WO1999013803A2

WO1999013803A2 - Femoral component of three-compartment knee prosthesis with variable anteroposterior space requirement

Info

Publication number: WO1999013803A2
Application number: PCT/FR1998/001947
Authority: WO
Inventors: Richard Minfelde
Original assignee: Richard Minfelde
Priority date: 1997-09-15
Filing date: 1998-09-11
Publication date: 1999-03-25
Also published as: WO1999013803A3; FR2768329A1; FR2768329B1

Abstract

The invention concerns a femoral component (16) of a three-compartment knee prosthesis formed by at least two elements (17, 18), one trochlear (18) carrying the main part of the trochlear articular surface (23), the other condylar (17) carrying the main part of at least a condylar articular surface (22), said elements being connected to each other by sliding connection means (24) extending substantially in the component (16) anteroposterior direction (AP), such that their relative position in this direction is adjustable and capable of being fixed by locking means (19).

Description

PROSTHETIC PEMORAE PIECE TRT € ( ^* MPARTMENTAL KNEE WITH VARIABLE ANTERO-POSTERIOR DIMENSION)

The present invention relates to endoprostheses or prostheses of the knee joint, in particular three-compartment knee prostheses.

The object of the invention relates to the technical sector of medical sciences.

Perfectly common three-compartment knee prostheses generally consist of three pieces, namely a femoral piece, a tibial piece and a patellar piece.

The femoral part is generally metallic and is implanted at the end of the femur to restore on the one hand the condylar surfaces, on the other hand the trochlean surface of the injured osteocartilaginous structures, or even replace the whole of the femoral end. The anatomical distinction of two condylar surfaces plus a trochlear surface leads to consider three articular compartments, justifying the tri-compartmental designation of this prosthesis, object of the present invention.

However, the case of a two-compartment prosthesis (relating to the trochlene surface and to one of the condylar surfaces) also comes within the scope of the invention. The tibial part, generally two-component, is most commonly made of both metallic material and synthetic material, in particular very high molecular weight polyethylene. Implanted at the upper end of the tibia, the tibial piece restores the articular surfaces of the tibia, namely the two tibial glenae. It is therefore on the prosthetic tibial glenes that the prosthetic femoral condyles roll and slide according to a complex femoro-tibial kinematics generally sought as similar as possible to the initial kinematics existing between the healthy femoral and tibial osteocartilaginous articular structures. Certain constructive provisions include an intermediate element between the femoral part and the tibial part. This intermediate element, most often referred to as a movable pad, makes it possible, as in the previous arrangement, to manage the femoro-tibial kinematics. The presence or absence of this movable pad in the prosthesis of the knee joint benefiting from the present invention does not in any way modify the scope of the invention.

The patellar part, for its part, is most often made of synthetic material, in particular very high molecular weight polyethylene.

It slides on the prosthetic trochlea of the femoral part according to a complex femoro-patellar kinematics generally also sought similar as possible to the initial kinematics existing between the healthy femoral and patellar osteocartilaginous articular structures; At least, this femoro-patellar kinematics is generally and very often only defined to obtain stability of the patella (or patella) prosthesis during flexion-extension movements of the knee joint.

Hitherto considered as a single piece, the femoral piece adapts to the morphology of the femur considered by choosing a size from a standard range. There is therefore for a majority of prosthetic knees, a dimensional difference between the end of the femur of the operated patient and the prosthetic femoral part envisaged for the arthroplasty.

This dimensional difference is characterized in particular by an anteroposterior obstruction of the femoral element different from the patient's healthy femur. Given this difference, the prosthetic articular surfaces replacing the injured osteocartilaginous articular surfaces cannot be positioned optimally in place of the previous healthy osteocartilaginous structures.

Indeed, if the prosthetic system is designed to position the prosthetic femoral condyles instead of healthy femoral condyles (Case A), it will not be the same for the femoral trochlea with the marginal exception of an identical dimensional between prosthesis and femur.

Conversely, if the prosthetic system is designed to position the prosthetic femoral trochlea in place of the healthy femoral trochlea (Case B), it will not be the same for the femoral condyles, with the marginal exception of an identical dimension between prosthesis and femur.

The management and ultimately the simultaneous restoration of the femoro-tibial kinematics and the femoro-patellar kinematics therefore prove impossible to achieve with one of the standard monobloc prosthetic femoral parts (from a range).

