Patent Publication Number: US-2016228156-A1

Title: Locking device for fixation mechanism of medical implant

Description:
RELATED APPLICATIONS 
     This application is related to U.S. patent application Ser. No. ______, (Attorney Docket No. 156238.000201), filed concurrent herewith, entitled “Locking Device For Fixation Mechanism Of Medical Implant.” This application is commonly assigned to the Assignee of the present invention and is hereby incorporated herein by reference in their entirety for all purposes. 
    
    
     FIELD OF INVENTION 
     A device for locking a bone fastening or fixation mechanism in a receiving member of a medical implant. 
     BACKGROUND OF INVENTION 
     The spine is the axis of the skeleton on which all of the body parts hang. In humans, the normal spine has seven cervical, twelve thoracic and five lumbar segments. The lumbar spine sits upon the sacrum, which then attaches to the pelvis, and in turn is supported by the hip and leg bones. The bony vertebral bodies of the spine are separated by intervertebral discs, which act as joints but allow known degrees of flexion, extension, lateral bending, and axial rotation and translation. 
     Typical vertebra has a thick anterior bone mass called the vertebral body, with a neural (vertebral) arch that arises from the posterior surface of the vertebral body. The central of adjacent vertebrae are supported by intervertebral discs. The spinal disc and/or vertebral bodies may be displaced or damaged due to trauma, disease, degenerative defects, or wear over an extended period of time. One result of this displacement or damage to a spinal disc or vertebral body may be chronic back pain. In many cases, to alleviate back pain from degenerated of herniated discs, the disc is removed along with all or part of at least one neighboring vertebrae and is replaced by an implant that promotes fusion of the remaining bony anatomy. 
     The success or failure of spinal fusion may depend upon several factors. For instance the spacer or implant or cage used to fill the space left by the removed disc and bony anatomy must be sufficiently strong to support the spine under a wide range of loading conditions. The spacer should also be configured so that it likely to remain in place once it has been positioned in the spine by the surgeon. Additionally the material used for the spacer should be biocompatible material and should have a configured that promotes bony ingrowth. 
     In combination with spacers or cages, a plating system is used to further stabilize the spine during the fusion process. These devices, commonly referred to as bone fixation plating systems (i.e., cervical plate), typically include one or more plates and fasteners (typically screws) for aligning and holding vertebrae in a fixed position with respect to one another. Plating systems independent of the spacers provide additional complications such as loosening and failure of the hardware. Two common failures are the breakage of the plates, and the backing out of screws into soft tissues of the patient&#39;s body. The backing out of the screws is typically a result of the screws failure to achieve a sufficient purchase in the bone, although the stripping of the screws has also been known to cause this problem. Another common problem is that plating systems require “carpentry” work to match fit aspects of the vertebral bodies. 
     Thus, it is important that the medical implant is properly held in place by the fastener. To keep the fastener from backing out, a locking device is typically utilized. The locking device physically impedes the top of the screw from rising, which prevents the fastener from rotating (as this would cause the fastener to rise). Once the locking device is in the “locked” position, the fixation mechanism is held in place. 
     It is further important that the locking device be properly positionable both in the unlocked position (so that the medical practitioner can have access to properly position and implant the fastener) and the locked position (so that the locking device can properly function). Accordingly, there is a need for an improved locking device for plating systems. 
     SUMMARY OF INVENTION 
     The present invention is a medical implant (cervical plate) that is held in place by a fixation mechanism, that is, typically, a screw. To keep the screw from backing out, a locking device is utilized. The locking device physically impedes the top of the screw from rising, which prevents the screw from rotating (as this would cause the screw to rise). The locking device has a retention device that controllably maintains the locking device in the unlocked and locked positions as the case may be. The retention device provides for hard stops for the locking device in its unlocked and locked positions, while maintaining a low profile. 
