Patent Application
20090030523
The present invention relates to an assembly for stabilizing vertebrae, in particular lumbar vertebrae. This assembly can be defined as a relief prosthesis having a dual effect, as will be appreciated below.
It is known that the mobility of two adjacent vertebrae, in particular in the lumbar region, is dependent on the intervertebral disc at the anterior side and pairs of articular surfaces at the posterior side.
The arrangement of the disc and articular surfaces ensures auto-limitation of movements both in the plane perpendicular to the vertebral column, during torsion, and in a sagittal plane, during flexions and extensions of the vertebral column.
The shape, the structure and the height of the disc confer on it additional functions of maintaining lordosis, absorbing shocks and distributing stresses. At the rear, the articular surfaces guide the movements and act as hinges.
The ageing process of the subject leads to disturbances in this anterior/posterior equilibrium involving the discs and the surfaces. Generally, the degeneration of the discs precedes that of the surfaces. Collapse and instability of the discs leads to a partial transfer of the stresses to the posterior columns which are formed by the surfaces, which brings about a loss in the surface congruence and a slackening of the ligaments. This results in deterioration of the articular surfaces, which leads to various pathologies having implications of a mechanical and neurological nature.
In order to treat these pathologies, an anterior arthrodesis has been proposed, by insertion of a graft between the plates of the two vertebrae in question. This graft is usually contained in a rigid cage, known as a “fusion cage”.
However, this technique does not prevent rotational instability which can compromise, in the medium term, the anticipated antalgic result, and it has now been established that the anterior arthrodesis must be complemented by a posterior arthrodesis.
An intervention of this type has limits and disadvantages. It is aimed at severe pathologies which are at an advanced stage and is not without risks, given that the patients are often treated at a relatively late stage in the pathological development. Intervention can further have consequences which are detrimental to adjacent articulations in the medium-term and long-term.
For these reasons, techniques known as “non-fusion” techniques have been developed and relate to the early and palliative treatment of degenerative disc/surface phenomena.
With regard to the disc space, there have been developed various shock-absorbent implants, which are intended to replace the nucleus pulposus, in the form of pairs of pads or elliptical or spiral elements.
These implants are introduced either via an anterior access point, which has the disadvantage of damaging the anterior common vertebral ligament, or via a posterior access point, which has the disadvantage of leading to the sacrifice of a large amount of bone, owing to the space requirement of the implants.
Techniques involving percutaneous injection of a colloid which can be polymerised in situ have also been proposed, as have techniques using solid, disc-like prostheses in the form of two metal plates which enclose a shock-absorbent material and which rest on each of the vertebral plates which are adjacent to the disc.
These techniques are not completely satisfactory as regards the treatment of disc degeneration combined with wear of the surfaces and/or ligament distension.
Devices intended to limit the articular play of the surfaces have also been proposed. A device of this type comprises in particular a continuous woven ligament which is positioned between the spinous processes or along the articular surfaces by means of pedicle screws, and/or a shock-absorbent dividing element which is positioned at the lamina/spinous process junction so as to alleviate the surface play while at the same time stretching the posterior capsule/ligament elements.
It has been found that these techniques are also not completely satisfactory with regard to the above-mentioned treatment.
The object of the present invention is to overcome this fundamental disadvantage by providing an assembly for stabilizing two adjacent vertebrae which sustain both disc degeneration with ligament distension, as well as possibly wear of the surfaces, this assembly further having to be relatively simple to implant and, in addition, relatively non-invasive.
In one embodiment, the present invention provides an implant assembly for implantation between upper and lower spinous processes that advantageously restores the anatomical tension to a supra-spinous posterior ligament extending between the spinous processes. The implant assembly comprises an interspinous implant and a removable clip. The interspinous implant comprises an interspinous portion having an upper surface for engagement with the upper spinous process and a lower surface for engagement with the lower spinous process. The interspinous portion has a thickness between the upper surface and the lower surface sufficient to restore anatomical tension to the supra-spinous posterior ligament. The implant also comprises an upper pair of lugs extending from the interspinous portion for interfacing with the upper spinous process and a lower pair of lugs extending from the interspinous portion in a direction substantially opposite from the upper pair of lugs, the lower pair of lugs for interfacing with the lower spinous process. At least one of the upper pair of lugs and at least one of the lower pair of lugs is movable between an insertion configuration and an retention configuration. The insertion configuration is substantially perpendicular to the retention configuration. The removable clip is for engagement with the relevant lugs to selectively retain the same in the insertion configuration. The implant may comprise a flexible, resilient material to allow motion between the spinous processes and to allow the at least one of the upper and lower lugs to resiliently return to the retention configuration from the implantation configuration. The implant may comprise a casing substantially surrounding the flexible, resilient material, which may advantageously be a woven casing. The relevant lugs are advantageously resiliently biased toward their retention configuration.
