GB2438170A

GB2438170A - Ball and socket joint prosthesis with ball retaining means and an axially split screw

Info

Publication number: GB2438170A
Application number: GB0610012A
Authority: GB
Inventors: Byron Robert Xavier Macdonald
Original assignee: MATZ INTERNAT FZE
Current assignee: MATZ INTERNAT FZE
Priority date: 2006-05-19
Filing date: 2006-05-19
Publication date: 2007-11-21
Also published as: GB0610012D0; WO2007135572A3; WO2007135572A2

Abstract

A joint prosthesis comprising a shank member (10) comprising a shank portion (12) terminating in a bulbous head (13), socket means (11) for receiving the bulbous head (13) of the shank member (10), and retaining means (19, 20) for retaining the bulbous head (13) within the socket means (11). The retaining means (19, 20) is arranged to apply a resilient bias to the bulbous member (13) so as to urge said bulbous member (13) into the socket means (11). The socket means 11 may have a lining which may be made of plastic. The retaining means may be mounted on the socket means 11 and may comprise at least one spring loaded member 20. The retaining means may be arranged equidistant around the socket means 11. The joint prosthesis may be implanted into a shoulder or hip. There is also a screw 17 which has an axial split 31 that may be screwed into a bore having a pin at its base to expand the split shaft.

Description

1 2438170 Joint prosthesis This invention relates to joint prostheses,

and in particular replacement hip joints.

A known joint prosthesis, a replacement hip joint, is shown in Figure 1. The joint comprises a shank member 1 and a socket means 2. The shank member 1 comprises a shank portion 3 and a bulbous head 4. The bulbous head 4 is spherical in shape. The inside of the socket means 2 is also spherical in shape, and includes a plastics material inner lining 5.

In use, the inner lining 5 acts as a cushion and reduces friction between the bulbous head 4 of the shank member 1 and the socket means 2, allowing the shank member 1 to move freely within the socket means 2.

However, over time the inner lining 5 becomes worn, allowing the head 4 to become dislocated from the socket means 2 under certain conditions, for example high-stress activities such as jogging. It is then necessary to replace the joint prosthesis. Depending on the type of implant and the wear it undergoes, replacement may he A&I 11897 GB required every 8 to 15 years, but subsequent replacements tend to be less successful than an initial placement.

There is a need for a joint prosthesis that is less susceptible to dislocation with use.

Another problem with known joint prostheses is the occurrence of infections after the joint has been implanted. There is a need for a joint prosthesis for which the risk of infection after implantation was reduced.

In accordance with the present invention, there is provided a joint prosthesis comprising a shank member comprising a shank portion terminating in a bulbous head, socket means for receiving the bulbous head of the shank member, and retaining means for retaining the bulbous head within the socket means, wherein the retaining means is arranged to apply a resilient bias to the bulbous member so as to urge said bulbous member into the socket means.

The retaining means acts to prevent the bulbous member from being dislocated from the socket means.

Preferably, the bulbous head is substantially A&I 1189/ GB spherical, and the retaining means applies the resilient bias at a level below the centre of the substantially spherical bulbous head. Having a substantially spherical bulbous head allows the bulbous head to move in the socket means easily.

Preferably, the socket means further includes an inner lining. This provides cushioning, and helps the bulbous head move in the socket means by reducing friction. Also, when an inner lining is used and becomes worn the invention is particularly advantageous, as the retaining means act to keep the bulbous head within the socket means and compensate for wear of the lining.

Preferably, the inner lining comprises a plastics material. Preferably, the plastics material is nylon.

Preferably, the retaining means is mounted on the socket means. Preferably, the retaining means comprises at least one spring-loaded retention member. Preferably, the retention member has a convex face to engage the ball member. Preferably, the retention member is spherical.

Preferably, the retention member is spring-loaded by means of a compression spring. Preferably, the retention member is located in a recess in the inner circumference A&T 11897 GB of the open end of the socket means. Preferably, the retaining means comprises a plurality of retention members arranged equidistantly around the open end of the socket means. The number of retention members may be, for example, three. Preferably, the number of retention members is four. Preferably, the retention members are arranged to be urged towards the bulbous head parallel to the open end of the socket means.

Advantageously, the socket means comprises at least two body portions held together by a ring member.

Preferably, the ring member is located at the open end of the socket means. Preferably, the ring member is fixed to the body portions by means of threaded screws.

Advantageously, the threaded screws are positioned next to the retaining means.

