PATIENT'S KNEE

The present application claims the benefit of U.S Provisional Patent Application Serial Number 61/528,005, filed on August 26, 201 1 , and claims the priority benefit of French Patent Application N ° FR1 157415, filed on August 19, 201 1 , both of which are incorporated by reference herein.

The present invention relates to patient-specific surgical instrumentation for preparing said patient's knee, typically with a view to implanting a prosthesis therein.

In this way, the invention relates to femoral and tibial instrumentation, also described as "custom-made" or personalised, linked with a specific patient, on whom the instrumentation is exclusively intended to be used. This type of patient-specific instrumentation is opposed to standard instrumentations, which are used without discrimination on various patients, reused a plurality of successive times if applicable, being cleaned and sterilised between each use.

The advent of "custom-made" instrumentations is linked with current possibilities for acquiring sufficiently precise preoperative data for designing, particularly in dimensional terms, instruments wherein the mechanical engagement interfaces with the patient's bones are specifically defined accounting for the precise shape, particularly of the surface relief features, of said bones. The preoperative data used are typically obtained from scan images or, more generally, from any bone mapping data record advantageously obtained non-invasively. These data are processed by computer to control the production of custom-made surgical instruments, once the surgeon has decided details of the surgical procedure to be monitored step- by-step in future surgery.

In this context, the invention relates more specifically to custom-made surgical instrumentations for preparing both the lower end of the femur and the upper end of the tibia in a patient, typically for the purposes of implanting the femoral and tibial components of a knee prosthesis, noting that said prosthesis may also equally be a custom-made prosthesis, i.e. specifically personalised for the patient to undergo surgery, or a "catalogue" knee prosthesis, i.e. a standard, mass-produced, prosthesis, broken down into size-based ranges if applicable. To prepare the lower end of the femur and the upper end of the tibia, the use of patient-specific instrumentation offers a genuine benefit, due to the complexity of the knee joint and the need to prepare the femur and the tibia with maximum precision, in that this preparation determines, directly and significantly, the implantation positioning of the prosthetic components on the femur and on the tibia: it is thus understood that the subsequent mechanical performances of the implanted prosthesis are directly associated with the best possible implantation in terms of the positioning of the prosthetic components with respect to the femur and tibia.

In practice, in the context mentioned above, current custom-made instrumentations generally consist of two monolithic blocks which, as explained above, have been produced using preoperative bone mapping data, relating to the specific patient to undergo surgery, and specifically used by the surgeon on that patient: after positioning the femoral block on the lower end of the femur and positioning the tibial block on the upper end of the tibia, according to a unique predetermined configuration, associated with the engagement based on complementary shapes between a bearing surface, defined by each of the two blocks, and the end of the corresponding bone, the surgeon uses these blocks to control the application of one or a plurality of bone preparation tools, such as a drill bit or an anchoring pin. This or these tool(s) thus enable(s) the surgeon to prepare the ends of the femur and the tibia, particularly for resecting these ends along one or a plurality of very specific geometric planes, these cutting planes being particularly designed to form corresponding plane bearing surfaces for fixing prosthetic components. By nature, these guide blocks, specific to the patient to undergo surgery, do not allow the surgeon any scope for adjustment in respect of the application of the abovementioned bone preparation tools: indeed, the use of such custom-made guide blocks is specifically intended to ensure easier and safer surgical procedures, conducted, during surgery, according to a surgical plan predetermined by the surgeon, particularly on the basis of preoperative bone mapping data. In principle, this one-way, constrained approach ensures an optimal implantation result. However, in practice, surgeons frequently observe that, even when following the surgical plan strictly, the relative positioning between the femoral block and the tibial block may diverge, if only slightly, with respect to the predefined projection: this is frequently associated with the surgeon's intention to correct, during the surgery, the ligament balance of the operated knee, more generally the surgeon's intention to modify, during surgery, the ligament or tissue environment of the operated knee joint. Whatever the reasons, this modification gives rise to unexpected relative displacement between the femoral block and the tibial block, and as a result the modification of the future implantation configuration of the femoral and tibial prosthetic components of the knee prosthesis. In particular, the implantation plan along the patient's HKA axis, i.e. along the axis joining the centre of the head of the femur to the middle of the patient's ankle, via the middle of the knee, is affected: in this way, while the femoral and tibial blocks of the custom-made instrumentation have been, at the preoperative stage, designed accounting for the patient's HKA axis as measured at the preoperative stage, these femoral and tibial blocks lose the benefit thereof in respect of this axis once the relative positioning thereof is affected during surgery.

