Patent Application
20120323326
The invention relates to the field of surgery of the spine and, in particular, to surgery involving replacement of the facet joints of the spine with prosthetic implants. The implants are secured to the lamina associated with the inferior articular facet and the pedicle associated with the superior articular facet. A ballottable chamber traverses the joint space. The prosthetic joints may be placed by percutaneous techniques using minimally invasive procedures; endoscopic techniques utilizing slightly more invasive techniques, or “open” surgical technique.
It is estimated that during the course of their lifetime, 65 million Americans will experience one or more significant episodes of back pain, with or without associated radiculopathy. It is the most common reason for adults to seek health care in the United States, and various forms of surgical treatment remain among the most common types of surgical procedures performed. It remains the most common cause of long-term disability from gainful employment. Multiple studies have demonstrated unambiguously that the overall effect of back pain, from this perspective, is almost immeasurable.
At one time, treatment of this disorder was in the hands of a variety of disciplines, including traditional medicine or “allopathic” physicians as well as variety of “alternative” physicians. These included chiropractors, acupuncturists, homeopathist, as well as a variety of less credentialed practitioners and frank charlatans. In sum, back pain was extremely poorly understood at the turn of the 20th century. A variety of potions, recipes, oils, liniments, and mythological regimens that “guaranteed” relief from back pain enjoyed short, but notable tenures as the “panacea” of this all to common disorder.
As a scientific approach began to establish itself, the intervertebral disc began to attract a great deal of attention, particularly as the primary source of symptoms related to the back.
This structure was first recognized as a source of pathology in 1934, when a report by Mixter and Barr appeared in the New England Journal of Medicine describing a herniated disc as a cause of pain in the back and leg (referred to as radiculopathy).
The initial surgical approach called for an incision in the midline of the back over the site of the disc presumed to be diseased. The muscles attached to the posterior elements of the vertebrae are stripped off, exposing the spinous process, lamina, and facet joint. Using a variety of tools, the lamina was then partially or totally removed, and the ligamentum flavum was then removed. The dura and nerve roots were gently retracted medially, and the disc itself could be visualized. The offending fragment was then removed and the incision was closed.
This procedure, either alone or in combination with fusion, was the mainstay of surgical treatment for low back pain and/or radiculopathy for many years. While this had some success, it was well known that many patients did not benefit from this type of surgical intervention. Beginning the late 70's and early 80's, alternatives were sought.
Consequently, there has been a dramatic increase in the technology involved in surgery for disease of the spine over the past two decades. Beginning with the introduction and widespread use of pedicle screws to enhance spinal fusion in the 1980's, there is now a wide armamentarium of devices available to the spinal surgeon.
The reason why a variety of approaches to spinal disorders have been developed is that there have been several key changes in both our scientific understanding, as well as our sense for the patient with back disorders. At one time, it was very common for the majority of physicians to “write off’ patients with back pain leaving these patients with both a sense of abandonment, as well as a sense of desperation, thus precipitating a search for alternative cures. With the advent of transaxial imaging, initially by CT scanning in the late 1970's and subsequently by MRI scanning in the 1980's, a better sense for the complexities of spinal pathophysiology is now appreciated by the average practicing physician. This has led to not only a lower threshold to conduct diagnostic evaluations of such patient's, but also a much lower threshold to refer such patients to spinal specialists. Additionally, it must be stated that changing medicolegal climate over the last quarter century with concerns about malpractice litigation and a sense of practicing “defensive medicine” has also led to an increase in the evaluation and referral patterns of such patients.
However, although such technical advances continue, the current understanding of spinal pathophysiology is only beginning to appreciate the role of all of the complex structures of the spine. As the knowledge base of spinal pathophysiology began to expand, it became obvious that the complex architecture of this articulated column of 24 mobile and 9 fused bones, with their intervening discs, associated facet joints, muscle, tendons and ligaments, there are many different possible “pain generators.” As such, it began to become appreciated that at the laminectomy which had become the standard treatment for any type of spinal disorder, not a panacea; rather it was an appropriate operation for some disorders, and actually, contraindicated for others. Hence, there was at last a logical explanation for the phenomenon of worsening back pain seen in many patients who stated that they actually felt worse after classic laminectomy. While this had long been thought to be a phenomenon was mostly rooted in secondary gain, as the understanding of the pathophysiology of spine disease improved, it became clear that at least a subpopulation of these patients actually were worse after surgery because of the adverse effects of the laminectomy upon their native pathophysiology. Once this was understood, the challenge that developed and still remains is identifying the source of the patient's pathology and pain, and devising surgical treatments that address the specific problem.
One of the structures of the spine that has attracted a great deal of attention as a possible pain generator is the so-called zygapophyseal joint, commonly known as the facet joint. The role of the facet joints in the production of chronic back pain has been noted for many years since the report by Goldthwait in 1911.
