Expandable interspinous process spacer with lateral support and method for implantation

An interspinous process spacer and method of implanting same is provided for maintaining separation between adjacent spinous processes of adjacent vertebrae. The spacer has two lateral portions and a medial portion therebetween, the medial portion adapted to reside between the adjacent superior and inferior spinous processes in the deployed configuration and the lateral portions each comprise a superior lateral portion and an inferior lateral portion adapted to reside on the lateral side of the respective superior and inferior spinous process in the deployed configuration to maintain positioning of the interspinous process spacer between the two adjacent vertebrae. The lateral portions each comprise an expandable lateral member.

FIELD OF THE INVENTION

The present invention relates generally to devices for treating spinal stenosis, and more particularly to interspinous process spacers that can be implanted in a minimally invasive manner to treat spinal stenosis.

BACKGROUND OF THE INVENTION

A large majority of the population will experience back pain at some point in their lives that results from a spinal condition. The pain may range from general discomfort to disabling pain that immobilizes the individual. One type of adverse spinal condition is spinal stenosis, which occurs when the spinal canal or nerve root canals become too narrow and reduce the space for the passage of blood vessels and nerves.

Lumbar spinal stenosis (“LSS”, and sometimes called sciatica) is a condition of the spine characterized by a narrowing of the lumbar spinal canal. With lumbar spinal stenosis, the spinal canal narrows and pinches the spinal cord and nerves, causing pain in the back and legs. It is estimated that approximately 5 in 10,000 people develop LSS each year. For patients who seek the aid of a physician specialist for back pain, approximately 12-15% are diagnosed as having LSS.

Several causes of spinal stenosis have been identified, including aging, heredity, arthritis, and changes in blood flow to the lower spine. Aging is believed to be the most common cause, because as a person ages the ligaments connecting the bones of the spine can thicken and spurs may develop on the bones and into the spinal canal. The cushioning discs between the vertebrae also frequently deteriorate, and the facet joints may begin to break down. Over time, loss of disk height in the lumbar regions can result in a degenerative cascade with deterioration of all components of a motion segment resulting in segment instability and ultimately in spinal stenosis. During the process of deterioration, disks can become herniated and/or become internally torn and chronically painful. When symptoms seem to emanate from both anterior (disk) and posterior (facets and foramen) structures, patients cannot tolerate positions of extension or flexion. Heredity is believed to play a role in some cases because it may cause some people to have a smaller than average spinal canal, typically leading to LSS symptoms even at a relatively young age.

The most common symptoms of spinal stenosis are pain and difficulty when walking, although numbness, tingling, hot or cold feelings in the legs, and weakness or tiredness may also be experienced. In extreme cases, spinal stenosis can cause cauda equina syndrome, a syndrome characterized by neuromuscular dysfunction that may result in permanent nerve damage.

Common treatments for LSS include physical therapy (including changes in posture), medication, and occasionally surgery. Changes in posture and physical therapy may be effective in flexing the spine to enlarge the space available to the spinal cord and nerves—thus relieving pressure on pinched nerves. Medications such as NSAIDS and other anti-inflammatory medications are often used to alleviate pain, although they are not typically effective at addressing the cause of the pain. Surgical treatments are more aggressive than medication or physical therapy, but in appropriate cases surgery may be the best way to achieve a lessening of the symptoms associated with LSS.

The most common surgery for treating LSS is decompressive laminectomy, in which the lamina of one or more vertebrae is removed to create more space for the nerves. The intervertebral disc may also be removed, and the vertebrae may be fused to strengthen unstable segments. The success rate of decompressive laminectomy has been reported to be in excess of 65%, with a significant reduction in LSS symptoms being achieved in many cases.

More recently, a second surgical technique has been developed in which the vertebrae are distracted and an interspinous process spacer is implanted to maintain the desired separation between the segments. This technique is somewhat less invasive than decompressive laminectomy, which may provide significant benefits to patients experiencing LSS symptoms.

As with other surgeries, when performing surgery to implant an interspinous process spacer, one consideration is the size of the incision that is required to allow introduction of the device. Medical treatments that can be performed in a less invasive manner are greatly sought after by the medical community and patients alike. In some procedures, less invasive techniques are advantageous because they have shorter recovery periods, result in little to no blood loss, and greatly decrease the chances of significant complications. Moreover, less invasive techniques are generally less expensive for the patient.