In another embodiment, the invention provides an implant assembly for implantation between first and second adjacent spinous processes. The assembly comprises an interspinous implant and a clip. The interspinous implant comprises a central body having first and second lateral portions. First and second arms extend from the first lateral portion and third and fourth arms flexibly extend from the second lateral portion. The third arm is moveable relative to the central body between a first position and a second position, and the fourth arm is moveable relative to the central body between a first position and a second position. The third and fourth arms include respective base portions proximate the central body and end portions distal therefrom; wherein the end portions of the third and fourth arms are closer together when the third and fourth arms are in their first positions than in their second positions. The first arm, central body, and third arm form a first saddle for receiving the first spinous process with the third arm in the second position. Likewise, the second arm, central body, and fourth arm form a second saddle for receiving the second spinous process with the fourth arm in the second position. The clip is a retaining clip removably coupled to the implant so as to selectively retain the third and fourth arms in their first positions. The third and fourth arms are advantageously biased toward their second positions. With reference to an axis of the central body, the third and fourth arms, in their first positions, fit within the vertical cross-sectional area of the central body projected onto a plane normal to the axis; but extend outside the vertical cross-sectional area of the central body when in their second positions.
Other features and aspects of the inventions(s) are disclosed below. These features and aspects may be used alone or in combination, as is desired.
In some embodiments, the assembly comprises a posterior implant and at least one inter-corporeal implant. The shock-absorbent posterior implant is formed to be positioned, via the lateral route, at the lamina/spinous process junction of the two adjacent vertebrae being treated, without resection of the supra-spinous posterior ligament. This posterior implant advantageously has a height such that, when it is positioned, it allows the supra-spinous posterior ligament to be reset at anatomical tension. The shock-absorbent inter-corporeal implant is formed to be inserted between the adjacent vertebral plates of the two vertebrae being treated via the same posterior/lateral route as that used during a dissectomy. This implant advantageously has a height such that, when it is positioned, it allows the anatomical height of the intervertebral disc to be restored and the anterior common ligament to be reset at anatomical tension. In this manner, the assembly not only allows the anatomical spacing of the vertebrae, both between the surfaces and between the vertebral plates, to be re-established, but also allows the anterior common ligament and the supra-spinous posterior ligament to be reset at anatomical tension while preserving the same. The effect of this tensioning is to restore the anatomical ligament “balance” which exists between these ligaments, while at the same time giving back to the disc and the surfaces the anatomical functions thereof such as absorbing shocks with regard to the disc and acting as hinges and of posterior balancing with regard to the surfaces.
The posterior implant is positioned directly behind the surfaces at the site of the inter-spinous ligament complex, and can be stressed in terms of both compression and extension. The inter-corporeal implant is itself positioned, preferably as far forwards as possible, along the circumference of the vertebral plates. In this manner, it is positioned where the stresses are at a maximum. The maximum spacing thereof from the posterior implant allows the anterior/posterior ligament balance to be optimally re-established.
Therefore, the posterior implant and the inter-corporeal implant have the function of absorbing the stresses, in terms of both compression and extension, which are generated during flexion movements of the vertebral column forwards and backwards. When the vertebral column flexes forwards, the supra-spinous posterior ligament, which is reset at functional tension by the posterior implant, ensures the anatomical function thereof of limiting the movement, which function is optimized and reinforced owing to the relief and the control brought about by the posterior implant, owing to the progressive extension which limits it. At the same time, the inter-corporeal implant provides relief to the defective disc by absorbing the stresses applied in terms of pressure by the superior vertebral body to the lower vertebral body and attenuates the so-called “creep” phenomenon, that is to say, the depression of the disc under the application of pressure. This inter-corporeal implant jointly provides limiting relief which limits the effect of extension which is undergone by the posterior flexible structures. When the vertebral column flexes backwards, the anterior vertebral ligament, which is reset at functional tension by the inter-corporeal implant, ensures the anatomical function thereof of progressively limiting the movement, which function is assisted and reinforced by the extended shock-absorbent implant. At the same time, the posterior implant is compressed and optimizes the play of the surfaces in terms of the function thereof as hinges and of posterior balancing.
