NL1018583C2 - Cage for lumbar fusion, has body which can be slid between two walls and rotated about its length axis - Google Patents

Abstract

The cage body can be slid between two walls in a direction at right angles to its length axis (L), and it can be rotated about its length axis. A cage used as an artificial invertebral disc comprises a body with a lateral surface (7) extending between two faces (3, 5). The body length axis extends essentially perpendicular to the faces. The body can be slid between two walls in a direction essentially at right angles to its length axis and it can be rotated about its length axis between the two walls. Independent claims are also included for: (a) a method of replacing an intervertebral disc with the above cage by initially sliding the cage along its faces and then rotating it about its length axis; (b) a method of replacing an invertebral disc with the above cage by fixing it between the vertebrae using a positioning device which has been releasably secured to the lateral surface of the cage prior to it being slid into place and which can be moved along this surface; and (c) a method for making the cage by extruding a tube or rod from PEEK, cutting the extrudate to size and cutting it to give the desired end shape, especially to form the profiling (4) on the faces used to control frictional resistance to sliding.

Description

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Title: Artificial intervertebral disc as well as methods for manufacturing and applying it.

The invention relates to an artificial intervertebral disc, also referred to as a cage, comprising a body bounded by a first end face, an opposite second end face and a side face extending between the end faces.

Such cages are known from practice. They are used in cases where an intervertebral disc between two successive vertebrae must be completely or partially removed, for example because the disc is worn out or presses part of it on an adjacent nerve path. One or more cages are placed in the space created after removal, with the end faces facing the vertebrae. Furthermore, a bone graft (graft) can be applied to the space, which can eventually grow into the vertebrae. The cages are constructed in such a way that they can absorb pressure and shear forces acting on the spine in use. The cages thereby provide stability to the spinal column and help to relieve the intervertebral disc, at least the remaining part thereof, and the bone graft, so that it can heal and grow into a rigid whole with the adjacent vertebrae.

A way known from practice in which the procedure described above can be carried out is via the so-called PLIF method (Posterior Lumbar Interbody Fusion), wherein an opening in the intervertebral disc to be removed is made from the back on either side of the spine protrusions of the respective vertebrae. is provided, through which two openings the load-causing part of the intervertebral disc is subsequently removed, whereafter a cage is slid into the vacated space between the vertebrae via each opening. An advantage of this method is that, thanks to the two openings, the cages can easily be arranged at a desired position between the vertebrae.

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On the other hand, this method entails the disadvantage that, because of the two required openings, more intervertebral disc material must be removed than is strictly necessary, which does not promote rapid healing. Moreover, the provision of two openings presents an additional risk of damage and possibly even permanent damage, and the final wound will be large and require a long recovery time.

A method that seeks to overcome the aforementioned disadvantages is the so-called TLIF method (transformal lumbar interbody fusion), wherein the above-described intervention is performed via a single opening on the back. In this case, only one elongated or banana-shaped cage is placed between the vertebrae. This cage is slid between the vertebrae from the one opening in a more or less radial direction, the cage as seen in a plane parallel to the vertebrae being at an angle of approximately 45 ° with the plane of symmetry of the vertebral column.

Although with this method a relatively large amount of intervertebral disc material can be retained, the method entails the disadvantage that the one opening only offers a very limited maneuvering freedom for applying the cage. This means that it cannot be positioned optimally. The asymmetrical location of the cage can moreover lead to an uneven load on the cage and the vertebrae, with all the associated disadvantages, such as, for example, an irregular wear pattern.

It is an object of the invention to provide a cage in which the disadvantages mentioned are avoided while maintaining the advantages thereof. To that end, a cage 25 according to the invention is characterized by the features of claim 1.

By shaping the cage in such a way that on the one hand it can be appropriately shifted between two walls in a direction perpendicular to its longitudinal axis and, on the other hand, it can be rotated between these two walls about its longitudinal axis, a cage is obtained which through a minimum opening at any desired position and in any desired position between two vertebrae 1018583 3 can be applied. The cage can herein be moved over a path to be covered between the vertebrae and possibly rotated over a part of the path, in view of the end position. Particularly due to this rotation, the cage can be brought even better into a desired position, in which it can offer optimum resistance to external loads to be expected in use. Furthermore, a plurality of cages can be brought through the same one opening to different positions between the vertebrae, by sliding these cages from the opening in a straight line to their respective desired end position and subsequently possibly rotating them in the desired position. The width of the one opening need only be about the same size as the width of the cages, that is to say the width of the widest part, often the end faces.

