WO1994013214A1

WO1994013214A1 - Ancillary material for fitting a femoro-patellar prosthesis

Info

Publication number: WO1994013214A1
Application number: PCT/FR1993/001244
Authority: WO
Inventors: Jacques-Philippe Laboureau
Original assignee: Lars
Priority date: 1992-12-14
Filing date: 1993-12-14
Publication date: 1994-06-23
Also published as: FR2699068A1; FR2699068B1

Abstract

The present invention relates to an ancillary material for setting in place a total or femoro-patellar knee prosthesis, said material comprising a prosthetic trochlear element configured like a pulley cooperating with a prosthetic rotulian inset (3) implanted in the posterior face of the patella (4), characterized in that it is comprised of: a test prosthesis (1a^_, 1b^_) having a shape substantially similar to that of said trochlear element and which is provided with direct position marking means (10, 11) or indirect position marking means (6, 7, 8) with an alignement axis (P^_) at an angle from 30 to 35° with respect to the diaphysary axis of the femur, a guiding pin (5) embodying said alignement axis (P^_) through the patella (4), and a bur (9) or a fluted trephine which is coaxially introduced about said guiding pin (5) in order to resect the posterior face of said patella (4) in order to implant said rotulian inset (3).

Description

ANCILLARY MATERIAL FOR LAYING A FEMOROPATAL PROSTHESIS

The present invention relates to ancillary equipment for the correct connection of the femoral trochlear element and the patellar medallion constituting a femoro-patellar prosthesis. To date, there is no technique for fitting a femoro-patellar prosthesis which makes it possible to ensure that the trochlear and patellar elements cooperate under suitable biomechanical conditions, that is to say close to those encountered in the anato ic femoropatellar joint. However, improper positioning of the patella not only generates premature wear of the prosthesis but also causes undeniable discomfort in the patient's movements, even a defect in knee stability. The present invention aims to remedy these drawbacks by proposing ancillary equipment, the objective of which is to ensure that the operated patella, provided with its prosthetic patellar medallion, can be perfectly centered relative to the implanted metal trochlear element.

Another objective of the invention is to facilitate the corrections that it may be necessary to practice on the position of the patella in the trochlea, to remedy certain femoro-patellar pathologies. To this end, the invention relates to ancillary equipment for the establishment of a femoro-patellar or total knee prosthesis which comprises a prosthetic trochlear element in the form of a pulley cooperating with a prosthetic patellar medallion implanted in the posterior face of the ball joint, characterized in that it comprises:

- a trial prosthesis of substantially identical shape to that of said trochlear element, which is provided with means for direct or indirect location of an alignment axis making an angle of 30 to 45 ° relative to the diaphyseal axis of the femur ,

- a guide pin intended to materialize this alignment axis through the patella, and

- A cannulated cutter or trephine which is introduced coaxially around said guide pin to resect the posterior face of said patella for implantation of said patellar medallion.

In most of the femoro-patellar prostheses envisaged, the trochlear element will have the shape of a toric pulley capable of responding to the convex articular surface in the shape of a spherical cap of the corresponding patellar medallion, but it is not excluded that the the trochlear element has a V-shaped cross section, symmetrical or not, cooperating with a patellar medallion also V-shaped on its posterior face, or that the trochlear element and its patellar medallion adopt more complex shapes (trapezoidal , etc ...).

By construction, the alignment axis is placed in the middle of the articular pulley of the trochlear element, normally at its most hollow place which is actually located on all femoral prostheses at an angle between 30 and 45 ° from l 'diaphyseal axis of the femur, so that, after the placement of the medallion in the patella, the latter is exactly centered in the trochlear element and cooperates with it in satisfactory biomechanical conditions.

Thus, for a normal patella, the alignment axis of the trial prosthesis is provided so that the guide pin passes substantially to the geometric center of the cartilaginous articular face of the patella, which is known to occupy approximately the three-quarters upper of its posterior face, that is to say so that the guide pin is located in the horizontal median plane of said articular face.

