FR2663839A1 - Knee prosthesis - Google Patents

Abstract

The invention relates to a knee prosthesis. According to the invention, the geometry of the intermediate component (PI) and of the tibial plate (PT) makes it possible to create a force which is directed from the rear towards the front, applied on the femoral complex in such a way that it compensates in a dynamic manner for the absence or insufficiency of the anterior cruciate ligament. The architecture of the various components, namely the femoral component (PF), the intermediate component (PI), the tibial component (PT) and the patellar components (PR) according to the invention, makes it possible to render the said prosthesis modular, the prosthesis therefore being adaptable for the largest possible number of cases.

Description

 KNEE PROSTHESIS.

 The invention relates to a knee prosthesis.

 There are already a number of devices of this type but none, until now, has been able to respond to all situations of increasing wear. All manufacturers of prostheses have sought to reproduce as faithfully as possible the joint concerned, both in its architecture and in its functioning: physiological axis of movement, load distribution, etc. This is true for all the joints and therefore for that of the knee, more particularly concerned by the present invention.

 The function of the meniscus is essential. This is how the temporomaxillary joint possesses an intraarticular meniscus which establishes a concordance between the elliptical convex maxillary surface and the concave convex temporal surface. The knee joint for its part has two movable intermediate parts: the menisci. Hence the idea for joint prostheses to use mobile replacement intermediate parts. From the years 1964, such intermediate moving parts are used for joint replacements. We can cite for example the concentric concave convex cups used in hip prostheses.

 Among the most recent knee prostheses, mention may be made of the prosthesis described in French patent 2,290,883 filed on November 18, 1974, and the prosthesis described in European patent 0.021,421 filed on June 25, 1980 with priority of July 02, 1979 These two prostheses use movable intermediate parts.

 In the case of the first cited, it should be noted that it is unicompartmental. It therefore only regulates certain cases of knee decay and is not a system that adapts to lesions of increasing severity.

It can certainly be placed in a two-compartment prosthesis, but then there is no trochleen shield to face a patellar prosthesis.

 It should also be noted, and this is important, that it can only be placed in the presence of the intact anterior cruciate ligament and undistended lateral ligaments. Finally, it does not present any possibility of adjustment, once the cuts have been made, except to modify the thickness of the moving part. It must, moreover, be obligatorily anchored to ltos by cement.

 The second prosthesis mentioned also presents a certain number of difficulties, the main ones of which are set out below: a) during a pose in unicompartmental prosthesis, the principle of the rail on the tibial implant imposes an extremely precise position of the femoral piece then that this is not determinable, because it is a function of the shape of the bone but especially of the ligament balance; b) the presence of the anterior cruciate ligament is also essential when laying in unicompartimental mode; c) there is no possibility of adjustment once the cuts have been made, except to modify the thickness of the moving part; d) moreover, the cursor which circulates in the curvilinear rail and which maintains the shoe there, is a fragile structure, little compatible with the expected longevity of the product; e) finally, during bending, the moving parts move back but also get closer. This leads to a loss of extended contact with overload on a linear condyle-moving parts surface; f) during the retraction of the movable parts by flexion, if the anterior cruciate ligament is absent, no anterior restoring force acts on the movable parts, so that in flexion, the femoral condyles will more and more take a retreated position, which aggravates the situation described above.

 This device therefore does not adapt well to lesions of increasing severity.

 The present invention aims to overcome these drawbacks and relates to a prosthesis used in the field of orthopedic surgery to replace the sliding surfaces of the knee joint, worn or destroyed during osteoarthritis, rheumatoid arthritis, or complex femoro-tibio-patellar fractures.

 This prosthesis abandons the imitation of anatomical forms and tends to reproduce the normal physiology of the knee with the help of a movable intermediate piece which allows a rolling and a sliding separated and differently dosed by the ligament apparatus itself.

The insufficiency or absence of the cruciate ligament does not preclude the placement of the prosthesis. It is compensated by the shape of the prosthesis which supplements its function.

 One of the essential characteristics of the invention is therefore the shape of the movable intermediate piece and of the tibial plateau which makes it possible to create a force directed from the rear towards the front, applied to the femoral piece - intermediate piece complex so that '' it dynamically compensates for the absence or insufficiency of the anterior cruciate ligament.

 In the different knee positions, flexion-extension, rotation, unipodal support even on a single compartment, the load is transmitted by large congruent surfaces. The longevity of the implants is thus increased.

 The invention also relates to the combination of another mobile intermediate part ensuring the connection between the femur and the patella.

 It also relates to a system comprising five types of parts in accordance with the invention, namely a femoral part (PF) provided with a trochlear shield, an intermediate part (PI), a tibial part (PT), a patellar part (PR ), and a patellar intermediate piece (PIr).