In an advantageous embodiment, a cage according to the invention is characterized by the features of claim 2.

By providing at least one end face of the cage with a profile that offers a lower resistance to shifting at least in one direction than in the other directions, the cage can be oriented during application such that this one direction coincides with the lower sliding resistance with the sliding direction so that the cage can be applied easily, with a small sliding force.

At the desired end position, the cage can then be rotated to a position in which the profile can offer the greatest possible sliding resistance to external forces acting on the cage in use, so that a cage once applied between the vertebrae can be prevented under the influence of said cervical vertebrae. forces are shifting.

In a particularly advantageous embodiment, a cage according to the invention is characterized by the features of claim 4.

When the cage has its largest width in a direction perpendicular to the sliding direction, the width of the opening and any channel following it between the vertebrae can be limited to the said largest width. The cage can be shifted within this width and then rotated if necessary.

The cage, in particular the end faces thereof, preferably has a substantially rotationally symmetrical shape with respect to the longitudinal axis, since as a result a maximum surface area of the end faces can be obtained for a given maximum width, which is favorable for the distribution of forces on the cage.

In a further advantageous embodiment, a cage according to the invention is characterized by the features according to claim 5.

By constructing the cage such that it is pressure-resistant at least in directions perpendicular to the longitudinal axis, it is achieved that the cage can simply be shifted between the vertebrae and rotated by pressing against the side surface of the cage with a suitable positioning tool. The compressive strength must in any case be greater than the compressive forces required for shifting and / or rotating the cage.

In addition, the cage in the direction of the longitudinal axis must be sufficiently compressive to withstand the forces acting on the spine in use.

In a further advantageous embodiment, a cage according to the invention is characterized by the features of claim 8.

A flat segment on the side surface offers a suitable pressure surface on which a force can be exerted by means of a suitable tool for causing the cage to shift and rotate.

The side surface is preferably provided with a plurality of flat segments, so that when the cage is rotated around the longitudinal axis, a new pressure surface always comes before it and the cage can simply be rotated through larger angles.

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In a further elaboration, a cage according to the invention is characterized by the features according to claim 11, 12.

By providing the side surface of the cage with at least one, preferably several, positioning means distributed along the circumference, via which a positioning tool can be releasably coupled to the cage, the insertion of the cage, in particular the displacement thereof, can be considerably be simplified. The positioning means can for instance comprise a number of threaded holes or a number of ribs extending perpendicular to the end faces, against the side surface, into which, respectively between which the positioning tool can be placed, and through which positioning means the tool during the shifting of the cage is held in a desired position relative to the cage. After reaching the end position, the tool can simply be detached, after which the cage can be rotated, possibly with the aid of the same tool. A hole as a positioning means is advantageous since it does not protrude beyond the contour of the body and therefore does not affect the possibilities of rotation and the maximum width of the cage.

In a particularly advantageous embodiment, a cage according to the invention is characterized by the features according to claim 13.

By making the cage hollow, a graft can be made therein. This will ultimately allow the cage to be completely encapsulated by the bone graft growing therein and around it and a homogeneous bone connection can be established between the vertebrae.

In further embodiments, a cage according to the invention is characterized by the features according to one of the claims 15 or 16.

By providing a cage with convex or divergent end faces, cages can be produced that are optimally matched to the different types of vertebral forms occurring in a spinal column, such as lumbar, thoracic and cervical, so that a good connection of the cage on the vertebrae and thus an even support of the spine can be achieved.

In a further embodiment, a cage according to the invention is characterized by the features of claim 19.

PEEK (Polyetheretherketone) is a suitable material for producing the cages, since PEEK is wear-resistant and dimensionally stable, even with prolonged exposure to a relatively humid environment, such as in the present application. In addition, PEEK is biocompatible, well sterilizable and has an elastic modulus (Young's modulus) which is approximately located between the elastic moduli of cortical and spongy bone, whereby comparable mechanical behavior can be obtained.

Since PEEK is not detectable with X-rays, it is preferable to use one or more so-called X-ray markers in the cage when this material is used, which can be observed with the aid of X-rays, and further preferably have such a shape, for example rod-shaped that a change in the position of the cage can be unambiguously deduced from a change in the position of the marker. In this way changes to the position of the cage can be traced at any time.

The invention further relates to a method for introducing a cage according to the invention, characterized by the features of claim 23.