The action of each implant is consequently advantageously combined with the action of the other implant. Extension of one of the implants is met with compression of the other implant, owing to an interdependent auto-limiting effect.
The use of a single access route further allows the intervention to be greatly simplified and the assembly according to the invention to be made extremely non-invasive.
Securing means are advantageously provided in order to ensure the continuity of the posterior implant in position, relative to the spinous processes. These securing means can comprise a suitable form of the posterior implant, defining opposed recesses for receiving the spinous processes and conferring on the posterior implant a “diabolo” or “H”-like shape, and/or means for fixing the posterior implant to the spinous processes, such as two independent cords or rigid anchoring pieces, which do not limit the deformability of the implant.
The posterior implant can be constituted as a single piece or can be in two parts which can be assembled and which are each brought via one side of the inter-spinous space and are assembled together in this space. When the posterior implant is of a “diabolo” or “H”-like shape and when it is in a single piece, the assembly can comprise a piece which keeps this implant in a deformed state, in which two lateral lugs, which the implant comprises, are brought closer towards each other, in order to allow lateral insertion of the implant between the spinous processes of the vertebrae being treated.
The inter-corporeal implant may be formed so as to extend in the anterior lateral zones of the vertebral plates in order to reinforce the lateral stability of the vertebrae and to allow relief of the peripheral annulus fibrosus. It can then have, in particular, a curved shape, in the form of a portion of a ring.
The assembly according to the invention may also comprise an inter-corporeal implant which is provided to replace and/or assist the nucleus. This implant can then be of a general “bean” or “omega”-like shape, with a central portion which is extended by two lateral lobes protruding at the posterior side. It can also be in the form of a sphere.
The inter-corporeal implant(s) may have a triangular or trapezoidal cross-section and is intended to be implanted with the largest lateral side thereof directed towards the anterior side. This implant, formed in this manner, corresponds to the anatomical inclination of the disc.
The inter-corporeal implant(s) can comprise means for ensuring the securing thereof between the vertebral plates. In particular, these means comprise a form of the inter-corporeal implant, which form is adapted to the shape of the vertebral plates and which can secure this inter-corporeal implant between these plates. When the inter-corporeal implant is in the form of a sphere, it can comprise an equatorial lip which reduces the risk of displacement thereof.
The posterior implant can comprise a core of shock-absorbent material, such as a silicone, a polyurethane, a hydrophilic polymer, a polycarbonate, or a piece of shape-memory metal, and a casing which surrounds the core. This casing allows the core or the piece to be advantageously protected from friction. The casing can be formed from woven fibers. The inter-corporeal implant can have an identical structure.
The positioning of this inter-corporeal implant can be carried out, in particular, by means of an introduction guide tube which is provided with a piston, the implant being engaged, with compression, in the introduction tube and being able to be expelled therefrom by means of the piston.
The introduction tube temporarily compresses the implant. This reduction in volume, that is to say, in the space requirement of the implant, makes only surgical access similar to that of a dissectomy necessary, avoiding any destabilizing sacrifice of bone. The tube is introduced into the disc space via the transligamentary posterior/lateral route (LVCP). A semi-rigid guide directs and controls the correct positioning of the inter-corporeal implant before being withdrawn by being passed back through the introduction guide tube.
With reference to the non-limiting illustrated embodiments,
The posterior implant 10 is formed by a core of silicone which is surrounded by a woven casing, in particular of polyester fibers, which ensures the protection of this core. It has an inter-spinous portion 15 and two pairs of lateral lugs 16 which protrude longitudinally at one side and the other of this portion 15.
