GB2551362A

GB2551362A - Taper Protector

Info

Publication number: GB2551362A
Application number: GB1610408.5A
Authority: GB
Inventors: Jolly Tom
Original assignee: DePuy Ireland ULC
Current assignee: DePuy Ireland ULC
Priority date: 2016-06-15
Filing date: 2016-06-15
Publication date: 2017-12-20
Also published as: GB201610408D0

Abstract

Disclosed is an orthopedic system comprising a joint prosthesis with a stem part having a neck bearing a taper [figure 1] with a removable taper protector 110 which covers at least part of the taper. The taper protector comprises a body portion 110 having a side wall 112, a top surface 114 and a bottom surface 116, and a bore 118, configured to receive at least part of the taper. The body portion is made from a compressible material which may be resiliently deformable open celled foam. The side wall may have a slit 120 or frangible region to allow the taper protector to be removed from the stem in a lateral direction. There may be a top plate 122 and bottom plate 124 secured to the body portion. The taper protector is used to prevent mechanically assisted crevice corrosion (MACC) of a modular orthopedic system as a surgeon trials an implanted femoral stem with a number of different femoral heads.

Description

TAPER PROTECTOR

Field of the invention

The present invention relates to a taper protector for protecting the taper of a stem part of a joint prosthesis component and orthopaedic joint prosthesis systems including the taper protector.

Background to the invention

Prosthetic implants can be used to replace ball and socket type joints such as shoulder joints and hip joints. Many of these prosthetic implants have the general construction of a stem component, which is received in a long bone (such as the femur or humerus) to which a head component is attached and which provides an articulating surface. A self-locking taper, such as a Morse taper, is often used to join modular parts of a prosthesis to one another. For example, the stem part of a hip joint prosthesis can have a tapered post at its proximal end and the head part can have a tapered bore. The post can be received in the bore.

Whilst modularity at the head-neck junction of a femoral component decreases implant inventory and allows adjustment of leg length, offset, and soft tissue balancing through different head options, there is a risk that a modular interface can lead to taper corrosion. This is caused by a complex interaction of crevice corrosion, initiated by changes in local chemistry within crevices, and fretting (micromotion between the interface of the taper surfaces), which disrupts the protective oxide layer on the taper. This process has also been termed “mechanically assisted crevice corrosion” (MACC). Over time this can cause severe wear within the implants and can lead to implant dissociation within the body. MACC can potentially produce by-products at the head-neck junction, primarily metal ions, which can migrate locally and systemically. MACC can be minimised by protecting the taper surfaces from bodily fluids and debris (e.g. bone) during surgery.

During a surgical procedure a surgeon may trial an implanted femoral stem with a number of different femoral heads. There is therefore a need for a taper protector that enables the surgeon to apply a trial head for sizing and then the definitive head whilst also protecting the taper.

Summary of the Invention

The invention provides a taper protector for fitting onto a taper of a stem part of a joint prosthesis component and protecting the taper. The taper protector includes a compressible body portion that can be compressed when the head part of a joint prosthesis component is pushed onto the stem part to form a self-locking taper.

Accordingly, the invention provides an orthopaedic system comprising; a stem part of a joint prosthesis component, the stem part having a neck bearing a taper; and a taper protector covering at least part of the taper and being removable from the taper, the taper protector comprising a body portion having a side wall, a top surface and a bottom surface, and a bore extending between the top surface and the bottom surface that is configured to receive the at least part of the taper, in which the body portion is made from a compressible material which allows it to be compressed.

The taper protector can be used to protect the taper of a stem part of a joint prosthesis component until the final head component of the joint prosthesis system has been secured onto the taper. This minimises the risk that the surface of the taper will become mechanically damaged (e.g., scratches) or coated with bodily fluids or debris formed during surgery (e.g. bone chips) that will disrupt the fix of the taper.

The taper protector may be applied to the taper immediately following the manufacture of the stem part. The taper protector is therefore pre-assembled on the taper prior to the surgeon using the stem part. This will minimise any mechanical damage to the taper during storage or transit.

The taper protector may be supplied as a separate component which the surgeon can assemble on the taper of the stem part prior to undertaking the trialing procedure.

