UNICOMPARTIMENTAL KNEE PROSTHESIS

Abstract

Prosthesis for knee arthroplasty comprising a femoral component with a minimum thickness and with two different systems for fastening to the femoral condyle and a tibial component with an upper surface which can have a double profile with a differentiated congruence profile. The tibial component can be made with a single body or in two parts of different materials.

Claims

1. A unicompartmental prosthesis for knee arthroplasty comprising: a first femoral component having a curved main body with a distal end and a rear end, a convex outer side and an inner side comprising fastening means at the end of a femur; a second tibial component having a single main body of substantially semi-discoidal shape comprising an upper surface adapted to be engaged with the surface of the convex outer side of said first femoral component and a lower surface comprising fastening means at the end of a tibia; said fastening means at the end of a femur comprising at least one pin; the maximum thickness of the main body of said first femoral component being less than or equal to 7 mm, wherein the upper surface of said second tibial component has a double profile, a first profile with higher congruence at the rear part of said second tibial component and a second profile with lower congruence at the front part of said second tibial component.

2. (canceled)

3. The prosthesis according to claim 1, wherein said first and second profiles are of the ellipse arch type.

4. The prosthesis according to claim 1, wherein said fastening means at the end of a tibia comprise at least one flap substantially orthogonal to the lower surface of said second tibial component.

5. The prosthesis according to claim 1, wherein said fastening means at the end of a femur comprise two pins.

6. The prosthesis according to claim 4, wherein the inner side of said main body comprises a first surface at the rear end, a second surface at the distal end and a third surface placed in an intermediate position with respect to said first surface and said second surface, said first surface and said second surface being inclined at an angle less than 90°.

7. The prosthesis according to claim 5, wherein said two pins are inclined at an angle between 55° and 65° with respect to the plane of said second surface.

8. The prosthesis according to claim 1, wherein said fastening means at the end of a femur further comprise an anti-rotational flap.

9. The prosthesis according to claim 7, wherein the maximum thickness of the main body of said first femoral component is less than or equal to 7 mm at the rear end and less than or equal to 4.5 mm at the distal end.

10. The prosthesis according to claim 1, wherein said second tibial component is made of polyethylene.

11. The prosthesis according to claim 1, wherein the main body of said second tibial component comprises a lower part having a lower surface comprising fastening means at the end of a tibia and an insert having an upper surface adapted to interface with the first femoral component, said lower part and said insert comprising suitable mutual engagement means.

12. The prosthesis according to claim 10, wherein said insert is made of polyethylene.

13. The prosthesis according to claim 9, wherein said polyethylene is selected from the group consisting of linear UHMWPE polyethylene, XLink polyethylene and XLink polyethylene with added Vitamin E.

14. The prosthesis according to claim 10, wherein said second tibial component comprises a pin, substantially orthogonal to the lower surface of the lower part of said second tibial component.

15. The prosthesis according to claim 13, wherein said pin has an axial hole adapted to house a screw adapted to improve the fastening of the lower part of said second tibial component the end of a tibia.

16. The prosthesis according to claim 1, wherein flap, the pin and the lower surface of said second tibial component the pins of said first femoral component are provided with transversal or longitudinal grooves or surface machinings adapted to promote cooperation with bone cement.

17. The prosthesis according to claim 1, wherein said first femoral component is made of cobalt chrome molybdenum alloy.

18. The prosthesis according to claim 1, wherein the lower part of the second tibial component is made of titanium alloy or cobalt chrome molybdenum alloy.

19. A kit of unicompartmental prosthesis for knee arthroplasty, comprising: at least a first femoral component comprising two pins, for each size of the six sizes corresponding to the widths of the main body of said first femoral component equal to 15 mm, 16 mm, 17 mm, 18 mm, 19 mm, and 20 mm; at least a first femoral component comprising a pin and an anti-rotational flap, for each size of the six sizes corresponding to the widths of the main body of said first femoral component equal to 15 mm, 16 mm, 17 mm, 18 mm, 19 mm, and 20 mm; at least a second tibial component comprising a single main body equipped with at least one flap, for each size of the six sizes corresponding to a dimension the mediolateral plane equal to about 24 mm, 26 mm, 28 mm, 30 mm, 32 mm, and 34 mm, and for each overall thickness equal to about 8.5 mm, 9.5 mm, 10.5 mm, and 12.5 mm; at least a second tibial component comprising a lower part about 3 mm thick and equipped with at least one flap, a pin and a screw, for each size of the six sizes corresponding to a dimension in the mediolateral plane equal to about 24 mm, 26 mm, 28 mm, 30 mm, 32 mm, and 34 mm, and an insert for each thickness equal to about 5.5 mm, 6.5 mm, 7.5 mm, and 9.5 mm.

