US 20050256576 A1
A total artificial expansible disc having at least two pairs of substantially parallel shells, which move in multiple directions defined by at least two axes, is disclosed. Several methods for implanting the total artificial expansile disc are also disclosed. The total artificial expansile disc occupies a space defined by a pair of vertebral endplates. An expansion device moves the pairs of shells in multiple directions. A core is disposed between the pairs of shells, and the core permits the vertebral endplates to move relative to one another.
1. A total artificial expansible disc, comprising:
at least two pairs of substantially parallel shells, that move in multiple directions defined by at least two axes, in order to occupy a space defined by vertebral endplates;
an expansion device that moves the pairs of shells in multiple directions; and
a core, disposed between the pairs of shells, that permits the vertebral endplates to move relative to one another.
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wherein the moveable shells form a left dorsal pair having rostral and caudal shells and a right dorsal pair having rostral and caudal shells;
wherein the moveable shells form a left ventral pair having rostral and caudal shells and a right ventral pair having rostral and caudal shells; and
wherein the left and right dorsal pairs simultaneously move apart form the left and right ventral pairs.
25. A total artificial expansible disc according to
wherein the left dorsal pair and left ventral pair simultaneously move apart from the right dorsal pair and the right ventral pair.
26. A total artificial expansible disc according to
wherein all the rostral shells simultaneously move apart from the caudal shells.
27. A total artificial expansible disc according to
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30. A total artificial expansible disc according to
31. A method of inserting a total artificial expansible disc, comprising the steps of:
inserting, into a space defined by vertebral endplates, at least two pairs of substantially parallel shells, that move in multiple directions defined by at least two axes;
expanding the pairs of shells in multiple directions; and
permitting the vertebral endplates to move relative to one another, when a core is disposed between the pairs of shells.
32. A method according to
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39. A medical instrument for performing a total discectomy, comprising:
a pituitary rongeur, that is hand operated;
a light emitting device, for illuminating a region at the end of the pituitary rongeur; and
an imaging device, for imaging the illuminated region at the end of the pituitary rongeur.
40. An instrument according to
41. A medical instrument for rotating a control member; comprising:
a rotatable member, disposed at the end of the instrument;
a light emitting device, disposed in the vicinity of the rotatable member for illuminating the control member;
a drive mechanism, for imparting rotational movement to the rotatable member, the drive mechanism including an input member having an axis of rotation and a transfer device for communicating the rotation of the input member to the rotatable member; and
an imaging device for imaging the illuminated region.
42. An instrument according to
43. An instrument according to
1. Field of the Invention
The present invention relates to artificial discs, and more specifically relates to artificial expansible total lumbar and thoracic discs for posterior placement without supplemental instrumentation, and to anterior placement of artificial discs for the cervical, thoracic and lumbar spine.
2. Description of the Relevant Art
Cervical and lumbar total artificial discs are entering the clinical neurosurgical and orthopedic markets. The benefits of these artificial discs are well known. They replace diseased discs, and preserve motion segment mobility. Discogenic and radicular pain are relieved without forfeiting segmental mobility, which is typical of traditional anterior or posterior lumbar fusions. Total artificial disc replacements aim to cover the entire expanse of the disc space because restoration of range of motion is reportedly greatest when roughly 80% of the vertebral endplate is covered. Thus it is only rational, currently to place prosthetic discs anteriorly where access can be easily obtained, and they can be secured by a variety of anterior screw fixations. This technology is adequate for single level disc replacement in the cervical spine. However based on the current anterior cervical prosthetic disc screw fixation methodology its implantation is periodically complicated by screw failures e.g. partial or complete screw pullouts or breaks, and in most designs it is limited to single level replacement. Furthermore, for lumbar total artificial discs, placement is limited to only the L4/5 and L5/S1 disc spaces, and not above, secondary to aortic and vena caval anatomical restraints. Likewise, for the thoracic spine. Thus far no type of thoracic prosthetic disc device has been reported or described. Furthermore, despite the purported safety of placement of the current total lumbar artificial discs, there is a significant risk of retrograde ejaculations in males, and the risk of vascular injury, which although small, is potentially catastrophic if it occurs.
