AU746310B2 - Ancillary equipment for preparing the setting of a knee prosthesis - Google Patents

Abstract

The invention concerns ancillary equipment for preparing the setting of a knee prosthesis, characterised in that it comprises a plate (6) not thicker than a tibial plate of the knee prosthesis, and to which is fixed a rod (8) along an inclination suitable for obtaining a femoral interval orthogonal to the mechanical axis of the lower member; this plate is provided with a block of variable thickness, and is designed to be urged to rest on a tibial cutting plane (4) after insertion of its rod in the medullary canal of the thigh bone to obtain ligamentary equilibrium and for the ulterior lengthwise and flectional adjustment of the spaces between the proximal cut of the tibia (3) and the distal and posterior cuts of the thigh bone (2); this ancillary equipment eliminates the need for a femoral cut to obtain ligamentary equilibrium, and enables the cutting of the distal end of the thigh bone with a single cut.

Description

"Ancillary device for preparing the fitting of a knee prosthesis" The present invention relates generally to knee prostheses and more particularly to preparing the fitting of a knee prosthesis by means of suitable equipment.

Fitting of a knee prosthesis can be effected either by restoring the bone thicknesses and without concerning oneself with the ligaments, or by restoring the ligamentary equilibrium, hence kinematics, by means of re-establishing good tensioning of the ligaments.

The general aim is to obtain good equilibrium in flexion-extension so that once the prosthesis is in place, there is no looseness in one direction or the other, which requires that this equilibrium be guaranteed.

The surgeon thus first makes a cut in the proximal end of the tibia, orthogonal to the mechanical axis of the tibia, which is in most cases coincident with the anatomical or centro-medullary axis of the tibia. This tibial cut does not cause any particular problem, anatomical markers allowing this cut to be made easily with a predetermined thickness.

As regards the cutting of the distal end of the femur, it must be orthogonal to the mechanical axis of the femur, which is inclined by a certain angle with respect to the anatomical axis of the femur. This cut is made, for example, with a thickness of 8 mm, which corresponds to the thickness of the femoral implant.

The surgeon then measures the deviation in extension between the two cutting planes of the tibia and femur using a spacer. It is possible that this deviation is not rectangular as it should be, that is to say that the cutting planes of the tibia and of the femur are not parallel. In this case, the surgeon effects an elongation of the retracted capsuloligamentary elements of the concavity in order to obtain a parallelism between the distal end of the 2 femur and the proximal end of the tibia.

At this stage, according to the prior art, the surgeon must make the anterior and posterior femoral cuts.

According to a first method, an anterior reference on the femur is used. The distance between the anterior cutting plane A and the posterior bicondylar plane P is measured, and the femoral implant is chosen whose antero-posterior dimension AP is equal to or immediately less than the determined value. The surgeon then makes the anterior cut along the anterior reference plane A. He then transfers the dimension

AP

previously chosen for the implant and makes the posterior cut. He thus obtains the deviation in flexion FG which must be equal to the deviation in extension

EG

for the kinematics of the knee to be correct.

At this stage, there are two possibilities: a) The dimension AP of the prosthesis is equal to the dimension AP of the femur. In this case there is 20 no problem.

b) The dimension AP of the prosthesis is smaller than the dimension AP of the femur. For this reason the deviation in flexion FG is greater than the :.:deviation in extension EG, which causes looseness on flexion. To remedy this drawback, the technique used to date involves repeating the distal cut with thickness e (FG-EG) However, this re-cutting operation is imprecise. In addition, it forces the surgeon to fit a thicker polyethylene tibial plateau.

ooe 30 According to a second method, conventionally called "posterior reference", as described by patent EP 0 327 249, after the distal femoral and proximal tibial cuts have been made, the surgeon performs the following operations: He transfers the value FG EG and makes the posterior cut of the distal end of the femur. He then transfers the reduced dimension AP of the posterior thickness of the implant (distance between the anterior and posterior cutting planes) and makes the anterior 3 cut of the femur. At this stage three new possibilities can arise: a) The dimension AP of the implant is equal to the dimension AP of the femur. In this case there is no problem.

b) If the dimension AP of the implant is greater- than the corresponding dimension of the femur, the latter does not conform in the anterior plane since there is a space between the upper part of the trochlea of the implant and the surface of the femur, which is not satisfactory.

c) If the dimension AP of the implant is smaller than the corresponding value of the femur, the trochlea of the implant lies in the anterior cortex, which can be the source of a risk of femoral fracture.

