GB2477981A

GB2477981A - Acetabular cup with bores to allow release of trapped fluid

Info

Publication number: GB2477981A
Application number: GB1002953A
Authority: GB
Inventors: Simon Collins; Sarah Kathryn Muirhead-Allwood
Original assignee: Corin Ltd
Current assignee: Corin Ltd
Priority date: 2010-02-22
Filing date: 2010-02-22
Publication date: 2011-08-24
Also published as: GB201002953D0

Abstract

An acetabular cup 4 comprising a substantially hemispherical, optionally coated, cup provided with at least one bore or channel 42 extending from an exterior, acetabulum-contact surface 4a to an interior surface 4b of the cup, whereby during impaction of the cup into the acetabulum A, an unobstructed fluid flow path exists from behind the exterior surface to the interior surface of the cup, in order to allow fluid trapped in gap 30 to be released. An acetabular impactor 20 (see figure 3) may be provided for impacting the acetabular shell or cup 4, the impactor having means 22, 24 being a fluid passage in the shaft, to allow venting of the cavity 30 formed by the reamed acetabulum A during impaction of the cup. The polar hole and nose 21 which connects to the impaction tool to the cup may be threaded. The fluid flow path may alternatively comprise grooves (410, see figures 6-9) on the exterior surface 4a which form bores through the rim of the cup to the interior surface 4.

Description

HW PROSTHESTS.

The present invention relates to an improved hip prosthesis, in particular an improved acetabular cup for introduction on to a patient's acetabulum, and to an acetabular cup in combination with a surgical introducer for said introduction.

Hip replacements or repairs commonly consist of the implantation of a prosthetic acetabular cup or shell and a prosthetic or resurfaced femoral head and stem, the head comprising a ball joint designed to he held inside the articulating surface of the acetabular cup. The acetabulum is prepared by the release and removal of soft tissue using a surgeon's preferred technique to gain adequate exposure for reaming. A reamer, conventionally comprising a reamer head and shaft, is configured to remove material from the acetabulum to create a roughly hemispherical void. The acetabulum is carefully under-reamed by about 1-2mm to ensure a tight fit during impaction of the acetabular cup. An appropriate size of acetabular cup (determined by prior trials) is then securely threaded onto an acetabular introducer and the cup is impacted until it is fully seated within the acetabular. Fixing screws may be used to secure the cup in position. Liners, for example, of ceramic or polyethylene material, may also be inserted within the cup, in which case the inner surface of the liner forms the articulating surface for receiving the femoral head.

Generally, the acetabular cup is stabilized by a press-fit technique with or without bone screws. Where good quality bone exists, it is generally desirable to rely only on the press-fit technique without the need for screws, in which case, further stabilisation of the cup relies solely on bone growth occurring on the textured outer surface of the cup. One drawback associated with this technique is that the cup is obviously bigger than the bone cavity prepared by reaming to create the press-fit. This results in an accumulation of air and/or viscous fluid in the space between the outer surface of the cup and the reamed surface of the acetabulum during cup insertion. It is proposed that this trapped air/fluid may contribute to incomplete cup seating which may lead to osteolysis, increased bone resorption and possible migration of the acetabular cup over time.

The present invention seeks to provide a solution to this problem.

According to a first aspect of the present invention, there is provided an acetabular cup comprising a substantially hemispheral, optionally coated, cup provided with at least one bore or channel extending from an exterior, acetabulum-contact surface to an interior surface of said cup, whereby during impaction of the cup, an unobstructed fluid flow path extends from behind the exterior surface of the cup to the interior surface.

In this manner, fluid or air that is trapped between the acetabulum and the prosthetic cup is able to be released via the fluid flow path during impaction of the cup.

A single fluid flow path may be provided on the cup or a plurality of paths may be provided. For example, a series of radial grooves or channels may be provided from a point on the exterior surface of the cup to a rim of the cup, the rim forming part of the interior surface of the cup which does not contact the acetabulum. Alternatively, a continuous helical groove may extend from a point on the exterior surface of the cup to a point on the rim of the cup.

The interior surface of the cup may be provided with engagement means for attachment to a surgical introducer, such as a vacuum impactor.

In another embodiment of the present invention, the acetabular cup may be provided with a single bore, hole or channel extending from its exterior surface to its interior surface whereby during impaction of the cup, an unobstructed fluid flow path extends from behind the exterior surface of the cup to the interior surface. The cup is introduced into the acetabulum by means of a surgical introducer comprising an elongate shaft having attachment means for receiving the acetabular cup, the introducer having at least one bore extending from the cup-receiving end at least part way along the shaft of the introducer, the bore terminating in at least one outlet. The bore of the cup engages with or abuts the bore of the surgical introducer thereby providing an uninterrupted fluid flow path extending from the exterior surface of the cup to the outlet of the introducer.