     In general, in one aspect, the invention features a medical implant that includes a receiving member body that has a first fastener opening. The first fastener opening is operable for allowing a first fastener to be inserted through the first fastener opening for fixing the medical implant to bone. The medical implant further has a locking mechanism located near the first fastener opening. The locking mechanism includes a rotating block cover operable to move between an unlocked position and a locked position. When the rotating block cover is in the unlocked position, the first fastener can be inserted through the first fastening opening. When the rotating block cover is in the locked position, a portion of the rotating block cover is covering the first fastener opening to prevent the first fastener for moving through the first fastener opening and which locks the first fastener in place. The medical implant further includes a retaining mechanism that has an engagement body rotatably coupled to at least two retaining levers. The engagement body is attached to the rotating block cover. The engagement body is operable for moving rotatably through the retaining levers. The engagement body is operable for moving in a first direction to a first position. When the engagement body is in the first position, the locking mechanism is in the unlocked position. The engagement body is blocked from rotating past the first position when moved in the first direction. The engagement body is retained in the first position by the retaining levers such that the engagement body cannot move without the application of a force in a second direction that is opposite to the first direction. The engagement body is operable for moving in a second direction to a second position. When the engagement body is in the second position, the locking mechanism is in the locked position. The engagement body is blocked from rotating past the second position when moved in the second direction. The engagement body is retained in the second position by the retaining levers such that the engagement body cannot move without the application of a force in the first direction. 
     Implementations of the invention can include one or more of the following features: 
     The medical implant can be a bone fixating plating system. 
     The bone fixating plating system can include a cervical plate. 
     The cervical plate can further include a second fastener opening. The second fastener opening can be operable for allowing a second fastener to be inserted through the second fastener opening for fixing the medical implant to bone. The locking mechanism can further be located near the second fastener opening. When the rotating block cover is in the unlocked position, the second fastener can be inserted through the second fastening opening. When the rotating block cover is in the locked position, a portion of the rotating block cover can be covering the second fastener opening to prevent the second fastener for moving through the second fastener opening and which locks the second fastener in place. 
     The first fastener can include a bone screw. 
     The retaining mechanism can include exactly two retaining levers. 
     Each of the retaining levels can have an indent that retains the engagement body in the first position and the second position. 
     The rotating block cover can have a hole operable for receiving a rotatable tool. The rotating block cover can be rotatable in the first direction and the second direction using the rotating tool. 
     The receiving member body can include a plurality of fastener openings and plurality of locking mechanisms. Each of the locking mechanisms can be operable for locking fasteners positioned in at most two of the fastener openings. 
     Each of the locking mechanisms can be operable for locking fasteners positioned in at most one of the fastener openings. 
     In general, in another aspect, the invention features a method that includes selecting a medical implant having a receiving body that includes a first fastener opening, a locking mechanism, and a retaining mechanism. The locking mechanism includes a rotating block cover operable to move between an unlocked position and a locked position. The locking mechanism is in the unlocked position. The retaining mechanism includes an engagement body rotatably coupled to at least two retaining levers. The engagement body is attached to the rotating block cover. The retaining mechanism retains the engagement body at a first position to maintain the rotating block cover in the unlocked position. The method further includes inserting a first fastener into the first fastener opening. The method further includes securing the first fastener to a bone. The method further includes rotating the locking mechanism from the unlocked position to the locked position. A portion of the rotating block cover is covering the first fastener opening to prevent the first fastener for moving through the first fastener opening and which locks the first fastener in place. The engagement body is blocked from rotating to prevent the rotating lock cover from rotating past the locked position. The retaining mechanism retains the engagement body at second position to maintain the rotating block cover in the locked position. 
     Implementations of the invention can include one or more of the following features: 
     The medical implant can be a bone fixating plating system. 
     The bone fixating plating system can include a cervical plate. 
     The cervical plate can further include a second fastener opening. The method can further include inserting a second fastener into the second fastener opening. The method can further include securing the second fastener to the bone while the locking mechanism is in the unlocked position. The step of rotating the locking mechanism can further include that a portion of the rotating block cover is covering the second fastener opening to prevent the second fastener for moving through the second fastener opening and which locks the second fastener in place. 
     The first fastener can include a bone screw. 
     The retaining mechanism can include exactly two retaining levers. 
     Each of the retaining levels can have an indent that retains the engagement body in the first position and the second position. 
     The step of rotating the locking mechanism can include inserting a rotating tool into a hole in the rotating block cover and rotating the rotating tool. 
