Today the state of the art concerning total spinal disc replacement device insertion is the anterior approach, i.e. true anterior, anterolateral (oblique) or true lateral. The surgeon decides between transperitoneal or retroperitoneal approaches, depending on the treated level or his personal experience. However, due to the presence of major vessels (e.g. aorta, vena cava) the anterior approach to the spine is often performed in the presence of vascular surgeons thereby causing extra costs.
In U.S. Pat. No. 6,719,794 GERBER a method for insertion of an intervertebral fusion implant is disclosed. The removal of the affected spinal disc as well as the insertion of the implant is performed via a posterior approach offset from the midline of the spine to the affected intervertebral disc. Disadvantageously, such a transforaminal approach includes a partial dissection of the facet joint.
A prosthetic device for transforaminal insertion into an intervertebral space is known from US 2004/0225365 EISERMANN. This known prosthesis comprises two components having an articulating surface each in order to permit articulating motion between the first and second components and consequently of the adjoining vertebrae. The transforaminal path disclosed might cause potential damage to important anatomical structures such as nerve roots, dura, ligamentum flavum and interspinous ligaments.
Therefore, it is an object of the present invention to provide a method for total spinal disc replacement device insertion including a dorsal approach to the spine without having to dissect the facet joint neither completely nor partially.
According to the method of the present invention the above object is achieved by means of an extraforaminal approach including an access portal in the Fibrocartilago Intervertebralis between the anterior and posterior longitudinal ligaments for removing the affected intervertebral disc as well as for insertion of a total disc prosthesis.
The method according to the invention offers the following specific advantages:
In a preferred embodiment the key element of the extraforaminal approach to the spinal disc is a path in front of the transverse processes (Processus Transversus).
In a further embodiment the method further comprises the steps of:
In another embodiment the disc material is removed with a surgical device through a protection sleeve. This permits the advantage that the use of a protection sleeve during removing the disc material allows a better protection of the surrounding soft tissue.
In a further embodiment the access portal is cut at a distance X>0 apart from the anterior longitudinal ligament and the posterior longitudinal ligament, therewith permitting the advantage that the anterior longitudinal ligament and the posterior longitudinal ligament remain intact in order to stabilize the treated segment of the vertebra.
In still another embodiment the distance X amounts between 2 mm and 38 mm.
In a further embodiment the width W of the access portal is between 8 mm and 36 mm.
In still a further embodiment the area A of the access portal is between 24 mm2 and 684 mm2 and the height is preferably between 3 and 19 mm.
In another embodiment the step of distracting of the vertebral bodies adjoining the disc space to be treated is performed through the protection sleeve.
In a further embodiment the distraction of the vertebral bodies adjoining the disc space to be treated is performed by slightly bending a distractor in order to keep the view to the situs free for the surgeon.
In yet a further embodiment the total disc replacement procedure is performed without dissecting the facet joints.
In another embodiment the total disc replacement procedure is performed without dissecting the transverse processes.
In a further embodiment the access to the intervertebral space to be treated is essentially straight. This allows the advantage that due to the almost straight access the use of essentially straight instruments e.g. for cleaning the endplates of the adjacent vertebral bodies or other surgical actions is possible.
In another embodiment the incision is reduced to a tube.
In a further embodiment the risk of damaging the neural structures is reduced by means of passing (not approaching) the spinal cord and locating, mobilising and marking the nerve root.
It is a further object of the invention to provide an intervertebral prosthesis having a contour when viewed orthogonally to its central axis which has a minimal width but still an adequate articulation area.