However, it is also possible, according to the invention, to make corrections to the position of the patella relative to the trochlea, either by playing on the positioning in height of the articular face of the patella not resected relative to the alignment axis of the trial prosthesis, or by playing on the depth of the digging of the bone insertion housing of the patellar medallion, that is to say by changing the ratios between the articular surfaces of the corrected patella and the trochlea. These purely mechanical corrections thus help in the treatment of the following pathologies:

- if the knee has a kneecap originally too high, it is necessary to bend the knee a lot so that said kneecap really engages in the hollowest part of the trochlea (place where it is most stable); this phenomenon is of course reversed if the patella is originally too low. The practitioners then speak respectively of a "patella alta" and a "patella bara". In the case of a ball joint located too high in the trochlea (called "patella alta") or, conversely, located too low (called "patella bara"), the ancillary material according to the invention allows to shift respectively towards down or up the guide pin of the bur relative to the alignment axis of the trial prosthesis; it should be noted that this substantially vertical offset is indeed to be taken into account relative to the middle of the natural articular face of the patella, and not relative to the middle of its posterior face (the lower quarter of the latter not being a contact surface with the trochlea).

- if the patella is normally very thick, the lever arm of the patellar tendons overlying the patella is larger than that of the overlying tendons of a less thick patella; therefore, to lift the leg, the effort to be provided by the quadriceps is greater. The reverse is also true. According to a complementary characteristic of the invention, the means for locating the alignment axis on the trial prosthesis include means for indicating an average depth of digging corresponding to a normal ball joint; therefore, it is possible to advance or move back the patella in the trochlea, i.e. to advance or move back the plane patellar tendon, to improve the effectiveness of said patellar tendons and quadriceps on the tibia. We can thus play directly on the femoropatellar tensions by modifying the digging depth of the bone insertion housing of the patellar medallion which, in this hypothesis, of course has a given thickness.

Other characteristics and advantages of the present invention will emerge more clearly from the following description of the two alternative embodiments of ancillary equipment for the placement of a femoro-patellar prosthesis comprising a trochlear element in the shape of a toric pulley. cooperating with a biconvex patellar medallion, these two variants being given by way of nonlimiting examples with reference to the appended drawings in which:

- Figure 1 is an anteroposterior perspective view of a first embodiment of the trial prosthesis and locating means used for the placement of the trochlear element on the femur, - Figure 2 is a side sectional view, in a vertical median plane passing between the two femoral condyles, of the unresected patella placed in the trochlear pulley of the trial prosthesis, with marks showing the position of the alignment axis above -defined with respect to the cartilaginous articular face of said patella,

FIG. 3 is a rear view of the patella after identification on the latter of a guide pin for producing the bone insertion housing of the prosthetic patellar medallion,

- Figures 4 to 11 are sagittal section views of the femoro-patellar joint at the lower end of the femur, in a plane located along the alignment axis identified on the trial prosthesis, these figures schematically showing some of the operating phases necessary for fitting the prosthetic patellar medallion using ancillary equipment as shown in FIG. 1, - Figure 12 is an anteroposterior perspective view of a second alternative embodiment of the trial prosthesis and means for locating the alignment axis, - Figures 13 to 16 are sectional views sagittal of the femoro-patellar joint at the level of the lower end of the femur, in a plane located along the alignment axis marked on the trial prosthesis, these figures schematically showing some of the operating phases necessary for the setting in place of a prosthetic patellar medallion by means of the trochlear test prosthesis as shown in figure 12.

First of all, it is recalled that the so-called "trial" prostheses generally have the same shape as the final prostheses, except that they carry means which facilitate the placement as well as the verification of the position of the implants in the joint . The trial prostheses la., Lb shown in FIGS. 1 and 12 are thus substantially identical to the trochlear element of the femoro-patellar prosthesis which they help to put in place.

In the type of femoro-patellar prosthesis chosen, the trial prostheses la, lk> both include a lower toric part 2, of known shape, reconstituting the surface of the affected trochlea and whose small and large radii of curvature are as close as possible to those of the natural trochlea; the lower toric part 2, which is the hollowest part of the trochlean pulley, is intended to come into contact with the articular surface 3a. convex, in the form of a portion of a sphere, of a prosthetic patellar medallion 3 normally made of high density polyethylene which is implanted for this purpose in the rear face of the patella 4.