The design of total artificial discs, which began in the 1970's, and in earnest in the 1980's, consists essentially of a core (synthetic nucleus pulposus) surrounded by a container (pseudo-annulus). Cores have consisted of rubber (polyolefin), polyurethane (Bryan-Cervical), silicon, stainless steel, metal on metal, ball on trough design (Bristol-Cervical, Prestige-Cervical), Ultra High Molecular Weight Polyethylene (UHMWPE) with either a biconvex design allowing unconstrained kinematic motion (Link SB Charite-Lumbar), or a monoconvex design allowing semiconstrained motion (Prodisc-Lumbar). There is also a biologic 3-D fabric artificial disc interwoven with high molecular weight polyethylene fiber, which has only been tested in animals. Cervical and lumbar artificial discs are premised on either mechanical or viscoelastic design principles. The advantages of mechanical metal on metal designs including the stainless steel ball on trough design and the UHMWPE prostheses include their low friction, and excellent wear characteristics allowing long term motion preservation. Their major limitation is the lack of elasticity and shock absorption capacity. The favorable features of the viscoelastic prosthetics include unconstrained kinematic motion with flexion, extension, lateral bending, axial rotation and translation, as well as its cushioning and shock absorption capacity. On the other hand, their long term durability beyond ten years is not currently known. Containers have consisted of titanium plates, cobalt chrome or bioactive materials. This history is reviewed and well documented in Guyer, R. D., and Ohnmeiss, D. D. “Intervertebral disc prostheses”, Spine 28, Number 15S, S15-S23, 2003; and Wai, E. K., Selmon, G. P. K. and Fraser, R. D. “Disc replacement arthroplasties: Can the success of hip and knee replacements be repeated in the spine?”, Seminars in Spine Surgery 15, No 4: 473-482, 2003.
It would be ideal if total lumbar artificial discs could be placed posteriorly allowing access to all levels of the lumbar spine. Also one could place these devices posteriorly in thoracic disc spaces through a transpedicular approach. Similarly if these devices can be placed anteriorly particularly in the cervical spine without anterior screw fixation, and custom-fit it for each disc in each individual, the ease of placement would reduce morbidity and allow for multi-level disc replacement. Placement of an artificial disc in the lumbar spine if inserted posteriorly through a unilateral laminotomy by using a classical open microscopic approach or by using a minimally invasive tubular endoscopic approach would significantly reduce the possibility of recurrent disc herniation. If placed without facet joint violation, or with only unilateral mesial facetectomy, and the device can purchase the endplates with spikes there would be no need for supplemental posterior pedicle screw fixation, thus obviating the associated morbidity associated with pedicle screws and bone harvesting. To take it one step further, if artificial lumbar discs can be posteriorly placed successfully and safely throughout the entire lumbar spine, every routine lumbar discectomy could be augmented by artificial disc placement which would simultaneously eliminate discogenic and radicular pain while preserving flexibility. Furthermore by so doing, the probability of recurrent herniation plummets, and subsequently the need for posterior pedicle instrumentation plummets, thereby diminishing overall spinal morbidity, expenditure, and leading to the overall improvement in the quality of life.
Presumably up to now, technology is not focusing on posterior placement of total lumbar prosthetic discs because of inadequate access to the disc space posteriorly. To circumvent this problem others have been working on the posterior placement, not of a total prosthetic disc but of a prosthetic disc nucleus (PDN), or essentially a core without a container (pseudo annulus). PDNs, which are considered post-discectomy augmentations, have consisted of one of the following materials: 1) hydrogel core surrounded by a polyethylene jacket (Prosthetic Disc Nucleus). Two of these devices have to be put in. There is a very high, 38% extrusion rate, 2) Polyvinyl alcohol (Aquarelle), 3) polycarbonate urethane elastomer with a memory coiling spiral (Newcleus), 4) Hydrogel memory coiling material that hydrates to fill then disc space, 5) Biodisc consisting of in-situ injectable and rapidly curable protein hydrogel, 6) Prosthetic Intervertebral Nucleus (PIN) consisting of a polyurethane balloon implant with in-situ injectable rapidly curable polyurethane and 7) thermopolymer nucleus implant. (See the two publications identified above). The approach of posteriorly placing artificial disc cores appears to be flawed in that: 1) there is a high extrusion rate, 2) it lacks good fixation as does total prosthetic devices that are placed anteriorly, 3) it is restricted only to early symptomatically disrupted discs which have only nucleus pulposus but not annulus or endplate pathology, and 4) are contraindicated in discs with an interspace height of less than 5 mm.