In view of the many advantages of less invasive procedures, it would be highly advantageous to have an interspinous process spacer and an associated procedure amenable to less invasive techniques. The present invention addresses that need.

SUMMARY OF THE INVENTION

The present invention addresses these and other problems associated with the prior art by providing a customized interspinous process spacer and associated method to insert it into a medical patient. The interspinous process spacer is to act as a spacing device for the spinous processes of two adjacent vertebrae. The interspinous process spacer is used to distract the vertebrae and relieve pressure on the posterior wall of the intervertebral disc. Furthermore, the interspinous process spacer is expected to relieve pain associated with the spinal canal and/or neural foramen stenosis, as well as potentially relieving pain associated with degenerative facet joints. The interspinous process spacer of the present invention will allow controlled flexion and limited extension at the implanted level.

According to one embodiment of the present invention, an interspinous process spacer is provided for maintaining separation between adjacent superior and inferior spinous processes of two adjacent vertebrae when in a deployed configuration, which comprises a first lateral portion, a second lateral portion, and a medial portion therebetween, wherein the medial portion is adapted to reside between the adjacent superior and inferior spinous processes in the deployed configuration to maintain separation therebetween. The first and second lateral portions each comprise a superior lateral portion adapted to reside on the lateral side of the superior spinous process in the deployed configuration and an inferior lateral portion adapted to reside on the lateral side of the inferior spinous process in the deployed configuration to maintain positioning of the interspinous process spacer between the two adjacent vertebrae. The first and second lateral portions each comprise an expandable lateral member that is expandable from an insertion configuration to the deployed configuration, and at least one of the first and second lateral portions comprises a lateral support member within the expandable lateral member, the lateral support member configured to be deformable for the insertion configuration and expanded in the deployed configuration. The expandable member may be expanded with a flowable material, such as a polymer, for filling the expandable member to the geometry.

In some embodiments of the invention, the medial portion may include a rigid medial member positioned between the superior and inferior spinous processes to maintain separation therebetween. The rigid member may be tubular in shape. In this instance, the medial portion may further comprise an expandable medial member, either positioned within the hollow portion of the tubular rigid medial member, or positioned surrounding the tubular rigid medial member. Alternatively, the expandable lateral portions may be connected to the rigid medial member with no expandable medial member. In any of these embodiments, the opposing lateral portions reside outside the rigid medial member and assist in maintaining the position of the interspinous process spacer. In yet another alternative embodiment, the opposing lateral portions and the medial portion are formed by expandable members, with no rigid medial member.

Another aspect of the invention is a method for implanting the interspinous process spacer for maintaining separation between adjacent superior and inferior spinous processes of two adjacent vertebrae. In one embodiment of the invention, the method comprises introducing a tubular delivery device to a region between the adjacent superior and inferior spinous processes and introducing an interspinous process spacer through the tubular delivery device in a non-expanded, insertion configuration to the region. The interspinous process spacer comprises an expandable member having a distal lateral portion with a distal lateral support member therein, a medial portion, and a proximal lateral portion with a proximal lateral support member therein. The method further includes positioning the interspinous process spacer in the region with the distal lateral portion on a distal side of the spinous processes, the medial portion between the spinous processes, and the proximal lateral portion on a proximal side of the spinous processes, and then retracting the tubular delivery device and expanding the expandable member and the distal and proximal lateral support members to an expanded, deployed configuration.

DETAILED DESCRIPTION

With reference to the Figures, wherein like numbers denote like parts throughout the several views, exemplary interspinous process spacers10a-dare shown in accordance with the invention for maintaining a desired spacing between the spinous processes of adjacent vertebrae12and14. According to embodiments of the invention,FIGS. 1-4illustrate interspinous process spacers10a-10dthat possesses a geometry generally in the form of an H-shape or dumbbell (used interchangeably herein). The spacers10a-10dcomprise a medial portion20adapted to reside between adjacent superior spinous process16and the inferior spinous process18. The medial portion20may comprise an expandable medial member38(FIGS. 2-4) and/or a rigid medial member40(FIGS. 1-3).

