FR2628316A1 - Whole knee prosthesis - has one piece implanted at end of femur, other at end of tibia articulating around cross member of T=piece - Google Patents

Abstract

The total knee prosthesis has one part implanted at the end of the fenum and the other part implanted at the proximal end of the tibia. These two parts are articulate around each other by a horizontal shaft in the front. It comprises a cross piece (51) of a T piece (55) on the tibia part. The femoral part comprises at least two separable parts, i.e. a main body piece (1) and a knee-cap cover (2). The body piece has an elongate section (10,11) in the central medullan fenam cavity and has a head with a pair of openings (15,16) to take the ends of the T-piece. The cap has a convex surface and rests against a plate on the tibia part; being fixed to the head, retaining the T-piece ends and holding the assembly together. ADVANTAGE - Easy surgical implantation and without risk of coming apart.

Description

TOTAL KNEE PROSTHESIS
The present invention relates to a total knee prosthesis, that is to say a prosthesis intended to restore the two articular surfaces of the knee.

 It relates more precisely to a knee prosthesis known as hinged, in which the flexion movement of the knee is controlled by a material axis located in the frontal plane and arranged horizontally.

 This type of prosthesis is generally opposed to prostheses without hinges, known as sliding, which are less stable, because they suppress the anterior cruciate ligament (ACL) and alter the function of the peripheral ligaments, in particular of the popliteal tendon.

Hinged total knee prostheses are described, for example, in patent documents EP-BO 069 683,
EP-AO 194 326, EP-BO 046 926, EP-AO 178 445 and DE-B-2 549 819.

 These prostheses must meet several imperatives which are not always compatible with each other. They must in particular be simple, inexpensive, relatively light, easy to set up by the surgeon, and to remove if necessary. They must, moreover, faithfully ensure the natural movements of the knee, that is to say provide the patient with as physiological a mobility as possible, while ensuring good stability, by preventing abnormal movements.

 The invention more specifically relates to a knee prosthesis which comprises a first so-called femoral part (intended to be implanted in the distal end of the femur) and a second so-called tibial part (intended to be implanted in the proximal part of the tibia) , these two parts being articulated one on the other by means of a horizontal axis located in the frontal plane, this axis constituting the transverse branch of a piece in "T" piece which is integral with the tibial part.

 Such an arrangement offers the advantage of simplicity and solidity; it has already been provided for in the last three above-mentioned documents EP-A-O 178 445, EP-B-O 046 926 and DE-B-2 549 819.

 These known devices however have the drawback that the positioning of the transverse branch of the "T" in the femoral part is difficult; this is done either by hooking, from top to bottom, in the profiled grooves provided in the femoral part, or through a transcondylar femoral tunnel, which requires significant bone sacrifice and an extensive release of muscle and ligament masses in this region ; moreover, in the event of abnormal unexpected movements, a subsequent separation of the two parts cannot be excluded. Finally, when the prosthesis has been put in place, the physiologically natural movements of the knee are rarely respected. When the device provides for knee mobility in the horizontal plane, it is the two compartments of the knee that are mobile, while the physiological knee has a stable internal compartment, only the external compartment being mobile; moreover, this mobility takes place at the expense of a reduction in the stability of the prosthesis in the frontal plane.

 The invention aims to solve these various problems by proposing a total knee prosthesis of the type mentioned which, while being simple and reliable, can be installed easily by the surgeon, without risk of untimely loosening.

Another objective of the invention is to propose a device which makes it possible to restore the various normal movements of the knee, while prohibiting the abnormal movements induced by the ligament sacrifices during the fitting of the prosthesis (LCA and popliteal)
Another objective of the invention is to propose a prosthesis of modular character, so that its shapes and dimensions can be perfectly adapted to the case being treated, in particular to the morphology of the patient, to the diameter of the central medullary canals of the bones, the location of healthy parts. Such a device allows absorption of all the stresses by the bone, made essential because of the inevitable ligament sacrifice (when the prosthesis is put in place).

