ZA200507916B

ZA200507916B - Intervertebral implant

Info

Publication number: ZA200507916B
Application number: ZA200507916A
Authority: ZA
Inventors: G Tlin Michael; Schor Manuel; Lechmann Beat
Original assignee: Synthes Ag
Priority date: 2005-09-30
Filing date: 2005-09-30
Publication date: 2006-10-25

Description

Co 1968/PCT " 24.4.2003

FR 1

English translation of the International Patent Application No. PCT/CH03/00273 “Intervertebral implant” in the name of Synthes AG Chur

Intervertebral implant

The invention relates to an intervertebral implant according to the generic term of Patent

Claim 1.

An intervertebral implant of a similar type is prior art from DE-A 196 22 827. In that device, the central implant section formed as a ring with internal thread is connected by the threading only to the upper, terminal implant section. The ring is moveable in relation to the lower, terminal implant section both in an axial and a rotational direction.

The lower, terminal implant section serves the ring merely as an axial limit stop, i.e. as a support area against which the ring can be turned, so that the upper, terminal implant section can be moved axially (nut/spindle drive). The two terminal implant sections are thus assembled loosely opposite each other, which is also shown in that a radial threaded hole is provided as an axial fixing device in one of the two implant sections, through which a tensioned attachment screw is conducted. This state-of-the-art intervertebral implant therefore has the disadvantage that it is not secured before or during operations and can disintegrate. If an implant section happens to fall out during an operation, major delays would result as sterilising measures would have to be carried out.

A telescoping intervertebral disk prosthesis with a threaded ring is prior art from EP-A 1 219 266 ULRICH, which is provided with a bevel-wheel gearing, which can be turned from the radial direction by means of a bevel-wheel! pinion. A disadvantage in this prior art device is the circumstance that the threaded ring is not fixed axially to one of the sleeve sections. This means that the structure of the implant is less stable, and it will also be necessary to provide a special instrument to induce the distraction of the implant. A further disadvantage of this known implant is in the bevel-wheel gearing used, which is less “forgiving” and thus a disadvantage. In the case of the bevel-wheel gearing, the drive instrument can no longer carry out its intended function in the case of even a slight axial shift and the surgeon will have to position the instrument anew in- situ.

= 2

The invention is intended to remedy this situation. The invention is based on the task of creating an intervertebral implant that forms a compact whole that is protected against the disintegration of the individual parts while retaining the lowest possible height and "that can be made available to the surgeon as a pre-assembled set.

The invention solves the set task by providing an intervertebral implant that contains the features of Claim 1.

Further advantageous embodiments of the invention are indicated in the sub-claims.

The advantages realised by the invention can be seen primarily in that the intervertebral implant in accordance with the invention allows easier handling, which on the one hand increases safety and on the other hand reduces the time required for the implant.

In a special embodiment, the ring of the intervertebral implant is secured in a way that prevents axial but allows rotational movement by means of a clip connection on the lower implant section. This means that the ring remains securing in position for the drive, i.e. the ring cannot shift in an axial direction.

The clip connection is preferably formed by a toroid undercut in the ring and a corresponding ring-shaped bead at the free end of the jacket of the lower implant section. In this way, the rotation of the ring is secured in that the rotation takes place around the same centre as the two sleeve-shaped implant sections.

In a further embodiment, the ring is provided with a lower circular ring surface facing the lower implant section and an upper circular ring surface facing the upper implant section, wherein the lower circular ring surface is provided with a crown gear, which is suitable for receiving a corresponding pinion. By radial rotation of the instrument supporting the pinion, this embodiment permits axial rotation of the ring. Compared to state-of-the-art implants in which the ring has to be moved tangentially, this system provides the advantage that less space is required for the turning instrument and a higher speed, as turning can be continuous without the need to for the turning instrument to be constantly inserted into new holes of the ring.

In a further embodiment, the jacket of the lower implant section is provided with a radial, preferably continuous depression, which is suitable for positioning and supporting a pinion in relation to the crown gear. This permits the advantage that bone chips can now be inserted in the cavity of the lower implant section through the continuous depression, after distraction of the vertebra has been completed.

