Complete Knee Prothesis

Abstract

This prothetic device for replacing the articulation of a human knee comprises two elements adapted to be inserted the one into the femur and the other into the tibia, the femoral element having a female articulation portion adapted to be engaged by the male articulation portion of the tibial element so as to retain the latter, the male portion being releasably engageable into the female portion only when the two elements are disposed substantially at right angles to each other ; the design is such that a certain locking action is obtained in the fully stretched leg position and that during the flexion movement a certain degree of lateral movement is allowed.

Description

BACKGROUND OF THE INVENTION:

1. Field of the Invention:

This invention relates to a novel complete prosthesis of the knee or, in other words, a prosthetics device for replacing completely the articulation of a human knee either diseased or wounded, for example as a consequence of an accident.

This device is based on the principle that movement of articulated objects which has the maximum amplitude and constitutes the nearest approach to perfection, that is, a movement that can take place in all directions, is the movement obtained by combining a solid sphere with hollow sphere the latter being rotatably fitted in the solid sphere.

2. Description of the Prior Art:

In the human skeleton this universal movement is obtained more or less completely in two joints : the hip articulation and the shoulder articulation, wherein the joint surfaces in mutual contact are com-parable to those of spherical segments. In prosthetics, consequently, when the problem to be solved consisted in making artificial joints or articulations, for example of plastic or metal, a relatively simple solution was found for the hip. In fact, it was only necessary to obtain the mutual engagement of two spherical segments, i.e., a hollow spherical segments secured to the hip-bone, as a substitute for the cotyle, and a solid spherical segment secured by means of a rod to the diaphysis as a substitute for the femoral apophysis.

The problem with which praticians were confronted consisted essentially in fastening an inert material to a living bone. At present this problem appears to be solved satisfactorily due to the use of acrylic cement (methyl methacrylate).

However, the making of prostheses for the other joints, notably in the case of human knees, is much more complicated. From the onset, when we observe the mode of operation of a knee, it apparently makes only flexure and extension movements about an axis. Therefore, the prosthesis solution seemed rather simple : only a hinge was required, i.e., a means permitting a movement of revolution. Thus, nearly all knee prostheses made up to now were based on this easy principle.

Yet, what occurs during a knee movement? If we observe the flexure extension movement of the knee, we see that from the stretched position a small movement of revolution obviously takes place initially, which does not exceed 10.degree. about a point, whereafter the tibia moves backwards little by little while rotating about a point also undergoing a backward movement, whereby each point taken individually has a different radius or curvature with respect to the preceding point. If we trace the loci of the centres of rotation, we see that they form or describe a line which not only moves backwards and downwards but has radii of decreasing lengths in the backward direction, so as to describe a spiral curve.

The joint bony surfaces of femoral condyles describe in the fore-and-aft direction (logarithmic) spiral paths which guide the movement. As to the tibial plates, in the fore-and-aft direction they are slightly convex (they should be concave to accommodate the antero-posterior condylian camber ; therefore, they slide and pitch). But in the transverse direction, they are concave to meet the requirements of the transverse convexity of the femoral condyles.

From the foregoing it will be seen that this compound movement is far from the simple movement of revolution, i.e., a circular movement about a point, but in addition and simultaneously with this compound movement a torsional movement takes place which is guided by the length of the internal condyle which is greater than the length of the external condyle. It is this last-mentioned movement that causes the leg to loose in flexion the abduction, the valgum it had in the extended position.

Moreover, if in the fully stretched position the knee is rigid, as it bends it can make slight lateral movements and torsional movements, which can take place due to the transverse contour or configuration of the joint surfaces (the femoral condyles are strongly convex in the transverse direction, especially the external one, and the tibial plates are concave transversely and rise at their intermediate portion on the peripheries of the spines of which the abutment function is of primary importance). This movement is a kind of "rolling" movement.