Spacers10a-10dfurther comprise opposing lateral portions24and26, which are located at the lateral ends of the medial portion20. Each lateral portion24,26consists of a superior lateral portion24a,26aadapted to reside on the lateral side of the superior spinous process16and an inferior lateral portion24b,26badapted to reside on the lateral side of the inferior spinous process18, to maintain position of the interspinous process spacer10awithin the desired space when in the expanded, deployed configuration, as shown in each ofFIGS. 1-4. Each lateral portion24,26may comprise at least one filling member30,32, such as a valve, to allow separate introduction of a flowable material (not shown), if desired, to each lateral portion24,26, such as if the medial portion20does not sufficiently permit the flow of fluid from one lateral portion to the other and/or where the medial portion20includes a rigid medial member40that is a solid rod configuration rather than a tubular configuration having a central conduit.

The lateral portions24,26each comprise an expandable lateral member22that is expandable from an insertion configuration, shown inFIG. 5Cdiscussed further below, to an expanded, deployed configuration shown inFIGS. 1-4and5D-5E. To that end, expandable lateral members22may be made of non-compliant material that will assume the desired geometry and position when expanded. In another embodiment, the expandable lateral members22may be made of compliant material that will maintain the desired geometry when expanded. Expandable as used herein includes any increase in the volume, dimension, circumference, etc. of a member. Expansion may include a stretching of the material of the member from its natural state whereby the dimensions of the member increases beyond a natural state, like a balloon. Alternatively, expansion may include no stretching of the material, but rather, an unfolding of the material from a collapsed position to its full natural geometry and dimensions. In yet another embodiment, the geometry may be further maintained by casting the expandable lateral member22with a fiber reinforcing mesh made to the desired geometry. The expandable lateral members22may comprise biocompatible materials, such as polyethylene terephthalate or polyethylene. Other suitable materials may comprise polyacrylates, polypropylene, polyolefin copolymers, polycarbonates, polyesters, ether-ketone copolymers, polytetrafluoroethylene fibers or silk. Of course, other suitable biocompatible materials are possible as well without departing from the scope of the present invention.

One or both of the lateral portions24,26further comprise a lateral support member23that resides within the expandable lateral member22to support the lateral portions24,26during expansion. The lateral support member23is configured to be deformable for the insertion configuration, shown inFIGS. 5C-5D, and expanded or returned to the deployed configuration, shown inFIGS. 1-4and5D-5E, after insertion.

In one embodiment, the lateral support member23is elastically deformable. In elastic deformation, the amount of deformation is proportional to the amount of applied force or stress. Upon application of stress (e.g., a compressive force), the material of the lateral support member23deforms to a configuration suitable for insertion. That stress is maintained either by continually applying the force or by treating the material to temporarily cause it to remain in the stress-state. After insertion, when the stress is removed, either by removing the applied force or by introducing a thermal change that releases the stress, the material completely or substantially resumes its original or undeformed state, i.e., it expands back to the expanded, deployed configuration. A perfectly elastic body will completely resume its shape with no plastic (i.e., permanent) deformation. A minor amount of plastic deformation, however, can be permitted. Shape memory alloys, such as nitinol (a NiTi alloy), can be treated (programmed) to maintain the induced stress, and thus the insertion configuration, until a temperature is applied (e.g., body temperature, a heated or cooled flowable material, a heated or cooled rinse fluid, etc.) that releases the stress, upon which the shape memory alloy remembers and reverts to it's original shape, which is the shape for the desired expanded, deployed configuration.

Thus, the lateral support members23may be manufactured to have the desired deployed configuration as the original or natural shape of the material, and the insertion configuration is a deformed state in which the size of the member is altered and/or reduced to allow for minimally invasive insertion into the surgical site between and/or laterally of the adjacent vertebrae12,14. After insertion, the deformation is released, allowing the lateral support member23to re-assume (expand to) the expanded, deployed configuration.