To be complete, some standard instrumentations are know to be able to balance the knee. EP-A-0 809 969 and WO-A-99/35972 provide examples of this type of instrumentation. However, these instrumentations are designed, in use, to space away the femur ant the tibia, which necessarily affects all of the geometric characteristics of the relative positioning between the femoral and tibial components of the instrumentations. In other words, such instrumentations are unable to measure a free fitting of the relative positioning between the femur and the tibia.

The aim of the present invention is that of providing custom-made instrumentation for preparing a patient's femur and tibia, enabling the surgeon, when the instrumentation is already in position on the femur and tibia during the actual surgical procedure, to account for any modification of the relative positioning between the femur and the tibia.

To this end, the invention relates to patient-specific surgical instrumentation, for preparing the patient's knee, comprising:

- a patient-specific femoral block, defining a fixed bearing surface on the patient's femur, shaped in a manner specifically fitted to the femur, and

- a patient-specific tibial block, defining a fixed bearing surface on the patient's tibia, shaped in a manner specifically fitted to the tibia,

characterised in that the instrumentation further comprises measurement means for measuring peroperatively, the relative positioning between the femur and the tibia, said measurement means including first and second portions, respectively borne by the femoral block and by the tibial block, and which are suitable for, while the femoral and tibial blocks respectively bear in a fixed manner on the femur and the tibia via the bearing surface thereof, cooperating with each other for measuring at least one geometric characteristic of the relative positioning between the femoral and tibial blocks without affecting this characteristic.

One of the underlying ideas of the invention is that of having the femoral and tibial blocks bear additional means for measuring, at the peroperative stage, the relative positioning between these blocks. According to the invention, at least one geometric characteristic of this relative positioning is thus monitored during the actual surgery, particularly after the femoral and tibial blocks have been positioned, in order to, if applicable, detect and quantify the modification thereof by the surgeon. Owing to the invention, the surgeon is thus free, during surgery, to monitor and, if required, adjust the ligament balance of the operated patient's knee joint, without the risk of having to continue the surgery without knowing the extent of the deviation from the predefined surgical plan. In practice, based on the measurement information, supplied by the instrumentation according to the invention, the surgeon is in a position to continue the surgery effectively, accounting for the modification of the relative positioning between the blocks, compared to the initial relative configuration thereof predetermined at the preoperative stage. For this purpose, the surgeon may, if applicable, lock the femoral and distal blocks in the relative configuration selected by the surgeon: advantageously, the instrumentation according to the invention includes ad hoc relative fixing means.

Obviously, particularly for the instrumentation according to the invention to be compatible with the peroperative monitoring and, if applicable, the immediately subsequent correction of the ligament balance of the knee of the patient to undergo surgery, the measurement means belonging to this instrumentation do not give rise, in operation, to constraints on the relative positioning between the femoral and tibial blocks of the instrumentation, at the very least on the geometric characteristic measured by these means. Indeed, the aim of the invention is that of measuring the free fitting of the relative positioning between these femoral and tibial blocks, without interfering with the scope of the fit, at least in respect of the geometric characteristic measured.