     The receiving member body can include a plurality of fastener openings and plurality of locking mechanisms. The method can further include moving each of the locking mechanisms in the plurality of locking mechanism to lock at most two fasteners positioned in at most two fastener openings. 
     The method can further include moving each of the locking mechanisms in the plurality of locking mechanism to lock at most one fastener. 
     The method can further include rotating the locking mechanism from the locked position to the unlocked position. No portion of the rotating block cover can be covering the first fastener opening which unlocks the first fastener. The engagement body can be blocked from rotating to prevent the rotating lock cover from rotating past the unlocked position. The retaining mechanism can retain the engagement body at the first position to maintain the rotating block cover in the unlocked position. 
     The foregoing has outlined rather broadly the features and technical advantages of the invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. 
     It is also to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is 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 
       For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
         FIG. 1A  is a top view of an embodiment of the present invention showing a cervical plate with the locking mechanism in the unlocked position. 
         FIG. 1B  is a perspective view of the embodiment of  FIG. 1A . 
         FIG. 2  is a bottom view of the embodiment of  FIG. 1A . 
         FIG. 3A  is a top view of the embodiment of  FIG. 1A  with fasteners (screws) inserted within. The locking mechanism is in the unlocked position. 
         FIG. 3B  is a top view of the embodiment of  FIG. 3A  with the locking mechanism in the locked position. 
         FIG. 3C  is a perspective view of the embodiment of  FIG. 3B . 
         FIG. 4  is a bottom view of the embodiment of  FIG. 3A . 
         FIG. 5  is an exploded view of the embodiment of  FIG. 1B . 
         FIG. 6A  is a top view of the embodiment of  FIG. 1A  with the locking mechanism removed to show the retaining mechanism. 
         FIG. 6B  is an enlarged top view of the retaining mechanism shown in  FIG. 6A . 
         FIG. 6C  is an enlarge perspective view of the retaining mechanism shown in  FIG. 6A . 
         FIG. 7A  is a top view of a locking mechanism used in embodiments of the invention. 
         FIG. 7B  is a bottom view of the locking mechanism shown in  FIG. 7A . 
         FIGS. 7C-7D  are perspective views of the locking mechanism shown in  FIG. 7A . 
         FIG. 8A  is an enlarged top view of locking mechanism shown in  FIG. 3A . 
         FIG. 8B  is the enlarged top view of the locking mechanism shown in  FIG. 8A  without the cover piece of the locking mechanism. 
         FIG. 8C  is a cut-out side view of locking mechanism shown in  FIG. 8A . 
         FIG. 9A  is an enlarged top view of locking mechanism shown in  FIG. 3B . 
         FIG. 9B  is the enlarged top view of the locking mechanism shown in  FIG. 9A  without the cover piece of the locking mechanism. 
         FIG. 9C  is a cut-out side view of locking mechanism shown in  FIG. 9A . 
     
    
    
     DETAILED DESCRIPTION 
     The technology relates to a device for locking a bone fastening or fixation mechanism in a receiving member of a medical implant. The bone fastening or fixation mechanism is used to mount the receiving member to a bone structure in the medical implant. The locking mechanism prevents the bone fastening mechanism for backing out of the receiving member. A retention mechanism is used to controllable move and retain the locking mechanism in the locked (closed) or unlocked (open) position. 
     Referring to the figures,  FIG. 1A  is a top view of an embodiment of the present invention showing a cervical plate  100  with the locking mechanism  101  in the unlocked position. The locking mechanism  101  has a rotating blocker cover  701  (shown in more detail in  FIGS. 7A-7D  discussed below) that can be rotated to partially cover holes (bone screw holes)  102  and  103 . (The holes are also referred to as “fastener openings”) As shown in  FIG. 1A , the locking mechanism  101  is in the unlocked (otherwise known as open) position in that fasteners (screws) can be fit through holes  102  and  103  for implantation to fasten the cervical plate  100 .  FIG. 1B  is a perspective view of the cervical plate  100 .  FIG. 2  is a bottom view of cervical plate  100 . 