It has been noted that each facet joint receives multiple sources of innervation, presumably, therefore, having multiple sources of potential pain transmission. Additionally, Putti in 1927 and Williams and Yglesias (1933) described the facet joint abnormalities that are commonly seen. Ghormley was the first to actually use the term facet joint syndrome in 1933.
In the 1970's, the facet joint became a focus of attention regarding these issues. Reiss successfully described denervation of the facet joints in 1971. This technique was further evaluated and refined by Shealy who introduced the use of radiofrequency thermocoagulation. Multiple other authors have further discussed and refined this technique, including Bogduk, Ogsbury, Simons, Lehman, Pawl, Rashbaum, Sluyter and Mehta.
Despite the extensive literature, the exact role of the facet joints in the overall spectrum of degenerative disease of the spine remains to be clarified further.
Not all authors have been in complete agreement regarding the role of facet disease. Montesano, in the early 80's, published several papers that mitigated very much against the facet joints as a source of pain. These papers became very well established in the orthopedic literature and for more than a decade the facet joints were completely ignored as a source of pain.
With the emergence of pain management clinics, however, the role of the facet joints in the production of back pain has been irrefutably re-established. Causes, however, of both facet arthropathy as well as facet pain itself are still a matter of speculation.
It has always been assumed that facet arthropathy developed as the result of years of microtrauma which is ultimately the consequence of factors such as genetics, heavy labor, poor posture, repeated microtrauma and other, as of yet unexplained factors. It was felt that such factors eventually led to calcium deposits around the facet joints as well as chronic inflammation of the joint proper. This then results in hypertrophy, loss of the stability provided by the joint, and hypermobility. It was further postulated that this ultimately led, in fact, to increased mobility (rather than the classic sense of “stiffness” associated with arthritis) that the increased mobility ultimately resulted in relative motion segment instability. It was felt that this in turn led to back pain as well as possibly nerve root irritation associated with mechanical irritation of the nerve roots as they pass through the foramen.
More recent papers have suggested that the pathophysiology could be even more complicated. Recent studies have evaluated the neurophysiologic and electrophysiologic response of the facet joints to injury. Some papers have suggested that this has kinematic and biomechanical implications.
Other theories have also been postulated. Recently, at the Spine Arthroplasty Society meeting, Ashish has proposed that the build up of nitric oxide within the facet joint could be responsible for some of the pain experienced by these patients. Obviously, these phenomenon need to be further evaluated.
Regardless of the exact cause of facet pain, one fundamentally important concept that has become clearer in recent years is the important biomechanical relationship between the facet joints and the intervertebral disc.
Clearly one important mechanical component regarding the facet joints is the reciprocal relationship with the intervertebral disc. The role of the disc appears to be involved in the governance of movement of the spine, particularly certain movement such as flexion and to a lesser degree lateral rotation and lateral bending. It is felt that the disc is responsible for bearing approximately 80% of the load of the spine while the facet share in approximately 20% of the load bearing. The facets are also responsible for limitation and extension and participate in lateral rotation and lateral bending as well. Recognizing the interrelationship and interplay between the disc and the facet joint becomes apparent that replacement of the disc without attention to the facet joint may create an imbalance. Nevertheless, while a plethora of disc replacement devices have been introduced and contemplated in recent years, few systems exist for the prosthetic replacement of the natural facet joint.
An early attempt to do so was provided by Fitz in U.S. Pat. No. 5,571,191. In this patent he discloses a system by which the facet joints are “capped,” by prostheses. This has not attracted a great deal of interest, and others, including Fallin, in U.S. Pat. No. 6,419,703 has pointed to the shortcomings of such systems. These include difficulties in establishing the correct size of the required cap, failure to relive pain in the setting of advanced osteoarthritis, and the failure of similar systems in other venues (i.e. hip). The system disclosed by Fallin provides a method for replacing the lamina and associated facet joints. Like other systems, discussed below, this requires a substantial surgical procedure.
Martin, in U.S. Pat. No. 6,132,464 also provides for a system that requires attachment to the lamina. It has been commented that the fashion by which this attaches to the lamina would predict substantial variability in the implants, thus being a limiting factor.
Other systems, including that provided by Goble (U.S. Pat. No. 6,579,319) and Reiley (U.S. Pat. No. 6,610,091) require extensive surgical procedures to accomplish implantation. The system disclosed by Reily has undergone initial clinical trials. This system has been the first system to be tested clinically, with the results still pending. Overall, it appears that the experience with such systems is limited, but the need for the surgical replacement of the natural facet joint is becoming increasingly better defined.
Another critical consideration has been the emergence of the artificial disc, or total disc replacement, as a viable surgical option. Early efforts to accomplish this were described at the Charite' hospital in Germany, and subsequently a number of embodiments have been provided by Ray, et al.