It will be observed that the description which follows could also apply to the case of a total prosthesis or a bi-compartmental knee prosthesis which "integrates", inter alia, a trochleo-patellar prosthesis of the same geometry. According to the invention, the trial prostheses la, 1] D are provided with means for locating an alignment axis P. located approximately 45 ° from the diaphyseal axis of the femur. The operation of placing the femoropatellar prosthesis is effected with the knee bent at 90 °, the femur being horizontal; as can be seen in FIG. 2, the lower hollow toric part 2 of the femoro-patellar joint is then located in equal parts on each side of said alignment axis .P. The objective pursued by the invention is to ensure that in this knee flexion position at 90 °, for which a normal ball joint 4 is supposed to come to be placed just in front of said lower toric part 2, the practitioner can make pass a guide pin 5 through said ball joint 4, along the alignment axis JP, said guide pin 5 then dividing the cartilaginous articular face of the latter into two parts of equal height - such that the height greater than is equal to the lower height b -. In the pathological cases mentioned in the introduction, the guide pin 5 will be offset from the center of the articular face of the ball joint 4, the alignment axis P_ then having to divide said articular face into two dissymmetrical parts, the ratio of which depends of the desired correction - such as a> b to correct a "patella bara" and a <b to correct a "patella alta" -.

Of course, the angle of 45 ° chosen is not limiting but constitutes an average angle which does not really depend on the position of the hollowest part of the prosthetic articular pulley of the type chosen relative to the axis of the femur.

In a first variant of the invention which will now be described with reference to FIGS. 1 to 11, the means for locating the alignment axis P_ on the trial prosthesis include it:

- a pointed centering stud 6, placed at the bottom of the toric part 2 of the trial prosthesis la., on the alignment axis P.; a lateral aiming gun 7 carried by the internal edge of the toric part 2 and the direction of which is substantially perpendicular to said alignment axis P, _r ′ - a lateral pin 8 intended to be housed transversely in the ball joint 4, this lateral pin 8 being guided for this purpose by the lateral aiming gun 7.

After placing the trial prosthesis la on the lower end of the femur then reduction of the natural patella 4 not resected (Figure 4), the practitioner plays the knee in flexion while pressing on the anterior face of the patella 4 (Figure 5) so as to draw a vertical median groove _4a, on the rear side of said patella cartilage 4 (Figure 3); the latter is then placed in the desired anatomical ratio opposite the toric part 2, generally such that a = b (FIG. 2), the practitioner being able to view this anatomical ratio laterally by the open side of the knee. The lateral pin 8 can then be introduced transversely into the ball joint 4 (FIG. 6) so as to define a locating axis located perpendicular to the vertical groove 4a. left by the centering stud 6 on the rear face of said ball joint 4.

The axis perpendicular to the vertical groove 4a. and to the lateral spindle 8 obviously corresponds, by construction, to the reproduction of the alignment axis P. through the ball joint 4. According to a complementary characteristic of the invention, the lateral aiming gun 7 is such that 'it allows a front release of the lateral spindle 8 without the latter being removed from the ball joint 4 (Figure 1); in this way, the practitioner can again dislocate the patella 4 on the external side of the knee while preserving the two viewing axes, pin 8 and groove 4a. ; this allows it to easily introduce the guide pin 5 on the articular face of the ball joint 4, perpendicular to these two axes (Figure 8).

Thanks to this guide pin 5, the practitioner can then proceed under good conditions to the resection of the articular face of the ball joint 4 by means of a cannulated cutter 9, which it introduces coaxially around said guide pin 5 (FIG. 9).

According to another characteristic of the invention, the distance between the lateral aiming barrel 7 and the pointed stud 6 corresponds substantially to the thickness of the patellar medallion 3 which has just been placed. In this way, the digging of a ball joint 4 can be carried out until the edges of the cutter 9 comes substantially flush with the end of the lateral pin 8, which has of course been slightly withdrawn to allow passage to the guide pin 5. In the case of a pathological patella 4, it is on the other hand possible to increase or on the contrary to reduce the depth of the digging of the patella 4 which makes it possible to move back or advance the patellar tendon plane -jacent to the ball joint 4 as much.

The patellar medallion 3, or a trial patellar prosthesis, is finally fixed in the bone insertion housing thus formed (Figure 10) and, after the usual checks, the practitioner can place the definitive trochlear element in front which he then reduces the ball joint 4 provided with its medallion 3 (Figure 11).

