WO2020079516A1

WO2020079516A1 - Intermediate device or under- tibial insert, prosthetic component provided with such intermediate device and method for assembling them

Info

Publication number: WO2020079516A1
Application number: PCT/IB2019/058413
Authority: WO
Inventors: Giovanni Faccioli; Renzo Soffiatti
Original assignee: Tecres S.P.A.
Priority date: 2018-10-18
Filing date: 2019-10-03
Publication date: 2020-04-23
Also published as: IT201800009555A1

Abstract

Prosthetic component adapted to be implanted in use at a patient's bone, such as a tibial component (1) of a knee prosthesis adapted to be implanted at one end of the patient's tibial bone at a knee joint, comprises a body provided with a bottom surface (1b), adapted in use to face the patient's bone, wherein the prosthetic component comprises an intermediate device (20), placed in use between the bottom surface (1b) of the prosthetic component and the patient's bone, adapted to stably constrain the prosthetic component to the patient's bone.

Description

“INTERMEDIATE DEVICE OR UNDER- TIB IAL INSERT, PROSTHETIC COMPONENT PROVIDED WITH SUCH INTERMEDIATE DEVICE AND METHOD FOR ASSEMBLING THEM” TECHNICAL FIELD OF THE INVENTION

The present invention refers to an intermediate device (or insert) to be inserted below a prosthetic component, such as the tibial component of a permanent prosthesis, adapted to be implanted at a patient’s bone such as the tibial bone of a knee joint.

In addition, the present invention also refers to a prosthetic component, such as a tibial component of a knee prosthesis, provided with one such intermediate device (or insert) and method for the assembly thereof.

STATE OF THE PRIOR ART

As is known, the joint prostheses, after having been implanted in the human body - even though they are so-called“permanent” devices - may require the removal thereof, in case, for example, of an infection that arose in the implant site.

Another cause which can determine the removal of a prosthesis or of one of its components is that there might not be the fixed constraint of connection of the same to the bone of the human body at which it was implanted.

Such possibility occurs for example with reference to the cemented knee prostheses, since the tibial component can“unstick” from the bone cement which is used for its connection to the tibial bone.

Generally this type of problem is encountered for the tibial component, and only rarely for the femoral component.

In addition, it is possible that one of the causes of this“default” of the prosthesis is to be found in the excessive viscosity of the bone cement which is used by the surgeon (which is defined high-viscosity cement). This type of cement, in fact, when used in a late step of its hardening process, can decrease the capacity of adhesion to the prosthesis and to the bone.

Another cause can be encountered in the structural conformation of the prosthesis (with particular reference to the bottom of the tibial component, facing the patient’s tibial bone), which lacks undercuts capable of retaining and“trapping” a certain quantity of bone cement, necessary for defining a stable connection and constraint with each other and with the patient’s bone.

Indeed it is known that in order to ensure a suitable seal and improve the duration of the implants, it is necessary that a uniform layer of bone cement be present between the tibial bone and the bottom of the tibial component (prosthesis - bone interface). In addition, it is necessary to prevent the metal prostheses of cemented type from coming into direct contact with the bone, even only at a few points.

Nevertheless, in order to implant the component on the bone, after having positioned a layer of bone cement in the implant site and on the lower face of the prosthesis, the prosthetic component is thrust with force against the patient’s bone, so as to allow the correct positioning and implant thereof. This pressure that is exerted by the surgeon, together with the absence of undercuts, ensures that the cement placed at the prosthesis - bone interface is crushed and exits from its site, leaving only a very thin layer thereof to exert its connection function.

This is also due to the fact that the cement does not enter deep enough into the spongy tissue of the tibial bone plate, hence there is no integral anchorage between bone and prosthesis.

Secondly, such pressure - and the substantial absence of bone cement - cause the contact with the bone of a raised edge (indicated with A in figure 1) which is normally present for example at the bottom of the tibial component, along the perimeter of the same (i.e. of the horizontal tibial flange) and directed towards the bone (below which the bone cement completely exits).

As a result, such edge A is in direct contact with the bone, canceling the force distribution action of the cement. Consequently the strong mechanical load stresses to which the patient subjects the joint are transferred - instead of to the prosthesis and to the intermediate bone cement - by means of such edge A directly to the bone, which can be reabsorbed and trigger the process of aseptic mobilization of the prosthesis itself. In addition, such edge A does not have a size such to form an undercut for locking the bone cement positioned by the surgeon. All these disadvantages signify that the contact surfaces between prosthesis and bone cement, as well as between bone cement and bone, are the weakest points of the implant which often cause the need to substitute the permanent prostheses.

OBJECTS OF THE INVENTION

One object of the present invention is to improve the state of the prior art.

A further object of the present invention is to provide an intermediate device or insert, adapted to be connected to a prosthetic component, such as a tibial component of a prosthesis, and to ensure a layer of biocompatible material (constituted by the intermediate device itself) to which the bone cement correctly adheres in a stable manner.

Still a further object of the present invention is to provide a prosthetic component such as a tibial component of a knee prosthesis, provided with an intermediate device adapted to ensure a layer of a biocompatible material to which the bone cement correctly adheres in a stable manner, with consequent stable constraint to the patient’s bone. A still further object of the present invention is to provide an easy application method for constraining a prosthetic component to an intermediate device, so as to obtain a stable and durable constraint with the patient’s bone.

In accordance with one aspect of the present invention, a prosthetic component is provided, possibly a tibial component of a knee prosthesis, provided with an intermediate device according to the enclosed claim 1.

In accordance with another aspect of the present invention, an intermediate device is provided according to the enclosed claim 14.

Finally, a method is provided for the assembly of a prosthetic component and of an intermediate device according to the enclosed claim 19.

