Patent Description:
Back pain takes an enormous toll on the health and productivity of people around the world. According to the American Academy of Orthopedic Surgeons, approximately <NUM> percent of Americans will experience back pain at some time in their life. On any one day, it is estimated that <NUM>% of the working population in America is disabled by back pain.

Common causes of back pain are injury, degeneration and/or dysfunction of one or more intervertebral discs. Intervertebral discs are the soft tissue structures located between each of the thirty-three vertebral bones that make up the vertebral (spinal) column. Essentially, the discs allow the vertebrae to move relative to one another. The vertebral column and discs are vital anatomical structures, in that they form a central axis that supports the head and torso, allow for movement of the back, and protect the spinal cord, which passes through the vertebrae in proximity to the discs. With age, intervertebral disks begin to shrink. In some cases, they may collapse completely and cause the bones to rub against one another. This is also referred to as osteoarthritis.

When a damaged intervertebral disc causes a patient pain and discomfort, surgery is often required. Typically, surgical procedures for treating damaged intervertebral discs involve discectomy (partial or total removal of a disc), often followed by interbody fusion of the superior and inferior vertebrae adjacent to the disc or implantation of an intervertebral prosthetic disc. Fusion is most commonly achieved by implantation of a cage or spacer together with bone graft material to promote bone growth to fuse the adjacent vertebrae together. Oftentimes, pins, rods, screws, cages and/or the like are placed between the vertebrae to act as support structures to hold the vertebrae and bone graft material in place while the bones permanently fuse together. Spinal fusion eliminates motion between the vertebrae. Fusion is an option when motion is the source of pain.

An alternative to spinal fusion which doesn't limit patient mobility is intervertebral disc replacement (TDR), also called total disc arthroplasty. The TDR procedure involves removing the natural disk from between the vertebrae and replacing it with and artificial disc prosthesis. Several types of intervertebral disc prosthesis are currently available. For example, one type of intervertebral disc prosthesis includes upper and lower prosthesis plates which locate against and engage the adjacent vertebral bodies and a mobile core positioned between the plates. The core may be movable or fixed, metallic, ceramic or polymer and generally has at least one convex outer surface which mates with a concave recess on one of the plates in a fixed core device. In a movable core device one or both of the outer surfaces of the core may be curved. In order to implant these intervertebral discs, the natural disc is removed and the vertebrae are distracted or forced apart in order to fit the artificial disc in place. The plates may be inserted individually or together and with or without a core. It is desirable to reduce the duration of the procedure by implanting the disc in an assembled configuration. However, when holding the disc for implantation it is desirable to hold the disc securely with a placement tool without damage to the disc or surrounding anatomy and remove the tool easily from the disc which it is in the appropriate position.

Currently available intervertebral prosthetic discs are held, delivered and removed with a variety of different instruments and techniques. Challenges with these known instruments and techniques include inadvertent changes to the prosthetic disc position during disconnection of the instrument or difficulty in disconnecting the instrument from the prosthetic disc because of interference of surrounding anatomy. It would be desirable to provide a disc system with a simple placement instrument which easily and securely grasps the implant for insertion and is then easily removed from the patient.

In addition, it would be desirable to hold the disc in the implantation instrument in an articulated or angled insertion configuration to prevent the need for over distraction of the disc space.

Further, it would be desirable to provide a disc removal system with an instrument to more easily and quickly separate the components of an intervertebral prosthetic disc for removal.

Therefore, a need exists for an improved artificial intervertebral disc placement and removal systems which improve speed and reliability of the surgical procedures.

Description of the Background Art. A variety of intervertebral disc prosthesis designs and methods of implanting are described in described in <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT> and <CIT>, and <CIT>.

<CIT> describes a device for positioning and attaching a member within a patient. The device includes a shaft, handle and actuation mechanism. A pair of grasping jaws on the shaft are movable by the actuation mechanism to grasp a prosthetic disc.

The present invention provides an intervertebral prosthetic disc placement instrument as set out in claim <NUM>. Further advantageous features are set out in the dependent claims.