To summarize the movements taking place during the flexion extension of the human knee, one could say that in the antero-posterior direction there is a "pitch" movement and in the transverse direction a "rolling" movement. The words "pitch" and "rolling" give a clear definition of the system of movements performed by the knee articulation.

But what matters most is the manner in which this movement is utilized when walking : the important fact is that the bearing phase of the step occurs substantially without any flexion. When a person is walking and the bearing phase begins, the limb engages the ground ahead, in a fully stretched position, or if not fully stretched, it assumes this position immediately when the plantar bearing is complete, whereafter the other limb bends its knee and moves forward while the bearing limb keeps its knee stretched and oscillates about the hip. During this phase, the knee is stiff, tensioned and the limb oscillates. When the limb under consideration becomes posterior, the bearing engage-ment is relieved, the knee is bent to permit the lifting of the foot which is then thrown forwards, and the same cycle is resu-med. Under these conditions it may be said that in the really dynamic phase of walking the knee is not bent and when it is bent it does not bear anymore. Therefore, the knee strength is required only in the stretched position. To make walking more comfortable it is even useful that the bent knee has a certain laxity. Now a hinge, due to its rigidity in all positions, cannot conform to these various notions.

SUMMARY OF THE INVENTION:

The improved knee prosthesis described hereinafter is designed for meeting these various imperative requirements by attempting to produce voluntary movements of the two types as explained in the foregoing.

Nature made this achievement through a complex play, thanks to the perfection potentialities governing all its constructions. Yet, a close approach of this complex play may be obtained through the prosthetic technique.

By way of preliminary explanation, let us consider firstly what takes place in a hip, while bearing in mind the mechanical system obtained by having a solid sphere movably housed in a hollow sphere and provided with a rod (the femoral apophysis carried by the diaphysal line).

This femoral sphere is movable in all directions in the fixed iliac spherical segment. This system permits a 360.degree. movement in all directions and about all axes.

The most logical method for measuring these movements consists apparently in expressing the data in latitudes and longitudes. In the language of space mechanics, assuming that the femoral apophysis consists of the centre thereof, and that the femur of thigh bone or lower limb is one of the radii extending from this center, it is an easy matter to measure all the movements as a functions of the latitudes and longitudes. Thus, for instance, all of the flexion movements are expressed in latitudes and all the lateral movements in longitudes. The only requirement is to take from the onset two axes of origin or references axes.

The novel prosthesis of the knee according to this invention is based accordingly on the principle of the spherical movement or ball-joint, but within accurately defined limits : very extensive latitudes, beyond 90.degree., but very limited longitudes, for example 10.degree.. These 10.degree. will correspond to the necessary "rolling" movement, the latitude reproducing the "pitch" movement.

In actual practice, this novel prosthesis is obtained as follows : in its essential structure it comprises a pair of relatively small generally hemispherical portions i.e., a movable solid spherical portion rolling in a fixed hollow spherical portion. The solid spherical member has a cylindrical extension and the hollow spherical member consists of a perfect sphere, therefore greater than the male solid spherical member. To approach the pitch movement and the rolling movement, the following solutions are applied : in the case of the pitch movement, the solid spherical member in its vertical position, as the leg is bent, slides at the same time backwards because the cavity containing this solid spherical member is spherical and therefore greater, so that as the flexion takes place the member recedes slightly, thus simulating the rolling and sliding movement (pitch). Regarding the rolling movement, it is obtained as follows : in the fully stretched position, the male member is locked in an antero-posterior cavity the shape of which constitutes an important factor and may be defined as being trapezoidal instead of rectangular. The minor base of the trapeze is at the front and as the ball rolls and recedes, since the groove is trapezoidal, it widens out and lateral movements become possible, inasmuch as the flexion increases : this is the "rolling" movement. From this basic diagram, the prosthetic device of this invention consists essentially of a hollow sphere and a solid sphere pivoting in the former, without any other element, whether bolts or screws. It is only necessary to pivot the two members to each other, they hold by themselves.

