Patent Application
20080262619
Aspects of the present invention relate to an implantable spacer adapted for placement between spinous processes of the human spine, and more particularly, to a cushioned spacer with provision for its fixation and an optional, associated instrument for preparing the spinous process to accept the implant.
Degenerative collapse of the human disc space is well known to be associated with disabling disc, facet joint and back pain. This is in part due to the buckling of annulus fibers of the disc, compromise or pinching of the exiting nerve space and an overriding of the posterior ancillary stabilizing facet joints attached in pairs to the vertebral bodies. Of the various forms of treatment, one of the more recently preferred methods involves placing a spacer between the posterior spinous processes in order to re-elevate the posterior structures, tightening the loosened fibers of the posterior disc annulus, spread open the exiting nerve foramen, and elevate the overriding facet joints. A variety of devices have been developed and successfully used as interspinous process spacers or spreaders that accomplish these desirable effects. Once implanted, it is imperative that the device not dislocate as a result of complex spine motions or the patient's lifting heavy objects. Therefore, some of the presently available devices developed for interspinal spacing are designed to prevent becoming displaced by being directly attached to the bony processes by clamps, wires, pins or screws. Unfortunately, such attachment means may lead to fracture or undesirable erosive changes in the spinous process bone.
An alternative approach is described in U.S. Pat. Nos. 6,761,720 and 6,946,000 in which an interspinous spacer system is described as including a multiperforated spacer to which is attached two belts. Each belt is assembled as a discrete, partial loop around an upper or lower spinous process, respectively, to an outer portion of the spacer for attachment and tightening. It is believed that this dual belt configuration lacks side shifting (translocation) resistance. The center mass of the relatively bulky spacer is provided in various sizes, the final size being determined by inserting a trial spacer among various sizes, without shaping the adjacent spinous process bones, A similar device was first reported by J Senegas in the European Spine Journal, October 2002, Supplement 2 pages 164-169 as “Mechanical supplementation by non-rigid fixation in degenerative intervertebral lumbar segments: the Wallis system,” and is currently undergoing clinical studies under the trade name Wallis® Mechanical Normalization System by the Abbott Spine Group, Austin Tex.
These and all other presently existing spinous spacer devices are constructed of metal or rigid polymers, and thus may damage the contacted bone over extended periods. Further, implantation of know spinous devices require the surgeon to perform delicate bone restructuring procedures in preparing/sizing the spinous processes for a close fit with the spacer device, especially where the spinous processes have worn against one another over time. This close fitting must be done carefully without perforating or fracturing the involved spinous processes. In the absence of appropriate tooling, this sizing procedure is difficult at best.
With the above Background in mind, improvements to, and advancement of, spinous process spacers and means for preparing the adjacent spinous processes, will be welcomed by spine surgeons and by appropriate patients alike.
Some aspects in accordance with principles of the present disclosure relate to an interspinous process spacer implant device adapted to be inserted between two adjacent spinous processes. The implant device comprises an implant body including a central portion, first and second superior legs, and first and second inferior legs. The central portion defines a left side, a right side, and a continuous, lateral passage extending through the central portion such that the lateral passage is open at both the left and right sides. The first and second superior legs extend upwardly from the central portion in an opposed, spaced fashion to define a superior zone for receiving a spinous process. The first and second inferior legs extend downwardly from the central portion in an opposed, spaced fashion to define an inferior zone for receiving a spinous process. With this configuration, the central portion is adapted to support opposing spinous processes disposed within the superior and inferior zones, respectively. In some embodiments, the lateral passage is sized to receive a separately-provided band. For example, the band (e.g., suture, strip, tape, etc.) is adapted for assembly through the lateral passage and about at least the first and second superior legs. In yet other embodiments, at least two segments of the band extend through the lateral passage, with other segments of the band extending about the superior legs and the inferior legs, defining a figure-8 construction, in securing the implant body to the adjacent spinous processes. In some embodiments, the implant device further includes a superior cushion disposed along the central portion between the first and second superior legs, and an inferior cushion positioned along the central portion between the inferior legs. The cushions are formed of a material that is softer than a material of the central portion (e.g., an elastomeric rubber), and reduce the point stresses placed upon the spinous process otherwise contacting the implant device.