In a second variant embodiment of the invention which will now be described with reference to FIGS. 12 to 16, the means for locating the alignment axis .P on the trial prosthesis lb consist only of a lateral extension 10 in the form of a square supporting, at an appropriate distance from the lower toric part 2 of said prosthesis 1] D (for example 3.5 centimeters), an aiming gun 11 located, by construction, along said alignment axis jP.

This geometry allows the guide pin 5 of the cannulated cutter 9 to pass directly through the ball joint 4 (FIG. 13), namely from the anterior face of the latter until it stops against the bottom of the toric lower part 2 , exactly where, in the first variant, was the stud centering 6.

For this purpose, it is obviously obvious that after the placement of the trial prosthesis lb on the lower end of the femur, the practitioner reduced the ball joint 4 and placed the latter in front of the lower toric part 2 as a function of the anatomical ratio to be obtained (that is to say in a manner identical to that which was mentioned with reference to the first variant).

This direct aiming is obviously preferable to the indirect aiming in several stages previously described.

According to an additional characteristic of the invention, the aiming gun 11 is formed of two concentric tubes mounted for rotation relative to one another, the internal tube being fixed; these two tubes are provided with longitudinal grooves capable of being brought into coincidence by rotation of the external tube, so as to provide lateral clearance to the guide pin 5 without the latter being removed from the ball joint 4. In this way, it becomes possible to luxate together the ball joint 4 and the guide pin 5 (Figure 14).

For the realization of the insertion socket of the patellar medallion 3, the practitioner can then slide said pin 5 almost completely on the posterior side of the ball joint 4 (figure 15) where it conventionally serves as a guide for the cannulated cutter 9 (figure 16). As in the first variant, the digging of the insertion housing makes it possible to move the ball 4 forward or back.

The two embodiments of ancillary equipment according to the invention described above are not limiting and, in particular, it is possible to adapt the same principles to femoropatellar prostheses whose articular surfaces adopt complementary shapes trapezoidal or "V" in particular.

Claims

1 - Ancillary material for the installation of a femoro-patellar or total knee prosthesis which comprises a prosthetic trochlear element in the form of a pulley cooperating with a prosthetic patellar medallion (3) implanted in the posterior face of the patella (4) , characterized in that it comprises:

- a test prosthesis (la, li>) of substantially identical shape to that of said trochlear element and which is provided with means for direct (10, 11) or indirect (6, 7, 8) location of an axis of alignment (£) making an angle of 30 to 45 ° relative to the diaphyseal axis of the femur, - a guide pin (5) intended to materialize this alignment axis (P_) through the ball joint (4), and

- A cutter (9) or a cannulated trephine which is introduced coaxially around said guide pin (5) to resect the rear face of said ball joint (4) for the implantation of said patellar medallion (3).

2 - ancillary equipment according to claim 1, characterized in that the means for locating the alignment axis (jP) on the trial prosthesis (la) comprise: - a pointed centering stud (6), disposed at bottom of the hollowest part of the trochlear pulley of the trial prosthesis (la), ^on the alignment axis (P.),

a lateral aiming gun (7) carried by the internal edge of said hollowest part of the trochlean pulley and the direction of which is substantially perpendicular to said alignment axis (P.),

- A lateral pin (8) intended to be housed transversely in the ball joint (4), this lateral pin (8) being guided for this purpose by the lateral aiming gun (7).

3 - ancillary equipment according to the preceding claim, characterized in that the lateral aiming barrel (7) is provided with means allowing a front clearance of the lateral spindle (8) without the latter either removed from the ball joint (4).

4 - Ancillary equipment according to any one of claims 2 or 3, characterized in that the distance between the lateral aiming cannon (7) and the pointed stud (6) corresponds substantially to the thickness of the patellar medallion (3) that we just set up.

5 - Ancillary equipment according to claim 1, characterized in that the means for locating the alignment axis (P.) on the trial prosthesis (lb) consist only of a lateral extension (10) in the form of bracket supporting, at an appropriate distance from the hollowest part of the trochlean pulley of the trial prosthesis (lb), an aiming gun (11) situated, by construction, along said alignment axis (J?). 6 - Ancillary equipment according to the preceding claim, characterized in that the sighting barrel (11) is formed by two concentric tubes mounted for rotation relative to one another, the internal tube being fixed, said tubes being provided with longitudinal grooves capable of being brought into coincidence by rotation of the outer tube so as to provide lateral clearance to the guide pin (5) without the latter being removed from the ball joint (4).