In a further embodiment, the circular-cylindrical shaft (6) of the upper implant section is provided - for securing against the upper rotating in relation to the lower implant section - with a guide aperture running parallel to the rotation axis and the jacket of the lower implant section is provided at its inner side with a guiding element (17) protruding inwards and engaging in the guide aperture, which element can preferably be inserted by a radial breach in the jacket. This prevents mutual rotation of the two implant sections. Mutual rotation would impair contact of the implant to the end plates and the lordosis forming angle.

In a further embodiment, the circular-cylindrical shaft (6) of the upper implant section (5) is provided with a smaller circumference than the hollow cylindrical cavity (3) of the lower implant section (2) so that the two parts does not come in contact.

In a further embodiment, the external thread of the circular-cylindrical shaft and the internal thread of the ring are self-locking. The advantage of this embodiment is that the self-locking feature of the threading allows the implant to be distracted at any height without the need for any additional arrest.

In a further embodiment, the gradient of the external thread and of the internal thread is within the range 0.5 to 1.0 mm, and preferably 0.6 — 0.8 mm. Larger gradients, for example within the range 2 mm, showed disadvantages during operations, as the distraction was shown to be too coarse and smaller gradients resulted in a longer turning.

In a further embodiment, both the external thread and the internal thread are formed as right-hand thread. This leads to the advantage that the instrument bearing the pinion can be turned in the normal way as a standard screwdriver in clockwise direction in order to distract the implant.

EATS NO : :

In a further embodiment, both the external thread and the internal thread are designed as multi-flighted, preferably as 2-flighted thread. In a 2-flighted thread, a double stroke is achieved for each turning of the ring. This ensures quicker and simpler handling of the implant, which shortens the operation time and spares the patient.

In a further embodiment, the two apposition sections are designed as plate-shaped elements standing perpendicular to the rotation axis with an apposition surface intended for contact on the top surface of the neighbouring vertebra.

In a further embodiment, the apposition surfaces are not arranged orthogonal to the rotation axis but preferably form an angle 83° to 85° with the rotation axis. This leads to better adaptation to the anatomic situation. The two apposition surfaces preferably form an angle of 10° to 14° to each other. In this way, the anatomic lordosis angle can be secured.

In a further embodiment, at least one of the two apposition surfaces, preferably that in the upper implant section, is arched on the outside. This ensures perfect adaptation to the vertebra body. The apposition surface of the lower implant section is preferably of generally flat design.

In a further embodiment, the crown gear is straight-toothed. Compared to a conical /slanted toothed crown gear, the straight toothed design is more “forgiving”.

The invention and refinements of the invention are described in more detail below on the basis of partially schematic illustrations of several embodiments.

Fig. 1 shows a perspective view of the intervertebral implant in assembled state;

Fig. 2 shows a perspective view of the intervertebral implant in dismantled state:

Fig. 3 shows a longitudinal section through the rotation axis of the intervertebral implant according to Fig. 1;

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Fig. 4 shows a front view of the intervertebral implant according to Fig. 1;

Fig. 5 shows a longitudinal section through the rotation axis of the intervertebral implant according to Fig. 1 in dismantled state; and

Fig. 6 shows a front view of the intervertebral implant according to Fig. 1 in dismantled state.

The intervertebral implant 1 illustrated in Fig. 1 - 6 generally consists of a lower implant section 2, an upper implant section 5 and a ring 9 arranged between the two implant sections 2,5. The lower implant section 2 is provided with a hollow cylindrical cavity 3 with a jacket 14 and a rotation axis 11 and an apposition section 4 intended for placement on the top surface of the neighbouring lower vertebra. The upper implant section 5 is provided with a generally circular-cylindrical shaft 6 with external thread 7 and rotation axis 11, reaching into the cavity 3 of the lower implant section 2 and an apposition section 8 intended for placement on the top surface of the neighbouring upper vertebra. The two implant sections are secured against rotation around their rotation axis 11.

The ring 9 has an internal thread 10 which interacts with the external thread 7 of the upper implant section 5, wherein the two implant sections 2,5 and the ring 9 are arranged coaxial along their common rotation axis 11, so that by twisting of the ring 9 on the external thread 7 of the shaft 6 the distance between the two apposition sections 4,8 can be adjusted continuously. The ring 9 is connected by means of a clip connection to the lower implant section 2 fixed in an axial but moveable in a rotation direction.