The dependent claims refer to preferred and advantageous embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the present invention will be clearer from the detailed description of a preferred but not exclusive embodiment of an intermediate device for a prosthetic component such as a tibial component of a knee prosthesis, illustrated as a non-limiting example in the enclosed drawing tables in which:

figure 1 is a bottom perspective view of tibial components of a knee prosthesis according to the state of the art;

figure 2 is a slightly bottom side perspective view of a tibial component of a knee prosthesis provided with an intermediate device according to a first version of the present invention;

figure 3 is a top view of an intermediate device according to a first version of the present invention pursuant to figure 2;

figure 4 is a bottom view of an intermediate device according to a further version of the present invention;

figure 5 is a bottom view of an intermediate device according to a further version of the present invention;

figure 6 is a perspective view of the intermediate device pursuant to figure 5; figure 7 is a side view of the intermediate device pursuant to figures 5 and 6; figure 8 is a top perspective view of the intermediate device pursuant to figure 6; figure 9 is a further side view of the intermediate device pursuant to figures 5 and 6;

figure 10 is a bottom perspective view of an intermediate device according to a still further version of the present invention;

figure 11 is a side view of the intermediate device pursuant to figure 10;

figure 12 is a top perspective view of the intermediate device pursuant to figure

10;

figure 13 is a further side view of the intermediate device pursuant to figure 10; figure 14 is a front perspective view of a tibial component of a knee prosthesis provided with an intermediate device according to the present invention and applied to a patient’s bone;

figure 15 is a cross section view of the assembly of figure 14.

EMBODIMENTS OF THE INVENTION

With reference to the enclosed figures, reference number 1 genetically indicates a tibial component of a (total) knee prosthesis. Even if in the following description and in the enclosed drawing tables, one such component will be described and illustrated, the present invention is to be intended as valid also for other prosthetic components, to be implanted also in other districts of the human body with respect to the knee joint.

The present invention mainly refers to the zone and/or to the surface of the prosthetic component adapted to be constrained to a patient’s bone.

The tibial component 1 comprises, at the patient’s bone placed in use at the implant site, an intermediate device 20.

Such device 20 is defined“intermediate” since it is positioned between the prosthetic or tibial component 1 (which is generally made of metal) and the bone tissue of the patient. The intermediate device 20 is therefore a kind of insert which is positioned in use below the tibial component, at the patient’s bone.

The intermediate device 20 improves and ensures an effective cementing of the tibial component 1 on the patient’s tibial bone.

On the opposite side with respect to the intermediate device 20, the tibial component 1 can be provided with a joint body 10, for example made of ultrahigh molecular weight polyethylene or UHMWPE.

This joint body 10 (illustrated in figure 2) allows an optimal articulation with another patient’s bone, for example the head of a femur at a joint of the human body, such as the knee, or with a further component of a prosthesis, such as for example the femur component of a knee prosthesis.

Such joint body 10 can be absent, in one version of the invention, and the tibial component 1 can directly have a joint surface with the same function. In addition, the joint body 10 can be connected removably or not removably to the upper surface la of the tibial component 1, depending on the specific versions.

Figures 2 and 3 illustrate a first version of the intermediate device 20 according to the present invention, respectively in a version assembled to a tibial component (fig. 2) and in single version (fig. 3).

The intermediate device 20 is positioned in use below the tibial component 1, so as to transfer to the patient’s bone (tibia) the load stresses that reach the prosthesis. In such a manner, one completely eliminates the risk of buckling load directed between the metal of the prosthesis and the bone, a deleterious possibility (as recalled above), but probable according to the conventional techniques that are normally used.

Most of the permanent prostheses, in fact, are still today cemented to the bone at the implant site. As stated above, the cementing of the bone-cement interface is one of the weak points of this technique.

In order to have a valid anchoring of the cement to the bone, it is necessary that the bone cement be able to diffuse into the bone itself. The resected bone (e.g. of the tibial plate) nevertheless presents considerable difficulties (mainly hydraulic) regarding the penetration of the cement since a hollow body, full of a liquid (such as the resected bone tissue, which is filled with blood, fat and biological fluids) cannot be filled with another liquid, such as the bone cement.

Therefore, a hollow body, in order to allow the penetration and the diffusion of the bone cement, must be empty.

The spongy bone is characterized by trabecular bones intertwined with each other which create an intercommunicating porous network with variable diameter, which can also reach 1 mm. In order for the bone cement to be able to enter into the spongy cavities, these must be free of fat, blood and other present biological fluids.

In order to obtain this result, washing techniques are effectively applied, such as systems termed“Jet lavage” or pulsed“Jet lavage”. These are systems which thrust pressurized water and simultaneously reabsorb it so as to empty the trabecular cavities of the fat and other indicated substances in the best possible manner.

After this, it is necessary to empty the trabecular cavities of the washing water and this is partially obtained due to the suctioning action of the washing system itself and also concluding by stopping up with a gauze in order to empty the cavities of water.

Nevertheless, such cavities do not remain empty for long, since blood slowly comes to once again occupy them, rendering the drying fruitless.

Therefore, it is necessary to quickly intervene by applying the cement with the objective that this penetrate into the cavities as deeply as possible, i.e. at least 3-5 mm. Indeed, the trabecular micro-holes present strong resistance to filling by means of bone cement (still due to hydraulic principles).

For such reason, the simple deposition of the cement, followed by a manual compression as usually occurs, produces a poor result or even has no success at all.

In addition, since high-viscosity cements tend to be used in order to prevent leaking into and dirtying of the surrounding tissues, this operation is even less probable, since a high-viscosity cement has a hard time entering into the intra-trabecular spaces.

The final result is that the overall anchoring of the cement to the bone is defective from the start.

The intermediate device 20, however, overcomes such drawbacks, according to that indicated hereinbelow.

First of all, the tibial component 1 comprises a (tibial) body provided with a bottom surface lb, adapted in use to face the patient’s bone, such as for example the tibial bone plate (resected), and an upper surface la, adapted in use to face towards the joint body 10 and/or to face towards a further component of a permanent joint prosthesis, and/or to face towards the femoral component of the knee prosthesis and/or to face towards the femoral bone of the patient.

