CA2524066C

CA2524066C - Intervertebral implant

Info

Publication number: CA2524066C
Application number: CA2524066A
Authority: CA
Inventors: Michael Guetlin; Manuel Schaer; Beat Lechmann
Original assignee: Synthes USA LLC
Current assignee: Synthes USA LLC
Priority date: 2003-04-28
Filing date: 2003-04-28
Publication date: 2011-03-15
Anticipated expiration: 2023-04-28
Also published as: CA2524066A1; DE50309438D1; BR0318221B1; AR044093A1; JP2006524513A; US20060100710A1; ES2300566T3; US7641693B2; CN1774219A; EP1620044A1; AU2003218855A1; TWI333416B; KR20060004965A; ATE389374T1; TW200422035A; JP4245566B2; CN100581506C; WO2004096103A1; EP1620044B1; NZ543180A

Abstract

Disclosed is an intervertebral implant (1) comprising: A) a bottom implant part (2) that is provided with a hollow cylindrical cavity (3) having a jacket (14) and an axis of rotation (11), and an appositioning part (4) that is to rest against the cover plate of the bordering bottom vertebra; B) a top implant part (5) that is provided with an essentially circular cylindrical shaft (6) which extends into the cavity (3) and encompasses an external thread (7) and an axis of rotation (11), and an appositioning part (8) that is to lean on the cover plate of the bordering upper vertebra, C) the two implant parts (2, 5) being secured against rotation about the axis of rotation (11) thereof; D) an internally threaded ring (9) which is disposed between the two implant parts (2, 5) and cooperates with the external thread (7). E) The two implant parts (2, 5) and the ring (9) are coaxially arranged along the common axis of rotation (11) thereof such that the distance between the two appositioning parts (4, 8) can be infinitely varied by twisting the ring (9) on the external thread (7) of the shaft (6). F) The ring (9) is connected in an axially fixed but rotationally movable manner to the bottom implant part (2). The inventive intervertebral implant allows for simplified handling, which increases safety while reducing the time required for the implant to be implanted.

Description

INTERVERTEBRAL IMPLANT
The invention relates to an intervertebral implant of the introductory portion of claim 1.
A generic intervertebral implant is known from the DE-A 196 22 827.
The central part of this implant, which is constructed as a ring with an internal thread, is connected by a thread connection only with the upper, terminal part of the implant.
The ring is freely movable axially as well as rotatively with respect to the lower, terminal part of the implant. The lower, terminal part of the implant serves only as an axial stop for the ring, that is, as a supporting surface, against which the ring can be twisted, so that the upper, terminal part of the implant can be moved axially (nut /
spindle driving mechanism. The two terminal implant parts accordingly are mounted loosely with respect to one another. This is also shown therein that a radial, threaded borehole, through which a traceable clamping screw is passed, is provided in one of the two implant parts in order to secure the latter axially. Accordingly, this known intervertebral implant has the disadvantage that it is not secured before or during the surgery and can fall apart. For sterility reasons, there would be an appreciable time delay if an implant part were to fall to the floor of the operating theater.
The EP-A 1 219 266 of ULRICH discloses a telescopable intervertebral prosthesis with a threaded ring, which has straight bevel gear teeth, which can be rotated from the radial direction over bevel pinion. It is a disadvantage of this known device that the threaded ring is not connected axially firmly with one of the sleeve parts. As a result, the implant is constructed less stably and, moreover, there is a need for a special instrument in order to bring about the traction of the implant.
The bevel gear teeth, which are less "forgiving" and therefore disadvantageous, are a further disadvantage of this known implant. In the case of a slight, axial displacement of the bevel gear teeth, the driving instrument already can no longer carry out its function and the surgeon must place the instrument once again in situ.
The invention is to provide a remedy here. It is an object of the invention to create an intervertebral implant, which, while retaining the least possible overall height, forms a compact whole, the individual parts of which are secured so that they cannot fall apart and which is made available to the surgeon as a preinstalled set.
Pursuant to the invention, this objective is accomplished with an intervertebral implant, which has the distinguishing features of claim 1.
Further advantageous developments of the invention are characterized in the dependent claims.
The advantages, achieved by the invention, are to be seen essentially therein that, due to the inventive intervertebral implant, simplified handling is possible, which, on the one hand, increases the safety and, on the other, reduces the time spent for the implantation.
For a special embodiment, the ring of the intervertebral implant is fastened axially fixed but rotatively movably by a clip connection at the lower part of the implant. Accordingly, the ring remains securely in position for the driving mechanism, that is, the ring cannot escape axially. Preferably, the clip connection is formed from a toroidal undercut in the ring and an annular bead corresponding thereto at the free end of the outer casing of the lower implant. By these means, the rotation of the ring is assured in such a manner that it and the two sleeve-shaped implant parts rotate about the same center.

