IE43513B1 - A tibial prosthesis - Google Patents

Description

This invention relates to a tibial prosthesis for use in correcting a defective tibio-femoral knee joint, and particularly in the human knee joint.

Heretofore, various prostheses have been proposed for use 5 in treating defective knee joints, for instance those described and claimed in British Patent Specification No. 1,395,896 and Patent No. 36395. Certain of these prostheses have been employed successfully, but have not always proved entirely satisfactory.

Some, for example, require a large amount of bone removal and a complexity of operative procedures - this applies particularly to those prostheses in which the entire joint between the tibia and femur is replaced. Other prior prostheses, while requiring a minimum amount of bone removal and relatively simple operative procedures, do not maintain the natural alignment between the lateral and medial articulating surfaces of the knee joint. Still other prior prostheses, while maintaining perfect alignment between the lateral and medial articulating surfaces of the knee joint, tend to interfere with the cruciate ligament of the knee joint, and are only of use in joints where the cruciate ligament and/or menisci !0 components of the knee joint are destroyed or have been removed.

The present invention seeks to provide a tibial prosthesis for the tibio-femoral joint that reduces or overcomes the problems and disadvantages of the prior prostheses.

Accordingly, this invention provides a tibial prosthesis for a tibio-femoral joint, which prosthesis comprises an elongate lateral plateau member and an elongate medial plateau member, each plateau member having an articulating surface for replacement of the corresponding articulating surface of the tibia and a longitudinal guide cooperable with the femur to maintain the natural configuration of the bones in the joint, a connecting member fixedly attached to and extending between the one ends of the plateau members so as to maintain the plateau membeis in a transit) versely spaced relationship with their elongate axes parallel and with their articulating surfaces in alignment, and means for anchoring the prosthesis to the upper end of the tibia adjacent the femur with the one ends of the plateau members positioned towards the anterior portion of the joint. It is the function of the connecting member to maintain the alignment and transverse spacing of the plateau members, so that the natural positioning of the lateral and medial articulating surfaces in the knee joint may be maintained when using the prosthesis of the invention; furthermore, the fixed spacing of the plateau members may simplify the operating procedures required for anchoring the prosthesis to the tibia.

It is important that the connecting member should not interfere with the cruciate ligament of the knee joint. This is achieved by forming the prosthesis so that when it is anchored to the tibia, the connecting member lies towards the anterior of the joint.

The articulating surfaces of the plateau members may be substantially planar; this allows the articulating surfaces on the femur to slide back and forth on those of the plateau members to find the best relative disposition of the surfaces for their co-action in the joint. However, in cases where the cruciate ligament of the knee is damaged, it may be desirable for the articulating surfaces of the plateau members to be concave so as to limit the amount of sliding movement possible for the femur on the articulating surfaces of the tibial prosthesis.

Each plateau member is provided with a longitudinal guide, the function of these being to maintain the natural configuration of the bones in the joint and to prevent the condyles of the femur from interfering with the cruciate ligament. The longitudinal guides preferably take the form of a longitudinally convexly curved abutment surface facing the articulating surface of each plateau member, the abutment surface of the lateral plateau member upstanding perpendicularly from the medial elongate edge thereof and the abutment surface of the medial plateau member upstanding perpendicularly from the lateral elongate edge thereof. The abutment surfaces of the medial and lateral plateau members are capable of abutting the corresponding condyles of the femur, thus maintaining a correct relative disposition in a mediallateral direction of the articulating surfaces of the condyles and the plateau members. The convex curvature of the abutment surfaces enables the femur to rotate to a limited degree on the tibial prosthesis of the invention above the vertical axis of the joint, so as to reflect the degree of rotation possible in a normal knee joint.

It is an important aspect of the present invention that the tibial prosthesis replaces substantially only the articulating surfaces of the tibia, and thus reduces to a minimum the amount of bone removal required when anchoring the prosthesis to the tibia.

