Interspinous process implant with slide-in distraction piece and method of implantation

Systems and method in accordance with embodiments of the present invention can includes an implant having an initiating piece and a distraction piece. The initiating piece can include a lower distraction element, a second wing, a lower portion of a spacer, and a lower portion of a first wing. The initiating piece can be positioned such that an interspinous ligament of the targeted motion segment is disposed between the first and second wing. The distraction piece can include an upper distraction element, an upper portion of the spacer, and an upper portion of the first wing, and can be mated with the initiating piece by mating a rail of the distraction piece with a slot of the initiating piece, thereby disposing the implant between adjacent spinous processes.

TECHNICAL FIELD

This invention relates to interspinous process implants.

BACKGROUND OF THE INVENTION

The spinal column is a bio-mechanical structure composed primarily of ligaments, muscles, vertebrae and intervertebral disks. The bio-mechanical functions of the spine include: (1) support of the body, which involves the transfer of the weight and the bending movements of the head, trunk and arms to the pelvis and legs, (2) complex physiological motion between these parts, and (3) protection of the spinal cord and the nerve roots.

As the present society ages, it is anticipated that there will be an increase in adverse spinal conditions which are characteristic of older people. By way of example only, with aging comes an increase in spinal stenosis (including, but not limited to, central canal and lateral stenosis), and facet arthropathy. Spinal stenosis results in a reduction foraminal area (i.e., the available space for the passage of nerves and blood vessels) which compresses the cervical nerve roots and causes radicular pain. Humpreys, S. C. et al.,Flexion and traction effect on C5-C6foraminal space, Arch. Phys. Med. Rehabil., vol. 79 at 1105 (September 1998). Another symptom of spinal stenosis is myelopathy, which results in neck pain and muscle weakness. Id. Extension and ipsilateral rotation of the neck further reduces the foraminal area and contributes to pain, nerve root compression and neural injury. Id.; Yoo, J. U. et al.,Effect of cervical spine motion on the neuroforaminal dimensions of human cervical spine, Spine, vol. 17 at 1131 (Nov. 10, 1992). In contrast, neck flexion increases the foraminal area. Humpreys, S. C. et al., at 1105.

Pain associated with stenosis can be relieved by medication and/or surgery. It is desirable to eliminate the need for major surgery for all individuals, and in particular, for the elderly.

Accordingly, a need exists to develop spine implants that alleviate pain caused by spinal stenosis and other such conditions caused by damage to, or degeneration of, the cervical spine. Such implants would distract, or increase the space between, the vertebrae to increase the foraminal area and reduce pressure on the nerves and blood vessels of the cervical spine.

A further need exists for development of a minimally invasive surgical implantation method for cervical spine implants that preserves the physiology of the spine.

Further, a need exists for an implant that accommodates the distinct anatomical structures of the spine, minimizes further trauma to the spine, and obviates the need for invasive methods of surgical implantation. Additionally, a need exists to address adverse spinal conditions that are exacerbated by spinal extension.

DETAILED DESCRIPTION

FIGS. 1 and 2illustrate an implant100in accordance with an embodiment of the present invention. The implant100comprises a wing130, a spacer120, and a lead-in tissue expander (also referred to herein as a distraction guide)110. The distraction guide110in this particular embodiment is wedge-shaped, i.e., the implant has an expanding cross-section from a distal end of the implant102to a region104where the guide110joins with the spacer120(referencing for the figures is based on the point of insertion of the implant between spinous processes). As such, the distraction guide functions to initiate distraction of the soft tissue and the spinous processes when the implant100is surgically inserted between the spinous processes. It is to be understood that the distraction guide110can be pointed and the like, in order to facilitate insertion of the implant100between the spinous processes of adjacent cervical vertebrae. It is advantageous that the insertion technique disturb as little of the bone and surrounding tissue or ligaments as possible in order to reduce trauma to the site and promote early healing, and prevent destabilization of the normal anatomy. In the embodiment ofFIGS. 1 and 2, there is no requirement to remove any of the bone of the spinous processes and no requirement to sever or remove from the body ligaments and tissues immediately associated with the spinous processes. For example, it is unnecessary to sever the ligamentum nuchae (supraspinous ligament), which partially cushions the spinous processes of the upper cervical vertebrae.

