WO1999038464A1

WO1999038464A1 - An orthopaedic apparatus

Info

Publication number: WO1999038464A1
Application number: PCT/US1999/001882
Authority: WO
Inventors: Paul Firer
Original assignee: Handelman, Joseph, H.
Priority date: 1998-01-28
Filing date: 1999-01-27
Publication date: 1999-08-05
Also published as: AU2480099A

Abstract

An orthopaedic apparatus includes an elongate member (74), which is inserted into a medullary canal of a femur (24), and a tibia (14). A bearing member (60) is arranged on a first end (74) of the elongate member (74) to bear against a prepared surface of the femur, and tibia. The bearing member (60) is positioned in a plane which is oriented at predetermined angles, taken from a front of the bearing member (60), and a side of the bearing member (60), relative to the elongate member (74). The invention extends to a method of balancing ligament tension in orthopaedic surgery.

Description

AN ORTHOPAEDIC APPARATUS

FIELD OF THE INVENTION

THIS INVENTION relates to an orthopaedic apparatus and to

a method of adjusting ligament tension in orthopaedic surgery.

BACKGROUND TO THE INVENTION

In Figures 1 and 2, reference numeral 1 0 generally indicates

a side view and a front view of a knee in extension and flexion, respectively, in this specification, Figures 1 and 2 are used to illustrate the background to the invention.

In knee replacement surgery, the following principles should be observed in order to achieve a satisfactory fit of a prosthesis and in

order to achieve sufficient stability and alignment. The principles should also be observed so that soft tissues around the joint are balanced.

(a) A proximal end portion 12 of the tibia 14 is cut to

define a substantially planar proximal tibial surface 1 6, which is at 90° , when viewed from the front, to a weight bearing iine 1 8. The

weight bearing iine 1 8 is a line extending from the centre of the hip joint 20 to the centre of the ankle 21 . 2 (b) A distal end portion 22 of the femur 24 is cut to define a substantially planar distal femoral surface 26, which is at

90° , when viewed from the front, to the weight bearing line 1 8.

The cuts to the tibia 14 and the femur 24 should thus be made so that both the tibial surface 1 6 and the femoral surface 26 are at an angle to the horizontal, taken from the front (known as the valgus angle, and hereinafter referred to as σ°) . The angle a° is determined pre-operatively by X-ray.

(c) The cuts should also be made so that the tibial and femoral surfaces are at an angle to the horizontal, when the knee is in extension and when viewed from the side, which may be from 0° upwards, depending on the prosthesis selected (hereinafter referred to as β°) .

(d) The soft tissue sleeve 28 around the joint, both medially and laterally, should be balanced for tension.

Further cuts of the distal end portion 22 or prosthesis bearing portion of the femur 24 are made to fit the prosthesis. These are

known as the anterior cut, shown in dotted lines as 30, and the posterior cut, shown in dotted lines as 32 and define anterior and posterior surfaces. The anterior and posterior surfaces should be parallel to each other.

Jigs are used to make the anterior and posterior cuts 30, 32. The jigs must be placed in the correct degree of rotation on the end portion 22 of the femur 24 so that, once the anterior and posterior cuts are made and when the knee 1 0 is in flexion, and the soft tissues around

the joint are balanced, the posterior surface is parallel to the proximal tibial surface 1 6. This is to ensure that the prosthesis fits correctly when the knee 1 0 is in flexion.

The soft tissues around the joint must also be balanced for both the extended and flexed positions. Generally, the soft tissues are first balanced when the knee is in extension. The balancing of the soft tissue should take into account the prosthesis which is to be positioned between the tibial and femoral surfaces 1 6, 26, when the knee is in extension or between the posterior surface 32 and the tibial surface 1 6 when the knee is in flexion.

The anterior and posterior cuts 30, 32 are made when the knee is in flexion. The jigs to make the anterior and posterior cuts 30, 32 are engaged with the distal end of the femur 24 and are rotated to keep the soft tissue balanced once the anterior and posterior cuts 30, 32 have

been made. 4 In US Patent 5,468,244, there is disclosed a device which

facilitates the balancing of the soft tissue once the proximal tibial surface

1 6 and the distal femoral surface 26 have been prepared. The device acts on the tibial and femoral surfaces 1 6, 26 to achieve balancing of the soft tissue. This is possible since the tibial and femoral surfaces 1 6, 26 are oriented as set out in principles (a) and (b) above. It is clear that the device would be substantially ineffective where one of the tibial and femoral surfaces is unprepared.

