(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2003/0100950 A1
`Moret
`(43) Pub. Date:
`May 29, 2003
`
`US 20030100950A1
`
`(54) CAGE-TYPE INTERVERTEBRAL IMPLANT
`
`(52) U.s. Cl.
`
`........................................................ .. 623/1716
`
`(76)
`
`Inventor: Olivier Moret, Sion (CH)
`
`Correspondence Address:
`BURNS DOANE SWECKER & MATHIS L L P
`POST OFFICE BOX 1404
`ALEXANDRIA, VA 22313-1404 (US)
`
`(21) Appl. No.:
`
`09/979,185
`
`(22) PCT Filed:
`
`Mar. 21, 2001
`
`(86) PCT No.:
`
`PCT/CH01/00179
`
`(30)
`
`Foreign Application Priority Data
`
`Mar. 22, 2000
`
`(CH) .............................................. .. 542/00
`
`Publication Classification
`
`(51)
`
`Int. Cl.7 ...................................................... .. A61F 2/44
`
`ABSTRACT
`(57)
`The invention relates to a cage-type intervertebral implant
`that is made up of a dished side wall (1), a cambered side
`wall (2), a front part (3), a rear part (4) and at least one
`intermediate wall (5, 6), thus comprising at least two cavities
`(7, 8, 9). An upper and a lower cage surface (10, 11) include
`a first lordosis angle (oL1) in the direction front part-rear part
`and a second lordosis angle (oL2) perpendicular thereto, said
`cage surfaces (10, 11) intersecting outside the cage. The cage
`structure is characterized by a doubler-wedge geometry
`(double-wedge-shaped cage) that
`is defined by the two
`lordosis angles (oL1) and (oL2) and that advantageously
`adapts itself to the anatomical conditions in the interverte-
`bral area. The cage is further characterized by a high
`moment of tilt that effectively counteracts a tipping of the
`cage. The method used for producing the cage structure is
`essentially characterized by working the cage material by
`means of a high-pressure water jet, said cold-cutting tech-
`nique having proved to be the most economical.
`
`4.99.
`
`MSD 1006
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`MSD 1006
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`1
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`Patent Application Publication May 29, 2003 Sheet 2 of 4
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`US 2003/0100950 A1
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`Patent Application Publicatlon May 29: 2003 Sheet 3 of 4
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`Patent Application Publication May 29, 2003 Sheet 4 of 4
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`US 2003/0100950 A1
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`US 2003/0100950 A1
`
`May 29, 2003
`
`CAGE-TYPE INTERVERTEBRAL IMPLANT
`
`[0001] The invention relates to a cage-type intervertebral
`implant, and also to a method for its production, according
`to patent claims 1 and 23 respectively.
`
`It relates to a vertebral column implant and its
`[0002]
`method of production, the implant being used for insertion
`between two vertebrae of the vertebral column. It serves as
`
`a means of fusion (arthrodesis) of the two vertebrae, and
`conse-quently the original intervertebral disk height is again
`reached by means of it, and also the nerve root foramen
`returns to its original size.
`
`[0003] The individual vertebrae of the vertebral column
`have a vertebral body, a vertebral arch, a spinous process,
`two transverse processes, and two upper and two lower
`articular processes. The vertebrae are connected to the
`abutting intervertebral disks (disci intervertebralis) and give
`rise to the vertebral body (corpus vertebrae). The interver-
`tebral disk consists of liquid-rich fibrous cartilage, and
`connects the individual vertebral bodies together. The size of
`the intervertebral disks increases from top to bottom, cor-
`responding to the loads arising in the human body. The
`intervertebral disks serve as elastic buffers, and resiliently
`damp impacts.
`
`It is known that the intervertebral disks can become
`[0004]
`displaced, or that the inner gelatinous core (nucleus pulpo-
`sus) can emerge through cracks in the cartilaginous outer
`ring (annulus fibrosus), which is similar to connective tissue.