According to the invention the above object is achieved through an intervertebral prosthesis which essentially comprises a first and a second prosthetic component each having an apposition surface disposed transversely to the central axis and apt for contacting the end plate of an adjoining vertebral body each. Furthermore, said first and second prosthetic components are connected by means of an articulation. When viewed parallel to said central axis said first and second prosthetic components have an elongated shape with a major axis and a transverse minor axis, whereby said central axis, major axis and transverse minor axis intersect each other and said central axis and transverse minor axis defining a middle plane. Said first and second prosthetic component have a cross-sectional area orthogonal to said central axis which is essentially oval or elliptical and said cross-sectional area comprises at least a first and a second concavity lying on different side of the middle plane and on the same side of the major axis.
The intervertebral prosthesis according to the invention offers the following specific advantages:
In a preferred embodiment of the intervertebral prosthesis said cross-sectional area of said first and second prosthetic component is kidney shaped with an enlargement arranged essentially symmetrical to said the middle plane.
In a further embodiment said at least two concavities have an essentially semi-elliptical or semi-oval shape.
In another embodiment said at least two convavities are disposed essentially symmetrical to said middle plane.
In still another embodiment said first and second prosthetic component have a length H measured parallel to said major axis and wherein each of said at least two concavities has a width W measured parallel to said major axis, said width W amounting to between 15% and 35% of said length H.
In yet another embodiment said first and second prosthetic component have a maximum width B measured parallel to said transverse minor axis and wherein each of said at least two concavities has a depth T measured parallel to said transverse minor axis, said depth T amounting to between 5% and 25% of said maximum width B.
In a further embodiment said cross-sectional area of said first and second prosthetic components has an essentially elliptical periphery with a smaller radius of curvature at the first subsidiary vertex than at the second subsidiary vertex of said periphery.
In another embodiment said first subsidiary vertex is on the same side of said major axis as said at least two concavities.
In a further embodiment, the ratio of the length H of the prosthetic components to the width B thereof is between 3:1 and 5:1. The advantage of this design essentially is that in order to implant the two prosthetic components in the intervertebral space (intervertebral disk) it is only necessary to clear a narrow access path such permitting an extraforaminal approach.
In yet a further embodiment said articulation is configured as a ball-and-socket joint comprising a spherical cap connected to one of the first and second prosthetic components and congruent to said spherical cap a spherical recess in the other of said first and second prosthetic components.
In another embodiment, the intervertebral prosthesis is realised in two pieces, i.e. the spherical cap is made in one piece with one of the two prosthetic components.
In a further embodiment, the intervertebral prosthesis is realised in three pieces, so that the spherical cap forming the third piece is connectable with one of the two prosthetic components. The advantage of this design is to be seen essentially in the fact that the plate and the spherical cap may be realised by using different materials, so that it is possible to achieve optimal sliding properties for the articular surfaces. Preferred materials for the plates are titanium or a titanium alloy as well as PEEK or coated variants, and for the spherical cap highly crosslinked polyethylene (X-UHMWPE), an alloy of cobalt and chrome, or a ceramic material.
In again a further embodiment, the intervertebral prosthesis is realised in at least three pieces and comprises an articular shell including the recess, whereby said articular shell is attachable to one of said first and second prosthetic components as a third piece. The advantage of this design is to be seen essentially in the fact that the plate and the spherical cap may be realised using different materials, so that it is possible to achieve optimal sliding properties for the articular surfaces.
In a further embodiment, the spherical cap and the articular shell consist of a material combination made of metal and plastic. The advantages of this embodiment are that it is possible to use proven combinations of joint replacement materials such as, for example, highly crosslinked polyethylene (X-UHMWPE) and an alloy of cobalt and chrome. Further advantages are to be seen in the fact that low frictional forces are achievable for the relative displacement of the articular surfaces and that a compensation of axial impact loads can be achieved.
In yet another embodiment a ceramic-to-ceramic articulation is used. In a further embodiment the surfaces of the spherical cap and the recess are coated with titanium carbide or with amorphous carbon (ADLC) therewith permitting a substantial reduction of the coefficient of friction.
