GB2192543A

GB2192543A - Peg for use in prosthetic devices

Info

Publication number: GB2192543A
Application number: GB08614461A
Authority: GB
Inventors: Michael Antony Tuke; Michael Alexander Reyk Freeman
Original assignee: FINSBURY
Current assignee: FINSBURY
Priority date: 1986-06-13
Filing date: 1986-06-13
Publication date: 1988-01-20
Anticipated expiration: 2006-06-13
Also published as: GB2192543B; GB8614461D0

Abstract

A peg of metal or ceramics, suitable for use as a fixator and/or a bone strengthener in connection with a prosthetic device, has a portion of generally tapered form. The tapered portion increases in cross-section from an insertion end. The surface of the tapered portion has alternating ridges and depressions along its length extending therearound, each successive ridge as one moves away from the insertion end having an outer surface spaced by a comparatively small amount at a greater distance from the axis of the peg than the outer surface of the preceding ridge. The peg may be discrete or form part of the prosthetic device. <IMAGE>

Description

SPECIFICATION Peg for use in prosthetic devices This invention relates to pegs suitable for use as fixators and/or bone strengtheners in conjunction with prosthetic devices.

The replacement of diseased or deformed parts of the human body by suitable artificial implants is a well known surgical practice. For example, artificial hip and knee joints are often fitted and can, in use, prove extremely satisfactory, giving much needed relief from conditions such as the various forms of arthritis. It is important to ensure good connections between the implant and the surrounding bone or between the implant and any cement used.

It is often desirable to promote integration between the bone and/or cement (if used) and the implant. Various fixing devices have been proposed, for example plain or flanged plastics pegs. Such pegs during insertion, but also during the life of the implant, can be subject to abrasion, possibly resulting in the presence of unwanted foreign debris in the body. Other methods of fixation rely upon bony integration with a porous surface or the use of an acrylic cement, both of which methods have some drawbacks.

The present invention seeks to provide an alternative type of peg fixation.

According to this invention, we provide a peg, suitable for use as a fixator and/or a bone strengthener in connection with a prosthetic device, the peg being of a material compatible with a body and selected from metal or ceramics and having a portion of generally tapered form increasing in cross-section from an insertion end of smaller crosssection, the surface of the peg having along its length alternating ridges and depressions extending around the peg, each successive ridge moving in a direction away from the insertion end having an outer surface spaced, by a comparatively small amount at a greater distance from the axis of the peg than the outer surface of the preceding ridge. Thus the peg presents a series of cutting edges as the peg is inserted into an aperture of initial cross-sectional dimension not greater than that of the insertion end of the peg.

The peg usually, though not necessarily, has a circular cross-section throughout its length.

The peg preferably has a series of discrete ridges separated by depressions, although the ridges may be linked so as to form a continuous helix in the form of a thread. The outer surfaces of the ridges are preferably flattened and adjacent faces on those sides of the ridges nearer the insertion end preferably extend substantially at right angles to the outer surfaces of the ridges.

The pegs may be discrete members with or without a head portion at the opposite end to the insertion end. Alternatively the pegs may form part of a larger implant and project therefrom to provide fixing means.

The invention will now be described by way of example with reference to the accompanying drawings, wherein: Figure 1 is a side view of the insertion end of a peg according to the invention; Figure 2 is an enlarged view of the insertion end of the peg of Figure 1 about to be inserted into a bone; Figure 3 is a side view of a modified insertion end of a peg; Figure 4 illustrates the use of a peg according to the invention as a fixator; Figure 5 illustrates the use of a peg according to the invention as a bone strengthener; and Figure 6 illustrates a modification of a peg as shown in Figure 5.

As shown in Figures 1 and 2, the peg 2 comprises a shank 4 of any suitable length, surmounted by a head (not shown) or attaching the peg to a larger prosthetic device, and an end portion 6 of circular cross-section which tapers towards an insertion end 8. The end portion 6 has a surface comprising a series of ridges 10 separated by a series of depressions 12 of generally concave shape.

Each ridge 10 has a planar outer surface 11 extending parallel to the axis of the peg and the cross-sectional diameter through each ridge 10 being greater than that of the immediately preceding ridge nearer the insertion end 8. Those faces 3 of ridges 10 adjacent the outer surfaces 11 and facing the insertion end 8 extend substantially perpendicular to the surfaces 11, so that if viewed longitudinally from the insertion end 8, the faces 13 present a series of annular cutting surfaces of gradually increasing diameter.

The peg may be of metal compatible with the body, titanium being a preferred metal or, alternatively, the peg may be of ceramics, dependent on its use.