Document EP 0 327 249 thus describes a method according to which the ligamentary equilibrium in extension is first effected, then the distal cut; finally the deviation in extension is transferred to flexion so that the two deviations are equal, and the posterior cut is made (Fig. 51).

Thus, apart from the case where the dimension AP of the implant is equal to the corresponding dimension of the femur, none of the solutions used to 25 date has proven really satisfactory.

Furthermore, the aforementioned EP patent uses an ancillary device with integral rod of U-shape adapted to fit on a complementary slide of a distractor. This equipment of modular design generates 30 clearances constituting angular imprecision scarcely compatible with the order of magnitude of the angles to be observed (between 3 and 11 degrees usually).

;i I P:\OPER\Ar \55(A6-98 spm.do-20I).O2 -4- According to the invention, there is provided an ancillary device for preparing the fitting of a femoral knee prosthesis comprising a tibial plateau and a femoral implant, this ancillary device comprising a centromedullary rod associated with a means for permitting ligamentary equilibrium to be obtained, characterized in that the device comprises a plate having a thickness at most equal to that of a tibial plateau of the knee prosthesis, and to which the rod is fixed at a suitable inclination to permit the femoral space or virtual space to be restored before wearing of the joint, this plate being intended to bear on a tibial cutting plane after insertion of the rod into the medullary canal of the femur in order to obtain ligamentary equilibrium and with a view to 1 5 subsequent adjustment of the deviations in extension between the proximal cut of the tibia and the distal end of ego the femur, and in flexion between the proximal cut of the tibia and the posterior cut of the femur, and in that it is provided with a wedge, which can be fitted on the plate and 20 which is of variable thickness, so that the total thickness of the plate and of the wedge is equal to the distance between the tibial proximal cutting plane and the distal end of the femur nearest to the said cutting plane, after 0 ligamentary equilibrium is obtained by distraction of the 25 joint between the plate and the distal end of the femur.

The device according to the invention makes it possible to position a reference distal cutting plane of the femur, perpendicular to the mechanical axis of the lower limb. This element also makes it possible to obtain ligamentary equilibrium without making a femoral cut beforehand, as is the case in the prior art mentioned above.

P:AOPERA535606-99 spe.dO- 19/02I02 A second important advantage of this device is that is allows the cut of the distal end of the femur, to be made without having to reposition the limb in extension, as in the prior art method set out above.

The object of preferred embodiments of the invention is to make available a specific ancillary device for defining an operating method making it possible to solve this above problem satisfactorily, in particular avoiding the problem of having to resort to a second distal cut on the femur by way of adjustment.

Preferred embodiments of the invention will now be described by way of example only, with reference to the drawings, as set out below.

Figure 1 is a diagrammatic view in elevation, shown in the frontal plane, of part of an embodiment of the device according to the invention and of a femur, as well S"as the upper end of the corresponding tibia, the rod of the equipment being inserted in the medullary canal of the femur.

S 20 Figure 2 is a view analogous to Figure 1 in the e* frontal plane showing the femur in the position of extension on the tibia and the plate of the equipment bearing on the tibial cutting plane.

"Figure 3 is a cross-sectional view along 3-3 in Figure 4 analogous to. Figures 1 and 2, in the frontal plane in extension, illustrating the embodiment with the complementary thickness wedge inserted between the upper end of the tibia and the distal end of the femur.

Figure 4 is a view along 4-4 in Figure 3.

P:\OPER\ArlM55606-98 spedoc-19/02/12 Figure 5 is a diagrammatic view in elevation in the sagittal plane showing the femur in flexion on the tibia and provided with an appliance for measuring the distance between the anterior reference plane and the posterior bicondylar plane of the femur for choosing the dimension AP of the corresponding implant.

Figure 6 is a diagrammatic view in the sagittal plane showing a femoral cutting block in the previously determined anterior and posterior planes as well as an associated feeler, the femur remaining in flexion.

Figure 7 is a diagrammatic view in elevation in the sagittal plane showing a spacer inserted between *e e ~r-~LL I_ Li I r; 6 the femur and the tibia, the femur being in flexion, in order to measure the true deviation in flexion.