In another embodiment, at least the spherical cap is made of a memory metal or of a material capable of swelling (e.g. hydrogels). In still another embodiment at least the spherical cap is made of a flowable, thermosetting material. The monomers, comonomers, homopolymers, oligomers, or mixtures which contain such thermosetting, flowable substances may suitably be selected from the group of:
a) polyethylene glycols, preferably polyethylene glycol(di)-acrylates;
b) n-vinylpyrrolidones; and
c) vinyls, preferably vinyl alcohols; and
d) styrenes.
The polymers thus obtained may be widely varied as regards their elasticity. The advantages of these designs are to be seen essentially in the fact that due to the reduced volume of the joint, the insertion of the intervertebral prosthesis becomes less invasive, the increased volume being best suited for achieving an optimal articular function.
In a further embodiment the first prosthetic component is selected from a first kit of at least M≧2 first prosthetic components and the second prosthetic component is selected from a second kit of at least N≧2 second prosthetic components. Said first and second kit may comprise first and second prosthetic components being provided with different heights, articulation radii or locations of the centre of the respective radii, i.e. the center of rotation. By means of this embodiment the following advantages may be achieved:
In yet a further embodiment said first and second prosthetic component each comprise an intermediate surface, said first and second intermediate surfaces facing each other. At least the first or second intermediate surface is provided with at least one cavity with an undercut being located at the first or/and second lateral end of said first and second prosthetic components, said cavity with an undercut being apt for acceptance of an anchoring member of an implant holder.
The implant holder according to the invention is provided with a sleeve and an anchoring member, e.g. a hook member being insertable into the cavity and undercut and being displaceably disposed in the central bore of the sleeve, said implant holder further having a front end being provided with a fore-part which is adapted to the lateral ends of the first and/or second prosthetic component of an intervertebral prosthesis according to invention. Furthermore, the implant holder is provided with a fastening mechanism permitting to pull the anchoring member towards the sleeve such pressing the lateral end of the intervertebral prosthesis against the fore-part.
Further objects and advantages of the invention will become apparent from the following description when read with reference to the accompanying drawings which illustrate the method according to the invention. In the drawings:
Description of the preferred method for replacement of a spinal disc through an extraforaminal approach according to the invention:
A detailed description of an extraforaminal approach to vertebral bodies in case of posterolateral fusion of vertebrae, e.g. by securing bone grafts to the pedicles or transverse processes by means of bone screws can be found in:
Each of the first and second apposition surfaces 108;109 is disposed transversely to the central axis 103. When viewed parallel to said central axis 103 said first and second prosthetic components 101;102 have an elongated shape with a major axis 127 and a transverse minor axis 128, whereby said central axis 103, major axis 127 and transverse minor axis 128 intersect each other. Said central axis 103 and said transverse minor axis 128 further define a middle plane 126. Furthermore, said first and second prosthetic component 101;102 have a cross-sectional area orthogonal to said central axis 103 which is essentially elliptical and comprises two concavities 125 lying on different sides of said middle plane 126 and on the same side of said major axis 127.
The two concavities 125 are disposed symmetrically to said middle plane 126 such that one of said two concavities 125 is arranged in a first quadrant of a circle the centre of which coincides with the point of intersection of the major axis 127, the transverse minor axis 128 and the central axis 103 and the circumference of which is tangent to the periphery 129 of said cross-sectional area at the principal vertices. The second of said two concavities 125 is arranged in a clockwise succeeding, second quadrant of said circle. Furthermore, the two concavities 125 have an essentially semi-elliptical shape and have a depth T measured parallel to said transverse minor axis 128 amounting to about 5% of the maximum width B of said first and second prosthetic components 101;102.
The first and second prosthetic component 101;102 each comprise an intermediate surface 109; 110, said first and second intermediate surfaces 109; 110 facing each other. As shown in
Number | Date | Country | Kind |
---|---|---|---|
2160/04 | Dec 2004 | CH | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/CH05/00776 | 12/27/2005 | WO | 00 | 6/27/2007 |