Patent Application
20060241766
Spinal columns have a plurality of vertebrae that are separated by discs. A disc may be displaced or damaged due to trauma or disease, resulting in disruption of the annulus fibrosis, and the eventual protrusion of the nucleus pulposus into the spinal canal. This condition is commonly referred to as a herniated or ruptured disc. The extruded nucleus pulposus may press on the spinal nerve, thereby causing nerve damage, pain, numbness, muscle weakness and/or paralysis. Alternatively, the normal aging process may cause a disc to deteriorate. For example, as a disc ages, it dehydrates and hardens, and this in turn reduces the effective thickness of the disc. As a result, there can be pain, decreased mobility, and/or instability of the spine.
It has become fairly common to surgically remove a damaged or problematic disc, in and to replace it with an artificial disc. One type of artificial disc is designed to secure the adjacent vertebrae against movement with respect to each other, and this is commonly known as fusion of the two vertebrae. When two vertebrae are fused in this manner, the rest of the spinal column provides sufficient movement to accommodate the needs of the patient.
A different type of artificial disc is designed to preserve motion between two vertebrae. This type of disc is designed to operate reliably for many years after it has been surgically implanted in a patient, typically for the natural lifetime of the patient. Nevertheless, in rare situations, problems may eventually develop. For example, even where the artificial disc is still functioning properly, the patient may be subjected to trauma or disease that leads to a physiological condition causing pain, numbness, muscle weakness or the like during the movement permitted by the artificial disc. Alternatively, trauma or long-term wear may cause the artificial disc itself to experience a problem that causes pain or discomfort during the movement permitted by the artificial disc. When one of these types of problems develops, the current solution is to subject the patient to another major surgical procedure, in which the motion preservation disc is surgically removed, and replaced with a new artificial disc. The new disc may be either a motion preservation disc or a fusion disc, depending on the particular circumstances of the patient.
One form of the invention involves an artificial joint for surgical insertion between two bones, the joint including: first and second parts supported for relative movement; and structure that can be selectively used to facilitate relative fixation of the first and second parts in a manner preventing the relative movement.
A different form of the invention involves a method of carrying out a surgical procedure that includes: inserting between two bones an artificial joint having first and second parts that are movable relative to each other and that each cooperate with a respective bone, the joint having structure that can be selectively used to facilitate fixation of the first and second parts against relative movement; and completing the surgical procedure with the first and second parts movable relative to each other.
Still another form of the invention relates to a method that involves an artificial joint disposed between two bones and having first and second parts movable relative to each other; wherein the method includes modifying the joint in situ to fix the first and second parts against relative movement.
The parts 16 and 17 each include a respective shell 26 or 27. The shells 26 and 27 each have a concave inner surface, and a convex outer surface. Further, the shells 26 and 27 each have a central post 28 or 29 that projects vertically toward the other thereof. An opening 31 or 32 extends vertically through each shell 26 or 27, and through the post 28 or 29 thereof. The outer end of each opening 31 and 32 is threaded. The shells 26 and 27 each have a respective annular groove 33 or 34 extending circumferentially around the periphery thereof. The shells 26 and 27 each have an upwardly-extending flange 36 or 37 on a rear side thereof, and a respective opening 38 or 39 extends horizontally through each of the flanges 36 and 37. The parts 16 and 17 also include respective plugs 42 and 43. The plugs 42 and 43 each threadedly engage the threaded outer end of a respective one of the openings 31 and 32. The shells 26 and 27 and the plugs 42 and 43 can each be made from a wide variety of biocompatible materials. In the embodiment of
Each of the parts 16 and 17 has on the convex outer surface thereof a respective coating 46 or 47 that promotes ingrowth of bone material, in order to help fixedly couple the parts 16 and 17 to the bones 12 and 13. In the embodiment of
The central body 19 is annular, with a vertical axial opening therethrough. The opposite ends of this opening receive the respective posts 28 and 29, with sufficient clearance to allow relative transverse movement. The central body 19 has convex top and bottom surfaces that each slidably engage the concave inner surface on a respective one of the shells 26 and 27. The central body 19 is resiliently deformable, and has surface regions that are harder then the interior region. This allows the central body 19 to be sufficiently deformable and resilient so that the disc 10 functions to provide resistance to compression and also to provide damping, while still providing adequate surface durability and wear resistance. In addition, the material of the central body is selected so that the surfaces are very lubricious, in order to decrease friction between the central body and each of the rigid shells 26 and 27.