 These parts are all compatible and can replace a single internal femoro-tibial, external femoro-tibial, femoro-patellar compartment as well as the whole of the joint depending on the extent of the destruction.

The invention will be better understood with the aid of the explanations which follow and of the appended figures among which:
- Figure 1 schematically illustrates the tibiafemur joint, the latter being shown in the folded position at 900;
- Figures 2, 3 and 4 schematically illustrate the tibial anchoring part (PT) according to the invention respectively in front view, in top view and in section along the line (IV-IV) of Figure 3, which is on a smaller scale;
- Figures 5, 6 and 7 schematically illustrate the movable femoro-tibial intermediate piece (PI) according to the invention respectively viewed from behind, from above and from the side;
- Figures 8, 9 and 10 schematically illustrate the femoral part (PF) according to the invention, with its trochleen shield, respectively viewed from the front, from above and from the side; ;
- Figure lla schematically shows the association of femoral, tibial and intermediate parts in the prosthesis according to the invention;
- Figure llb schematically illustrates the return to the front of the intermediate piece after it has moved rearward on the tibial piece;
- Figure 12 is a plan view, from behind, of the patellar anchor (PR);
FIG. 13 is a front view of the intermediate piece (PIr) complementary to the patellar anchoring piece,
FIGS. 14 and 15 are respectively a vertical axial section and a horizontal axial section of the two parts (PR) and (PIr) associated,
- Figure 16 illustrates the modular configuration of the femoral part.

 For the sake of clarity, the same elements are given the same references in all the figures.

 Figure 1 schematically illustrates the joint according to the invention between the femur (8) and the tibia (1), in the folded position at 900. The fibula bears the reference (10). This connection is ensured by means of a femoral anchoring piece (PF), a tibial anchoring piece (PT) and a mobile intermediate piece (PI) inserted between the two previous ones. The arrows (f1, f2, f3) respectively show the possible sliding forwards, backwards and in rotation of the tibial anchoring piece (PT).

 The tibial anchoring piece (PT) illustrated by means of FIGS. 2, 3 and 4 comprises anchoring means (23) intended to be made integral with the tibia, as well as a plate (22). The latter has a flat face (2b) secured to the anchoring means (23) and a bearing face (2a) on the opposite side. This bearing face (2a) is intended to receive the mobile intermediate part (PI) on which it can rest and slide freely.

 According to an important characteristic of the invention, this bearing face (2a) is in the form of a bowl having a concave part. In fact, it is a segment of a sphere whose radius of curvature is (ra). A stud (4) having for example substantially the shape of a truncated cone is projecting on the bearing surface (2a). It is intended, as will be explained below, to slide into an anteroposterior trench formed for this purpose in the intermediate movable part (PI).

 According to another characteristic of the invention, the center of the sphere is shifted forward. The truncated cone (4) is then behind the maximum hollow (Cm).

 Figures 5, 6 and 7 schematically illustrate the movable intermediate piece (PI) intended to come to bear on the bearing surface (2a) of the tibial piece (PT). This part (PI) has a convex spherical lower face (3a) with the same radius of curvature (ra) as that of the bearing face (2a), so as to be congruent with the latter. Only internal-external freedom is suppressed by the truncated cone (nipple 4) sliding in an anteroposterior trench (5) of the moving part and allowing a retraction thereof. On the other hand, the latter is completely free to pivot around this cone (4) in each recoil position and this, throughout its anteroposterior course. The intermediate piece is produced in progressively increasing thicknesses, ending in a profile (36) in excess thickness, providing reinforcement in terms of resistance to stresses. It has in its middle part, a rear notch (37) to allow the passage of the cruciate ligament in the case where it is recoverable, notch which is also found on the back of the tibial plateau and which is referenced (27) on Figure 3.

 The upper face of this part (PI) is hollowed out by two concave spherical caps, constituting two offset depressions (dia) and (d2a) intended to receive the femoral anchoring part (PF) described below.

 The femoral piece (PF) illustrated by Figures 8, 9 and 10 is composed of two segments of spheres (in d2b) playing the function of condyles and a segment of anterior central pulley (40), constituting a trochlear shield (BT ). The latter has a trochlean groove (41) intended to receive the patellar intermediate piece (PIr).