Other embodiments in accordance with principles of the present disclosure relate to a kit for repairing a damaged vertebral column including adjacent vertebral segments each having a posterior spinous process. The kit includes first and second interspinous process spreader implant devices. Each of the implant devices includes a central portion, first and second superior legs, and first and second inferior legs. The first and second superior legs extend upwardly from the central portion in a spaced fashion to define a superior zone for receiving a spinous process. The first and second inferior legs extend downwardly from the central portion in a spaced fashion to define an inferior zone for receiving a spinous process. Finally, the central portion forms a continuous, lateral passage extending therethrough such that the lateral passage is open at both of a left side and a right side of the central portion. With this in mind, a lateral spacing between the superior legs of the first implant device is greater than a lateral spacing of the superior legs of the second implant device. With this configuration, upon evaluating a size of the spinous processes in question, the implant device providing a best fit thereto can be selected for subsequent implantation. In other embodiments, the kit further includes a bone shaping tool including a trough-like or U-shaped blade defining a lateral spacing commensurate with a lateral spacing between the superior legs of at least the first implant device.
Yet other aspects in accordance with principles of the present disclosure relates to a method of repairing a damaged vertebral column including adjacent superior and inferior vertebral segments each having a posterior spinous process. The method includes providing an interspinous process spacer implant device. The implant device includes an implant body having a central portion, first and second superior legs, and first and second inferior legs. The superior legs define a superior receiving zone, whereas the inferior legs define an inferior receiving zone. Further, the central portion defines a continuous, lateral passage extending through the central portion such that the lateral passage is open at both a left side and a right side thereof. With this in mind, the method further includes positioning the spinous process of the superior vertebral segment within the superior receiving zone, and positioning the spinous process of the inferior vertebral segment within the inferior receiving zone, A band is passed through the lateral passage and at least about the superior legs and the spinous process of the superior vertebral segment to secure the implant body to the superior vertebral segment. Upon final implant, the implant device establishes a near-normal spacing between the vertebral segments. In some embodiments, the method further includes extending a first segment of the band through the lateral passage; extending a second segment of the band around the superior legs and the spinous process of the superior vertebral segment; extending a third segment of the band through the lateral passage such that the first and third segments coexist within the lateral passage; and extending a fourth segment of the band about the inferior legs and the spinous process of the inferior vertebral segment. With this methodology, the band assumes a figure-8 shape.
Some non-limiting embodiments of the present disclosure provide an “H-shaped” spinous process spacer implant device in a plurality of sizes to accommodate a plurality of widths of the spinous processes, as encountered during spine surgery. The implant device in accordance with some embodiments also includes an interposed bioacceptable, elastomeric (rubbery) cushion formed within the valleys of the spacer at the central connecting area where there will be bone contact pressure. The elastomeric cushion bonded inside the vertical surfaces of the implant body can be an implantable grade silicone, polyurethane or polysulfone rubber or equivalent. The durometer rating of this elastomeric cushion should be moderately firm and withstand roughly 200-400 pounds psi compression repeatedly over several million cycles without fracture. Additionally, a lateral passage or slot is formed in the center of the spacer mass through which a resilient, bio-acceptable, non-absorbable band or multiple strands of suture may be passed. Such a band or bundle of sutures is brought above and below the adjacent spinous processes, then crosses through the spacer's mid portion slot, in an optional figure-eight style, stabilizing the implant and preventing its displacement. Where the spacer implant device is provided as part of a kit, an additional adjunct to the kit is one or more open “U” shaped sharp bone trims or tools that is used to prepare the spinous processes for a close fitting between the spinous process and the selected spacer implant device. During an implantation procedure, both the upper and lower facing, articulating spinous process margins are trimmed using the tool for proper fit inside the selected spacer and for optimal contact with the interposed elastomeric cushion. The plurality of widths of the novel bone trim cutters is matched with those of the spacers.