FIGS. 4A-M illustrate in detail the mechanical cylinder-spur-gear-spring (CSGS) system incorporated into the cross-connecting 8 titanium shells of the three-dimensional Lumbar/Thoracic prosthesis which enable expansion of the device in x, y and z dimensions. A system of springs is incorporated into the y-axis of the CSGS so as not to hinder the flexibility of the inner core.
FIGS. 9A-E illustrates a sixth embodiment of the expansile total lumbar/thoracic artificial disc implant. This simpler design expands in two not three dimensions (height and width). FIGS. 9A-E therefore represent a two-dimensional expansile prosthesis, using the elastic polymer nuclear design as the prototype.
The Medical Device
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The outer titanium shells Q1-Q8 themselves when ratcheted width-wise have titanium spikes 103 inserting themselves into and purchasing the endplates, thus securing permanent integration into the vertebral endplates. The outer shell titanium surfaces can be treated with hydroxyappetite to facilitate bone incorporation. There is currently available a vertebral ratcheting corpectomy construct which can be ratcheted up vertically until it purchases the rostral and caudal endplates with spikes. There are currently transpedicular/posterior lumbar interbody fusion (T/PLIF) bean shaped constructs, which can be unilaterally inserted into disc spaces. There are currently static total artificial discs (anteriorly placed). The present invention, however, constructs an expansile disc core within a boomerang (bean) shaped titanium construct which can be unilaterally inserted posteriorly into the lumbar and thoracic disc spaces, and can then be ratcheted in vertical and horizontal dimensions to custom fit the implant with the height and length of the individual vertebral body, and ratcheted width wise to conform to the individual width of the a disc space. This total prosthetic device can be secured to the endplates with spike attachments (teeth).
Once the construct 100 has been fine-tuned to conform to the height and length of the vertebral body 104, it can now be ratcheted to conform to the width of the disc space and to be secured to the endplates 105.
FIGS. 4A-M illustrate the relationship of the screws to the internally incorporated expansion device 102 or cylinder-spur-gear-spring (CSGS) system allowing expansion of the prosthesis in all three planes. There are a total of three screws. 111, 112, 113. Any one screw controls the highly adjustable simultaneous movements of the appropriate titanium shells with respect to one another on both rostral and caudal leaflets, in any one given dimension (x, y or z). This is accomplished by internalizing and embedding within the titanium shells Q1-Q8 the expansion device 102 or the gear mesh, a cylinder-spur-gear spring (CSGS) system. This system is designed such that turning screw 111 adjusts the height of the prosthesis by moving the appropriate titanium shells in the z axis. Turning screw 112 adjusts the length of the prosthesis by simultaneously moving the appropriate shells in the x-axis. Finally turning screw 113 leads to simultaneous expansion of the appropriate shells in the y axis. Turning screw 113 ensures the final locking position of the prosthesis by engaging and incorporating the outer spikes into the opposing rostral and caudal vertebral endplates.
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The present invention depends on an expansile disc core 101 that is molded to the titanium shells (Embodiment I). Rubber, silicon, or polyurethane variants are potential candidates for the core. Because there is already well-documented safe experience with elastic polyurethane, this would be the most likely candidate. One skilled in the art would need to select the most appropriate synthetic core, which has the physico-chemical properties of expansion upon release of pressure, while still maintaining elastic resilience
Depending on the feasibility of finding and adapting a core with such properties,
FIGS. 6B(1)-6B(3) illustrate different positions of the inner and outer surfaces of each of the separate three shells per leaflet, which mechanically allow expansion of the implant in x, y, and z dimensions while maintaining a static relationship between the metal on metal ball and trough.
