WO2001023014A1

WO2001023014A1 - Bone tissue repair kit

Info

Publication number: WO2001023014A1
Application number: PCT/GB2000/003713
Authority: WO
Inventors: John Robert Naybour; Marcus Orton
Original assignee: Depuy International Limited
Priority date: 1999-09-28
Filing date: 2000-09-28
Publication date: 2001-04-05
Also published as: GB9922872D0

Abstract

A kit for making a repair to damaged bone tissue which has an opening extending through it, comprises a fabric material which can be placed over the opening, and a matrix material which can be applied to the fabric material so as to impregnate it and which can cure so as to form with the fabric material a hard composite structure. The kit includes means which can be applied over the fabric material when positioned over the opening, for supporting the fabric material so that it can withstand pressure applied to the fabric and the matrix material by which the matrix material is made to fill the opening and to impregnate the fabric. The support means will usually be made from a material which does not bond to the matrix material. For example, when the matrix material comprises an acrylic based polymeric material, the surface of the support means which contacts the matrix material can be made from a silicone rubber.

Description

BONE TISSUE REPAIR KIT

This invention relates to a kit for making a repair to damaged bone tissue which has a opening extending through it.

Bone tissue can be damaged so that it requires repair as a result of trauma or surgery. The damage can be in the form of a perforation. It can also be damaged in surgery, including for example surgery to repair or to replace a part of a bone. In particular, bone damage can require repair during joint replacement surgery. Such surgery generally involves removal of tissue from each of the articulating bones of the joint, and implantation of prosthesis components in each of the articulating bones. Tissue is generally removed from the end of each of the bones in the joint. A cavity often has then to be prepared in the bone to receive the prosthesis component, for example by drilling or cutting bone tissue.

When the bond between natural bone tissue and a component of a joint prosthesis has failed, for example due to a change in bone tissue density or to micromovement of the prosthesis component, it is necessary to remove the joint prosthesis component and to replace it. Such techniques are referred to as "revision surgery". In preparing the bone tissue to receive the new prosthesis component, material (especially bone cement) that was used to provide the bond between the bone tissue and the failed component must be removed from the cavity within the bone. The bone can be significantly weakened as a result of this removal, leading in particular to localised areas of reduced thickness, including perforations.

It is known to reinforce weakened bone tissue by using bone graft materials which are formed from natural bone tissue and also using curable polymeric cement materials, for example based on acrylic acid polymers. Such materials are used to fill space within a bone cavity to prepare it for implantation of a prosthesis component. The bone graft materials and also some bone cement materials are able to accommodate ingrowth of the patient's natural tissue. The present invention provides a bone tissue repair kit which comprises a matrix material (such as a bone graft material or a bone cement), a fabric material for reinforcing the matrix material, and a support for the fabric while it is being impregnated with the natrix material.

Accordingly, in one aspect, the invention provides a kit for making a repair to damaged bone tissue which has a opening extending through it, comprising: a. a fabric material which can be placed over the opening, b. a matrix material which can be applied to the fabric material so as to impregnate it and which can cure so as to form with the fabric material a hard composite structure, and c. means which can be applied over the fabric material when positioned over the opening, for supporting the fabric material so that it can withstand pressure applied to the fabric and the matrix material by which the matrix material is made to fill the opening and to impregnate the fabric.

The kit of the invention has the advantage that it can provide a densely packed composite structure comprising the fabric and the matrix material, arranged so that it covers and fills the opening in the bone tissue. The fibres of the fabric are able to support the matrix material in the initial period when it is applied to the bone, and also subsequently. For example, when the matrix material is a curable cement material, the fabric can support the cement before it has cured and restrict its tendency to flow. Subsequently, after the cement has cured, the fabric can contribute to the load bearing capacity of the composite structure, at least initially. It might be that the fabric is formed from a material which is resorbed on contact with body fluids (for example a polyacrylate material), in which case, any contribution that it makes to the load bearing capacity of the composite will be assumed by the matrix material, or by bone tissue that has grown into the matrix material.

The support can be arranged to be left in place over the opening in the bone. Preferably, however, the support is provided over the opening only while the composite material is being provided in the bone opening. Preferably, the support means is arranged to be applied to the external surface of the bone. The matrix material can then be applied to the opening from the inside of the bone. This has the advantage that access can be gained readily to the support after creation of the composite material, in particular for removal of the support means.