20. The kit according to claim 18, wherein said at least a first femoral component said at least a second tibial component are of the RM/LL type or of the LM/RL type or of both the aforesaid types.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Further features and advantages of the invention will become apparent from the following detailed description provided by way of example and not by way of limitation, with the aid of the Figures shown in the accompanying drawings, in which:

[0051] FIG. 1 illustrates a preferred embodiment of the RES type femoral component according to the present description;

[0052] FIG. 2 illustrates a preferred embodiment of the 3CUT type femoral component according to the present description;

[0053] FIG. 3 illustrates a preferred embodiment of the AllPoly type tibial component according to the present description;

[0054] FIG. 4 illustrates a preferred embodiment of the MetalBlack type tibial component according to the present description, and

[0055] FIG. 5 illustrates the preferred embodiment of the tibial insert according to the present description.

[0056] The following description of exemplary embodiments refers to the accompanying drawings. The same reference numerals in the various drawings identify the same or similar elements. The following detailed description does not limit the invention. The scope of the invention is defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

[0057] With reference to the appended FIGS. 1-6, the femoral-tibial unicompartmental knee prosthesis with a fixed insert for knee arthroplasty according to the present description comprises a first femoral component 10 adapted to be connected to the end of a femur and a second tibial component 11 adapted to be connected to the end of a tibia.

[0058] The first femoral component 10 has a curved main body 12 with a distal end 13 and a rear end 14, a convex outer side and an inner side comprising fastening means at the end of a femur. The maximum thickness 15 of said main body is preferably less than or equal to 7 mm. In particular, the maximum thickness 15 of said main body 12 may be equal to 6.75 mm.

[0059] In a preferred embodiment, shown in FIG. 1, known as RES, the first femoral component 10 has a curved main body 12 with an inner side comprising a pin 18 facing a substantially radial direction. Advantageously, said pin 18 may be associated with an anti-rotational flap 19 oriented in the longitudinal direction. In this preferred embodiment, the maximum thickness of said main body 12 is preferably less than or equal to 7 mm at said rear end 14 and less than or equal to 4.5 mm at said distal end 13. In particular, the maximum thickness of said main body 12 may be equal to 6.75 mm at said rear end 14 and may be equal to 4 mm at said distal end 13.

[0060] In another preferred embodiment, shown in the appended FIG. 2, the first femoral component 10, known as 3CUT, has a curved main body 12 with an inner side comprising two pins 20, 21 facing in a substantially radial direction. Furthermore, the inner side of said main body 12 comprises a first surface 22 at the rear end 14, a second surface 23 at the distal end 13 and a third surface 24 placed in an intermediate position with respect to said first surface 22 and said second surface 23. Preferably, said first surface 22 and said second surface 23 are inclined by an angle of less than 90° and, in particular, said first surface 22 and said second surface 23 are inclined by an angle equal to 85°.

[0061] In another preferred embodiment, said two pins 20, 21 are inclined by an angle comprised between 55° and 65° with respect to the plane of said second surface 23. In particular, said two pins 20, 21 are inclined by an angle equal to 60° with respect to the plane of said second surface 23. Inclinations comprised between 55° and 65° allow the fastening of said first femoral component 10 at the end of a femur to be optimized.

[0062] Advantageously, said pins 18, 20, 21 are provided with transversal or longitudinal grooves or surface machinings adapted to promote the cooperation with the bone cement used for fastening the prostheses.

[0063] Said first femoral component 10 may be made of cobalt chrome molybdenum alloy (e.g. CoCrMo ISO 5832/4 alloy) and may be made in a version to be cemented or a version not to be cemented. For the cementless version a porous titanium coating can be used (Ti-Growth C) deposited through the so-called Vacuum Plasma Spray technique on which a layer of hydroxyapatite (Osprovit) is superimposed.