Optionally, the side wall of the body portion has a slit or a frangible region configured to allow the taper protector to be removed from the stem part in a lateral direction with respect to the stem part. This allows the taper protector to be removed from the stem part without the need to remove the head part of the joint prosthesis. This is advantageous as it prevents the taper connection from having to be disrupted in order to remove the taper protector, and the risk of damage being made to the taper surface. In some constructions, the slit or frangible region extends between an outer surface of the side wall and the bore and extends from the top surface to the bottom surface of the side wall.

Preferably, the opposing edges of the slit abut when the taper protector is in place on the taper. This minimises the risk that body fluids are able to ingress through the slit and coat the taper. In some constructions, the opposing edges of the slit may include a means for temporarily holding the edges in abutment, for example, a channel and groove arrangement.

The frangible region may be provided by, for example a row of perforations. A barrier may be provided at a point along the perforation to prevent ingress of bodily fluids through the perforation to the taper surface. A possible disadvantage with the provision of a slit on the body region is that the slit may gape open during compression. The provision of a frangible region addresses this problem.

In other constructions, the body portion of the taper protector may be formed from a roll of compressible material. The body portion is wrapped around the taper, in a manner similar to a “swiss roll”. Removal of the taper protector involves unfurling the body portion from the taper.

The body portion comprises a compressible material. Preferably, the material is substantially impermeable to bodily fluid, is capable of withstanding the sterilisation techniques used to sterilise the parts of joint orthopaedic systems, is biologically-safe and has a low cost of manufacture. Preferably, the material is bioabsorbable. Preferably, the material is a compressible foam. More preferably, the foam material is a closed cell foam, such as a polyurethane closed cell foam. An open cell foam may be used in some constructions of the taper protection, although it is envisaged that a substantially liquid impermeable coating may be applied to the outer surface of the body portion, thereby preventing ingress of bodily fluids through the open cells. This coating may be hydrophobic.

In some constructions, the body portion comprises a resiliently deformable material. The ability of the body portion to be compressed and then to resume its original configuration is of particular use when a surgeon is trialing various head parts on the stem part. When a surgeon pushes a trial head part onto the taper for sizing, the head part will push against the top surface of the body portion leading to the compression of the body portion. A taper connection will form between the taper of the stem part and a tapered bore within the head part. After the surgeon has removed the trial head part, and prior to the application of the definitive head part or an alternative trial head part, the body portion of the taper protector will spring back to its original configuration. This protects the taper until the surgeon is ready to apply the definitive head part or an alternative trial head part.

When trialing an orthopaedic prosthesis system, it is advantageous that the taper protector does not impinge on the range of movement. Preferably, the side wall of the taper protector does not extend beyond the diameter of the spherical head part, when the head part is positioned on the taper.

In some constructions, the body portion is an annular ring. Preferably, the diameter of the annular ring is equal to or less than diameter of the spherical head part.

In some constructions, the system further includes at least one of a top plate located at the top surface of the body portion and a bottom plate located at the bottom surface of the body portion, each of the top and bottom plates having a bore configured to receive part of the stem part of the joint prosthesis component.

In some constructions, the at least one of the top plate and the bottom plate is secured to the top face and/or the bottom face of the body portion, for example by an adhesive. In other constructions, the at least one of the top plate and the bottom plate can be provided as a part of the body portion. The part functioning as the top plate and/or bottom plate will have a different structural characteristic (e.g., compressibility, deformability) than the other parts of the body portion. In some other constructions, the top plate and the bottom plate are provided as separate components to the taper protector, and can be positioned by the surgeon so as to abut the top face and/or the bottom face of the body portion.

Preferably, the at least one of a top plate or bottom plate includes a slit or a frangible region that is aligned with the slit or frangible region on the side wall of the body portion. This allows the top plate and/or the bottom plate to be removed from the stem part at the same time that the body portion is removed.

An area of increased flexibility within the top and/or bottom plate, that is located on the opposite of the plate to the slit or frangible region, allows the plates to be readily opened for removal in a lateral direction with respect to the stem part. In some constructions, this area of increased flexibility is provided by a hinge.

In some constructions, the hinge is provided by an elasticated hinge.

In some other constructions, the hinge is provided by a locally thinned portion of the plate. This is advantageous because it allows the plate to be manufactured as a unitary component.