At present, there are a substantial number of knee replacement systems available which require the anterior and posterior cuts to be made before the distal femoral surface is prepared. It follows that the soft tissue must be balanced by judging the orientation of the yet to be prepared femoral surface 26. This is an imprecise method subject to error in all but the most experienced hands. The rotational position of the jig to do the anterior and posterior cuts is judged by anatomical

landmarks known as the epicondyles. This is not always an accurate method of achieving correct rotational positioning so that soft tissue balance in flexion occurs.

It is an object of this invention to provide a means whereby the soft tissue 28 can be balanced without the need for the surgeon to judge the position of the femoral surface 26. 5

BROAD DESCRIPTION OF THE INVENTION

According to a first aspect of the invention, there is provided an orthopaedic apparatus, which includes an elongate member, which is insertable into a medullary canal of

a femur; and a bearing member, which is arranged on a first end of the elongate member to bear against a prepared surface of the tibia, the bearing member being positioned in a plane which is oriented at predetermined

angles, taken from a front of the bearing member and a side of the bearing member, relative to the elongate member.

The elongate member may be in the form of a fluted rod having a tapered second end.

A locating member may be mounted on the first end of the elongate member, to locate the bearing member relative to the elongate member. The locating member and the bearing member may define complementary mounting formations which are configured so that the bearing member is positioned in said plane.

The complementary mounting formations may be in the form of tongue and slot formations defined on the locating member and the

bearing member so that the bearing member can be slid into and out of 6 engagement with the locating member.

The bearing member may define a substantially planar

surface which is oriented to be parallel to, and to bear against, the

prepared tibial surface, in use.

A handle may be fast with the bearing member and may extend from the bearing member. The handle may be in the form of a straight bar, which is positioned parallel to the plane in which the bearing member is positioned. The handle may include alignment check rod engaging means.

According to a second aspect of the invention, there is provided a method of balancing ligament tension in orthopaedic surgery, the method including the steps of: cutting a tibia to obtain a planar tibial surface which is substantially at right angles to a weight bearing line; positioning an elongate member of an orthopaedic apparatus in the medullary canal of the femur so that a bearing member on an end of the elongate member is positioned between the tibial surface and the femur; and

balancing the soft tissue about the knee joint with the bearing member in position, prior to cutting the femur, to obtain a complementary planar femoral surface.

The invention is now described, by way of example, with

reference to the accompanying drawings

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, Figure 1 shows a schematic side view of a knee joint in flexion; Figure 2 shows a schematic front view of a knee joint in extension;

Figure 3 shows a side view of a rod and locating member of an orthopaedic apparatus, in accordance with the invention;

Figure 4 shows a front view of the rod and locating member of the orthopaedic apparatus;

Figure 5 shows a schematic front view of the knee joint with the orthopaedic apparatus in an operative position;

Figure 6 shows a three dimensional view of the rod and locating member of the orthopaedic apparatus;

Figure 7 shows a side view of a bearing member and handle of the orthopaedic apparatus;

Figure 8 shows a front view of the bearing member and handle of the orthopaedic apparatus; and

Figure 9 shows an end view of the bearing member and handle of the orthopaedic apparatus.

DETAILED DESCRIPTION OF THE DRAWINGS

In Figures 1 and 2, reference numeral 1 0 generally indicates a knee joint prior to knee replacement surgery. The relevant parts of the knee joint 1 0 and their role in knee replacement surgery have been described under "Background to the Invention" above.

In Figure 3, 4 and 6, there is shown a rod 40 and a locating member or locator 42 attached to the rod 40.

The rod 40 and the locator 42 are of surgical steel.

A first or proximal end 44 of the rod 40 is tapered or rounded to facilitate insertion of the rod 40 into the medullary canal of the femur 24. Further, the rod 40 has flutes 46 defined therein to reduce compressive forces exerted by the rod 40 when the rod 40 is inserted into the medullary canal of the femur 24.

The locator 42 has a rectangular body 48 with two opposed

major faces 50. One of the major faces 50.1 is fast with the rod 40. The major face 50.1 is oriented at 90° - σ°, taken from the front, relative to the rod 40 and at 90° - β°, taken from the side, relative to the rod 40. 9 The angles a° and β° are described earlier in the specification.

A tongue 52 extends from each of a pair of opposed minor

faces 54 of the body 48.

In Figures 7 to 9, reference numeral 60 generally indicates a bearing member in the form of a plate for positioning between the proximal tibial surface 1 6 and the distal end 22 of the femur 24.

The plate 60 is roughly pear shaped, having a narrow side

64 and a broad side 66. The plate 60 also has a pair of opposed, planar major faces 62. The plate 60 is of a predetermined thickness and has a pair of openings 78 defined therein. The openings 78 permit shims to be attached to the plate 60 to vary an effective thickness of the plate 60.

The plate 60 is marked on one of the faces 62 at 80 to indicate to a user whether that side 62 is to face the femur 24 or the tibia 14.