Thanks to the shape of the cages suitable for rotation and shifting, these can be introduced into a intervertebral disc at least a space between two vertebrae via a minimal opening and therefore in a minimally invasive manner. The dimensions of the opening can thereby approximately correspond to the height and width of the cage to be introduced. Thanks to the minimal opening, a relatively large part of the intervertebral disc can be retained, which is conducive to a rapid recovery, since less new bone has to be produced. In addition, multiple cages can be inserted through a single opening and positioned symmetrically relative to a plane of symmetry of the spinal column. This will result in a likewise symmetrical and therefore favorable load on the cages.

In the further subclaims, further advantageous embodiments of a cage according to the invention, as well as methods for applying and manufacturing thereof, are described.

To clarify the invention, an exemplary embodiment 10 of a cage will be described with reference to the drawing. In the drawing: Figs. 1A-D show an embodiment of a cage according to the invention, in top, side, front and perspective view, respectively; Fig. 2 shows a detail of alternative positioning means on a side surface of a cage according to the invention, in cross-sectional top view; Fig. 3 shows a number of top views of rotationally symmetrical cages according to the invention; Fig. 4 shows a simplified representation of a spinal column, in side view; and Fig. 5 shows a top view of a cross-section of an intervertebral disc along line IV-IV in Fig. 4, provided with two cages according to the invention.

Figures 1 and 2 show an artificial intervertebral disc, hereinafter referred to as customary cage 1, which is used to replace at least a part of an existing intervertebral disc 25 between two successive vertebrae. To this end, the cage 1 is placed between the two successive vertebrae in a manner to be described below. Once applied, the cage 1 can absorb pressure and shear forces acting on the spinal column and thereby relieve the existing intervertebral disc, at least the remaining part thereof, as well as any bone graft (graft) that may have been introduced. This gives the JO 1 858 3 · 8 graft the opportunity to grow into a rigid whole with the adjacent vertebrae.

The cage 1 shown in figures 1 and 2 is bounded by a first end face 3, a second end face 5 opposite it and a side face 7 joining the end faces 3, 5. The cage 1 is rotationally symmetrical with respect to a substantially perpendicular longitudinal axis L extending on the end faces 3, 5. Rotational symmetrical is understood here to mean any shape that can rotate at least fittingly between two parallel walls within a substantially square plane. A number of examples of this are shown in Fig. 3. These examples should not be construed as limiting in any way. Furthermore, in the following description the height H of the cage 1 will be understood to mean the distance between the first and second end face 3, 5 and the width B will be understood to mean the maximum width of the cage 1 in a plane perpendicular to the longitudinal axis L .

In the embodiment shown, the end faces 3, 5 are ring-shaped and each has a rib-shaped profile 4 on a side facing away from each other. This profile gives the cage 1 a great resistance to shifting in a direction X perpendicular to the longitudinal direction of the ribs 4 and a relatively small shear resistance in a direction Y, parallel to the longitudinal direction of the ridges 4. The advantage of this will be explained in more detail below. In the embodiment shown, the ridges 4 extend parallel to each other and lie on the two end faces 3, 5 in the same direction Y. However, they can also have a different orientation on the two end faces, for example enclosing a sharp angle with each other. The side face 7 is made up of a series of contiguous flat segments 10, which extend between the first and second end faces 3, 5 and which, seen in a plane perpendicular to the longitudinal axis L, describe the circumference of a polygon, for example a hexagon as in the embodiment shown. The segments 10 are provided with positioning means 16, in which a tool suitable for 101 8583; 9, the fitting of the cage 1 can be positioned such that it will not undesirably shift relative to this cage 1 during the introduction of the cage 1 or will come off it. In the embodiment shown in Fig. 1, the positioning means 16 comprise a bore 12, 5 provided with thread 14.

FIG. 2A, B show two alternative embodiments of suitable positioning means 16. Thus, Fig. 2A shows an embodiment in which the segments 10 are provided with ribs 13, which extend substantially at right angles to the end faces 3, 5 over at least a part of the height 10 H of the cage 1 and between which a rectangular head of a positioning tool can be locked against displacement. FIG. 2B shows an embodiment in which the outward facing sides of the segments 10 are concave, suitable for receiving a somewhat cylindrical positioning tool. By way of positioning means 16 openings can also be provided in the segments 10 in which an end of the positioning tool with a sliding fit can be received. Naturally, embodiments as shown in Figs. 1 and 2 can be combined, as shown in Fig. 2 in broken lines.

