FR2777453A1 - Complete knee prosthesis - Google Patents

Abstract

The prosthesis consists of a spherical component with two sliding condyle spherical surfaces (4, 5), a trochlea, and an extension locking member, and a tibial component with seats (8, 9) for the spherical surfaces and a locking surface opposite the locking member. The two components are joined by lugs (10, 11) which represent the joint's ligaments, and the axis of the joint passes through the centres of the spherical surfaced elements, is aligned exactly with the actual anatomical position and is perpendicular to the femoral diaphysis axis (2).

Description

The design, but also the implementation, therefore the immobilization of a

  knee prosthesis causes difficulties. Some of these difficulties are linked to the very principle of operation of the knee joint, others to the means used to immobilize the prosthesis, to these are added other difficulties linked to the materials used ( toxicity, wear, corrosion) playing on the reliability of the prosthesis, without forgetting also the eternal

financial problem.

  April 1995, I wrote a simple and rational operating principle of the knee joint based on a single axis obtained on two flexible seats, the menisci; principle that I strive to have recognized. This work allowed me to bring out three essential criteria that it is imperative to respect for the proper functioning of a knee prosthesis; criteria that can quickly accelerate a

  loosening if they are not respected.

  Then, I read a book on biomechanics:

ORTHOPEDIC BIOMECHANICS

  Under the supervision of D. POITOUT - Edition Masson I condense certain chapters and paragraphs as follows:

  Many studies have been done on biomaterials.

  * Metallic biomaterials, metals, alloys ... bringing out impurities, hardening, brittleness, corrosion, diffusion, toxicity ... Heat treatments lead to important phenomena such as restoration, recrystallization, polygonization, aging. * CAD / CAM in orthopedics - CAD: Computer Aided Design - CAM: Computer Aided Manufacturing From a three-dimensional image the prospects for the future are numerous. Thus, the existence of CAD / CAM in orthopedics is certain and becomes essential for

positive results.

  -2- As in all areas, money remains the essential brake. Even if the cost of this process remains higher than the other solutions, the advantages which it is possible to draw from it (rational operation, reliability, therefore lifespan) largely compensate. ò Ceramics and metal-ceramic, colonisable ceramics, glass and vitroceramics, composites. * Fixation by bone colonization, bone-bioverre connection,

  bioactive bone-vitroceramic bond.

  Direct inking for prostheses is therefore to be retained.

  * Carbon composites L. SEDEL, professor at the University of Paris Lariboisière, wrote a conclusion entitled: prospects for the future of new materials, which shows that the association of certain materials between them can be promising. Association allowing the use of different properties, for example flexibility of one ally

to the resistance of another.

  The prospects for these studies remain promising, but if certain difficulties are overcome, it appears that with the materials currently used a shadow remains; wear often linked to corrosion, itself linked to the environment. It's always possible to imagine being able to master

  in the future bone and cartilage reconstruction ...

  In the meantime, there are still reliable solutions. The wear can be countered by processes widely used for a long time, corrosion due to the ambient environment also, several solutions are possible, more solutions allowing to recreate a hinge axis allowing the

  almost perfect replica of natural reality.

  Certain conclusions drawn from observations highlight the wear problems for metal-polyethylene, improvement with polyethylene ceramic or ceramic ceramic, alumina

  for spheres rubbing on polyethylene seat ...

  The present invention relates to a total knee prosthesis. I applied myself to recreate reality while taking into account the three criteria previously mentioned and which are: 1-precise positioning of the articulation axis 2-suppression of the moment of inertia generated by the tibia-femur angle (angle of Valgus) during movement (walking, running) this action with the essential aim of avoiding rotational stresses in one direction and then in the other at each step; repetitive stresses that eventually cause loosening and the like

additional wear trouble.

  3-precise positioning of the trochlea relative to the patella, therefore to the insertion of the patella so that the pressure exerted by the patella is distributed harmoniously on both sides of the trochlea, because an imbalance automatically causes stresses

harmful, among others in rotation.

  The drawings for a left knee.

  The prosthesis is made up of two elements.

  * Plate 1/4 - figure 1 - rear view of the femoral element which reconstructs the base of the femur; dotted on

real contour of the condyles.