To this end, a second aspect of the present invention provides a surgical introducing kit comprising an acetabular cup according to the first aspect of the present invention in combination with a surgical introducer, the introducer comprising an an elongate shaft having attachment means for receiving the acetabular cup, the introducer having at least one bore extending from the cup-receiving end at least part way along the shaft of the introducer, the bore terminating in at least one outlet, whereby the bore of the cup engages with or abuts the bore of the surgical introducer thereby providing an uninterrupted fluid flow path extending from the exterior surface of the cup to the outlet of the introducer.

Preferably, the attachment means of the introducer comprises a threaded portion at the end of the shaft for mating with a threaded bore provided in the acetabular cup.

Preferably, each bore is provided substantially centrally within the shaft and cup respectively.

The introducer may he provided with projections or recesses for mating with complimentary recesses or projections provided in the cup, preferably provided in the periphery thereof, to assist in retention of the cup on the introducer.

The shaft may incorporate a handle at one end thereof remote from the head. The shaft and/or handle may be modularly connectable to the head, for example, being screwthreadingly engagable.

Optionally, the shaft may have at least one jointed member to enable the end of the introducer to be maneouvred during impaction of the cup. The introducer may comprise a handle pivotally attached to an arm. The arm may be pivotally attached to an end nose piece that contains a threaded region. Preferably, the bore is contained within the nose piece only.

Preferably, the acetahular cup has a single centra' bore or a plurality of channds or grooves extending from the interior to the exterior surface of the cup with the rest of the exterior surface being solid. The cup may comprise a metal or ceramics material, such as a high carbon cobalt chrome alloy, zirconia or alumina. The outer surface of the cup is preferably coated with an artificial bone substitute material such as hydroxyapatite (HA), and/or may include a porous or plasma coating, such as Titanium or any other osteoconductive coating or biocompatible textured surface.

A third aspect of the present invention provides a method of implanting an acetabular cup within an acetahulum, the method comprising the steps of: (a) reaming an acetabulum to provide a reamed cavity; (b) attaching an acetabular cup to an introducer such that a fluid path exists from an outer, acetabulum-contacting surface of the cup to the interior surface of the cupz (c) impacting the cup within the cavity whereby, during impaction, fluid within the cavity passes through the fluid path; and (d) releasing the introducer from the impacted cup.

Preferably, the method utilises a surgical introducing tool kit according to the second aspect of the present invention whereby a fluid path exists at least part way through the introducer during impaction of the cup. Preferably, the cavity is reamed to a diameter that is approximately 1-2mm less than the diameter of the acetabular cup to implanted.

For a better understanding of the present invention and to show more clearly how it may be put into effect, reference will now be made, by way of example only, to the accompanying drawings, in which: Figures 1A to 1D provide a simplified illustration of a prior art surgical technique for acetabular hip replacement; Figure 2 is a schematic drawing illustrating the impaction of an acetabular cup using a surgical introducer according to the present invention Figure 3 is a schematic side view of a surgica' introducer according to one embodiment of the present invention; Figure 4 is a perspective side view of the end region of the surgical introducer shown in Figure 3; Figure 5 is a perspective front view of the end region of the surgical introducer shown in Figure 3; Figure 6 ia a perspective view of an acetabular cup according to a second embodiment of the present inventiom Figure 7 is a perspective view of an acetabuar cup according to a third embodiment of the present invention; Figure 8 is a perspective view of an acetabular cup according to a fourth embodiment of the present invention; and Figure 9 is a perspective view of an acetabular cup according to yet a further embodiment of the present invention.

Figures 1 a to 1 d of the accompanying drawings provide a simplified illustration for an operating technique for acetabular hip replacement. The acetabulum A is prepared using techniques known in the art and is progressively reamed using a series of reamers 2 having incrementally larger cutting heads to deepen the socket until it becomes a true hemisphere. An acetabular cup or shell 4 is attached to a threaded portion of an impactor tool 6 by means of a threaded bore provided through the cup. The cup is then impacted into the prepared acetabulum A. Once the cup is seated in the correct position within the acetahulum, the impactor tool is removed by unscrewing it from the cup. A liner 10 may he inserted within the cup (Figure ic) prior to fitting the prosthetic femoral head 8 (Figure id). It is to be appreciated that, although not shown in the accompanying drawings, a trial cup and liner is inserted into the prepared acetabulum prior to impaction of the acetabular cup.

A standard feature of the implantation of an acetabular cup by a press-fit technique is that the cup is 1-2mm larger in diameter than the reamed cavity of the acetahulum. This results in there being a gap 30 between the reamed surface of the acetabulum A and the exterior surface 4a of the cup 4, as shown in Figure 2. One embodiment of the present invention provides an impactor tool 20 that has a fluid passage 22 extending from the centre of a threaded end 21 of the tool to an outlet 24 partway along the impactor. A solid acetabular cup 4 having a central threaded bore 42 is attached to the threaded end 21 of the impactor whereby the fluid passage communicates with the bore of the cup 4. In this manner, a fluid passage is created extending between the cavity 30 of the acetabulum behind the impacted cup to atmosphere thereby enabling air trapped in the cavity to be released during impaction of the cup. Fluid ingress from the acetabulum may also occur within the cavity leading to increased pressure. Again, this is released by means of the vented impactor. Prior hereto, no fluid path existed from the interior cavity to atmosphere during impaction of the acetabular cup.