As can be seen inFIGS. 1-3, the spacer120can be teardrop-shaped in cross-section perpendicular to a longitudinal axis125of the implant100. In this way, the shape of the spacer120can roughly conform to a wedge-shaped space, or a portion of the space, between adjacent spinous processes within which the implant100is to be positioned. In other embodiments, the spacer120, can have alternative shapes such as circular, wedge, elliptical, ovoid, football-shaped, and rectangular-shaped with rounded corners and other shapes, and be within the spirit and scope of the invention. The shape of the spacer120can be selected for a particular patient so that the physician can position the implant100as close as possible to the anterior portion of the surface of the spinous process. The shape selected for the spacer120can affect the contact surface area of the implant100and the spinous processes that are to be subject to distraction. Increasing the contact surface area between the implant100and the spinous processes can distribute the force and load between the spinous frame and the implant100.

As can be seen inFIGS. 1 and 2, the wing130in an embodiment can be elliptically shaped in cross-section perpendicular to the longitudinal axis125. The dimensions of the wing130can be larger than that of the spacer120, particularly along the axis of the spine, and can limit or block lateral displacement of the implant100in the direction of insertion along the longitudinal axis125. As illustrated in the embodiment ofFIG. 3, the wing130can alternatively have other cross-sectional shapes, such as teardrop, wedge, circular, ovoid, football-shaped, and rectangular-shaped with rounded corners and other shapes, and be within the spirit and scope of the invention. The wing130has an anterior portion138and a posterior portion136.

In other embodiments, the implant100can include two wings, with a second wing160(shown inFIG. 4) separate from the distraction guide110, spacer120and first wing130. The second wing160can be connected to the distal end of the spacer120. The second wing160, similar to the first wing130, can limit or block lateral displacement of the implant100, however displacement is limited or blocked in the direction along the longitudinal axis125opposite insertion. When both the first wing130and the second wing160are connected with the implant100and the implant100is positioned between adjacent spinous processes, a portion of the spinous processes can be sandwiched between the first wing130and the second wing160, limiting any displacement along the longitudinal axis125.

As can be seen inFIG. 4, the second wing160can be teardrop-shaped in cross-section. The wider end166of the second wing160is the posterior end and the narrower end168of the second wing160is the anterior end. Unlike the first wing130, however, an opening164is defined within the second wing160, the opening164being at least partially circumscribed by a lip162that allows the second wing160to pass over the distraction guide110to meet and connect with the spacer120. The second wing160can be secured to the spacer120once the second wing160is properly positioned. The second wing160can be connected with the implant after the implant100is positioned between the spinous processes.

It is to be understood that the implant can be made in two pieces. The first piece can include the first wing130, the spacer120, and the distraction guide110. The second piece can include the second wing160. Each piece can be manufactured using technique known in the art (e.g., machining, molding, extrusion). Each piece, as will be more fully discussed below, can be made of a material that is bio-compatible with the body of the patient. An implant can be formed with multiple pieces and with the pieces appropriately joined together, or alternatively, an implant can be formed as one piece or joined together as one piece.

Further embodiments of implants in accordance with the present invention are depicted inFIGS. 5-7. In such embodiments, the spacer220can be rotatable about the longitudinal axis225relative to the first wing130, or relative to the first wing130and a second wing160where two wings are used. The spacer220can be rotatable or fixed relative to the distraction guide110. Where the spacer220is rotatable relative to the distraction guide110, the spacer220can include a bore222running the length of the longitudinal axis225, and a shaft224inserted through the bore222and connecting the distraction guide110with the first wing130. It can be advantageous to position any of the implants taught herein as close as possible to the vertebral bodies. The rotatable spacer220can rotate to conform to or settle between adjacent spinous processes as the implant200is inserted and positioned during implantation, so that on average the contact surface area between the spacer220and the spinous processes can be increased over the contact surface area between a fixed spacer120and the spinous processes. Thus, the rotatable spacer220can improve the positioning of the spacer220independent of the wings130,160relative to the spinous processes. The embodiment ofFIG. 6includes a teardrop-shaped first wing130, and a teardrop-shaped second wing160, similar to the second wing160depicted in the embodiment ofFIG. 3. As discussed below, the shape of the wings130,160inFIGS. 3 and 6is such that the implants100,200accommodate the twisting of the cervical spine along its axis, for example, as the head of a patient turns from side to side.

