Patent Application
20090297603
This disclosure relates generally to spinal implants. More particularly, the present disclosure relates to an interspinous dynamic stabilization system which can uniquely address the dynamic stabilization of a spinal segment and facet joint concurrently and which can be useful as a drug delivery device. The present disclosure also relates to methods of implanting such an interspinous dynamic stabilization system in a patient.
The human spine consists of segments known as vertebrae linked by intervertebral disks and held together by ligaments. There are 24 movable vertebrae—7 cervical (neck) vertebrae, 12 thoracic (chest) vertebrae, and 5 lumbar (back) vertebrae. Each vertebra has a somewhat cylindrical bony body (centrum), a number of winglike projections (processes), and a bony arch. The arches are positioned so that the space they enclose forms the vertebral canal. The vertebral canal houses and protects the spinal cord, and within it the spinal fluid circulates. Ligaments and muscles are attached to various projections of the vertebrae. The bodies of the vertebrae form the supporting column of the skeleton. Five fused vertebra make up the sacrum and coccyx, the very bottom of the vertebral column.
The spine is subject to abnormal curvature, injury, infections, tumor formation, arthritic disorders, and puncture or slippage of the cartilage disks. Injury or illness, such as spinal stenosis and prolapsed discs may result in intervertebral discs having a reduced disc height, which may lead to pain, loss of functionality, reduced range of motion, and the like. Scoliosis is one relatively common disease which affects the spinal column. It involves moderate to severe lateral curvature of the spine, and, if not treated, may lead to serious deformities later in life. One treatment involves surgically implanting devices to correct the curvature.
In addition to spinal stenosis, other conditions such as spinal arthritis, facet joint disease, sprains and strains, soft tissue diseases, and acute disc herniations tend to be worsened by extension of the spine (bending backward) and relieved by flexion (bending forward) or the neutral position. For example, the facet joint is loaded or compressed on extension and unloaded and stretched on flexion. They have been found to be a source of pain in patients presenting with low back pain and can refer pain into the lower extremity. In the case of thoracic extension dysfunctions, which may include rotation and lateral bending dysfunctional elements, compensation for such extension restrictions may occur in the lower lumbar spine, in the form of increased extension. Increased extension can increase pressure on, the spinal cord and cause increased posterior disc and facet compression. The same principle applies to upper lumbar extension restrictions. Increased extension can thus lead to low back pain, hip pain, and even knee complaints. A non-surgical treatment may be a physical therapy program directed at minimizing stress to the painful area while improving the biomechanics by stretching structures that have become tight and strengthening the muscles that support and unload these painful areas. In some cases, anesthetic injections can be used to confirm the source of pain and perhaps control the symptoms.
Modern spine surgery often involves spinal fixation through the use of spinal implants or fixation systems to correct or treat various spine disorders or to support the spine. Spinal implants may help, for example, to stabilize the spine, correct deformities of the spine, facilitate fusion, or treat spinal fractures.
A spinal fixation system typically includes corrective spinal instrumentation that is attached to selected vertebra of the spine by screws, hooks, and clamps. The corrective spinal instrumentation includes spinal rods or plates that are generally parallel to the patient's back. The corrective spinal instrumentation may also include transverse connecting rods that extend between neighboring spinal rods. Spinal fixation systems are used to correct problems in the cervical, thoracic, and lumbar portions of the spine, and are often installed posterior to the spine on opposite sides of the spinous process and adjacent to the transverse process.
Often, spinal fixation may include fused and/or rigid support for the affected regions of the spine. Such systems when implanted inhibit movement in the affected regions in virtually all directions. More recently, so called “dynamic” systems have been introduced. These systems allow at least some movement (e.g., flexion, extension, lateral bending, or torsional rotation) of the affected regions of the spine in at least some of the directions.
Embodiments of an interspinous dynamic stabilization system disclosed herein take advantage of existing technologies to uniquely and simultaneously provide dynamic stabilization of a spinal segment and facet joint in a minimally invasive manner. Embodiments of the interspinous dynamic stabilization system disclosed herein rely on the anisotropic expansion feature of specially manufactured hydrogels to resist and control the extension of the spine.