This dimensional difference - difference in particular between the anteroposterior obstruction of the femoral element and the patient's healthy femur - has the direct consequence of limiting the mobility of the prosthetic knee, either by hyperpressure in the femoro-patellar joint ( Case A), either by excessive traction in the ligament structures (Case B), excessive traction also also causing hyperpressure in the femoro-patellar joint by lowering the tibia during flexion.

These excessive mechanical stresses, limiting mobility, impoverish the performance of current knee joint systems and increase the risks and the development of wear. It is not uncommon also to observe a harmful bone remodeling or even a fracture of the lower end of the femur, a direct consequence of the anteroposterior dimensional difference between prosthesis and prosthetic bone site.

By the invention, it is proposed to remedy these drawbacks by means of a knee prosthesis allowing the management and the simultaneous restoration of the femoro-tibial kinematics and the femoro-patellar kinematics by means of its femoral part, the size of which anteroposterior is variable.

To this end, the invention therefore relates to a femoral component comprising a trochlear femoral element and at least one condylar femoral element and at least one means for guiding or assembling or connecting these elements.

The term “condylar femoral element” is understood to mean a part implanted to restore at least one of the two condylar surfaces of the end of the femur. The association of the two condylar femoral elements each restoring one of the condylar surfaces of the femur is a possible variant and included in the term "condylar femoral element" below used.

According to the invention, the trochlear femoral element can be positioned relative to the condylar femoral element at an adjustable distance in a substantially anteroposterior direction. These elements can then be optionally assembled according to at least one means making it possible to fix the appropriate anteroposterior size.

Still according to the invention, the design of the trochlene surface of the trochlear femoral element will be - whatever the anteroposterior size - in continuity with the central condylar surfaces of the femoral condylar element so that the prosthetic patella, which generates with the trochlear surface a trochleo-patellar articulation, becomes in significant flexion (beyond 60 °), a condylo-patellar articulation. In a similar way to the anatomy, the union of the trochleo-patellar joint and the condylo-patellar joint, constitutes the femoro-patellar joint.

Within the meaning of the invention, the continuity of these articular surfaces does not imply a strict belonging of the trochlene surface to the trochlear femoral element and of the central condylar surfaces to the condylar femoral element, each of these surfaces being able to continue on the complementary element in the vicinity of their meeting.

Furthermore, the invention does not prejudge contiguous materials of the femoral elements, conventionally metallic, they may for example be ceramic or synthetic. The advantage of this structure, in addition to the independent restoration of the kinematics described, lies in the possibility of reducing by a factor of three the number of femoral parts generally present in a range of knee prostheses. In addition, a total modularity can be envisaged between the trochlear femoral elements and the condylar femoral elements. The combination of these advantages therefore allows an increase in the performance and longevity of the prosthetic joint system and a significant reduction in the cost of knee prostheses. Other characteristics and advantages of the invention will emerge from the description and some examples of embodiments given below. Reference will be made to the accompanying drawings, in which:

- Figure 1 is a schematic perspective view of a femoral piece of three-compartment knee prosthesis according to the state of the art.

- Figures 2 and 3 are schematic sectional views of knee prostheses according to the state of the art.

- Figure 4 is a schematic perspective view of one of the embodiments of the femoral part with adjustable anteroposterior dimensions according to the invention.

- Figure 5 is a schematic perspective view of one of the embodiments of the trochlear femoral element according to the invention.

- Figure 6 is a schematic perspective view of one of the embodiments of the condylar femoral element according to the invention.

- Figures 7a, 7b, 7c illustrate the adjustable aspect of the anteroposterior size of the femoral element.

Figure 1 is a schematic perspective view of a knee prosthesis. In known manner, the femoral part 1 is substantially U-shaped, the outer surface of which defines one or more condylar surfaces 2 and a trochlear surface 3.

Figures 2 and 3 are schematic sectional views of knee prostheses according to the state of the art. They respectively represent a prosthetic system called rolling-sliding, and a prosthetic system called movable shoe. These sectional views are located at one of the condyles of the knee joint. The femoral part 1 is attached by any known means to the femur (F) previously cut to match the inner faceted surface 4 of the femoral part. In a manner also known, the prosthesis comprises a tibial part 5 comprising a plate 6, a coupling element 7 to the condylar surfaces 2 and means 8 for fixing this plate to the tibia (T). This coupling element 7 has a substantially cylindrical or spherical upper surface 9 matching the condylar surface 2 and is either secured to the plate 6 in the case of FIG 2, or movable relative to the plate 6 (movable pad) in the case of Figure 3. In the latter case, the movable shoe 7 has a lower surface 10 substantially cylindrical or spherical or planar to slide on the upper surface 11 of the plate. The prostheses are shown when the knee is in extension, the knee flexion operating by rotation around an instantaneous axis of rotation 12 in the S direction.