Advantageously, the socket means and shank member are made from titanium.

Advantageously, the joint prosthesis has an antimicrobial coating over at least part of its surface.

Preferably, the antimicrobial coating is a composition comprising silver. Preferably, the silver is approximately 5 to 7 microns thick.

A&I 11897 GB The joint prosthesis may be a replacement hip joint.

Alternatively the joint prosthesis may be a replacement shoulder joint.

The joint prosthesis may be an implantable prosthetic joint. Alternatively, the joint prosthesis may be for use in a robotic device.

Further, in accordance with the invention there is provided a screw of which the shaft has an axial split extending from the distal end of the screw, the screw being arranged to be screwed into a threaded bore having an expansion pin at its base for expanding the split shaft against the walls of the threaded bore.

Preferably, the shaft is split into two portions.

Advantageously, the shaft has a central circular bore.

Preferably, the split extends over approximately three-quarters of the shaft. Preferably, the distal end of the shaft is tapered. Preferably, the split portion of the shaft is tapered.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: A&I 11897 GE Figure 1 is a known joint prosthesis, Figure 2 is a perspective view of a joint prosthesis according to the present invention, Figure 3 is a side view of the joint prosthesis, Figure 4 is a view of a part of Figure 3 to a larger scale showing the movement of a retention member of the joint prosthesis, Figure 5 is a perspective view of a screw used for the present invention, Figure 6 is an end view of the screw, Figure 7 is a side view of the receiving hole for the screw.

Referring to Figures 2 to 4 of the accompanying drawings, a joint prosthesis according to the present invention comprises a shank member 10 and a socket means ii. The shank member 10 comprises a shank portion 12 terminating in a bulbous head 13. The bulbous head 13 is spherical in shape, and is located within the socket means 11.

The socket means 11 is formed from two body portions (not shown, for clarity) held together by a ring member A&I 11897 GB 16. The body portions each comprise half a hemisphere.

The ring member 16 is attached to the body portions by threaded screws 17, thus holding the socket. means together as a single piece, and helping to distribute any stress on the socket means 11. The recess in the socket means 11 into which the bulbous head 13 is located is spherical in shape, and forms slightly more than a hemisphere. The socket means 11 also comprises an inner lining to the recess in which the bulbous head 13 is located, the lining being omitted for clarity in the accompanying Figures.

Each body portion further includes a respective pair of recesses 18, positioned so that the socket means has four recesses located equidistantly around the open end of the socket means 11, next to the threaded screws 17.

Each recess 18 contains a retention member comprising a compression spring 19 and a ball 20. The ball is located at the open end of the recess 18, so that it is pushed by the spring 19 into contact with the bulbous head 13 of the shank member 10 at a level below the centre of the bulbous head 13.

In use, the bulbous head 13 of the shank member 10 A&I 11897 GB is kept in place in the socket means 11 by the shape of the recess in the socket means ii. If, over time, the inner lining becomes thinner, for example because of wear, then as shown in Figure 4 the ball 20 of the retention member is pushed outwards by the spring 19, and so remains in contact with the bulbous head 13 of the shank member 10. This serves to prevent the fit of the bulbous head 13 in the socket means 11 from becoming loose.

The shank member 10 and socket means 11 are made from titanium. The shank member 10 and socket member 11 are coated with a thin layer of medical grade silver, preferably with a thickness of approximately 5 to 7 microns thick. Silver is antimicrobial, and reduces the occurrence of post-operative infections such as staphylococci, which can result in the need for further surgery. After implantation the silver layer dissolves over a period of 14 to 16 months, and reduces the possibility of post-operative infections. A compound that, when applied, leaves a coating of pure medical grade silver may be used.

Preferably the threaded screws 17 are as shown in A&I 11897 GB more detail in Figures 5 and 6. The shaft 30 of the screw has a split 31 for approximately three quarters of its length, and has a central circular bore. The shaft is cylindrical at the proximate end and then tapers over the split portion of the shaft. A threaded bore for the screw 17 is shown in Figure 7. The threaded bore has at its base an expansion pin 31. When the screw 17 is screwed into the threaded bore the expansion pin 17 forces the shaft 30 of the screw on either side of the split 31 outwards, so ensuring a tight fit within the receiving hole and serving to prevent the screw from coming loose. The threaded screw is made from medical grade 400 series stainless steel. (This is preferable to making the screw from titanium, which would not flex sufficiently to maintain friction against the receiving hole.) Although the specific example shown is a replacement hip joint, the invention can be applied equally to other prosthetic joints such as shoulder joints, for humans or other animals. The invention can also be applied to joints that are used in robotic devices, such as industrial robots.

