WO1995023567A1

WO1995023567A1 - Modular ceramic knee prosthesis

Info

Publication number: WO1995023567A1
Application number: PCT/AU1995/000110
Authority: WO
Inventors: Besim Ben-Nissan; Ronald L. Huckstep; Phillip Lutton; Allan Pollack; Greg Etherington; Michael Swain; Warwick M. Payten; Don MERCER
Original assignee: Ben Nissan Besim; Huckstep Ronald L; Phillip Lutton; Allan Pollack; Greg Etherington; Michael Swain; Payten Warwick M
Priority date: 1994-03-03
Filing date: 1995-03-03
Publication date: 1995-09-08
Also published as: AUPM417794A0

Abstract

A modular ceramic knee prosthesis device is disclosed. The device consists of a ceramic femoral component (17) attached to a metal base plate (18) having an adjustable stem (4) with lateral bore holes to accept bone screws (3). The device further comprises a single tibial component having a metal base plate (20) with a central stem (32) with lateral bore holes (28) to accept bone screws (31), superimposing the base plate is a plastic load bearing surface (33). Further the device comprises two partial tibial components having a metal base plate with an angled stem with bore holes and screws similar in design to the single stem, superimposing the base plates is either a plastic or ceramic load bearing surface (23a, 23b). This device can be used to replace a total or partially dysfunctional human knee joint.

Description

MODULAR CERAMIC KNEE PROSTHESIS

TECHNICAL FIELD

The present invention relates to impiantable knee joint prosthesis for replacement of the engaging surfaces of the distal femur and proximal tibia of a dysfunctional human knee joint.

BACKGROUND

In the past, the design and development of total knee replacement prosthesis for diseased and/or damaged human knees have typically been restricted to no more than three factory assembled components; namely, the femoral, tibial and patellar replacement components. These devices have been designed to fit the anatomical variations and surgical needs of the largest possible segment of the eligible population while maintaining a manageable inventory of component parts. Such prior art designs typically incorporate plastic tibial articulating surfaces which are permanently assembled at a factory to a metal base plate having some configuration of a rigid integral stem.

Conventional prostheses usually use a metal femoral surface which is cemented into place on the lower portion of the femur. This means that the femoral prosthesis although secure at the time of the operation can loosen in time due to the different moduli of elasticity between the cement and bone. The cement sets exothermically and can cause extensive thermal necrosis to the surrounding bone. The prosthesis can also loosen due to infection or other factors. Due to the wide variation of natural, anatomical configurations of the human distal femur and proximal tibia, the unpredictable bone quality and the varying degrees of deterioration resulting from arthritis, trauma, or failed previous prostheses, a need has existed for a versatile knee prosthesis which can be custom fit to meet the needs presented by the above described variables.

Also, because joint prosthesis in general, and particularly knee replacer ients, are being implanted in patients with increasingly longer life expectancies, the need also exists for a prosthesis which allows for later replacement of a worn bearing surface without disturbing the components firmly affixed in or to the bones.

Further, the usual type of tibial prosthesis is made in one piece, the anterior cruciate ligament of the knee is usually destroyed in order that the prosthesis can be fitted. Often the posterior cruciate ligament is destroyed as well, due to most of the upper surface of the proximal tibia having to be replaced.

It is therefore an object of the present invention to provide an impiantable knee joint prosthesis which allows several of its component parts to be mass produced while allowing a custom fit for each patient and his or her particular therapeutic need. It is also an object of the present invention to allow such custom fitting to be easily accomplished without sacrificing overall prosthesis quality and performance. This feature also provides the surgeon with a range of articulating /bearing surfaces with varying amount of constraint, and congruency with the femoral component for patients with various degrees of soft tissues laxity which could not be preoperatively anticipated. The surgeon may therefore tailor the implant to better fit the patient's knee as it is found to exist and thereby decrease the probability that the knee prosthesis would require future adjustment, modification or replacement.

It is a further object of the present invention to allow the surgeon to cater for all types of knee operations from primary through to revision. It is envisaged a similar, if not identical jig system would be used.

Finally, it is an object of the invention is to obviate the need for bone cenient thereby avoiding problems associated with the use of such cement.

These and other advantages will become apparent to one of ordinary skill in the art in light of the following disclosure and drawings.