The means for anchoring the prosthesis to the tibia preferably comprise one or more pegs upstanding from each plateau member on an internal surface thereof facing the tibia when the prosthesis is anchored to the tibia. Thus, when the prosthesis is in position, the pegs may extend into holes formed in the tibia, generally being bound to the tibia by a bone cement. One or more grooves are advantageously provided in and around each peg, which effectively increases the ability of the pegs to bind securely with the bone.

The anchorage of the prosthesis to the tibia may be further assisted by the provision of one or more channels formed in the internal surface of each plateau member, around each peg. Preferably, each channel is undercut.

The tibial prosthesis of the invention may be employed in a tibio-femoral joint in conjunction with a normal healthy femur.

However, it often is the case that the femur and the tibia are both damaged, and both must be replaced. In that event it is preferable to use the tibial prosthesis of this invention in conjunction with a femoral prosthesis such as is described and claimed in Patent No. 1036/75 out of which this Patent has been divided. References herein to the femur, or to specific parts thereof, are to be interpreted as including within their scope a femur fitted with a femoral prosthesis, or appropriate parts thereof. 3513 Some preferred aspects of the present invention will now he described, though only by way of illustration, with reference to the drawings in which:Figure 1 is a side elevational view of a femoral prosthesis constructed in accordance with the aforesaid patent.

Figure 2 is a front elevational view of the femoral prosthesis of Figure 1.

Figure 3 is a top plan view of the femoral prosthesis of Figure 1.

Figure 4 is a top plan view of a tribial prosthesis of the present invention.

Figure 5 is a front elevational view of the tibial prosthesis of Figure 4.

Figure 6 is a bottom plan view of the tibial prosthesis of Figure 4.

Figure 7 is a sectional view as taken on line VII-VII of Figure 5.

Figure 8 is a sectional view similar to Figure 7 but showing an alternative embodiment of a tibial prosthesis of this invention.

Figure 9 is a somewhat diagrammatic side view of a tibio-femoral joint comprising a femoral prosthesis according to the aforesaid patent application and a tibial prothesis of the present invention.

Figure 10 is a somewhat diagrammatic front view of the tibiofemoral joint of Figure 9.

The tibial prosthesis 15 of the present invention is for use in replacing the articulating surfaces of the tibia 47 in a tibiofemoral joint 11 in a human knee. The prosthesis 15 comprises an elongate lateral plateau member 49 and an elongate medial plateau member 51 for replacing the articulating surfaces of the lateral plateau 53 and the medial plateau 55 of the tibia 47. Each plateau member 49, 51 has a substantially planar articulating surface 61 for coacting with the femur. The planar articulating surface 61 allows the condyles of the femor to freely slide back and forth on the tibial prosthesis 15, thus enabling the femur and the tibial prosthesis to find the best relative disposition for their co-action. However, where the ligaments of the knee joint are not strong, each plateau member 49, 51 preferably has a concave articulating surface 61' (see Figure 8) for limiting the amount of sliding movement of the femur on the tibial prosthesis 15. The tibial prosthesis 15 comprises also a connecting member 57 for fixedly connecting the lateral and medial plateau members 49, 51 in a transversely spaced relationship with their elongate axis parallel and their articulating surfaces in alignment. The separation of the plateau members 49, 51 is necessary to prevent them from interfering with the cruciate ligament of the knee joint, and the connecting member 57 is positioned adjacent the anterior end 59 of the plateau members 49, 51 so as not itself to cause such interference.

Each plateau member 49, 51 has a longitudinal guide which is co-operable with the femur to maintain the natural configuration of the bones in the joint. In the case of the lateral plateau member 49, 313 this is an abutment surface 63 upstanding perpendicularly from the medial edge of the articulating surface 61 so as to abut the lateral condyle of the femur; and in the case of the medial plateau member 51, the longitudinal guide is an abutment surface 65 upstanding perpendicularly from the lateral edge of the articulating surface 61. so as to abut the medial condyle of the femur. The abutment surfaces 63, 65 each face the articulatinq surface from which they upstana, and are longitudinally convexly curved so as to allow the femur a limited degree of rotation on the tibial prosthesis 15 about a vertical axis as their articulating surfaces coact. The abutment surfaces 63, 65 thus ensure that the articulating surfaces of the femur and the tibial prosthesis coact propertly, and prevent the condyles of the femur from interfering with the cruciate ligament of the knee joint.