The provision of a top plate comprising a material that is less compressible than the compressible material of the body portion ensures that the compressible body portion is able to withstand the load of applying the head part and also causes the body portion to deform evenly as the head part is pushed onto the taper. The top plate also prevents the body portion bunching around and over the head part, thereby minimising any impingement by the taper protector on the range of movement testing when using trial head parts. The following additional considerations may also be taken into account when selecting the material for the top plate: ability to be sterilised; biological safety; cost of manufacture. In some constructions, the top plate is made from a polymeric material. A suitable polymer is polyethylene (PE). PE is capable of withstanding gamma radiation and steam autoclaving, is biologically safe and has a low cost of manufacture. An alternative material for the top plate is acrylonitride butadine styrene (ABS).

The system may also include a bottom plate. The bottom plate preferably comprises a deformable material which is capable of deforming around the neck of the stem part, thereby providing a snug fit. This ensures that the taper protector is maintained on the part of the taper that it is designed to protect, and minimises the risk that the taper protector is slips downwardly when an impaction force is applied to the head part to form the taper connection between the head part and the stem part. In some constructions, the deformable material comprises a rubber, preferably a rubberised polymer.

During surgery it is common for surgeons to desensitise to the colour red. The taper protector (and optionally the top plate and/or bottom plate) therefore advantageously has a colour that is on the opposite side of the colour wheel to red, such as blue or green. The use of such a colour has the effect of re-sensitising the eyes to red. This will be useful in enabling the surgeon to spot any blood or fluid on the implants or the taper protector during surgery. This will also advantageously, minimise the risk that the taper protector (and optionally the top plate and/or bottom plate) is accidentally left on the stem part of the joint prosthesis once the definitive head part has been secured in place.

It may be considered advantageous to manufacture the body portion, top plate and/or bottom plate from the same material, but having different mechanical properties (e.g., compressibility and deformability). This simplifies the design and means that the components are more readily disposed of.

In some constructions, the body portion, top plate and/or bottom plate are made from bioabsorbable polymers, such as polylactic acid (PLA) or polyglycolic acid (PLGA) or copolymers thereof. When the body portion of the taper protector is tom open, crumbs of the foam could break off and stay in the body. An advantage of using a bioabsorable polymer is that these crumbs would not cause adverse tissue reactions, they would bioabsorb.

In some other constructions, the body portion, top plate and/or bottom plate are made from polyethylene (PE).

The stem part of the joint prosthesis component may be, for example a femoral component of a hip prosthesis or a humeral component of a shoulder prosthesis.

According to a further aspect of the invention, there is provided a taper protector for use in protecting a taper region of a joint prosthesis component, the taper protector comprising a body portion having a side wall, a top surface and a bottom surface, and a bore extending between the top surface and the bottom surface that is configured to receive the at least part of the taper, the body portion being made from a compressible material which allows it to be compressed, and a plate secured to at least one of a top surface and a bottom surface of the body portion.

According to a further aspect of the invention there is provided a kit comprising; a stem part of a joint prosthesis component, the stem part having a neck bearing a taper; a plurality of trial head part joint prosthesis components; and a taper protector covering at least part of the taper and being removable from the taper, the taper protector comprising a body portion having a side wall, a top surface and a bottom surface, and a bore extending between the top surface and the bottom surface that is configured to receive the at least part of the taper, in which the body portion is made from a compressible material which allows it to be compressed.

Detailed description of the invention

The invention will now be described, by way of example only, with reference to the following drawings, in which: FIG. 1 is a perspective view of a femoral stem part of a joint prosthesis component. FIG. 2 is a perspective view of a first construction of the taper protector. FIG. 3 is a top view of the taper protector of FIG. 2. FIGS. 4a and 4b are views of the top plate and the bottom plate of the taper protector of FIG. 2. FIG 5. is a perspective view of a second construction of the taper protector. FIGS. 6a to 6c is a view of the top plate of the taper protector of FIG. 5, and shows the component parts of the top plate. FIGS. 7a to 7c is a view of the bottom plate of the taper protector FIG. 5 and shows the component parts of the bottom plate. FIG. 8 is an isometric view of a third construction of the taper protector. FIGS. 9a-d are a series of views showing the compression of the taper protector when the head part is pushed onto the stem part of the joint prosthesis. FIGS. lOa-d are a series of views showing the removal of the taper protector when the definitive head part or a trial head part is in place on the stem part of the joint prosthesis.