FIG. 8is a perspective view andFIG. 9Ais an end view of still another embodiment of an implant in accordance with the present invention, wherein the posterior portion336of the teardrop-shaped first wing330is truncated, making the first wing330more ovoid in shape. In this configuration, the anterior portion138of the first wing330can be longer than the truncated posterior end336of the first wing330. As in previous embodiments, the spacer120can alternatively be a rotatable spacer rather than a fixed spacer.FIG. 9Billustrates a second wing360for use with such implants300, the second wing360having a truncated posterior end366. Truncation of the posterior ends336,366of the first and second wings330,360can reduce the possibility of interference of implants300having such first and second wings330,360positioned between spinous processes of adjacent pairs of cervical vertebrae, e.g., implants between cervical vertebrae five and six, and between cervical vertebrae six and seven. During rotation of the neck, the spinous process move past each other in a scissor-like motion. Each cervical vertebra can rotate relative to the next adjacent cervical vertebra in the general range of about 6°-12°. In addition, about 50 percent of the rotational movement of the neck is accomplished by the top two neck vertebrae. Thus, such embodiments can accommodate neck rotation without adjacent embodiments interfering with each other.

With respect to the prior embodiments which have first and second wings130,160, the second wing160, can be designed to be interference-fit onto the spacer120(where the spacer is fixed) or a portion of the distraction guide110adjacent to the spacer120(where the spacer is rotatable). Where the second wing160is interference-fit, there is no additional attachment device to fasten the second wing160relative to the remainder of the implant. Alternatively, various fasteners can be used to secure the second wing relative to the remainder of the implant. For example,FIGS. 10-12illustrate an embodiment of an implant400including a teardrop-shaped second wing460having a bore463through a tongue461at the posterior end of the second wing460. The bore463is brought into alignment with a corresponding bore440on the spacer120when the second wing460is brought into position by surgical insertion relative to the rest of the implant400. A threaded screw442can be inserted through the aligned bores463,440in a posterior-anterior direction to secure the second wing460to the spacer120. The direction of insertion from a posterior to an anterior direction has the screw442engaging the bores463,440and the rest of the implant400along a direction that is generally perpendicular to the longitudinal axis125. This orientation is most convenient when the surgeon is required to use a screw442to secure the second wing460to the rest of the implant400. Other securing mechanisms using a member inserted into corresponding bores463,440on the spacer120and second wing460are within the spirit of the invention. It should be understood that a rotatable spacer220also can be accommodated by this embodiment. With a rotatable spacer220, the second wing460would be attached to a portion of the distraction guide110that is located adjacent to the rotatable spacer220.

FIGS. 13A-14Bdepict a further embodiment500wherein the second wing560is secured to the spacer120by a mechanism including a flexible hinge565, with a protrusion561on the end of the hinge565adjacent to the lip562of the opening564defined by portions of the second wing560. The securing mechanism also encompasses an indentation540on the spacer120, wherein the indentation540accommodates the protrusion561on the end of the flexible hinge565. During surgery, after insertion of the distraction guide110, spacer120, and first wing130, the second wing560is received over the distraction guide110and the spacer120. As the second wing560is received by the spacer120, the flexible hinge565and its protrusion561deflect until the protrusion561meets and joins with the indentation540in the spacer120, securing the second wing560to the spacer120. Again in embodiments where the spacer can rotate, the indentation540is located on an end of the distraction guide110that is adjacent to the rotatable spacer220. With respect to the flexible hinge565, this hinge is in a preferred embodiment formed with the second wing560and designed in such a way that it can flex as the hinge565is urged over the distraction guide110and the spacer120and then allow the protrusion561to be deposited into the indentation540. Alternatively, it can be appreciated that the indentation540can exist in the second wing560and the flexible hinge565and the protrusion561can exist on the spacer120in order to mate the second wing560to the spacer120. Still alternatively, the flexible hinge565can be replaced with a flexible protrusion that can be flexed into engagement with the indentation540in the embodiment with the indentation540in the spacer120or in the embodiment with the indentation540in the second wing560. One of ordinary skill in the art will appreciate the myriad different ways with which the second wing can be mated with the implant.