[0064] Whereas titanium alloy prostheses are hypoallergenic, cobalt chrome molybdenum alloy prostheses are not, therefore, for patients sensitive to metal ions such as nickel and, more rarely, cobalt or chromium, cobalt chrome molybdenum alloy prostheses can be made hypoallergenic for example through a coating made of inert ceramic material such as titanium niobium nitride (TiNbN), perfectly biocompatible.

[0065] All the metal joint surfaces are preferably mirror polished.

[0066] The first femoral component 10 is preferably made in different sizes or measurements, corresponding to the width of said main body 12. For example, 6 sizes corresponding to widths of said main body 12 can be identified, equal to 15 mm, 16 mm, 17 mm, 18 mm, 19 mm and 20 mm.

[0067] With reference to the appended FIG. 3, the second tibial component 11 has a main body 16 of substantially semi-discoidal shape comprising an upper surface 25 adapted to be engaged with the surface of the convex outer side of said first femoral component 10 and a lower surface 26 comprising fastening means at the end of a tibia.

[0068] In a preferred embodiment, said upper surface 25 of the second tibial component 11 has a double profile, a first profile with greater congruence in the rear part of said upper surface 25 and a second profile with lower congruence in the front part of said upper surface 25. Preferably, said first and said second profile are of the ellipse arch type. This particular profile creates a light congruence and a partial contact area but allows the coupling of all the femoral measurements of the prosthesis according to the present description with all the tibial ones, without any constraints and guaranteeing complete modularity. Thus the advantages of a larger contact area (which implies a reduction in contact stress of the two main parts of the prosthesis) are combined with the possibility to perfectly adapt the femoral and tibial components to the anatomical characteristics of the individual patient without the usual limitations dictated by the compatibility tables.

[0069] In another preferred embodiment of the prosthesis according to the present description, the fastening means at the end of a tibia of said tibial component 11 comprise at least one flap 17 substantially orthogonal to the lower surface 26 of said second tibial component 11. Said flap 17 allows the stabilization of the tibial component on the resected bone and, through the bone cement, the fixation thereof. In fact, the space created in the bone through the relevant broach allows a convenient housing of the flap 17 and the creation of a layer of cement which fastens the tibial component also creating an anti-rotational stabilization. In fact, rotational loads act on the tibial component 11 during walking and the flap 17 opposes such loads, guaranteeing stability. To increase the contact area with the cement, grooves or appropriate machinings can be advantageously performed on the flap 17.

[0070] Preferably, the flap 17 of the tibial component 11 according to the present description has a half-moon shape, a height of about 5 mm, a length of about 22 mm and a width of about 4 mm; it is substantially positioned in the center with respect to the anteroposterior direction, whereas, with respect to the mediolateral direction, it is positioned in proximity to the center of the knee.

[0071] Advantageously, the lower surface 26 of said second tibial component 11 can have grooves or surface machinings adapted to promote the adhesion of the bone cement and therefore the correct connection of the second tibial component 11 at the end of a tibia. Likewise, also said flap 17 can be shaped so as to promote the stability thereof when in use.

[0072] Said second tibial component 11 may, advantageously, be made of polyethylene. In particular, it may be made of linear UHMWPE (Ultra-High-Molecular-Weight PolyEthylene), XLink or cross-linked polyethylene or XLink or cross-linked polyethylene with added Vitamin E. Vitamin E is a powerful antioxidant and has an anti-aging effect. The addition of Vitamin E therefore prevents the oxidation phenomena to which XLink polyethylene is subject and, therefore, reduces the wear thereof. In fact, as well as being the result of the contact stress and shear strain which act between the components of the prosthesis, wear is also caused by the oxidation of the materials used.

[0073] With reference to the preferred embodiment of the present invention illustrated in FIG. 4 and in FIG. 5, said second tibial component 11 comprises two parts, a lower part 27 adapted to interface with the end of a tibia and an insert 28 adapted to interface with the first femoral component 10. Said lower part 27 and said insert 28 of the second tibial component 11 comprise appropriate mutual engagement means. For example, said lower part 27 may comprise a seat 29 adapted to accommodate the insert 28. Advantageously, the edges of said seat 29 and of said insert 28 comprise appropriate mutual locking means made, for example, by one or more protuberances present on the vertical walls of said seat 29, adapted to engage with corresponding grooves present on the outer vertical walls of said insert 28.