Furthermore, in the embodiment shown, one of the segments 10 is not provided with a bore 12. This segment 10 can for instance be printed with production data and / or information relevant to a user, such as for instance the specific dimensions of the cage 1.

The shown cage 1 can be manufactured from various materials, such as metal or plastic. A suitable plastic is, for example, PEEK (polyetheretherketone). This material has a high wear and dimensional stability, is also biocompatible and well sterilizable and has an elastic modulus that lies approximately between the elastic moduli of cortical and spongy bone.

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If the cage 1 is made from an X-ray material that is not perceptible, such as, for example, the aforementioned PEEK, it is preferable to equip the cage 1 with one, preferably two, elements that can be detected with X-rays.

These so-called X-ray markers may, for example, consist of a metal strip or wire which during manufacture can be co-formed in the side surface 7 of the cage, for example injection-molded or extruded. In the cage 1 shown in figure 1, the X-ray markers are in the form of two metal pins 15, which extend in two opposite segments 10 of the cage 1 from the first end face 3, towards the second end face 5. Due to this shape and orientation of the markers, a change in the position of the cage 1 will produce a changed x-ray image of the markers, regardless of the direction from which the image was taken, and therefore a change in the position of the cage can be detected at all times. It will be clear that many other embodiments of X-ray markers are possible, wherein, among other things, the shape, orientation and the starting material may differ. The advantage of using two X-ray markers is that a better three-dimensional image of the location of the cage 1 can be obtained with this. Depending on the material from which the cage 1 is made, it can be injection molded (most plastics), molded (metal) or extruded and then milled (when PEEK is used, for example).

Figure 4 shows in side view a part of a vertebral column 20, in which the described cage 1 can be applied. The vertebral column part shown comprises three vertebrae 22, separated from each other by intervertebral discs 23. Before an intervertebral disc or part thereof is removed, a pin 25 is fitted against the vertebral column 20, on the backside thereof, which pin is screwed with 26 (in Figure 3) 30 is shown only schematically in broken line) on the individual vertebrae 11. With this construction, the vertebrae 22 can be fixed in a desired mutual position during the operation and the distance between the two vertebrae 22 bounding the intervertebral disc to be replaced can be slightly stretched, in order to create more space for the total or partial removal of the disk 23 and subsequent fitting of the cages 1.

After a portion of the vertebrae 20 is thus fixed, an opening 28 is provided from the backside in the intervertebral disc 23 to be replaced, next to a mandrel protrusion of the vertebrae 22, 10 in question, as is best seen in Figure 5. Via this opening 28 two channels 30A, B drilled in the intervertebral disc 23, through which the malfunctioning parts of the intervertebral disc can be removed.

With a view to a speedy cure, as little intervertebral disc as possible is preferably removed during treatment. For this purpose, the dimensions of the aperture 28 and the channels 30A, B are

kept to a minimum, that is to say, sufficiently large to allow a cage 1 to pass. The opening 28 and the channels 30A and B therefore have a width B and a height H, corresponding to the width and the height of the cage 1 to be introduced. The channels 30A and B extend from the common opening 28 to two end positions located symmetrically with respect to a plane of symmetry M, approximately halfway between the former intervertebral disc.

After removing the intervertebral material, the cages 1 can be slid through the channels 30A, B between the vertebrae 22.

To that end, a special positioning tool 40, a possible embodiment of which is shown in Figure 6, can be screwed into one of the bores 12 of the cage 1 with a threaded end 42. The tool 40 is preferably fixed in that bore 12, wherein the tool 40 will extend in the longitudinal direction of the ridges 4, the Y-30 direction. As a result, when the cage 1 is slid into one of the channels 30A, B by means of 101 8583 · 12, the said longitudinal direction Y in which direction the sliding resistance of the ripple profile 4 is the lowest coincides with the sliding direction of the cage 1, as a result of which the cage 1 will only experience a slight sliding resistance during insertion. After the cage with the positioning tool 40 has been brought near or to a desired end position, in the case shown in Figure 5 corresponding to an end of the channel 30A, B, the tool is unscrewed. Subsequently, the cage 1 can be rotated about its longitudinal axis L to a position where the X direction of the profile 4, i.e. the direction in which the profile can offer the greatest resistance to displacement, coincides with a direction in which during use the greatest forces are to be expected. The cage 1 can also be rotated such that said X direction approximately coincides with the sliding direction with which the cage 1 is inserted, so that the cage 1 will not move back in the same way under the influence of the external forces, towards the opening 28.