These various results are achieved, in accordance with the invention, thanks to the fact that the femoral part is composed of at least two separable parts
- a main part which has an elongated rod capable of being implanted in the medullary canal of the femur, and has a head provided with a pair of openings adapted to receive the ends of said transverse branch
- a resurfacing part, with a convex outer surface, shaped to come into abutment against a plate secured to the tibial part, this part being adapted to be fixed to said head of the main part, so as to trap the ends of the transverse branch and thus ensure the retention of the whole.

 In a preferred embodiment, the head has the general shape of a yoke which has two flat internal faces whose mutual spacing corresponds to the diameter of the cylindrical base of the "T" part, so that after assembly the clevis tightly encloses the base, which ensures stability of the knee by allowing to control the abnormal lateral movements of valgus and varus.

 Preferably, the openings which are adapted to receive the ends of said transverse branch are grooves each formed in one of the internal faces of the yoke and each have a section of groove which opens out at the bottom of this face, while the resurfacing part also has the general shape of a yoke and is provided with a pair of fingers capable of being housed in these sections of grooves when this part is fixed to the main part, so as to retain the ends of the 'axis in the grooves, at the same time that they ensure the stability of the resurfacing piece.

 It is easy to understand that thanks to this arrangement, the positioning of the axis in the femoral part is done simply from front to back during the intervention (knee bent at right angles), ie from bottom to top relative to the drawing (Figure 5); fixing by fitting of the resurfacing piece is then done in a similar manner.

 According to an interesting characteristic of the invention, the opening situated on the external side has the form of a lumen, elongated from front to rear (in the sagittal plane), so as to allow pivoting of limited amplitude, of the transverse branch relative to the femoral part, in the direction of rotation outward (external rotation), but also of the femur relative to the tibia, this time inward (internal rotation of the femur), which corresponds to an external rotation of the entire lower limb. It is the elective mobility of the external compartment.

 In # the preferred embodiment of the invention, the resurfacing piece is supported on the tibial plateau by means of two pads, for example made of synthetic material, integral with the latter; these pads are arranged laterally on either side of the "T" piece, and have a concave surface adapted to allow rolling and / or sliding of the convex surface of the resurfacing piece. The external bearing is advantageously movable in a direction perpendicular to the frontal plane, that is to say horizontally in the sagittal plane.

 This arrangement facilitates mobility of the external compartment and reduces friction between the resurfacing piece and the pad during rotational movements of the knee.

Preferably, the femoral part has a modular character and comprises the following three separable elements which can be selected to adapt in size, as exactly as possible, to the femur -treated in order to be anchored therein effectively
- the main room already mentioned
- the resurfacing part also already mentioned
- a proximal end piece, which guides and centers the other two pieces.

Similarly, the tibial part advantageously has a modular character and comprises the following three separable elements, which can be selected to adapt exactly to the treated tibia and to anchor therein effectively
- the tibial plateau already mentioned
- a main part which has an elongated rod capable of being implanted in the central medullary canal of the tibia
- a distal end piece, which guides and centers the other two pieces.

 The assembly of the different elements of the femoral and / or tibial modular parts can be done quite simply, in a manner known per se, by interlocking with cones and using screws.

 Other characteristics and advantages of the invention will appear; - will be from the description and the accompanying drawings which show a preferred embodiment thereof.

On these drawings
- Figure 1 is an exploded view (separate component parts) from the side of the femoral part, cut by its vertical plane of symmetry
- Figure 2 is a left view of Figure 1
- Figure 3 is an exploded side view of the tibial part
- Figure 4 is a left view of Figure 3
- Figure 5 is a detail view showing from the front the articulation of the prosthesis after its implantation, this view corresponding to the broken section plane VV of Figure 6
- Figure 6 is a side view in section of the prosthesis, in the flexion position, the cutting plane being the sagittal plane VI-VI of Figure 5
- Figure 7 is a partial section seen from above along the horizontal plane VlI-VII of Figure 5
- Figures 8 and 8 A are views similar to Figure 7 respectively showing a rotational movement of the tibia outward and the femur inward
FIG. 9 is a top view of the resurfacing part 2 fitted to the femoral part of FIGS. 1 and 2.