The material used to make the central body 19 is a biocompatible polymeric material that is slightly elastomeric, and that may be coated or impregnated to increase surface hardness, lubricity or both. Coating may be carried out by any suitable technique, such as dip coating, and the coating solution may include one or more polymers. The coating polymer may be the same as or different from the polymer used to form the interior of the central body, and may have a different Durometer hardness than that of the interior material. The coating thickness can be greater than about 1 mil, for example from about 2 mil to about 5 mil. Examples of suitable commercially-available materials include polyurethanes such as polycarbonates and polyethers, including CHRONOTHANE P 75A or P 55D (P-eth-PU aromatic, CT Biomaterials), CHRONOFLEX C 55D, C 65D, C 80A, or C 93A (PC-PU aromatic, CT Biomaterials), ELAST-EON II 80A (Si-PU aromatic, Elastomedic), BIONATE 55D/S or 80A-80A/S (PC-PU aromatic with S-SME, PTG), CARBOSIL-10 90A (PC-Si-PU aromatic, PTG), TECOTHANE TT-1055D or TT-1065D (P-eth-PU aromatic, Thermedics), TECOFLEX EG-93A (P-eth-PU aliphatic, Thermedics), or CARBOTHANE PC 3585A or PC 3555D (PC-PU aliphatic, Thermedics).
The disc 10 includes two retaining rings 61 and 62 that each sealingly hold a respective axial end of the sheath 21 within a respective one of the grooves 33 or 34. An annular chamber 66 is defined within the disc 10, between the sheath 21, the periphery of the central body 19, and the peripheral edges of the shells 26 and 27. In the embodiment of
A fitting 71 is mounted on the sheath 21, in angular alignment with the flanges 36 and 37. The fitting 71 extends through the sheath 21, and has a passageway 72 that can provide communication between the annular chamber 66 and the exterior of the disc 10. In the embodiment of
Following manufacture of the disc 10, the disc 10 is surgically inserted in a known manner between two vertebrae, such as the vertebrae shown at 12 and 13 in
After surgical insertion of the disc 10, and after recovery of the patient, the disc will facilitate a degree of relative movement between the bones 12 and 13. In particular, the shells 26 and 27 can each carry out limited lateral sliding movement relative to the central body 19. Since the cooperating surfaces on the central body 19 arid the shells 26 and 27 are curved, the relative movement will effectively be limited pivotal movement about any of various horizontal axes. In addition, the inherent resilience of the central body 19 will allow a limited degree of vertical compression that permits movement of the shells toward each other, and also a limited degree of relative rocking movement of the shells that is effectively limited pivotal movement about horizontal axes.
In rare cases, it is possible that a problem may develop over time. For example, even where the disc 10 is still functioning properly, the patient may experience trauma or disease that leads to a physiological condition causing pain, numbness, muscle weakness or the like during the relative vertebral movement permitted by the disc 10. As another example, trauma or long-term wear may cause the disc 10 itself to experience a problem that causes pain or discomfort to the patient during the movement permitted by the disc. In either case, the standard solution with pre-existing artificial discs is to subject the patient to a further major surgery in order to replace the artificial disc with a different artificial disc. In contrast, the disc 10 allows a different approach.
More specifically, in a relatively minor surgery, a small incision is made in the skin and muscle of the patient, order to allow access to the fitting 71. The obstruction within the passageway 72 is punctured with a sharp and sterile object, in order to permit fluid flow through the passageway 72. One end of a tube 91 is then coupled to the fitting 71 in any suitable manner, so that the passageway 72 is in fluid communication with the passageway that extends through the tube 91. A syringe 92 or other suitable device is then used to inject a fluid material through the tube 91 and fitting 71, in order to fill the chamber 66 with the material. The material then cures or hardens, preferably in a relatively short period of time. Since this material engages the entire peripheral edge of each of the shells 26 and 27, the shells 26 and 27 will become fixed against relative movement when the material hardens. Consequently, the disc 10 will be converted from one operational mode in which the shells 26 and 27 are capable of relative movement to a different operational mode in which the shells 26 and 27 are fixed against any relative movement. The material injected into the chamber 66 is a biocompatible material. In the embodiment of
After the material has been injected, the tube 91 is detached from the fitting 71, and the opening 72 is closed. For example, a small plug may be force-fit into the opening 72. Alternatively, the opening 72 could be closed in any other suitable manner. The small incision made through the skin and muscle of the patient is then sutured or stapled. If necessary, the patient is kept immobilized until the material in the chamber 66 has had time to harden. However, in the embodiment of
The parts 116 and 117 each include a respective plate-like center portion 126 or 127. The center portion 126 has in the underside thereof an approximately hemispherical recess with a concave surface 131. The center portion 127 has on an upper side thereof an approximately hemispherical projection with a convex surface 132. The surfaces 131 and 132 slidably engage each other, to facilitate approximately pivotal movement of the parts 116 and 117 with respect to each other.