  * figure 2 - top view of this element.

  * Figure 3 - rear view of the tibial element, again in

  dotted the real contour of the tibial plateau.

  * figure 4 - top view of this element.

  Taking into account the criteria already mentioned, among other things the elimination of the moment of inertia created by the angle of Valgus (see operating mode written in 1995), it is appropriate in the design and the very manufacture of these two elements to make disappear this angle. For this, it suffices to locate the axis of articulation 1 perpendicular to the diaphyseal axis 2 of the femur and the tibia 3. (Diaphyseal axes in

their whole).

  Thus axes 2 and 3 will be one, the mechanical axis of the lower limb will be slightly displaced inward at the knee, and the angle of this axis with the axis of the femur

  and the tibia will then be very slightly reduced.

  Each element reproduces the natural elements.

  - The femoral element reproduces the two condyles (see operating principle that I wrote), namely two large portions of spheres, 4 for the external, 5 for the internal, but the axis of articulation being found perpendicular at the diaphyseal axis the two portions of spheres will be of an identical diameter, slightly smaller

  so to dotted reality.

  The connection with the femur will be done by a tenon 6 whose characteristics will have to respond either to a bone colonization, or to a direct inking (process of mechanical type or chemical type) for that the choice of materials will have to be made. Figure 1 - the post 6 is designed to

  bone colonization in the grooves 7.

  Depending on the anchoring mode chosen, it is possible to use the most suitable material, just as it is possible in the event of insufficient army resistance internally for the part concerned. In this field studies and tests have been made and the conclusions of these

  research offers optimistic perspectives.

  - The tibial element, Figure 3 rear view and Figure 4 top view, reproduces the tibial plateau; it is a cap which covers the tibial plateau, no machining to be done, and which has on its upper rear part the two seats S and

  9 which will receive the portions of spheres or sliding surfaces corresponding to the condyles.

  -5 - Two "ears" 10 and 11 ensure, at the level of the articulation axis, the connection with the femoral element, again

  the material will be chosen correctly.

  After this simple presentation, before giving a

  precise description, it seems to me necessary to insist on

  the means to be put in place to obtain an impeccable design and manufacture for a result close to

perfection.

  - The tibial cap element, like the femoral element, especially the S-post, requires great precision in shape and size, which can be obtained using a particular technique, that of CAD / CAM.

  (Computer Aided Design and Manufacturing).

  By working on three-dimensional images everything is still possible, we must give ourselves the means, and in this case I believe that giving a real meaning to life to a disabled person deserves more sacrifices than many

other optics.

  * Plate 2/4 - figure 5 from the front and figure 6 from the side

  show the two elements in the operating position.

  The condyles 4 and 5 take place in their cavity, their respective seats 8 and 9, cavity, seats made of wear-resistant material, for example polypropylene, etc. (in the grid in Figures 4, 5 and 6). These two cavities which are the very seats of the articulation can be mounted by simple fitting in a cavity provided in the tibial element, a stud 12, FIGS. 5 and 6 in the mass, situated in the bottom immobilizes the seat in position and authorizes its replacement without great difficulty in the event of significant wear. -6- The connection between the femoral and tibial element is done by means of the "ears" 10 and 11 figure 3 and of a reported axis. For the axis, different assemblies are possible, the axis crosses the portions of spheres 4 and 5 (by their center of course) as well as the ears, it has on one side a head, on the other side immobilization Made by

clips, lock pin or nut.

  In the drawing - Figure 5 - on each side an attached axis 13 is aimed and locked on each portion of the sphere. They include a large head with hollow blocking imprint, an articulation portion, or a simple added spacer, and the threaded rod, a friction washer 14 is interposed. The ear bore will be downward ovalized 15 to

  prevent and monitor seat wear.

  The "ears" 10 and H represent in reality the function of the cruciate ligaments and the lateral ligaments, they could be simple artificial ligaments. For example, in Figure 6, the inner ear 11, the front band A in dark represents the internal lateral and the rear band in dark also, the posterior crusader (LCP). For more resistance these two elements united in the mass as

  shown in the figures is more rational.