A&I 1189/ GB

Claims

Claims: 1. A joint prosthesis comprising: a shank member comprising a

shank portion terminating in a bulbous head socket means for receiving the bulbous head of the shank member, and retaining means for retaining the bulbous head within the socket means, wherein the retaining means is arranged to apply a resilient bias to the bulbous member so as to urge said bulbous member into the socket means.

2. A joint prosthesis as claimed in claim 1, wherein the bulbous head is substantially spherical, and the retaining means applies the resilient bias at a level below the centre of the substantially spherical bulbous head.

3. A joint prosthesis as claimed in claim 1 or 2, wherein the socket means further includes an inner lining.

A&I 11897 GB I' 4. A joint prosthesis as claimed in claim 3, wherein the inner lining comprises a plastics material.

5. A joint prosthesis as claimed in claim 4, wherein the plastics material is nylon.

6. A joint prosthesis as claimed in any preceding claim, wherein the retaining means is mounted on the socket means.

7. A joint prosthesis as claimed in any preceding claim, wherein the retaining means comprises at least one spring-loaded retention member.

8. A joint prosthesis as claimed in claim 7, wherein the retention member has a convex face to engage the ball member.

9. A joint prosthesis as claimed in claim 8, wherein the retention member is spherical.

A&I 11897 GB 10. A joint prosthesis as claimed in any one of claims 7 to 9, wherein the retention member is spring-loaded by means of a compression spring.

11. A joint prosthesis as claimed in any one of claims 7 to 10, wherein the retention member is located in a recess in the inner circumference of the open end of the socket means.

12. A joint prosthesis as claimed in any one of claims 7 to 11, wherein the retaining means comprises a plurality of retention members arranged equidistantly around the open end of the socket means.

13. A joint prosthesis as claimed in claim 12, wherein the number of retention members is three.

14. A joint prosthesis as claimed in claim 12, wherein the number of retention members is four.

15. A joint prosthesis as claimed in any one of claims 12 to 14, wherein the retention members are arranged to A&J 11897 GB be urged towards the bulbous head parallel to the open end of the socket means.

16. A joint prosthesis as claimed in any preceding claim, wherein the socket means comprises at least two body portions held together by a ring member.

17. A joint prosthesis as claimed in claim 16, wherein the ring member is located at the open end of the socket means.

18. A joint prosthesis as claimed in claim 16 or 17, wherein the ring member is fixed to the body portions by means of threaded screws.

19. A joint prosthesis as claimed in claim 18, wherein the threaded screws are positioned next to the retaining means.

20. A joint prosthesis as claimed in any preceding claim, wherein the socket means and shank member are made from titanium.

&I 11897 GB 21. A joint prosthesis as claimed in any preceding claim, wherein the joint prosthesis has an antimicrobial coating over at least part of its surface.

22. A joint prosthesis as claimed in claim 21, wherein the antimicrobial coating is a composition comprising silver.

23. A joint prosthesis as claimed in claim 22, wherein the silver is approximately 5 to 7 microns thick.

24. A joint prosthesis as claimed in any preceding claim, wherein the joint prosthesis is a replacement hip joint.

25. A joint prosthesis as claimed in any one of claims 1 to 23, wherein the joint prosthesis is a replacement shoulder joint.

26. A joint prosthesis as claimed in any preceding claim, wherein the joint prosthesis is an implantable A&I 11897 GB prosthetic joint.

27. A joint prosthesis as claimed in any one of claims 1 to 23, wherein the joint prosthesis is for use in a robotic device.

28. A screw of which the shaft has an axial split extending from the distal end of the screw, the screw being arranged to be screwed into a threaded bore having an expansion pin at its base for expanding the split shaft against the walls of the threaded bore.

29. A screw as claimed in claim 28, wherein the shaft is split into two portions.

30. A screw as claimed in claim 28 or 29, wherein the shaft has a central circular bore.

31. A screw as claimed in any one of claims 28 to 30, wherein the split extends over approximately three-quarters of the shaft.

A&I 1189/ GB 32. A screw as claimed in any one of claims 28 to 31, wherein the distal end of the shaft is tapered.

33. A screw as claimed in any one of claims 28 to 32, wherein the split portion of the shaft is tapered.

PI 11897 GB