In one embodiment, the lateral support members are made of a shape memory material programmed to maintain the deformation within a temperature range that encompasses expected room temperature variations, and to release the deformation upon exposure to an elevated temperature. The elevated temperature may correspond to expected body temperatures in the applicable vertebral region, such that the lateral support members are self-expanding in the applicable vertebral region upon reaching temperature equilibrium with the body temperature. Alternatively, or in addition, a heated fluid may be used to bring the lateral support members up to the elevated temperature, such as by heating the flowable material. In another embodiment, the shape memory material may be programmed to release the deformation upon exposure to a low temperature (e.g., below expected room temperatures), which may be achieved by cooling a fluid.

In yet another embodiment, the lateral support members are made of a spring-type material that may be deformed to a contracted or collapsed state by a delivery tube for insertion to the vertebral region. Upon removal of the delivery tube, the material springs back to its full shape. Thus, the spring-type material is self-expanding in the vertebral region upon removal of the constraining delivery tube.

InFIGS. 1-4, the opposing lateral portions24,26are shown in the expanded, deployed configuration. The means utilized to expand the opposing lateral portions24,26may include a flowable material. In one embodiment, the flowable material may consist of bone cement, polyurethane, silicone, copolymers of silicone and polyurethane, polyolefins, neoprene, nitrile or combinations thereof. Of course, other suitable fluids are possible as a means of expansion without departing from the scope of the present invention.

Another aspect of the invention is the interspinous process spacer10a-10dmay be fixed in the interprocess space by connecting members (not shown) integrated with the medial portion20or the lateral portions24,26. Exemplary connecting members may include connecting members to allow attachment to the superior and inferior spinous processes16,18by bone darts, fibers of sufficient length to enable tying to the superior and inferior processes16,18, or sutures that anchor the interspinous process spacer10a-10dto neighboring biological tissue, i.e. sutured to adjacent soft tissue such as the interspinous and supraspinous ligament. Moreover, the interspinous process spacer may be designed with tissue in-growth capability for long-term fixation, if desired. It will be appreciated that manners of fixation known in the art, other than the exemplary manners described herein, may be used without departing from the scope of the present invention.

In the embodiments ofFIGS. 1-3, the interspinous process spacers10a-10cinclude a rigid medial member40in the medial portion20. The rigid medial member40may be comprised of a biocompatible metal or polymer, such as titanium or polycarbonate urethane. Other suitable materials may include poly(lactic acid), poly(glycolic acid), p-dioxanone fibers, polyarylethyl, polymethylmethacrylate, polyurethane, amino acid-derived polycarbonate, polycaprolactone, aliphatic polyesters, calcium phosphate, unsaturated linear polyesters, vinyl pyrrolidone, polypropylene fumarate diacrylate, or mixtures thereof. Of course, other suitable biocompatible materials are possible as well without departing from the scope of the present invention. Additionally, the height of the medial portion20may vary between 5 mm and 20 mm.

The interspinous process spacer may have a relationship between the rigid medial member40and the expandable members22,38that exists in three general forms. First, in the embodiment depicted inFIG. 1, the rigid medial member40may be the medial portion20of the interspinous process spacer10a, with a pair of expandable lateral members22forming opposing lateral portions24and26at the lateral ends of the medial portion20. In this embodiment, the rigid medial member40may be attached to the expandable lateral members22. In this instance, the expandable lateral members22form the opposing lateral portions of the interspinous process spacer after expansion with a flowable material or other fluid and complete the dumbbell or H-shape of the interspinous process spacer10a. Where the rigid medial member40is a solid rod, or the connection between the rigid medial member40and the expandable lateral members22is such that there is no fluidic coupling between the pair of expandable lateral members22, then each lateral member may be expanded by introducing fluid through a respective filling member30,32. Where the rigid medial member40is a cylinder or tube and a fluidic coupling is maintained between the pair of expandable lateral members22, then a single filling member30may be used, or opposed filling members30,32may be used, as desired. Alternatively, no filling members may be provided where a syringe needle can be used to achieve filling of the expandable lateral members22. In addition, a lateral support member23is shown in the lateral portion26. A second lateral support member23may or may not be present in the lateral portion24. Lateral support member23, upon expansion, may also cause at least partial expansion of the expandable lateral member22.