According to advantageous additional features of the instrumentation according to the invention, taken alone or according to any technically possible combinations:

- the geometric characteristic is an angle defined, in projection in a frontal plane with respect to the patient, between a femoral geometric axis, which is associated in a fixed manner with the femur, particularly by joining the centre of the head of the femur and the middle of the knee, and a tibial geometric axis, which is associated in a fixed manner with the tibia, particularly by joining the middle of the knee and the middle of the patient's ankle;

- the geometric characteristic is a distance, in projection in a frontal plane with respect to the patient, separating a femoral geometric axis, which is associated in a fixed manner with the femur, particularly the axis of the trochlear groove of the femur, and a geometric tibial axis, which is associated in a fixed manner with the tibia, particularly the axis of the anterior femoral tuberosity;

- the geometric characteristic is an angle defined, in projection in a sagittal plane with respect to the patient, between geometric axes which are respectively associated in a fixed manner with the femur and the tibia along the longitudinal direction thereof;

- the femoral, or tibial, geometric axis is defined by the femoral, respectively tibial, block, and in that the first, respectively second, portion of the measurement means is borne by the femoral, respectively tibial, block and Is oriented in a fixed manner with respect to the femoral, respectively tibial, geometric axis;

- the femoral, respectively tibial, geometric axis is defined by the first, respectively second, portion of the measurement means, and the first, respectively second, portion of the measurement means is borne by the femoral, respectively tibial, block and is oriented in a fixed manner with respect to the femoral, respectively tibial, geometric axis;

- the first and second portions of the measurement means are suitable for cooperating with each other with no mechanical contact;

- the first and second portions of the measurement means are a laser transmitter and receiver;

- the first and second portions of the measurement means are mechanically engaged with each other;

- the first and second portion of the measurement means are shafts articulated in respect of each other and borne in a freely sliding manner along the longitudinal direction thereof by the femoral block and by the tibial block, respectively.

The invention will be understood more clearly on reading the description hereinafter, given merely as an example with reference to the figures wherein:

- figures 1 and 2 are perspective views, from different respective viewing angles, of instrumentation according to the invention, in use on a patient's knee;

- figure 3 is an elevation view along the arrow III in figure 1 ;

- figure 4 is a section along the line IV-IV in figure 3; and

- figure 5 is a similar view to figure 3, showing a different configuration of use to that in figures 1 to 4.

Figures 1 to 5 show surgical instrumentation 1 comprising a plurality of components which will be detailed in succession, in the course of the description of use of this instrumentation on a patient's knee typically for preparing both the lower end of the patient's femur F to receive the implantation of a femoral component of a knee prosthesis, not shown, and preparing the upper end of the patient's tibia T, to receive the implantation of a tibial component of a knee prosthesis.

Hereinafter, the terms "upper", "lower", "posterior", etc. refer to the usual anatomical meaning thereof, assuming that the operated patient remains upright on a horizontal surface.

Prior to the actual implantation surgery, mapping data are compiled in relation to the femur F and the tibia T of the patient to undergo surgery. In practice, these preoperative mapping data may be obtained by various means. For example, scan, X- ray and/or MRI images of the femur F and tibia T are used.

In any case, following this prior data acquisition step, sufficient information is obtained to design and produce a femoral block 10 and a tibial block 20, which are patient-specific, shown in figures 1 to 5.

More specifically, the femoral block 10 has a surface 10A which is shaped in a specifically fitted manner with respect to the lower end of the femur F and which, in use, bears in a fixed manner on said end of the femur, moulding the surface thereof by means of shape complementarity. It is understood that, to arrive at such a precise fit between the bearing surface 10A and the lower end of the femur F, the surface 10A is designed using the preoperative mapping data relating to the femur. In this way, the bearing surface 10A has specifically personalised relief features with respect to the operated patient which, by engaging with complementary relief features defined by the surface of the lower end of the femur, only allow one bearing configuration fitted on the femur F, as shown in figures 1 to 5. For example, in the embodiment shown in the figures, the bearing surface 10A covers the anterior and distal areas of the lower end of the femur F, moulding the relief features of these areas in a fitted manner.

In the same way, the tibial block 20 has a surface 20A which is shaped in a specifically fitted manner with respect to the upper end of the tibia T and which, in use, bears in a fixed manner on said end of the tibia, moulding the surface thereof by means of shape complementarity. Similar technical considerations to those developed above for the bearing surface 10A are applicable to the bearing surface 20A. For example, in the embodiment shown in the figures, the bearing surface 20A covers the anterior and distal areas of the upper end of the tibia T, moulding the relief features of these areas in a fitted manner.