`The intervertebral disk can then partially enter the interver-
`tebral foramina (foramina intervertebralia) or into the spinal
`canal. Furthermore, this prolapse can be dorsal, medial, or
`lateral. Such prolapses most frequently occur at the L4-L5-
`S1 and C6-C7 vertebrae. If such prolapses are not treated,
`irreversible pressure damage of nerve roots, foramina, or
`transverse lesions, result. If physiotherapy according to the
`symptoms, e.g., remedial exercises or massage, show no
`promise of success, the intervertebral disk (discus interver-
`tebralis) has to be operatively removed. There now exists the
`possibility of implantation of such an implant (cage), by
`means of which an arthrodesis between the two vertebral
`
`bodies can take place.
`
`is known from EP
`implant
`[0005] An intervertebral
`0916323-A1 which has a bean-shaped structure and can be
`inserted between two vertebrae. The implant has a wedge
`shape, conferred by a different height of the two longitudinal
`sidewalls. The walls surrounding the implant are provided
`with rows of holes in order to promote the ingrowth of bone
`tissue.
`
`It is disadvantageous that the implant has a wedge
`[0006]
`shape in only one direction, and is expensive to manufac-
`ture because of the many laterally formed holes.
`
`[0007] Furthermore, cage structures are known under the
`designation “Brantigan cage”, which have many teeth on
`their cage surfaces in order to prevent an undesired displace-
`ment of the cage. Made of polyether ether ketone (PEEK),
`as so-called PEEK moldings, they have inadequate strength,
`which can lead to breakage of the cage structure under load.
`A single thread is provided to receive instruments, resulting
`in unsatisfactory instrument manipulation.
`
`[0008] A relatively small tilting moment is conferred by
`the cuboidal geometry, with disadvanta-geous effects.
`
`[0009] The invention has as its object to provide a cage-
`type intervertebral
`implant which has a double wedge-
`shaped geometry, depending on two lordosis angles, and
`which ensures an improved instrument manipulation.
`
`[0010] A further object of the invention consists of the
`production of such an implant.
`
`[0011] According to the invention, this object is attained
`with an implant according to the wording of patent claim 1
`and by a method of production of the same according to the
`wording of patent claim 23.
`
`[0012] The invention is described hereinbelow using the
`accompanying draw-ings.
`
`[0013] FIG. 1 shows a perspective view of a cage
`
`[0014] FIG. 2 shows a plan view of the cage according to
`FIG. 1
`
`[0015] FIGS. 3A-3D show sectional views of FIG. 2
`
`[0016] FIGS. 4A-4C show sectional views of FIG. 2
`
`[0017] FIG. 5 is a sectional view of FIG. 2 along the
`developed radius line a-a@
`
`[0018] FIG. 6A-6B show side views of the rear portion
`with differently arranged guide ele-ments
`
`[0019] FIG. 7 is a plan view of an embodiment example
`of a cage with a partition and oblique rear portion with
`openings.
`
`[0020] FIG. 1 shows a cage 100 in a perspective view,
`consisting of a concave curved sidewall 1, a convex curved
`sidewall 2, a front portion 3 and a rear portion 4. The
`sidewalls 1 and 2 are connected together by partitions 5 and
`6, so that the interior of the cage is divided into cavities 7,
`8 and 9. Afirst, inner, radius of curvature R1 is then allocated
`to the internal sidewall 1, and a second, outer, radius of
`curvature R2 is allocated to the outer sidewall 2.
`
`[0021] The sidewalls 1, 2, the partitions 5, 6, the front
`portion 3 and the rear portion 4 have upper, or lower,
`respective boundaries which define an upper or a lower cage
`surface.
`
`[0022] The concave curved sidewall 1 has rounded open-
`ings 13, 14 and 15, which are placed about in the middle of
`the cavities 7, 8 and 9, and are conducive to the formation
`of bone substance. The convex curved sidewall 2 can
`
`likewise have such openings (not shown).
`
`[0023] The cage surfaces 10, 11 have, in the region of the
`front portion 3, the rear portion 4 and the partitions 5, 6,
`tabular raised portions 24, 25, 26, 27 which run substantially
`parallel
`to the cage surfaces and whose properties are
`described hereinafter.