 The femoral part shown in FIGS. 1 and 2 has a modular character and is composed of three separable elements, an intermediate or main part 1, a resurfacing part 2 and a proximal end part 3.

 The main part i has a rod composed of a frustoconical part 10. and of a more tapered part also frustoconical or cylindrical 11. This rod is adapted to be implanted in the central medullary canal of the femur, after preparation thereof .

The part 1 has a head 18 which has the general shape of a yoke 14 having, in top view, (with respect to FIG. 1) the general shape of a "U". In the wall of each of the internal faces 17 of the yoke, a groove is formed comprising an upper part 16 and a vertical section 15 which opens at the lower part of this face.

 The proximal end part 3 has a cylindrical shape comprising an end chamfer 32.

 The resurfacing piece 2 has a convex outer surface, composed of two lateral parts corresponding to the condyles of the knee. This part therefore also has the general shape of a "U" clevis, seen from above (see FIG. 9). The space separating the two arcuate lateral parts 20 has been designated by the reference 21, by 23 the posterior zones of the parts 20, and by 22 the front zone, in the form of a curved tongue, of the resurfacing part, corresponding to the zone patella resurfacing.

 It will be noted that the prosthesis shown in FIG. 1 is a left knee prosthesis, the front part being located to the right of FIG. 1.

 The end piece 3 has a frustoconical cavity 30 adapted to receive a cone 12 provided at the proximal end of the intermediate piece 1; moreover, a bore 31 is provided in the part 3 while a tapped hole 120 is provided in the part 1, allowing the assembly and mutual fixing of these two parts using a screw. Similarly, the resurfacing part 2 is provided with a frustoconical prominence 26 capable of being housed in a frustoconical hole 13 formed in the part 1, and a smooth hole 260 as well as a tapped hole 130 are provided respectively in the parts 2 and 1 to allow them to be assembled and fixed to the use. the other by means of a screw.

 On either side of the median space 21, there are provided, on the internal side of the resurfacing part 2, a pair of fingers 24 adapted to be housed in the through groove sections 15 formed in the wings of the yoke 17, when the part 2 is fixed to the part 1.

 The role of these fingers 24 will be explained later.

 The tibial part, shown in FIGS. 3 and 4, also has a modular character and comprises a main part 4, a tibial plate 5 and a distal end part 6.

The main part 4 comprises a base 41, of generally oval shape, as well as a tapered rod 40, slightly frustoconical, the parts 41 and 40 being connected by a connecting part of converging shape 45; the latter has lateral ribs 42
The end piece 6 has a cylindrical part 60 with a rounded end 62, as well as a frustoconical prominence 61 adapted to be housed in a complementary recess 44 formed in the distal end of the part 4; the assembly can be completed using a screw, holes not shown being provided for this purpose in the two parts 4 and 6.

 The tibial plateau 5 comprises a plate 50 whose shape corresponds to that of the base 41 and which has a frustoconical part 54 adapted to be housed in a corresponding recess 43 formed in part 4, allowing the assembly of these two parts , also by interlocking and screwing.

 The plate 50 carries, on its upper face (proximal face), a "T" shaped part 55. The "T" part 55 is arranged in the frontal plane, at the rear part of the plate 50. Its vertical branch is composed of two cylindrical parts: a base 52 whose diameter corresponds to the mutual spacing of the two faces 17 of the yoke constituting the head 18 of the part 1 described above, and a part of smaller diameter # 53. The horizontal branch 51 of the part 55, also cylindrical, is intended to constitute the axis of articulation of the prosthesis, as will be seen below.

 Laterally, on either side of the base 52, are arranged two pads 56, 56 ′ which have an upper face of concave shape capable of serving as a support for the two parts 20 of the resurfacing part 2.

 Advantageously, the external pad 56 is movable in the sagittal plane relative to the tibial plateau 5; for this purpose, a sliding groove can be provided in the plate 50, a groove in which is housed a key 560 provided on the underside of the external cushion 56. The internal cushion 56 'is fixed; it is for example glued to the plate 50.

 The pads 56, 56 'are preferably made of a flexible material with a low coefficient of friction such as polytetrafluoroethylene (PTFE) or polyethylene.