 The femoral part (PF) is defined: a) by the spacing (D) of the two centers (C1, C2) of its spheres and by their radius (rc), which is chosen so that they are congruent with the depressions ( dia) and (d2a); b) by the position of the axis (X) parallel to the line (C1, C2) of the anterior and central pulley, by the radius (Rg) of its groove and by the radius of its center of groove (rg) ( Figures 8 and 16); these three data are also constant in all the systems of parts listed below which make the prosthesis according to the invention modular; the axis (X) of the pulley, as shown in Figure 16, is located above the line (C) joining the centers (C1, C2) of the two condylar spheres at the same distance (H) in all cases of the figure of said system; c) the different sizes of (PF) are obtained by modulated spacing between the assembly formed by the anterior and central pulley and that formed by the two posterior condylar spheres; three gaps are illustrated in Figure 16.

 Anchoring in the femur (8) is ensured by any known means such as a walrus cone (42).

 Figure 11a illustrates the stacking of the three tibial (PT), intermediate (PI) and femoral (PF) pieces. In the equilibrium position, knee support extended, this moving part (PI) tends to lodge in the maximum hollow of the tibial part (PT). It is pushed there by the weight of the body applied to its rear part. She carries the femur (8) forward if the deficient anterior cruciate ligament has not done so.

 When bending the femur (8), the femoral part (PF) rolls backwards and drives the moving part (PI), the normal ligament play of the knee during bending associates with the rearward bearing of the femur ( 8) a forward sliding (AV) of this femur (8).

 As shown in Figure 116, this recoil raises the moving part (PI) on the concave inclined plane of the tibial anchor (PT), spreads the femur (8) from the tibia (1) with, in reaction, increased tension of all ligaments. The compressive force (F) applied to the rear part of the moving part (PI) causes the moving part-femoral anchor piece assembly to slide on the slope inclined towards the front; this creates a permanent dynamic substitution (F1) for the anterior cruciate ligament, provided that the lateral ligaments have been re-tensioned by a femoro-tibial mobile part (PI) of selected thickness (an internal internal asymmetric compensation has been provided).

 The same characteristics are applicable when a single internal or external femoro-tibial compartment is to be replaced. In this case, in accordance with the invention, congruence is observed between the single condyle of the femoral part and the single depression of the intermediate part on the one hand, and between the convexity of this intermediate part and the concavity of the tibial anchor.

 After having described the three tibial (PT), intermediate (PI) and femoral (PF) parts, we now describe, with reference to FIGS. 12 to 15, the combination of a patellar anchoring part (PR) with a part intermediate (PIr). The part (PR) is a concave sphere segment with close to its center, a truncated cone (100) with retentive apex (101).

The intermediate piece (PIr) is in the form of a ring segment (convex pulley) having a surface (sf) intended to come to be applied on the anterior part, that is to say in the groove ( 41) of the femoral part (PF) in the form of a pulley. The surface (sr) opposite the surface (sf) is congruent with the internal face of the patellar anchoring part (PR) and comprises a horizontal trench (102) in which the cone trunk (100) slides with retentive apex ( 101). Under these conditions, the freedom of up-down sliding is eliminated but, on the other hand, the possibility of rotation and of internal-external sliding is preserved. Under these conditions, this intermediate moving part (par) can, during the up-down sliding of the patella, pivot and move laterally to perfectly follow the femoral pulley. For each position of the anchors defined by the musculoligamentary action itself, the moving part permanently provides extended contact between the patella and the anterior face of the femur with reduced stresses.

 In each position of its internal-external displacement, the intermediate patellar part (par) pivots around the axis of the patellar anchoring part and takes a position in congruent support in the pulley of the shield of the femoral part (PF). A different position of the patellar intermediate piece (par) is imposed by the play of the lateral stabilizers of the patella for each flexion-extension position of the knee. Thus the stresses supported by the patellar intermediate piece (PIr) are significantly reduced.

 The architecture of the various parts constituting the knee prosthesis with permanent contact, according to the invention, makes it possible to provide a system of parts listed below which makes it modular and therefore adaptable to the greatest possible number of cases: 4 Femoral parts ( PF) referenced: (PFP) small femoral piece.

 (PFM): medium femoral piece.

(PFG): large femoral component.

 (PFu): unicondylar femoral component.

26 Intermediate parts referenced: (PI1): intermediate part for conservation of the only posterior crossover;
- 5 of increasing thickness from 2 to 2 mm,
- 5 increased by 2 mm on the right,
- 5 increased by 2 mm on the left.

(PIu): unicompartmental intermediate part:
- 6 of increasing thickness from 2 to 2 mm (PI0): zero intermediate piece used in the absence of the 2 crossed ligaments:
- 5 pieces of increasing thickness from 3 to 3 mm;
it can only pivot around the truncated cone (pin 4) of the
tibial piece; the trench on the underside is replaced by
a hollow truncated cone.

15 Tibial pieces (PT) referenced (pu1): tibial piece used in the absence of the anterior cruciate ligament with
conservation of the posterior cruciate ligament:
- 5 progressively increasing surface sizes.