The cage 1 can be rotated by pressing with a tool, for example the aforementioned positioning tool 40 or a variant 50 also shown in Fig. 6 with a flattened end 52, eccentrically against the side surface 7, in particular one of the segments 10 . Thanks to the flat course of the segments 10 as well as the slightly protruding edge of the end faces 3, 5, sliding of the tool 40, 50 is prevented. A tool 40, in conjunction with positioning means 16, in particular bores 12 with screw thread 14, is also advantageous for other types of cages, for proper placement thereof.

After a first cage 1 is thus arranged, a second cage 1 can be arranged in a similar manner via the second channel 30B. Of course, if the applied cages 1 have a relatively small width B, in order to further reduce the required width of the aperture 28 and the channels 30A, B, more than two cages 1 can be arranged in the intervertebral disc 23, via as many channels 30 provided for this purpose in the intervertebral disc 23.

FIG. 7 shows an alternative embodiment of a cage 101 according to the invention, wherein the side surface 107 is substantially open, built up of ribs 113, which extend at an even distance from each other between the end faces 103, 105, near an outer circumference of the end faces.

It will be clear that many other embodiments of cages 1 are possible, all suitable for being slid through an opening 28 with a minimum width B and / or being rotated within a square with a width B. Which possible alternative cages moreover have a pressure stiffness in radial direction that is greater than the force required to shift and / or rotate cage 1, 101 during insertion. Furthermore, which cages have a pressure rigidity in the axial direction, which is sufficiently large to be able to absorb forces acting on the spinal column during use. Which cages 1, 101 moreover, in view of the most favorable possible distribution of forces, preferably as large as possible end faces 3, 5; 103, 105, given the maximum width B of the opening 28 through which these cages must be able to be fitted and the square with a width B within which the cages must be able to be rotated.

The invention is in no way limited to the exemplary embodiment shown in the description and the drawing. Many variations thereof are possible within the scope of the invention as set forth in the claims.

The cage can thus be manufactured from a plastic other than PEEK, preferably a plastic that can be injection molded. The cage can also be made from metal or a biodegradable material. When the cage is made from metal, X-ray markers can be dispensed with. Furthermore, the cage can be filled with a bone growth promoting material, such as for example metal wool or another porous material. It will further be clear that the cage can be manufactured in any desired size, tailored to the specific dimensions of the various types of vertebrae (cervical, lumbar, etc.). Furthermore, the cage can have any other substantially rotationally symmetrical shape, and the end faces can be provided with a different profile, for example a diamond-shaped ribbed profile, a toothed profile or a profile provided with protruding studs.

These and many variations are understood to fall within the scope of the invention as set forth in the claims.

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Claims (32)