In use, the femoral block 10 bears in a fixed manner, via the surface 10A thereof, on the lower end of the femur F, whereas the tibial block 20 bears in a fixed manner, via the surface 20A thereof, on the upper end of the tibia T. In a manner not shown in the figures, this fixation is, for example, produced by means of bone anchoring pins inserted into through holes defined by the blocks 10 and 20 and opening onto the surface 10A and 20A thereof, until they are set and thus locked in the bone substance of the femur F and tibia T. The blocks 10 and 20 are then as shown in figures 1 to 4: it is understood that, for initial relative positioning between the femur F and the tibia T, the blocks 10 and 20 are positioned with respect to each other in a predefined initial configuration, wherein the geometric characteristics are known in advance, based on the preoperative mapping data. In particular, the relative angular positioning between the blocks 10 and 20 along the longitudinal direction of the patient's leg is predefined: more specifically, the relative angular positioning between the blocks 10 and 20 may be characterised by the angle HKA, i.e. the angle formed, in projection in a frontal plane with respect to the patient, as in figure 3, between a between a femoral geometric axis HK, joining the centre H of the head of the femur F and the middle K of the knee, and a tibial geometric axis KA, joining the middle K of the knee and the middle A of the ankle situated at the lower end of the tibia T. In this way, in the example shown in figure 3, it is observed that the femoral 10 and tibial 20 blocks are designed, after the initial positioning thereof on the femur F and tibia T, to be positioned with a relative angle HKA, i.e. an angle defined between the axes HK and KA, equal to 180 °.

Moreover, in a manner not shown in the figures, it should be noted that the femoral 10 and tibial 20 blocks are, at the preoperative stage, designed to guide the peroperative application, on the femur F and tibia T respectively, of at least one bone preparation tool, such as a drill bit, anchoring pin or cutting blade: during the custom design of the blocks 10 and 20, specific arrangements of these blocks, such as through holes and/or slots, are incorporated in these blocks to guide, in a non-adjustable manner, i.e. with no scope for the surgery, the positioning of means for subsequently cutting the femur and the tibia, such as a cutting block, so as to resect the ends of the femur and tibia along one or a plurality of resection planes designed to subsequently act as corresponding plane bearing surfaces for fixing prosthetic components, on the femur and tibia respectively, of a knee prosthesis.

In this context, it is understood that the positioning between the preparation of the femur F, guided by the block 10, and the preparation of the tibia T, guided by the block 20, is based on predetermined knowledge of the relative positioning configuration between the blocks 10 and 20 after these blocks have been positioned and borne in a fixed manner on the femur and tibia while the latter are in a predefined original configuration, on the basis of the preoperative mapping data obtained prior to the actual surgery. In particular, in the example herein, the preparation of the femur F with the block 10 and the preparation of the tibia T with the block 20 are designed to be carried out while the blocks 10 and 20 are positioned with respect to each other with an angle HKA of 180°, as mentioned above. It should be noted that this value of 180° for the angle HKA is not limiting for the instrumentation 1 , in that, even if this value of 180° is frequently an optimal value, a slightly different value may be sought by the surgeon or required by the surgeon in view of the operated patient.

Consequently, as explained in the introductory part of this document, as soon as the surgeon modifies, even slightly, the relative configuration between the femur F and the tibia T after fixing the blocks 10 and 20 thereon, the angular positioning between the blocks 10 and 20 along the axes HK and KA is modified; in other words, the angle HKA between the blocks 10 and 20 is no longer equal to 180 °. The instrumentation 1 addresses this issue using the measurement means 30 described in detail hereinafter. In practice, modification, by the surgeon, of the initial relative configuration between the femur F and the tibia T occurs regularly, in that it systematically takes place once the surgeon seeks to monitor and, if applicable, correct the ligament balance of the knee joint.