SUMMARY OF THE INVENTION

The present invention relates to an impiantable knee joint prosthesis which is designed to replace the engaging surfaces of the distal femur and proximal tibia of a dysfunctional human knee joint. In its most general form, the invention comprises an impiantable knee joint prosthesis having a tibial stem portion, a tibial tray portion, an interchangeable modular articulating surface member which is removably attached to the tibial tray portion, and a femoral portion adapted to cooperatively bear upon the articulating surface.

The present invention is intended to provide certain improvements over the prior art. One feature of the present invention is to offer modular tibial stem configurations which can be affixed to the tibial tray component. The tibial stem portion and tibial tray portion may be permanently attached into an integral piece although it is preferable that the tibial stem portion, the tibial tray portion and the articulating surface member be removably attached to form a complete assembly. Such an arrangement facilitates 85 easier implantation while allowing the interchange of articulating surface members of various dimensions.

The tibial stem portions may be of various lengths and in various configurations, such as round or cruciate shaped. The tibial stems having at least one locking screw 90 passing through a bore into the surrounding bone. A coat can be used on the underside of the implant / bone contact surface to encourage bone adhesion to the implant. The coat and locking screw member construction therefore provide a dual locking mechanism.

95 The present invention also provides an interchangeable modular articulating surface member which is removably attached to the tibial tray portion. The articulating surface member may therefore be selected from a collection of such members having various thicknesses, dimensions and shapes, which can be interchangeably attached to the tibial tray portion to form a complete tibial plateau portion. This may be accomplished

100 by any appropriate mechanical locking arrangement. In the circumstance where the distal femoral bone is in good condition and is left intact, it is recommended a tibial tray design with a ceramic articulating surface member be used directly against the femoral bone.

105 An alternative design to the just described tibial component is also part of the present invention. In this aspect, two partial tibial trays covering the medial and lateral meniscal surfaces respectively are used instead of the single tibial tray covering the entire surface. One feature of the partial tibial trays is to offer modular tibial stem configurations which can be affixed to the partial tibial tray component. The tibial stem 110 portion and partial tibial tray portion may be permanently attached into an integral piece although it is preferable that the tibial stem portion, the partial tibial tray portion and the articulating surface member be removably attached to form a complete assembly. Such an arrangement facilitates easier implantation while allowing the interchange of articulating surface members of various dimensions.

115

The tibial stem portions may be of various lengths and in various configurations, such as round or cruciate shaped. The tibial stems having at least one locking screw passing through a bore into the surrounding bone. A coat can be used on the bone contact surface to encourage bone adhesion to the implant. . The coat and locking

120 screw member construction therefore provide a dual locking mechanism.

The present invention also provides an interchangeable modular articulating surface member which is removably attached to the partial tibial tray portion. The articulating surface member may therefore be selected from a collection of such members having 125 various thicknesses, dimensions and shapes, which can be interchangeably attached to the partial tibial tray portion to form a medial or lateral tibial portion. This may be accomplished by any appropriate mechanical locking arrangement.

The present invention also comprises a femoral portion, attached to the distal portion of 130 the femur, adaptively shaped to co-operatively bear upon the bearing surface of the articulating surface member so as to produce a prosthesis which allows restored knee action.

One feature of the present invention is to offer modular femoral stem configurations 135 which can be added to the femoral tray component. The femoral tray portion may include an integral stub piece to which the femoral stem may be attached to form a complete assembly. Such an arrangement allows optional use of a central femoral stem should this be required because of poor bone condition. The femoral tray has provision to use screws to attach this to the bone without the use of cement.

140

The femoral stem portions may be of various lengths and in various configurations, such as round or cruciate shaped. The femoral stems having at least one locking scre passing through a bore into the surrounding bone. A coat can be used on the bone contact surface to encourage bone adhesion to the implant. As with the^'tibial stem, the 145 coat and locking screw member construction therefore provide a dual locking mechanism.

The present invention also provides an interchangeable modular articulating surface member which is removably attached to the femoral tray portion. The articulating 150 surface member may therefore be selected from a collection of such members having various thicknesses, dimensions and shapes, which can be interchangeably attached to the femoral tray portion to form a complete femoral plateau portion. This may be accomplished by any appropriate mechanical locking arrangement.