FIGS. 15A-16illustrate an embodiment of an implant600wherein anterior ends of a first wing630and second wing660flare out at an angle away from the spacer120and away from each other. The cervical spinous processes are themselves wedge-shaped when seen from a top view. The first wing630and second wing660flare out so that the implant600can roughly conform with the wedge shape of the spinous processes, allowing the implant600to be positioned as close as possible to the vertebral bodies of the spine where the load of the spine is carried. The first and second wings630,660are positioned relative to the spacer, whether the spacer is fixed120or rotatable220, so that the wings flare out as the wings approach the vertebral body of the spine.FIG. 15Bis a top view of the implant600ofFIG. 15Aremoved from proximity with the spinous processes. The first wing630is aligned at an angle with respect to an axis along the spinous processes perpendicular to the longitudinal axis (also referred to herein as the plane of symmetry). In one embodiment, the angle is about 30°, however, the angle θ can range from about 15° to about 45°. In other embodiments, other angles outside of this range are contemplated and in accordance with the invention. Likewise, the second wing660can be aligned along a similar, but oppositely varying range of angles relative to the plane of symmetry.

As described above in reference toFIG. 4, the second wing660defines an opening which is outlined by a lip. As is evident, the lip can be provided at an angle relative to the rest of the second wing660so that when the lip is urged into contact with the spacer120, the second wing660has the desired angle relative to the spacer120. As discussed above, there are various ways that the second wing660is secured to the spacer120.FIG. 15Adepicts a top view of one such implant600placed between the spinous processes of adjacent cervical vertebrae.FIG. 16is a top view illustrating two layers of distracting implants600with flared wings630,660.

Systems and methods in accordance with the present invention can include devices that can be used in cooperation with implants of the present invention.FIG. 17illustrates “stops” (also referred to herein as “keeps”)656, which are rings of flexible biocompatible material, which can be positioned around the spinous processes of adjacent cervical vertebrae and located posteriorly to the implant600. The keeps656can prevent posterior displacement of implants. In one embodiment, the keeps can include a ring having a slit658. The keeps656can be somewhat sprung apart, so that the keep656can be fit over the end of the spinous process and then allowed to spring back together in order to hold a position on the spinous process. The keep656can act as a block to the spacer120in order to prevent the implant600from movement in a posterior direction.

FIGS. 18A and 18Bare perspective end views of an alternative embodiment of an implant800in accordance with the present invention. The implant800can include an initiating piece804and a slide-in distraction piece802that can be slidably coupled with the initiating piece804. The initiating piece804and the slide-in distraction piece802, when positioned between adjacent spinous processes and coupled together as shown inFIG. 18B, has a saddle shape including a first wing830and a second wing860that straddle one of the adjacent spinous processes. The implant800approximates implants as shown above inFIGS. 1-17. For example, the implant800includes the first wing830at a proximal end of the implant800, a fixed spacer820extending from the first wing830, the second wing860extending from the spacer820so that the spacer820is disposed between the first wing830and the second wing860, and a distraction guide810at a distal end816of the implant800.

The initiating piece804includes a slot884within a lower sliding surface888that extends through a substantial portion of the length of the initiating piece804, the slot884being adapted to receive a rail882of the slide-in distraction piece802. The slot884can optionally include a flange or some other structure to retain the rail882within the slot884. One of the slot884and the rail882can further optionally include a recess (not shown) adapted to receive a catch (not shown) of the other of the slot884and the rail882so that when the catch passes over the recess, the catch is extended, locking the distraction piece802in place, and limiting or blocking movement along the longitudinal axis825.

As shown, the initiating piece804includes a first tab894extending from the first wing834, the first tab894including a first perforation893. The distraction piece802likewise includes a second tab892including a second perforation891adapted to be aligned with the first perforation893so that when the slide-in distraction piece802is mated with the initiating piece804and the rail882is seated within the slot884, the first perforation893and the second perforation891are aligned and can be pegged together so that relative movement between the distraction piece802and the initiating piece804is limited or substantially blocked. In other embodiments, the initiating piece804and distraction piece802need not include tabs892,894, for example where a catch and recess of the slot and rail is employed. Further, where a first tab894or other structure protrudes from the initiating piece804, the distraction piece802can include a slot for receiving the tab894, rather than a second tab892abutting the first tab894. As will be obvious to one of ordinary skill in the art, tabs having myriad different shapes and sizes can extend from one or both of the initiating piece804and the distraction piece802, and perforations having myriad different shapes and sizes can be formed within such tabs to limit relative movement between the initiating piece804and the distraction piece802. Further, myriad different locking mechanisms (e.g., a tab and slot arrangement) can be employed with one or both of the initiating pieces804and the distraction piece802to limit relative movement. Embodiments of implants800in accordance with the present invention are not intended to be limited to those arrangements shown inFIGS. 18A-19E.