Positioning of an intervertebral prosthetic disc properly in the spine is an important part of a successfully total disc arthroplasty (TDR) procedure. The position of the implant in the intervertebral space can influence the range of motion, implant behavior and clinical result. Proper position in the anterior/posterior direction between the vertebral bodies is particularly important but can be difficult due to surrounding anatomy. Surgeon experience, surgeon training, use of imaging modalities and patient anatomy are all factors which can influence accuracy of prosthetic disc placement.

An intervertebral prosthetic disc placement system according to the present disclosure includes a multi-part prosthetic disc and an associated placement instrument. The placement instrument holds the prosthetic disc securely for placement into an intervertebral disc space and quickly releases the disc within the disc space at a desired position between the vertebral bodies. The quick release is facilitated by providing the instrument with an ejector which helps disengage the prosthetic disc from the instrument.

One example of an intervertebral prosthetic disc for insertion between adjacent vertebrae includes an upper plate, a lower plate and a core between the upper and lower plates, such as the prosthetic discs described in <CIT> and <CIT>. The core is retained between the upper and lower plates by a retention feature and is designed to allow the plates to slide over the upper and lower surfaces of the core in the anterior/posterior direction and in the lateral direction and to allow the plates to articulate and rotate with respect to each other and the core. The upper and lower plates are provided with a side groove, notch, slot, channel or other feature which can be grasped by the placement instrument.

<FIG> illustrates a first embodiment of a prosthetic disc placement instrument <NUM> formed of a shaft <NUM>, a distal end effector <NUM> and a proximal handle end <NUM>. The proximal handle end <NUM> includes a grasping handle <NUM> and an activation mechanism <NUM>. A pair of grasping jaws <NUM> on the distal end <NUM> are configured to move with respect to one another to grasp a multipart prosthetic disc. Preferably, the jaws <NUM> grasp the prosthetic disc from the sides of the disc in a non-articulating configuration so that the multiple parts of the prosthetic disc can be placed simultaneously. The grasping jaws <NUM> are movable from a loading or grasping position shown in <FIG> to a tightened position, a release position, an eject position and a cleaning position by the activation mechanism <NUM>. The loading or grasping position shown in <FIG> has an activation mechanism nut <NUM> not in contact with the handle <NUM> allows the grasping jaws <NUM> to flex outward to receive the prosthetic disc. Once the prosthetic disc is in place between the jaws <NUM>, the nut <NUM> is tightened against the handle <NUM> to hold the disc in the tightened position in the jaws. After placement of the disc in the disc space, the nut <NUM> is loosened to a release position which looks can be the same as the loading position and the jaws <NUM> are no longer tightly grasping the disc.

A prosthetic disc ejector <NUM> on the distal end of the instrument shaft <NUM> moves distally with respect to the pair of grasping jaws <NUM> to contact the prosthetic disc to fully disengage the prosthetic disc from the placement instrument <NUM>. The activation mechanism <NUM> includes the nut <NUM> used to open and close the jaws <NUM> and a thumb activated button <NUM> used to advance the ejector <NUM>.

<FIG> is a top view of the placement instrument <NUM> with the jaws <NUM> shown in a loading or grasping position. In the tightened position, the distal end <NUM> of the instrument looks the same, but the jaws <NUM> securely hold the disc because the nut <NUM> is tightened against the proximal end of the handle <NUM>. As can be seen through a window <NUM> in the handle <NUM>, the shaft <NUM> is formed of an inner shaft <NUM> and an outer shaft <NUM>. The inner shaft <NUM> has a threaded portion at the proximal end which receives the activation mechanism nut <NUM>. The inner shaft <NUM> is also connected to the ejector <NUM> at a distal end and rotation of the nut <NUM> moves the inner shaft <NUM> within the outer shaft to loosen and tighten the jaws <NUM>. Inner cam surfaces <NUM> on the ejector <NUM> engage the outer cam surfaces <NUM> on the outer shaft <NUM> to tighten the jaws <NUM> upon rotation of the nut <NUM>. The inner and outer cam surfaces <NUM>, <NUM> can be seen more clearly in <FIG> which show top views of the inner ejector rod and the outer handle and grasping assembly of the instrument <NUM> in the disassembled configuration. Also shown clearly in <FIG> is the slot <NUM> in the outer shaft allows the movement of the jaws <NUM> between the loosened loading position and tightened position by flexion of a portion of the shaft. Although the jaws <NUM> are shown as grasping the upper and lower plates at notches in the lateral surfaces of the plates other grasping arrangements can be employed. For example, only one of the upper and lower plates can be grasped; the plates can be grasped at their upper or lower surfaces or on another grasping feature of the plates; or the grasping jaws can grasp the plates and/or the core of the prosthetic disc.