The support means can be arranged so as to extend around the entire periphery of the bone in the region of the opening. For example, it can be function on the bone surface as a tubular or band-like member with a closed cross-section, either being provided with that configuration or being closed around the bone. Removal of such a support means will generally involve cutting or otherwise opening it. The support means might be arranged instead so as to extend around only a part of the periphery of the bone. This has the advantage that it is not necessary to have access to the bone around its entire periphery. It will generally be necessary however to attach the support means to the bone along at least a part of its edge. The support might be attached by, for example, a bonding material such as an adhesive, or mechanically such as by means of rivets.

When the composite material is to be provided at or close to an exposed edge of a bone, the support means can fit over that edge, and can cover the bone on each of its opposite surfaces. Such a support can be appropriate when the matrix material is a fluid which can be injected into the space within the support means, for example through one or more injection ports therein.

When the support means is intended to be removed from the bone after the composite material has been provided securely in the opening in the bone, it will be preferred for the support means to be made from a material which does not bond securely to the matrix material when it has hardened so that it can be removed from the bone without disturbing the composite material, especially on the surface of the support which contacts the matrix material. For example, a silicone rubber material can be used. This has particular advantage when used with bone cement materials such as those based on acrylic-based polymers, which do not bond strongly to it. The support means can be provided in the form of a sheet of material which can be applied over the surface of the bone to be repaired. The material of the sheet will be selected so that it can be removed from the bone after the composite has been formed in and over the bone opening. Preferably, the sheet is formed from a material which can be deformed, especially elastically, so that the sheet can be made to conform to irregularities in the surface configuration of the bone. Generally, the sheet will be formed from a polymeric material. An example of a suitable material might be a silicone rubber.

The support means can be formed in situ on the surface of the bone. For example, it might be formed from a formable material which can be fitted over the bone surface, manually or using a tool.

The support means can comprise a mould which can be fitted over an edge of the bone so as to contact both the internal surface of the bone and the external surface thereof. The structure can be custom moulded to suit the configuration of the particular patient's bone on which it is to be used, or selected from a range of moulded support means of different sizes and configurations. A suitable material for use in a moulded support means might be, for example, a silicone rubber.

The kit can be arranged so that it provides more than one layer of the fabric over the opening in the bone. For example, the kit might provide a structure with layers of the fabric located towards the opposite inner and outer surfaces of the bone, both being impregnated with the matrix material and with matrix material between them. When the opening in the bone is located at or towards and edge of the bone, the inner and outer layers of the fabric might be provided by a single piece of the fabric which is folded over at the edge of the bone. To use the kit of the invention in this way, a support might be provided on one of the surfaces of the bone, with a layer of the fabric provided between the support and the bone, and extending beyond the edge of the bone. Matrix material can then be applied to the fabric within the support so as to impregnate it and to fill the opening in the bone. The fabric is then folded at the edge of the bone so as to cover the opening on the side opposite to the support. The fabric might then be sealed against the matrix material by application of another thin layer of the matrix material. The support can be removed from the bone after the matrix material has stabilised (that is hardened when it is applied as a liquid).

In another technique, a support is provided on one of the surfaces of the bone. Matrix material is then applied within the support and to fill the opening in the bone. The fabric is then applied to the exposed surface of the opening and sealed by application of a thin layer of the matrix material. The support is then removed and the fabric folded at the edge of the bone so as to cover the surface of the matrix material that has been exposed by removal of the support. The fabric can then be sealed against that matrix material by application of another thin layer of the matrix material.

The nature of the reinforcement that is provided by the fabric can be selected to meet particular requirements by selection of, for example, its construction and the material of the fibres. It might be preferred for some applications for the fabric to have a stable structure, for example such as might result from formation by use of certain weaving techniques. Stability of the fabric might be achieved by forming connections between fibres at points at which they contact one another. For example, when the fibres comprise a material which softens reversibly when heated, the fibres can be connected to one another by heat setting them, involving exposure to heat and moderate pressure. However, other fabric constructions might be preferred for some applications, for example because of particular deformation characteristics which they provide. For example, the fabric might be formed by processes such as knitting and braiding. The fabric might also be a non-woven fabric, for example as formed by wet or dry laying, melt blowing and spun bonding techniques. Certain non- woven fabrics have particular advantages because of their stability against deformation.