The tibial prosthesis 15 has anchoring means for fixedly anchoring the tibial prosthesis 15 to the upper end of the tibia 47. The anchoring means comprises a peg 67 upstanding from an internal surface 69 of each plateau member 49, 51, the peg being substantially adjacent the centre of the internal surface. The peg 67 is for extension into a corresponding cavity 71 in the tibial 47. The pegs 67 are circular in transverse cross section. Also, each peg 67 is tapered toward the distal end thereof to provide a tapered lock with the corresponding cavity 71.

Each peg 67 has a circumferential groove 73 for increasing the fixation thereof. The anchoring means also includes a plurality of channels 75 located in the internal surface 69 of each of the plateau members 49, 51 around each of the pegs 67. Each of the channels 75 preferably includes an undercut portion 77 for increasing the fixation thereof.

The tibial prosthesis of the invention may be used in a tibiofemoral joint in conjunction with a healthy femur, but where the tibia is damaged it is preferably used in conjunction with the femoral prosthesis described and claimed in our aforesaid patent, embodiments of which are shown in Figure 1 to 4 and 10 to 12.

The femoral prosthesis 13 comprises an elongate lateral condyle member 19 and an elongate medial condyle member 21 for replacing the articulating surfaces of the lateral condyle 23 and the medial condyle 25 of the femur 17. The articulating surface 29 of each condyle member 19,21 is substantially the same shape as the normal articulating surface of each condyle 23, 25 of the femur 17. More specifically, the articulating surface of each condyle member 19, 21 is a convex polycentric curve. The femoral prosthesis 13 also comprises a connecting member 27 for fixedly connecting the lateral and medial condyle members 19,21 together in a transversely spaced relationship to maintain perfect alignment therebetween and to prevent the condyle members 19, 21 from interfering with the cruciate ligament of the knee joint. The connecting member 27 holds the condyle members 19, 21 apart a distance equal to the natural separation of the condyles 23, 25 of the femur 17. The connecting member 27 is recessed from the articulating surface 29 of each of the condyle members 19, 21 and is positioned adjacent the anterior end 31 of each of the condyle members 19, 21 so as not to interfere with the cruciate ligament of the knee joint and to allow full extension of the knee. The anterior side 33 of the connecting member 27 is concave as it 13 extends between the lateral and medial condyle members 19, 21 for preventing the femoral component 13 from interfering with the patella of the knee joint.

The femoral prosthesis 13 has anchoring means for fixedly anchoring the femoral prosthesis 13 to the lower end of the femur 17. The internal surface 37 of each of the condyle members 19,21 consists of a substantially planar anterior portion and a longitudinally concavely curved posterior portion there being a peg 35 upstanding from the anterior portion of each of the condyle members 19, 21, for extending into a corresponding cavity 39 in the condyles 23, 25 of the femur 17.

The pegs 35 are preferably square in transverse cross section, and are tapered towards the distal end thereof to provide a taper lock fit with the corresponding cavity 39. A plurality of grooves 41 are provided in and around each peg 35 for increasing the fixation thereof. The anchoring means also includes a plurality of grooves 43 extending across the inward face 37 of each of the condyle members 19, 21, adjacent the posterior ends 45 thereof.

The femoral prosthesis 13 is preferably a one-piece construction composed of a metallic material such as stainless steel or chromium cobalt alloy. The tibial prosthesis 15 of the invention is preferably a one-piece construction composed of a plastics material, which is most preferably an ultra-high molecular weight polyethylene. It should be noted that each peg 67 of the tibial prosthesis 15 is preferably provided with a marker 79 of stainless steel or chromium cobalt alloy wire or the like to provide an accurate reference for radiographic determination of position and wear rates of the tibial prosthesis 15.