As shown in figures 1 to 5, the measurement means 30 include two main components, i.e., in the example of an embodiment shown in the figures, a laser transmitter 31 and a laser receiver 32, which are respectively borne in a fixed manner by the femoral block 10 and the tibial block 20. This transmitter 31 and this receiver 32 are based on a technology known per se: a laser beam 31 A, transmitted by the transmitter 31 , is envisaged to strike a detection surface 32A defined by the receiver 32 such that, based on the specific portion of the surface 32A touched by the beam 31 A, signal processing means, connected to the transmitter 31 and to the receiver 32, are capable of reverting, by calculation, to the inclination of the beam 31 A with respect to the surface 32A.

According to the invention, so that the transmitter 31 and receiver 32 cooperate with each other so as to measure, during the surgery, the angle HKA between the femoral 10 and tibial 20 blocks, the transmitter 31 is fixedly mounted on the block 10 such that the beam 31 A thereof extends along the axis HK, whereas the receiver 32 is fixedly mounted on the tibial block such that a median axis of the detection surface 32A thereof extends along the axis KA. For this purpose, two embodiment options may be envisaged. In this way, in the case of the transmitter 31 , a first option consists of the femoral block 10 being designed by defining the axis HK, the transmitter 31 in this case being mounted and fixed on the block 10 oriented in a fixed and predefined manner with respect to the axis HK defined by the block 10: for this purpose, as in the example of an embodiment shown in the figures, the transmitter 31 is mounted on the block 10 while being received in a fitted housing, defined by the block 10, particularly the face thereof opposite the bearing surface 10A. According to one second embodiment option, the transmitter 31 is designed to define the axis HK, the orientation of the beam 31 A thereof being for example adjustable with respect to the rest of the transmitter 31 : in this case, the transmitter 31 is mounted on the block 10 such that the block is oriented in a fixed and predefined manner with respect to the axis HK defined by the preset beam 31 A in the transmitter 31 .

Obviously, the above considerations in respect of the definition of the axis HK by either the block 10 or the transmitter 31 may be transposed to the definition of the axis KA by either the tibial block 20 or the receiver 32.

The components of the measurement means 30 having been described in detail, the progress of the surgery, the first steps of which are described above, is contained in the remainder of the description. In this way, after the surgeon has modified the relative initial configuration between the femur F and the tibia T, particularly for reasons associated with the monitoring of the ligament balance of the knee, an example of a modified configuration obtained is shown in figure 5: as can be seen in this figure, the angle HKA is strictly greater than 180 °, however noting that the relative inclination between the femur and the tibia is voluntarily exaggerated in this figure, for visibility reasons. It is understood that, as soon as the angle HKA is modified from the initial value thereof, equal to 180 ° in the example shown herein, the surgeon is immediately warned by the measurement means 30: indeed, in this case, the laser beam 31 A points towards a portion of the surface 32A thereof, different to that through which the axis KA passes. By means of signal processing provided by the receiver 32, the angular variation applied to the angle HKA is quantified and communicated to the surgeon, particularly by an ad hoc display, not shown in the figures.

Based on this information supplied by the measurement means 30, the surgeon is then capable of continuing the surgery while accounting for the modification of the relative positioning between the blocks 10 and 20, with respect to the initial configuration thereof on the basis whereof the surgical procedure was planned. In practice, various surgical options are available to the surgeon. For example, a first option consists of the surgeon readjusting the ligament balance to reposition the blocks 10 and 20 according to the initial configuration thereof, particular to restore a relative angular positioning such that the angle HKA thereof is again equal to 180°: in this case, subsequent surgical procedures may be carried out in compliance with the initial plan decided at the preoperative stage, as explained above.

