[0001] This invention relates to prostheses for treating various types of spinal pathologies, as well as to methods of treating spinal pathologies.
[0002] I. Vertebral Anatomy
[0003] As
[0004]
[0005] Two short bones, the pedicles 16, extend backward from each side of the vertebral body 14 to form a vertebral arch 18. At the posterior end of each pedicle 16 the vertebral arch 18 flares out into broad plates of bone known as the laminae 20. The laminae
[0006] Two transverse processes
[0007] The superior and inferior articular processes
[0008] The facet joint 32 is composed of a superior half and an inferior half. The superior half is formed by the vertebral level below the joint 32, and the inferior half is formed by the vertebral level above the joint 32. For example, in the L4-L5 facet joint, the superior portion of the joint is formed by bony structure on the L-5 vertebra (e.g., a superior articular surface and supporting bone on the L-5 vertebra), and the inferior portion of the joint is formed by bony structure on the L-4 vertebra (e.g., an inferior articular surface and supporting bone on the L-4 vertebra).
[0009] As also shown in
[0010] II. Facet Joint Dysfunction
[0011] Back pain, particularly in the “small of the back”, or lumbosacral (L4-S1) region, is a common ailment. In many cases, the pain severely limits a person's functional ability and quality of life. Such pain can result from a variety of spinal pathologies.
[0012] Through disease or injury, the laminae, spinous process, articular processes, or facets of one or more vertebrae can become damaged, such that the vertebrae no longer articulate or properly align with each other. This can result in an undesired anatomy, pain or discomfort, and loss of mobility.
[0013] For example, the vertebral facet joints can be damaged by either traumatic injury or by various disease processes. These disease processes include osteoarthritis, ankylosing spondylolysis, and degenerative spondylolisthesis. The damage to the facet joints often results in pressure on nerves, also called a “pinched” nerve, or nerve compression or impingement. The result is pain, misaligned anatomy, and a corresponding loss of mobility. Pressure on nerves can also occur without facet joint pathology, e.g., a herniated disc.
[0014] One type of conventional treatment of facet joint pathology is spinal stabilization, also known as intervertebral stabilization. Intervertebral stabilization prevents relative motion between the vertebrae. By preventing movement, pain can be reduced. Stabilization can be accomplished by various methods.
[0015] One method of stabilization is posterior spinal fusion. Another method of stabilization is anterior spinal fusion, fixation of any number of vertebrae to stabilize and prevent movement of the vertebrae.
[0016] Another type of conventional treatment is decompressive laminectomy. This procedure involves excision of the laminae to relieve compression of nerves.
[0017] These traditional treatments are subject to a variety of limitations and varying success rates. Furthermore, none of the described treatments puts the spine in proper alignment or return the spine to a desired anatomy. In addition, stabilization techniques, by holding the vertebrae in a fixed position, permanently limit the relative motion of the vertebrae, altering spine biomechanics.
[0018] There is a need for prostheses, installation tools, and methods that overcome the problems and disadvantages associated with current strategies and designs in various treatments for spine pathologies.
[0019] The invention provides prostheses, installation tools, and methods designed to replace natural facet joints at virtually all spinal levels including L1-L2, L2-L3, L3-L4, L4-L5, L5-S1, T-11-T12, and T12-L1. The prostheses, installation tools, and methods can restore a desired anatomy to a spine and give back to an individual a desired range of relative vertebral motion. The prostheses, installation tools, and methods also can lessen or alleviate spinal pain by relieving the source of nerve compression or impingement.
[0020] For the sake of description, the prostheses that embody features of the invention will be called either “cephalad” or “caudal” with relation to the portion of a given natural facet joint they replace. As previously described, a given natural facet joint has a superior half and an inferior half. In anatomical terms, the superior half of the joint is formed by the vertebral level below the joint (which can thus be called the caudal portion of the facet joint, i.e., because it is near the feet). The inferior half of the joint is formed by the vertebral level above the joint (which can thus be called the cephalad portion of the facet joint, i.e., because it is near the head). Thus, a prosthesis that, in use, replaces the caudal portion of a facet joint (i.e., the superior half) will be called a “caudal” prosthesis. Likewise, a prosthesis that, in use, replaces the cephalad portion of a facet joint (i.e., the inferior half) will be called a “cephalad” prosthesis.
[0021] One aspect of the invention provides a cephalad facet joint prosthesis to replace a cephalad portion of a natural facet joint (e.g., an inferior articular surface and its supporting bone structure on the posterior elements of the vertebra) in the posterior elements of a vertebra. According to this aspect of the invention, the prosthesis includes an artificial facet joint element adapted and configured to replace a cephalad portion of the natural facet joint and a fixation element extending from the artificial facet joint element, the fixation element being adapted and configured to be inserted through a lamina portion of a vertebra to affix the artificial facet joint element to the vertebra, preferably without blocking access to a pedicle portion of the vertebra. The fixation element may also extend through a second lamina portion of the vertebra, such as by traversing the midline of the vertebra through or adjacent to the spinous process. In one embodiment, after installation the cephalad bearing element is disposed between a caudal facet joint bearing surface and a portion of the vertebra, such as a lamina portion.