`
`[0024] The front portion 3 is rounded, and connects the
`sidewalls 1, 2 of the cage by means of an equal wall
`thickness. On the front side it has bevels 23, 23@ which
`facilitate the introduction and positioning of the cage in the
`interver-tebral region.
`
`[0025] The rear portion 4 is of a rectangular constitution,
`and connects the sidewalls 1, 2 of the cage, likewise by
`means of an equal wall thickness. It has a bore 20 on the rear
`side which is provided with an internal
`thread and is
`provided for instrument attachment. Guide elements 21 and
`22 are arranged on respective sides of the bore 20, and are
`constituted here as, e.g., ribs, but can also consist of open-
`ings in the form of a half cylinder. The guide elements serve
`
`6
`
`

`
`US 2003/0100950 A1
`
`May 29, 2003
`
`to guide instrument introduction, and prevent any improper
`rotary movement of the cage when the instrument
`is
`released. As soon as the cage is situated in its final position
`between the two vertebrae, which among other things is the
`case when the axis of the instrument is perpendicular to the
`dorsal plane of the patient, the instrument can be detached
`from the cage. It has become apparent that this possibility of
`control has turned out to be very helpful and useful.
`
`[0026] The transition of the guide elements, or ribs, 21, 22
`to the surface of the rear portion 4 is rounded off on both
`sides of the ribs, in order to avoid possible notch effects,
`which is of importance in embodiments in plastic or com-
`posite materials. Holes 31, 32 or 33 are provided in the rear
`portion 4 and in the front portion 3, to receive a marker of
`a high density metal. Tantalum balls and/or pins are par-
`ticularly suitable for this purpose. The pins are arranged in
`bores which are arranged either perpendicular or parallel to
`the bore 20. The position of the cage can thereby be
`observed and assessed during the operation by means of an
`image intensifier.
`
`[0027] FIG. 2 shows a plan view of the cage 100 accord-
`ing to FIG. 1, with data on the position of the sections
`A-A@ through D-D@ and E-E@ through G-G@. The
`course of a radius line a-a@ which runs through the middle
`of the cage can likewise be seen.
`
`[0028] FIGS. 3A-3D show sectional illustrations of the
`cage, with section posi-tions according to FIG. 2. FIG. 3A
`shows a section A-A@ through the rear portion 4. The hole
`20 to receive an instrument, and the holes 31 and 32 for the
`markers, are visible. It can furthermore be recog-nized that
`the height at the outer side of the rear portion is greater than
`that at the inner side. Thus the upper surface of the rear
`portion no longer runs parallel to the lower surface, as
`portions of the cage surfaces 10 and 11. The two surfaces
`form a lordosis angle @2, which is 0.1-4°, but preferably 2°.
`This lordosis angle is shown on an exaggerated scale in FIG.
`3A, to be seen more easily. It is shown by @2/2 at the lower
`side of the rear portion.
`
`In the case that the height at the outer side of the
`[0029]
`rear portion is smaller than that at the inner side, there results
`an opposed slant of the cage, or a wedge shape formed by
`the cage surfaces 10 and 11, with the point of the wedge
`facing in the reverse direction If the lordosis angle @2 in the
`two described cases is identically zero, the cage surfaces 10
`and 11 are then parallel, as a special case or bounding case,
`which of course represents a less preferred constitu-tion of
`the cage.
`
`[0030] The raised portions 24, 24@ are affixed to the
`portions 10, 11 of the cage surfaces, and here are constituted
`parallel to the cage surfaces, although this by no means has
`to be obligatory.
`
`[0031] FIGS. 3B and 3C show a section B-B@, or C-C@,
`through the partitions 5 or 6, with the raised portions 25,
`25@, or 26, 26@, which are positioned on the portions of
`the cage surfaces 10, 11. These raised portions again run
`substantially parallel to the cage surfaces which likewise
`enable the lordosis angle @2 to be perceived.
`
`[0032] FIG. 3D shows a section D-D@ through the front
`portion 3. The bore 33 for the marker can be seen The raised
`portions 27, 27‘ can also be seen, which are affixed to the
`portions 10, 11 of the cage surfaces of the front portion 3.