The arrangement may be described as follows : the femoral member is the female hollow member ; it has a circular rear aperture having the diameter of the male member. This aperture is such that the male member must be presented in a perpendicular position with respect to said aperture for engaging same. In other words, it can penetrate only in this right-angle position. When it has thus penetrated into the female member, it cannot be removed therefrom, unless said perpendicular relative position is restored, with a tolerance of a few minutes (max. 3 degrees), which cannot occur under normal operating or walking conditions since the stretching apparatus locks the parts together. Therefore, any risk of posterior dislocation is safely precluded.

The male member is the tibial one comprising a shank adapted to be sunk into the tibia ; a plate fitting to the tibial surface with a transverse posterior spur bears on said shank. The essential elements of the tibial prosthesis are disposed there over and consist of a relatively bulky, substantially prismatic pivot member having a trapezoidal configuration with an antero-posterior major side and vertical faces, i.e., a front face and a rear face, and a top face divided into two segments, namely an oblique anterior segment inclined downwards and forwards, connected by an edge to the rear face, for locking the prosthesis in the fully stretched leg position, and a posterior segment carrying the joint member to be described hereinafter, two non-parallel (trapezoidal) lateral faces constituting the guide walls and locking the assembly laterally in the stretched position, said two non-parallel faces permitting and limiting in the flexion position a certain degree of lateral movements.

The pivot member proper projects above this irregular parallelipiped by forming firstly a generally hemispherical cap or portion having its base on the top and connected to a cylindrical segment carrying the other articular generally hemispherical cap or portion constituting the spherical joint portion proper. These two generally hemispherical portions or caps assembled by said cylindrical segment have two different centres, whereby the length of the vertical axis of the assembly is less than the theoretical diameter of the sphere. This constitutes a very important feature of the mechanism to be described presently.

The female member comprises likewise a shank adapted to be sunk into the thigh-bone or femur, and carries thereunder the articular member proper. The latter comprises essentially a spherical cavity having the same radius as the generally hemispherical portions of the male member, said cavity being therefore greater than the male member pivotally fitted therein. Hence the possibility of performing lateral and antero-posterior movements (retroposition in the bent position). Finally, at the bottom, and this constitutes one of the essential features of this prosthesis, the cavity opens into a relatively large trapezoidal recess having an anterior minor base. This recess is of primary importance because it is the key of the holding device of the prosthetic device ; it is capital and holds the complete device ; it replaces all locking and fastening means hitherto contrived in known prostheses. Therefore, it must be carefully studied and fitted with precision.

In the backward and upward direction this curved recess widens out to constitute a cylindrical recess of which the opening diameter is only slightly greater than that of the cylinder of the male member disposed between the two generally hemispherical portions; It is through this cylindrical passage, having its aperture in the vertical plane, that the articular tibial head or apophyse which is then retained therein, for as explained in the foregoing, when the angle is + or - 90.degree., it is possible to remove this apophyse from the femur. Considering the leg movement from the fully stretched position and as the knee is bent, there is obtained on the one hand by virtue of this trapezoidal arrangement and on the other hand by means of the sphero-cylindrical combination of the articular surfaces, on the other hand, the possibility of accomplishing lateral (rolling) movements and retroposition (pitch) movements. This system affords a movement approaching that of normal physiology, through an amplitude of 130.degree..

Another advantageous feature characterising the novel prosthesis of this invention lies in the fact that it requires but a minimum bone sacrifice. This is due to the specific operating technique which is as follows :

In practice, no particular difficulty is experienced ; The cut is directed vertically, longitudinally, internally and parallel to the knee-cap, to permit the luxation of the complete extension system outwards. The chief points to be adhered to are :

The surgeon must carefully free the lower end of the femur, including the popliteal surface, a very important factor because it constitutes one of the bearing points of the femoral prosthesis.

The surgeon must then resect all the rear segments of the condyles which projects from the plane of said popliteal surface.