       FIG. 3A  is a top view of cervical plate  100  with fasteners  201  (bone screws) inserted within holes  102  and  103 .  FIG. 4  is a bottom view of cervical plate  100  with the fasteners  201  inserted. Such insertion of fasteners  201  can incur into holes  102  and  103  because rotating blocker cover  701  of locking mechanism  101  is in the open position. Locking mechanism  101  is rotatably connected to cervical plate  100 . Locking mechanism  101  can be rotated using the star-shaped hole  104  that can be engaged with a rotatable tool. As shown in  FIGS. 3A-3B , rotating locking mechanism  101  in the clockwise direction moves locking mechanism to the locked (otherwise known as closed) position.  FIG. 3B  is a top view of the embodiment of cervical plate  100  with the locking mechanism  101  in the locked position.  FIG. 3C  is a perspective view of the embodiment of  FIG. 3B . 
     When locking mechanism  101  is in the locked position, the fastener  201  is blocked for moving upwards and out through holes  102  and  103 . Because fastener  201  cannot move upward and out, the fastener  201  cannot itself rotate (as rotating would cause it to move upward and out). Such blocking occurs due to the shape of rotating blocker cover  701  which, when the locking mechanism  101  is rotated such that a portion of rotating blocker cover  701  overlays holes  102  and  103 . Examples of locking mechanisms known in the art are shown in U.S. Pat. No. 8,702,766, issued Apr. 22, 2014 to Mueller and U.S. Pat. No. 8,641,768, issued Feb. 4, 2014, to Duffield et al. 
       FIG. 5  is an exploded view of cervical plate  100  in which locking mechanism  101  has been separated from the cervical plate  100  to show the retaining mechanism that lies beneath.  FIG. 6A  is a top view of cervical plate  100  with the locking mechanism  101  removed to show the retaining mechanism  600 .  FIG. 6B  is an enlarged top view of the retaining mechanism shown in  FIG. 6A . 
     The retaining mechanism  600  has a pair of retaining levers (or arms)  601  and  602 . Hole  605  is positioned within the retaining mechanism  600  and is where locking mechanism  101  (not shown) is rotatably connected to cervical plate  100 . Each of retaining levers  601  and  602  has an indent  603  and  604 , respectively, which is utilized in the retaining of the locking mechanism. 
     The retaining levers  601  and  602  oppose one another to apply a force to the locking mechanism  101  when retaining it in either the locked or unlocked position. The retaining levers  601  and  602  also control the rotational movement of the locking mechanism  101  such that it cannot be over rotated when moving from one position to the other. 
       FIGS. 7A-7D  are illustrations of locking mechanism  101 .  FIGS. 7A-7B  are top and bottom views of locking mechanism  101 .  FIGS. 7C-7D  are perspective view of locking mechanism  101 . The locking mechanism  101  includes a rotating blocker cover  701 , which is the portion of the locking mechanism  101  that, when rotated, will partially cover holes  102  and  103  when the locking mechanism is in the locked position. 
     Locking mechanism  101  has a post  703  that is rotatably connected within hole  605  (shown in  FIG. 6B ). Locking mechanism  101  further has an engagement body  702  that is engagable with retaining levers  601  and  602  to retain locking mechanism  101  in its locked and unlocked position, as the case may be. As shown in  FIGS. 7B and 7D , engagement body  702  can be geometric shaped, such as the multisided shaped body shown in those figures. Engagement body  702  includes sides  704 - 709 , which, when the locking mechanism  101  is in place, are positioned to engage with retaining levers  601  and  602  (and their respective indents  603  and  604 ). 
