WO2002085261A1

WO2002085261A1 - Intervertebral disc implant device

Info

Publication number: WO2002085261A1
Application number: PCT/AU2002/000495
Authority: WO
Inventors: Douglas Stafford Maclennan; William Robert Sears
Original assignee: Douglas Stafford Maclennan; William Robert Sears
Priority date: 2001-04-20
Filing date: 2002-04-19
Publication date: 2002-10-31

Abstract

An intervertebral disc implant device is disclosed. The device is arranged to be positioned within a disc space between and to interconnect two vertebrae (eg. C3 and C4). The device includes two fixing elements (10,11) each of which has an insertion portion (14) that is shaped for location within the disc space between the vertebrae, and a flange portion (15) formed integrally with the insertion portion and arranged for securing to a respective one of the vertebrae. A pad (12) is locatable in use between the two fixing elements and connecting means (13) interconnects the fixing elements in a manner that permits relative displacement of the fixing elements with respect to each other in use. A surgical procedure is also disclosed which comprises anteriorly inserting an intervertebral disc implant device as set forth above between two selected vertebrae of a patient.

Description

INTERVERTEBRAL DISC IMPLANT DEVICE FIELD OF INVENTION

This invention relates to an intervertebral disc implant device which may be used to replace diseased, prolapsed, fragmented or otherwise damaged intervertebral discs in the spinal columns of humans or animals.

BACKGROUND TO THE INVENTION

The current surgical technique for correcting intervertebral disc damage or degeneration and associated instability of the spinal column involves removing damaged disc material and fusing the vertebrae immediately above and below the damaged disc by inserting, anteriorly, a piece or pieces of bone to promote bone grafting in the intervertebral space that previously was occupied by the damaged disc. The insertion of bone for the purpose of promoting fusion between adjoining vertebrae is often accompanied by positioning a rigid (usually metal) plate across the graft area of the intervertebral disc space and by securing the plate by screws to the anterior face of the vertebrae immediately above and below the graft area. The purpose of the plate is to provide immediate stability to the spinal column at the treated level and to facilitate fusion of the bone graft. The difficulty with this fusing technique, with or without the fixing of a plate across the graft area, is that anatomical mobility, including rotation, is reduced from the normal range of movement, increasingly with the number of vertebrae that are fused together. Also, the fusing of two or more vertebrae in this manner results in increased wear on the discs immediately above and below those which are fused, resulting usually in accelerated breakdown of and damage to the discs immediately above and below the fused section. This often leads to pain and discomfort for a patient and often to the need for further corrective surgery. The rigidness created by fusing a portion of the spinal column, which by nature and function should remain flexible, has long been recognised as not being entirely satisfactory and as providing a compromise solution.

SUMMARY OF THE INVENTION In a first aspect the present invention provides an intervertebral disc implant device that is arranged to be positioned within a disc space between and to interconnect two vertebrae, and including:

(a) two fixing elements, each of which has an insertion portion that is shaped for location within the disc space between the vertebrae;

(b) a pad locatable in use between the two fixing elements;_, and

(c) connecting means interconnecting the fixing elements in a manner that permits relative displacement of the fixing elements with respect to each other in use. In a second aspect the present invention provides an intervertebral disc implant device that is arranged to be positioned within two or more disc spaces between three or more vertebrae and to extend to interconnect those vertebrae, the device including: (a) at least three fixing elements, each of which has:

(i) an insertion portion that is shaped for location within a disc space between the vertebrae, and (ii) a flange portion formed integrally with the insertion portion and arranged for securing to a respective one of the vertebrae; (b) two or more pads locatable in use between respective adjacent fixing elements; and

(c) connecting means interconnecting the respective adjacent fixing elements in a manner that permits relative displacement of the fixing elements with respect to each other in use.

The invention may also be defined in terms of a surgical procedure which comprises inserting an intervertebral disc implant device as defined above between two selected vertebrae of a patient.

The device has been developed for surgical insertion into any intervertebral disc spaces and can be fixed to adjoining vertebral bodies of the spinal column. The device is intended, when inserted, to restore or otherwise provide adequate stability, flexibility and/or mobility to the spinal column.

The intervertebral disc implant device may be constructed in various sizes, depending upon the position within the spinal column in which a given such device is to be located. For example, an intervertebral disc implant device that is intended to be positioned within the cervical region will have a size that is smaller than that appropriate intervertebral disc implant device that is intended to be inserted in the thoracic or lumbar regions .