At the bottom surface lb, the tibial component 1 can be provided with a stem 2, adapted to be inserted in use in the medullary canal of the tibia of the patient.

The stem 2 is substantially perpendicular to the body of the tibial component 1 and/or to its bottom surface lb and is substantially coaxial with the longitudinal central axis of the patient’s bone, such as his/her tibia.

The tibial component 1 has a thickness 3 corresponding to the distance between upper surface la and bottom surface lb.

The body of the tibial component 1 is substantially flat, in the sense that the distance between bottom surface lb and upper surface la is substantially constant.

Analogously, the intermediate device 20 comprises a lower surface 20b, adapted in use to face towards the tibial bone plate (resected) and an overlying surface 20a, opposite the lower surface 20b and adapted in use to face towards the tibial component 1.

In substantially central position, the intermediate device 20 also comprises a through opening 20c, adapted in use to allow the passage of the stem 2 of the tibial component 1

The intermediate device 20 has a thickness 23 corresponding to the distance between overlying surface 20a and lower surface 20b.

In at least one version of the invention, the thickness 23 of the intermediate device 20 measures at least 2 mm.

In one version of the invention, for example illustrated in figure 3, the intermediate device 20 has substantially flat conformation in which the overlying 20a and lower 20b surfaces are substantially parallel to each other.

In one version of the invention, the lower surface 20b comprises at least one hollow cell 22 or, in a preferred version of the invention, a plurality of hollow cells 22.

Such at least one hollow cell 22 is extended starting from the lower surface 20b of the intermediate component 20 towards the patient’s bone, in particular the tibial bone (resected) of the knee joint.

Each cell 22 has three-dimensional conformation substantially in the shape of a prism or of a cylinder having polygonal base, for example a triangle, square, pentagon, hexagon, octagon etcetera or circular base.

One base of such cell 22, that closest to the patient’s bone, is open, in a manner such that the cell 22 is internally hollow.

The lateral wall of each cell 22 is instead extended as stated above from the lower surface 20b of the intermediate device 20, resulting overhanging from the latter.

The lateral wall of each cell is formed by lateral faces 24, having a parallelogram or polygonal shape.

In at least one version of the invention, such at least one cell 22 is made in a single piece with the intermediate device 20, e.g. via molding, for example of conventional or three- dimensional type.

Naturally, the intermediate device 20 has a plan conformation substantially corresponding to that of the tibial component 1, i.e. a plan conformation that is substantially C-shaped.

Such C-shaped conformation (considering the position at which it is implanted in use) comprises a first front section 28 that is substantially continuous and substantially flat and/or slightly convex, a rear section 29 that is concave and provided with a receding area 29a.

Two lateral sections (one right and one left) are then present, 30a, 30b, which are also substantially continuous and substantially flat and/or slightly convex (with the convexity of one mirrored to that of the other).

The lateral sections 30a, 30b laterally connect the front section 28 and the rear section 29; the receding area 29a is positioned substantially in central position with respect to the rear section 29 and is extended towards the center of the intermediate device 20, in the direction of the opening 20c (but without reaching it)

The sizes of each cell 22 can be equal to or different from those of the adjacent cells 22. For example, the diameter or the diagonal or the side of the base of the cell 22 can have a size comprised between 3 mm and 15 mm or preferably between 5 mm and 10 mm or still more preferably 8 mm.

Analogously, the height H of the lateral wall can be the same for each cell 22 or it can be different from cell to cell.

In particular, the height H of the cell 22 and/or of its lateral wall 24 can have a size comprised between 3 mm and 15 mm or preferably between 5 mm and 10 mm or still more preferably 8 mm.

Such at least one cell 22 is in use adapted to be forced to enter and/or infiltrate into the spongy part of the patient’s bone. Therefore, the greater the dimensions of the at least one cell 22, the smaller the shear strength exerted on the spongy bone of the patient himself/herself.

If the height H of the lateral wall 24 varies from cell to cell, in one version of the invention, e.g. illustrated in the section of figures 7, 9, 11, 13 and 1, such height can decrease moving towards the external perimeter (lateral periphery at the lateral sections 30a, 30b) of the intermediate device 20. For example, in the central part of the insert, the cells 22 can have a certain height, or maximum height H2, while in the outermost part these can have a reduced height, or minimum height Hl.

Such decrease of height H can be progressive and/or scalar.

In this case, also the height of a single cell 22 varies, passing from the lateral face 24 placed at the central area of the intermediate device 20 up to the lateral face 24 placed at the lateral sections 30a, 30b of the intermediate device 20.

As is visible for example in figure 9, in which the intermediate device 20 and its rear section 29 are illustrated, the plurality of cells 22 have a height H2 at the center of the device and a height Hl at the lateral sections 20a, 30b, considering that this is a progressive decrease and therefore also the height of each cell 22 progressively decreases from cell to cell.

In addition, as is visible in figure 6, the plurality of cells 22 is arranged to form a kind of 3-shape or double C-shape, in which the free ends of the 3 and/or of the double C are positioned at the first front section 28 and/or at the sides of the opening 20c, the common apex or central vertex of the 3-shape is positioned at the center of the intermediate device 20, and/or at the rear with respect to the opening 20c, while finally the convex sections of the 3 -shape or of the double C-shape are positioned at the rear section 29 of the intermediate device 20, at and/or frontally with respect to the receding area 29a.

This conformation ensures that the plurality of cells 22 act as an inlet for the insertion of the device 20 in the spongy part of the patient’s bone.

As illustrated for example in figure 10, in another version of the invention, the plurality of cells 22 is arranged according to two opposite Cs, in which a first end of each C is positioned at the first front section 28 and/or at the sides of the opening 20c, the other end or second end of each C is positioned at the center of the intermediate device 20, and/or at the rear with respect to the opening 20c, while finally the convex sections of each C are positioned at the lateral sections 30a, 30b of the intermediate device 20.