Interspinous process spacer10binFIG. 2illustrates a second relationship where the medial portion20comprises a rigid medial member40residing within an expandable medial member38, wherein the rigid medial member40is generally shaped in the form of a cylinder or tube. The expandable medial member38and the expandable lateral members22may together form a single, seamless (one-piece) expandable member42that has the deployed configuration generally in the form of the H-shape or dumbbell. Alternatively, the two expandable lateral members22and the expandable medial member38may be joined to form a single expandable member42having seams between the three joined pieces. The expandable medial member38and the single, seamless expandable member42may be made of the same materials as described above for the expandable lateral members22. The material of the expandable medial member38may be the same or different than the material of the expandable lateral members22. A single filling member30is illustrated in lateral portion24, contemplating filling through the rigid medial member40to the lateral portion26. It may be appreciated that filling members may be provided in both lateral portions24,26, such as depicted in the embodiment ofFIG. 1, or no filling members may be provided where a syringe needle can be used to achieve filling of the expandable member42. In addition, a lateral support member23is shown in the lateral portion24. No lateral support member23is present in the lateral portion26. Lateral support member23, upon expansion, may also cause at least partial expansion of the expandable lateral member22.

Interspinous process spacer10c, illustrated inFIG. 3, represents a complementary third relationship wherein the medial portion20comprises the rigid medial member40, again generally shaped in the form of a tube, but this time surrounding the expandable medial member38. In this embodiment, the expandable medial member38and the expandable lateral members22again together form the single expandable member42(seamless or with seams) that has the deployed configuration generally in the form of the H-shape or dumbbell. One of the expandable lateral members22may be inserted through the rigid medial member40to position the expandable medial member38within the rigid medial member40. Again, a single filling member30is illustrated in lateral portion24, contemplating filling through the expandable medial member38to the lateral portion26. As stated above, however, two filling members30,32or no filling member may be used to achieve expansion of the expandable member42. In addition, a lateral support member23is shown in the lateral portion26. A second lateral support member23may or may not be present in the lateral portion24. Lateral support member23, upon expansion, may also cause at least partial expansion of the expandable lateral member22.

In the embodiment illustrated inFIG. 4, interspinous process spacer10dincludes a medial portion20having an expandable medial member38, but no rigid medial member. The expandable medial member38and the expandable lateral members22again together form the single expandable member42. In this exemplary embodiment, two lateral support members23are contained within the expandable member42, one in each expandable lateral member22, to support each of the lateral portions24,26during expansion and in deployment. Lateral support member23, upon expansion, may also cause at least partial expansion of the expandable lateral member22. No filling member is depicted, contemplating filling by use of a syringe having a needle (not shown).

The lateral support members23may be generally in the form of a circle, ellipse, or a C-shape (seeFIGS. 4A and 4B), and constructed of polycarbonate urethane (PCU), nitinol (NiTi) or steel, for example. Moreover, lateral support members23may be positioned in the lateral portions24,26and connected by a medial support member21across the medial portion20, as illustrated inFIG. 4C. Advantageously, PCU or nitinol are amenable to elastically deforming or altering the shape of the lateral support members23to facilitate delivery of the interspinous process spacer10a-10dthrough a tube to the space between the superior and inferior spinous processes16,18. After the interspinous process spacer10a-10dis positioned in the desired space, the lateral support members23are allowed to relax to their pre-altered shape. Other shape memory materials besides any specifically mentioned herein may be contemplated for the lateral support members23.

Another aspect of the invention is a method for implanting the interspinous process spacer10a-dfor maintaining separation between adjacent superior and inferior spinous processes16,18of two adjacent vertebrae12,14. One exemplary method of implantation is depicted schematically inFIGS. 5A-5Eusing the interspinous process spacer10c. The method comprises the exploration of the interspinous region with a delivery tube device90, as illustrated inFIG. 5A, and opening the interspinous ligament, as shown schematically inFIG. 5B. A dilator92may be used to determine the desired diameter of the medial portion of the interspinous process spacer10c. As illustrated inFIG. 5C, the interspinous process spacer10c, comprising the rigid medial member40, the expandable member42with opposing lateral portions24,26shown in a non-expanded, insertion configuration, and a pair of lateral support members23shown in a deformed, insertion configuration, is introduced between the adjacent superior and inferior spinous processes16,18. In this embodiment, the filling member30in the proximal lateral portion24of the expandable member42is coupled to a catheter94, which will function as a conduit to deliver the flowable material. A syringe could be used in the alternative.