Figure 8 is a diagrammatic view in elevation in the sagittal plane illustrating the distal cutting of the femur by means of a suitable appliance, the femur still being in flexion.

-Figure 9 is a view in elevation, in the frontal plane, of an embodiment of the ancillary element appearing in Figures 1 to 8.

Figure 10 is a partial perspective view of the ancillary element in Figure 9.

Figure 11 is an exploded perspective view of a second embodiment of the invention with an ancillary element and its associated wedge.

Figure 12 is a view in side elevation of the ancillary device and the wedge in Figure 11.

Figure 13 is an exploded perspective view of an industrial embodiment of the measuring appliance shown diagrammatically in Figure 5 for measuring the antero- 20 posterior femoral distance of the implant and fixing the rotation with respect to the tibial proximal cut.

Figure 14 is a partial view in longitudinal section of the device for supporting and blocking the rod/plate in Figure 13.

25 Figure 15 is an exploded perspective view, on a reduced scale, of an industrial embodiment of the appliance shown diagrammatically in Figures 6 and 8 for the distal cut of the femur.

Figure 16 is a perspective view, on a reduced *oo *30 scale, of an embodiment of the spacer illustrated *diagrammatically in Figure 7.

Figure 17 is a perspective view, on a reduced scale, of a block for cutting chamfers at the distal end of the femur.

Figure 18 is a view, in frontal elevation, of the inner side of a variant of the cutting block in Figure 17.

Figure 19 is a plan view of the cutting block in Figures 17 and 18.

i- I P:\OPER\ArI\55,6.98 sp.doc-19MZA -7- Figure 20 is a diagrammatic view in elevation in the frontal plane corresponding to Figure 6.

Figure 1 shows the distal end 1 of a femur 2 and the upper end of a tibia 3 connected to the femur 2 by internal 16 and external 17 ligaments. On the tibial end, a cut has been made defining a tibial cutting plane 4 perpendicular to the mechanical axis 5 of the tibia. An ancillary element 6 including a plate 7 and a rod 8 integral with the plate 7, with which it forms a one-piece assembly, is arranged in the joint between the tibia 3 and the femur 2, with its rod 8 inserted in the medullary canal 10 of the femur 2.

The rod 8 is inclined on the surface of the plate 7 in the frontal plane by an appropriate angle C as a function of the patient's anatomy, the surgeon having a set of equipment elements 6 available for this purpose.

The rod is usually fixed at a suitable inclination called "femoral valgus" (angle formed by the anatomical axis and the mechanical axis of the femur) in order to be able to 20 restore a femoral space or virtual space orthogonal to the mechanical axis. The rod 8 is perpendicular to the plate 7 in the sagittal plane (Figure The angle C ((Figure 9) can be between approximately 3 degrees and 11 degrees. The surgeon thus chooses the approximate ancillary device from a set whose rods 8 have an angle C variable within these limits, for example in steps of 2 degrees 50, 90, The rod 8 can have a diameter of about 10 mm for example, and the plate 7 can have a thickness of about 5 mm.

As regards the plate 7, its thickness d is at most equal to that of the tibial plateau of the knee P:OPER\Arl55606-98 spe.doc-20/02A12 -7Aprosthesis which is to be fitted subsequently, this prosthesis being of a type known per se and not shown.

The device 6 is completed by a wedge 9 (Figures 3 and 4) which can be fitted on the plate 7 and is of variable thickness. To this end, the wedge 9 is equipped with means for removable connection to the plate 7. In the example shown, these means are formed by the wedge 9 having a U-shaped profile which can be engaged on the plate 7 and of which the two opposite branches 11 are continued by transverse flanges 12 lodging in conjugate clearances 13 formed on the sides of the plate 7.

I

C

C C o *oo fr 8 The wedge 9 has a median recess 14 made starting from one of its sides and extending parallel to the flanges 12. This recess 14 receives the rod 8 and thus allows the wedge 9 to slide on the plate 7 after the flanges have been fitted in the clearances 13.

_Preparation of the anterior, posterior and distal cuts of the femur 2, using the assembly 6 and its thickness wedge 9, is performed in the following manner.