Referring now to FIG 1 there is shown a perspective view of a femoral stem part 100 of a joint prosthesis component that includes a stem region 102 and a tapered neck region 104. The femoral stem part includes a trunnion 106 at the proximal end. FIG. 2 shows a perspective view of a first construction of the taper protector 108. The taper protector includes a body portion 110 of compressible foam which has a side wall 112, a top face 114 and a bottom face 116. The body portion also includes a bore 116 extending between the top face and the bottom face. A slit 120 extends from the top face and the bottom face and also extends from the outer surface of the side wall to the bore. A top plate 122 is secured, by an adhesive, to the top surface 114 of the body portion. A bottom plate 124 is secured, by an adhesive, to the bottom surface 116 of the body portion. The top plate has a bore 126. The bottom plate also has a bore (not shown). The top plate and the bottom plate each has a slit 128, 130, which is aligned with the slit 120 in the body portion. In the construction shown, the slit 128, 130 in the top plate 122 and the bottom plate 124 is wider than the slit 120 in the body portion. FIG. 3 shows a top view of the taper protector of FIG. 2 and illustrates that bore 126 of the top plate 122 has substantially the same diameter as the bore 116 of the body portion. The bores 126 and 116 are aligned. FIGS. 4a and 4b show the geometry of the top plate 122 and bottom plate 124, respectively. The inner profile of the top plate 122 is circular. This allows the top plate to slide smoothly over the taper part of the stem part. The inner profile of the bottom plate 124 is rectangular. This allows the bottom plate to snugly fit about the stem part of the joint prosthesis. FIG. 5 is a perspective view of a second construction of the taper protector. The taper protector 208 includes a body portion 210 of compressible foam which has a side wall 212, a top face (not shown) and a bottom face (not shown). The body portion also includes a bore 216 extending between the top face and the bottom face. A slit 220 extends from the top face and the bottom face and also extends from the outer surface of the side wall to the bore. A top plate 222 is secured, by an adhesive, to the top surface 214 of the body portion. A bottom plate 224 is secured, by an adhesive, to the bottom surface 216 of the body portion. The geometry of the top plate 222 and bottom plate 224 are shown in more detail in the views in FIGs., 6a to 6c (top plate) and FIG. 7a to 7c (bottom plate). As shown, the top plate 222 includes a horseshoe-shaped component 226 (FIG. 6c) which provides an elasticated hinge. Two identical arm components 228 (FIG. 6b) are each secured to the horseshoe-shaped component 226 to form the final assembly as shown in FIG. 6a. The hinge provides increased flexibility to the top plate, which allows the top plate to be easily removed along with the body portion 210 of the taper protector.

Similarly, the bottom plate 224 includes a horseshoe-shaped component 226 (FIG. 7c) which provides an elasticated hinge. Two identical arm components 230 (FIG. 7b) are each secured to the horse shoe-shaped component 226 to form the final assembly as shown in FIG. 7a. The hinge provides increased flexibility to the bottom plate, which allows the top plate to be easily removed along with the body portion 210 of the taper protector. FIG. 8 is an isometric view of a third construction of the taper protector. The components of the third construction are similar to the first and second constructions of the taper protection. In the third construction, the taper protector 308 includes a frangible region formed by a row of perforations 332 replaces the slit within the body portion 310. A region of flexibility in the top plate 322 and the bottom plate 324 is provided by a locally thinned region of material, shown at 334 on the top plate. FIGS. 9a-d are a series of views showing the compression of the taper protector when the head part is pushed onto the stem part of the joint prosthesis. FIGS. lOa-d are a series of views showing the removal of the taper protector when the definitive head part or a trial head part is in place on the stem part of the joint prosthesis.

Claims

1. An orthopaedic system comprising; a stem part of a joint prosthesis component, the stem part having a neck bearing a taper; and a taper protector covering at least part of the taper and being removable from the taper, the taper protector comprising a body portion having a side wall, a top surface and a bottom surface, and a bore extending between the top surface and the bottom surface that is configured to receive the at least part of the taper, in which the body portion is made from a compressible material which allows it to be compressed.

