WO2008146124A2

WO2008146124A2 - Humeral prosthesis for the articulation of the shoulder

Info

Publication number: WO2008146124A2
Application number: PCT/IB2008/001298
Authority: WO
Inventors: Paolo Dalla Pria
Original assignee: Lima - Lto Spa
Priority date: 2007-05-25
Filing date: 2008-05-23
Publication date: 2008-12-04
Also published as: WO2008146124A3; ITUD20070089A1

Abstract

A humeral prosthesis (10) for the articulation of a head of a humerus in a mating glenoid seating of a shoulder comprises a prosthetic cap (20) which is able to articulate in the glenoid seating and which, to cover the head of the humerus, has a cavity (27) into which the head of the humerus is able to be inserted, a rod (22) able to be positioned inside the humerus, to connect the prosthetic cap (20) to the head of the humerus. The rod (22) is a distinct component with respect to the prosthetic cap (20) and is able to be coupled with the prosthetic cap (20) inside the cavity (27).

Description

<'τHUMERAL PROSTHESIS FOR THE ARTICULATION OF THE SHOULDER"

FIELD OF THE INVENTION The present invention concerns a humeral prosthesis for the articulation of a shoulder, of the so-called covering type, that is, a prosthesis suitable to be fixed to the head of a humerus, leaving it substantially intact. The humeral prosthesis is able on the one hand to articulate in a corresponding glenoid seating of the shoulder, and on the other hand to be inserted and clamped in the upper part of the humerus. By glenoid seating we mean both a natural glenoid seating of the shoulder, and also a corresponding glenoid prosthesis which replaces the natural glenoid seating of the shoulder.

BACKGROUND OF THE INVENTION A humeral prosthesis is known, or so-called covering prosthesis, for the articulation of a humerus in a shoulder. The prosthesis comprises, as its essential parts, a prosthetic cap, which is able to articulate in the glenoid seating of the shoulder and a metal rod, made in a single piece with the prosthetic cap, which is inserted and fixed through the humerus, in a suitable seating made in the meta- epiphyseal part of the humerus. This type of prosthesis is called a covering prosthesis because, once implanted, the prosthetic cap covers the natural humeral head, and the humerus is not sectioned. This entails a minimum alteration of the natural humeral head and allows to conserve the bone tissues in favor of possible subsequent interventions of revision, which can thus be carried out as if it were a normal implant. It is also known that covering humeral prostheses are made in different sizes, that is, with directly correlated sizes of the prosthetic cap and the rod, so as to adapt to the sizes both on the meta-epiphyseal part of the humerus, where the seating for the rod is made, and also on the head of the humerus, which normally vary greatly, in a manner directly correlated, both according to sex and also according to the build of the patient who will receive the prosthesis.

One disadvantage of known humeral prostheses is that they are not always easy to use for the surgeon, nor optimum with regard to effective articulation, if the size of the meta-epiphyseal part where the seating of the rod is made, or meta-epiphyseal seating, and the head of the humerus are not directly correlated, that is, if a humeral head with limited size corresponds to a very large seating for the rod, or vice versa, or in any case if said sizes are not regularly coordinated.

One purpose of the present invention is to achieve a humeral prosthesis which can be used both if the size of the meta-epiphyseal part where the seating of the rod is made, or meta-epiphyseal seating, and the humeral head are directly correlated to each other, and also if the seating of the rod and the humeral head are irregularly coordinated in size with each other, that is, if the seating of the rod is very large and the humeral head is small, and vice versa. Another purpose is to facilitate the operations to implant the humeral prosthesis by the surgeon.

The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages. SUMMARY OF THE INVENTION

The present invention is set forth and characterized in the independent claim, while the dependent claims describe other characteristics of the invention or variants to the main inventive idea.

In accordance with the above purposes, a covering humeral prosthesis for the articulation of a head of a humerus in a mating glenoid seating of a shoulder comprises a prosthetic cap which is able to articulate in the glenoid seating and which, to cover the humeral head, has a cavity into which the humeral head is able to be inserted, and a rod able to be positioned in a suitable seating in the humerus, to connect the prosthetic cap to the humerus. According to a characteristic feature of the present invention, said rod is a distinct component with respect to the prosthetic cap and is able to be coupled with the prosthetic cap, in its cavity.

According to an advantageous variant of the present invention, the rod is a distinct component and removable from the prosthetic cap. This allows to combine several prosthetic caps, one at a time, of different shape and/or size, with the same rod, and vice versa.