While the expandable member42is in a non-expanded, insertion configuration, the orientation and position of the medial portion20, including rigid medial member40, and the lateral portions24,26of the expandable member42may be verified radiographically or endoscopically prior to introducing a measured amount of a flowable material via the catheter94to fill the expandable member42to the geometry. Exemplary flowable materials consist of polymers consisting of bone cement, polyurethane, silicon, copolymers of silicone and polyurethane, polyolefins, neoprene, nitrile or combinations thereof.

As depicted inFIG. 5D, the distal lateral portion26of expandable member42is first expanded by releasing the stress and/or force applied to the lateral support member23in distal lateral portion26to allow it to assume the deployed configuration and delivering a flowable material to the expandable member42through filling member30and through the rigid medial member40. The presence of the delivery tube90surrounding the proximal lateral portion24hinders the expansion thereof. After the distal lateral portion26has achieved the desired level of expansion with support by its lateral support member23, the delivery tube90is removed (or retracted) to allow the lateral support member23in proximal lateral portion24to assume the deployed configuration and the proximal lateral portion24to expand by continued feed of flowable material via catheter94through filling member30, as depicted inFIG. 5E. After allowing time for the delivered flowable material to cure, the catheter body94is removed or severed from the filling member30of expandable member42containing the cured material. A connecting member may be used for fixation of the interspinous process spacer10bin the desired space, as previously described. In this embodiment, and as described above, the flowable material may be heated or cooled to a temperature that causes the lateral support members to return to the deployed configuration. In other words, a shape memory material may be programmed (treated) to release the stress and thus release the elastic deformation in the presence of a designated temperature (or temperature range), either an elevated or a reduced temperature relative to the body temperature and/or the ambient (room) temperature, and that designated temperature condition may be provided by means of the flowable material. Alternatively, or in addition, the designated temperature may correspond to the expected body temperature in the desired space, such that the lateral support members self-expand upon retraction of the delivery tube and upon reaching the body temperature, which may be with or without assistance by heating the flowable material. In yet another alternative, the lateral support members23may be in the nature of a spring material, with the delivery tube90providing an applied compressive force, upon retraction of which the lateral support members23one by one spring back to the deployed configuration, thus self-expanding.

In an alternative embodiment of the invention, the method differs from that previously described inFIG. 5Cby first introducing the rigid medial member40ofFIG. 3, between the adjacent superior and inferior spinous process16,18(method not illustrated). The expandable member42having expandable medial member38is introduced into the interprocess space, while in a deflated, insertion configuration, through the central, open space of the rigid medial member40. In this embodiment, the expandable member42may have a geometry generally in the form of a dumbbell or an H-shape whereby the expandable medial member38may be positioned in the interprocess space within the hollow portion of the rigid medial member40. The method according to this embodiment may be completed as previously described inFIGS. 5D and 5E.

In yet another alternative embodiment, wherein lateral support members23are positioned in each of the opposing lateral portions24,26of the interspinous process spacer10d, as illustrated inFIG. 4A, an alternative method of implanting comprises elastically altering the shape of the lateral support members23to facilitate delivery through a delivery tube device to the space between the superior and inferior spinous processes16,18of two adjacent vertebrae12,14. After the interspinous process spacer is positioned in the desired space between the superior and inferior spinous processes16,18with the medial portion20therebetween, distal lateral portion26and a lateral support member23on a distal side of the space, and proximal lateral portion24and a lateral support member23on a proximal side of the space, the delivery tube device is retracted and the lateral support members23are allowed or caused to relax to their pre-altered shape, which will cause at least partial expansion of lateral portions24,26. In this embodiment, a shape memory material of the lateral support members23may be programmed to resume the deployed configuration at a temperature substantially equivalent to the temperature of the human body. Alternatively, a heated or cooled fluid may flushed into and subsequently removed from the lateral portions24,26to provide the necessary thermal conditions for a programmed shape memory material. In yet another alternative, a spring-type material may be used that springs back to a non-deformed state upon retraction of the delivery tube device. The expandable member42can then be filled with flowable material, such as via a syringe or via a filling member and catheter, as previously described.

