US 20080294259 A1
An intervertebral prosthesis for insertion between adjacent vertebrae includes upper and lower prosthesis plates locatable against respective vertebrae and having opposing, concavely curved recesses therein, and a core located between the plates. The core has opposed, convexly curved surfaces received in the recesses of the plates to allow the plates to slide in articulated manner over the core. The opposed surfaces of the core and the recesses of the plates have cooperating spherical curvatures. The recess of each plate surrounds a locating peg projecting centrally from the base of the recess and is bounded by an annular rim, such that the annular rims of the plates are arranged to contact one another at a predetermined limit of sliding movement of the plates over the core. The peg locates loosely in an opening located centrally in a curved surface of the core, whereby the plates can slide over the core in all directions while the peg holds the core captive.
18. A method for implanting an intervertebral prosthesis between adjacent vertebrae, the method comprising:
providing a prosthesis comprising,
upper and lower prosthesis plates having at least one upstanding elongate fin, at least one of the upper and lower prosthesis plates having a concavely curved, spherical bearing surface therein,
a movable core having at least one convexly curved, spherical surface configured to cooperate with the concavely curved surface of the upper or lower plate, and
a protrusion on at least one of the plates and corresponding opening on the core which hold the core captive and prevent the core from slipping out sideways from between the plates;
placing the upper and lower plates into place between adjacent vertebrae with the at least one fin entering a slot cut in an associated vertebral surface; and
inserting the movable core between the plates, wherein the upper and lower plates are able to both translate and rotate with respect to each other and with respect to the core.
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The present application is a continuation of Ser. No. 11/084,224 (Attorney Docket No. 022031-001710US) filed Mar. 18, 2005, which is a continuation-in-part of PCT/IB2003/001529 (Attorney Docket No. 022031-001700PC) filed on Apr. 24, 2003, designating the United States, which claimed priority from South African application 2002/7517 filed on Sep. 19, 2002, the full disclosures of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to an intervertebral prosthesis.
In the event of damage to a spinal disc it is known practice to implant an intervertebral prosthesis surgically to replace the damaged organ. Several types of prosthesis for this purpose are known and in common use.
One type of known intervertebral prosthesis is sold by Waldemar Link GmbH & Co under the trade mark LINK® SB Charité. This prosthesis includes upper and lower prosthesis plates which locate against and engage the adjacent vertebral bodies, and a low friction core between the plates. The core has upper and lower convexly curved surfaces and the plates have corresponding, concavely curved recesses which cooperate with the curved surfaces of the core. This allows the plates to slide over the core to allow required spinal movements to take place. The curved recesses in the plates are surrounded by annular ridges which locate, at the limit of sliding movement of the plates over the core, in opposing peripheral channels surrounding the curved surfaces of the core.
This type of configuration is also described in EP 0 560 140 and EP 0 560 141 (both Waldemar Link GmbH & Co). However a drawback of such configurations is that the provision of the peripheral ribs and channels limits the areas available for bearing and sliding contact between the plates and core, and accordingly the loads which can be transmitted by the prosthesis. As a result of the relatively small bearing areas, it is believed that at least the core will be subject to rapid wear and have a relatively short life-span.
EP 0 560 141 also describes one alternative arrangement in which the curved surfaces of the core carry opposing, elongate keys that locate in elongate grooves in the plates and another alternative arrangement in which the plates have opposing elongate keys that locate in elongate grooves in the opposite curved surfaces of the core. These key and groove arrangements allow the plates to slide freely over the core, within the limits of the length of the grooves, in one plane only. Although allowance is made for some lateral play of the keys in the grooves, very little sliding movement of the plates over the core can take place in the orthogonal vertical plane, and this is considered to be a serious drawback of this design.
2. Description of the Background Art
European Patent Publications EP 0 560 140 and EO 0 560 141 have been discussed above. U.S. Patent Publications US2002/0035400 and US2002/0128715 describe intervertebral prostheses with center-posts received in passages in a core. The core possesses an annular flange structure engaged by extensions on the plates.
According to the invention there is provided an intervertebral prosthesis for insertion between adjacent vertebrae, the prosthesis comprising upper and lower prosthesis plates locatable against the respective vertebrae and having opposing, concavely curved recesses therein and a core located between the plates, the core having opposed, convexly curved surfaces received in the recesses of the plates to allow the plates to slide in articulated manner over the core, characterized in that:
the opposed surfaces of the core and the recesses of the plates have cooperating spherical curvatures,
the recess of a plate surrounds a locating peg projecting centrally from the base of the recess, and
the peg locates loosely in an opening located centrally in a curved surface of the core, whereby the plates can slide over the core in all directions while the peg holds the core captive.