The replacement of the articulating surfaces of the tibio-femoral joint with the tibial prosthesis 15 of the present invention, and the femoral prosthesis 13 will now be described. An incision is first made to allow access to the lower end of the femur 17 and the upper end of the tibia 47 by means and methods well know to those skilled in the art. The lateral and medial plateaux 53, 55 of the tibia 47 are then contoured by well known means to propertly accommodate the tibial prosthesis 15. Next, the lateral and medial condyles 23, 25 of the femur 17 are contoured by well known means to property accommodate the femoral prosthesis 13 taking into account any varus or valgus deformities, flexion contacture or hyper-extension of the tibiofemoral joint. The tibial prosthesis 15 is then fixedly anchored to the upper end of the tibia 47 with the aid of a typical bone cement well known to those skilled in the art. The bone cement coacts with the pegs 67, circumferential grooves 73, channels 75 and undercut portions 77 to fixedly anchor the tibial prosthesis 15 to the upper end of the tibia 47. Next, the femoral prosthesis 13 is fixedly anchored to the lower end of the femur 17 with the aid of bone cement.

The bone cement coacts with the pegs 35 and the grooves 41 formed 2i therein, and the grooves 43 to fixedly anchor the femoral prosthesis 13 to the lower end of the femur 17. It should be noted that the grooves 43 help prevent excess cement from escaping from between the femoral prosthesis 13 and the femur 17 as the femoral prosthesis 13 is being anchored to the femur 17. The incision is then closed in the manner well known to those skilled in the art.

Claims (11)

1. A tibial prosthesis for a tibio-fen»ral joint, which prosthesis comprises an elongate lateral plateau member and an elongate medial plateau member, each plateau member having an articulating surface for replacement of the corresponding articulating surface of the tibia and a longitudinal guide co-operable with the femur to maintain the natural configuration of the bones in the joint, a connecting member fixedly attached to and extending between the one ends of the plateau members so as to maintain the plateau members in a transversely spaced relationship with their elongate axes parallel and with their articulating surfaces in alignment, and means for anchoring the prosthesis to the upper end of the tibia adjacent the femur with the one ends of the plateau members positioned towards the anterior portion of the joint.

2. A tibial prosthesis as claimed in Claim 1, in which the articulating surfaces are substantially planar.

3. A tibial prosthesis as claimed in either Claim 1 or Claim 2, in which the longitudinal guide on each plateau member comprises a longitudinally convexly curved abutment surface facing the articulating surface, the abutment surface of the lateral plateau member upstanding perpendicularly from the medial elongate edge thereof and the abutment surface of the medial plateau member upstanding perpendicularly from the lateral elongate edge thereof.

4. A tibial prosthesis as claimed in any of Claims 1 to 3, in which the anchoring means comprises one or more pegs upstanding from each plateau member on an internal surface thereof facing the tibia when the prosthesis is anchored to the tibia.

5. A tibial prosthesis as claimed in Claim 4, in which the pegs are circular in cross-section and are tapered inwardly towards the distal end.

6. A tibial prosthesis as claimed in either Claim 4 or Claim 5, in Which there are one or more grooves formed in and around each peg.

7. A tibial prosthesis as claimed in any of Claims 4 to 6, in which the anchoring means also comprises one or more channels formed in the internal surface of each plateau member around each peg.

8. A tibial prosthesis as claimed in Claim 7, in which each channel is undercut.

9. A tibial prosthesis as claimed in any of Claims 1 to 8, and formed of a plastics material.

10. A tibial prosthesis as claimed in Claim 9, in which the plastics material is a high molecular weight polyethylene.

11. A tibial prosthesis as claimed in Claim 1, and substantially as described hereinbefore with reference to Figures 5, 6 and 7 or Figure 8.