The assembly 6 is put in place as shown in Figure 1 with its rod 8 in the medullary canal 10 of the femur 2. After distraction with the aid of distraction forceps 41 or any other extensor system, it is observed in this initial position that there is no ligamentary equilibrium, the plate 7 not coinciding with the tibial proximal cutting plane 4, the external ligament 16 being shorter than the internal ligament 17, or vice versa.

The surgeon then effects'an elongation of the retracted capsulo-ligamentary elements of the concavity, which creates an elongation or "release" of the limb, by straightening the femur 2 in order to place it in the position of extension in Figure 2 by means of the distractors 41, in which the plate 7 comes to bear, by distraction, on the tibial cutting plane 4.

In this position, the contact of the plate 7 with the tibial cutting plane 4 ensures effective ligamentary equilibrium irrespective of the femoral wear and without any reference means other than the medullary canal of the femur.

The surgeon then places the wedge 9 on the plate 7 by fitting it via its edges 11 on the sides thereof, while the rod 8 takes up a position in the recess 14 (Figures 3 and The thickness of the wedge 9 is chosen by the surgeon on the basis of an estimate made by trials. The thickness of this wedge can thus vary in increments of 2 mm, the best wedge 9 making it possible to obtain good tensioning of the ligaments 16 -9 and 17 by contact of its upper surface with the nearest distal part 18 of the femur 2. At this stage, the total thickness E of the wedge 9 is equal to the distance between the plane 4 of the tibial proximal cut and the distal part 18 of the femur 2 nearest the tibial cut 4.

The wedge 9 thus makes it possible to determine the total-thickness

E.

In the following step, shown in Figure 5, the surgeon withdraws the wedge 9 and then flexes the femur 2 through 900.

The plate 7 includes a lateral face 7a perpendicular to its distal face used for bearing on the tibial cutting plane 4. This lateral face 7a constitutes a reference surface for the tibial cutting plane 4 to which it must be disposed parallel in the frontal plane (Figures 5-6).

The surgeon proceeds to rotate the assembly 6 so that the lower lateral face 7a of the plate 7 is parallel to the tibial cutting plane 4 in the frontal plane, then he mounts a block 19 on the plate 7. This block 19 forms part of an appliance 21 including an arm 22 bearing on the anterior cortex, and a flange 23 which comes to bear on the posterior cortex. The appliance 21 is known per se and will not therefore be described in detail. It makes it possible to measure the antero-posterior deviation AP between the ends of the arms 22 and 23, that is to say the femoral anteroposterior deviation, in order to determine the corresponding dimension of the femoral implant.

In the following step, illustrated in Figures 6 and 20, the surgeon has removed the measurement appliance 21 and positions, on the plate 7, a cutting block 24 adapted to slide on the plate 7. This block 24, designed in a manner known per se, is equipped with a reference feeler 25 which is able to bear on the anterior reference plane A for the cut that is to be made. The feeler 25 is adjustable in a manner known per se by way of a control button 26.

0 0 0 *0 0 00 0 0 0 0 0 00 0 00 0 10 The surgeon fixes the rotation of the cutting block 24 in such a way that the lower face of this block is parallel to the tibial proximal cut 4. (An embodiment of these means for fixing in rotation is illustrated in Figure 13) The surgeon proceeds with the anterior cut of the part 29 by means of the blade 27, bearing on the anterior face of the block 24, and likewise, with the blade 28, he bears on the posterior face of the block 24 in order to proceed with the cutting of the posterior part 31. The characteristics of the chosen implant determine the distance between the anterior and posterior cutting planes.

The distance EF between the tibial cutting plane 4 and the posterior cutting plane P of the part 31 by the blade 28 is the true deviation in flexion.

This true deviation in flexion EF can then be exactly measured by means of a spacer 32 (Figure 7) inserted between the tibial cutting plane 4 and the posterior cutting plane 33. As has already been indicated, E is the distance between the tibial cutting plane 4 and the nearest distal part 18 of the femur 2. Distance ed, which is the thickness of the distal cut to be made, is determined by the relation ed EF-E in order to ensure 25 correct functioning of the prosthesis to be fitted by the equality and rectangularity of the deviations in extension and flexion.