[0022] This aspect of the invention also provides a method of implanting an artificial cephalad facet joint prosthesis on a vertebra and/or the posterior elements of a vertebra. According to this method, a fixation element is inserted through a lamina portion of the vertebra, and a cephalad facet joint bearing surface is placed in a position to form a cephalad portion of a facet joint. An artificial facet joint element is attached to a distal end of the fixation element either after or prior to insertion of the fixation element. The fixation element preferably does not block access to a pedicle portion of the vertebra. The fixation element may also extend through a second lamina portion of the vertebra, such as by traversing the midline of the vertebra through or adjacent to the spinous process. In one embodiment, the placing step includes disposing the artificial facet joint bearing surface between a caudal facet joint bearing surface and a portion of the vertebra, such as a lamina portion. The method may also include the steps of using a guide to define an insertion path for the fixation element and forming a passage through the lamina corresponding to the insertion path.
[0023] Another aspect of the invention provides a prosthesis to replace a cephalad portion of a natural facet joint on a vertebra. In this aspect of the invention the prosthesis includes an artificial facet joint element adapted and configured to replace a cephalad portion of the natural facet joint; and a fixation element adapted and configured to affix the artificial facet joint element to the vertebra without blocking access to a pedicle portion of the vertebra. In one embodiment, after installation the cephalad bearing element is disposed between a caudal facet joint bearing surface and a portion of the vertebra, such as a lamina portion.
[0024] This aspect of the invention also provides a method for implanting a cephalad facet joint prosthesis to replace a removed cephalad portion of a natural facet joint on a vertebra. The method includes the steps of aligning the cephalad facet joint prosthesis with a caudal facet joint bearing surface; and attaching the cephalad facet joint prosthesis to the vertebra without blocking a pedicle portion of the vertebra. The attaching step of the method may also include disposing the cephalad facet joint prosthesis between the caudal facet joint bearing surface and a portion of the vertebra. The attaching step may also include the step of inserting a fixation element through a portion of the vertebra, such as the lamina. In this case, the method may include the steps of defining an insertion path in the vertebra prior to the inserting step and forming a passage in the vertebra corresponding to the insertion path. A guide may be used to direct the location and orientation of the insertion path.
[0025] Another aspect of the invention provides a facet joint prosthesis to replace, on a vertebra, a caudal portion of a natural facet joint (e.g., a superior articular surface and supporting bone structure on the vertebra). The prosthesis includes an artificial facet joint element with a vertebra contacting surface and a caudal bearing surface, the caudal bearing surface being adapted and configured to replace a caudal portion of a natural facet joint and to be substantially entirely posterior of a contact portion of the vertebra when the vertebra contacting surface contacts the contact portion. The prosthesis also includes a fixation element extending from the artificial facet joint element, the fixation element being adapted and configured to be inserted into the vertebra to affix the prosthesis to the vertebra.
[0026] Another aspect of the invention provides a prosthesis for replacing a caudal portion and a cephalad portion of a natural facet joint of cephalad and caudal vertebrae of a spine motion segment. The prosthesis includes an artificial cephalad facet joint element adapted and configured to replace a cephalad portion of the natural facet joint, the artificial cephalad facet joint element having a cephalad bearing surface; a cephalad fixation element, the cephalad fixation element being adapted and configured to be inserted through a lamina portion of a vertebra to affix the artificial cephalad facet joint element to the cephalad vertebra; and an artificial caudal facet-joint element adapted and configured to replace a caudal portion of the natural facet joint, the artificial caudal facet joint element including a caudal bearing surface adapted and configured to mate with the cephalad bearing surface.
[0027] Yet another aspect of the invention provides a method for implanting a facet joint prosthesis to replace removed cephalad and caudal portions of a natural facet joint of cephalad and caudal vertebrae. The method includes the steps of: affixing an artificial caudal facet joint element to the caudal vertebra; inserting a cephalad fixation element through a lamina portion of the cephalad vertebra; and placing an artificial cephalad facet joint bearing surface in a position to form a cephalad portion of a facet joint. The method may also include attaching an artificial cephalad facet joint element comprising the cephalad facet joint bearing surface to an end of the fixation element either prior to or after the inserting step. In one embodiment, the fixation element does not block access to a pedicle portion of the cephalad vertebra. The cephalad fixation element may also extend through a second lamina portion of the cephalad vertebra, such as by traversing the midline of the cephalad vertebra through or adjacent to the spinous process. The placing step may also include the step of disposing the artificial cephalad facet joint bearing surface between the artificial caudal facet joint element and a portion of the cephalad vertebra. An installation fixture may be used to align the caudal and cephalad elements, although the prosthesis may also be installed without using an installation fixture. The method may also include the step of using a guide to define an insertion path for the cephalad fixation element, although the prosthesis may also be installed without using a guide.