In the case of a further embodiment, the ring has a lower annular surface, which faces the lower implant part, and an upper annular surface, which faces the upper implant part, the lower annular surface having a ring gear, which is suitable for accommodating a corresponding pinion. By radially rotating the instrument carrying the pinion, this construction permits axial rotation of the ring. In comparison to known implants, for which the ring must be moved tangentially, the advantage arises that less space is required for the rotating instrument. Furthermore, the procedure can be carried out more quickly because the instrument can be rotated infinitely variably without the need for introducing the rotating instrument time and again into new boreholes of the ring.
For a further embodiment, the outer casing of the lower implant part has a radial, preferably continuous depression, which is suitable for positioning and supporting a pinion with respect to the ring gear. As a result, the advantageous possibility arises that, after traction of the vertebra, bone chips can be introduced through the continuous depression into the cavity of the lower implant part.
For a further embodiment, the circular cylindrical shaft (6) of the upper implant part has a guiding slot, which extends parallel to the axis of rotation as a safeguard to prevent rotation of the upper implant part with respect to the lower implant part and the outer casing of the lower implant part, at its inside, has an inwardly protruding guiding element (17), which engages the guiding slot and can be brought into the outer casing preferably through a radial opening. By these means, the mutual rotation of the two implant parts is prevented. A mutual rotation would adversely affect the contact between the implant and the end plates and the lordosing angles.
In the case of a further embodiment, the circular, cylindrical shaft (6) of the upper implant part (5) has a smaller circumference than does the hollow cylindrical cavity (3) of the lower implant part (2), so that the two components do not touch one another.
In the case of a further embodiment, the external thread of the circular, cylindrical shaft and the internal thread of the ring are constructed to be self locking.
Due to the self locking of the thread, the implant can be stretched to any height without the need for any additional locking device. For a further embodiment, the pitch of the external thread and of the internal thread ranges from 0.5 to 1.0 mm and preferably from 0.6 to 0.8 mm. Larger pitches, for example of the order of 2 mm, showed intraoperative disadvantages, since the traction turned out to be too coarse and smaller pitches resulted in temporally longer rotation.
For a further embodiment, the external thread as well as the internal thread is constructed as a right-handed thread. This has the advantage that the instrument, which carries the pinion, can be rotated in the usual manner in the right-handed direction like a normal screwdriver, in order to stretch the implant.
In the case of a further embodiment, the external thread as well as the internal thread is constructed as a multiple thread, preferably as double-lead thread.
In the case of a double-lead thread, a double lift is achieved by one revolution of the ring. Consequently, the implant is handled more rapidly and more easily, so that the time required for the surgery is shortened to the benefit of the patient.
In the case of a further embodiment, the two apposition parts are constructed as panel-shaped elements, which are aligned transversely to the axis of rotation with an apposition surface intended to be in contact with the covering surface of the adjoining vertebra.
In the case of a further embodiment, the apposition surfaces are not disposed orthogonally to the axis of rotation and, instead, preferably form an angle of 83° to 85° with the axis of rotation, so that a better adaptation to anatomical relationships results. Preferably, the two apposition surfaces enclose an angle of 10°
to 14° with one another. By these means, it is possible to ensure the anatomic lordosis angle.
In the case of a further embodiment, at least one of the two apposition surfaces, preferably that of the upper implant part is curved towards the outside, so that optimum adaptation to the vertebrae results. The apposition surface of the lower implant part preferably is constructed essentially flat.
In the case of a further embodiment, the ring gear is straight-cut.
Compared to a taper-cut or helical-cut ring gear, a straight-cut gearing is "more forgiving".
The invention and further developments of the invention are explained in even greater detail in the following by means of partially diagrammatic representations of several examples. In the drawings, Fig. 1 shows a perspective view of the intervertebral implant in the assembled state, Fig. 2 shows a perspective view of the intervertebral implant in the disassembled state, Fig.3 shows a longitudinal section through the axis of rotation of the intervertebral implant of Fig. 1, Fig. 4 shows front view of the intervertebral implant of Fig. 1, Fig. S shows a longitudinal section through the axis of rotation of the intervertebral implant of Fig. 1 in the disassembled state and Fig.6 shows a front view of the intervertebral implant of Fig. 1 in the disassembled state.
The intervertebral implant 1, shown in Figs. 1 to 6, comprises essentially a lower implant part 2, an upper implant part 5 and a ring 9, which is disposed between the two implant parts 2, 5. The lower implant part 2 has a hollow cylindrical cavity 3 with an outer casing 14 and an axis of rotation 11 and an apposition part 4, which is intended to be in contact with the covering surface of the adjoining lower vertebra. The upper implant part 5 has an essentially circularly cylindrical shaft 6 with an external thread 7 and an axis of rotation 1 l, which extends into the cavity 3 of the lower implant part 2, and an apposition part 8, which is intended to be in contact with the covering surface of the adjoining upper vertebra.
The two implant parts are secured against rotating about their axis of rotation 11.
The ring 9 has an internal thread 10, which interacts with the external thread 7 of the upper implant part 5, the two implant parts 2, 5 and the ring 9 being disposed coaxially along their common axis of rotation 11, so that, by rotating the ring 9 on the external thread 7 of the shaft 6, the distance between the two apposition parts 4, 8 can be changed infinitely variably. By means of a clip connection, the ring 9 is connected axially fixed but rotatively movably with the lower implant part 2. As shown in Fig. 3, the clip connection consists of a toroidal undercut 21 in the ring 9 and, corresponding thereto, an annular bead 22 at the free end of the outer casing 14 of the lower implant part 2.
The ring 9 has a lower annular surface 12, which faces the lower implant part 2, and an upper annular surface 13, which faces the upper implant part, the lower annular surface 12 having a straight-cut ring gear 23, which is suitable for accommodating a corresponding pinion.
The outer casing 14 of the lower in plant part 2 has a radially continuous depression 15, which is suitable for positioning and supporting a pinion (not shown in the drawing) with respect to the ring gear 23.
As safeguard against rotation of the upper implant part 5 with respect to the lower implant part 2, the circularly cylindrical shaft 6 of the upper implant part 5 has a guiding slot 16, which extends parallel to the axis of rotation 11, and the outer casing 14 of the lower implant part 2, at its inside, has an inwardly protruding guiding element 17 (Fig. 2), which engages the guiding slot 16 and can be introduced through a radial opening 18 in the outer casing 14. The external thread 7 of the circularly cylindrical shaft 6 and the internal thread 10 of the ring 9 are constructed to be self locking. The pitch of the external thread 7 and of the internal thread 10 is 0.7 mm.
The external thread 7 as well as the internal thread 10 are constructed as double-lead, right-handed threads.
As shown in Fig. 3, the two apposition parts 4, 8 are constructed as panel-shaped elements, disposed transversely to the axis of rotation 11, with an apposition surface 19, 20 intended for contacting the covering surface of the adjoining vertebra. The apposition surfaces 19, 20 are not disposed orthogonally to the axis of rotation 11 and, instead, enclose an angle of 85° with the axis of rotation 11. The two apposition surfaces 19, 20 accordingly enclose an angle of 10° with one another. The upper apposition surface 20 is, as shown in Fig. 3, curved towards the outside, whereas the apposition surface 19 of the lower implant part is constructed essentially flat.
The intervertebral implant may be produced from conventional implant materials. Preferably, x-ray-transmitting PEEK is used, in order to permit an a evaluation of the fusion by means of x-ray beams. The intervertebral implant is suitable particularly as a vertebrae replacement in the cervical and higher thoracic region of the spinal column.