155

DESCRIPTION OF THE DRAWINGS

An embodiment of the present invention will now be described with reference to the 160 accompanying figures.

FIG.1 illustrates both embodiments of the femoral prosthesis and full tibial tray prosthesis in anterior view. FIG.2a illustrates the femoral stub component of the femoral prosthesis prosthesis in 165 anterior view.

FIG.2b illustrates the apparatus of FIG.1 in medial view.

FIG.3 illustrates the apparatus of FIG.1 in posterior view.

FIG.4 illustrates the apparatus of FIG.1 , 2 and 3 in 3D view.

FIG.5 illustrates the femoral component and both partial tibial components in 3D. 170 FIG.6 illustrates both partial tibial component in 3D.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

175 The contiguous surfaces of all prostheses are hard, non porous, and should be highly polished to allow smooth movement between the components.

To assist the stabilisation of the prostheses to bone, the designs presented make use of cortical bone screws passing through the implant into the bone. It is also envisaged 180 that the underside of the prostheses which abuts bone directly should have a coating that encourages bone to adhere directly to the implants. If necessary, bone cement can be used with these or instead of these fixation methods.

As illustrated in FIG.1 to 5, the femoral prosthesis 1 is attached to distal femur 2 by 185 either screws through the femoral tray 18 or by means of attaching a modular femoral stem 4 and passing cortical bone screws 3 through bores 8 into the surrounding bone 2.

The femoral prosthesis 1 , comprises load bearing surfaces 5 with an anterior 190 projection 6 extending upwardly and two posterior projections 7, extending in the sam direction from a rear portion of the femoral prosthesis 1. The articulating femoral member 17 is attached to a femoral backing tray 18 by mechanical interlock 9. This backing tray 18 includes femoral stub 19 and bores for attachment to the bone. If required, the modular femoral stem 4 is locked into the integral femoral stub 19 as 195 illustrated in FIG.2a and placed intermediate the anterior and posterior projections 6 and 7 respectively. The modular femoral stem 4 is at an angle to the horizontal in order to take into account a corresponding angle present in the bone structure.

As the invention covers a wide range of bone conditions, the attachment of the femoral 200 backing tray 18 to the bone may take several forms. If the bone is sound, then bores are made to locate the tray with the femoral stubs 19 and to allow screws to attach the femoral backing tray 18 directly to the bone. If necessary, the femoral stub bore is extended to allow the modular femoral stem 4 to be positioned. The modular femoral stem 4 has lateral bores 8 through which the screws 3 pass, securing the femoral 205 prosthesis 1 into position on the distal femur 2.

The prosthesis 1 is attached to the distal femur 2 as illustrated in FIG.1 by the removal of part of the lower portion of the distal femur 2 and cutting the femur 2 along the place 10, 11 , 12, 13 and 14. A bore corresponding in diameter to the femoral stub 19 is then

210 drilled into the distal femur 2 thereby allowing the prosthesis 1 to be positioned. If required, this bore is extended to accommodate femoral stem 4 which is fixed to the backing tray 18. The backing tray 18 is then pushed into position and is secured to the distal femur 2. This is done by either using screws through the backing tray 18 or by drilling lateral holes through the distal femur 2 using a jig system that ensures

215 matching with the bores 8 on the modular femoral stem 4 and passing through screws 3 to secure the backing tray 18 and modular femoral stem 4 to the distal femur 2. The articulating femoral member 17 is then attached to the backing plate 18. Beneath the femoral prosthesis 1 is the tibial prostheses 15 or 16 which may or may 220 not be required depending upon the condition of the proximal tibia 21 after the damage has been caused. If tibial prostheses 15 or 16 are not required due to the good and wholesome condition of the proximal tibia 21 , then the smooth nature of the femoral prosthesis 1 is such that friction is minimised, thereby allowing the original bone material to remain intact. This offers a distinct advantage over conventional femoral 225 prostheses which require the removal of bone material in good condition to be replaced with a harder wearing surface due to the nature of conventional implant femoral designs. The corresponding destruction of cruciate ligaments usually accompanies the use of the conventional tibial prosthesis and therefore, the present invention only requires a full tibial tray prosthesis 15 or partial tibial tray prosthesis 16, 230 when it is essential due to prior damage.