In some embodiments, an interspinous dynamic stabilization system may comprise a hydrogel manufactured to expand axially in a predetermined direction upon absorption of fluid and a casing for constraining or housing the hydrogel. In some embodiments, the casing may comprise a top surface conforming to a bottom portion of a superior spinous process and a bottom surface conforming to a top portion of an inferior spinous process. Upon absorption, the hydrogel in hydrated form can lift the superior spinous process, advantageously providing dynamic spinal stabilization and relieving facet joint pain.
According to embodiments disclosed herein, the casing may vary from implementation to implementation. In some embodiments, the casing has folds for accommodating expansion of the hydrogel. In some embodiments, the casing is partially enclosed. In some embodiments, the casing comprises tabs for attaching to the superior spinous process and to the inferior spinous process. In some embodiments, the attachment may be bi-lateral or in an anterior-posterior direction. In some embodiments, the casing may comprise a pocket area where the hydrogel is to be constrained or housed. In some embodiments, one of the tabs may extend over the pocket area, leaving a gap through which the hydrogel can be inserted.
In some embodiments, the casing may have its own dampening elements. In some embodiments, the casing comprises an upper portion, a lower portion, and dampening elements. In some embodiments, the top surface of the casing is part of the upper portion of the casing, the bottom surface of the casing is part of the lower portion of the casing, and the dampening elements are positioned between the upper portion and the lower portion of the casing.
In some embodiments, the casing may comprise side walls, each of which may have two or more holes. Bone fasteners may be utilized to attach these side walls bi-laterally to adjacent spinous processes through those holes, leaving a space between the adjacent spinous processes and the side walls where the hydrogel may be constrained and directly attachable to the adjacent spinous processes.
According to embodiments disclosed herein, the casing may be made of any suitable biocompatible materials, including metal and composite, and the hydrogel is specially manufactured to expand axially in a predetermined direction upon absorption of fluid. In one embodiment, the hydrogel is radially compressed to a bullet form, making it particularly suitable for minimally invasive easy insertion. In some embodiments, the exterior or interacting surface of the hydrogel is made bioactive, making these embodiments particularly suitable for drug delivery applications.
Embodiments disclosed herein include methods of implanting an interspinous dynamic stabilization system. One embodiment may comprise the steps of making an incision in a patient, placing a casing of the interspinous dynamic stabilization system between adjacent spinous processes of a spinal segment of the patient, and inserting one or more units of a hydrogel in dehydrated form into the casing through an opening thereof. Upon absorption of fluid, the hydrogel expands axially in a predetermined direction, lifting the superior spinous process. The method may further comprise supplying a saline solution to the hydrogel to speed up the swelling process. In some embodiments, the method may further comprise preparing the bottom portion of the superior spinous process and the top portion of the inferior-spinous process to accommodate the top surface and the bottom surface of the casing. In embodiments where the hydrogel has a bioactive surface, the method may further comprise utilizing the interspinous dynamic stabilization system as a drug delivery device.
In some embodiments, a method of implanting an interspinous dynamic stabilization system may comprise the steps of making an incision in a patient, attaching, bi-laterally or in an anterior-posterior direction, a casing of the interspinous dynamic stabilization system to adjacent spinous processes of a spinal segment of the patient, and inserting one or more units of a hydrogel in dehydrated form into the casing through an opening thereof. The method may further comprise hydrating the hydrogel by supplying a saline solution to the hydrogel. In some embodiments of an interspinous dynamic stabilization system, the casing may have an open-style that allows the hydrogel constrained therein to directly attach to both the superior spinous process and the inferior spinous process when the hydrogel is fully hydrated. The hydrogel thus utilized may have a bioactive exterior or interacting surface, making the interspinous dynamic stabilization system particularly useful for drug delivery purposes.
Embodiments of the interspinous dynamic stabilization system disclosed herein can provide many advantages, including but not limited to, reducing, resisting, and controlling the extension of the spine in order to achieve the following: soft (dynamic) stabilization of the affected spinal segment; minimize the loads experienced by facet joints in a damaged disc/spine; minimize the facet joint articulation for pain relief; drug delivery device/carrier; and minimally invasive surgery and faster recovery.
Other objects and advantages of the embodiments disclosed herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings.