`
`Again, these raised portions run substantially parallel to the
`cage surfaces, which likewise enable the lordosis angle @2
`to be recognized.
`
`[0033] The raised portions 24, 25, 26 and 27, which all
`project from the cage surfaces 10, 11, but are only 0.3-0.8
`mm, serve for the “anchoring of the cage” after the success-
`ful operation, and help to prevent a migration of the cage.
`
`[0034] FIGS. 4A-4C show sectional diagrams of the cage,
`with positions of the cross sections according to FIG. 2.
`There can be seen the sidewalls 1, 2; the upper and lower
`cage surfaces 10, 11; and the half lordosis angle @2, which
`is only shown in FIG. 4A on one side.
`
`[0035] FIG. 5 shows a sectional diagram of FIG. 2 along
`the developed radius line a-a@. The hole 33 for the marker,
`the bevels 23, 23@, and the raised portions 27, 27@ can be
`seen in the front portion 3;
`the hole 20 and the raised
`portions 24, 24@ can be seen in the rear portion 4. The
`partitions 5, 6 respec-tively have the raised portions 25, 25@
`or 26, 26@.
`
`It can further be seen that the height of the front
`[0036]
`portion 3 is greater than that of the rear portion 4. Thus the
`cage surfaces 10 and 11 no longer run parallel. The two
`surfaces form a so-called lordosis angle @1, which is 2-8°,
`but preferably 3°, 5°, or 7°. This non-parallelism condi-
`tioned by the lordosis angle @1 is shown on an exaggerated
`scale in FIG. 5, to be more easily visible.
`
`[0037] The cage structure can of course be modified
`within wide limits within the scope of this invention. Thus,
`for example, the number of the partitions 5, 6, or that of the
`cavities 7, 8, 9, is not limited to 2 or 3. Cage structures with
`one or more partitions are possible.
`
`[0038] FIGS. 6A and 6B each show a side view of the rear
`portion with different guide elements 21 and 22 arranged
`around the hole 20.
`
`In FIG. 6A, the guide elements are arranged about
`[0039]
`parallel to the cage surfaces 10, 11, while those in FIG. 6B
`have an angle of about 45° to the cage surfaces. However,
`this angle can assume an optional value from 0 to 90°. The
`guide elements 21, 22 in their turn of course do not neces-
`sarily have to be arranged parallel to one another; they can
`also have a V-shaped arrange-ment.
`
`[0040] Possible materials are plastics, carbon fiber rein-
`forced plastics and metals or metal alloys. Plastics such as
`polyether ether ketone (PEEK), polyether ketone ether ether
`ketone (PEKEEK) and polysulfone (PS) are preferably used,
`and particularly preferred as composite materials, carbon
`fiber reinforced composites of polyether ether ketone (CFK/
`PEEK) and polyether ketone ether ether ketone (PEKEEK),
`which are also known under the names of ULTRAPEK and
`OSTAPEK.
`
`[0041] As metals or metal alloys, titanium and its alloys
`are preferably used, such as e.g., the titanium alloy Ti6-
`Al4-V according to ISO standard 5832-3.
`
`[0042] The metallic cage can have a hydroxyapatite
`ceramic
`coating or a tricalcium phosphate (TCP)
`coating, which advantageously affect the long-term proper-
`ties of the implant.
`
`[0043] The curved shape of the cage gives this an advan-
`tageous high tilting moment M, which effectively opposes
`an overturning of the cage. In comparison with the tilting
`
`7
`
`

`
`US 2003/0100950 A1
`
`May 29, 2003
`
`moment of a cuboidal cage with equal middle cross section,
`equal length, and comparable cage structure,
`it has been
`found that the cage structures according to the invention
`exceed this by a factor of at least 1.30. For a cage according
`to FIG. 1, the factor is 1.58.
`
`[0044] The advantages of the cage structure according to
`the invention result from the double-wedge geometry, which
`depends on the two lordosis angles @1 and @2, and which
`outstandingly matches the anatomy in the intervertebral
`region.
`
`[0045] The designation “double wedge-shaped cage” or
`“DWS cage” is therefore used for such a cage.