Regardless, over time, the bone of each wrapped spinous process is expected to show some accommodation or retreat of the bone where the relatively narrow, resilient band or suture bundle tightly passes. This remolding or accommodation will cause slight loosening of the band and an increase in flexion-extension angulation of the spine segment. This is a desirable effect of the present invention not found in other designs.
Other aspects of the present disclosure provide a spacer implant device having a low mass construction of a metal such as an implantable grade alloy of titanium or preferably an x-ray transparent, suitable polymer or composite such as carbon fiber reinforced Victrex® PEEK™ (polyetheretherketone) or epoxamide formulation. The torsional strength of the implant should be higher than that of the spinous process bone but still maintain substantial flexibility, greater than the elastic modulus of bone.
As a point of reference, if it is determined that the implant devices and methods described herein do not suffice for a particular patient, other means or methods may subsequently be employed, such as a bone fusion, or implantation of a prosthetic disc nucleus or a total artificial disc.
Embodiments of the invention are better understood with reference to the following drawings. The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts.
For one skilled in the art, other implant and fixation designs may be substituted without changing the intent and performance of the invention.
In the following Detailed Description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology, such as “top,” “bottom,” “front,” “back,” “leading,” “trailing,” etc., is used with reference to the orientation of the Figure(s) being described. Because components of embodiments of the present invention can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.
The present disclosure relates to an interspinous process spacer implant device useful in effectuating and maintaining an increased spacing between vertebral segments of a damaged vertebral segment of a damaged vertebral column. The implant device is described in detail below. As a point of initial reference,
With the above anatomical description in mind,
The implant body 32 includes a central portion 40, superior legs 42a, 42b, and inferior legs 44a, 44b. In some embodiments, the components 40-44b are integrally formed of a biologically acceptable, highly rigid material such as an implant-grade alloy of titanium, a polymer reinforced with fibers (e.g., carbon fibers), etc. Regardless, the central portion 40 defines a left side 50, a right side 52, and anterior face 54, a posterior face 56, a superior face 58, and an inferior face 60. With these designations in mind, the central portion 40 further forms a continuous, lateral passage 62 extending between the left and right sides 50, 52. The lateral passage 62 is exteriorly open at both the left and right sides 50, 52 (it being understood that in the view of
In some embodiments, the lateral passage 62 is centered between the superior and inferior faces 58, 60 and/or centered between the exposed surfaces of the cushions 34a, 34b. In other embodiments, however, the lateral passage 62 can be positioned closer to one or the other of the superior or inferior faces 58 or 60. Finally, and as best shown in
Apart from the lateral passage 62 described above, the central portion 40 is preferably characterized by the absence of other slots or apertures extending through a thickness or width thereof. More particularly, the central portion 40 does not, in some embodiments, include any continuous bores or passages extending completely between, and open at both of, the anterior and posterior faces 54, 56. With this one construction, and in combination with the superior and inferior legs 42a, 42b, 44a, 44b as described below, the implant body 32 has an H-shape when viewed posteriorly or anteriorly. In other embodiments, however, one or more partial or complete bores or passages through the central portion 40, in addition to the lateral passage 62, can be provided.