Figures 3 to 5 of the accompanying drawings illustrate in further detail a preferred acetabular cup in combination with an introducer according to this embodiment of the present invention. The introducer 200 comprises a cranked handle 202 (although this may be straight) having a rotatable end region 204 comprising a jointed arm 204a attached to a jointed nose piece 204b, the nose piece having a threaded part 205 for attachment to an acetabular cup. A central bore 206 is provided through the end threaded region 205 of the nose piece 204b (see Figure 5) and terminates with a T-junction, wherein the fluid path extends to the side walls of the nose piece to provide two outlets 208. However, it is to be appreciated that other configurations for the fluid path may be utilised. The acetabular cup is provided with a continuous bore extending between its interior and exterior surface for providing uninterrupted fluid communication between the reamed cavity and the fluid path of the introducer.

The introducer and acetabular cup according to the present invention minimise the build up of pressure behind the cup during impaction into the cavity of the acetabulum which may prevent optimised seating of the cup. The vented impactor and cup may reduce the likelihood of oestolysis and bone resorption following implantation of the cup.

Figures 6 to 9 of the accompanying drawings illustrate acetabular cups according to alternative embodiments of the present invention. These solid cups 400 are of the type normally impacted by means of a vacuum impactor wherein the cup is held on to the introducer during impaction by means of suction which is released once the cup is in place. It is to be appreciated that a vented impactor as detailed in the first embodiment of the present invention would not be suitable for achieving venting of the cavity during impaction of the cup. Tnstead, the cups 400 are provided with one or more channds or grooves 410 extending from a point on the exterior surface 400a of the cup to a point on the rim 400b of the cup forming part of the interior surface of the cup. In this manner, fluid and/or air is able to travel along the channels or grooves away from the cavity during impaction of the cup.

Claims

CLAIMS1. An acetabular cup comprising a substantially hemispherical, optionally coated, cup provided with at least one bore or channel extending from an exterior, acetabulum-contact surface to an interior surface of the cup, whereby during impaction of the cup into the acetabulum, an unobstmcted fluid flow path exists from behind the exterior surface to the interior surface of the cup.
2. A cup as claimed in claim 1 wherein a single fluid path is provided between the exterior and interior surface of the cup.
3. A cup as claimed in claim 1 wherein a pluralitiy of fluid paths is provided between the exterior and interior surface of the cup.
4. A cup as claimed in claim 3 wherein a series of radial grooves or channels are provided from a point on the exterior surface of the cup to a point on a rim of the cup, the rim forming part of the interior surface of the cup.
5. A cup as claimed in claim 2 wherein a continuous helical groove or channel extends from a point on the exterior surface of the cup to a point on a rim of the cup, the rim forming part of the interior surface of the cup.
6. A cup as claimed in claim 2 wherein the single fluid path is a central bore extending from the exterior to the interior surface of the cup, with the rest of the exterior surface being solid.
7. A surgical introducing kit comprising the acetabular cup according to claim 1 in combination with a surgical introducer, the introducer comprising an elongate shaft having attachment means for receiving the acetahular cup, the introducer having at least one bore extending from the cup-receiving end at least part way along the shaft of the introducer, the bore terminating in at least one outlet, whereby the bore or channel of the cup engages with or abuts the bore of the introducer thereby providing at least one fluid flow path extending from the exterior surface of the cup to the outlet of the introducer.
8. A surgical introducing kit as claimed in claim 7 wherein the attachment means of the introducer comprises a threaded portion at the end of the shaft for mating with a threaded bore provided in the acetabular cup.
9. A surgical introducing kit as claimed in claim 8 wherein each bore is provided substantially centrally within the shaft and cup respectively.
10. A surgical introducing tool kit as claimed in any one of claims 7 to 9 wherein the shaft incorporates a handle at one end thereof remote from the cup-receiving end.
11. A surgical introducing tool kit as claimed in any one of claims 7 to 10 wherein the shaft has at least one jointed member to enable the end of the introducer to be maneouvred during impaction of the cup.
12. A surgical introducing tool kit as claimed in claim 11 wherein the introducer comprises a handle pivotally attached to an arm and the arm is pivotally attached to an end nose piece that contains the attachment means.
13. A surgical introducing tool kit as claimed in claim 12 wherein the bore is contained within the nose piece only.
14. A method of implanting an acetabular cup within an acetabulum, the method comprising the steps of: (a) reaming an acetahulum to provide a reamed cavity: (b) attaching an acetabular cup to an introducer such that a fluid path exists from an outer, acetabulum-contacting surface of the cup to an interior surface of the cup; (c) impacting the cup within the cavity whereby, during impaction, fluid within the cavity passes through the fluid path and (d) releasing the introducer from the impacted cup.
15. A method according to claim 14 further comprising the step of reaming the acetabulum cavity to a diameter approximately 1-2mm less than the diameter of the acetabular cup to he implanted.
16. A method according to claim 14 or claim 15 carried out using the surgical introducing tool kit as claimed in any one of claims 7 to 13.