PREFERRED FEATURES OF THE INVENTION In a most preferred form, each fixing element includes a flange portion formed integrally with the insertion portion and arranged for securing to a respective one of the vertebrae. Whilst the employment of a flange portion is usual (because it enables immediate and secure fastening of the device to the spine) an embodiment can be provided where the flange is omitted and eg. the insertion portion is adhesively fastened to its vertebra (eg. using a contact cement) .

Preferably the flange is arranged for being secured anteriorly to its respective vertebrae. Preferably the insertion portion is disc-like.

The insertion portion can include a lip around a perimeter of a non-vertebra-engaging surface thereof for retention of the pad or to assist with retention of the pad. The lip preferably extends peripherally around the insertion portion of the fixing element, except where the flange portion is situated, and can be shaped in such a way that it retains the pad against lateral movement , or even in a push-fit therein.

Preferably the pad is further retained between and on the insertion portions of the fixing elements by a pin extending centrally therethrough. In this regard the pin can comprise the connecting means. Preferably the pin extends through and interconnects the fixing elements and the pad. More preferably the pin passes axially through both of the fixing elements and the pad, in a manner that permits relative displacement and movement of the fixing elements in rotational, lateral and/or pivotal directions. In this regard, preferably the tolerance between the pin and each element allows for some controlled play between them to allow movement in said directions.

Preferably the rotational displacement of the fixing elements is about a central axis therethrough. Preferably the lateral displacement involves the insertion portion of one fixing element shifting sideways relative to the insertion portion of the other fixing element. Preferably the pivotal displacement involves the insertion portion of one fixing element pivoting up or down relative to the insertion portion of the other fixing element.

Alternatively, the connecting means may be constituted by an embossment at one of the fixing elements that connects with a mating recess or other embossment at the other of the fixing elements.

Preferably the pad is disc-like and is formed from a material that is biocompatible and exhibits mechanical properties similar to those possessed by biological intervertebral discs. In this regard, preferably the pad is formed from a resilient and/or compressible material and is locatable in use between the two insertion portions of the fixing elements.

The fixing elements preferably are formed from a metal, such as titanium or a titanium alloy, that is not biochemically or otherwise degradable, although they may be formed from a plastics material such as polytetrafluoroethylene .

Also, the vertebra-engaging surface of each fixing element preferably is formed with or coated to provide a surface structure that encourages or enhances grafting between the fixing element and the engaged vertebra.

The flange portion of each fixing element preferably comprises a thin wall which extends peripherally around a portion of each fixing element. Also, at least one hole preferably is provided in the flange portion to receive a screw by which the fixing element can be screw fastened, typically anteriorly, to the associated vertebra body.

The fixing elements preferably are formed in a manner to permit bending of the flange portion relative to the insertion portion of each fixing element, so as to permit shaping of the intervertebral disc implant devices to match the shapes of vertebrae to which they are to be secured.

The insertion portion of each fixing element and the pad are typically circular in shape in plan and of a size so as to ensure that when inserted into an invertebral disc space contact will not occur between any portion of the intervertebral disc implant device and the spinal cord, and encroachment on the foramen will not occur. Preferably the implant device further includes a buffer element between each insertion portion and the pad. Preferably the buffer element is a disc-like element formed from a material having a limiting friction less than that of the pad.

The pad may also have a peripheral groove defined in its side wall to enhance its flexibility in use. In particular, when the pad is formed from a rigid material such as high density polyurethane or high density polyethylene, the groove can enhance the pad's compressibility at its periphery. Preferably in the second aspect, the device includes one or more intermediate fixing element (s) , each constituted by a U-shaped plate element, with one stem of the U-shaped plate constituting an insertion portion for location in a disc space on one side of a vertebra, and the other stem of the U-shaped plate constituting an insertion portion for location in a disc space on the other side of the vertebra. In other words, each intermediate fixing element can span a given vertebra, however, each intermediate fixing element can also be sized to span multiple vertebrae. Also, in the second aspect, the fixing elements at either end of the device are typically as defined above (eg. constituted by an L- shaped plate) . The device of the second aspect is otherwise as defined for the first aspect .

The invention will be more fully understood from the following description of preferred embodiments of intervertebral disc implant devices that are suitable for location in cervical, thoracic and lumbar regions of a spinal column, the description being provided with reference to the accompanying drawings .