As illustrated in Fig. 3, the clip connection consists of a toroid undercut 21 in the ring 9 and a corresponding ring-shaped bead 22 at the free end of the jacket 14 of the lower implant section 2.

The ring 9 has a lower circular ring surface 12 facing the lower implant section 2 and an upper circular ring surface 13 facing the upper implant section, wherein the lower circular ring surface 12 is provided with a straight-toothed crown gear 23, which is suitable for receiving a corresponding pinion.

The jacket 14 of the lower implant section 2 is provided with a radial, continuous depression 15, which is suitable for positioning and supporting a pinion (not illustrated) in relation to the crown gear 23.

To secure against the upper implant section 5 rotating in relation to the lower implant section 2, the circular-cylindrical shaft 6 of the upper implant section 5 is provided with a guide aperture 16 running parallel to the rotation axis 11 and the jacket 14 of the lower implant section 2 is provided at its inner side with a guiding element 17 protruding in an inward direction and engaging in the guide aperture 16 (Fig. 2), which can be inserted by a radial breach 18 in the jacket 14.

The external thread 7 of the circular-cylindrical shaft 6 and the internal thread 10 of the ring 9 are designed with a self-locking feature. The gradient of the external thread 7 and of the internal thread 10 measures 0.7 mm. Both the external thread 7 and the internal thread 10 are designed with right-hand thread.

As shown in Fig. 3, the two apposition sections 4,8 are designed as plate-shaped elements standing perpendicular to the rotation axis 11 with an apposition surface 19,20 intended for placement on the top surface of the neighbouring vertebra, wherein the apposition surfaces 19,20 are not positioned orthogonal to the rotation axis 11 but rather form an angle of 85 ° to the rotation axis 11. The two apposition surfaces 19,20 thus form an angle of 10° to each other. The upper apposition surface 20 is — as illustrated in Fig. 3 - arched on the outside, whereas the apposition surface 19 of the lower implant section is generally designed as a flat surface.

The intervertebral implant is manufactured from standard implant materials. X-ray- transmissible materials, preferably manufactured by PEEK, can preferably be used, so that the fusion can be assessed by x-ray.

The intervertebral implant is particularly suitable as a vertebral body replacement in the cervical and higher thoracic section of the spinal column.

Claims

) i 2005707916 Patent claims

1. Intervertebral implant (1) with A) a lower implant section (2), that has a hollow cylindrical cavity (3) with a jacket (14) and a rotation axis (11) and an apposition section (4) intended for placement on the top surface of the neighbouring lower vertebra; B) an upper implant section (5) with a shaft (6) of generally circular-cylindrical design with external thread (7) and rotation axis (11), reaching into the cavity (3) of the lower implant section (2) and an apposition section (8) intended for placement on the top surface of the neighbouring upper vertebra; wherein C) the two implant sections (2,5) are secured against rotation around their rotation axis (11); and D) a ring (9) with internal thread (10) positioned between the two implant sections (2,5) which interacts with the external thread (7) upper implant section (5); wherein E) the two implant sections (2,5) and the ring (9) are arranged coaxial along their common rotation axis (11), so that F) by twisting of the ring (9) on the external thread (7) of the shaft (6) the distance between the two apposition sections (4,8) can be adjusted continuously; characterised in that G) the ring (9) is connected to the lower implant section (2) fixed in an axial but moveable in a rotation direction.

2. Intervertebral implant (1) according to Claim 1, characterised in that the ring (9) is attached by means of a clip connection to the lower implant section (2) fixed in an axial but moveable in a rotation direction.

3. Intervertebral implant (1) according to Claim 2, characterised in that the clip connection is formed from a toroid undercut (21) in the ring (9) and a corresponding ring-shaped bead (22) at the free end of the jacket (14) of the lower implant section

(2).

4. Intervertebral implant (1) according to one of the claims 1 to 3, characterised in that the ring (9) is provided with a lower circular ring surface (12) facing the lower Implant ia : ! v section (2) and an upper circular ring surface (13) facing the upper implant section, wherein the lower circular ring surface (12) is provided with a crown gear (23) which is suitable for receiving a corresponding pinion.