[0074] In another preferred embodiment of the prosthesis according to the present description, the fastening means at the end of a tibia of said second tibial component 11 comprise at least one flap 17 substantially orthogonal to the lower surface 26 of said second tibial component 11 and a pin 32, also substantially orthogonal to the lower surface 26 of said second tibial component 11. Both the flap 17 and the pin 32 are adapted to be engaged with an end of a tibia in a stable way and such as to promote correct cooperation with the aforesaid femoral component 10 when in place on a patient.

[0075] Said pin 32 may further present an axial hole adapted to accommodate a screw adapted to improve the fastening of said second tibial component 11 to the end of a tibia. The use of a screw, for example a cancellous bone screw, is particularly useful in the event that bone cement is not used for fastening the tibial component 11. An example of a cancellous bone screw which may be employed is the Ti6Al4V titanium alloy (ISO 5832/3) screw having diameter 6.5 mm. The screw may be oriented in the hole with an angle of 10°, hence describing a cone with a 20° angle.

[0076] Furthermore, advantageously, the outer surface of said pin 32 comprises a porous coating adapted to promote the adhesion to the trabacular bone of the tibia. Preferably, said porous coating is made of titanium plasma spray and hydroxyapatite, two materials which promote bone regrowth in their structure and therefore the fastening of the component. In particular, a porous coating of this type with two materials can be deposited on the lower and vertical surface of the flap 17, whereas the pin 32 can be coated with hydroxyapatite only.

[0077] In this preferred embodiment, said lower part is preferably made of titanium alloy (e.g. Ti6Al4V alloy ISO 5832/3) or cobalt chrome molybdenum alloy (e.g. CoCrMo alloy ISO 5832/4) and can be made in the version to be cemented and in the version not to be cemented. For the cementless version a porous titanium coating can be used (Ti-Growth C) deposited through the so-called Vacuum Plasma Spray technique on which a layer of hydroxyapatite (Osprovit) is superimposed.

[0078] Whereas titanium alloy prostheses are hypoallergenic, cobalt chrome molybdenum alloy prostheses are not, therefore, for patients sensitive to metal ions such as nickel and, more rarely, cobalt or chromium, cobalt chrome molybdenum alloy prostheses can be made hypoallergenic for example through a coating made of inert ceramic material such as titanium niobium nitride (TiNbN), perfectly biocompatible.

[0079] Said insert 28 may, instead, be made of polyethylene. In particular, it may be made of linear UHMWPE (Ultra-High-Molecular-Weight PolyEthylene), XLink (or Cross-linked) polyethylene or XLink polyethylene with added Vitamin E.

[0080] All the metal joint surfaces are preferably mirror polished.

[0081] The second tibial component 11 is preferably made in 6 sizes or measurements corresponding to six different measurements of the dimension 30 in the lateral median plane equal to about 24 mm, 26 mm, 28 mm, 30 mm, 32 mm and 34 mm, which correspond to measurements of the dimension 31 in the anteroposterior median plane equal to about 39 mm, 42 mm, 45 mm, 48 mm, 51 mm and 54 mm.

[0082] Furthermore, said second tibial component 11 can be advantageously made with different thicknesses, thickness meaning the distance between the upper surface 25 and the lower surface 26. For example, said second tibial component 11 can be advantageously made in four different thicknesses, selected about equal to 8.5 mm, 9.5 mm, 10.5 mm and 12.5 mm.

[0083] In the case where the second tibial component 11 comprises two parts, the aforesaid measurements shall be related to the sum of the thicknesses of the lower part 27 and of the insert 28. In this case, in a preferred embodiment of the prosthesis according to the present description, the minimum thicknesses of the four versions of the insert 28 shall be for example equal to about 5.5 mm, 6.5 mm, 7.5 mm and 9.5 mm which, associated with a lower part 27 with a thickness equal to about 3 mm, reach a total thickness of the second tibial component 11 about equal to 8.5 mm, 9.5 mm, 10.5 mm and 12.5 mm.