Although early evaluations of the use of such prostheses suggest that there is a role for such surgical procedures, it is beginning to be recognized that in some cases, failure of the artificial disc may be related to facet joint pathology. Specifically, the inventors herein postulate that given the reciprocal functional relationship that exists between the facet joints and the disc, it is likely that in a number of cases, disease of the facet joints and the intervertebral disc is most likely coexistent. In such settings, it is readily postulated that replacement of the disc without attention to the [diseased] facet joints will result in failure of the prosthesis.
The facet joint prostheses that have thus far been provided, appear to satisfy the biomechanical requirements placed upon such a prosthesis. These requirements would include the ability to share in the biomechanical load of the spine, particularly the lower spine. This has been estimated to be approximately 2000N in the erect individual, and it is thought that the disc bears approximately 80% of this physiological load while the facet joints bear approximately 20%, or approximately 400N.
There are also shear and strain forces placed upon the facet joint, and, therefore, upon any prosthesis that might be implanted as a replacement of the facet joint. Additionally, the joint participates in the limitation of movement in flexion, lateral rotation, lateral bending, and, in particular, extension. Such a prosthesis would, necessarily, have to perform such functions.
Therefore, a need exists for a system of facet joint replacement that is minimally-invasive yet able to satisfy the biomechanical requirements of the natural facet joint.
The invention is made bearing the above needs in mind, and in accordance with those needs, one aspect of the invention provides for a system by which the surgeon may identify the facet joints in an efficient, accurate, and technically facile manner. Such a system has been provided for by the inventors in a previous application. As such, the surgeon can utilize fluoroscopy in conjunction with purpose-specific templates that are laid against the back of the patient. This template is impregnated with a radioopaque marker that simulates the outline of the lateral profile of the spine in the posteroanterior projection. Lateral to this outline is a raised aperture that will direct the trajectory of a needle/guide pin that has been passed through it. Aligning the outline on the template with the radiographic image of the spine will allow the surgeon to identify an entry point through which a needle/guide pin may be passed into the facet joint without difficulty. The position of the needle is then confirmed using radiologic techniques.\
In another aspect of the invention, when an adequate position of the needle has been established, a series of dilators are passed over the needle ultimately defining a pathway for passage of a working channel. The working channel is unique, as described in a previous application, insofar that the shape of the working channel is ovoid, or elliptical in shape. This device is tubular is structure, and demonstrates a leading end, a long axis, and a trailing end. The leading end is passed through the incision and brought against the target facet. The long axis then connects the leading end to the trailing end, the trailing end being the site whereupon the surgeon may be provided with access to the interior of the working channel for passage of appropriate additional devices as well as insertion of the prosthesis. Furthermore, in the preferred embodiment, the working channel is provided with a modification of its leading end in that there is an extension seen arising from the lateral aspect of the leading end. This extension is designed in such a fashion that this extension can be brought along the lateral aspect of the superior articular process and docked against the junction of the superior articular process and the transverse process. This design will add additional stability to the working channel during the balance of the procedure.
In yet another aspect of this invention, the diseased facet joint is removed with a burr, box chisel, or by some other means. The preferred embodiment favors the use of a burr, in a fashion similar to the previous application provided by the inventor. As such, the preparation for removal of the facet joint will involve similar steps. These steps include proper identification of the facet joint, passage of a series of dilators to separate the muscular attachment to the facet joint, passage of a working channel through which a burr or other instrument can be used to remove the facet joint. Removal of the facet joint includes removal of both the superior and inferior articular [processes] components of the joint. This maneuver leaves behind an entry into the pedicle as well as an area along the lateral lamina for attachment of the joint prosthesis.
In the preferred embodiment, after removal of the natural facet joint, the prosthesis is passed down so that it may engage the entry point into the pedicle. The prosthesis is composed of a leading end and a trailing end. The leading end, in turn, is represented by a screw which shall be passed through the target pedicle and anchors the prosthesis into the vertebral body. The leading end of the screw may be designed in such a way that it can either be self-tapping and/or self-drilling. Alternatively, a drill and tap may be used in the classic fashion for insertion of a screw into bone.