Claims

The embodiments of the present invention for which an exclusive property or privilege is claimed are defined as follows:

1. An intervertebral implant comprising:

a lower implant part having a hollow cylindrical cavity with an outer casing and an axis of rotation, and an apposition part intended for contacting a covering surface of an adjoining lower vertebra, the cavity in communication with a depression extending through the outer casing;

an upper implant part having a circularly, cylindrical shaft having an external thread and an axis of rotation, and an apposition part intended for contacting a covering surface of an adjoining upper vertebra, wherein the shaft extends into the cavity of the lower implant part; and a circular ring with an internal thread which is disposed between the upper implant part and the lower implant part and interacts with the external thread of the upper implant part, wherein the upper implant part and the lower implant part are secured to prevent rotation about the axis of rotation, wherein the upper implant part, the lower implant part and the ring are disposed coaxially along the axis of rotation, so that by rotating the ring on the external thread of the shaft, a distance between the two apposition parts can be variably changed, wherein the ring includes a toroidal undercut and the outer casing of the lower implant part includes an annular bead, the toroidal undercut mates with the annular bead so that the ring is axially fixed but rotatively movably with the lower implant part, the toroidal undercut and the annular bead forming a continuous cylinder about the intervertebral implant; and wherein the ring has an outer surface, an inner surface, a lower annular surface facing the lower implant part and an upper annular surface facing the upper implant part, the ring including a straight-cut ring gear suitable for accommodating a corresponding pinion, the straight-cut ring gear extending from the outer surface to the inner surface, and from the lower annular surface thereof.

2. An intervertebral implant according to claim 1, wherein the depression is comprised of a radially continuous depression, which is suitable for positioning and supporting a pinion with respect to the ring gear.