As always known, the prosthesis comprises a patellar part 13 comprising means of attachment 14 to the patella P. The patellar part has a substantially spherical or cylindrical surface 15 matching the trochlear surface 3 opposite. These three parts during their relative movement during flexion-extension, describe kinematics specific to the functionality of the knee joint.

Due to the one-piece concept of the femoral part 1, the respective positions of the condylar 2 and trochlean surfaces 3 relative to the end of the femur F are not independent. This non-independence induces a non-compliance with at least one of the two femoro-tibial or femoro-patellar kinematics; This leads to excessive mechanical stresses which limit mobility and reduce the performance of the articular system. In addition, the dimensional difference, in particular anteroposterior between prosthesis and femur, can generate primers of bone remodeling or invoices bankrupting the anchoring of the prosthesis, therefore reducing its lifespan.

A solution to these problems is illustrated in Figures 4 to 7c. In Figure 4 is shown one of the embodiments of the femoral part 16 comprising a condylar femoral element 17 and a trochlear femoral element 18 and optionally at least one fixing means 19. The femoral part 16 is attached by any means known on the femur previously cut to match the faceted interior surfaces 20 and 21 respectively of the condylar and trochlear femoral elements.

The condylar femoral element 17 is substantially L-shaped whose external surface defines one or more condylar surfaces 22. The trochlear femoral element 18 is substantially L-shaped whose external surface defines a trochlear surface 23 (not visible).

The guidance or assembly of these elements is carried out using a slide 24 allowing a substantially anteroposterior translation, characterized by the variation of the distance AP.

The continuity of the trochlene surface of the trochlear femoral element with the central condylar surfaces of the condylar femoral element is in this embodiment ensured by an overlap of the trochlear femoral element on the condylar femoral element. Thus, the patellar part 13 which has a substantially spherical or cylindrical surface 15 conforms to the trochlean surface 23 opposite and furthermore marries the central condylar surfaces 26 in a significant flexion (FIGS. 5 and 6).

FIG. 5 illustrates the trochlear femoral element comprising one of the elements of one of the embodiments of the slide connection 23 by tenon 27. There is also one of the non-limiting solutions for achieving the continuity of the articular surfaces opposite the patellar part 13, illustrated by the covering 23 and the central condylar surfaces 26.

FIG. 6 illustrates the condylar femoral element comprising one of the elements of one of the embodiments of the slide 24 by mortise 28. There is also one of the non-limiting solutions for achieving the continuity of the articular surfaces opposite. the patellar part 13, illustrated by the central condylar surfaces 26.

FIG. 7a illustrates the minimum anteroposterior size of the femoral part according to the invention. FIG. 7b illustrates the maximum anteroposterior size of the femoral part according to the invention.

The difference between these two dimensions is characterized by the distance D which, for example, can be of the order of 10 mm. FIG. 7c illustrates the infinity of possible value of the distance AP which characterizes the variable size of the femoral part 16, object of the present invention.

Claims

1. Femoral part (3) of a three-compartment knee prosthesis comprising an essentially anterior trochlear part and essentially posterior condylar parts, carrying convex articular surfaces (22,23) in continuity and surfaces (20,21) of its attachment to the resected end of the femur (F) in shape correspondence with this end, characterized in that it is formed by at least two elements (17,18), one of which is trochlear (18) carrying most of the trochlear articular surface (23), the other condylar (17) carrying most of at least one condylar articular surface (22), these elements being connected to each other by means (27,28 ) of sliding link extending substantially in the anteroposterior direction (AP) of the part (16), so that their relative position in this direction is adjustable and able to be fixed by means (19) of blocking.

2. Femoral component according to claim 1 characterized in that, whatever the relative position of the two elements (17,18), the central condylar articular surfaces (26) which they comprise are continuous.

3. Femoral component according to one of the preceding claims characterized in that the trochlear element (18) has a tenon

(27) oriented parallel to the anteroposterior dimension of the part (16) while the condylar element (17) has a mortise

(28) for sliding reception of the post (27).