Cage (artificial intervertebral disc) comprising a body bounded by a first end face (3), an opposite second end face (5) and a side face (7) extending between the end faces (3, 5), wherein a longitudinal axis ( L) of the body extends substantially perpendicular to the end faces (3, 5) and wherein the body is suitably slidable between two walls in a first direction extending substantially perpendicular to the longitudinal axis (L) and rotatable between those two walls around the longitudinal axis (L). Cage according to claim 1, wherein at least one of the end faces 10 (3, 5) is provided with a sliding resistance influencing profile (4), the sliding resistance of which is smaller in the sliding first direction (Y) than in one or any other direction. A cage according to claim 2, wherein the sliding resistance influencing profile (4) is substantially corrugated. Cage according to one of the preceding claims, wherein the body, in particular the end faces (3, 5) measured substantially perpendicular to the first direction (Y), has a maximum width that is greater than or equal to the maximum width of the body measured in a direction approximately parallel to the first direction (Y). Cage according to one of the preceding claims, wherein the cage (1) is pressure-resistant in a direction parallel to and in directions perpendicular to the longitudinal axis (L). 6. Cage according to one of the preceding claims, wherein at least the end faces (3, 5) have a substantially rotationally symmetrical shape with respect to the longitudinal axis (L). Cage according to one of the preceding claims, wherein the body is substantially cylindrical. 1018583 Cage according to one of the preceding claims, wherein the side surface (7) is provided with at least one substantially flat segment (10). Cage according to any of claims 1-7, wherein the side surface (7) is provided with at least one substantially concave segment (10). Cage according to one of the preceding claims, wherein the side surface (7) is formed from a series of continuous, flat segments (10), such that the body over at least a part of its height (H) between the end surfaces (3, 5) has a polygonal outline. Cage according to one of the preceding claims, wherein the side surface 10 (7) is provided with positioning means (16) for releasably placing a positioning tool (40) therein. The cage of claim 11, wherein the positioning means (16) comprises at least one threaded bore (12). 13. Cage according to any of the preceding claims, wherein the body is substantially hollow. 14. Cage according to one of the preceding claims, wherein the body is open on one or both sides. Cage according to any of the preceding claims, wherein the end faces (3, 5) are convex. Gage according to any of claims 1-10, wherein the end faces (3, 5) diverge relative to each other, so that the body is wedge-shaped. 17. Cage according to one of the preceding claims, wherein the body is made of a plastic. 18. A cage according to any one of the preceding claims, wherein the body is made of a material whose elastic modulus is approximately located between the elastic moduli of cortical and spongy bone. The gage of any one of the preceding claims, wherein the body is made of PEEK (polyether ether ketone). 1018583 Cage according to one of the preceding claims, wherein the body is provided with at least one X-ray detectable element (15). 21. Cage according to claim 20, wherein the at least one X-ray marker (15) has a direction-sensitive shape and position in the cage (1), such that a change in the position or position of the cage (1) can be clearly read. is on the at least one X-ray marker (15). Cage according to any of the preceding claims, wherein the body is made from a biodegradable material. io A method for applying a cage (1) according to any one of the preceding claims in or replacing an intervertebral disc (23) between two successive vertebrae (22), wherein the cage (1) is to be deposited over a part of a trajectory along the first and second end face (3, 5. is shifted and rotated about a longitudinal part of the trajectory 15 to be rotated about the longitudinal axis (L). A method according to claim 23, wherein the end faces (3, 5) of the cage (1) are provided with a profile (4) influencing the sliding resistance, which has a reduced resistance to shifting in at least one direction (Y) and one, preferably every other direction, has an increased sliding resistance, wherein the cage (1) is oriented during shifting such that the direction (Y) in which the sliding resistance is least coincides with the sliding direction and wherein the cage (1) in the desired end position is rotated about the longitudinal axis (L) in such a way that the or each direction in which the profile (4) offers the highest displacement resistance coincides with the direction or directions in which the highest external loads are expected during use. A method according to claim 23 or 24, wherein the cage (1) is arranged between the vertebrae (22) through a single opening (28) whose width and height substantially correspond to that of the cage (1). 101 8583 * A method according to any of claims 23-25, wherein the cage (1) is shifted between the vertebrae (22) by a channel (30A, B), which is previously in an intervertebral disc (23) located between the vertebrae (22) ), which extends between the single opening (28) and a desired end position of the cage (1), with a height and width that substantially correspond to that of the cage (1). A method according to claim 26, wherein at least two cages (1) are arranged between the vertebrae (22), via one opening (28) and two channels (30A, B extending from said opening (28) to a desired end position ). A method according to any of claims 23-27, wherein the or each cage (1) is applied between the vertebrae (22) with the aid of a positioning tool (40, 50), which is displaced prior to the displacement of the cage (1) can be releasably placed in positioning means (16) provided for this purpose along the circumference of the side surface (7), and with which a force can be exerted on successive segments (10) for rotating the cage (1). A method of applying a cage (1) according to any of claims 1-22 in or replacing an intervertebral disc (23) between two successive vertebrae (22), wherein the cage (1), wherein the or each cage (1) is placed between the vertebrae (22) with the aid of a positioning tool (40, 50), which is detachably positioned prior to the displacement of the cage (1) in positioning means (16) provided for this purpose along the circumference of the side surface (7) ) can be placed. The method of claim 29, wherein the positioning tool (40, 50) can be applied to successive segments (10) of the side face (7) to rotate the cage (1) about the longitudinal axis (L). A method for manufacturing a cage (1) according to claim 30, wherein from PEEK a tubular or bar-shaped base element is extruded 101 8583, which is then cut to size, whereafter the desired final shape, in particular influencing the sliding resistance profile (4) on the end faces (3, 5) and the or each segment (10) on the side face (7) is milled from the cut-to-size base elements. The method of claim 31, wherein at least one X-ray marker (15) is co-extruded into the tubular or bar-shaped base element. 10 101 858.3