Finally, it remains for the surgeon to proceed with cutting the distal part 34 (Figure 8) by thickness 30 ed. For this purpose, the surgeon puts in place a device 35 of a type known per se and which does not require detailed description. This device 35 includes a lateral arm 36 which is adjustable in position by means of a control button 37 and which is equipped with a distal cutting block 40. This block 40 slides on the support arm 36 and can bear on the anterior cutting plane 38. A blade 39, whose position is adjustable, makes it possible to effect cutting of the part 34 S according to the desired thickness ed.

I 11 After this, the surgeon can remove the device and can withdraw the assembly 6 from the femur 2.

With a view to fitting the knee prosthesis, chamfers can then be made if the geometry of the implant so justifies.

In the second embodiment illustrated in Figure 11, the ancillary element 51 comprises a rod 52, a rectangular plate 53 fixed to one end of the rod 52, and a wedge 54 of elongate shape and approximately rectangular. The wedge 54 has a width 1 substantially equal to half the length L of the rectangular plate 53, so as to occupy only substantially half of the surface of the plate 53 when this wedge 54 is slid underneath.

The wedge 54 includes an anterior part 55 of thickness dl less than the thickness d2 of its posterior part 56, and which can be slid between the plate 54 and the tibial cutting plane 4.

The thickness dl is variable, so that the total thickness E of the plate 53 and of the anterior part of the wedge 54 is equal to the distance between the tibial proximal cutting plane 4 and the distal end 18 of the femur 2 nearest the said cutting plane, after obtaining ligamentary equilibrium by distraction of the joint between the plate 53 and the distal end of the femur.

Compared to the wedge 9 in Figure 3, the wedge 54 has the advantage of occupying only the left-hand part of Figure 3 for the longest distal part 18 of the femur 2 serving to measure the deviation in extension E. By virtue of this freedom of the right-hand part of the plate 7, situated on the other side of the rod 8, it is possible to accommodate a distractor there, which was difficult to do previously because of the lack of available space. The elongate wedge 54 is easier to manoeuvre and to put in place between the plate 53 and the tibial cutting plane 4, also because of the fact that it is not necessary to fit it on corresponding lateral profiles of the plate 53. Its thicker part 56 serves as a manoeuvring flange for the surgeon.

12 The devices illustrated in Figures 13 to 16 are industrial embodimenmts of the appliances shown diagrammatically in Figures 5 and 8.

Figure 13 shows the block 19, consisting of an upright 57 of U-shaped profile, in which there can slide a support 58 of the arm 22, the horizontal position of the latter relative to the support 58 being adjustable by means of a device 59 known per se. On the upright 57 there may also slide a system 61 for blocking the height position of the rod/plate 51. For this purpose, the plate 53 is pierced with a hole 62 for receiving a screw 63 which can pass axially through the blocking system 61 in order to connect the latter to the ancillary element 51.

The adjusting and blocking system 61 includes (Figure 14) a nut 61 enveloping the head 63a of the screw 63 and which can be screwed onto the threaded rod 63b passing through an opening 70 in the upright 57, a slide 80 and the plate 53. The slide 80 can be displaced in translation in a groove 90 of complementary shape, for example dovetail-shaped, of the upright 57. Once the position of the ancillary element 51 in translation on the upright 57 has been adjusted by sliding the screw 63 in this upright 57, the position thus chosen can be blocked by screwing the nut 61 onto the threaded rod 63b until this nut is blocked on the upright 57.

The slide 80 is connected to the plate 53 by the screw 63. This slide being also engaged in translation in the groove 90, its lower or posterior face 53a is parallel to the arm 23 bearing on the tibial cut 4. The result of this is that the face 53a is always parallel to the proximal tibial cut 4.

The device illustrated in Figure 15 comprises a block 24 identical to that in Figure 6 and a distal cutting block 40 mounted slidably on an arm 36 forming a bracket itself adjustable in vertical position on the block 24. The latter is also equipped with a knurl system 65 passing through the feeler 25 mounted 13 slidably relative to the knurl 65. The block 24 is provided with a device 61 for adjusting and blocking the position of the plate 53 of the ancillary element 51 relative to the block 24, which can be connected to the plate 53 by two screws 66 and one screw 63 engaged in the blocking device 61.