`
`[0046] The raised portions positioned on the cage surfaces
`effectively prevent a migration of the cage during the healing
`process after a successful operation.
`
`[0047] Cage structures of the described kind are distin-
`guished by high strength attained in spite of a small pro-
`portion of material. The formation of bone material
`is
`thereby strongly accelerated.
`
`this property can be
`It has been found that
`[0048]
`described by a Cage Mass Index (CMI), which is defined
`according to Equation (1),
`CMI=Volume of cage material/Volume of cage
`
`(1)
`
`namely as the ratio of the cage material volume to
`[0049]
`the total cage volume. The results are:
`
`(a) for CFK/PEEK, CFK/PEKEK [sic], CFK/PS
`[0050]
`less than 0.25, preferably 0.22, and
`
`(b) for titanium or Ti alloys,
`[0051]
`preferably 0.17,
`
`less than 0.20,
`
`the variations being dependent on the cage sizes
`[0052]
`and giving only unimportant differences.
`
`corresponding to the lordosis angle @1, the wedge-shaped
`raised portions 24, 25, 26, 27 corresponding to the second
`lordosis angle @2, the beveled surfaces 23, 23@ of the front
`portion 3, the at least one opening of the sidewalls 1, and the
`first hole 20. Likewise in this step, the hole 20 is provided
`with an internal thread, which is intended to receive an
`instrument. Small-calibered milling inserts are used here on
`an automatic, computer numerically controlled milling
`machine.
`
`If openings are likewise to be provided in the outer
`[0059]
`sidewall 2, the cage blank has to be newly clamped once
`more.
`
`[0060]
`
`3. Affix Markers
`
`In a third step, the markers are mounted on the cage
`[0061]
`blank; later, during the operation and thereafter, they make
`it possible to assess the position of the cage by means of an
`image intensifier. Second holes 31, 32, 33 are installed for
`the markers in the rear portion and the markers in the front
`portion, and the markers are inserted into them as tantalum
`balls and/or pins.
`
`[0062]
`
`4. Finishing
`
`[0063] The last operations, which are summarized as fin-
`ishing, can take place in a fourth step, namely trovalization
`in order to de-burr or round off the partially sharp edges.
`Then follows the marking of the cage, which can take place
`by means of a laser marking device. The cage is next
`subjected to a cleaning process, which includes,
`for
`example, multi-step ultrasonic cleaning. The packaging of
`the cage likewise belongs in these finishing operations.
`
`[0064] A more important process step is cutting with a
`water jet under high pressure. An advantageous cutting
`process was thereby selected, which has been found to be
`particularly effective.
`
`[0053] The process for the production of such a cage is
`described hereinafter. It is divided into of four process steps,
`as follows:
`
`[0065] The examples described hereinafter give an insight
`into the diversity of the cage design, and their enumeration
`is not to be considered as final in any way.
`
`[0054]
`
`1. Water Jet Cutting
`
`In a first step, a blank of cage material is machined
`[0055]
`in a first direction by means of a high pressure water jet. This
`known and economical cold cutting process is as a rule
`operated with an abrasive addition at 3,000 bar (U. W.
`Hunziker-Jost, Swiss Precision Manufacturing Technique, p.
`81-86, C. Hanser Verlag, Munich (1991)).
`
`is
`the water jet
`[0056] The blank is clamped so that
`directed perpendicularly to the later cage surface. The con-
`tours of the sidewalls 1, 2, of the front portion 3, of the rear
`portion 4, of the at least one partition 5, 6, of the at least two
`cavities 7, 8, 9, and of the guide elements 21, 22 are cut with
`high precision The cut edges have little fraying. With
`material thicknesses of 10 mm, cutting speeds are attained of
`up to 100 mm/min for metals and up to 300 mm/min for
`composite materials.
`
`[0057]
`
`2. Milling
`
`[0058] The cage blank cut from the blank in this manner
`is now clamped again in a second step, and in fact in a
`second direction, substantially perpendicular to the first
`direction, in which the cage blank is further machined with
`a miller. The surfaces milled are the cage faces 10, 11
`
`[0066] FIG. 7 shows in plan view, as an embodiment
`example, a cage with one partition and an oblique rear
`portion with openings.