The portion 15 has a thickness slightly greater than the anatomical inter-spinous space when the vertebrae 2, 3 are in lordosis, so that the portion 15 is slightly compressed by the spinous processes 17 when the implant 10 is positioned at the lamina/spinous process junction. The implant 10 thereby allows, in this position, the supra-spinous posterior ligament 5 to be reset at anatomical tension.
The portion 15 is perforated by two transverse channels 20 which are intended to receive, as shown in
The lugs 16 have substantial heights relative to the total height of the implant 10 in the order of, for the upper and lower lugs, 33% and 40% of the total height, respectively. The internal faces of two lugs 16 of the same pair of lugs are inclined so as to converge towards each other in the direction towards the base of the recess which they together delimit. The lugs 16 further have a relatively large mean thickness relative to the mean width of the implant 10 in the order of, for the upper and lower lugs, 27% and 30% of this mean width, respectively. These lugs 16 allow the securing of the implant 10 between the processes 17 to be ensured in spite of the relative movements of the vertebrae 2,3, in particular the pivoting movements about the axis of the vertebral column.
The inter-corporeal implant 11 is also formed by a core of silicone which is surrounded by a woven casing, in particular of polyester fibers, ensuring the protection of this core. It has a curved shape, in the form of a portion of a ring, and is sized so as to extend, after positioning, along a wide anterior portion of the peripheral edges of the vertebral bodies 7, 9. It has a height such that it allows, when it is positioned, the anatomical height of the disc 4 to be restored and the anterior common ligament 6 to be reset at anatomical tension.
In practice, an ablation of the inter-spinous ligament complex is carried out via the lateral access route, then the vertebrae 2, 3 are separated and the posterior implant 10 is positioned between the spinous processes 17, directly behind the surfaces 8, that is to say, at the lamina/spinous process junction. The flexibility of the lugs 16 does not inhibit this insertion. The two lugs 16 which are located at the side at which the implant 10 is inserted can be secured in a position turned towards each other in order to facilitate the insertion of the implant 10. Each cord 21 is then engaged through the ring which it comprises and is secured tightly around the corresponding process 17 by sliding through this ring. The ring is then crimped to the cord 21 in order to keep the cord in a position for securing the process 17. The implant 10, being secured in this manner, can be stressed in terms of both compression and extension.
The implant 11 is itself inserted between the vertebral plates of the two vertebrae 2, 3 via the same posterior/lateral access route as that used during a dissectomy. As shown by
The implants 10 and 11 jointly allow the anatomical spacing of the vertebrae 2, 3 to be re-established both between the surfaces 8 and between the vertebral plates, but also allow the anterior common ligament 6 and the supra-spinous posterior ligament 5 to be conserved, with these ligaments being placed at anatomical tension.
When the vertebral column flexes forwards, the supra-spinous posterior ligament 5 can then once more ensure the anatomical function thereof of limiting the movement. The implant 10 allows, owing to its ability to be extended, the action of this ligament to be assisted and controlled. Simultaneously, the implant 11 restores the shock-absorbent function of the disc 4 and takes up the stresses applied in terms of pressure by the superior vertebral body 7 on the inferior vertebral body 9, with relief being provided for the peripheral annulus fibrosus. In this manner, it provides progressive absorption of shocks for this superior vertebral body 7, with any risk of contact between the vertebral bodies 7,9 being prevented.
When the vertebral column flexes backwards, the anterior vertebral ligament 6 can again ensure the anatomical function thereof of progressively limiting the movement. Simultaneously, the implant 10 is compressed and then assists the surfaces 8 in the function thereof as hinges and of posterior balancing.
While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only some embodiments have been shown and described and that all changes and modifications that come within the meaning and equivalency range of the appended claims are intended to be embraced therein.
| Number | Date | Country | Kind |
|---|---|---|---|
| FR0110604 | Aug 2001 | FR | national |
| PCT/FR02/02834 | Aug 2002 | FR | national |
This application is a continuation of prior U.S. patent application Ser. No. 10/486,046, filed 2 Jul. 2004, which claims the benefit of PCT/FR02/02834, filed 8 Aug. 2002, which claims benefit of French application FR 01.10604, filed 8 Aug. 2001. The above referenced applications are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10486046 | Jul 2004 | US |
| Child | 12248320 | US |