Figure 16 shows a spacer 67 constituting an industrial embodiment of the spacer 32 (Figure The spacer 67 includes a handle 68 continued by a semicylindrical piece 69 of appropriate thickness.

Figures 17 to 19 show an industrial embodiment of a block 71 for cutting chamfers at the distal end of the femur 2, after execution of the anterior, posterior and distal cuts. The block 71 comprises a substantially U-shaped body 72 which is equipped with two lateral handles 73 for manoeuvring and in which the femur 2 can be engaged. Formed in the outer face of the body 72, half way up, on either side of a central opening 74, there are two slots 75 for introduction of cutting 20 blades (not shown). The block 71 is designed in such a way that each slot 75 opens, via diverging passages, onto two slots 81, 82 opening on the inner face of the block, receiving the femur 2: a lower slot 81 and an upper slot 82, the blade introduced via the slot having one or other of the inclinations corresponding to one of the slots 81 and 82. Two other openings 76, 77 formed in the body 72 also make it possible to introduce into the latter cutting blades (not shown) :for forming the other chamfers.

30 The anterior part 85 of the block 71 has a contour composed of a first part 83 corresponding to the outer edge of a right-side prosthesis, and a second part 84 corresponding to the outer edge of a left-side prosthesis.

This arrangement has the advantage of optimum positioning in the medio-lateral direction.

The posterior and distal cuts obtained by means of the ancillary device and the surgical method according to preferred embodiments of the invention are precise and ensure good 0/ 14 ligament tensioning. The rod/plate 6 permits ligamentary equilibrium in extension without the distal cut being made.

On account of the precision of these cuts, it is possible to form the secondary cuts consisting of the chamfers on the femoral end by means of the single block-71 or 79.

According to the surgical method also covered by the present invention and described above, the femoral antero-posterior spacing (AP) is measured in order to determine the corresponding dimension of the femoral implant; a cut is made in the anterior part 29 and then the posterior part 31 of the femur; the true deviation in flexion (EF) between the tibial cutting plane and the posterior femoral cutting plane is measured, the thickness ed of the distal cut to be made is determined by measuring EF-E ed, E being the distance between the tibial cutting plane 4 and the nearest distal part 18 of the femur 2; and finally the cut is made in the distal part 34 with thickness ed.

In addition to the advantages previously indicated, the equipment 6 (rod/plate) according to the invention also makes it possible to effect the entire operational sequence consecutive to obtaining ligamentary equilibrium, itself obtained at the step in Figure 2.

Thus, the invention eliminates the need to make an imprecise second distal cut of the femur and to reposition the latter in extension, which represents a particularly appreciable double advantage.

It should be noted that the antero-posterior cuts of the parts 29, 31 and the distal cut of the part 18 can be executed simultaneously or consecutively as described above, this choice being made by the surgeon.

The invention is open to a number of variant embodiments. Thus, the inclination of the rod 8 on the plate 7 can vary within the limits indicated above, and the wedge 9 can be removably connected to the plate 7 by any appropriate means known per se.

lr I; P:\OPER\Arl55606-98 spe.doc-19/02/(12 14A- Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in Australia.

6* g

Claims (9)

1. Ancillary device for preparing the fitting of a femoral knee prosthesis comprising a tibial plateau and a femoral implant, this ancillary device comprising a centro-medullary rod associated with a means for permitting ligamentary equilibrium to be obtained, characterized in that the device comprises a plate having a thickness at most equal to that of a tibial plateau of the knee prosthesis, and to which the rod is fixed at a suitable inclination to permit the femoral space or virtual space to be restored before wearing of the joint, .9 this plate being intended to bear on a tibial cutting plane after insertion of the rod into the medullary canal of the femur in order to obtain ligamentary equilibrium 9 and with a view to subsequent adjustment of the deviations in extension between the proximal cut of the tibia and the distal end of the femur, and in flexion between the proximal cut of the tibia and the posterior cut of the femur, and in that it is provided with a wedge, which can be fitted on the plate and which is of variable thickness, so that the total thickness of the plate and of the wedge is equal to the distance between the tibial proximal cutting plane and the distal end of the femur nearest to the said cutting plane, after ligamentary equilibrium is obtained by distraction of the joint between the plate and the distal end of the femur.