In this or also in other versions of the intermediate device 20, additional walls 34, 34’ can be present.

Such additional walls 34, 34’ can act as reinforcement for the lateral wall 24 of the at least one cell 22, and/or they can further facilitate the entry and/or the insertion of the intermediate device 20 in the spongy part of the patient’s bone.

As is visible for example in figure 10 and in figure 13, two additional walls 34 are present, each of connection respectively between the first and between the second free ends of the two Cs of the conformation of the plurality of cells 22.

These additional walls can have a triangular conformation, with apex directed in use towards the patient’s bone, with the above-indicated objectives.

Still in figure 10, also the additional walls 34’ are visible, set against the lateral faces 24 of the cells 22, and in particular against the internal lateral faces which are shared among adjacent cells 22.

Such additional walls 34’ can have triangular conformation, in particular right triangle shape, with the perpendicular sides of such triangle respectively adjacent to the lateral face 24 and to the lower surface 20b of the intermediate device 20.

In this manner, the diagonal of the triangle that constitutes the additional wall 34’ is tilted towards the lateral wall 24 starting from the lower surface 20b.

In this manner, it is possible to stiffen and/or strengthen the structure of the at least one cell 22, in a manner so to be able to sustain the forces for making such at least one cell 22 enter into the spongy part of the patient’s bone.

The at least one additional wall 34, 34’ can also have polygonal conformation, without departing from the protective scope of the enclosed claims.

The at least one cell 22 or the plurality of cells 22 can also have other configurations without departing from the protective scope of the enclosed claims.

For example, the at least one cell 22 can be spatially separated from other cells 22 present at the lower surface 20b of the intermediate device 20. For example, such cells

22 can be arranged along a transverse direction of the human body (i.e. be arranged substantially along a direction that connects the lateral sections 30a and 30b), with the cells 22 separated from each other or connected to each other (with an interval naturally at the opening 20c of the intermediate device 20).

In addition, such cells 22 can be arranged in a substantially random manner at the lower surface 20b.

Also in such conformations, the height H of the lateral wall 24 of the at least one cell can be equal to that of other cells 22 or the cells can have a height H2, Hl or intermediate between these two values depending on the position.

As stated above, each cell can have its lateral faces 24 all with the same height H but with height different from that of the adjacent cells 22. Alternatively, one cell can have its lateral faces 24 at different heights, in a manner so as to have a height H2 at the lateral faces 24 and/or at the cells 22 closest to the center of the intermediate device 20 and a height Hl at the lateral faces 24 and/or of the cells 22 closest to the lateral periphery of the intermediate device 20.

In an alternative version, the greater height H2 is situated in proximity to the lateral periphery of the intermediate device 20 while the height Hl is situated in proximity to the center of the intermediate device 20.

The thickness of the lateral wall 24 of the at least one cell 22 can have a size comprised between 0.3 and 0.9 mm or between 0.5 and 0.7 mm.

As can be observed in the drawings, in at least one version, the upper edge of the lateral wall of the cells 22 is tilted, like a blade or wedge, so as to facilitate the cutting of the spongy part of the patient’s bone and the insertion of the intermediate device 20.

The at least one cell 22 is adapted to house the bone cement which serves for constraining the tibial component 1 to the resected bone, by means of the interposition of the intermediate device 20.

Such bone cement, in at least one version of the invention, is for example a bone cement based on polymethylmethacrylate or PMMA, with low viscosity.

Such cement, nevertheless, notwithstanding the fact that it is a low-viscosity cement, does not run the risk of leaking into the soft tissues surrounding the patient’s bone since it is contained and housed in the at least one cell 22.

In one version of the invention, for example illustrated in figures 5, 6, 8, 10 and 12, at at least one cell 22 or at at least several of the plurality of cells 22, the intermediate device 20 comprises at least one hole 25.

Such at least one hole 25 passes through the thickness 23 of the intermediate device 20. In use, such at least one hole 25 allows the bone cement C contained in the cells 22 to pass into at least one corresponding interspace present in the tibial component 1 and/or acts as an outlet for possible air present within the at least one cell 22.

Advantageously, in fact, according to at least such version of the invention, the bottom surface lb of the tibial component 1 will be provided with at least one interspace or undercut, so as to allow the insertion or gripping of the bone cement C in those zones. Such interspaces also have the function of discharging the air possibly trapped by the cement on the bottom of the cells 22, acting as air escape-ways and - since they are not very deep - they do not compromise the mechanical properties of the prosthesis itself. The interspaces present in the bottom surface lb of the tibial component 1 can have the configuration of at least one pair of grooves, so as to house respective ridges present in the overlying surface 20a of the intermediate device 20 (or vice versa).

Alternatively, at least one pair of recesses and/or impressions can be present, adapted to house respective pins 26 and/or raised elements 27 (visible for example in figures 8 and 12) which are extended starting from the overlying surface 20a in the direction of the bottom surface lb of the tibial component 1.

Such raised elements 27 can also act as“thickness” which separates the bottom surface lb from the overlying surface 20a, creating a free space in which the fluid cement C (exited from the holes 25) can flow, for the gripping between these two elements.

The pins 26 can have a cylindrical conformation (as visible in figure 8) or tubular conformation and/or open section (as visible in figure 12) or closed section, depending on the specific requirements of anchoring to the tibial component 1.

In figures 14 and 15, it is possible to see such bone cement C at the contact surface between the bottom surface lb of the tibial component 1 and the overlying surface 20a of the intermediate device 20.

In particular, in the section of figure 15, it is also seen that the bone cement C contained in the cells 22 penetrates into the spongy bone tissue of the bone O of the patient (together with the cells 22 themselves).

In detail, the bone cement C embeds into the spongy bone for at least 5 mm, constituting a strong and tenacious foundation on which cemented prosthesis is effectively rooted. The intermediate device 20 is also made of an acrylic cement based on methyl methacrylate (PMMA), such as a bone cement based on methyl methacrylate (PMMA). In this manner, in fact, the intermediate device 20 will in use be firmly joined with the bone cement C used for cementing the tibial component 1 of the prosthesis itself.