 The other parts making up the femoral and tibial parts can be made of materials commonly used for implants, for example titanium.

 We will now explain, with more specific reference to FIGS. 5 and 6, in what manner the surgeon proceeds with the fitting of the total knee prosthesis which has just been described.

 The surgeon traditionally begins to remove diseased or damaged joint parts from the femur bone (OF) and the tibia bone (OT).

 Then, using a grater, he digs the centromedullary canals of these bones to provide a space for implantation of the prosthesis.

 The surgeon then selects the different parts of the modular femoral and tibial parts so that they correspond as exactly as possible to the patient's morphology and to the shapes and dimensions of the central medullary spaces he has just prepared, so as to allow a good anchoring of the prosthesis.

 It then assembles together, by interlocking and screwing, the selected parts 1 and 3 of the femoral part, and the selected parts 6 and 4 of the tibial part, then implants them respectively in the femur and in the tibia. This implantation can be done without cement, because the shapes and dimensions of the implanted parts correspond exactly to their housing.

 The head 18 of the main femoral part 1 is positioned in the inter-condylar cavity, and the part 5 is fixed to the part 4.

 Then, the surgeon brings the tibial part closer to the femoral part, by introducing the ends of the transverse branch 51 into the two side lateral grooves 15 of the part 1, so that the ends of the branch 51 abut in the grooves 16. The surgeon then fixes the resurfacing part 2 on the part 1, by interlocking and screwing, the fingers 24 coming to be housed in the grooves 15 and thus trapping the ends of the branch 51. At the same time, the base 52 of the "T" piece 55 is received between the two faces 17 of the yoke 14, while the lateral surfaces 20 of the resurfacing piece 2, forming condyles, have come to bear against the lateral pads 56, 56 ', forming menisci.

 The prosthesis is then properly implanted, the femoral and tibial parts being connected to each other by means of the transverse branch 51 forming a hinge axis.

 As seen on examining FIGS. 7, 8 and 8 A, the groove 16 ′, located on the internal side of the prosthesis, has a circular shape, with a diameter slightly greater than that of the branch 51 forming a hinge axis ; on the other hand, the groove 16, located on the external side, has the form of an elongated lumen (see also Figure 1).

 Thanks to this arrangement, the knee has a certain mobility on the external side, the tibia being able to pivot by a certain angle, preferably of the order of 150 towards the outside (arrow F, FIG. 8). It is the same for the femur which can rotate inward, which corresponds to an external rotation of the entire lower limb (arrow G, Figure 8 A). This corresponds to the physiological kinematics of the knee.

 As can be seen in the observation of FIG. 6, the axis 51 is positioned so as to be substantially further back with respect to the axis XX 'of the femur than with respect to the axis YY' of the tibia.

This location corresponds to a more natural flexion of the knee.

During the bending movement, represented in FIG. 6, the resurfacing part 2 rolls and slides by its convex external face 20 on the bearings 56, 56 ′, the external bearing 56 being able, moreover, to move slightly by sliding in the sagittal plane, during flexion or rotation movements.

 At any time, the abnormal movements of the knee are controlled, in particular the movements of varus and valgus, because the internal faces 17 of the yoke 14 very tightly enclose the cylindrical base 52 of the "T" part 55. Thus, any unexpected movement of the tibia relative to the femur in the frontal plane is made impossible.

 Thanks to the modular nature of the prosthesis, one obtains a perfectly stable anchoring thereof in the bone support. Due to the fact that the axis of the prosthesis is very posterior, this prosthesis ensures normal flexion, while controlling the hyper extension of the knee. It allows elective mobility of the external compartment of the knee in the horizontal plane while controlling the stability of the internal compartment; it thus reduces the stresses in the horizontal rotary plane and allows the normal play of the extensor apparatus, whose role is essential in the active stability of the knee.

 The stability of the articulation system is ensured in the three planes of space thanks to the monobloc axis 55 in the shape of a "T" which is articulated in the inter-condylar femoral part 1; the control of abnormal movements in the frontal plane (varus and valgus) is rigorously controlled, regardless of the degree of knee flexion.