[0028] Another aspect of the invention provides a prosthesis to replace a caudal portion and a cephalad portion of a natural facet joint of cephalad and caudal vertebrae. The prosthesis may include an artificial cephalad facet joint element adapted and configured to replace a cephalad portion of the natural facet joint, with the artificial cephalad facet joint element including a cephalad bearing surface; a cephalad fixation element adapted and configured to affix the artificial cephalad facet joint element to the cephalad vertebra without blocking access to a pedicle portion of the cephalad vertebra; and an artificial caudal facet joint element adapted and configured to replace a caudal portion of the natural facet joint, the artificial caudal facet joint element including a caudal bearing surface adapted and configured to mate with the cephalad bearing surface. In one embodiment, after installation the cephalad facet joint bearing surface is disposed between a caudal facet joint bearing surface and a portion of the vertebra, such as a lamina portion. In one embodiment, the cephalad bearing surface and the caudal bearing surface each has a width along its respective transverse axis, with the cephalad bearing surface width being shorter than the caudal bearing surface width. The artificial caudal facet joint element may also include a vertebra contacting surface, with the entire caudal bearing surface being adapted and configured to be posterior of a contact portion of the caudal vertebra when the vertebra contacting surface contacts the contact portion.
[0029] This aspect of the invention also includes a method for implanting a facet joint prosthesis to replace removed cephalad and caudal portions of a natural facet joint of cephalad and caudal vertebrae. The method includes the steps of affixing an artificial caudal facet joint element to the caudal vertebra; and affixing an artificial cephalad facet joint element to the cephalad vertebra in alignment with the artificial caudal facet joint element and without blocking access to a pedicle portion of the cephalad vertebra. The second affixing step may also include the step of disposing the artificial cephalad facet joint element between the artificial caudal facet joint element and a portion of the cephalad vertebra. An installation fixture may be used to align the caudal and cephalad element, although the prosthesis may also be installed without using an installation fixture. The method may also include the step of using a guide to define an insertion path for the cephalad fixation element, although the prosthesis may also be installed without using a guide.
[0030] Other features and advantages of the inventions are set forth in the following Description and Drawings, as well as in the appended Claims.
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[0048] FIGS.
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[0053] The invention may be embodied in several forms without departing from its spirit or essential characteristics. The scope of the invention is defined in the appended claims, rather than in the specific description preceding them. All embodiments that fall within the meaning and range of equivalency of the claims are therefore intended to be embraced by the claims.
[0054] Although the disclosure hereof is detailed and exact to enable those skilled in the art to practice the invention, the physical embodiments herein disclosed merely exemplify the invention that may be embodied in other specific structure. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims.
[0055]
[0056] Depending on the patient's disease state, the condition of the patient's natural facet joint-including the facet joint's strength, location and orientation-may not be acceptable. As shown in
[0057] In one embodiment of the invention, fixation element
[0058] In the embodiment shown in
[0059] In this embodiment of the invention, the cephalad facet joint prosthesis attaches to a posterior element of the vertebra, such as one or portions of the lamina and/or the spinous process. For example, as shown in
[0060] Unlike other facet joint prostheses that attach to the pedicle, this embodiment's use of one or more posterior elements of the vertebra to attach the cephalad facet joint prosthesis of this invention does not block access to the pedicle area, leaving this area free to be used to attach other prostheses or devices. Other embodiments of the invention may block the pedicle area, of course, without departing from the scope or spirit of the invention. In addition, because of the inherent strength of the lamina, the cephalad facet joint prosthesis may be affixed without the use of bone cement, especially when using a bone ingrowth surface or trabecular metal.
[0061] In the orientation shown in
[0062] Prosthesis
[0063]
[0064] In one embodiment, the natural caudal facet surface has been removed, and fixation element
[0065] As shown in the embodiment of
[0066] In this embodiment, bearing element
[0067] Prosthesis
[0068] FIGS.
[0069] The prostheses of
[0070] As shown in
[0071] When attached to installation fixture
[0072] In use, after preparing the implant site by removal of all or a portion of existing natural cephalad and caudal facet joint portions of the cephalad and caudal vertebrae 60 and 70, respectively, of the spine motion segment, bearing elements
[0073] Thereafter, the cephalad bearing elements are attached to the cephalad vertebra
[0074] After all four bearing elements have been affixed, the installation fixture
[0075]
[0076] As shown, tool
[0077] In the embodiment shown in
[0078] A mirror image tool may then be used to define an insertion path or to form a hole for the right cephalad bearing element, which is then affixed to the vertebral body in the same way. The installation fixture is then removed, such as by unscrewing screws
[0079] As mentioned above, in alternative embodiments the guide tool may be used to define a path for a self-tapping screw or other fixation element that does not require the use of a drill. In those embodiments, element
[0080] In some embodiments, the entire prosthesis other than the bearing surface may be coated with bone ingrowth material.
[0081] The above described embodiments of this invention are merely descriptive of its principles and are not to be limited. The scope of this invention instead shall be determined from the scope of the following claims, including their equivalents.