The intermediate device 20, in fact, has the task of adhering, for example being fitted into undercut, to the bottom surface lb of the tibial component 1, and of ensuring an optimal thickness of at least 2 mm between bone and metal prosthesis (in a manner such that the forces exerted on the prosthesis are unloaded on the bone always by means of the intermediate device 20 itself). In addition, this has the object - in at least one version thereof of the invention - of adhering and/or penetrating the bone cement C within the patient’s bone, and being joined (or glued) therewith, obtaining a stable and secure connection.

In such a manner, in order to overcome the drawbacks of the conventional surgical techniques, due to the intermediate device 20 it is possible“to cover” the prosthesis- bone interface with a layer of PMMA fixed to the prosthesis itself by the manufacturer; subsequently, such prosthesis can be conventionally fixed with cement, obtaining an anchorage that is considerably improved and, consequently, a longer duration of the implant.

Indeed, in use the intermediate device 20 is applied as follows.

The manufacturer will fix (possibly by means of an undercut or interference or by means of the pins 26 and the respective openings or another suitable technique such as ultrasounds or other) an intermediate device 20 to the bottom surface lb of a tibial component 1. Such bottom surface lb can be suitably processed in order to stably receive such intermediate device 20.

Afterwards, in the operating room, an abundant layer of bone cement C will be applied on the lower surface 20b of the intermediate device 20, possibly inserting it within the at least one cell 22.

Then, the implant will take place of the tibial component 1, provided with the intermediate device 20, placing the latter in contact with the resected tibial bone of the patient.

By exerting considerable pressure (that normally used for implanting the prosthetic components in the patient’s bone), the tibial component 1 and the intermediate device 20 will be implanted in the bone in the surgical site.

The bone cement C present at the interface between the bone and the intermediate device 20, having the same chemical nature as the material with which the latter is attained, will be melted with the intermediate device 20, ensuring an optimal adhesion of this element to the patient’s bone.

In addition, due to the possible presence of the at least one hole 25, such bone cement can pass through such holes 25 (and hence through the thickness 23 of the intermediate device 20) and reach a possible interspace present in the bottom surface lb of the tibial component 1. In this manner, in addition to the constraint already present between the intermediate component 1 and the intermediate device 20, a further union will be created between such two elements, ensuring an even more improved adhesion of implant of the prosthesis itself.

The at least one hole 25, described above for the version of the invention provided with at least one cell 22, can be present and also passing through the intermediate device 20 in flat configuration.

In at least one version, when such holes 25 are present, it is also possible that the intermediate device 20 is not fixed to the prosthesis by means of ultrasounds, delegating the adhesion of these two elements to the bone cement that, through the holes 25, passes from the lower surface 20b to the overlying surface 20a and then to the bottom surface lb of the tibial component 1, ensuring a stable and secure fixing thereof, i.e. a cementing in a single block.

The interspace present in the bottom surface lb of the tibial component 1, when present, in order to carry out such task will have a depth of at least 1 mm.

In the case of the at least one cell 22, moreover, the at least one hole 25 also permits that - within the cells 22 - bubbles or air chambers are not created, which reduce the adhesion of the cement. Such holes 25 in fact create openings through which the air present in the cells 22 exits outward, allowing the optimal filling of such cells 22 with the fluid bone cement C and, consequently, an optimal penetration of the latter in the spongy bone of the patient.

In order to facilitate the implant of the tibial component 1 provided with the aforesaid intermediate device 20, and to reduce the necessary force to be applied on the patient’s bone (an actual compression on the tibial plate of the resected bone), it is possible to provide for a suitable (metal) template provided with the same conformation of the lower surface 20b of the intermediate device 20, possibly also corresponding to the at least one cell 22, adapted to impart on the bone a series of slits which guide and facilitate the consequent implant of the prosthetic component. The conventional templates have an element adapted to make a central hole (substantially at the medullary canal) in which the stem 2 is inserted, and lateral references or“markers” for its correct positioning. Naturally, these elements will also remain in the possible template pre- arranged for the present invention.

In one version of the invention, the tibial component 1 is assembled with the intermediate device 20 and constrained to the latter directly by the manufacturer; the resulting prosthetic component is therefore preformed.

Alternatively, the tibial component 1 and the intermediate device 20 can be separately made and they can be constrained together also at a later time.

The methods of assembly of these two elements can be, as stated above, by means of bone cement, ultrasounds, high-frequency vibrations, etcetera.

The latter technique provides that, by means of the high-frequency vibrations, the material is heated and softens, being melted together.

Once the finished piece is obtained, the thickness to be considered of the prosthetic component is given by the thickness 23 of the intermediate component 20, by the thickness 3 of the tibial component 1 and, possibly, also by the thickness of the joint body 10.

Therefore, the present invention also refers to a method for the assembly of a prosthetic component adapted to be implanted in use at a patient’s bone, such as a tibial component 1 of a knee prosthesis adapted to be implanted at one end of the patient’s tibial bone at a knee joint, comprising the following steps: providing a prosthetic component comprises a body provided with a bottom surface lb, adapted in use to face towards the patient’s bone, providing an intermediate device 20 provided with a lower surface 20b, adapted in use to face towards and/or be constrained in use to the patient’s bone and with an overlying surface 20a, opposite the lower surface 20b and adapted in use to face towards and/or be constrained to the bottom surface lb of the prosthetic component, positioning the intermediate device 20 at the bottom surface lb of the prosthetic component, and finally stably constraining the prosthetic component to the intermediate device 20.

The constraining step comprises at least one of the following techniques: adhesion by means of bone cement in the fluid state (cold) with consequent self-polymerization and/or solidification of the bone cement, high frequency vibration, ultrasounds or interference fixation.