A rectangular slot 68 is defined in the plate 60 to open at the broad side 66. A groove 70 is defined in each of a pair of opposed, inner surfaces 72 defining the slot 68. 10 Relative dimensions of the body 48 and the slot 68 are such that the body 48 is a sliding fit in the slot 68, with the faces 50 of the locator 42 flush with the faces 62 of the plate 60 (Figure 6) . Similarly, relative dimensions of the tongues 52 and the grooves 70 are such that

the tongues 52 are a sliding fit in the grooves 70.

A handle 74 is fixed to the narrow side 64 of the plate 60. The handle 74 is elongate and is circular cylindrical in cross section. The handle 74 is in a parallel orientation with respect to the plate 60.

A pair of spaced guide passages 76 are defined in the handle 74. The guide passages 76 are parallel to each other and are oriented at β° relative to the handle 74. An alignment check rod (not shown) is received through each guide passage 76 to permit a surgeon to confirm

alignment of the tibia 14 and the femur 24. It will be appreciated that the orientation of the passages 76 results in the guide rods being parallel to the tibia 14 and the femur 24.

In use, σ° of a particular patient is determined prior to carrying out the knee replacement surgery. The angle β° is dependent on the prosthesis being used in the surgery and is usually 0° or 7 ° . For each selected β° a range of locators having different σ° , for the left and right knee, are provided. 11

In the method of the invention, the proximal tibial surface 1 6

is first prepared by making the necessary cuts to the tibia. The rod 40 is then inserted into the medullary canal of the femur 24, through a tunnel prepared for later use by the distal femoral cutting jig, which is an

instrument for the preparation of the femoral surface 26.

The plate 60 is engaged with the locator 42 in the manner described above so that the major face 62.1 of the plate 60 bears against the femoral condyles 82. It will be appreciated that, as a result of the orientation of the locator 42, the faces 62 of the plate 60 are at 90° to the weight bearing line 1 8.

What is known as vaigus alignment can be checked by external alignment techniques common to knee replacement surgery, by using the alignment check rods positioned in the passages 76.

The soft tissue sleeves 28 can now be balanced with normal surgical techniques, without the necessity of preparing the femoral surface 26. The reason for this is that, as a result of the orientation of the plate 60, the femur is oriented as if the femoral surface 26 had already been prepared.

The Applicant believes that the orthopaedic apparatus 12 described above provides a simple and convenient means for accurately balancing a tension in the soft tissue 28 prior to making the femoral cut in knee replacement surgery.

Claims

13CLAIMS

1 . An orthopaedic apparatus, which includes an elongate member, which is insertable into a medullary canal of

a femur; and a bearing member, which is arranged on a first end of the elongate

member to bear against a prepared surface of the tibia, the bearing member being positioned in a plane which is oriented at predetermined angles, taken from a front of the femur and a side of the femur, relative to the elongate member.

2. The apparatus as claimed in Claim 1 , in which the elongate member is in the form of a fluted rod having a tapered second end.

3. The apparatus as claimed in Claim 1 or 2, in which a locating member is mounted on the first end of the elongate member to locate the bearing member with respect to the elongate member, the locating member and the bearing member defining complementary mounting formations which are configured so that the bearing member is positioned in said plane.

4. The apparatus as claimed in Claim 3, in which the complementary mounting formations are in the form of tongue and slot 14 formations defined on the locating member and the bearing member so that the bearing member can be slid into and out of engagement with the

locating member.

5. The apparatus as claimed in Claim 4, in which the bearing member defines a substantially planar surface which is oriented to be parallel to, and to bear against, the prepared tibial surface, in use.

6. The apparatus as claimed in any one of Claims 3 to 5, inclusive, in which a handle is fast with the bearing member and extends from the bearing member.

7. The apparatus as claimed in Claim 6, in which the handle is in the form of a straight bar, which is positioned parallel to the plane in which the bearing member is positioned.

8. The apparatus as claimed in Claim 7, in which the handle includes alignment check rod engaging means.

9. A method of balancing ligament tension in orthopaedic surgery, the method including the steps of: cutting a tibia to obtain a planar tibial surface which is substantially at right angles to a weight bearing line; 15 positioning an elongate member of an orthopaedic apparatus in the medullary canal of the femur so that a bearing member on an end of the elongate member is positioned between the tibial surface and the femur;

and balancing the soft tissue about the knee joint with the bearing member in position, prior to cutting the other of the femur and tibia, to obtain a complementary planar surface.

10. A new orthopaedic apparatus, substantially as described herein, with reference to the accompanying drawings.

1 1 . A new method of balancing ligament tension in orthopaedic surgery, substantially as described herein.