<FIG> and <FIG> are side and bottom views, respectively, of the instrument <NUM> in the same loading or released position of <FIG> with the nut <NUM> threaded onto threads near the proximal end of the inner shaft <NUM>. In the fully tightened position, the nut <NUM> will contact a proximal end of the outer shaft <NUM>.

<FIG> shows a top view of the instrument of <NUM> in a cleaning position. In the cleaning position, the nut <NUM> is fully unthreaded or disengaged from threads <NUM> of the inner shaft <NUM>, however, the nut <NUM> does not fall off the instrument since it is prevented from fully separating from the instrument by the disc shaped thumb button <NUM> of the inner shaft. In the cleaning position, all parts of the instrument <NUM> are connected and unable to be completely separated and are in a loose configuration to allow cleaning fluid to pass through all parts of the instrument. The cleaning window <NUM> in the handle <NUM> and an addition cleaning window <NUM> (<FIG>) and slot <NUM> in the outer shaft <NUM> assist in allowing cleaning fluid to circulate through all parts of the instrument and particularly between the inner and outer shafts and within the threads of the nut.

<FIG> show a top view of the distal end of the instrument <NUM> in three different positions including the tightened position (<FIG>); the released position (<FIG>); and the ejecting position (<FIG>). In the tightened position of <FIG>, the nut pulls the inner shaft proximally sliding the inner cam surfaces <NUM> of the ejector against the outer cam surfaces <NUM> of the outer shaft <NUM> to move the jaws together in the grasping or tightened position. In the released or disengaged position of <FIG>, the nut is released to allow the cam surfaces <NUM>, <NUM> to disengage with one another and allow the jaws <NUM> to move apart out of the notches or grooves in the sides of the prosthetic disc. In the ejecting position of <FIG>, a distal end of the ejector <NUM> functions to both push the jaws <NUM> further apart and to push the prosthetic disc off of the instrument jaws. The ejector <NUM> is moved forward to the ejecting position by pressing on the thumb activated button <NUM> at the proximal end of the instrument. The particular cam arrangement shown in <FIG> are just one example of a cam system which can be employed to move the jaws <NUM> and the ejector <NUM> between the tightened, released and ejecting positions. In addition, a distal end of the ejector <NUM> can be configured to mate with and apply a force to any part of the prosthetic disc to achieve the desired separation of the instrument from the disc. For example, the ejector distal end can be configured to mate with the core, one or more of the plates or both the core and the plates.

When the ejector <NUM> is in the ejecting position shown in <FIG>, the ejector can be used to adjust the position of one or more parts of the prosthetic disc or the entire prosthetic disc. For example, the distal end of the ejector <NUM> can be shaped to engage an upper and lower plate of the prosthetic disc to advance the upper and/or lower plate posteriorly by tapping with a mallet on the proximal end of the placement instrument <NUM>. The use of the ejector <NUM> to advance the plates proximally either separately or together eliminates the need to use a separate final placement instrument to adjust the plates of the prosthetic disc to a final position between the vertebrae. In one example, the distal edge of the ejector <NUM> has a concave curvature to match a corresponding convex posterior edge of the upper and/or lower plates.