A more complete understanding of the present invention and the advantages thereof may be acquired by referring to the following description, taken in conjunction with the accompanying drawings in which like reference numbers indicate like features and wherein:
While this disclosure is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the disclosure to the particular form disclosed, but to the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
The inventive interspinous dynamic stabilization system and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments detailed in the following description. Descriptions of well known starting materials, manufacturing techniques, components and equipment are omitted so as not to unnecessarily obscure the invention in detail. Skilled artisans should understand, however, that the detailed description and the specific examples, while disclosing preferred embodiments of the invention, are given by way of illustration only and not by way of limitation. Various substitutions, modifications, and additions within the scope of the underlying inventive concept(s) will become apparent to those skilled in the art after reading this disclosure. Skilled artisans can also appreciate that the drawings disclosed herein are not necessarily drawn to scale.
As used herein, the terms “comprises,” “comprising,” includes, “including,” “has,” “having” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, product, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements, but may include other elements not expressly listed or inherent to such process, article, or apparatus. Further, unless expressly stated to the contrary, “or” refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).
Additionally, any examples or illustrations given herein are not to be regarded in any way as restrictions on, limits to, or express definitions of, any term or terms with which they are utilized. Instead these examples or illustrations are to be regarded as being described with respect to one particular embodiment and as illustrative only. Those of ordinary skill in the art will appreciate that any term or terms with which these examples or illustrations are utilized encompass other embodiments as well as implementations and adaptations thereof which may or may not be given therewith or elsewhere in the specification and all such embodiments: are intended to be included within the scope of that term or terms. Language designating such non-limiting examples and illustrations includes, but is not limited to: “for example,” “for instance,” “e.g.,” “in one embodiment,” and the like.
In some cases, surgery may be required to prevent the spine from pressing on the spinal cord and/or to stabilize the affected vertebrae. One treatment option involves preventing the spine from overextension while restoring a natural height of the space between adjacent spinous processes when the spine is in the neutral position.
Hydrogels, in general, are hydrophilic (water loving) in nature. They can absorb water, body fluid, etc. and can expand up to 200 to 400% of their initial volume. This expansion is generally isotropic, which means that they will swell in equal amount in all directions. Using special manufacturing techniques, such as those disclosed by U.S. Pat. No. 7,204,897, and U.S. Patent Application Publication No. 2005/0171611, both of which are incorporated herein by reference, the hydrogel expansion can be made anisotropic, which means that the specially manufactured hydrogel will expand only in the preferred direction (say, Z) and will not expand, or at least not significantly, in two other directions (say, X and Y). Hydrogels with anisotropic expansion have been successfully manufactured for spinal nucleus implants (e.g., NeuDisc by Replication Medical Inc. of New Jersey). These hydrogels are traditionally used for spinal nucleus implants and will expand in axial direction by absorbing water, body fluid, etc.
Using special techniques, such as those disclosed by U.S. Patent Application Publication No. 2006/0136065, hydrogels can also be made in a variety of shapes in a dry-state” or “pre-insertion state”, some of which may be suitable for minimally invasive insertion. U.S. Pat. No. 6,264,695, issued to Stoy, describes a swellable plastic that, in folded form, can be inserted, through an incision, into a cavity of a spinal disc. After insertion, the swellable plastic is then unfolded and hydrated within the cavity to replace a portion of nucleus pulposus tissue removed from the spinal disc.
As one skilled in the art can appreciate, hydrogels can be reinforced using a variety of materials, including, but not limited to, polyester fiber, polyester mesh, Dacron® mesh, etc. Dacron is a ® ™ of Invista, Inc. These hydrogels may have the ability to exert swelling force (i.e., lifting force) in the range of 100 newton (N) to 800 N, depending upon the composition and upon absorption of fluids. All these features can be advantageously used to the objectives mentioned above.
In the example of
In practice, the desired spacing between the adjacent spinous processes will determine the number of hydrogel units required. In some embodiments, the casing of an interspinous dynamic stabilization system for treatment of a single level spinal segment may contain one or more hydrogel units.
In
The casing may also vary from implementation to implementation, so long as it is formed with features that can constrain and/or house the hydrogel. The shape and features of the casing should be adapted so that they are similar to the portion of the spinous processes to which the casing attaches. In some cases, preparation of spinous process(es) may be required to conform to the casing.