The fabric material can be selected so that the fabric capable of being set in a desired configuration prior to impregnation by the matrix material. Setting the configuration of the fabric might be achieved by heating it to a temperature at which the fabric material softens, forming it, and then allowing it to cool. The fabric can include means for reinforcing a region thereof. The reinforcement can help to control the configuration of the fabric adequate support is provided for it by the matrix material. For example, the fabric might incorporate an elongate stiffener which can prevent the fabric from sagging. An example of such a stiffener might include a length of a wire made from a metallic (for example a titanium based alloy) or other rigid material. The fabric might also be localised by stabilising the fibres thereof locally, for example by heat setting them. The fabric might be stiffened in a region in which it does not contact bone, which might be at an edge of the fabric or at an edge of the bone. The reinforced region of the fabric might be a region in which the fabric is folded. For example, when the opening in the bone extends up to an edge of the bone, the stiffened region of the fabric might extend across the opening at the edge of the bone.

The stability of the fabric towards deformation will be selected according to factors which include the degree of support that the patient's natural bone tissue can provide. For example, if the opening in the bone tissue is relatively large, the fabric can be required to provide more support for the matrix material than in the case of a bone with a smaller perforation.

The fabric should be constructed so that it can withstand the forces to which it will be exposed while being impregnated by the matrix material. For some applications, the fabric might be arranged to deform when being fitted over the opening, for example by stretching or by movement of some fibres relative to other fibres with which they contact in the fibrous structure of the fabric. For example, in the case of a woven fabric, deformation might involve a change in the angle between the warp and weft fibres.

When it is intended that bone tissue should grow into the matrix material, the fabric should be constructed so that it has sufficient open area for bone tissue material to be able to grow into the composite material between the fibres of the fabric. It can be preferred for example for the construction of the fabric bag to be such that the proportion of the surface area that is open for ingrowth of bone tissue is at least about 20%, more preferably at least about 30%, especially at least about 40%, for example at least about 50%. It can be particularly preferred when using fabrics which are constructed so that they have a high open area to stabilise the fabric, for example by heat setting.

The matrix material that is used in the kit of the invention should be capable of accommodating ingrowth of bone tissue so that the assembly and also the prosthesis that is implanted within the bone cavity become fixed securely in the cavity. The material might be a bone cement, for example based on an acrylic acid polymer. Appropriate bone cement materials are well known. It might sometimes be appropriate for the matrix material to comprise crushed or morcellised bone tissue, especially of cancellous bone, which can be used to promote bone grafting. Such materials are capable of being revascularised after implantation. Techniques for preparing such materials are well known.

The matrix material can be supplied to the fabric so as to impregnate it by techniques such as injection using a syringe or other delivery device. This can be preferred when the matrix material is a relatively low viscosity liquid. Other techniques for supplying the matrix material include hand delivery, which can be appropriate when the matrix material is a paste or high viscosity liquid.

Characteristics of the fabric can be determined by the materials from which it is made. The physical properties of the fabric (tensile strength, extensibility etc) can be affected by choice of fibre materials. The materials of the fabric will generally be polymeric. Examples of suitable polymers include certain polyolefins, polyesters and polyamides. It can be particularly preferred for the fibres of the fabric are formed from a material which resorbs over a period after implantation. Resorption might involve dissolution in body fluids with which the fibres come into contact after implantation, possibly after reaction such as a hydrolysis reaction with the fluids. Examples of resorbable materials which might be used to form the fabric include those based on acrylic acid polymers. Different fabric properties might be required in different regions of the fabric, for example in terms of deformation characteristics, and different properties might be required along different axes. Such differential properties might be obtained for example by using different materials to form the fabric. The kit of the present invention can be used to repair perforations and other openings which extend through bone tissue which are located at an end of a bone or at a point along its length. Generally, the opening will be closed to end of the bone so that access can be gained from that end to both surfaces of the bone tissue. The kit of the invention finds particular application in the repair of bones during surgery, for example to replace a joint prosthesis component, when bone can require reinforcement to provide secure fixation of a new prosthesis component.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings in which:

Figures 1(a) and 1(b) are isometric schematic views of the top of a resected bone showing steps of a method of reinforcing a bone using the kit of the present invention.

Figures 2(a) and 2(b) are isometric schematic views of the top of a resected bone showing steps of another method of reinforcing a bone using the kit of the present invention.

Figures 3(a) to 3(c) are isometric schematic views of the top of a resected bone showing steps of a further method of reinforcing a bone using the kit of the present invention.

Referring to the drawings which all show a bone 2 which has been resected to expose an edge 4 and the intramedullary cavity 6. The cavity has previously contained a stem part of a joint prosthesis component. The component has been removed for replacement. Reasons for the replacement might include failure of the bond between the bone tissue and the implanted prosthesis component.