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings :

Figure 1 shows a diagrammatic lateral view of a portion of the cervical spinal region of a spinal column with an intervertebral disc implant device according to the invention positioned to be moved anteriorly into a clear intervertebral gap between vertebrae C3 and C4 ; Figure 2 shows a view similar to that of Figure 1, but in relation to a portion of the thoracic spinal region; Figure 3 shows a lateral view of a portion of the lumbar region of the spinal column with an intervertebral disc implant device according to the invention inserted between vertebrae L2 and L3 ;

Figure 4 shows a typical anterior view of the spinal column with an intervertebral disc implant device according to the invention located in position between two vertebrae ;

Figure 5 shows a cross-sectional plan view of a typical cervical vertebra with an intervertebral disc implant device according to the invention located in position; Figure 6 shows a perspective view of one form of an intervertebral disc implant device according to the invention; Figure 7 shows an exploded view of the intervertebral disc implant device as illustrated in Figure 6; Figure 8 shows a cross-sectional view of the intervertebral disc implant device as illustrated in Figure 6 ;

Figure 9 shows a typical anterior view of a portion of the spinal column with an intervertebral disc implant device according to the invention located in position, with the two vertebrae to which the implant device is fixed being rotated with respect to each other;

Figure 10 shows an exploded view similar to Figure 7, but of a variation to the intervertebral disc implant device shown in Figure 7;

Figure 11 shows a view similar to Figure 2 but of an alternative intervertebral disc implant device according to the invention; and

Figure 12 shows a view similar to Figure 3 but of the alternative invertebral disc implant device according to the invention.

MODES FOR CARRYING OUT THE INVENTION As shown in the drawings and, in particular, in Figures 6 and 7, a first intervertebral implant device according to the invention includes two fixing elements 10 and 11 (typically formed from a metal such as titanium) . A disc-like pad 12 is located between the fixing elements 10 and 11, and a pin-type connector (typically a rivetlike device) 13 interconnects the fixing elements 10, 11 and the disc-like pad 12. Typically the tolerances between the pin-type connector and each of the fixing elements are such as to allow a predetermined amount of play or give, to facilitate and simulate natural disc behaviour, but without comprimising the strength of the device.

In the assembled device the connector pin can be flattened at its free end to fasten the elements and pad together. Alternatively, the connector pin can be fastened at its free end by a connector element 13A.

In a further alternative, the connector pin can be replaced and, instead, an embossment at one fixing element can engage with a matching recess or embossment at the other fixing element. For example, the pad can constitute an annular embossment affixed to one of the fixing elements and a second smaller pad can project from the other fixing element to be received within the annular pad (eg. received interferingly therein) . In any case, a connection is typically employed that facilitates rotation, pivoting and/or lateral movement of the fixing elements with respect to each other.

The disc-like pad 12 is preferably formed from a resilient and/or compressible material that exhibits mechanical properties similar to those of biological intervertebral discs. In this regard, the pad can be formed from a compressible but still resilient material such as a silicon based polymer. One such polymer that might be suitable is marketed under the trade mark Molloplast-B. Alternatively, the pad can be formed from a relatively rigid but resilient material such as a known bio-compatible high density polyurethane or high density polyethylene. Other rigid or compressible polymers may be employed as appropriate . The disc-like pad 12 is positioned between the fixing elements 10 and 11 in a manner that permits relative rotation of the fixing elements about the axis of the pin- type connector 13, and in a manner that can also allow pivoting and lateral movement of the fixing elements with respect to each other. The pad can additionally be bonded to intermediate low friction buffer elements (as described below) which then interface with the fixing elements 10, 11. Alternatively, the pad may be adhesively bonded directly to the fixing elements and the pad itself can provide for rotation, pivoting and lateral movement.

As shown in the drawings (see Figures 1, 2 and 3) three differently sized intervertebral disc implant devices are provided for location in intervertebral disc spaces in cervical, thoracic and lumber regions. However, apart from size, the three illustrated devices have substantially the same configuration and construction.

Each of the fixing elements 10 and 11 is formed with an insertion portion in the form of disc-like portion 14, that is shaped to locate within the disc space between two vertebrae. An integral flange portion 15 is usually provided that is arranged to be secured, typically anteriorly, to an adjacent vertebra when the intervertebral disc implant device is inserted into position. The flange portion might also be secured laterally to the adjacent vertebra. Where a flange portion is not employed, the portion 14 can be fastened to its vertebra using eg. an adhesive such as a biocompatible contact cement that may be activated upon vertebra contact .