Casing 650 further comprises tabs 651 for attaching casing 650 to superior spinous process 203a and inferior spinous process 203b. Tabs 651 are connected to pocket 652 on either end of pocket 652 and can be formed separate from or monolithically with pocket 652. Each tab 651 may have at least one hole 660 through which bone fastener 680 can be fastened or otherwise secured onto a spinous process. Suitable bone fasteners 680 may include, but are limited to, bone screws. In the example of
In some embodiments, units of hydrogel are inserted into the casing prior to surgery or prior to attaching the casing to the adjacent spinous processes during a surgical procedure. In some embodiments, during a surgical procedure, once the casing is attached to the adjacent spinous processes using bone fasteners, units of hydrogel are then inserted, perhaps one by one, inside the casing between the spinous processes. As
Upon absorption of the fluid, the superior spinous process will experience the lifting force due to an anisotropic expansion of the hydrogels and the distance between the adjacent spinous processes will be increased. This process will occur within the first 4 to 18 hours. This lifting can minimize the loads experienced by facet joints and can also minimize the painful articulation between the interacting fact joints.
In some embodiments, the casing can be monolithically made of a metal material. In some embodiments, the metal material is titanium. The relatively rigid casing can provide the stability to the affected spinal segment and the hydrogel material within the casing can act as a “cushion” or “dampening element,” providing a unique blend of stability and range of motion (ROM) in the flexion-extension direction. In some embodiments, the casing can be monolithically made of a composite material to induce additional ROM without affecting stability.
Depending upon the casing design, in some embodiments, the hydrogel exterior surface may be made to be bioactive. This bioactive surface, upon interaction with respective surfaces of spinous processes, will attach to the spinous process. The hydrogels with such a bioactive surface can then act as a drug delivery device/carrier in a manner known to those skilled in the art.
As mentioned above, casings suitable for implementing interspinous dynamic stabilization systems disclosed herein may take various forms and sizes. For example, some casings may attach to the adjacent spinous processes bi-laterally and some casings may attach to the adjacent spinous processes in the anterior-posterior direction. In some cases, existing inter-spinous devices may be utilized as casings to constrain and/or house the specially manufactured anisotropic hydrogels. Examples of suitable inter-spinous devices may include the coflex™ interspinous implant and the Wallis® System. The coflex™ interspinous implant, invented by Dr. Jacques Samani in 1994, can be obtained from Paradigm Spine, LLC of New York. An exemplary implementation is described below with reference to
Casing 750 further comprises four tabs 751 for attaching casing 750 to superior spinous process 203a and inferior spinous process 203b. In this example, two tabs 751 extend upwardly from either end of pocket 752 and two tabs 751 extend downwardly from either end of pocket 752. Tabs 751 and pocket 752 are formed monolithically out of a biocompatible material. Each tab 751 may have at least one hole 760 through which bone fastener 780 can be fastened or otherwise secured onto a spinous process. Suitable bone fasteners 780 may include, but are limited to, bone screws. In the example of
In some embodiments, casings of an interspinous dynamic stabilization system disclosed herein may be made without its top and bottom being enclosed.
Currently, there does not seem to be a dynamic stabilization system that utilizes a combination of an interspinous process implant and anisotropic hydrogels for spinal treatment. It is contemplated that embodiments of the interspinous dynamic stabilization system disclosed herein can be one of the most versatile systems in the market, providing solutions for dynamic stabilization and facet joint pain resulting from spinal instability and/or abnormal facet joint loading and articulation. Due to its attachment to spinous processes, the system would also offer enhanced stability for torsional and lateral bending ROM. Further, some embodiments of the system can be implemented to act as a drug delivery device/carrier. More importantly, embodiments of the interspinous dynamic stabilization system disclosed herein can be reversibly removed in case if the surgery is deemed unsuccessful.
Embodiments of an interspinous dynamic stabilization system have now been described in detail. Those skilled in the art will appreciate that any of the embodiments described above may be used individually or in combination with other spinal implants. Further modifications and alternative embodiments of various aspects of the disclosure will be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the disclosure. It is to be understood that the forms of the disclosure shown and described herein are to be taken as examples of embodiments. Elements and materials may be substituted for or implemented from those illustrated and described herein, as would be apparent to one skilled in the art after having the benefit of the disclosure. Changes may be made in the elements or to the features described herein without departing from the spirit and scope of the disclosure as set forth in the following claims and their legal equivalents.