The initiating piece804includes a lower distraction element814having a contact surface that tapers to the distal end816from above as well as below the distal end816so that the lower distraction element814has a “V” shape in cross-section along an axis of the spine. The initiating piece804further includes a first portion834of the first wing, the second wing860, and a lower portion824of the spacer. In an embodiment, the portions824,834and the second wing860can be integrally formed with the lower distraction element814, thereby avoiding discontinuities in a lower sliding surface888of the initiating piece804. A relatively continuous sliding surface888with smooth transitions improves ease of implantation and minifies obstruction of the initiating piece804by the adjacent spinous processes and/or related tissues. It is preferable that the initiating piece804include smooth transitions between the lower distraction element814, the second wing860, and the lower portion824of the spacer, as such transitions can increase obstruction of implant movement during implantation. The lower sliding surface888of the initiating piece804is substantially flat and preferably smooth to ease receipt of the rail882within the slot884.

As described above, the slide-in distraction piece802includes the rail882extending over a substantial portion of the length of the distraction piece802, roughly corresponding to a length of the slot884of the initiating piece804within which the rail882is adapted to be received. The height of the rail882from the upper sliding surface886approximately corresponds to the depth of the slot884so that when the rail882is received within the slot884, the upper sliding surface886of the distraction piece802is substantially flush with the lower sliding surface888. In other embodiments, a gap can exist between the upper sliding surface886and the lower sliding surface888. As described above, the surface of the rail882can include a catch (or a recess) arranged along the length of the rail882so that the catch (or recess) roughly corresponds to the recess (or catch) disposed within the slot884. In other embodiments, the rail882and slot884need not include a catch and recess arrangement, but rather the initiating piece804and the distraction piece802can be held in relative position along the longitudinal axis825when the first and second holes891,893are pegged together. In still other embodiments, some other mechanism can be used to limit or block relative movement of the initiating piece804and the distraction piece802.

The distraction piece802further includes an upper distraction element812, a second portion832of the first wing and an upper portion822of the spacer. The upper distraction element812has a contact surface that tapers at a distal end of the distraction piece802so that the upper distraction element812has a ramp shape. The second portion832of the first wing can have a shape that roughly conforms to the shape of the first portion834of the first wing so that when the distraction piece802is coupled to the initiating piece804, the first and second portions832,834form a first wing830, as shown inFIG. 18B. The upper portion822of the spacer can have a thickness greater or less than that of the lower portion824of the spacer. As shown, the upper portion822is thicker than the lower portion824. By minifying the thickness of the lower portion824, distraction of the adjacent spinous processes during implantation of the initiation piece804can be minified to cause less distraction at the surgical site by the second wing860as the second wing860is urged between the adjacent spinous processes. Alternatively, a plurality of distraction pieces802can be provided each having an upper portion822of the spacer having a different thickness. Thus the doctor can select the appropriate distraction piece802for the amount of distraction desired. As with the lower sliding surface888, the upper sliding surface886of the distraction piece802is substantially flat and preferably smooth to ease positioning of the rail882within the slot884. Embodiments of systems in accordance with the present invention can include a initiating piece804and a plurality of distraction pieces802, the distraction pieces802having a variety of thicknesses. In such a system, a distraction piece802can be chosen so that the overall spacer820thickness is suitable for the patient and the motion segment targeted.