FIGS. 6C(5) and
FIGS. 7A(1)-7A(2) illustrate a fourth alternative embodiment of the lumbar/thoracic design (Embodiment IV). This embodiment is an expansile, custom-fit, mechanical metal on metal, biconvex ultrahigh molecular weight polyethylene (UHMWPE) design. It consists of two leaflets 161, 162, rostral and caudal. Each leaflet in turn consists of three shells; 1) An inner UHMWPE convex shell 163, 2) An intermediate thin titanium plate 164 which is molded to the outer surface of the UHMWPE shell 163, and to the inner surface of the outer moveable titanium shells Q1-Q8, and 3) Outer titanium shells Q1-Q8, four on each leaflet which when ratcheted glide over the intermediate titanium plate 164 allowing expansion of the prosthetic height and length to conform, i.e. custom fit to the individual vertebral endplate.
FIGS. 7B(1)-7B(3) illustrate an axial composite view of the lumbar/thoracic metal on metal, biconvex UHMWPE prosthesis. It illustrates the horizontal and vertical movements of the four titanium shells Q1-Q4 of one leaflet expanding in height and length conforming to the particular vertebral body dimensions.
FIGS. 7C(1) and 7C(2) illustrate the axial views of the outer and inner UHMWPE biconvex shell 163 surfaces. The axial views of the outer and inner surfaces of the outer titanium shells Q1-Q8 are identical to those illustrated in FIGS. 6C(1) and 6C(2). The axial views of the outer and inner surfaces of the intermediate titanium shell is identical to that illustrated in FIGS. 6C(3) and 6C(4).
FIGS. 9B(1) and 9B(2) illustrate the dorsal surgeon's view. Note the central width bar 224 which connects the rostral and caudal titanium shells Q′1-Q′4 dorsally and ventrally. Ratcheting the central screw 225 expands the dorsal width driving the dorsal rostral and caudal shell titanium spikes 203 into the vertebral bodies. Ratcheting a ventral central width screw (not shown) widens the ventral rostral and caudal shells Q′3, Q′4 leading to engagement of spikes 203 into the bone. This screw can be accessed endoscopically as will be described below.
This two-dimensional expansile variation is also applicable to embodiments II, III, IV and V. The two-dimensional expansile variants of embodiments II-V is identical to that described above, except that Embodiments II through V retain their specific cores, as outlined above. To compensate for the lack of length expansion of this design, it would become necessary to design this variant with the appropriate range of differing length options.
a. The Surgical Method
The surgical steps necessary to practice the present invention will now be described.
For posterior lumbar spine prosthetic implantation there are two embodiments of the surgical approach: A) Classic microscopic open lumbar hemilaminotomy and discectomy, and B) Minimally invasive microendoscopic hemilaminotomy and discectomy.
Classic microscopic open hemilaminotomy/discectomy (Approach A):
Step 1. After the adequate induction of general anesthesia, the patient is placed prone on a radiolucent Jackson table. The patient is prepped and draped and using x-ray or fluoroscopic guidance, the correct disc space is identified. The microscope is brought in for appropriate magnification of the operative site. A routine hemilaminotomy is performed as fully described elsewhere.
Step 2. A complete discectomy is performed, and the endplates are curetted thereby preparing the disc space for prosthesis implantation. An endoscope can be employed to verify from a unilateral hemilaminotomy a successful circumferential discectomy.
Step 3. The boomerang shaped artificial lumbar/thoracic disc, embodiment I, II, III, IV, V or VI is unilaterally inserted into the disc space by gently retracting the thecal sac and nerve root, and using a forceps or a similar specifically designed instrument to grab and secure the device. Once the edge of the boomerang is introduced into the disc space, it is then curvalinearly further inserted into the disc space underneath the thecal sac and nerve root, aligning the horizontal axis of the prosthesis with the horizontal axis of the vertebral endplate.
Step 4. Once the construct is beneath the thecal sac, using live fluoroscopy, adjust (ratchet) the construct height (Screw 1) until the outer titanium shells conform to the individual vertebral endplate height. Specifically designed screwdrivers, straight or right-angled, of appropriate length and screw fittings are employed.
Step 5. Now again using live fluoroscopy adjust (ratchet) the length of the titanium shells until the prosthesis conforms to the desired individual length of the vertebral body (Screw 2). In embodiment VI there is no length adjustment. Measurements of the length of the vertebral bodies will determine the selection of prefabricated prostheses of different lengths.