The disc-like portion 14 of each fixing element is typically circular in shape in plan, as best seen in Figure 5, so as to avoid contact with the spinal cord, any nerve root canal or any other sensitive anatomical portion of the spinal column. Also, although not shown expressly in the drawings, the vertebra-engaging surface 21 of the disc-like portion 14 of each fixing element (ie. the upper surface of element 10 and the lower surface of element 11) is typically provided with a surface texture which facilitates barb-like binding between the fixing element and the engaging surface of the vertebra. The vertebra- engaging surface may also be coated to provide a surface structure that encourages or enhances grafting between the fixing element and the engaged vertebra.

The periphery of the disc-like pad 12 is typically located wholly within the periphery of each of the fixing elements 10 and 11 and can be retained by a lip 20 (Figure 8) formed at the disc-like portion of each fixing element. The pad can also be push-fit into the recess defined by the lip. The lip is advantageous where the pad deteriorates, breaks down, or fails after extended use. In this regard, the spent pad can be removed and a new pad inserted (eg. a pad having a slit or slot extending from the periphery to its centre to enable it to be positioned around the pin 13) . The lip then functions to assist in retaining the newly inserted pad in the device. The flange portion 15 of each fixing element typically comprises a thin wall that extends periperally around a portion of the disc-like portion 14. Preferably two holes 16 are provided in the flange portion to accommodate screws 17 which, when the intervertebral disc implant device is fitted in position, are employed to secure the device permanently in place, as best seen in Figure 4. However, the flange may also or alternatively be cemented or glued to the vertebra.

The fixing elements 10 and 11 are typically each formed from a metal that is sufficiently thin and ductile as to permit bending of the flange portion 15 relative to the disc-like portion 14. Alternatively a bendable biocompatible plastic can be employed. This, when required, facilitates adaptation of the shape of the fixing elements to individual vertebra as shown particularly in Figure 3.

Holes 18 and 19 within the fixing elements 10, 11 and the disc-like pad 12 are also dimensioned, relative to the connector pin 13, so as to permit relative movement of the fixing elements in rotational, lateral and pivotal directions. Also, as described above, the material from which the disc-like pad 12 is formed accomodates compressive forces and facilitates movement of the fixing element 10 relative to the other fixing element 11, yet is sufficiently resilient to retain its shape.

Referring now to Figure 10, where like reference numerals are used to denote similar or like parts, a particularly preferred variation on the implant device is depicted. This device additionally comprises two buffer elements in the form of washers 23. The washers are typically made from teflon or other bioco patible material having a limiting surface friction less than that of pad 12. By employing a lower friction intermediate element between the pad 12 and each of the portions 14, pad 12 is rendered more free for movement in relation to elements 10 and 11 and the flexibility (ie. for rotation, pivoting and lateral movement) of the device as a whole can be improved. The pad can be adhesively bonded to the buffer elements, to define a composite unit where the pad core provides resilience and/or compressibility whilst the external buffer elements provide low friction with the fixing elements.

Particularly where the pad is formed from a rigid but known biocompatible material such as high density polyurethane or polyethylene, the pad 12 can be provided with a circumferentially extending peripheral groove 24 in its side wall to increase pad compressibility at its periphery and to enhance its compliance and "give" in use.

Referring now to Figures 11 and 12, where like reference numerals are used to denote similar or like parts, a second alternative intervertebral disc implant device in accordance with the invention is depicted. As with the devices of Figures 1 to 10, the device includes an upper fixing element 10 and a lower fixing element 11. However, in accordance with this embodiment of the invention, the device includes at least one intermediate element 26. The intermediate element is in the form of a U-shaped plate, with one stem 27 of the U-shape opposing the portion 14 of the upper fixing element 10, and the other stem 28 opposing the portion 14 of the lower fixing element 11. Between each stem 27, 28 and its respective portion 14, a respective pad 12 is positioned, and the upper, lower and intermediate fixing elements are connected together using two pins 13 as shown.

Typically the intermediate element is sized to span at least one vertebra, although in some embodiments it may be sized to span more than one vertebra. In another embodiment, a plurality of intermediate elements can be positioned in series between upper fixing element 10 at one end, and lower fixing element 11 at the opposite end. Such an arrangement can be used to rebuild a spinal column where multiple natural discs have deteriorated and/or where vertebrae have compression fractures resulting in eg. wedge-shaped vertebrae, and/or where osteoperosis and/or scoliosis result in spinal column abnormality. Figure 12 shows the device of this embodiment inserted and fixed to three vertebrae L2 , L3 and L . It will be seen that intermediate element 26 spans and is fixed to respective vertebra L3 via pin 17, however, such fixing is optional.