2. An orthopaedic system according to claim 1, in which the side wall has a slit or a frangible region configured to allow the taper protector to be removed from the stem part in a lateral direction with respect to the stem part.

3. An orthopaedic system according to claim 1, in which the slit or frangible region extends between an outer surface of the side wall and the bore and extends from the top surface to the bottom surface of the side wall.

4. An orthopaedic system according to any of claims 1 to 3, in which the compressible material comprises a foam, preferably a closed cell foam.

5. An orthopaedic system according to any of claims 1 to 4, in which the body portion comprises a resiliently deformable material.

6. An orthopaedic system according to any of claims 1 to 5, in which system further includes at least one of a top plate located at the top surface of the body portion and a bottom plate located at the bottom surface of the body portion, each of the top and bottom plates having a bore configured to receive part of the stem part of the joint prosthesis component.

7. An orthopaedic system according to any of claims 1 to 6, in which the at least one of the top plate and the bottom plate is secured to the body portion.

8. An orthopaedic system according to claim 6, in which the at least one of the top plate or bottom plate includes a slit or a frangible region that is aligned with the slit or frangible region on the side wall of the body portion.

9. An orthopaedic system according to any of claims 6 to 8, in which the top plate comprises a material that is less compressible than the compressible material of the body portion.

10. An orthopaedic system according to claim 9, in which the top plate comprises polyethylene.

11. An orthopaedic system according to any of claims 6 to 10, in which the bottom plate comprises a deformable material capable of deforming around the neck of the stem part, thereby providing a snug fit.

12. An orthopaedic system according to any of claims 6 to 11, in which the bottom plate comprises a rubber, preferably a rubberised polymer.

13. An orthopaedic system according to any of claims 6 to 12, in which at least one of the top plate and the bottom plate comprises a hinge.

14. An orthopaedic system according to claim 13, in which the hinge is provided by a locally thinned portion of the plate.

15. An orthopaedic system according to any of claims 7 to 14, in which the body portion and at least one of the top plate and bottom plate are made from the same material, preferably polyethylene (PE) or polylactic acid (PLA).

16. A taper protector for use in protecting a taper region of a joint prosthesis component, the taper protector comprising a body portion having a side wall, a top surface and a bottom surface, and a bore extending between the top surface and the bottom surface that is configured to receive the at least part of the taper, the body portion being made from a compressible material which allows it to be compressed, and a plate secured to at least one of a top surface and a bottom surface of the body portion.

17. A taper protector according to claim 16, in which the side wall has a slit or a frangible region configured to allow the taper protector to be removed from the stem part in a lateral direction with respect to the stem part.

18. A taper protector according to claim 17, in which the slit or frangible region extends between an outer surface of the side wall and the bore and extends from the top surface to the bottom surface of the side wall.

19. A taper protector according to any of claims 16 to 18, in which the compressible material comprises a foam, preferably a closed cell foam.

20. A taper protector according to any of claims 16 to 19, in which the body portion comprises a resiliently deformable material.

21. A taper protector according to any of claims 16 to 20, in which the at least one of the top plate and the bottom plate is secured to the body portion.

22. A taper protector according to any of claims 17 to 21, in which the at least one of the top plate or bottom plate includes a slit or a frangible region that is aligned with the slit or frangible region on the side wall of the body portion.

23. A taper protector according to any of claims 16 to 22, in which the top plate comprises a material that is less compressible than the compressible material of the body portion.

24. A taper protector according to claim 23, in which the top plate comprises polyethylene.

25. A taper protector according to any of claims 16 to 24, in which the bottom plate comprises a deformable material capable of deforming around the neck of the stem part, thereby providing a snug fit.

26. A taper protector according to any of claims 16 to 25, in which the bottom plate comprises a rubber, preferably a rubberised polymer.

27. A taper protector according to any of claims 16 to 26, in which at least one of the top plate and the bottom plate comprises a hinge.

28. A taper protector according to claim 27, in which the hinge is provided by a locally thinned portion of the plate.

29. A taper protector according to any of claims 16 to 29, in which the body portion and at least one of the top plate and bottom plate are made from the same material, preferably polyethylene (PE) or polylactic acid (PLA).