FIG. 19Ais a posterior view of the initiating piece804positioned adjacent to the interspinous ligament6. As can be seen, the initiating piece804has a maximum thickness from the lower sliding surface888to the second wing860. As the initiating piece804is urged into the interspinous ligament6, the lower distraction element814pierces and/or distracts the fibers of the interspinous ligament6. As shown inFIG. 19B, the initiating piece804is further urged through the interspinous ligament6so that the second wing860passes between the adjacent spinous processes2,4and can distract the space between the adjacent spinous processes2,4to accommodate the second wing860. The distraction of the space between the adjacent spinous processes is reduced by positioning the initiating piece804prior to coupling the distraction piece802to the initiating piece804. Referring toFIG. 19C, the initiating piece804is further urged through the interspinous ligament6so that the lower portion824of the spacer is positioned between the adjacent spinous processes2,4. The second wing860and the first portion834of the first wing straddle the lower spinous process4. Once the initiating piece804is properly positioned, the rail882of the distracting piece802can be positioned within the proximal end of the slot884, as shown inFIG. 19D. The distraction piece804can then be urged along the lower sliding surface888so that the upper distraction element812distracts the space between the adjacent spinous processes. As shown inFIG. 19E, the initiating piece804is further urged along the lower sliding surface888until the distraction piece802is mated with the initiating piece804.

Materials For Use In Implants Of The Present Invention

In some embodiments, the implant can be fabricated from medical grade metals such as titanium, stainless steel, cobalt chrome, and alloys thereof, or other suitable implant material having similar high strength and biocompatible properties. Additionally, the implant can be at least partially fabricated from a shape memory metal, for example Nitinol, which is a combination of titanium and nickel. Such materials are typically radiopaque, and appear during x-ray imaging, and other types of imaging. Implants in accordance with the present invention, and/or portions thereof can also be fabricated from somewhat flexible and/or deflectable material. In these embodiments, the implant and/or portions thereof can be fabricated in whole or in part from medical grade biocompatible polymers, copolymers, blends, and composites of polymers. A copolymer is a polymer derived from more than one species of monomer. A polymer composite is a heterogeneous combination of two or more materials, wherein the constituents are not miscible, and therefore exhibit an interface between one another. A polymer blend is a macroscopically homogeneous mixture of two or more different species of polymer. Many polymers, copolymers, blends, and composites of polymers are radiolucent and do not appear during x-ray or other types of imaging. Implants comprising such materials can provide a physician with a less obstructed view of the spine under imaging, than with an implant comprising radiopaque materials entirely. However, the implant need not comprise any radiolucent materials.

One group of biocompatible polymers are the polyaryletherketone group which has several members including polyetheretherketone (PEEK), and polyetherketoneketone (PEKK). PEEK is proven as a durable material for implants, and meets the criterion of biocompatibility. Medical grade PEEK is available from Victrex Corporation of Lancashire, Great Britain under the product name PEEK-OPTIMA. Medical grade PEKK is available from Oxford Performance Materials under the name OXPEKK, and also from CoorsTek under the name BioPEKK. These medical grade materials are also available as reinforced polymer resins, such reinforced resins displaying even greater material strength. In an embodiment, the implant can be fabricated from PEEK 450G, which is an unfilled PEEK approved for medical implantation available from Victrex. Other sources of this material include Gharda located in Panoli, India. PEEK 450G has the following approximate properties:

It should be noted that the material selected can also be filled. Fillers can be added to a polymer, copolymer, polymer blend, or polymer composite to reinforce a polymeric material. Fillers are added to modify properties such as mechanical, optical, and thermal properties. For example, carbon fibers can be added to reinforce polymers mechanically to enhance strength for certain uses, such as for load bearing devices. In some embodiments, other grades of PEEK are available and contemplated for use in implants in accordance with the present invention, such as 30% glass-filled or 30% carbon-filled grades, provided such materials are cleared for use in implantable devices by the FDA, or other regulatory body. Glass-filled PEEK reduces the expansion rate and increases the flexural modulus of PEEK relative to unfilled PEEK. The resulting product is known to be ideal for improved strength, stiffness, or stability. Carbon-filled PEEK is known to have enhanced compressive strength and stiffness, and a lower expansion rate relative to unfilled PEEK. Carbon-filled PEEK also offers wear resistance and load carrying capability.