The part 116 has on the upper side of its center portion 126 an upwardly-extending projection or keel 136. Similarly, the part 117 has on the lower side of its center portion 127 a downwardly-extending projection or keel 137. The projections 136 and 137 each have a pair of transverse openings extending therethrough. Before the disc 110 is inserted between two vertebrae, the surgeon creates a recess in each vertebra. Then, when the disc 110 is surgically implanted, the projections 136 and 137 are each received in one of those recesses. This helps to anchor the disc 110 in the proper position. Further, as bone growth occurs over time, there will be bone growth into the transverse openings through the projections 136 and 137, thereby helping to anchor the disc 110 in place. The parts 116 and 117 can be made from a wide variety of biocompatible materials. In the embodiment of
The sheath 121 is made of a biocompatible material that is durable and flexible, and that may be slightly elastic. For example, the sheath 121 can be made from materials of the type discussed above in association with the sheath 21 of
As best seen in
A tube 174 is provided within the chamber 166, and has one end fixedly secured to the inner side of the fitting 171. The opening through the tube 174 communicates with the passageway 172, and effectively serves as an extension of the passageway 172. The other end of the tube 174 is positioned on a side of the chamber 166 that is remote from the fitting 171. Although
When the disc 110 is surgically implanted in a patient, the parts 116 and 117 are initially capable of relative movement, due to the sliding engagement of the surfaces 131 and 132. If necessary, at a later time, a material can be injected into the chamber 166 in a fluid state, through the fitting 171 and the tube 174. The material then hardens within the chamber 166. The engagement of this hardened material with the peripheral surfaces of the parts 116 and 117 serves to fix the parts 116 and 117 against relative movement. The injection of this material is carried out in a minor surgical procedure that is similar to the procedure already described above in association with the embodiment of
In a not-illustrated variation of the embodiment of
Later, when it becomes necessary to introduce a material such as cement into the chamber 66, there will be a need to remove most or all of the lubricant that is in the chamber 66. In that event, the fitting 71 and the tube 90 may each have two passageways, one of which carries the material that is being injecting into the chamber, and the other of which allows the lubricant to escape from the chamber. With respect to the passageway for the material being injected, the disc 10 would include a tube similar to that shown at 174 in
The part 216 has an approximately rectangular recess 223 in the center thereof. A cylindrical hole extends horizontally through the part 216, and has two portions 224 and 225 of different diameter. The portion 224 is of smaller diameter than the portion 225, and communicates at its inner end with the recess 223. The outer end of the portion 225 opens through an exterior surface of the part 216. The part 217 has an upwardly projecting post 251, and an opening 252 extends horizontally through the upper end of the post 251.
The disc 210 includes a pin 253 that is axially slidably disposed within the opening 224 and 225 in the part 216. The pin 253 has an annular groove near its inner end. A coil spring 256 encircles the pin 253, and resiliently urges the pin 253 to move axially outwardly. The recess 223 in the part 216 is filled with a material 258. As shown in
In the embodiment of
Instead of the TERFENOL-D product discussed above, the material 258 could alternatively be any other suitable material that. can transition between two states, such as hard and soft states. For example, the material 258 could be a polyethylene material having an electrically conductive part embedded in it. When subjected to a rapidly varying magnetic field, an electric current is induced in the electrically conductive part and causes it to heat up, which in turn heats the polyethylene in order to soften it sufficiently so that the pin 253 is released.
Although selected exemplary embodiments have been disclosed above in detail, many modifications and variations are possible. For example, it would alternatively be possible to provide a disc having a cam or other mechanical element that can be selectively manually moved between two positions in which it respectively permits and obstructs relative movement of two parts. As another alternative, a mechanical element that is not initially present in the disc could be selectively manually inserted in order to obstruct relative movement of two parts. Persons skilled in the art will readily appreciate that many other modifications and variations are possible without departing from the spirit and scope of the invention, as defined by the claims that follow.
The foregoing description uses spatial references such as “horizontal,” “vertical,” “top,” “upper,” “lower,” “bottom,” “left,” and “right”, in relation to orientations that are shown in the drawings. These spatial references are used for purposes of convenience, and are not intended to limit the scope of protection provided by the claims that follow. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures.