As well as removing an existing prosthesis component from within a bone cavity, it is necessary to ensure that material associated with the implanted prosthesis is also removed, leaving only healthy natural bone tissue. Material to be removed might include bone cement and natural bone tissue which is not fully healthy. The material can be removed by techniques which include, for example, cutting, drilling, reaming and broaching. A consequence of removing tissue from within the bone cavity is that the structure provided by the patient's bone tissue can be weakened, in particular as a result of localised reductions in the thickness of the bone. The reductions in the thickness of the bone can create openings in the bone wall, such as the broken portion 8 at the resected edge 4, as shown in the drawings.

Figure 1(a) shows the bone 2 with a support 10 applied to the outer surface. The support is provided by an elastomeric sheet formed from a silicone rubber. The opening 8 in the bone is then filled with a bone cement 12. A fabric 14 is then applied to the cement in the opening and the fabric is then covered with an additional layer 16 of the cement. The fabric is positioned so that it extends above the resected edge 4 of the bone.

As shown in Figure 1(b), the support 10 is then removed and the fabric is folded over the edge of the bone, so as to overlap the surface of the bone cement which has been exposed by removal of the support. A further layer 18 of the bone cement is then applied to the fabric to seal it to the external surface of the bone.

The resulting repair has the advantage of being resistant to damage, arising from the multilayer structure including, in particular, the presence of two layers of the fabric.

Figure 2 shows a bone repair technique which is similar to that shown in Figure 1. The first stage of the repair, as shown in Figure 2(a) involves the same steps as in Figure 1(a), except for the fact that the fabric 14 might be applied to the cement within the opening 8 while the matrix material only partially fills the opening.

As shown in Figure 2(b), the fabric is folded inwardly after providing the additional layer 16 of the cement, so as to cover the said additional layer, and is then coated on the internal surface of the bone by the further layer of cement 22.

Figure 3(a) shows the bone 2 with a titanium rail 28 provided along the edge 4 across the opening 8. The rail is anchored in appropriately drilled holes in the bone. The fabric 14 is draped over the rail so as to overlap the inner and outer surfaces of the bone. As shown in Figure 3(b), the fabric is then covered with a moulded support 30 which defines a space 32 at the bone edge. Bone cement 34 can be injected into the space so as to impregnate the fabric. The support can be removed after the cement has cured.

In each of the repair techniques that is shown in the drawings, the bone cement comprises a material which is able to accommodate ingrowth of natural bone tissue so that, with time, the bone cement is displaced by the bone tissue which then closes the opening in the bone. Appropriate resorbable bone cement materials are known. The fabric that is used is preferably formed from a material whose fibres tend to be resorbed on contact with body fluids.

Claims

CLAIMS:

1. A kit for making a repair to damaged bone tissue which has a opemng extending through it, comprising: a. a fabric material which can be placed over the opening, b. a matrix material which can be applied to the fabric material so as to impregnate it and which can cure so as to form with the fabric material a hard composite structure, and c. means which can be applied over the fabric material when positioned over the opening, for supporting the fabric material so that it can withstand pressure applied to the fabric and the matrix material by which the matrix material is made to fill the opening and to impregnate the fabric.

2. A kit as claimed in claim 1, in which the support means is arranged to be applied to the external surface of the bone.

3. A kit as claimed in claim 1 , in which the support means is arranged so as to extend around the entire periphery of the bone in the region of the opening.

4. A kit as claimed in claim 1, in which the support means is arranged so as to extend around only a part of the periphery of the bone.

5. A kit as claimed in claim 1, which includes means for forming a bond between the bone and the support means.

6. A kit as claimed in claim 1 , which includes means for forming a mechanical connection between the bone and the support means.

7. A kit as claimed in claim 1, in which the fabric material is capable of being set in a desired configuration prior to impregnation by the matrix material.

8. A kit as claimed in claim 1, which includes means for reinforcing a region of the fabric material.

9. A kit as claimed in claim 1, in which the support means comprises a mould which can be fitted over an edge of the bone so as to contact both the internal surface of the bone and the external surface thereof.

10. A kit as claimed in claim 1, in which the support means comprises a cured layer of a liquid sealing material.

11. A kit as claimed in claim 10, in which the liquid sealing material and the matrix material are substantially the same.

12. A kit as claimed in claim 1 , in which the matrix material comprises morcellised bone graft material.

13. A kit as claimed in claim 1, in which the matrix material comprises a bone cement material.