 This prosthesis can be perfectly adapted to the endomedullary anatomy of the lower end of the femur and the upper end of the tibia, thanks to its modular character; moreover, this modular character allows the implantation of the cementless prosthesis and ensures a transmission and a harmonious absorption of the stresses on the bone cortices avoiding the zones of hyperpressure (sources of pain :) as well as the zones of hypopressure ( sources of bone fragility).

 By design, which provides an attached resurfacing piece, the assembly of the prosthesis during the surgical intervention, that is to say the establishment of the hinge pin and its retention, is are relatively easy for the surgeon.

 Finally, because the prosthesis can be placed without cement, it can be easily removed in the event of recovery.

Claims (9)

 1. Total knee prosthesis, which includes a first part - called femoral - intended to be implanted in the distal end of the femur, and a second part - called tibial - intended to  be implanted in the proximal end of the tibia, these two parts being articulated to each other by means of a horizontal axis, located in the frontal plane, which constitutes the transverse branch  (51) of a “T” part (55) integral with said tibial part, characterized in that the femoral part is composed of at least two separable parts  - a main part (1) which has a rod (10-11), of elongated shape, capable of being implanted in the central medullary canal of the femur, and has a head (18) provided with a pair of openings ( 15, 16) adapted to receive the ends of said transverse branch (51)  - a resurfacing piece (2), with a convex outer surface, shaped to come into abutment against a plate (5) integral with the tibial part, this piece (2) being adapted to be fixed to said head (18) so as to trap the ends of the transverse branch (51) there and secure the assembly.  2. Prosthesis according to claim 1, characterized in that the head (18) has the general shape of a yoke (14) which has two flat internal faces (17) whose mutual spacing corresponds to the diameter of the cylindrical base ( 52) of said "T" piece (55), so that after assembly, the yoke (14) tightly encloses the base (52), which ensures the stability of the knee by allowing the abnormal lateral movements of the valgus to be controlled and varus.  3. Prosthesis according to claim 2, characterized in that the openings (15, 16-16 ') adapted to receive the ends of said transverse branch (51) are grooves each formed in one of the internal faces (17) of said yoke (14) and each have a section (15) which opens at the bottom of this face, while the resurfacing piece (2) also has the general shape of a yoke and is provided with a pair of fingers (24) able to be housed in the groove sections (15) when this part (2) is fixed to the main part (1), so as to retain the ends of the axis (51) in the grooves (16 , 16 ').  4. Prosthesis according to claim 3, characterized in that the opening (16) located on the outer side has the shape of a lumen, elongated from front to rear, so as to allow a relative pivoting, of amplitude limited, of the transverse branch (51) relative to the femoral part, which corresponds either to a rotational movement of the knee outwards, or vice versa, if the tibia is fixed, to a movement of the femur inwards.  5. Prosthesis according to one of claims 2 to 4, characterized in that the resurfacing piece (2) bears on the tibial plateau (5) by means of two pads (56, 56 ') integral with the latter , arranged laterally on either side of said "T" part (55), these bearings having a concave shape capable of allowing rolling and sliding of the convex surface (20) of the resurfacing part (2).  6. Prosthesis according to claim 5, characterized in that the external pad (56) is mounted movable in a direction perpendicular to the frontal plane.  7. Prosthesis according to one of claims 1 to 6, characterized in that the femoral part has a modular character and comprises the following three separable elements which can be selected to adapt exactly to the treated femur, and to anchor therein effectively  - the main room (1)  - the resurfacing piece (2)  - a proximal end piece (3)  8. Prosthesis according to one of claims 1 to 7, characterized in that the tibial part has a modular character and comprises the following three separable elements, which can be selected to adapt exactly to the tibia treated, and to anchor therein effectively  - the tibial plateau (5)  - a main part (4) which has a rod (40) of elongated shape, suitable for being implanted in the central medullary canal of the tibia  - a distal end piece (6).  9. Prosthesis according to one of claims 7 or 8, characterized in that the assembly of the different elements (1, 2, 3; 5, 4, 6) is carried out by interlocking with cones and screwing.