`
`[0067] Sidewalls 1, 2, front portion 3 with raised portion
`and bevel 23, partition 5 with raised portion, and the cavities
`7, 9, correspond to the cage elements described in FIG. 1.
`The rear portion 4 with a portion raised with respect to the
`cage surface has here, however, a rhomboidal constitution.
`While the guide elements 21, 22 are constituted as recesses
`here, but are arranged on the rear portion surface 4@ as in
`FIG. 1, the direction of the hole for receiving an instrument
`is shown at the edge of the cavity 7 by the position of the
`axis 30 for the hole. The hole is provided with an M4
`internal thread.
`
`[0068] The cage surfaces form a lordosis angle @1 of 3°
`in the front portion—rear portion direction, and a lordosis
`angle @2 of 2° in the direction of the centers for the
`curvature radii of the curved sidewalls 1 and 2. Thus the
`
`height of the partition with raised portion is 8.1 mm on the
`outer side and 7.8 mm on the inner side. The sidewall 1 has
`
`two lateral openings which are situated about in the middle
`of the cavities 7 and 9. The inner radius of curvature R1 is
`11 mm, and the outer radius of curvature R2 is 19 mm, the
`
`8
`
`

`
`US 2003/0100950 A1
`
`May 29, 2003
`
`respective centers being 1.1 mm apart. The cage was made
`of CFK/PEEK,
`a BYJET water
`jet cutting apparatus
`(Bystronic Laser AG, CH-3362 Niederonz) being used in the
`first process step.
`
`[0069] As a further embodiment example, the cage struc-
`ture according to FIG. 6 was manufac-tured from a titanium
`alloy, Ti6-A14-V according to ISO Standard 5832-3, a
`BYJET water jet cutting apparatus likewise being used in the
`first process step.
`
`1. Cage for a cage-like intervertebral implant, comprising
`a member divided into cavities, wherein the cage (100) is
`constituted by a concave-curved sidewall (1), a convex-
`curved sidewall (2), a front portion (3), and a rear portion
`(4), a first, inner radius of curvature (R1) being allocated to
`the inner sidewall (1), and a second, outer radius of curva-
`ture (R2) being allocated to the outer sidewall (2);
`the
`sidewalls are connected to the front portion and the rear
`portion; the sidewalls (1, 2) are connected to at least one
`partition (5, 6) substantially perpendicular to the sidewalls,
`whereby the cage (100) has at least two cavities (7, 8, 9); and
`the sidewalls (1, 2), front portion (3), rear portion (4), and
`the at least one partition (5, 6) form an upper and a lower
`cage surface (10, 11), the latter forming a lordosis angle
`(@1) in the front portion-rear portion direction, and a second
`lordosis angle (@2) perpendicular thereto, in that the cage
`surfaces (10, 11) intersect outside the cage.
`2. Cage according to claim 1, wherein the inner sidewall
`(1) has a smaller height than the outer sidewall (2), or the
`outer sidewall (2) has a smaller height
`than the inner
`sidewall (1), whereby a second lordosis angle (@2) is
`formed.
`
`3. Cage according to claim 1 or 2, wherein the front
`portion (3) and the rear portion (4) have a substantially equal
`second lordosis angle (@2).
`4. Cage according to one of claims 1-3, wherein the
`lordosis angle (@1) is 2-8°, preferably 3, 5, or 7°.
`5. Cage according to one of claims 1-4, wherein the
`lordosis angle (@2) is 0.1-4°, preferably 2°, and in the
`limiting case is identically zero.
`6. Cage according to one of claims 1-5, wherein the first,
`inner radius of curvature (R1) and the second, outer radius
`of curvature (R2) have substantially the same centers, but
`preferably centers arranged offset.
`7. Cage according to one of claims 1-6, wherein the inner
`radius of curva-ture (R1) is 15-23 mm, preferably 22 mm,
`and the outer radius of curvature (R2) is 18-26 mm, pref-
`erably 19, 21 or 23 mm.