The constraining step comprising adhesion by means of bone cement comprises the following steps: providing bone cement in the fluid state, applying bone cement in the fluid state and/or molten at the overlying surface 20a of the intermediate device 20, in a manner such that the bone cement adheres to the material constituting the intermediate device 20 by means of at least partial melting of the latter and is inserted in at least one suitable interspace present at the bottom surface lb of the prosthetic component, and/or applying bone cement in the fluid state and/or molten at the lower surface 20b of the intermediate device 20, in a manner such that the bone cement adheres to the material constituting the intermediate device 20 by means of at least partial melting of the latter, flows through at least one through hole 25 present in the intermediate device 20 and is inserted in at least one suitable interspace present at the bottom surface lb of the prosthetic component, and consequent self-polymerization and/or solidification of the bone cement and stable constraint of the prosthetic component to the intermediate device 20.

The contact between bone cement in the fluid state and the material of the intermediate device 20 (made of solidified bone cement or PMMA) determines a perfect joining as a consequence of the fact that the two parts have the same chemical origin and the second (intermediate device 20) is soluble in the and/or from the first (bone cement in the fluid state).

The constraining step comprising high-frequency vibration or ultrasounds comprises the following steps: application of high-frequency vibration or ultrasounds at the bottom surface lb of the prosthetic component and/or at the overlying surface 20a of the intermediate device 20, heating and consequent softening of the material that constitutes the bottom surface lb and/or the overlying surface 20a, melting together and/or joining the bottom surface lb with the overlying surface 20a with consequent constraint between the same.

When in the text“bone cement” is defined as an element for joining or melting the intermediate device 20 with the prosthetic component, it is intended a bone cement (which, once constituted by joining its polymer and monomer components, is a fluid and cold pasty mass) for which a chemical reaction is immediately activated, termed polymerization, which in a few minutes hardens the mass, imprisoning and blocking the different parts in contact, i.e. the intermediate device 20 and the prosthetic component itself.

When instead the technique of ultrasounds or of vibration is indicated, reference is made to a kind of“hot melting”, it being intended the thermal melting at least of the interface of the intermediate device 20 when it is abutted against the respective surface of the prosthetic component. The vibration by means of ultrasounds or vibration indeed determines (thermal) melting between the materials of the two elements, and a penetration thereof (for example with insertion within the possible undercuts present and/or obtained in the respective surface of the prosthetic component), tenaciously being locked and tenaciously locking the intermediate device 20 and the prosthetic component itself.

Finally, the constraint step comprising interference fixation comprises the following steps: making at least one pair of recesses and/or impressions in the bottom surface lb of the prosthetic component, providing at least one pair of pins 26 and/or raised elements 27 which are extended starting from the overlying surface 20a of the intermediate device 20 in the direction of the bottom surface lb, housing the pins 26 in the respective recesses of the bottom surface lb and constraining the prosthetic component with the intermediate device 20, and/or spacing the prosthetic component from the intermediate device 20 by means of the raised elements 27, in a manner such that the adhesion bone cement can be situated between the bottom surface lb and the overlying surface 20a, solidifying and constraining the intermediate component 20 and the prosthetic component.

A particularly advantageous expedient, during the implant of the prosthetic component, is that of applying a small hole at the patient’s bone, which places the spongy tissue in communication with the outside at the lateral bone wall.

In this manner, when the intermediate device 20 (provided with the tibial component 1) is compressed on the resected part of the tibial plate (and hence on the spongy part of the bone), the possible air, trapped in the spongy part and compressed by the device itself and by the bone cement present at its lower surface 20b, can escape through this lateral hole, facilitating the filling of the spongy tissue with bone cement.

Naturally, due to the presence of the intermediate device 20, the bottom surface lb of the tibial component 1 will be attained ad hoc. In particular, the small edge A present in the present prostheses will no longer be necessary.

According to one variant of the invention, the material that forms the intermediate device 20 can be enriched with one or more medical substances, such as an antibiotic or a drug in general, adapted to be released into the surrounding tissues of the patient. In case of antibiotic, these substances can seek to prevent the onset of a future infection at the implant site. Otherwise, they can be drugs of different type, or substances capable of facilitating the bone growth, etcetera.

Such enrichment can be carried out directly by the manufacturer or even by the surgeon at the time of implantation, due to the intrinsic porosity present in such material.

The tibial component 1, instead, can comprise a (biologically compatible) metallic material, such as for example a metal, a metal alloy, an organo-metallic compound, etcetera.

As stated above, therefore, the prosthetic component according to the present invention is constituted by the prosthetic component itself and by the intermediate device 20, which becomes an integral part of the prosthetic component. In this manner, the aforesaid element of a permanent prosthesis will be constituted by two materials: a metal material for the prosthetic component, and an acrylic material for the intermediate device 20, so as to ensure an optimal adhesion of the latter (and therefore of the entire prosthetic component) to the bone cement which is applied in the fluid state in order to cement the prosthesis and, consequently, to the patient’s bone.

The intermediate device 20 therefore forms a single body or is in a single piece with the prosthetic device and, at least in one version of the invention, when provided with the at least one cell 22, serves for making the bone cement in the fluid state penetrate within the bone (with particular reference to its spongy part) of the patient.

Indeed, only in this manner is it possible to prevent the compression forces - necessary for implanting the prosthetic component in loco - from making (for the above-described reasons) the bone cement in the fluid state (present at the surgical site) flow away, such bone cement necessary for the adhesion of the prosthetic component itself to the bone tissue of the patient.

The invention thus conceived is susceptible of numerous modifications and variations, all falling within the scope of the inventive concept.

In addition, all details can be substituted with other technically equivalent elements. In practice, the materials used, as well as the contingent shapes and sizes, can be of any type depending on the requirements without departing from the protective scope of the following claims.