[0084] Because of the anatomy of the tibial plateau which substantially appears to comprise two halves, an inner one (known as medial) and an outer one (known as lateral), the second tibial components 11 are preferably made in two specular versions adapted to be positioned on each of the two halves, the medial half and the lateral half. It is clear that a tibial component 11 adapted to be positioned on the right medial half (RM) will also be adapted to be positioned on the left lateral half (LL). Vice versa, a tibial component 11 adapted to be positioned on the left medial half (LM) will also be adapted to be positioned on the right lateral half (RL). Said tibial components 11 can therefore be advantageously made in two specular versions, indicated respectively as RM/LL and LM/RL on the basis of their destination with respect to the two halves of the head of the tibia.

[0085] Correspondingly, also the first femoral components 10 are preferably made in two specular versions adapted to be positioned on each of the two femoral condyles, the medial condyle and the lateral condyle. A femoral component 10 adapted to be positioned on the right medial condyle (RM) will also be adapted to be positioned on the left lateral condyle (LL) in this case too. Vice versa, a femoral component 10 adapted to be positioned on the left medial condyle (LM) will also be adapted to be positioned on the right lateral condyle (RL). Said femoral components 10 can therefore be advantageously made in two specular versions, indicated respectively as RM/LL and LM/RL on the basis of their destination with respect to the two condyles of the femur.

[0086] The prosthesis according to the present description introduces a very high degree of flexibility as it is fully compatible and interfaceable between femoral and tibial components made in various sizes and dimensions. The femoral component described is characterized by reduced dimensions and is compatible with the tibial component regardless of the size, also thanks to the double ellipse profile geometry of the contact surface of the tibial component, which identifies areas with differentiated congruence.

[0087] The prosthesis according to the invention allows the operating surgeon to choose intraoperatively, during the unicompartmental knee prosthesis operation, which type of femoral component to use between 3CUT and RES, also after having performed all the tibial preparation.

[0088] Given the aforesaid flexibility and intraoperativity, the prosthesis according to the present description is suitable to be provided also as a kit comprising all the variations and measurements of the femoral component 10 and of the tibial component 11. In a particular embodiment said kit can therefore comprise:

[0089] at least a first femoral component 10, in the version known as 3CUT, for each size of the six sizes corresponding to the widths of the main body 12 of said first femoral component 10 equal to 15 mm, 16 mm, 17 mm, 18 mm, 19 mm, and 20 mm;

[0090] at least a first femoral component 10, in the version known as RES, for each size of the six sizes corresponding to the widths of the main body 12 of said first femoral component 10 equal to 15 mm, 16 mm, 17 mm, 18 mm, 19 mm, and 20 mm;

[0091] at least a second tibial component 11, in the version known as Allpoly, for each size of the six sizes corresponding to dimensions 30 in the mediolateral plane equal to about 24 mm, 26 mm, 28 mm, 30 mm, 32 mm, and 34 mm, for each overall thickness equal to about 8.5 mm, 9.5 mm, 10.5 mm and 12.5 mm and for each RM/LL and LM/RL type;

[0092] at least one lower part 27 of the second tibial component 11 in the version known as Metalback, for each of the six sizes corresponding to dimensions 30 in the lateral medial plane equal to about 24 mm, 26 mm, 28 mm, 30 mm, 32 mm and 34 mm and for each RM/LL and LM/RL type, each preferably comprising at least one cancellous bone screw;

[0093] at least one insert 28 for each thickness equal to about 5.5 mm, 6.5 mm, 7.5 mm and 9.5 mm and for each RM/LL and LM/RL type.

[0094] Advantageously, said kit can be made in the versions with femoral components 10 and tibial components 11 of the RM/LL and/or LM/RL type.

[0095] Furthermore, advantageously, said kit can be made in the versions in which said at least one first femoral component 10—in the version known as 3CUT and in the version known as RES—and said at least one lower part 27 of the second tibial component 11 in the version known as Metalback, are made in the version to be cemented, in the version not to be cemented, in the hypoallergenic version or in all three versions.

[0096] Furthermore, advantageously, said kit can be made in the versions in which said at least one second tibial component 11, in the version known as Allpoly, and said at least one insert 28 are made of linear UHMWPE polyethylene, XLink (cross-linked) polyethylene or XLink polyethylene with added Vitamin E.