The full tibial tray design 15 with single articulating surface member 33 encompassing both menisci respectively is shown in FIG.1 to 4. The partial tibial tray design 16 with its two articulating members 22a and 22b is shown in FIG.5 and 6. Selection of tibial 235 component is based on the condition of the underiyiπg bone stock. If only one tibial bone portion requires replacement then only a one of the articulating members 22a or 22b of the partial tibial prosthesis will be required.

The partial tibial tray design is illustrated in FIG.5 and FIG.6. The medial and lateral 240 tibial articulating members 22a, 22b, of different sizes are located on the tibial base piate 26a, 26b by mechanical interlock. Each tray also has a modular tibial stem 24a, 24b with transfixing screws 25a, 25b passing through bores 29a, 29b and attach the prosthesis to the proximal tibia 21. The partial tibial prosthesis comprises a load bearing surface 23ε, 23b which mates with the load bearing surface 5 of the femoral prosthesis 1 , and a tibial stem 24a, 24b is provided to receive screws 25a, 25b.

The prosthetic components 1 , 22a, 22b are designed so that each can be used in isolation or in any combination. It is therefore possible to use one or both partial tibial components 22a, 22b of different heights articulating direct on the distal femur 2. Alternatively, it is possible to replace the distal femur 2 with a femoral prosthesis 1 and leave the proximal tibia 21 intact or replace proximal tibia 21 using one or both partial tibial components 16.

The full tibial tray design 15 is shown in FIG.1-4. The full tibial prosthesis comprises a load bearing surface 27 which mates with the load bearing surface 5 of the femoral prosthesis 1 , and a tibial stem 32 is provided to receive screws 31. The tibial stem having additional flanges 30 and bores 28 to accept locking screws 31. The tibial stem 32 attaches directly to the tibial tray portion 20. A modular articulating surface member 33 is then attached to the tibial tray portion 20 via a mechanical lock.

An advantage of using this form of tibial prosthesis 15, apart from the fact that both load bearing surfaces 5 and 27 do not need to be replaced if not necessary, is that various heights and thicknesses of articulating surface member 33 can be used to correctly proportion and angle the proximal tibia 21 with respect to the distal femur 2.

Next adjacent to the anterior projection 6 of the femoral prosthesis, is located a knee cap or patella. A retropatella ceramic button can be inserted, if necessary, into the patella by means of a screw thread in order to provide a smooth articulating surface with the front of the femoral prosthesis. The foregoing describes some embodiment of the present invention, however, modifications by those skilled in the art may be made thereto without departing from the scope of the present invention.

Claims

The claims defining the invention are as follows

1. A modular knee prosthesis comprising a femoral component having anterior projections extending upwards and two posterior projections extending in the same direction to approximate the shape of the distal femoral bone, said femoral component comprising a ceramic or metal load bearing surface portion secured to a metal femoral backing tray.said load bearing surface of said femoral component adapted to mate with plastic load bearing surface of tibial component, said plastic bearing tibial component superimposed on a metal tray.

2. A modular knee prosthesis as defined in claim 1, said femoral backing tray having an adjustable angled femoral intermedullary stem extending therefrom, said stem being provided with a plurality of lateral bores therethrough to accommodate respective bone screws by which said stem is securable within the distal femur.

3. A prosthesis as defined in claim 1 wherein a tibial intermedullary stem extends from said tibial backing tray, said stem including a plurality of lateral bores, therethrough to accommodate respective bone screws by which said tibial stem is securable within the proximal tibia.

4. A prosthesis as defined in claim 3 wherein said tibial component furthercom prises a pair of angled flanges secured to said stem and located to support said tibial component.

5. A prosthesis as defined in claim 1 wherein said tibial prosthesis load bearing component and metal tray is a two part device, one each of said parts being adapted to mate with respective medial and lateral projections of said femoral component.

6. A prosthesis as defined in claim 5 wherein each said part of said two part device is provided with an angled stem, each said stem being provided with a plurality of lateral bores to permit securement of said part by bone screws to the proximal tibia.

7. A prosthesis consisting of two partial tibial devices comprising a ceramic upper surface attached to a metal base plate as defined in claim 6, one each of said devices being adapted to accommodate respective medial and lateral condyles of the distal natural femoral articular cartilage surface.

8. A modular knee prosthesis as herein described with reference to the accompanying drawings.