A further solution, in principle more respectful of the natural ligament environment of the knee joint, consists of accounting for the measurement of the relative positioning between the femur F and the tibia T, obtained in figure 5, to modify the subsequent application on the femur and/or on the tibia of the bone preparation tool(s) accordingly, noting that, in this case, the tool(s) can no longer, at least for one of the bones of the femur and tibia, be guided by the corresponding femoral 10 or tibial 20 block: in other words, the surgeon then clears at least one of the blocks 10 and 20, in favour of a further ancillary, for example a standard ancillary, whereby the surgeon will be able to account for the value measured for the angle HKA in the configuration presented by the femur F and tibia T to receive the femoral and tibial components of the knee prosthesis.

A further solution consists of continuing the surgery with the blocks 10 and 20 while the femur F and tibia T are in the configuration not initially envisaged in figure 5 but, in this case, the components of the subsequently implanted prosthesis would be adjusted to compensate for the variation in the angle HKA. For example, an insert, generally present between the femoral and tibial prosthetic components of such a knee prosthesis, would be selected as dissymmetrical with respect to the internal and external condyles, to accommodate the variation in the angle HKA.

Regardless of how the surgery intended to implant the knee prosthesis continues and ends, it should be noted that, according to the invention, the measurement, by the means 30, of any alteration of the relative positioning between the femoral block 10 and the tibial block 20, particularly that of the angle HKA between same as explained above, is carried out without said measurement means 30 interfering between the free relative positioning of the blocks 10 and 20. In other words, the measurement means 30 are not designed to adjust or constrain the relative positioning of the blocks 10 and 20, but merely to measure this positioning, more specifically any change of this position during the subsequent actual surgery. For the embodiment shown in figures 1 to 5, this aspect of the invention is obvious in that the cooperation between the transmitter 31 and the receiver 32 is optical in nature, associated with the interaction between the laser beam 31 A and the detection surface 32A. More generally, in that, for alternative embodiments not shown, the measurement means 30 have other embodiments, preference will be given to the embodiments wherein the portion of these means, borne by the femoral block 10, does not create any mechanical interaction with the part of these means, borne by the tibial block 20.

Taking the above into account, one alternative embodiment, not shown, of the measurement means 30 may take the form of an ad hoc mechanism, physically connecting the femoral 10 and tibial 20 blocks. In this way, for example, to measure the relative angular positioning according to the angle HKA between the blocks 10 and 20, the block 10 is provided with a rigid shaft, extending lengthwise along the axis HK, while being mounted on this blockl O in a freely sliding manner along this axis, whereas the tibial block 20 is also provided with a rigid shaft extending lengthwise along the axis KA, while being free to slide along this axis KA, both shafts mentioned above being articulated with respect to each other with a pivot connection substantially centred on K, about a joint axis perpendicular to both the axis HK and the axis KA.

Various arrangements and alternative embodiments of the instrumentation 1 described herein can also be envisaged:

- instead of providing the surgeon with feedback via a display screen, in respect of the measurements made by the means 30, audio, light or tactile feedback may be provided;

- other geometric characteristics than the angle HKA, in respect of the relative positioning between the femoral block 10 and the tibial block 20 may be measured by instrumentation according to the invention; for example, this applies to the distance, in projection in a frontal plane with respect to the patient, separating the axis of the trochlear groove of the femur F and the axis of the anterior tuberosity of the tibia T, this distance having a direct impact on the stability of the kneecap of the prosthetic knee; a further example is the angle, in projection in a sagittal plane with respect to the patient, defined between longitudinal geometric axes, respectively associated with the femur and the tibia, while the knee is fully extended, this angle generally being called "genu flexum" when open to the rear, whereas it is called "genu recurvatum" when open to the front; and/or

- instead of the femoral 10 and tibial 20 blocks, bearing the measurement means 30, being blocks to be used at the start of the prosthesis implantation procedure, particularly to guide the application of the preparation of the ends of the femur and tibia, as explained above, the measurement means 30 may be borne by custom femoral or tibial blocks designed to bear on the femur and tibia after the ends thereof have at least partly been resected; in this case, the corresponding instrumentation is used to check, retrospectively, that the relative positioning between these femoral and tibial blocks, particularly the angular positioning thereof along the angle HKA, continues to meet the specifications of the surgical plan decided in advance.