The trailing end of the prosthesis is represented by a multi-component structure which reproduces the movement accorded to the motion segment by the facet joint to be replaced. These components include a superior articular replacement component, as well as a ballottable chamber and a laminar component. The superior articular replacement component is similar in size and configuration to a normal superior articular process. The trailing end of the screw is contained within a chamber that is located within the superior articular replacement component. Specifically, the trailing end of the screw is secured within a chamber that is located within the central portion of this superior articular process replacement. The trailing end of the screw is designed to accommodate a Philips-type screwdriver, a regular or flat screwdriver, an Allen wrench, or any other similar drive mechanism. The trailing end of this chamber is continuous with an aperture on the superior surface of the superior articular replacement, and this aperture provides access of such a screwdriver or other drive mechanism to the trailing end of the screw. At the leading end of the chamber, the trailing end of the screw, which is noted to be slightly enlarged in diameter when compared to the diameter of the shaft of the screw, interfaces with an engagement mechanism. In the preferred embodiment, this is represented by a narrowing of the chamber, so that as the screw passes into the pedicle, a point is reached whereby the trailing end of the screw becomes secured against the walls of the chamber. A number of embodiments are contemplated, with the primary goal to provide a system by which the screw can be initially rotated so that it may be passed into the pedicle. When an adequate depth has been achieved, in the preferred embodiment, the trailing end of the screw is brought against the walls of the chamber and irreversibly secured into position. One or more washers/bushings may be incorporated into the construct of the engagement mechanism to achieve this. A locking or securing “cap” or plug may be passed into the trailing end of the chamber to further secure the screw.
On the medial side of the superior articular process replacement there is found a discoid, flattened area which shall serve as the base of attachment for a ballotable chamber which may be filled with fluid, air, a granular substance or any other substance. This chamber then subserves the main functions of the mobility of the facet joint. The fluid nature of this chamber will allow for rotational as well as shear movement, and extension of the chamber as well as compression. On the medial side of this ballottable chamber is yet another discoid base that secures to the chamber. This discoid base in turn is irreversibly coupled to a vertical extension of the most medial component of the prosthesis, that component being referred to as the laminar component. The laminar component has a vertically-oriented extension which attaches to the ballottable chamber. The vertical extension then forms an angle with a somewhat horizontally-oriented extension which is designed to lie against the lateral aspect of the lamina. Another embodiment of the laminar component replaces the angle between the horizontal and vertical components with a single, smooth curvilinear embodiment. This is designed to more easily conform to the area of the lamina that has been removed by the burr. In either embodiment, the surface that interfaces with the bone would ideally be roughened or in some other fashion finished, coated, or treated so as to promote bony ingrowth. This is secured to the lamina by a plurality of screws, pins, or other similar securing devices. The screws or other securing devices may be oriented to secure into the lamina, or conversely, may be directed to be passed through the base of the spinous process. In yet another alternative embodiment, the screws may be passed through the base of the spinous process and secured with a bolt or nut on the exterior surface of the contralateral lamina. These screws are secured into place by right angled screwdrivers. Alternatively, panels in the working channel may be removed to allow access to the proper angle for insertion.
On the medial aspect of the ballotable chamber is yet another discoid surface which is anchored to the chamber. This discoid surface is in turn on the lateral aspect of the component that is secured to the lateral aspect of the lamina.\
The presence of the ballotable chamber provides movement in a variety of planes and accounts for the shear and stress movements typically mitigated by the facet joint.
In another embodiment, the inflatable chamber is replaced by a 2-piece mechanical chamber that is designed to limit extension; at the same time this mechanical chamber is fashioned in such a way that it will not constrain shear movement of the joint nor will it constrain lateral rotation or lateral bending. This is achieved by the inner design of the mechanical chamber, which is composed of two ramps that are spiraling in opposite directions. Furthermore, there is a space between the high points of both ramps such that this space closes and is eliminated in extension, but opens in flexion and remains neutral in lateral bending and lateral rotation. Furthermore, the space will again open with shear movements of the facet joints. This embodiment is, again, unitized and inserted using the same sequence of steps that are used to insert the preferred embodiment outlined above—namely, the target facet joint is radiographically identified; a guide pin is passed into the joint; dilators and a working channel are then passed into place; burr is used to remove the joint; and the prosthesis is inserted. The prosthesis can be secured to the lamina using the preferred or alternative embodiments outlined above.
Referring now to the drawings, in which like reference numerals identify similar or identical elements throughout the many views. Turning now to
As demonstrated in
In
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In
In preparation for passage of the prosthetic device (11), an insertion tool (54) is now introduced into the procedure. As seen in
An alternative embodiment of the joint disc is also herein provided. This embodiment replaces the liquid or gel center with a mechanical joint disc (71). As seen in an exploded perspective view in
In
Additionally, it is to be remembered that one of the principal functions of the facet joint is to limit extension. To that end, an alternative embodiment of the discoid surface (13) and discoid base (17) is seen in
While the invention has been shown and described with reference to certain preferred embodiments, it will be understood by those skilled in the arts that various changes and modifications in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
This is a continuation of U.S. patent application Ser. No. 13/114,240, filed May 24, 2011 which is a divisional of U.S. patent application Ser. No. 11/224,009 filed Sep. 13, 2005.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11224009 | Sep 2005 | US |
| Child | 13114240 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13114240 | May 2011 | US |
| Child | 13347196 | US |