  - The tibial element by its underside reproduces the exact profile of the tibial plateau, therefore requires the use of CAD / CAM, and is therefore positioned automatically without machining on it; the very profile of the plateau (glenoid cavities and tibial spines) already ensures a fairly large positioning and stability which will be increased by a rim which "capsizes" the periphery of the tibial plateau and in addition two long wings 16 descend on the lateral parts of the tibia , the immobilizations will then be made by screws along the axis 17. -7- Two notches, one before it figure 4 - top view ensures the passage of the patellar, a rear notch 11, the passage of the rear bundle (twin tendons, ischial muscles

crow's feet).

  - The femoral element is fixed using the

tenon 6.

  To meet the requirements of direct anchoring, the manufacture of this post will require great precision in order to ensure intimate contact between the material and the wall of the medullary canal in order to facilitate the connection between the implant and the bone, hence the need there again to apply

new CAD / CAM techniques.

  This process seems positive to me because by the very shape of the medullary canal, slightly conical at the start along a longitudinal and oval plane in its section, it already ensures positioning and immobilization in rotation, moreover the cutting section of the femur also ensures a support base which against the effects of the conical fitting, hence once again the need for precision in order to ensure the nesting which positions perfectly without risk of

  stress causing bursting.

  The base of the prosthesis 20 receiving the support of the cut of the femur may have a collar which traps the outside of the femur on its periphery, or more simply four portions of collar 21 helping with positioning while pinching the bone mass and causing an anti-rotation action at the hollow of the primers of the condyle departures which must be

  reproduced on the support of prosthesis 22 - figure 2.

  We note that with the means that it is possible to

  implementing such prowess is achievable.

  -8- The femoral element in its upper posterior part will have a notch 23 receiving the posterior zone of the tibial element in order to ensure sufficient flexion, 140 in FIG. 6. In its base anterior part, in front of the sliding zones 4 and 5, a flap 24 comes into contact

  with the front surface of the tibial element 25.

  To block the extension in its normal maximum, one or two buffer zones, attached flexible elements 26 - Figure 4 top view - allowing to absorb the small contact shock, the thickness being able to be modulated without difficulty according to flexibility of the pads. In reality, these flat surfaces are curves which generate a progressive damping which can cause a tiny displacement on strong to violent constraints, corresponding

deformation of the menisci.

  The trochlea will be reproduced in the diaphyseal axis.

  - The surgeon will have to determine with precision the level of the cut of the femur in order to determine the height to be given to the replacement femoral element and to the thickness of the tibial element. Cut level determined by the height of the insertions on the posterior surface of the femur and by the size of the tibial plateau 23, but the lower the cut, the closer it will be to the axis of articulation and the better the stability at the level of the femur implant connection. It will also be necessary to determine the length of the post 6 according to the material used and the method of anchoring as well as the weight of the person / Tedious work for a result bringing a lot

satisfaction to all.

  -9- The choice of materials: resistance to compression and wear for the femoral element, the post responding to

anchor requirements.

  A certain elasticity for the tibial element linked to a high tensile strength flexion torsion. And an

  certain flexibility for the seats themselves.

  All specialists must provide assistance, surgeons, manufacturers, IT specialists. Because with a choice

  judicious materials it is possible to reproduce the knee joint with great fidelity.

  By recreating seats as flexible as the menisci (see operating principle that I wrote, as well as the many arguments that I presented) we can find the same behaviors

  with such a prosthesis as a normal joint in the face of the various stresses that it undergoes at all times.

  I would add again with insistence that the great rigidity obtained with a well-designed single-axis prosthesis has nothing harmful, nothing handicaping, on the contrary, to convince I would remind (as I have been trying to do since 25 1995) that multiple small all-round displacements that can be observed between a tibial plateau and

  the condyles are only the result of the deformations that menisci undergo under stress (very simply, deformations equal to 30 displacements).

  These deformations are only possible thanks to the flexibility of the menisci and that this flexibility has for essential objective the protection of the cartilages! - 10- With a prosthesis there is no more cartilage to protect, therefore greater rigidity is not incompatible, all the more so when the moment of inertia due to the angle of Valgus has been eliminated . On a healthy joint the effects of this moment of inertia are also absorbed by the menisci without forgetting that the patella of

  hip offers huge cushioning possibilities

  sement in all directions which largely compensate ... just as it is easy to pivot on a heel a tiptoe without creating great constraints

  on the prosthesis (the other leg is still there). And finally, from the age of fifty, the stresses that are put on a joint are lower15 than during the good years of youth ...