In yet another embodiment within the scope of the invention is an interspinous process spacer10ecomprising at least one superior component202, at least one inferior component204and at least one central component206, as illustrated inFIGS. 6 and 7. The superior component202is adapted to reside on a lateral side of the superior spinous process16and to be affixed to the superior spinous process16when the spacer10eis in the deployed configuration (i.e., when implanted into the body). The inferior component204is adapted to reside on a lateral side of the inferior spinous process18and to be affixed to the inferior spinous process18in the deployed configuration. In other words, the superior and inferior components202,204are lateral portions intended and suited to be located laterally adjacent the spinous processes upon implantation. Additionally, the central component206, which is adapted to reside on a lateral side of the interprocess space34, connects the superior and inferior components202,204to form a single member200.

The superior and inferior components202,204may comprise biocompatible metal or polymers, wherein at least the surface of the components consists of a porous material, such as Sulmesh®, which is a titanium-containing metal mesh. Other exemplary porous materials may comprise Trabecular Metal™, a fiber metal, a hydroxyapatite-coated material or any other suitable porous coated substrate such as Ti-VPS (vacuum plasma sprayed titanium coating) or Ti-APS (atmospheric plasma sprayed titanium coating), porous engineering polymer structures or combinations thereof, which may facilitate bone in-growth.

Moreover, the central component206may comprise a biocompatible elastomer, such as polycarbonate urethane. Other suitable materials may include poly(lactic acid), poly(glycolic acid), p-dioxanone fibers, polyarylethyl, polymethylmethacrylate, polyurethane, amino acid-derived polycarbonate, polycaprolactone, aliphatic polyesters, calcium phosphate, unsaturated linear polyesters, vinyl pyrrolidone, polypropylene fumarate diacrylate, or mixtures thereof. Of course, other suitable biocompatible materials are possible as well without departing from the scope of the present invention.

The central component206may be direct melted or injection molded to the superior and inferior components202,204to form single member200. The interspinous process spacer10eof this embodiment may possess rigid characteristics in flexion and extension. As illustrated inFIGS. 8 and 9, a slot210may be introduced into the central component206to facilitate flexion (FIG. 9) and extension (FIG. 8), thereby reducing the overall rigidity. In this context, the term “slot” refers generally to a vacancy created in the central component206and does not denote any limitations to size or shape. As will be described and shown further below, more than one slot210may also be provided. Another aspect of the invention is enlarging a terminal end212(for example, seeFIG. 14) of the aforementioned slot210to form a circular vacancy thereby reducing the flexion stress at this terminus.

Referring toFIGS. 10 through 24, another aspect of the invention is varying the degree of flexibility or stiffness in flexion and extension by varying the location, size, shape, number and orientation of the slots210. In some embodiments, the slots210begin from an edge214of the central component206, proceed generally in a horizontal, vertical, diagonal, or curved direction, and terminate at an interior terminal end212. In other embodiments, additional or alternative slots210may be internal, extending between terminal ends216and218, and not extending to an exterior edge214, such as shown inFIG. 17. In yet other embodiments, larger amounts of material may be removed to form a slot210to accommodate a customized flexibility (see, e.g.,FIGS. 22-24). Moreover, the internal surfaces220,222of the slots210may be shaped, as illustrated inFIGS. 25 through 27, to minimize torsional freedom or side-slippage of the two surfaces220,222.

In an alternative embodiment of an interspinous process spacer10f, a pair of central components206are connected between a superior component302and an inferior component304, each configured in the form of a clip, as illustrated inFIG. 28. The clips302,304may be made from biocompatible sheet metal, each having one or more notched teeth308for stability, as shown respectively inFIGS. 28 and 29. Moreover, the clips302,304may have a titanium vacuum plasma sprayed coating thereon or the surfaces of the clips302,304may consist of a porous material, such as Sulmesh® which is a titanium-containing metal mesh. Other exemplary porous materials include Trabecular Metal™, fiber metal, a hydroxyapatite-coated material, porous engineering polymer structures, or combinations thereof, which may facilitate bone in-growth. The pair of central components206may be direct melted, as illustrated inFIG. 30, or injection molded to the lateral portion of clips302,304to form interspinous process spacer10f, thereby providing bilateral support. The pair of central components206may contain one or more slots210, as described above.