In this way the surgeon can select the most appropriate sizes and also the desired shape and geometry of the rod and the prosthetic cap, according to operating needs.

In this way we achieve a humeral prosthesis of a modular type, in which the base modules are represented by the prosthetic cap and the rod in different shapes and/or sizes, which can be coupled according to operating requirements. Advantageously, the prosthesis according to the present invention comprises coupling means able to determine the selectively releasable coupling of the rod and the prosthetic cap. The coupling means allows a direct and stable coupling of the rod and cap.

Therefore, the covering humeral prosthesis according to the present invention can be used both when the size of the meta-epiphyseal seating into which the rod is inserted and the humeral head are directly correlated, and also when the meta- epiphyseal seating and the humeral head are of irregularly coordinated sizes, that is, when the meta-epiphyseal seating is very large and the humeral head is small, and vice versa. Moreover, the rod can be implanted through the humerus in a first operating step, ensuring the coupling means is accessible, and in a second step the prosthetic cap can be easily applied by the surgeon who can orientate and position it as necessary.

The rod, according to the various embodiments of the invention, can be shaped like a cone, a truncated cone or cylindrical. Furthermore, the rod can be substantially straight, or curvilinear or a combination of the two, according to specific applications.

Furthermore, the rod can be positioned with its longitudinal axis aligned with the axis of symmetry of the cap, or with its longitudinal axis inclined with respect to said axis.

In another variant according to the invention the rod can be coupled with the prosthetic cap in a polar position, that is, axial to the axis of symmetry of the cap, or in an eccentric position, according to needs.

Another variant provides to position the rod in a central position with respect to the axis of symmetry of the cap, or displaced from the center, parallel or inclined to the axis of symmetry.

According to one form of embodiment, the coupling means comprises an open housing seating, made longitudinally in the rod, into which a mating constraining - A -

element is able to be inserted and supported, such as for example an insertion cone or truncated cone, solid with the internal surface of the prosthetic cap.

Alternatively, the housing seating can be made in the prosthetic cap and instead the constraining element can be provided at the end of the rod. According to an advantageous variant of the invention, the prosthetic cap and the rod are constrained to each other by means of conical coupling, which confers stability and security to the coupling.

In another variant embodiment, to increase the adherence and integration of the humeral head to the bone walls, the rod has, at least on part of its length, a cross- or star-shaped cross section.

According to another variant embodiment, the rod has a plurality of longitudinal ribs, able to increase the surface of contact with the humeral bone.

According to another variant solution, instead of ribs there are corresponding grooves, or there are no ribs and no grooves, in both cases the rod being attached by means of bone cement or bioactive linings, such as porous titanium or hydroxyl apatite.

Advantageously, the present invention allows to combine rod and prosthetic cap of different materials. For example the prosthetic cap can advantageously be made of a cobalt-based alloy, for example cobalt-chrome-molybdenum, or titanium or titanium alloy with suitable surface treatments, or of ceramic or other material with high mechanical resistance, whereas the rod can be made of titanium or titanium alloy, thanks to its high capacity for bone integration.

According to another variant, the rod and/or the internal surface of the prosthetic cap are made so as to optimize their bone integration with the humeral head.

In particular, these components can be made of bioactive linings, such as porous titanium or hydroxyl apatite, or with an at least partly trabecular or reticular structure, of the three-dimensional type.

This type of at least partly trabecular structure achieves a plurality of open and intercommunicating cavities, connected both toward the inside and also toward the outside, and advantageously consists of a plurality of meshes that are repeated in space according to a predefined model and each consisting of contiguous elementary cells in polygons. This reticular structure is advantageously obtained by melting metal powders, titanium- or cobalt-based, according to a predefined geometry, for example exploiting the known electronic-ray melting technologies of EBM (Electric Beam

Melting), or DLSMS (Direct Laser Selective Metal Sintering) or equivalent technologies.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other characteristics of the present invention will become apparent from the following description of a preferential form of embodiment, given as a non-restrictive example with reference to the attached drawings wherein: - fig. 1 shows part of a human skeleton with a humerus inserted in a glenoid seating of a shoulder;

- fig. 2 is a front view of a humeral prosthesis according to the present invention;

- fig. 3 is a plane view from below of the prosthesis in fig. 2;

- fig. 4 is a perspective view of the prosthesis in fig. 2; - fig. 5 is a view of separate parts of the prosthesis in fig. 2;

- fig. 6 is a section of the prosthesis in fig. 2;

- fig. 7 shows part of a variant of a humeral prosthesis according to the present invention;

- fig. 8 is a section of the variant in fig. 7; - fig. 9 shows a part of another variant of a humeral prosthesis according to the present invention; and

- fig. 10 is a section of the variant in fig. 9.