  From this first presentation and from the very principle of operation, it is possible to modify the profile

  even sliding surfaces as we please.

  * For example - 3/4 board - the portions of spheres can be replaced by a simple roller 27

  receiving in the middle the imprint of the trochlea.

  The design, assembly and materials remain the same as before.

  This profile could be in W, the two low points representing the condyles, the inverted V of the middle the trochlea. But for even more ease, that is to say to further reduce wear and tear, the oxidation of certain materials, as well as produce less effort for a simple extension flexion maneuver, it is possible to replace the

  sliding surfaces by rolling surfaces while retaining the same original articulation axis.

  * Plate 4/4 - the establishment and immobilization of

  femoral and tibial elements remain unchanged.

  The basic criteria are also respected, axis of articulation perpendicular to the diaphyseal axis, as well as its original position. Only a modification of the design of these elements at the level of the articulation axis

is operated.

  - The portions of spheres 4 and 5 - plate 1/4 and 2/4 -

  are each replaced by a cavity receiving a pin 23 and 29 board 4/4 - Figures 9 and 10 - belonging to the tibial element and in which a bearing will be mounted

waterproof needle.

  Figure 9 - partial section S seen from the outer needle bearing. The outer cage 30 of the bearing is fitted (different methods can be used, flange on one side, clips on the other ...) in a corresponding bore made in the lug 29,. the axis 31 passes through the femoral element, in FIG. 9, blind hole on the inner side and on the outer face, a clip 32 ensures its immobilization. The lateral positioning can be ensured by two spacers 33 on the axis on either side of the bearing; the tightness of the two bearings being ensured by a SPI or lip seal

and other.

  It remains to know the reliability of needle roller bearings constrained to a particular work of going and returning according to a fairly regular arc of a circular angle (amplitude of the steps for example, or sitting upright). Because if this reliability simply doubles the lifespan compared to a prosthesis using sliding surfaces the interest

is indisputable.

  And why not consider replacing the sliding surfaces of the condyles only while keeping the trochlea intact. The reported sliding surfaces are articulated on the tibial element; or alternatively replace the sliding strips with treads as I have already presented it (Patent 96/05744); treads that can be fitted on the tibial hood element. - 12-

Claims (5)

  1) Total knee prosthesis characterized in that it consists of two elements faithfully reproducing the knee joint: - A femoral element reproducing the sliding surfaces of the condyles, two portions of spheres 4 and, the trochlea, without forgetting a blocking surface extension (24, 25, 26).   - A tibial element reproducing the seats 8 and S of the sliding surfaces, seats receiving the portions of spheres 4 and 5; this element has an extension blocking surface (24, 25, 26).   corresponding surface of the femoral component.   2) Total knee prosthesis according to claim 1 characterized in that the connection between the femoral element and the tibial element is via two "ears" l and II which are only the associated reproduction of the ligaments crusaders and lateral ligaments.   3) Total knee prosthesis according to claim 1 characterized in that the articulation axis 1, single axis of flexion 'extension passing through the center of the two portions of sphere 4 and 5, is located exactly in its anatomical position real and is   perpendicular to the diaphyseal axis of the femur. 2.   4) Total knee prosthesis according to claim 1 characterized in that the articulation axis 1 on the tibial element is also perpendicular to the axis tibial diaphyseal 3.   ) Total knee prosthesis according to claims 3 and 4   characterized by the fact that the diaphyseal axis of the femur and the tibia are one, thus eliminating   35. voluntarily the angle of Valgus.   6) Total knee prosthesis according to claim 1 characterized in that the positioning of the element - 13 -   tibial is achieved by its seat base to the imprint of the tibial plateau that it will cap like a cap, and immobilization by two "wings" 16, the positioning and immobilization of the femoral element being achieved by a post 6 at the exact imprint of the medial canal of the femur   (post which will meet the requirements of direct anchoring).