In one intended use, the interspinous process spacer10f, as illustrated inFIG. 31, may be attached to the superior and inferior spinous processes16,18by being placed over the spinous processes and crimping the clips302,304with forceps. The notched teeth308grip the bone for stability. In an alternative aspect, the superior and inferior clips302,304of interspinous process spacer10fand the superior and inferior components202,204of interspinous process spacer10eare adapted to be, and in use may be, affixed to their respective spinous processes16,18by mechanical means, such as bone screws or bone darts.

Another embodiment of an interspinous process spacer10gof the invention is illustrated inFIG. 32. Interspinous process spacer10gis a side-loaded elastic device, such as a spring, comprising first and second end supports402,404and a central connecting member406, wherein the central connecting member406is characterized by being adapted to reside laterally of the two spinous processes16,18and being constructed from biocompatible spring steel. The central connecting member406may be constructed generally in the form of a C-shape. Alternative embodiments for central connecting member406may be constructed in different shapes, such as a spring or spiral, as exemplified inFIGS. 49 and 50, respectively.

The interspinous process spacer10gaccording to this embodiment may be undesirably too rigid. In this case, the relative stiffness or rigidity may be optimized by varying the cross-sectional area of the central connecting member406, as illustrated inFIG. 33throughFIG. 35. Moreover, the central connecting member may be structured to provide a stop410in extension, as illustrated inFIG. 35.

Another aspect to this embodiment is the first and second end supports402,404possessing shaped configurations for accommodating the surfaces of the spinous processes16,18. The shaped end supports402,404may be selected from a group consisting of generally flat, generally U-shaped, and generally V-shaped, as illustrated inFIG. 36,FIG. 37, andFIG. 38, respectively. Moreover, end supports402,404may vary by providing short to wide support, as shown inFIG. 39andFIG. 40, respectively, and may accommodate angular or tilted support, as shown inFIG. 41.

The shaped end supports402,404may each further comprise a pre-formed liner412, wherein each liner412conforms to the respective shaped end supports402,404, as illustrated in various embodiments inFIGS. 42 to 44, to accommodate spinous process seating. The liners412may also comprise one or more tabs414to enable fastening the liners412to their respective first and second end supports402,404. These liners412may be prepared from biocompatible polymers, such as polycarbonate urethane. Other suitable materials may comprise poly(lactic acid), poly(glycolic acid), p-dioxanone fibers, polyarylethyl, polymethylmethacrylate, polyurethane, amino acid-derived polycarbonate, polycaprolactone, aliphatic polyesters, calcium phosphate, unsaturated linear polyesters, vinyl pyrrolidone, polypropylene fumarate diacrylate, or mixtures thereof.

The interspinous process spacer10gmay comprise at least one fixation member, and advantageously at least one for each end support402,404, wherein the fixation members are selected from a group consisting of engaging teeth420, bone darts422, bone screws424, and tying members426, respectively illustrated inFIG. 45 through 48. Moreover, the spinous process16and/or18may be sculptured to accommodate fixation means.

Another aspect to this invention is a method of implanting an interspinous process spacer10gaccording to this embodiment. The method comprises accessing the spinous processes16,18from the lateral side and removing a section of the interspinous ligament to accommodate the first and second end supports402,404. The interspinous process spacer10gis compressed using a compressing mechanism (not shown) and then the first and second end supports402,404of the interspinous process spacer10gare inserted between the superior and inferior spinous processes16,18, while the interspinous process spacer10gis still in a compressed configuration. The position may be verified. The compression mechanism is released and the interspinous process spacer10gis allowed to spring open to distract the spinous processes16,18of the adjacent vertebrae12,14.

While the present invention has been illustrated by a description of various embodiments and while these embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. The described embodiments are simply intended to clarify the technical idea of the present invention. As such, the technical scope of the present invention should not be construed solely on the basis of the specific embodiments described above. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative aspects and methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope of applicant's general inventive concept.