Claims

1. Prosthetic component adapted to be implanted in use at a patient's bone, such as for example a tibial component (1) of a knee prosthesis adapted to be implanted at one end of the patient's tibial bone at a knee joint, comprising a body provided with a bottom surface (lb), adapted in use to face towards the patient's bone, characterized in that said prosthetic component comprises an intermediate device (20), placed in use between said bottom surface (lb) of said prosthetic component and the patient's bone, adapted to firmly constrain said prosthetic component to the patient's bone, wherein said intermediate device (20) comprises a lower surface (20b), adapted in use to face towards and/or to be constrained to the patient's bone and an overlying surface (20a), opposite to said lower surface (20b) and adapted in use to face towards and/or to be constrained to said bottom surface (lb) of said prosthetic component, wherein said intermediate device (20) is made of an acrylic cement based on methyl methacrylate (PMMA), such as for example a methyl methacrylate (PMMA)-based bone cement, and in that said lower surface (20b) comprises a plurality of hollow cells (22), wherein at least one cell (22) of said plurality of cells (22) extends from said lower surface (20b) of said intermediate component (20) towards the patient's bone and is adapted for housing bone cement, possibly in fluid and/or few viscous form, for the connection to the patient's bone of said prosthetic component.

2. Prosthetic component according to the claim 1, wherein said at least one cell

(22) has a three-dimensional conformation substantially in the shape of a prism or of a cylinder having a polygonal base, for example a triangle, square, pentagon, hexagon, octagon, etc., or a circular base, wherein a first base of said at least one cell (22), closer to the patient's bone, is open so that said at least one cell (22) is internally hollow, and/or wherein said at least one cell (22) comprises a side wall and/or side faces (24) having a parallelogram or polygonal shape.

3. Prosthetic component according to claim 1 or 2, wherein said at least one cell (22) has equal or different size with respect to that of at least one adjacent cell (22), and/or wherein said at least one cell (22) has a diameter or a diagonal or a side of the base and/or a height (H) having a size ranging between 3 mm and 15 mm or preferably between 5 mm and 10 mm or even more preferably 8 mm and/or has a thickness of said side wall (24) having a size ranging between 0.3 and 0.9 mm or between 0.5 and 0.7 mm .

4. Prosthetic component according to any one of the preceding claims, wherein said intermediate device (20) has a plan conformation substantially corresponding to that of said prosthetic component, and in the case where said prosthetic component is a tibial component (1), said plan conformation is substantially C-shaped, comprising in use a first front portion (28) substantially continuous and substantially flat and/or slightly convex, a rear portion (29), concave and provided with a receding area (29a), and two side portions (30a, 30b), also substantially continuous and substantially flat and/or slightly convex, which laterally connect said first front portion (28) and said rear portion (29).

5. Prosthetic component according to any one of the preceding claims, wherein said plurality of cells (22) have a height (H) which varies from a cell (22) to another cell (22), wherein said plurality of cells have a maximum height (H2) at the centre of said intermediate device (20) and a minimum height (Hl) at side portions (30a, 30b) of said intermediate device (20), and/or wherein the passage from said maximum height (H2) to said minimum height (Hl) is progressive and/or scalar.

6. Prosthetic component according to any one of the preceding claims, wherein said body of said prosthetic component comprises an upper surface (la), opposite to said bottom surface (lb) and suitable in use to face towards a joint body (10) and/or towards a further prosthetic component and/or towards the femoral component of a knee prosthesis and/or again, one end of the patient's femoral bone, and/or wherein said body is substantially flat and/or the distance between said bottom surface (lb) and said upper surface (la) is substantially constant.

7. Prosthetic component according to any one of the preceding claims, wherein said prosthetic component, at said bottom surface (lb), is provided with a stem (2), suitable to be inserted in use in the medullary canal of the patient's bone and said intermediate device (20) comprises a through opening (20c), suitable in use for allowing the passage of said stem (2).

8. Prosthetic component according to any one of the preceding claims, wherein said plurality of cells (22) have a 3-shape or double C-shape and/or wherein said at least one cell (22) comprises at least one additional wall (34, 34'), preferably of triangular or polygonal conformation, suitable to act as reinforcement for said at least one cell (22) and/or to facilitate the entry and/or insertion of said intermediate device (20) into the patient's bone.

9. Prosthetic component according to any one of the preceding claims, wherein said prosthetic component is made of a biologically compatible metallic material, such as for example a metal, a metal alloy, an organo-metallic compound, etc. e/o wherein said intermediate device (20) also comprises one or more medical substances, such as for example an antibiotic or a drug, suitable for being released into the tissues surrounding the patient's bone.

10. Prosthetic component according to any one of the preceding claims, comprising at least one through hole (25) at at least one of said at least one cell (22).

11. Prosthetic component according to any of the preceding claims, wherein said bottom surface (lb) of said prosthetic component comprises at least one interspace for said overlying surface (20a) of said intermediate device (20), wherein said at least one interspace comprises at least one undercut and/or at least one pair of grooves, in order to house respective ridges present in said overlying surface (20a) of said intermediate device (20) or vice versa, and/or at least one pair of recesses and/or impressions, suitable to house respective pins (26) and/or raised elements (27) extending from said overlying surface (20a) in the direction of said bottom surface (lb) or vice versa, and/or wherein said raised elements (27) function in use as a "thickness" which separates said bottom surface (lb) from said overlying surface (20a), creating a free space in which bone cement (C) can flow.

12. Intermediate device (20) adapted to be constrained to a prosthetic component, such as for example a tibial component (1) of a knee prosthesis suitable to be implanted at one end of the patient's tibial bone at a knee joint and to be placed in use between said prosthetic component and the patient's bone, characterized in that said intermediate device (20) comprises a lower surface (20b), suitable in use to face towards and/or to be constrained to the patient’s bone, and an overlying surface (20a), opposite to said lower surface (20b) and suitable in use to face towards and/or to be constrained to a bottom surface (lb) of said prosthetic component, wherein said intermediate device (20) is made of an acrylic cement based on methyl methacrylate (PMMA), such as for example a methyl methacrylate (PMMA)-based bone cement, and in that said lower surface (20b) comprises a plurality of hollow cells (22), wherein at least one cell (22) of said plurality of cells (22) extends from said lower surface (20b) of said intermediate component (20) towards the patient's bone and is suitable for housing bone cement, possibly in fluid and/or few viscous form, for the connection to the patient's bone of said prosthetic component.