In use, as illustrated in Figure 2 the peg 2 is inserted in a preformed aperture 14 in a bone 15. The aperture is of a diameter corresponding approximately to that of the first ridge 11 at the insertion end 8. As the peg is tapped home into the aperture 14, the faces 13 provide a series of cutting members to gradually enlarge the aperture to the correct size to give a tight fit between the peg and the bone. As the peg is introduced, bone debris produced will collect in depressions 12 rather than being pushed to the exterior of the bone. This bone debris can assist in promoting integration between the peg and the bone and this integration is in any case helped by the ridged nature of the peg itself. As shown in dotted lines in Figure 1, the insertion end may terminate in a cylindrical non-ridged portion 9 to facilitate introduction of the peg into a drilled aperture.

If desired, the ridged portion of the peg, while still of circular cross-section, may taper exponentiaily as shown in Figure 3. Such a taper can be advantageous in that adjacent the insertion end 8 the annular cutting faces are of comparatively narrow width whereas they increase in width exponentially towards the shank 4. The narrower cutting faces penetrate more deeply into the bone than the wider cutting faces nearer the shank, thus tending to even out the total amount of debris produced by each cutting face which collects in each depression 12.

It will be appreciated that the size of the peg will-depend on its end use. However a suitable size for example would be a peg having a tapered portion of approximately 20mm.

length with a series of ridges and depressions, for example about 10, with the ridges increasing in diameter from an insertion end of about 4mm. to a widest diameter of about 7 to 8mm., with each ridge providing an annular cutting edge of about 0.4mm. width. The depressions 12 may for example be of a depth of 0.5 to 1.0mum..

Figure 4 shows the use of a peg 16 in accordance with the invention as a fixator projecting from a plate 17, preferably of metal such as titanium, providing a base plate for a tibial implant component 18, for example of polyethylene. The base plate 17 and component 18 are secured by any suitable means.

The peg 16 can be inserted in a suitably resected tibia as described above to give good immediate fixation in a knee implant operation.

Figure 5 shows the use of a peg 20 in accordance with the invention as a bone strengthener. Thus peg 20 terminates in a flattened surface opposite its insertion end and does not have a head. It is tapped into a suitable aperture in a tibia 21 to provide a strengthening member so that the tibia presents a face 22 of suitable strength to receive tibial implant 23. The peg 20, or several such pegs, can be inserted where desired in areas which could otherwise collapse on loading of the tibia. They are intended to integrate with the surrounding bone to strengthen the weak areas and- give a stable -platform for the implant 23 to give less chance of damage when the tibia is loaded.

A A modification is shown in Figure 6 in which a peg 30 is provided with a spigot 31 projecting beyond the face of the bone 32 in which the peg is engaged. The spigot is positioned in an aperture 33 formed in the implant body 34, initially with a clearance 35. In use, there is a delay time before the peg is likely to be loaded due to settling of the implant, thus allowing time for integration of the peg with the bone. The insertion of the peg into the implant may initially be comparatively small, for example 1 mm.

Claims

1. A peg, suitable for use as a fixator and/or a bone-strengthener in connection with a prosthetic device, the peg being of a material compatible with the body and selected from metal and ceramics and having a portion of generally tapered form increasing in cross-section from an insertion end of small cross-section, the surface of the tapered portion of the peg having along its length alternating ridges and depressions extending around the peg, each successive ridge moving in a direction away from the insertion end having an outer surface spaced, by a comparatively small amount, at a greater distance from the axis of the peg than the outer surface of the preceding ridge.

2. A peg according to claim 1, wherein the portion of generally tapered form has a circular cross-section throughout its length.

3. A peg according to claim 1 or 2, wherein the portion of generally tapered form has a series of discrete ridges separated by depressions.

4. A peg according to claim 1 or 2 wherein the ridges are linked in the form of a thread.

5. A peg according to any one of the preceding claims wherein the outer surfaces of the ridges are flattened.

6. A peg according to any one of the preceding claims wherein the transverse faces on those sides of the ridges facing the insertion and extend substantially at right angles to the outer surfaces of the ridges.

7. A peg according to any one of the preceding claims wherein the taper of the portion of generally tapered form increases exponentially from the insertion end towards the opposite end.

8. A peg according to any one of the preceding claims in the form of a discrete member.

9. A peg according to claim 8 wherein the peg has a head portion at the opposite end to the insertion end.

10. A prosthetic device provided with one or more pegs in accordance with any one of claims 1 to 7.

11. A peg suitable for use as a fixator and/or a bone stengthener in connection with a prosthetic device, substantially as shown in Figures 1 and 2, Figure 3, Figure 4, Figure 5 or Figure 6 of the accompanying drawings and described herein with reference thereto.