GB2406278A

GB2406278A - A reamer

Info

Publication number: GB2406278A
Application number: GB0322452A
Authority: GB
Inventors: Paul Smirthwaite; Angus Wallace
Original assignee: Biomet Merck Ltd
Current assignee: Biomet UK Ltd
Priority date: 2003-09-24
Filing date: 2003-09-24
Publication date: 2005-03-30
Anticipated expiration: 2023-09-24
Also published as: GB0322452D0; GB2406278B

Abstract

A reamer having a cutting face 8 from which a pilot guide 6 projects, the pilot guide 6 being aligned with the rotary axis of the reamer, the cutting face 8 having a cutting region extending radially of the cutting face 8, an anular recess 24 being provided in the cutting face 8 between the inner edge of the cutting region and the pilot guide 6.

Description

A Reamer This invention relates to a reamer, and is particularly, although

not exclusively, concerned with a reamer for bone, for example for forming a surface on a glenoid of a scapula during a shoulder replacement operation.

In a shoulder replacement operation, a prosthesis comprising a numeral component and a glenoid component are fixed respectively to the patient's numerous and scapula.

The glenoid component comprises a tray, for example of metal, which is secured to the scapula, and a glenoid insert or liner, for example of polyethylene, is then secured to the metal tray.

Preparation of the bone to receive the glenoid tray is a critical part of the operation, since the depth and orientation of the resulting surface affect the range of movement of the resulting joint. In a known technique, a pilot hole is drilled in the glenoid, using a jig to determine the position of the pilot hole, and a reamer is then used to form a circular surface on the glenoid, the reamer being centred by means of the pilot hole. Depth control of the reamer is very important, and reaming usually takes place in stages with the surgeon inspecting the resulting recessed cut face at each stage to check the depth and orientation of the cut face. However, it is difficult to achieve a consistent, controlled depth of cut at each stage.

According to the present invention there is provided a reamer having a cutting face from which a pilot guide projects, the pilot guide being aligned with the rotary axis of the reamer, the cutting face having a cutting region extending radially of the cutting face, an anular recess being provided in the cutting face between the inner edge of the cutting region and the pilot guide.

During cutting, material is removed by cutting elements in the cutting region, but leaving uncut material between the pilot guide and the inner edge of the cutting region.

Thus, as cutting proceeds, the uncut material around the pilot guide extends into the recess until it engages the base of the recess, when cutting terminates. Consequently, the depth of the recess provides control of the depth of cut at each cutting stage. At the end of each stage, the resulting boss of material left by the recess is removed to leave a flush surface over the total area of the cut face. A further reaming operation can then be conducted or the resulting cut face can be regarded as the final face to which the glenoid tray is fitted.

The cutting region may comprise at least one radially extending blade edge. In a preferred embodiment, the cutting region is defined by inner and outer circumferential walls, with a plurality of blades extending with their blade edges aligned generally radially with respect to the rotary axis of the reamer. In a preferred embodiment suitable for forming a glenoid surface in a shoulder replacement operation, the depth of the recess may be not less than 2 mm and not more than 4 mm, for example approximately 3 mm. Thus, the reamer provides a depth of cut at each stage of approximately 3 mm. In the context of the present invention, references to the depth of the recess mean the depth of the base of the recess measured from the plane of the blade edges, or corresponding cutting elements.

The width of the recess, measured radially of the rotary axis of the reamer, needs to be sufficient to provide an adequate volume of uncut material to support the reamer during a reaming operation in order to terminate cutting. In a reamer suitable for forming a surface in bone, the width of the recess is preferably not less than 2 mm and may, for example, be approximately 3 mm.

According to another aspect of the present invention, there is provided a prosthesis kit comprising prosthesis components and a reamer as defined above.

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figures 1 to 6 comprise various views of a reamer for use in a shoulder replacement operation: and Figure 7 shows a scapula having a surface formed by a reamer in accordance with the present invention.

The reamer shown in Figures 1 and 3 comprises a cutting disc 2 having a drive shaft 4 extending from one axial face and a pilot guide 6 extending from the other axial face.

The axial face from which the pilot guide 6 extends constitutes a cutting face 8.

The disc 2 is welded at 10 (Figure 5) to a pin which constitutes both the drive shaft 4 and the pilot guide 6. The disc 2 comprises a diametrically extending support 12 which carries inner and outer circumferential walls 14 and 16. Between these walls 14 and 16 extends a structure which includes inner and outer blades 18, 20, each blade having a blade edge 22.

A recess 24 is provided between the pilot guide 6 and the inner circumferential wall 14, this recess being anular and having a depth to a base 32 of the recess 24 of 3 mm and a width of 3 mm.

For use in a surgical operation, for example to form a glenoid surface on a scapula during a shoulder replacement operation, the reamer is mounted by means of the drive shaft 4 in a surgical drill and advanced towards the surface to be prepared. A pre- drilled hole 26 (Figure 7) receives the pilot guide 6 to ensure accurate positioning of the reamer. As material is removed, a flat glenoid surface 28 (Figure 7) is formed, and the reamer advances into the bone. However, because the cutting surface 8 has the recess 24, the cutting region of the cutting surface, constituted by the blades 18, 20, terminates short of the pilot guide 6, at the inner circumferential wall 14. Consequently, an anular boss 30 is left between the pilot hole 26 and the surface 28. Eventually, this boss will contact the base 32 of the recess 24, so preventing a further advancement of the reamer. The surgeon is thus able to withdraw the reamer, and inspect the resulting flat glenoid surface 28 for alignment and depth. The depth is considered to be correct when bleeding subchondral bone is encountered.

The boss 30 is then removed in a separate reaming operation to leave an entirely flat cut surface. This surface can either be reamed again in a further stage if greater depth is required, or can be used for the fixing of a glenoid tray.

The reamer thus enables successive material removal stages to be conducted to accurate depths governed by the depth of the recess 24.

Claims

1. A reamer having a cutting face from which a pilot guide projects, the pilot guide being aligned with the rotary axis of the reamer, the cutting face having a cutting region extending radially of the cutting face, an anular recess being provided in the cutting face.

2. A reamer as claimed in claim 1, in which the anular recess is provided in the cutting face between the inner edge of the cutting region and the pilot guide.

3. A reamer as claimed in claim 1 or 2, in which the cutting region comprises at least one radially extending blade edge.

4. A reamer as claimed in any of the preceding claims in which the cutting region is defined by inner and outer circumferential walls, with plurality of blades extending with their blade edges aligned generally radially with respect to the rotary axis of the reamer.

5. A reamer as claimed in any of the preceding claims, in which the Jepth of the recess is not less than 2mm and not more than 4mm.

6. A reamer as claimed in claim 5, in which the depth of the recess is 3mm.

7. A reamer as claimed in any one of the preceding claims, in which the width of the recess is not less than 2mm.

8. A reamer as claimed in claim 7, in which the width of the recess is 3mrn.

9. A prosthesis kit comprising prosthesis components and a reamer as claimed in any one of the preceding claims.

10. A reamer substantially as described herein, with reference to and as shown in the accompanying drawings.