`8. Cage according to one of claims 1-7, wherein the inner
`sidewall (1) has at least one opening (13, 14, 15).
`9. Cage according to one of claims 1-8, wherein the outer
`sidewall (2) has at least one opening.
`10. Cage according to one of claims 1-9, wherein the front
`portion (3) is rounded and has at least one beveled surface
`(23).
`11. Cage according to one of claims 1-10, wherein the rear
`portion (4) has in its middle a hole (20) with an internal
`thread, which is surrounded by two guide elements (21, 22)
`which run substantially parallel or in a V-shape.
`12. Cage according to claim 11, wherein the guide ele-
`ments [21, 22] are arranged about perpendicular, or about
`parallel, or at an angle of 0° to 90°, preferably 45°, to the
`cage surfaces around the hole (20).
`
`13. Cage according to claim 11 or 12, wherein the guide
`elements (21, 22) are constituted as ribs or recesses.
`14. Cage according to one of claims 1-13, wherein holes
`(31, 32, 33) are provided in the front portion (3) and in the
`rear portion (4) for markers of a metal of high density as
`balls and/or pins.
`15. Cage according to claim 14, wherein tantalum is
`provided as the metal for the markers.
`16. Cage according to claim 14 or 15, wherein the markers
`are arranged as pins about perpendicular or parallel to the
`hole (20).
`17. Cage according to one of claims 1-16, wherein the
`cage surfaces (10, 11) have tabular raised portions (24, 25,
`26, 27) which run substantially parallel to the cage surfaces.
`18. Cage according to one of claims 1-17, wherein it has
`a tilting moment (M) directed in the direction of the center
`of the inner radius of curvature (R1) and, in comparison with
`the tilting moment of a cuboidal cage of the same cross
`section, same length and comparable cage structure, exceed-
`ing this tilting moment by a factor of at least 1.30.
`19. Cage according to one of claims 1-18, wherein it
`consists of polyether ether ketone (PEEK), polyether ketone
`ether ether ketone (PEKEEK), or of polysulfone (PS), or of
`a composite material, preferably carbon fiber reinforced
`composites of CFK/PEEK and CFK/PEKEEK.
`20. Cage according to one of claims 1-18, wherein it
`consists of titanium or a Ti alloy.
`21. Cage according to claim 20, wherein it has a
`hydroxyapatite ceramic (HAK) coating or a tricalcium phos-
`phate (TCP) coating.
`22. Cage according to one of claims 1-21, wherein it has
`a Cage Mass Index (CMI) according to Equation (1)
`CMI=Volume of cage material/Volume of cage
`
`(1)
`
`which for CFK/PEEK, CFK/PEKEEK, and PS is less than
`0.25, preferably 0.22, and for titanium or Ti alloys, less
`than 0.20, preferably 0.17.
`23. Process for the production of a cage according to one
`of claims 1-22, wherein in a first step a blank of cage
`material is machined in a first direction by means of an
`ultrahigh pressure water jet, the contours of the sidewalls (1,
`2), of the front portion (3), the rear portion (4), the at least
`one sidewall (5, 6), the at least two cavities (7, 8, 9), and the
`guide elements (21, 22) arising; and in a second step the
`blank is milled in a direction substantially perpendicular to
`the first direction; and in a third step,
`the markers are
`installed; and finishing follows in a fourth step.
`24. Process according to claim 23, wherein, in the second
`step, the cage surfaces (10, 11) are milled according to the
`first lordosis angle (@1), the tabular raised portions (24, 25,
`26, 27) are milled corresponding to the second lordosis angle
`(@2); and the beveled surfaces (23, 23@) of the front
`portion (3), the at least one opening (13, 14, 15) of the
`sidewall (1), and the first hole (20) are milled.
`25. Process according to claim 24, wherein the first hole
`(20) is provided with an internal thread.
`26. Process according to one of claims 22-25, wherein, in
`the third step, second holes (31, 32, 33) are formed for the
`markers, and the markers are inserted.
`27. Process according to one of claims 22-26, wherein the
`final processing of the machine blank includes trovalization,
`marking, cleaning, and packaging.
`*
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