As will be appreciated, other suitable similarly biocompatible thermoplastic or thermoplastic polycondensate materials that resist fatigue, have good memory, are flexible, and/or deflectable, have very low moisture absorption, and good wear and/or abrasion resistance, can be used without departing from the scope of the invention. As mentioned, the implant can be comprised of polyetherketoneketone (PEKK). Other material that can be used include polyetherketone (PEK), polyetherketoneetherketoneketone (PEKEKK), polyetheretherketoneketone (PEEKK), and generally a polyaryletheretherketone. Further, other polyketones can be used as well as other thermoplastics. Reference to appropriate polymers that can be used in the implant can be made to the following documents, all of which are incorporated herein by reference. These documents include: PCT Publication WO 02/02158 A1, dated Jan. 10, 2002, entitled “Bio-Compatible Polymeric Materials;” PCT Publication WO 02/00275 A1, dated Jan. 3, 2002, entitled “Bio-Compatible Polymeric Materials;” and, PCT Publication WO 02/00270 A1, dated Jan. 3, 2002, entitled “Bio-Compatible Polymeric Materials.” Other materials such as Bionate®, polycarbonate urethane, available from the Polymer Technology Group, Berkeley, Calif., may also be appropriate because of the good oxidative stability, biocompatibility, mechanical strength and abrasion resistance. Other thermoplastic materials and other high molecular weight polymers can be used.

It is to be understood that embodiments in accordance with the present invention can be constructed without a pliant material. It is also to be understood that the embodiments in accordance with the present invention can have other dimensions.

Methods for Implanting Interspinous Implants

A minimally invasive surgical method for implanting an implant400in the cervical spine is disclosed and taught herein. In this method, as shown inFIG. 20A, preferably a guide wire80is inserted through a placement network or guide90into the neck of the implant recipient. The guide wire80is used to locate where the implant is to be placed relative to the cervical spine, including the spinous processes. Once the guide wire80is positioned with the aid of imaging techniques, an incision is made on the side of the neck so that an implant in accordance with an embodiment of the present invention, can be positioned in the neck thorough an incision and along a line that is about perpendicular to the guide wire80and directed at the end of the guide wire80. In one embodiment, the implant can be a sized implant400(i.e., having a body that is not distractable), such as described above inFIGS. 1-17and including a distraction guide110, a spacer120, and a first wing130. The implant400is inserted into the neck of the patient. Preferably during insertion, the distraction guide110pierces or separates the tissue without severing the tissue.

Once the implant400is satisfactorily positioned, a second wing460can be optionally inserted along a line that is generally colinear with the line over which the implant400is inserted but from the opposite side of the neck. The anatomy of the neck is such that it is most convenient and minimally invasive to enter the neck from the side with respect to the implant400and the second wing460. The second wing460is mated to the implant and in this particular embodiment, the second wing460is attached to the implant400by the use of a fastener, for example by a screw442. Where a screw is used, the screw442can be positioned using a screw driving mechanism that is directed along a posterior to anterior line somewhat parallel to the guide wire80. This posterior to anterior line aids the physician in viewing and securing the second wing460to the implant. The second wing460is positioned so that a bore463formed in a lip461of the second wing460is aligned with a bore440of the implant400, as described above. The screw442is positioned within both bores and secured, at least, to the bore440of the implant400. In other embodiments, the second wing can be interference fit with the implant, as described above, or fastened using some other mechanism, such as a flexible hinge and protrusion.

In other embodiments of methods in accordance with the present invention, the implant can include an initiating piece804and a distraction piece802, such as described above in FIGS.18A-19E. In such embodiments, as shown inFIG. 20B, preferably a guide wire80is inserted through a placement network or guide90into the neck of the implant recipient (as shown and described above). Once the guide wire80is positioned with the aid of imaging techniques, an incision is made on the side of the neck so that an initiating piece804of the implant800can be positioned in the neck thorough an incision and along a line that is about perpendicular to the guide wire80and directed at the end of the guide wire. The initiating piece804can include a lower distraction element814, the second wing860, a lower portion824of the spacer, and a lower portion834of the first wing. The implant800is inserted into the neck of the patient, between adjacent spinous processes. Preferably during insertion, the lower distraction element814pierces or separates the tissue without severing the tissue, and the implant800is positioned so that the upper portion824of the spacer is disposed between the adjacent spinous processes.

Once the initiating piece804is satisfactorily positioned, a distracting piece802can be inserted along a line that is approximately colinear with the line over which the initiating piece804is inserted, but positioned so that a rail882of the distracting piece802mates with a slot884of the initiating piece804. The anatomy of the neck is such that it is most convenient and minimally invasive to enter the neck from the side with respect to the implant800. The distracting piece802can be mated to the initiating piece804, by pegging the first and second perforations891,893, through an interference fit, or using a catch881and recess887as described above, or, alternatively by connecting the distracting piece804with the initiating piece802using a fastener, or by some other device, as described above.