He must then attack the bone in the intercondylian notch, so that all the lateral and anterior portions of the lower end of the femur, notably the femoral trachlea, are left completely untouched. Similarly, the lower portion of the femoral condyles will be resected as little as possible(only a few millimeters).

The surgeon will then prepare the axis of the femoral prosthesis about which he will subsequently dig the recess for the substantially cylindrical (3 to 4 cm in diameter) femoral member. This recess extended at its front portion by the shank channel, is stopped laterally and at the rear by a plane to be engaged by the prosthesis to be fitted into the rear portion of the femur by means of a small vertical stud similar to the tibial one.

Upon completion of this sequence, the surgeon will test the femoral prosthesis to ascertain whether it properly fits in its recess or not.

Preparing the tibial end. After the femoral member has been properly fitted in position, the surgeon may consider the tibial end. The tibial resection in the vertical direction is more important. A piece about one centimeter thick, perhaps slightly more, must be removed from the upper end of the tibia ; the resection depends on the lesions. Sometimes, very important unflateral destructions are observed which make it compulsory to effect more extensive resections. This resection is performed after locating the tibial axis;

Then the surgeon prepares the groove for the pivot by using a drill of variable size. At the rear, at a distance of about 15 mm from this groove, he cuts a small channel to be used as an anchoring means.

When the two members have been fitted separately in position, thesurgeon tests the assembly. To do this, it is only necessary to place the leg at right angle and to introduce the tibial apophysis into the femoral cavity of the prosthesis.

Thus, the preparation is completed ; then all the tools are renewed and the two members are placed in their final positions and sealed with methyl methacryle cement.

From the foregoing it is clear that this invention can be regarded as constituting a prosthetic apparatus acting as a substitute for the human knee, this apparatus being remarkable in that it comprises two elements ; on the one hand, the upper femoral and female member fitted into the thigh-bone and provided with an articular portion having a convex front face and defining internally and behind this face a cavity of spherical contour opening downwards and backwards, and, on the other hand, a lower male tibial element formed at its upper end with an articular portion comprising two opposite generally hemispherical portions or caps interconnected by a cylindrical segment, this male articular portion being engageable only in the above-defined 90.degree. position at 90.degree. into the female femoral element but retained therein in all the other angular position so as to constitute an articulation or joint that cannot be disengaged by itself while permitting the flexion-extension movements as well as a slight lateral movement as required for the joint plays.

This prosthetic apparatus is characterised in general in that the spherical cavity of the femoral articular portion is open at the rear, this aperture forming a circle of same diameter as that of the cylindrical portion of the male tibial articular portion.

According to a specific feature characterising this prosthetic device, the male articular portion comprises a relatively bulky and substantially prismatic pivot element with a trapezoidal base having an antero-posterior side and two vertical faces namely a front face and posterior face, the upper face of this pivot being divided into two segments : namely a front segment extending obliquely downwards and forwards, connected through an edge to the upper face and adapted to lock the device in the fully stretched leg position, and a rear segment carrying the articular portion consisting of a pair of opposite generally hemispherical caps or portions interconnected by a cylindrical segment, the two non-parallel trapezoidal lateral faces of this pivot acting as guide means for locking the joint in the stretched-leg position while permitting and limiting in the bent position the lateral movements of the knee.

According to another feature characterising this prosthetic device the articular piece proper projects above the pivot having the shape of an irregular parallelipiped, and consists of a first generally hemispherical cap connected through a cylindrical segment to another opposite generally hemispherical cap these two caps having the same curvature but different centres so that the vertical axis of the male articular assembly be smaller than the theoretical diameter of the sphere.

According to a further distinguishing feature of this invention, each male and female element carries a projecting plate located on this side of the articulation proper and a rear tongue perpendicular to said plate and adapted to be fitted into the bony portion located behind, in order to ensure a proper anchorage.