<FIG> illustrate another embodiment of a placement instrument <NUM> with a different configuration of grasping jaws and ejector and illustrate the interaction of the placement instrument with one example of a prosthetic disc <NUM>. As shown in <FIG>, the prosthetic disc includes an upper plate <NUM>, a lower plate <NUM> and a mobile core (not shown) between the upper and lower plates. The upper and lower plates <NUM>, <NUM> articulate with respect to one another in the implanted configuration and are locked in a non-articulating insertion position when the prosthetic disc <NUM> is secured to the placement instrument <NUM>. Notches <NUM> on the sides of the upper and lower plates <NUM>, <NUM> are sized and shaped to receive the placement instrument jaws.

Similar to the embodiment of <FIG>, the placement instrument <NUM> of <FIG> includes inner and outer shafts which move with respect to one another. However, in the placement instrument <NUM> the inner shaft <NUM> is connected to the jaws <NUM> while the outer shaft <NUM> is connected to the ejector <NUM>. <FIG> is a perspective view of a distal end of the placement instrument <NUM> without a prosthetic disc showing the jaws <NUM> formed on the inner shaft <NUM>. The inner shaft <NUM> has a split <NUM> which allows the jaws <NUM> to flex between the tightened or locked position and the released position. In the tightened position of <FIG>, the jaws <NUM> are pressed toward each other by sliding the inner shaft <NUM> distally within the outer shaft <NUM> (or sliding the outer shaft proximally over the inner shaft) to contact an inner shaft cam surface <NUM> with an outer shaft cam surface <NUM>. Although a single set of cam surfaces are shown, a pair of cam surfaces can also be used. For example, cam surfaces can be provided on the other jaw on the left and right sides of the instrument or on the opposite top and bottom surfaces of the instrument. The jaws <NUM> of the instrument <NUM> are configured to be released from the upper and lower plates <NUM>, <NUM> by moving laterally out of the notches <NUM> of the plates and/or by moving the plates apart and pulling the jaws out between the plates.

<FIG> is a perspective view of the instrument <NUM> with a prosthetic disc <NUM> locked in and fully tightened on the instrument with tabs <NUM> at the distal ends of the jaws <NUM> positioned within and engaging the notches <NUM> in the plates <NUM>, <NUM>. As shown in <FIG> the plates <NUM>, <NUM> are arranged for insertion in an angled configuration in which the plate edges at the posterior side of the disc (furthest away from the instrument) are closer together than the edges of the plates at the anterior side of the disc. This angled implantation position provides a wedge shape for lower force insertion. <FIG> shows the cam surfaces <NUM>, <NUM> of the instrument engaged to hold the prosthetic disc in this wedge shape in a locked arrangement for insertion.

<FIG> shows the instrument <NUM> with the inner shaft <NUM> starting to be pulled back within the outer shaft <NUM> to release the inward pressure on the tabs <NUM> and allow the disc <NUM> to be released from the instrument <NUM>. However, although there is no inward pressure on the tabs <NUM> holding the disc on the instrument <NUM>, it may not be easy to remove the instrument from the disc because the surrounding anatomy of the patient at the implant site continues to prevent to tabs <NUM> from fully disengaging from the plate notches <NUM>. In the case that the instrument <NUM> does not easily release from the prosthetic disc <NUM>, the ejector <NUM> can be used to push the disc off of the instrument. The ejector <NUM> includes two wedge shaped members <NUM> which pass between the plates <NUM>, <NUM> to separate the plates and allow the plates to slip off the tabs <NUM>. The ejector <NUM> also has four disc contacting surfaces <NUM> or abutment surfaces which engage the posterior edges of the plates <NUM>, <NUM> to separate the disc from the instrument. The disc contacting surfaces <NUM> are preferably shaped to match the shapes of the corresponding anterior edges of the disc. <FIG> shows the instrument and prosthetic disc in a position in which plates are lifted off the tabs <NUM> by the wedge <NUM> of the ejector <NUM> and the disc contacting surfaces <NUM> of the ejector are in contact with the disc for ejecting.

<FIG> shows the prosthetic disc <NUM> in the ejecting position with the plate notches <NUM> popped off the tabs <NUM> and the plates passing over the top and bottom of the tabs of the jaws <NUM>. This allows the jaws <NUM> to be drawn straight back toward the instrument and avoids any difficulty disengaging the instrument when the patient's anatomy prevents the jaws from moving laterally in the disc space. In the event that the patient's anatomy does not prevent the jaws <NUM> from moving laterally, the prosthetic disc <NUM> can be released from the jaws without the need for the ejector by drawing the jaws back away from the disc.