Step 6. Now under direct microscopic or endoscopic visualization adjust (ratchet) the prosthesis width screw. As the width is expanded conforming to the precise disc width, the titanium outer spikes will engage, and then penetrate the bony endplates. Once total spike-bone penetration has occurred with complete purchase of the spikes, the implant is now safely secured in its position, and custom fit with respect to all x, y and z planes. Final lateral and anterior-posterior fluoroscopic images are then obtained to verify the precision fit. Verification of prosthetic purchase to the endplates can be performed by grasping and testing the prosthesis with a forceps verifying lack of motion. For Embodiment VI, once width expansion has been achieved, and the spikes 200 incorporated into the bone, the width bars 224, 228 are removed by turning screws 225, 229 counter clockwise (see FIGS. 9C(1) and 9C(2)).
B) Posterior Lumbar Minimally Invasive Microendoscopic Lumbar Hemilaminotomy (Approach B).
Step 1. After the adequate induction of general anesthesia the patient is placed prone on a radiolucent Jackson table. The patient is prepped and draped. Then using fluoroscopic guidance a minimally invasive microendoscopic approach is used to gain access to the appropriate disc space as described in detail elsewhere. In brief, serial tubular dilators are sequentially placed in the dorsal musculature and fascia through which a working channel is created and an endoscope is docked on the appropriate laminar landmark.
Step 2. Through the working channel a discectomy is performed. The endoscope can be repositioned to verify complete discectomy.
Steps 3-6 are then performed identically to steps 3-6 mentioned above (Approach A; Posterior lumbar placement using an open classical microscopic technique).
The steps for anterior implantation of lumbar/thoracic prosthetic devices, embodiments I, II, III, IV, V or VI into the lumbar L4/5 and L5/S1 disc interspaces will now be outlined.
Step 1. After the adequate induction of general anesthesia the patient is placed supine on the radiolucent Jackson table. The patient is prepped and draped. A General abdominal surgeon creates an infraumbilical incision, and then using a retroperitoneal or transperitoneal approach as described in detail elsewhere, the L4/5 or L5/S1 disc spaces are identified using fluoroscopic or x-ray guidance.
Step 2. The microscope is now brought in and a complete discectomy is performed which can be verified under direct microscopic vision.
Step 3. The prosthetic disc, embodiment I, II, III, IV, V or VI is placed with forceps directly into the disc space with the horizontal axis of the device aligned with the horizontal axis of the vertebral body. The convex lower aspect of the device is placed above the ventral surface of the thecal sac. The dorsal upper aspect of the prosthesis with its ratcheting screws is in the surgeon's field.
Step 4. The prosthesis is secured with a forceps, and using fluoroscopic guidance, the prosthesis height is expanded to custom fit the vertebral endplate by ratcheting screw 1 with the appropriately designed screwdriver.
Steps 5 and 6 are now identical to steps 5 and 6 used for posterior lumbar placement (Approach A).
The surgical steps necessary to practice the present invention for posterior implantation of the lumbar/thoracic artificial disc, embodiment I, I, III, IV V or VI into the thoracic disc interspace will now be described.
Step 1. After the adequate induction of general anesthesia the patient is positioned prone on a radiolucent Jackson table. The patient is prepped and draped. Then utilizing fluoroscopic or x-ray guidance, the correct and relevant spinous processes and posterior elements are identified. Then using a standard extracorporeal, transpedicular approach, the rib head is removed and the pedicle drilled overlying the appropriate disc space as fully described in detail elsewhere.
Step 2. The microscope is now brought in for appropriate magnification. The discectomy is performed routinely. An endoscope can be employed to verify complete circumferential discectomy.
Step 3. The lumbar/thoracic prosthesis, embodiment I, II, III, IV, V or VI is introduced into the disc space using a forceps aligning the horizontal axis of the device with the horizontal axis of the vertebral body. The concave surface of the prosthesis is now placed several millimeters under the spinal cord. Specifically designed right-angled screwdrivers, are introduced ventral to the cord, and custom fit the prosthesis to the vertebral endplate by ratcheting the length, height and width of the prosthesis.
