GB2290473A

GB2290473A - Fixator

Info

Publication number: GB2290473A
Application number: GB9412197A
Authority: GB
Inventors: Allen Stanley Baker; Raymond Clarence Chance Wadey
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-06-17
Filing date: 1994-06-17
Publication date: 1996-01-03
Anticipated expiration: 2014-06-17
Also published as: GB2290473B; GB9412197D0

Abstract

A fixator assembly, preferably for use in bone surgery, comprises a component 1 essentially a plate, of two parts 1g and 1c wherein flanges 1g form a groove 1c therebetween. A screw 2 extends through a bore 1e in the component 1. It is intended that two elongate elements 3 such as Steinman pins or Kirschner wire 3, supported by flanges 1g run longitunidally along the groove. Component 1 bears directly upon a bone 4 by the force applied to each pin 3 by the screw head 2a. The bone contacting surface 1a of the component 1 is preferably a knurled, convex spherical surface. The device allows different sized wires to be used and permits the readjustment of bone fragment alignment. <IMAGE>

Description

IMPROVEMENTS IN OR RELATING TO PIN FIXATOR ASSEMBLIES According to one aspect of the present invention, there is provided a component for a fixator assembly and in the form of a member comprised of first and second parts extending at an angle to each other such that the two parts define a groove therebetween, the first part being formed with a hole therethrough extending transversely of said groove for receiving the shank of a headed screw and the second part providing a shoulder for supporting an elongate element extending along said groove against lateral pressure from the head of said screw.

According to a second aspect of the present invention, there is provided a fixator assembly, comprising: (i) an elongate element, (ii) a headed screw for screwing into a surface of bone, and (iii) a component in the form of a member for extending over said surface comprised of first and second parts extending at an angle to each other such that the two parts define a groove therebetween for extending substantially parallelly to said surface, the first part being formed with a hole therethrough extending transversely of said groove for receiving the shank of said screw screwed into said surface, and said second part providing a shoulder for supporting said elongate element extending along said groove against lateral pressure from the head of said screw.

The member may include a third part extending at an angle to the first part such that those two parts define a groove therebetween, also for extending substantially parallely to the bone surface, whereby the three parts in effect define a channel thereamong. The third part provides a shoulder for supporting a second elongate element extending along the second groove against lateral pressure from the head of the screw.

The or each elongate element may take the form of a Steinman pin or a Kirschner wire.

The first part may bear directly against the bone, with the bone-contacting surface of the first part being of a convex, preferably convex spherical, form to enable the component to sit at an angle on the bone surface if the latter is curved. Additionally or alternatively, the bonecontacting surface of the component may be of an uneven form, for example toothed or knurled, to resist rotary sliding of the component on the surface during turning of the screw.

The component may be provided in a plurality of sizes, for example three sizes, for holding elongate elements of respective differing diameters. The elements can range in diameter from .75mm. to 2.00mm., (and larger, if the assembly, with a plurality of components and screws, is used to replace bone plates in some circumstances, and thus avoid stress shielding). By using screws of differing head shapes and/or angles, it is possible to vary the clamping forces on the elongate elements with respect to the components.

In order that the invention may be clearly understood and readily carried into effect, reference with now be made, by way of example, to the accompanying drawings, in which: Figure 1 shows a sectional view through a fixator assembly for two elongate elements, Figure 2 is a view similar to Figure 1 through a modified version of the assembly, Figure 3 shows an assembly such as shown in Figure 1 or Figure 2, implanted in a soft tibia, and Figure 4 shows such assembly implanted in a thin humerus having an established non-union.

Referring to Figure 1, the assembly comprises a component 1, a bone screw 2, and two elongate elements 3 in the form of Steinman pins. The component 1 bears directly upon a bone 4 under the component force fy produced on the component 1 by the head 2a of the screw 2 via each pin 3.

The bounding surfaces of the component 1 include a convex spherical surface la and two planar, chordal, lateral surfaces 1b which are parallel to each other. Extending through the component 1 is a channel lc which is open at both ends and is of substantially rectangular cross-section.

It extends parallelly to the surfaces 1b and has a flat floor surface id, except where a bore le is countersunk at if. The bore le extends through the component 1 perpendicularly to the surface id and centrally of the surface la. The surface la is knurled to improve its grip on the bone 4.There are thus formed between the channel lc and the respective surfaces ib respective flanges ig projecting perpendicularly with respect to the floor surface id. The channel ic effectively provides two lateral grooves 1h receiving the respective pins 3, whilst the flanges ig effectively provide lateral shoulders li supporting the respective pins 3 against the laterally outward component force fx applied to each pin 3 by the screw 2.It will be noted from Figure 1 that the tensile force F in the screw 2 results in an oblique force applied to each pin 3, which force ft resolves into the forces fx and fy. It is thus possible to select the order of the force fy for example, by varying the size and/or shape of the head 2a of the screw. In Figure 1, the screw head 2a is shown as having a spherical underneath surface 2b. It will be understood that, by adopting a screw 2 with a spherical underneath surface 2b of a different radius, the relative values of the component forces fx and fy can be varied. In Figure 2, the underneath surface 2b is shown as being frusto-conical. It will be understood that by varying the cone angle, the relative values of the component forces fx and fy can be varied.In practice, and as indicated in Figures 1 and 2, the adoption of standard bone screws with differing standard heads permits variation of that force relationship.