3. An intervertebral implant according to claim 1, wherein the circularly, cylindrical shaft of the upper implant part includes a guiding slot which extends parallel to the axis of rotation, and the outer casing of the lower implant part includes an inwardly protruding guiding element which engages the guiding slot to prevent rotation of the upper implant part with respect to the lower implant part, the guiding element being insertable via a radial opening formed in the outer casing.

4. An intervertebral implant according to claim 1, wherein the circularly, cylindrical shaft of the upper implant part has a smaller circumference than does the hollow cylindrical cavity of the lower implant part, so that the two components do not touch one another.

5. An intervertebral implant according to claim 1, wherein the external thread of the circularly cylindrical shaft and the internal thread of the ring are constructed to be self-locking.

6. An intervertebral implant according to claim 5, wherein the external thread pitch and the internal thread pitch ranges from 0.5 to 1.0 mm.

7. An intervertebral implant according to claim 1, wherein the external thread as well as the internal thread are constructed as right-handed threads.

8. An intervertebral implant according to claim 1, wherein the external and internal threads are constructed as double-lead threads.

9. An intervertebral implant according to claim 1, wherein the two apposition parts, each having an apposition surface, are constructed as panel-shaped elements which are aligned transversely to the axis of rotation with an apposition surface intended to be in contact with the covering surface of the adjoining vertebra.

10. An intervertebral implant according to claim 9, wherein the apposition surfaces form an angle between 83 degrees and 85 degrees with the axis of rotation.

11. An intervertebral implant according to claim 10, wherein the two apposition surfaces enclose an angle of 10 degrees to 14 degrees with one another.

12. An intervertebral implant according to claim 9, wherein at least one of the two apposition surfaces is curved to the outside.

13. An intervertebral implant according to claim 9, wherein the apposition surface of the lower implant part is constructed flat.

14. An intervertebral implant comprising:

a lower implant part having a hollow cylindrical cavity with an outer casing and an axis of rotation, and an apposition part intended for contacting a covering surface of an adjoining lower vertebra, the outer casing having a depression extending therethrough and being in communication with the cavity;

an upper implant part with a circularly, cylindrical shaft having an external thread and an axis of rotation, and an apposition part intended for contacting a covering surface of an adjoining upper vertebra, wherein the shaft extends into the cavity of the lower implant part;
and a circular ring with an internal thread which is disposed between the upper implant part and the lower implant part and interacts with the external thread of the upper implant part, wherein the ring includes a toroidal undercut and the outer casing of the lower implant part includes an annular bead, the toroidal undercut mates with the annular bead so that the ring is axially fixed but rotatively movably with the lower implant part, the toroidal undercut and the annular bead forming a continuous cylinder about the intervertebral implant;

wherein the upper implant part, the lower implant part and the ring are disposed coaxially along the axis of rotation, so that by rotating the ring on the external thread of the shaft, a distance between the two apposition parts can be variably changed, wherein the ring has an outer surface, an inner surface, a lower annular surface facing the lower implant part and an upper annular surface facing the upper implant part, the ring including a straight-cut ring gear suitable for accommodating a corresponding pinion, the straight-cut ring gear extending from the outer surface to the inner surface, and from the lower annular surface thereof, the ring gear being located on a plane generally perpendicular to the axis of rotation; and wherein the upper implant part, the lower implant part and the ring are made from an X-ray-transmitting material.

15. The intervertebral implant of claim 14 wherein the X-ray transmitting material is a PEEK material.

16. An intervertebral implant comprising:

a lower implant part having a hollow cavity and an axis of rotation, and an apposition part intended for contacting an adjoining lower vertebra, the hollow cavity in communication with a depression in the lower implant part;

an upper implant part having a shaft having an external thread and an axis of rotation, and an apposition part intended for contacting an upper vertebra, wherein the shaft extends into the cavity of the lower implant part; and a circular ring disposed between the upper implant part and the lower implant part, the ring having an internal thread for engaging the external thread of the upper implant part;
wherein the upper implant part and the lower implant part are secured to prevent rotation about the axis of rotation;

wherein rotating the ring about the shaft causes a change in distance between the two apposition parts; and wherein the ring is axially fixed but rotatively movably with respect to the lower implant part, the ring and lower implant part being coupled together by a continuous surface that extends circumferentially about the axis of rotation; and wherein the ring has an outer surface, an inner surface, a lower annular surface facing the lower implant part and an upper annular surface facing the upper implant part, the ring including a straight-cut ring gear suitable for accommodating a corresponding pinion, the straight-cut ring gear extending from the outer surface to the inner surface, and from the lower annular surface thereof, the ring gear facing directly toward the apposition part of the lower implant part.