A method for inserting an intervertebral prosthetic disc with the placement instruments <NUM>, <NUM> described herein involved securing the prosthetic disc to the instrument by tightening the instrument jaws, inserting the prosthetic disc to a desired location between the vertebrae, releasing the instrument jaws from the prosthetic disc, ejecting the disc from the instrument and removing the instrument from the patient. The intervertebral prosthetic disc is surgically implanted between adjacent spinal vertebrae in place of a damaged disc. Those skilled in the art will understand that the damaged disc is partially or totally removed according to known procedures and the adjacent vertebrae are forcibly separated from one another prior to inserting the prosthetic disc to provide the necessary space for insertion of the disc.

To connect the prosthetic disc securely in the placement instrument <NUM>, <NUM>, the tabs of the instrument jaws are seated in the upper and lower plate notches formed at the sides of the plates. The placement instrument is tightened around the disc by tightening the activation knob or other activation mechanism which may be at the proximal end of the handle or at another location on the handle. Once the prosthetic disc is loaded and tightened on the placement instrument the disc is inserted between the vertebral bodies with the patient lying flat on the operating table and the instrument straight up and down, perpendicular to the body. If the prosthetic disc includes fins or teeth requiring slots to be cut in the vertebral bodies, the disc is inserted with the fins or teeth aligned with the precut slots. Using lateral imaging and a mallet to tap the distal end of the placement instrument, the prosthetic disc is inserted into the space between vertebral bodies until the upper and lower plates are at or within about <NUM> of the posterior margin of the vertebral bodies. When the prosthetic disc is in the proper position as verified by X-ray or fluoroscopic imaging, the placement instrument is removed by activation of the activation mechanism. In one embodiment, the activation nut is rotated counter-clockwise until the upper and lower plates are released by the jaws. If the placement instrument is loose after releasing the jaws, the instrument can be removed. Slight side to side motion can be used to remove the instrument. However, if the instrument is not easily removed, the ejector is activated to press the implant off of the instrument. Preferably, the activation mechanism for the ejector is manually activated without the need for a mallet. The ejector in the ejecting position shown in <FIG> can be used as a final placement instrument to adjust the position of one or more parts of the prosthetic disc by advancing the disc posteriorly. Once the disc has been inserted to a desired position as confirmed by lateral imaging, distraction of the vertebra is released and the vertebra move together to hold the assembled disc in place.

In another version of a method for placement of a prosthetic disc, the placement instrument is tightened around the disc in the manner described above. Once the prosthetic disc is loaded and tightened on the placement instrument the disc is inserted between the vertebral bodies with the fins or teeth aligned with the precut slots. Using lateral imaging and a mallet to tap the distal end of the placement instrument, the prosthetic disc is inserted into the space between vertebral bodies until the disc is about half way into the space as viewed on lateral fluoroscopy, just past <NUM>% of the anterior/posterior depth or until the jaws come into contact with the vertebral body. When the prosthetic disc is in the proper position as verified by X-ray or fluoroscopic imaging, the placement instrument is removed. The ejector in the ejecting position shown in <FIG> is used as a final placement instrument to advance the prosthetic disc posteriorly. Advancement may be performed by contacting one or both articulating plates of the prosthetic disc to advance the prosthetic disc either all together or by sequential advancement of upper and lower plates to a final position.

The activation mechanisms used for both the jaws and the ejectors in each of the embodiments of the placement instrument can include any of the known handle mounted activator mechanisms for instruments including one or more rotatable knobs, movable levers or other known mechanisms.

The prosthetic disc can be inserted laterally, from an anterior side, or from a posterior or posterior/lateral side of the patient's spine. In the embodiment shown, the disc is designed for insertion anteriorly into an intervertebral space. Although the disc has been described herein as inserted anteriorly and is shown in a size appropriate for the cervical spine, the system can be modified to accommodate other locations in the spine, such as the lumbar spine, and other implantation approaches.