Steps 4-6 are now identical to steps 4-6 of the posterior lumbar surgical approach A.
The surgical steps necessary to practice the present invention for the anterior implantation of artificial discs, embodiment I, II, III, IV, V or VI into the thoracic spine will now be described.
Step 1. After the adequate induction of general anesthesia, the patient is positioned on a beanbag in the lateral position, with the right or left side up depending on the side of the disc herniation. A thoracic surgeon now performs a thoracotomy, the lung is deflated, and using fluoroscopic or x-ray guidance, the appropriate disc space is identified and visualized as described in detail elsewhere.
Step 2. The microscope is now brought in and a discectomy is performed routinely. Complete and adequate discectomy is confirmed under direct visualization.
Step 3. The lumbar/thoracic prosthesis, embodiment I, II, III, IV, V or VI is placed with forceps directly into the disc space aligning the horizontal axis of the device with the horizontal axis of the vertebral body. The convex lower surface of the device is placed under the ventral surface of the cord. The concave dorsal surface is facing the surgeon such that there is direct visualization of the ratchetable screws.
Steps 4-6 are now identical to steps 4-6 of the posterior lumbar placement approach A.
FIGS. 11A(1)-11D(3) illustrate an alternative cervical disc embodiment or prosthetic disc 400 which includes a core similar to embodiments I, II, III, IV and V, and it is specifically configured for anterior implantation. These figures illustrate the axial views of this cervical disc alternative embodiment. They illustrate expansion of prosthetic cervical disc height and length. For the cross-sectional axial views of all outer and inner surfaces of the multiple shells, and for the mechanical infrastructure (CSGS), and for the dorsal surgeons view illustrating prosthetic width expansion refer to the corresponding figures illustrating these views for lumbar/thoracic disc alternative embodiments, embodiments I, II, III, IV and V (
The surgical steps necessary to practice the present invention for anterior implantation of prosthetic discs, embodiment I, II, III, IV, V, or VI into the cervical spine will now be described.
Step 1. After the adequate induction of general anesthesia, the patient is positioned supine on the radiolucent Jackson table. An interscapular roll is placed and the patient's neck is prepped and draped. A horizontal incision is made overlying the appropriate disc interspace with the aide of fluoroscopy or x-ray. The platysma is divided, the esophagus and trachea retracted, the anterior spine exposed, and the appropriate disc space verified radiographically as described in detail elsewhere.
Step 2. The microscope is brought in for appropriate magnification of the operative site. A complete discectomy is performed under direct visualization.
Step 3. The cervical prosthesis embodiment, embodiment I, II, III, IV, V or VI is placed with a forceps directly into the disc space aligning the horizontal axis of the device with the horizontal axis of the vertebral body. The dorsal surface of the prosthesis with ratchetable screws is facing the surgeon. The ventral surface of the prosthesis is above the cervical spinal cord.
Step 4. Once the prosthesis is in the disc space above the spinal cord, using fluoroscopic guidance screw 1 is rotated thereby ratcheting the outer titanium shells until they conform to the individual vertebral plate height.
Steps 5 and 6 are now identical to steps 5 and 6 of posterior placement of lumbar/thoracic artificial discs—approach A.
Because the current embodiment of cervical prosthetic discs lack anterior screw fixation, multi-level disc replacements can now be entertained. Furthermore with respect to all the lumbar, thoracic and cervical prosthetic disc embodiments surgically implanted via posterior or anterior approaches, it is unnecessary to have multiple sizes of each prosthesis. For embodiments I-V one lumbar/thoracic prosthesis of each of the five design embodiments can be custom fit for the individual lumbar or thoracic disc space. One cervical prosthesis of each particular design embodiment can be custom fit for the individual cervical disc space. For embodiment VI only two or maximum three length options can be chosen. The ease of placement diminishes operating room time and decreases morbidity and mortality. This feature of Embodiments I II III IV, V and VI is unique compared to all other designs to date.
The present invention may provide an effective and safe technique that overcomes the problems associated with current techniques, and for most degenerative disc conditions it could replace pedicle screw instrumentation and fusions.