In some embodiments, only one of the plates, typically the operatively lower plate, includes a peg. In other embodiments, both plates include pegs, the pegs opposing one another and locating loosely in respective openings located centrally in the opposed curved surfaces of the core. In each embodiment it is preferred that each peg and the opening in which it locates are conical in shape.
According to another aspect of the invention there is provided a prosthesis plate for use in a prosthesis as summarized above, the prosthesis plate having a coarse surface locatable against a vertebra, an oppositely facing concavely curved surface which is complemental in shape to a convexly curved surface of a core of the prosthesis, characterized in the concavely curved surface of the plate has a spherical curvature and in that the plate includes a conical locating peg extending centrally from the concavely curved surface, the peg being locatable loosely in a central opening in the convexly curved surface of the core.
According to yet another aspect of the invention there is provided a core for use in the prosthesis, the core comprising a one piece plastics body having operatively upper and lower curved surfaces, characterized in that the curved surfaces of the body are spherically curved and at least one of the surfaces has a central, conical opening therein dimensioned to receive a conical locating peg of a prosthesis plate loosely.
Other features of the invention are set forth in the appended claims.
The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which:
The prosthesis plate 10 seen in
A first embodiment of prosthesis of the invention, indicated generally. by the numeral 28 in
The core surfaces 32 and recess surface 26 have the same radius of curvature which is, in this case, 18 mm.
In the assembled prosthesis 28, the plates 10 are arranged in opposition to one another with the core 30 located between them. The pegs 22 of the plates locate in the openings 34, i.e. in the ends of the passage 36. The combined length of the pegs is less than the length of the passage 36, so the inner ends of the pegs are spaced apart from one another by a short distance 38, as shown in
The cooperating spherical surfaces 26 and 32 and the relative dimensions of the pegs 22 and the passage 36 allow the plates 10 to slide or articulate over the core through a fairly large range of angles and in all directions or degrees of freedom, including rotation about the central axis.
At a predetermined limit of articulated movement of the plates relative to the core, the rims 24 of the plates contact with one another as indicated by the numeral 40 in
It will also be noted in
Throughout the range of possible articulation, the pegs 22 remain in the passage 36 and prevent the core from separating laterally from the plates 10. In other words, the core is held captive by the pegs during all possible articulations which can take place. In the illustrated embodiment, the plates 10 are limited to 12° of articulation before the rims 24 abut one another, i.e. 12° is the maximum articulation which can take place.
In the prosthesis 28 described above, the pegs 22 locate in a passage 32 which passes right through the core 30. It will however be understood that in other embodiments, the pegs could merely locate in blind recesses or openings in the opposite surfaces of the core without such openings actually being joined to one another to form a continuous passage.
The lower prosthesis plate 10 in
In the assembled prosthesis 50, the core is held captive by the action of the single peg 22 carried by the lower prosthesis plate 10. The core 30 is identical to the core described previously but once again it will be appreciated that core could have a blind recess in its downwardly facing, curved surface 32 only to receive the single peg 22.
The prosthesis 28, 50 is surgically implanted between adjacent spinal vertebrae in place of a damaged disc. Those skilled in the art will understand that the adjacent vertebrae are forcibly separated from one another to provide the necessary space for insertion. The plates 10, 10.1 are slipped laterally into place between the vertebrae with their fins 16 entering slots cut in the opposing vertebral surfaces to receive them.
After insertion of the core between the opposing plates, the vertebra are allowed to move together to hold the assembled prosthesis in place.
The surfaces 12 of the plates 10, 10.1 locate against the opposing vertebrae and, with passage of time, firm connection between the plates and the vertebrae will be achieved as bone tissue grows over the serrated finish. Bone tissue growth will also take place about the fins 16 and through the holes 18 therein, further enhancing the connection which is achieved.
Annular grooves 44 are provided in the plates 10, 10.1 to facilitate holding and manipulation of the prosthesis by appropriate instruments during placement into the intervertebral disc space.
Compared to known prostheses, the prostheses 28, 50 described above have a number of advantages, as follows:
1. The peg or pegs 22 hold the core captive and prevent it from slipping out sideways.
2. At a predetermined maximum limit of articulation, the rims 24 contact one another to prevent further articulation. At the same time, the peg or pegs 22 contact the sides of the openings 34, also preventing further articulation.
3. An acceptable bearing area of the plates on the core is obtained with the central peg/central opening configurations described above. This is particularly advantageous compared to prior art prostheses where the core has peripheral channels on its upper and lower surfaces to receive peripheral rims on the plates at the limit of articulation.
In practice, it may happen that there is imperfect alignment of the prosthesis plates. In the case of very poor alignment, the dual peg configuration of
The principles of the invention are applicable to prosthetic disc implants for lumbar vertebrae as well as cervical vertebrae. In the latter case, the fins 16 will typically be omitted.