The superior legs 42a, 42b extend upwardly from the central portion 40 in a spaced fashion. In some embodiments, the first superior leg 42a is formed as a continuation of the left side 50 of the central portion 40, whereas the second superior leg 42b is a continuation of the right side 52. Regardless, a transverse spacing is established between the superior legs 42a, 42b, defining a superior receiving zone 64 sized to receive a portion of a spinous process. Each of the superior legs 42a, 42b terminates at a tip 66 opposite the superior face 58 of the central portion 50. In some embodiments, the superior legs 42a, 42b have a substantially identical length in extension to the corresponding tip 66; alternatively, the superior legs 42a, 42b can have different dimensions. Regardless, and as best shown in
The inferior legs 44a, 44b are, in some embodiments, identical to the superior legs 42a, 42b described above, and extend downwardly from the central portion 40. Thus, the inferior legs 44a, 44b are transversely spaced from one another, combining to define an inferior receiving zone 70 sized to receive a spinous process. The transverse spacing defined between the inferior legs 44a, 44b (i.e., width of the inferior receiving zone 70) is preferably substantially identical to that defined between the superior legs 42a, 42b (e.g., within 5% of an identical size); alternatively, the inferior receiving zone 70 can be substantially (e.g., greater than 10%) wider or narrower than the superior receiving zone 64. As with the superior legs 42a, 42b, the inferior legs 44a, 44b each terminate at a tip 72 opposite the inferior surface 60, and each optionally forms a tapered groove 74 (shown for the first inferior leg 44a in
With the above construction of the implant body 32 in mind, the optional cushions 34a, 34b are secured (e.g., bonded) to the implant body 32 as shown. More particularly, the first cushion 34a is secured to the superior face 58 of the central portion 40, thus defining an abutment surface 80 of the superior zone 64. Conversely, the second cushion 34b is affixed to the inferior face 60 of the central portion 40, and thus defines an abutment surface 82 of the inferior zone 70.
The cushions 34a, 34b effectively serve as shock absorbers for the contacted spinous processes following implant. The cushions 34a, 34b are formed of a softer material as compared to that of the implant body 32. In some embodiments, the cushions 34a, 34b are formed of elastomeric rubber material, for example, an implant grade silicone, polyurethane, or polysulfone rubber or other material exhibiting a durometer rating that is moderately firm and able to withstand roughly 200-400 psi compression repeatedly over several million cycles without fracture. In other embodiments, however, one or both of the cushions 34a and/or 34b can be eliminated. Further, while the cushions 34a, 34b are illustrated in
Implantation of the device 30 to the vertebral column 10 (
In
To assist in achieving a best fit between the implant device and the spinous processes in question, an optional shaping tool 120 can be provided as shown in
In some embodiments, the implant device 30 (
In other embodiments, the implant device 30 can have a self-spacing or expanding feature such that a single implant device 30 can be used with a variety of differently-sized patients. For example, and with specific reference to
Regardless of an exact construction,
An otherwise healthy, suitable patient having disc collapse with associated discogenic pain or other vertebral column 10 damage at adjacent vertebral segments 12a, 12b is selected. With reference to
With anticipated accommodation of the bone of the spinous processes to the tight band, tape or sutures, the tight configuration will slacken slightly allowing more freedom of spinal column flexion-extension, a desirable trait.
The invention has the ability to restore the height of the posterior annulus of the disc and open the facet joints and exiting nerve foramens while stabilizing the construct with a band of tape or sutures placed in, for example, a figure-eight fashion around the spinous processes and across through a central slot in the implant to the other side. This configuration restores and establishes considerable torsional strength to the degenerated spinal segment and over time will slowly permit some desirable increase of flexion-extension mobility to the segment. The implant uniquely provides, in some embodiments, interposed elastomeric rubber shock absorbers facing the prepared ends of the spinous processes.
The implantation method is minimally invasive, performed through a small posterior incision, perhaps under local anesthesia and is extremely simple for spine surgeons. The implantation is facilitated by using the optional bone-shaping and trimming tool that is under control by the surgeon at all times. The device and method can be used with or without temporary adjunctive external bracing as required by the particular patient. The surgeon may apply the tape, band or sutures as tightly or loosely as desired.
Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof.
The application of the spinous process spacer implant device is devoid of any undesirable side effect such as rejection of the implant materials, an inadvertent subsequent promotion of a segmental fusion or uncomfortable overlying muscle abrasion that can occur by protruding parts of implants. The segmental stabilizing and pain relieving effects are immediate and continuous. The implant and the optional elastomeric bumpers can be constructed and attached together in a variety of ways. Preferred means to prepare for and install the implant are disclosed here although persons skilled in the mechanical arts can adapt the concept to a variety of means to cause desirable alternative means.
No other inter spinous spreading device or method serving this application or in combination with the interposed elastomeric bumper and means of strapping fixation between the spinous processes under surgeon control is known to exist at this time.