(PTu): unicompartmental tibial piece:
- 5 progressively increasing surface sizes.

(PT2): tibial part used during the conservation of the two crossbars:
- 5 progressively increasing surface sizes.

9 Patellar parts (PR) referenced: (PRM): patellar part with mobile polyethylene.

 (P RD): patellar piece with dome on a metal plate.

(PRP): patellar dome piece made entirely of polyethylene.

These different pieces exist in 3 sizes of each type (small / medium / large).

Anchors (6):
Spongy screw admitting a walrus cone: increasing width.

 To avoid lowering the patella during significant femoral resection, shims are provided which are positioned on the two walrus cones of the femoral part, shims provided with increasing thickness, for example from 2 mm to 2 mm.

 Likewise, a tibial adjustment device is also provided for large varus or valgus. To do this, bone loss is compensated for by a suitable angle metal wedge which fits onto the underside of the tibial anchorage.

 Finally, a third adjustment is made at the level of the ball joints. lt consists of providing polyethylene parts whose thickness is adapted to the desired amplitude of bending.

 The knee prosthesis according to the invention has many advantages: in particular a possible fitting with or without an anterior ligament, the absence of the latter being compensated for by the shape of the prosthesis, as well as an adaptation facilitated by a modular system of the various elements constituting the said prosthesis.

Claims (12)

 1. Knee prosthesis of the type comprising a tibial anchoring piece (PT), a femoral anchoring piece (PF) and an intermediate piece (PI) inserted between the two; characterized in that on the one hand the tibial piece (PT) comprises a plate having a flat face (2b) on the side of the tibia and a concave bearing face (2a) taking the form of a sphere segment of radius of curvature (ra), the center of the sphere being shifted forward; on the other hand the part (PI) has a convex spherical lower face (3a) of the same radius of curvature (ra) as that of the bearing face (2a) and an upper face containing at least one concave spherical cap intended for receive the femoral anchoring piece (PF) composed of at least one segment of sphere playing the function of condyle.  2. Prosthesis according to claim i; characterized in that the upper face of the intermediate piece (PI) comprises two spherical caps forming two depressions (dia, d2a) and the femoral anchoring piece (PF) two condyles (ten, d2b).  3. Prosthesis according to claim 2, characterized in that a stud (4) protrudes from the bearing surface (2a) of the tibial anchoring piece (PT) and slides freely in an anteroposterior trench (5 ) performed in the moving part (PI).  4. Prosthesis according to one of claims 2 and 3, characterized in that the two sphere segments (d1 b 'd2b) of center (C1, C2) of the femoral part (PF) are connected by a segment of anterior central pulley constituting a trochlear shield (40).  5. Prosthesis according to claim 4, characterized in that this trochlear shield (40) has a trochlear groove (41).  6. Prosthesis according to one of claims 2 to 5, characterized in that the femoral anchoring piece (PF) is characterized by the spacing (D) of the two centers (C1, C2), by their radius (rc); by the position of the axis (X) parallel to the line (Ci, C2); the radius (Rg) of the groove, the radius of its circle (rg), the axis (X) being located above the line (C) joining the centers (Ci, C2).  7. Prosthesis according to one of the preceding claims, characterized in that, when the femur is flexed (8), the femoral part (PF) rolls backwards and drives the movable part (PI) so that the compression force (F) being applied to the rear part of the moving part (PI) slides on the slope inclined towards the front (AV) the assembly (PI-PF), which creates a supply (Fi) dynamics of the anterior cruciate ligament.  8. Prosthesis according to one of the preceding claims, characterized in that it comprises the combination of a patellar intermediate piece (PIr) with a patellar anchoring piece (PR).  9. Prosthesis according to claim 8, characterized in that the patellar anchoring piece (PR) is a segment of concave sphere with, close to its center, a truncated cone (100) with a retentive apex (101).  10. Prosthesis according to one of claims 8 and 9, characterized in that the intermediate piece (PIr) is in the form of a ring segment forming a convex pulley congruent on its surface (ground) with the trochlear groove (41), and having on its opposite surface (s2) a horizontal trench (102) in which the truncated cone (100) slides.  11. System of components of a prosthesis according to one of the preceding claims, characterized in that, for each of the parts (PT, PI, PF, PIr, PR), it consists of a plurality of elements of different and complementary dimensions with respect to the other elements so that it is possible to find a combination suitable for each morphology on the one hand, and in the dilapidated state of the anterior and posterior cruciate ligaments on the other hand.  12. System according to claim 11, characterized in that different sizes of the femoral part (PF) are obtained by modulated spacing between the assembly formed by the anterior and central pulley and that formed by the two posterior condylar spheres.