facet connection plate  130  together through the incision and the dilated passage to the facet joint  140 . 
     At the facet joint  140 , the delivery device  90  is manipulated to position and orient the facet joint implant  10  relative to the posterior opening  141  of the facet joint  140  as desired, and then to insert the facet joint implant  10  into the facet joint  140  as illustrated in  FIGS.  28 A and  29 A . As described herein, preferably the first or outer first connector  51  of the facet joint implant  10  is dimensioned to be larger than the intended posterior spacing between the superior and inferior facets  143 ,  145 , in other words larger than the intended posterior opening  141  of the facet joint  140 . This feature helps provide suitable positioning of the facet joint implant  10  in the facet joint  140  by allowing the outer part  12  and the inner part  14  of the facet joint implant  10  to be positioned in the facet joint  140 , but helps prevent the facet joint implant  10  from being over-inserted into the facet joint  140 . 
     If an inter-facet connection plate  130  is used, the delivery device  90  can be manipulated to hold the facet joint implant  10  in the desired position while a hole  147  is drilled in the external surface  142  of the facet  143  superior to the facet joint  140  and a screw  146  is inserted to attach the inter-facet connection plate  130  to the superior facet  143  as shown in  FIGS.  29 A- 29 D . Similarly, a hole  148  is drilled in the facet  145  inferior to the facet joint  140  and a screw  146  is inserted to attach the inter-facet connection plate  130  to the inferior facet  145  as shown in  FIGS.  29 A- 29 D . As also shown in  FIGS.  29 C- 29 E , the inter-facet connection plate  130  can be shaped as necessary to help achieve the desired stabilization and alignment of the facet joint  140  and the adjacent vertebrae. 
     Methods for drilling holes and securing screws or other suitable fasteners in in bone, such as vertebrae, are well known to persons skilled in the art and need not be described here. Similarly, various drills, drill guides, etc. are well known for this purpose and need not be described here. 
     Once the facet joint implant  10  is properly positioned in the facet joint  140  and the inter-facet connection plate  130  is secured and shaped (if one was used), the delivery device  90  is manipulated in the manner described above and as illustrated in  FIGS.  25 A,  25 B , and others to distally expand the facet joint implant  10  and distally distract the facet joint  140  as illustrated in  FIGS.  28 B and  29 E . With the lock switch  124  of the delivery device  90  in the second (locked) position, the inner shaft control knob  121  of the delivery device  90  is rotated in the first direction to cause the facet joint implant  10  to distally expand from the closed state to the open state in the manner previously described herein. Preferably, the inner shaft control knob  121  is rotated until the facet joint implant  10  reaches its fully distally expanded open state as illustrated in  FIGS.  28 B and  29 E , the first set of teeth  40  on the outer part  12  of the facet joint implant  10  engage the second set of indents  74  on the inner part  14  of the facet joint implant  10 , and a physical feedback, for example a click, is sensed. 
     With the facet joint implant  10  properly positioned in the facet joint  140  in the fully distally expanded open state, the first exterior surface  24  of the first facet plate  20  will preferably be in substantial physical contact with an anterior portion  149  of the interior surface  150  of the superior facet  143  facing the facet joint  140 , and the second exterior surface  34  of the second facet plate  30  will preferably be in substantial physical contact with an anterior portion  151  of the interior surface  152  of the inferior facet  145  facing the facet joint  140  as seen in  FIGS.  28 B and  29 E . In this position, the first plurality of serrations  25  on the first exterior surface  24  of the first facet plate  20  and the second plurality of serrations  35  on the second exterior surface  34  of the second facet plate  30  help adhere the facet joint implant  10  to the bony surfaces of the superior and inferior facets  143 ,  145  facing the facet joint  140 . 
     If the position of the facet joint implant  10  in the facet joint  10  is not as desired, however, the delivery device  90  may be manipulated to distally contract the facet joint implant  10  and to reposition the facet joint implant  10  in the facet joint  140 . With the lock switch  124  on the delivery device  90  in the second (locked) position, the inner shaft control knob  121  on the delivery device is rotated in the direction opposite to the direction it was rotated to expand the facet joint implant  10 . Preferably, the inner shaft control knob  121  is rotated in the opposite direction until the facet joint implant  10  has distally contracted sufficiently to be repositionable within the facet joint  140  or removed from the facet joint  140  if desired. The delivery device  90  can then be manipulated to reposition the facet joint implant  10  in the facet joint  140  as desired. Once the facet joint implant  10  is in the desired position, the delivery device can be manipulated to distally re-expand the facet joint implant  10  in the manner previously described. 
     Once the facet joint implant  10  is properly positioned in the facet joint  140  as desired and in its distally expanded open state, the delivery device  90  may be disconnected from the facet joint implant  10 , and may be withdrawn posteriorly from the body of the patient through the dilated passageway and posterior incision. The delivery device  90  is disconnected from the facet joint implant  10  by simply reversing the order of the steps described above to connect the delivery device  90  to the facet joint implant  10 . 
     If desired or necessary, additional steps can be performed before completing the procedure and closing the posterior incision. For example, bone paste may have been introduced in the facet joint  140  before the facet joint implant  10  was introduced to facilitate joint fusion in the future. The first opening  23  in the first facet plate  20  and the second opening  33  in the second facet plate  30  facilitate the dispersion of the bone paste or other medicinal or therapeutic substances in the facet joint  140 , and also facilitate the growth of natural bone in, around, and through the facet joint implant  10 . This in turn helps fuse the facets  143 ,  145  of the vertebrae adjacent to the facet joint  140  and further stabilize and strengthen the facet joint  140  and adjacent vertebrae. 
     A particularly beneficial effect of the distal expansion of the facet joint implant  10  as described is that the facet joint  140  is distracted distally, which results in widening of both the intervertebral disc space and intervertebral foramina and provides relief from the symptoms of cervical radiculopathy. Another possibly beneficial effect is that distraction of the facet joint  140  distally may help maintain the natural lordotic alignment of the cervical spine while avoiding the condition of kyphosis. This effect may be further enhanced by the use of inter-facet connection plate as described herein. 
     Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar to or equivalent to those described herein can be used in the practice or testing of the distally expanding facet implant and delivery device, suitable methods and materials are described above. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety to the extent allowed by applicable law and regulations. The distally expanding facet implant and delivery device may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and it is therefore desired that the present embodiment be considered in all respects as illustrative and not restrictive. Any headings utilized within the description are for convenience only and have no legal or limiting effect.