Referring to Figure 3, there is diagrammatically illustrated a knee joint with a femur 10 and a tibia 11.

Proximal portions of the tibia 11 are soft and therefore, to reinforce its proximal end, two Steinman pins have been introduced into the bone, as indicated at 3a. Those portions 3b of the roughly parallel pins 3 outside the bone extend parallely to each other through first and second components 1 anchored to the tibia by respective screws 2.

Referring to Figure 4, the thin humerus 12 has an established non-union indicated at 13 and is fixed employing two Steinman pins 3 extending parallely to each other through three components 1 with respective bone screws 2.

The above-described fixator assembly has the advantage of being very simple and thus inexpensive and providing a very simple method of stabilisation of fractures.

Moreover, such assemblies are better able to flex resiliently than are plates and thus impose less stress on the implant-to-bone interface.

The fixator assembly permits the use of stainless steel wires for internal fixation of fractured or osteotomised bone. A particular advantage of the assembly is that it allows the use of different-sized wires in many different applications and permits the readjustment of bone fragment alignment until a satisfactory position has been achieved, without any need to replace or reinsert the fixator into the bone. It is particularly useful in the fixation of realignment osteotomies such as those performed in the upper femur and the upper tibia. It may be used internally to fix slipped upper femoral epiphyses, malunited fractures, upper tibial osteotomies and upper femoral osteotomies, and to aid the fixation or fusion of various joints.

The assembly also allows the implant to be maintained just off the bone surface, which protects the periosteal blood vessels.

Claims

1. A component for a fixator assembly and in the form of a member comprised of first and second parts extending at an angle to each other such that the two parts define a groove therebetween, the first part being formed with a hole therethrough extending transversely of said groove for receiving the shank of a headed screw and the second part providing a shoulder for supporting an elongate element extending along said groove against lateral pressure from the head of said screw, a surface of said first part further from said shoulder being intended to face towards a surface of a bone.

2. A component according to claim 1, wherein said member includes a third part extending at an angle to the first part such that those two parts define a groove therebetween, whereby the first, second and third parts define a channel thereamong, said third part providing a shoulder for supporting a second elongate element extending along the second groove against lateral pressure from the head of the screw.

3. A component according to claim 1 or 2, wherein surface of said first part is of convex form.

4. A component according to claim 3, wherein said surface of said first part is of convex spherical form.

5. A component according to any preceding claim, wherein said surface of said first part is of uneven form.

6. A range of components each according to any preceding claim, the components being in a plurality of sizes, for holding elongate elements of respective differing diameters.

7. A fixator assembly, comprising: (i) an elongate element, (ii) a headed screw for screwing into a surface of bone, and (iii) a component in the form of a member for extending over said surface comprised of first and second parts extending at an angle to each other such that the two parts define a groove theeeSetweon f0 extending substantially parallelly to said surface, the first part being formed with a hole therethrough extending transversely of said groove for receiving the shank of said screw screwed into said surface, and said second part providing a shoulder for supporting said elongate element extending along said groove against lateral pressure from the head of said screw.

8. An assembly according to claim 7, wherein the member includes a third part extending at an angle to the first part such that those two parts define a groove therebetween, also for extending substantially parallely to the bone surface, whereby the first, second and third parts define a channel there among, the third part providing a shoulder for supporting a second elongate element extending along the second groove against lateral pressure from the head of the screw.

9. An assembly according to claim 7 or 8, wherein the or each elongate element takes the form of a Steinman pin.

10. An assembly according to claim 7 or 8, wherein the or each elongate element takes the form of a Kirschner wire.

11. An assembly according to any one of claims 7 to 10, wherein the first part serves to bear directly against the bone and the bone-contacting surface of the first part is of convex form to enable the component to sit at an angle on the bone surface if the latter is curved.

12. An assembly according to claim 11, wherein said bonecontacting surface is of convex spherical form.

13. An assembly according to any one of claims 7 to 12, wherein the first part serves to bear directly against the bone and is of uneven form, to resist rotary sliding of the component on the surface during turning of the screw.

14. A range of components, elongate elements and screws, each according to any one of claims 7 to 13.

15. A range according to claim 14, wherein the elongate elements are of a plurality of differing diameters and the components are of a plurality of differing sizes for holding the respective elongate elements.

16. A range according to claim 14 or 15, wherein the respective elements range in diameter from .75mm. to 2.00mm.

17. A range according to any one of claims 14 to 16, wherein the screws are of differing head shapes and/or angles.

18. An assembly according to any one of claims 7 to 13, and including a plurality of components each according to claim 7, 8, 11, 12 or 13 and a plurality of screws each according to claim 7.

19. A component for a fixator assembly, substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

20. A fixator assembly, substantially as hereinbefore described with reference to Figures 1 and 2, Figure 3, or Figure 4, of the accompanying drawings.