DETAILED DESCRIPTION OF A PREFERENTIAL FORM OF

EMBODIMENT With reference to fig. 2, a covering humeral prosthesis 10 comprises a prosthetic cap 20, axial-symmetrical with respect to an axis Y, having a semi- spherical external surface 24 and a mating semi-spherical internal surface 26, so as to define a semi-spherical cavity 27 to accommodate a head 14 of a humerus 12. A rod 22 is mounted inside the cavity 27, protruding from the internal surface 26, to attach the cap 20 to the head 14 of the humerus 12. According to one solution of the invention, the rod 22 is coaxial with said axis Y, that is, substantially in correspondence with the angular position of the pole of the cap 20 (fig. 4). The rod 22 has a length sufficient to allow it to be inserted through the humerus 14 into the meta-epiphyseal part 15, and to be stably positioned therein. According to the size, the rod 22 may or may not protrude from the cavity 27.

The prosthesis 10 is able to be mounted on the head 14 of a humerus 12, so as to be positioned between the head 14 and the mating glenoid seating 16 of a shoulder 18 (fig. 1). As we said, the cavity 27 is able to accommodate the head

14 of the humerus 12 and the rod 22 is able to be inserted into the bone of the meta-epiphyseal part 15 that makes up the head 14, previously holed to make a suitable meta-epiphyseal seating. On the contrary, the external surface 24 is able to be geometrically coupled with the glenoid seating 16, whether it is anatomical or prosthetic.

According to a characteristic feature of the present invention, the cap 20 and the rod 22 are two distinct elements and able to be coupled together, according to operating necessities (fig. 5). In other words, the rod 22 is able to be selectively positioned in the cap 20, and different shapes and sizes of rod 22 can be combined with different types of cap 20, according to needs.

A preferential embodiment of the present invention provides to make, in a single piece with the cap 20, an insertion cone, or insertion truncated cone, or similar constraining element 28,protmding from the surface 26, coaxial with the axis Y, that is, disposed in an angular position in correspondence with the pole of the cap 20 (fig. 6). Correspondingly, the rod 22 has a conical seating, or axial cavity 30, of size and shape mating with those of the insertion cone 28. The insertion of the insertion cone 28 into the seating 30 determines said coupling of the rod 22 and cap 20. Advantageously, the insertion cone 28 and the seating 30 are shaped so as to allow a conical coupling between them, which determines an effective clamping ofthe rod 22 and cap 20.

It should be noted, as can be seen in figs. 5 and 6, that the insertion cone 28 has a much smaller length, or in any case not comparable, with the length of the rod 22, since it has a different function from the latter.

Alternatively, the insertion cone 28 is fixed to the seating 30 of the rod 22 by screwing, nailing or cement.

Another alternative, not shown in the drawings, provides to make the seating 30 in the cap 20 and the cone 28 at the end of the rod 22.

Another form of embodiment provides not to make the cone 28 and the seating 30, and instead to couple the selected rod 22 to the internal surface 26 of the cap 20 by means of a suitable adhesive element or cement. In the solution shown here, to give a non-restrictive example, the rod 22 is conical, advantageously to give a stable insertion into the corresponding meta- epiphyseal seating of the head 14 of the humerus 12, and has a plurality of longitudinal ribs 32, made over the whole lateral surface and equidistant from each other (fig. 3), which are able to increase the contact surface with the bone of the head 14 of the humerus 16.

It is clear that modifications and/or additions of parts may be made to the humeral prosthesis 10 as described heretofore, without departing from the field and scope of the present invention.

For example, the internal surface 26 and the cavity 27 defined thereby can be shaped like a truncated cone.

Another variant, shown in figs. 7 and 8, provides to position the insertion cone 28 displaced with respect to the center of the cap 20 and with its longitudinal axis Y' in an inclined position with respect to the axis of symmetry Y of the prosthetic cap, for example inclined in a radial direction. A variant of the prosthetic cap 20, indicated for convenience by the reference number 120 in figs. 9 and 10, provides to make an extension surface 21, called "hat" in jargon, on the prosthetic cap 120, so as to increase the size of the cavity 27 and, correspondingly, the external surface 24. Thanks to the present invention, this variant cap 20 too can advantageously be used with a rod 22 of a size decided by the surgeon. In particular, the cap 20 is used in case of Cuff Tear Arthropathy, or in cases of massive rotator cuff tear.