       FIGS. 8A-8C and 9A-9C  illustrate the operability of the retaining mechanism  600  with respect to locking mechanism  101 .  FIG. 8A  shows locking mechanism  101  in cervical plate  100  in the unlocked position.  FIG. 8C  is a cut-out side view of the cervical plate  101  shown in  FIG. 8A .  FIG. 8B  is the same view as  FIG. 8A , except without showing rotating blocker cover  701 . This allows the underworking to be more readily viewed and described. As shown in  FIG. 8B , engagement body  702  is positioned within retaining levers  601  and  602 , such that sides  704  and  705  are nestled in place in retaining lever  601 . As shown in  FIG. 8B , indent  603  is to the immediate right of side  704 , which maintains engagement body in this position and keeps engagement body  702  from rotating in the clockwise direction. Likewise, sides  706  and  708  are nestled in place in retaining lever  602 , with indent  604  to the immediate left of side  707 , and which likewise maintains engagement body in this position and keeps engagement body  702  from rotating in the clockwise direction. Thus, the engagement between the engagement body  702  and retaining levers  601  and  602  prevents engagement body  702  (and thus locking mechanism  101 ) from rotating clockwise into the locked position. 
     Furthermore, walls  801  and  802  block engagement body  702  from being able to rotate counter-clockwise (i.e., to rotate in the backwards direction). If that were not the case, then locking mechanism could rotate counter-clockwise into a locked position. 
     Accordingly, the engagement between the engagement body  702  and retaining levers  601  and  602  will maintain the locking mechanism in the unlocked position once positioned there. Moreover, as over-rotation is not possible, the practitioner using the cervical plate  100  will know that it has been properly positioned. 
       FIG. 9A  is shows locking mechanism  101  in cervical plate  100  in the locked position.  FIG. 9C  is a cut-out side view of the cervical plate  101  shown in  FIG. 9A . Because retaining levers  601  and  602  have some limited flexibility, rotation of the engagement body  702  in the clockwise direction with the application of a force, will allow the retaining levers  601  and  602  to move radially outward to allow engagement body  702  to rotate from the position shown in  FIG. 8B  to the position shown in  FIG. 9B . During such clockwise rotation, sides  704 - 706  rotate past indent  603  of retaining lever  601 , such that side  706  is now to the immediate right of indent  603 . This then precludes engagement body  702  from being able to rotate back counter-clockwise to the position shown in  FIG. 8B . Likewise, sides  707 - 709  rotate past indent  604  of retaining lever  602 , such that side  709  is now to the immediate left of indent  604 . This then also precludes engagement body  702  from being able to rotate back counter-clockwise to the position shown in  FIG. 8B . Thus, the engagement between the engagement body  702  and retaining levers  601  and  602  prevents engagement body  702  (and thus locking mechanism  101 ) from rotating clockwise into the locked position. 
     Furthermore, walls  801  and  802  are positioned such that this stops engagement body from turning further clockwise, i.e., walls  801  and  802  prevent over-rotation of engagement body  702 . Accordingly, the practitioner cannot over-rotate when moving from the unlocked to the locked position. 
     When the locking mechanism is in the locked position, an application of force in the counter-clockwise direction will allow retaining levers  601  and  602  to expand radially, which then permits the engagement body  702  (and thus the locking mechanism  101 ) to return to the unlocked position shown in  FIG. 8A-8C . Again, this cannot be over-rotated due to the walls  801  and  802 . 
     The locking mechanism used in combination with the retaining mechanism has significant advantageous. It provides for hard stops when moving between the open and closed positions. It also precludes over-rotation by the practitioner when implanting the cervical plate. Moreover, once the locking mechanism is set in place, locked or unlocked, it will be maintained in that position. The locking mechanism maintains its low profile because the retaining mechanism is able to fit in the space beneath it. 
     The disclosures of all patents, patent applications, and publications cited herein are hereby incorporated herein by reference in their entirety, to the extent that they provide exemplary, procedural, or other details supplementary to those set forth herein. It will be understood that certain of the above-described structures, functions, and operations of the above-described embodiments are not necessary to practice the present invention and are included in the description simply for completeness of an exemplary embodiment or embodiments. In addition, it will be understood that specific structures, functions, and operations set forth in the above-described referenced patents and publications can be practiced in conjunction with the present invention, but they are not essential to its practice. It is therefore to be understood that the invention may be practiced otherwise than as specifically described without actually departing from the spirit and scope of the present invention. 
     While embodiments of the invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the invention. The embodiments described and the examples provided herein are exemplary only, and are not intended to be limiting. Many variations and modifications of the invention disclosed herein are possible and are within the scope of the invention. Accordingly, the scope of protection is not limited by the description set out above.