5. Intervertebral implant (1) according to Claim 4, characterised in that the jacket (14) of the lower implant section (2) is provided with a radial, preferably continuous depression (15), which is suitable for positioning and supporting a pinion in relation to the crown gear (23).

8. Intervertebral implant (1) according to one of the claims 1 to 5, characterised in that, to secure against rotation (6) of the upper (5) in relation to the lower implant section (2), the circular-cylindrical shaft (6) of the upper implant section (5) is provided with a guide aperture (16) running parallel to the rotation axis (11), and the jacket (14) of the lower implant section (2) is provided at its inner side with a guiding element (17) protruding inwards and engaging in the guide aperture (16), which can preferably be inserted by a radial breach (18) in the jacket (14).

7. Intervertebral implant (1) according to one of the claims 1 to 6, characterised in that the circular-cylindrical shaft (6) of the upper implant section (5) has a circumference less than the hollow cylindrical cavity (3) of the lower implant section (2), so that the two sections do not come in contact.

8. Intervertebral implant (1) according to one of the claims 1 to 7, characterised in that the external thread (7) of the circular-cylindrical shaft (6) and the internal thread (10) of the ring (9) have a self-locking feature.

9. Intervertebral implant (1) according to Claim 8, characterised in that the gradient of the external thread (7) and of the internal thread (10) is within the range 0.5 to 1.0 mm, and preferably 0.6 — 0.8 mm.

10. Intervertebral implant (1) according to one of the claims 1 to 9, characterised in that both the external thread (7) and the internal thread (10) are designed as right-hand thread.

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11. Intervertebral implant (1) according to one of the claims 1 to 10 characterised in that both the external thread (7) and the internal thread (10) are formed as multi-flighted, preferably as 2-flighted thread.

12. Intervertebral implant (1) according to one of the claims 1 to 11, characterised in that the two apposition sections (4,8) are designed as plate-shaped elements standing perpendicular to the rotation axis (11) with an apposition surface (19,20) intended for placement on the top surface of the neighbouring vertebra.

13. Intervertebral implant (1) according to Claim 12, characterised in that the apposition surfaces (19,20) are not arranged orthogonal to the rotation axis (11) and preferably form an angle 83° to 85 ° to the rotation axis (11).

14. Intervertebral implant (1) according to Claim 13, characterised in that the two apposition surfaces (19,20) form an angle of 10° to 14° to each other.

15. Intervertebral implant (1) according to one of the claims 12 to 14, characterised in that at least one of the two apposition surfaces (19,20), preferably that of the upper implant section (5) is arched on the outside.

16. Intervertebral implant (1) according to one of the claims 12 to 15, characterised in that the apposition surface (19) of the lower implant section is generally designed as a flat surface.

17. Intervertebral implant (1) according to one of the claims 4 to 15, characterised in that the crown gear (23) is straight toothed.

Summary

The Intervertebral implant (1) comprises

A) a lower implant section (2), which is provided with a hollow cylindrical cavity (3) with a jacket (14) and a rotation axis (11) and an apposition section (4) intended for placement on the top surface of the neighbouring lower vertebra;

B) an upper implant section (5) with a generally circular-cylindrical shaft (6) with external thread (7) and rotation axis (11), reaching into the cavity (3) and an apposition section (8) intended for placement on the top surface of the neighbouring upper vertebra; wherein

C) the two implant sections (2,5) are secured against rotation around their rotation axis (11); and

D) a ring (9) positioned between the two implant sections (2,5) with internal thread (10) which interacts with the external thread (7); wherein

E) the two implant sections (2,5) and the ring (9) are arranged coaxial along their common rotation axis (11), so that by twisting of the ring (9) on the external thread (7) of the shaft (6) the distance between the two apposition sections (4,8) can be adjusted continuously; and

F) the ring (9) is connected to the lower implant section (2) fixed in an axial but moveable in a rotation direction.

The intervertebral implant in accordance with the invention allows easier handling, which on the one hand increases safety and on the other hand reduces the time required for the implant.