It is also clear that, although the present invention has been described with reference to some specific examples, a person of skill in the art shall certainly be able to achieve many other equivalent forms of humeral prosthesis, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby.

Claims

1. Humeral prosthesis for the articulation of a head (14) of a humerus (12) in a mating glenoid seating (16) of a shoulder (18) comprising:

- a prosthetic cap (20, 120) which is able to articulate in the glenoid seating (16) and which, to cover the head (14) of the humerus (12), has a cavity (27) into which the head (14) of the humerus (12) is able to be inserted; and

- a rod (22) able to be positioned inside the humerus (12), to connect the prosthetic cap (20, 120) to the head (14) of the humerus (12), characterized in that said rod (22) is a distinct component with respect to said prosthetic cap (20, 120) and is able to be coupled inside the cavity (27) of said prosthetic cap (20, 120).

2. Prosthesis as in claim 1, characterized in that it comprises coupling means (28, 30) which are able to determine the coupling of the rod (22) and the prosthetic cap (20, 120).

3. Prosthesis as in claim 2, characterized in that the coupling means comprise a constraining element (28), disposed in the cavity (27) and made in a single piece with the prosthetic cap (20, 120), and a mating housing seating (30), made longitudinally in the rod (22), in which the constraining element (28) is able to be inserted and clamped.

4. Prosthesis as in claim 2, characterized in that the coupling means comprise a constraining element (28), made at one end of the rod (22), and a mating housing seating (30), disposed in the cavity (27), in which the constraining element (28) is able to be inserted and clamped.

5. Prosthesis as in claim 3 or 4, characterized in that the constraining element comprises an insertion cone (28) able to be coupled by conical coupling with the housing seating (30).

6. Prosthesis as in claim 3 or 4, characterized in that the constraining element (28) and the housing seating (30) are able to be coupled by screwing, nailing or cement.

7. Prosthesis as in claim 3 or 4, characterized in that the constraining element (28) is disposed coaxial with an axis of symmetry (Y) of the prosthetic cap (20, 120). 8. Prosthesis as in claim 3 or 4, characterized in that the constraining element

8

- 9 -

(28) is disposed eccentric with respect to an axis of symmetry (Y) of the prosthetic cap (20, 120).

9. Prosthesis as in claim 3 or 4, characterized in that the constraining element (28) is disposed inclined with respect to an axis of symmetry (Y) of the prosthetic cap (20, 120).

10. Prosthesis as in any claim hereinbefore, characterized in that the rod (22), on the external surface, has gripping means (32) able to increase the interference and gripping capacity of the rod (22).

11. Prosthesis as in any claim hereinbefore, characterized in that the rod (22) and the prosthetic cap (20, 120) are made of different materials.

12. Prosthesis as in any claim hereinbefore, characterized in that the rod (22) is made of titanium-based material.

13. Prosthesis as in any claim from 1 to 11, characterized in that the rod (22) is made of cobalt-based material.

14. Prosthesis as in any claim hereinbefore, characterized in that at least part of the rod (22) consists of a three-dimensional lattice achieving a plurality of open and intercommunicating cavities, connected both toward the inside and toward the outside of the rod (22).

15. Prosthesis as in any claim hereinbefore, characterized in that the prosthetic cap (20, 120) is made of cobalt-based material.

16. Prosthesis as in any claim from 1 to 14, characterized in that the prosthetic cap (20, 120) is made of titanium-based material.

17. Prosthesis as in any claim from 1 to 14, characterized in that the prosthetic cap (20, 120) is made of ceramic material.

18. Prosthesis as in any claim hereinbefore, characterized in that at least part of the prosthetic cap (20, 120) consists of a three-dimensional lattice achieving a plurality of open and intercommunicating cavities, connected both toward the inside and toward the outside of the cap (20, 120).

19. Prosthesis as in any claim hereinbefore, characterized in that it comprises an external surface (24), shaped mating with the glenoid seating (16), and an internal surface (26), which defines the cavity (27).

20. Prosthesis as in claim 19, characterized in that the internal surface (26) is substantially semi-spherical.

21. Prosthesis as in claim 19, characterized in that the internal surface (26) is shaped substantially like a truncated cone.

22. Prosthesis as in any claim hereinbefore, characterized in that the prosthetic cap (120) comprises a portion of extension surface (21) so as to determine an enlargement of the cavity (27) in which the head (14) of the humerus (12) is housed.