According to a complementary feature of this prosthetic device, each one of its two main component elements comprises a shank adapted to be driven into the femoral diaphysis and into the tibial diaphysis, respectively; They are disposed on this side of the male or female articular portion and lie on a common axis, so that the prosthesis can be used for one or the other leg, indifferently. However, they can be inclined slightly, for example by an angle of 5.degree. to 10.degree. (either on the tibial side or on the femoral side), in order to distinguish the right-hand prosthesis from the left-hand one.

The shanks of the two prosthetic elements are engageable into the medullary cavities, respectively, or into cavities specially formed to this end in the patient's femur and tibia.

As already suggested hereinabove, these shanks may advantageously be sealed in their corresponding cavities by using an acrylic cement (such as methyl methacrylate cement).

The walls of the articular members of the prosthetic elements are advantageously lined with thin layers of a suitable and known lubricant such as Teflon, to avoid any seizing.

BRIEF DESCRIPTION OF THE DRAWING:

The diagrammatic drawing attached hereto illustrates a typical form of embodiment of the novel complete prosthesis of the knee according to this invention. In the drawing :

FIG. 1 is a perspective view showing the two main elements of this prosthesis, the upper femoral element and the lower tibial element being seen from the rear and separate from each other to afford a clearer understanding of their relationship ;

FIG. 2 is a similar view of the same elements but in their assembled condition ;

FIG. 3 is a front elevational view of the two elements in the position shown in FIG. 2 ; and

FIG. 4 is a fragmentary sectional view showing the bending or flexion movement of the joint, the section being taken along the line IV--IV of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT:

As illustrated the novel prosthesis of the knee according to this invention comprises two elements : an upper femoral female element 10 provided with an articular portion 11 having a convex front wall 12 providing internally of and behind this wall 12 a cavity 13 having a spherical wall open in the downward and backward directions, and a lower tibial male element 14 formed at its upper end with an articular portion 15 consisting of a pair of opposite generally hemispherical portions or caps 16, 17 interconnected by a cylindrical segment 18. This male articular portion 15 can penetrate into the spherical cavity 13 of femoral element 10 only when the former is presented in a 90-degree angular position with respect to the latter, but it is retained in this cavity in all the other permissible positions, so as to constitute an articulation that cannot be separated while permitting the flexion and stretching movements as well as a slight lateral movement as necessary for normal articulation movements.

The spherical cavity 13 formed in the femoral articular portion 11 is open at the rear and this aperture is of circular configuration as shown at 19 and has the same diameter as that of the cylindrical portion 18 of the male tibial articular portion 15. This male portion 15 comprises a relatively bulky and substantially prismatic pivot having a trapezoidal base 20 with antero-posterior major side and two vertical faces, namely a front face 21 and a rear face 22. The top face of this pivot is divided into two segments, i.e., a front segment inclined downwards and forwards, connected to the front face 21 through an edge and adapted to lock the device in the fully stretched position, and a rear segment carrying the articular portion comprising the pair of opposite generally hemispherical portions or caps 16, 17 interconnected by the cylindrical segment 18. The pair of nonparallel trapezoidal lateral faces of the pivot thus formed act as guide means for locking laterally in the stretched position the patient's leg while permitting and limiting the lateral movements of the knee.

The articular portion 15 projects above the prismatic pivot 20 and comprises the above-mentioned lower generally hemispherical cap 16 connected through a cylindrical segment 18 to the upper generally spherical hemispherical 17, these two generally hemispherical caps having the same curvature but different centres, so that the vertical axis of the male articular assembly thus formed be shorter than the theorectical diameter of the sphere.

Each element 10 and 14 of this prosthesis of the knee carries a projecting plate designated by the reference numerals 23 and 24, respectively, each plate being located on this side of the articulation proper, and a rear tongue 25, 26 extending at right angles to said plate and adapted to be fitted into the bony portion located behind, in order to improve the anchoring action.