2. Ancillary device according to Claim 1, characterised in that the wedge is equipped with means for removable connection to the plate, for example by virtue of a U- shaped profile which can be fitted on the plate and whose P:\OPER ri5506-98 spe.do-20/)2/)2 -16- arms are continued by flanges which lodge in conjugate clearances formed on the sides of the plate.

3. Ancillary device according to one of Claims 1 and 2, characterised in that the rod has an inclination in the frontal plane, with respect to the plate, of about 3 degrees to 11 degrees in extension.

4. Ancillary device according to one of Claims 1 to 3, characterised in that the wedge has, starting from one of its edges, a median recess in which the rod fixed to the plate can be inserted. S. Ancillary device according to Claim 1, characterised in that it is provided with a wedge of elongate shape, having a width substantially equal to half the length of ee: the plate, and in that this wedge includes an anterior part of thickness less than that of its posterior part and which can be slid between the said plate and the 20 proximal cut of the tibia, its thickness being variable so that the total thickness of the plate and of the wedge go is equal to the distance between the tibia proximal cutting plane and the distal end of the femur nearest to the said cutting plane, after ligamentary equilibrium is I obtained by distraction of the joint between the plate and the distal end of the femur.

6. Ancillary device according to Claim 1, comprising a device for measuring the antero-posterior femoral distance of the implant, having an upright in which there can slide a support of an arm whose end is adapted to be applied on the anterior distal end of the femur, and a P:\OPER.ArI55616-98 spc.doc-2/I2A)2 -17- system for adjusting the position of the rod/plate in height relative to the upright, mounted slidably on the latter and designed to be able to be connected to the plate.

7. Ancillary device according to Claim 1, comprising a femoral distal cutting block, an arm for supporting this block mounted slidably on a second block provided with a feeler and with a system for adjusting and blocking the position of the plate with respect to the said second block, this system of adjustment being mounted slidably on the said second block and being designed to be able to be connected to the plate.

8. Ancillary device according to Claim 6 or 7, characterised in that the system of adjustment includes a screw passing through an opening in the upright, fixed to a slide movable on the said upright and mechanically 2connected by the screw to the plate, and a nut which is screwed onto the screw in order to block the assembly in the selected position on the upright.

9. Ancillary device according to Claim 9, characterised in that the slide is adapted to slide in a complementary groove of the upright, this groove extending perpendicular to an arm supporting the upright on the proximal tibial cut, so that the posterior face of the plate is parallel to the said support arm. I i. P:\OPER\Arl55M6M6-98 sp.doc-20i)2/02

18- Ancillary device according to Claim 1, characterised in that it comprises a block for cutting the chamfers of the distal end of the femur after execution of the anterior, posterior and distal cuts, and in that this block includes a body which is provided with handles for manoeuvring and in which there are slots and openings for introduction of a cutting blade. 11. Ancillary device according to Claim characterised in that the cutting block has a contour composed of a first part corresponding to the outer edge of a right-side prosthesis, and a second part corresponding to the outer edge of a left-side Sprosthesis. S. 12. Ancillary device according to Claim 1, characterised in that the plate includes a lateral face perpendicular to its distal face used to bear on the tibial cutting plane, this lateral face constituting a reference surface 20 for the tibial cutting plane to which it must be disposed parallel in the frontal plane. 13. Surgical method for preparing the fitting of a femoral knee prosthesis, by means of an ancillary device according to Claim 1, characterised in that the femoral antero-posterior spacing is measured in order to determine the corresponding dimension of the femoral implant; a cutting the anterior femoral part is effected, then of the posterior femoral part; the true deviation in flexion EF between the tibial cutting plane and the posterior femoral cutting plane is measured; the 1/ X^ thickness ed of the distal cut to be made is determined P:\OPER\Ari\556)6-98 spc.doc-20)2/02 -19- by measuring EF-E ed, E being the distance between the tibial cutting plane and the nearest distal part of the femur; and cutting the distal part is effected with thickness ed. Method according to Claim 14, characterised in that after execution of the anterior, posterior and distal femoral cuts, chamfers are formed on the distal end of the femur. 16. Ancillary device, substantially as described with reference to the drawings and/or examples. 15 DATED this 20th day of February, 2002 Memento S.A. a By DAVIES COLLISON CAVE S 20 Patent Attorneys for the Applicant a *i I