Whilst devices of varying standard sizes can be produced for the cervical, thoracic and lumber regions of various sized and aged patients, it is also possible to custom-make the device to suit a particular user. In this regard, an image such as an MRI image or CT scan (or another diagnostic technology) can be taken of the spine, and the device can then be digitally machined, molded or fabricated to exactly match the spine of the user. Other manufacturing mapping techniques can also be employed.

In use, a surgeon makes an incision and exposes anteriorly the vertebrae in which the device is to be inserted. The surgeon typically expands the spine (to open the disc space) and then removes the natural disc (or any remnants thereof) to be replaced. The surgeon then anteriorly inserts the device as described above, fastens the device to its respective vertebrae (eg. using the screws etc.), and then closes the incision. The device can be used on humans and animals alike. The incision and insertion may also be made laterally.

Variations and modifications may be made in respect of the invention as above described, thus it should be appreciated that the invention can be embodied in other forms.

Claims

1. An intervertebral disc implant device that is arranged to be positioned within a disc space between and to interconnect two vertebrae, and including:

(a) two fixing elements, each of which has an insertion portion that is shaped for location within the disc space between the vertebrae, and

(b) a pad locatable in use between the two fixing elements; and

(c) connecting means interconnecting the fixing elements in a manner that permits relative displacement of the fixing elements with respect to each other in use.

2. A device as claimed in claim 1 further including a flange portion formed integrally with the insertion portion and arranged for securing to a respective one of the vertebrae .

3. A device as claimed in claim 1 or 2 wherein the flange is arranged for being secured anteriorly to its respective vertebrae.

4. A device as claimed in any one of the preceding claims wherein the insertion portion is disc-like.

5. A device as claimed in any one of the preceding claims wherein the insertion portion includes a lip around a perimeter of a non-vertebra-engaging surface thereof .

6. A device as claimed in claim 5 wherein the pad is further retained between and on the insertion portions of the fixing elements by a pin extending centrally therethrough.

7. A device as claimed in claim 6 wherein the pin comprises the connecting means.

8. A device as claimed in any one of the claims 1 to 5 wherein the connecting means includes a pin extending centrally through and interconnecting the fixing elements and the pad. 9. A device as claimed in any one of the preceding claims wherein the connecting means permits rotational, lateral and/or pivotal displacement of the fixing elements with respect to each other.

10. A device as claimed in claim 9 wherein: the rotational displacement of the fixing elements is about a central axis therethrough; the lateral displacement involves the insertion portion of one fixing element shifting sideways relative to the insertion portion of the other fixing element; and the pivotal displacement involves the insertion portion of one fixing element pivoting up or down relative to the insertion portion of the other fixing element .

11. A device as claimed in any one of the preceding claims wherein the pad is disc-like and formed from a resilient and/or compressible material and locatable in use between the two insertion portions of the fixing elements.

12. A device as claimed in any one of the preceding claims further including a buffer element between each insertion portion and the pad.

13. A device as claimed in claim 12 wherein the buffer element is a disc-like element formed from a material having a limiting friction less than that of the pad. 14. A device as claimed in any one of the preceding claims wherein the pad has a peripheral groove defined in its side wall to enhance its flexibility in use .

15. A device as claimed in any one of the preceding claims wherein each flange portion has hole(s) therethrough for introducing respective screw (s) therethrough to screw fasten the fixing element to its vertebra.

16. An intervertebral disc implant device that is arranged to be positioned within two or more disc spaces between three or more vertebrae and to extend to interconnect those vertebrae, the device including:

(a) at least three fixing elements, each of which has:

(i) an insertion portion that is shaped for location within a disc space between the vertebrae, and

(ii) a flange portion formed integrally with the insertion portion and arranged for securing to a respective one of the vertebrae;

(b) two or more pads locatable in use between respective adjacent fixing elements; and

17. A device as claimed in claim 16 wherein one or more intermediate fixing elements are provided between end fixing elements, each intermediate element being constituted by by a U-shaped plate element, with one stem of the U-shaped plate constituting an insertion portion for location in a disc space on one side of a vertebra, and the other stem of the U-shaped plate constituting an insertion portion for location in a disc space on the other side of the vertebra.

18. A device as claimed in claim 16 or 17 that is otherwise as defined in any one of claims 1 to 15.

9. A surgical procedure which comprises inserting an intervertebral disc implant device as claimed in any one of the preceding claims between two selected vertebrae of a patient.