The two elements 10, 14 of this prosthesis are provided with shanks 27, 28 adapted to be driven into the femoral diaphysis or into the medullary groove, and into the tibial diaphysis, on this side of the male articular portion 15 or female articular portion 11, respectively.

These shanks 27, 28 of the prosthesis elements are adapted to be fitted into medullary cavities or cavities specially formed in the patient's thigh-bone and tibia. Advantageously, the shanks 27, 28 of elements 10, 14 are sealed in their cavities by means of an acrylic cement (methyl methacrylate).

The walls of the articular portions of the corresponding elements 10, 14 of this prosthesis are advantageously lined with thin layers of a suitable lubricant such as tetrafluorethylene known under the Trademark "TEFLON", to avoid any seizing.

The mode of operation and the specific method of positioning this novel prosthesis in the knee area of the patient has already been explained in detail in the foregoing.

Obviously, the component elements of this prosthesis may be made of any suitable plastic material or metal or stainless alloy as a function of the specific clinical applications and requirements, and it is also clear that the various steps of the operation necessary for fitting this prosthesis, as set forth hereinabove, may be modified without departing from the basic principles of the invention, as will be readily understood by those conversant with the art.

Claims

What is claimed as new is:

1. A prosthetic device for replacing the articulation of a human knee, which comprises two elements, on the one hand an upper female femoral element provided with an articular portion having a convex front wall adapted to carry the human knee ball and forming internally and behind said wall a cavity having a spherical contour opening downwards and backwards and, on the other hand, a lower male tibial element carrying at its upper end an integral articular portion comprising two opposite generally hemispherical portions interconnected by a cylindrical segment, said cavity and male integral articular portion being dimensioned so that said male articular portion is releasably engageable into said female femoral element only when the two elements are disposed at 90.degree. to each other, but remaining locked therein in any other relative angular position in order to constitute an articulation that cannot be released while permitting flexion and extension movements as well as a slight lateral displacement as required for the normal plays of the articulation.

2. A prosthetic device as set forth in claim 1, wherein said spherical cavity of the femoral articular portion is open at the rear through a circle having the same diameter as the cylindrical segment of the male tibial articular portion.

3. Prosthetic device as set forth in claim 2, wherein said male articular portion comprises a relatively bulky pivot of substantially prismatic configuration with a trapezoidal base having antero-posterior major sides and two vertical faces, namely a front face and a rear face, the upper face of said pivot being divided into two segments, that is, a front segment inclined forwards and downwards, connected through an edge to the the front face and adapted to lock the device in the fully stretched position, and a rear segment carrying the articular portion consisting of the pair of opposite generally hemispherical portions interconnected by a cylindrical segment, said base having two lateral non-parallel trapezoidal faces, the two lateral non-parallel trapezoidal faces of said pivot acting as guide means for locking the joint laterally in the stretched-leg position thereof while permitting and limiting the lateral movements of the knee in the flexion position.

4. Prosthetic device as set forth in claim 3, wherein said male articular portion proper projects above said pivot of paralle lipipedic irregular configuration, and consists of a first generally hemispherical portion or cap, connected through a cylindrical segment to another, opposite generally hemispherical portion or cap, these two generally hemispherical portions or caps having the same curvature but different centres, whereby the vertical axis of the male articular assembly be shorter than the theoretical diameter of the sphere.

5. Prosthetic device as set forth in claim 4, wherein each male and female element carries a projecting plate to be located on the side of the articulation proper and a rear tongue extending at right angles to said plate and adapted to be fitted into the bony portion located behind in order to improve the fastening of the corresponding element.

6. Prosthetic device as set forth in claim 5, wherein each element carries an integral shank adapted to be fitted or driven into the femoral diaphysis or medullary groove and into the tibial diaphysis, said shank being disposed on the same side of the male or femal articular portion that said plate is located.

7. Prosthetic device as set forth in claim 1, wherein the walls of the articular portions of said elements are lined with thin layers of a suitable lubricant such as Teflon to prevent the seizing between the interfitting surfaces.