13. Intermediate device (20) according to claim 12, wherein said at least one cell (22) has a three-dimensional conformation substantially in the shape of a prism or of a cylinder having a polygonal base, for example a triangle, square, pentagon, hexagon, octagon, etc., or a circular base, wherein a first base of said at least one cell (22), nearest to the patient's bone, is open so that said at least one cell (22) is internally hollow, and/or wherein said at least one cell (22) comprises a side wall and/or side faces (24) having a parallelogram or a polygonal shape.

14. Intermediate device (20) according to any one of the preceding claims, when dependent on claim 12, wherein said at least one cell (22) has dimensions that are the same as or different from those of at least one adjacent cell (22), and/or wherein at least one cell (22) has a diameter or a diagonal or a side of the base and/or a height (H) having a size ranging between 3 mm and 15 mm or preferably between 5 mm and 10 mm or even more preferably 8 mm and/or has a thickness of said side wall (24) having a size ranging from 0.3 to 0.9 mm or from 0.5 to 0.7 mm, and/or wherein said plurality of cells (22) have a height (H) which varies from one cell (22) to another cell (22), wherein said plurality of cells have a maximum height (H2) at the centre of said intermediate device (20) and a minimum height (Hl) at side portions (30a, 30b) of said intermediate device (20), and/or wherein the passage from said maximum height (H2) to said minimum height (Hl) is progressive and/or scalar.

15. Intermediate device (20) according to any one of the preceding claims, when dependent on claim 12, having a plan conformation which is substantially C-shaped, comprising in use a first front portion (28) substantially continuous and substantially flat and/or slightly convex, a rear portion (29), concave and provided with a receding area (29a), and two side portions (30a, 30b), also substantially continuous and substantially flat and/or slightly convex, which laterally connect said first front portion (28) and said rear portion (29).

16. Intermediate device (20) according to any one of the preceding claims, when dependent on claim 12, wherein said intermediate device (20) also comprises one or more medical substances, such as for example an antibiotic or a drug, suitable for being released into the tissues surrounding the patient's bone.

17. Method for assembling a prosthetic component adapted to be implanted in use at a patient's bone, such as, for example, a tibial component (1) of a knee prosthesis adapted to be implanted at one end of the tibial bone of the patient at a knee joint, according to one or more of the claims from 1 to 11, comprising the following steps:

providing a prosthetic component comprising a body having a bottom surface

(lb), suitable in use to face the patient's bone,

providing an intermediate device (20) having a lower surface (20b), suitable in use to face and/or to be constrained in use to the patient's bone and an overlying surface (20a), opposite to said lower surface (20b) and suitable in use to face towards and/or to be constrained to said bottom surface (lb) of said prosthetic component, wherein said intermediate device (20) is made of an acrylic cement based on methyl methacrylate (PMMA), such as for example a methyl methacrylate (PMMA)-based bone cement, and said lower surface (20b) comprises a plurality of hollow cells (22), wherein at least one cell (22) of said plurality of cells extends from said lower surface (20b) of said intermediate component (20) towards the patient's bone and is suitable for housing bone cement, possibly in fluid and/or few viscous form, for the connection to the patient's bone of said prosthetic component,

positioning said intermediate device (20) at said bottom surface (lb) of said prosthetic component,

firmly constraining said prosthetic component to said intermediate device (20).

18. Method according to claim 17, wherein said constraining step comprises at least one of the following techniques: adhesion using bone cement in the fluid state with subsequent self-curing and/or consequent solidification of said bone cement, high frequency vibration, ultrasounds or interference fixation.

19. Method according to claim 18, wherein said constraining step comprising adhesion using bone cement comprises the following steps:

providing bone cement in the fluid state,

applying bone cement in the fluid and/or molten state at said overlying surface (20a) of said intermediate device (20), so that said bone cement adheres to the material with which said intermediate device (20) is made by at least partial melting of the latter and inserts in at least one designed interspace present at said bottom surface (lb) of said prosthetic component, and/or

applying bone cement in the fluid and/or molten state at said lower surface (20b) of said intermediate device (20), so that said bone cement adheres to the material with which said intermediate device (20) is made by at least partial melting of the latter, flows through at least one through hole (25) present in said intermediate device (20) and inserts in at least one designed interspace present at said bottom surface (lb) of said prosthetic component,

consequent self-polymerization and/or solidification of said bone cement and stable constraining of said prosthetic component to said intermediate device (20).

20. Method according to claim 18, wherein said constraining step comprising high frequency vibration or ultrasound comprises the following steps:

applying high frequency vibrations or ultrasounds at the bottom surface (lb) of said prosthetic component and/or of said overlying surface (20a) of said intermediate device (20),

heating and consequent softening of the material constituting said bottom surface (lb) and/or said overlying surface (20a),

melting together and/or joining said bottom surface (lb) with said overlying surface (20a) with consequent constraint between them.

21. Method according to claim 18, wherein said constraining step comprising interference fixation comprises the following steps:

making at least one pair of recesses and/or impressions in said bottom surface (lb) of said prosthetic component,

providing at least one pair of pins (26) and/or raised elements (27) extending from said overlying surface (20a) of said intermediate device (20) in the direction of said bottom surface (lb),

housing said pins (26) in the respective recesses of said bottom surface (lb) and constraining said prosthetic component to said intermediate device (20), and/or

spacing said prosthetic component from said intermediate device (20) through said raised elements (27),

so that the adhesion bone cement can be placed between said bottom surface (lb) and said overlying surface (20a), solidifying and constraining said intermediate component (20) and said prosthetic component.