Occasionally an implanted intervertebral prosthetic disc needs to be surgically removed from a patient. Currently intervertebral prosthetic discs are removed with a variety of different instruments and techniques. Often disc removal surgery involves removing each plate from the vertebrae separately. One challenge with this known technique is that the plates are difficult to remove without significantly distracting the vertebrae. Excessive distraction of the vertebra is undesirable because of the stretching and damage to the adjacent ligaments and structures. The plates are much easier to remove from the vertebrae and distraction is minimized if the core is first removed from between the plates. A core removal instrument <NUM> is shown in <FIG>. The core removal instrument <NUM> can grasp and remove a core <NUM> from between the upper and lower plates <NUM>, <NUM> of the disc <NUM>.

<FIG> are perspective views of the core removal instrument <NUM> with the instrument in the grasping position and the removing position, respectively. The core removal instrument <NUM> includes a pair of core removal arms <NUM>, <NUM> having inner surfaces shaped to correspond substantially to a shape of the outer perimeter of the core. The shapes of the two core removal arms <NUM>, <NUM> can be mirror images of one another or can be different shapes, as shown. The arms <NUM>, <NUM> in one embodiment are tapered from a thinnest portion at their distal ends to thicker portion at some distance from the distal end to allow the arms to act like wedges to separate the plates <NUM>, <NUM> a distance which will allow the core to be removed from between the plates. The thicker portion of the arms <NUM>, <NUM> is at least two times as thick as the thinnest portion and the thicker portion is located a distance from the thinnest portion that corresponds substantially to a diameter or largest dimension of the core. Insertion of the arms <NUM>, <NUM> between the disc plates distracts the plates away from one another to allow the core to be more easily removed.

The arms <NUM>, <NUM> of the core removal tool <NUM> are connected to an inner shaft <NUM> of the core removal tool <NUM> which slides within an outer shaft <NUM>. Any known activation mechanism can be used to move the inner and outer shafts with respect to one another including knobs, levers, cams, ratchets or the like. Distal motion of the inner shaft <NUM> within the outer shaft <NUM> to the position shown in <FIG> causes the arms <NUM>, <NUM> to securely hold the core for removal from the plates and causes the plates <NUM>, <NUM> to abut an outer housing <NUM> at the end of the outer shaft. The outer housing <NUM> holds the plates in place as the arms <NUM>, <NUM> withdraw the core from between the plates.

In an alternative embodiment, the core removal tool arms and distraction wedge can be separate members which move with respect to one another and can be activated sequentially or simultaneously to grasp the core and separate the plates. In one embodiment, the core removal tool sequentially allows the surgeon to grasp the core, distract the plates and then pull out the core from between the plates. The pulling of the core out from between the plates can be performed by an activation mechanism of the handle or manually by the surgeon with the core grasped by the core removal tool arms.

Claim 1:
An intervertebral prosthetic disc placement instrument (<NUM>, <NUM>) comprising:
an instrument shaft (<NUM>) having a distal end and a proximal end;
an instrument handle (<NUM>) on the proximal end having an activation mechanism (<NUM>);
a pair of grasping jaws (<NUM>, <NUM>) on the distal end of the instrument shaft (<NUM>), the grasping jaws (<NUM>, <NUM>) configured to move with respect to one another to grasp a multipart prosthetic disc (<NUM>) in a non-articulating configuration, the grasping jaws (<NUM>, <NUM>) being movable from a tightened to a released position by the activation mechanism (<NUM>); and
characterized by further comprising a prosthetic disc ejector (<NUM>, <NUM>) on the distal end of the instrument shaft (<NUM>) which moves distally with respect to the pair of grasping jaws (<NUM>, <NUM>) when the grasping jaws (<NUM>, <NUM>) are in the released position and wherein the ejector (<NUM>, <NUM>) is configured to contact the prosthetic disc (<NUM>) to fully disengage the prosthetic disc (<NUM>) from the placement instrument (<NUM>, <NUM>).