Humeral implant for a shoulder prosthesis

Abstract

The invention discloses a support element for humeral implant comprising a central body extending along an axis and at least three arms extending outwardly from the central body, the arms being transversal to said axis and bearing a ring element at their ends opposite to said central body, wherein at least a first and a second pair of arms form different angles.

Claims

1. Support element for humeral implant comprising a central body extending along an axis and at least three arms extending outwardly from said central body, said arms being transversal to said axis and bearing a ring element at their ends opposite to said central body wherein an angle α formed between a first and a second adjacent arms being different from an angle β formed between a third arm that is adjacent to the first arm and the second arm, wherein there are no other arms between adjacent arms.

2. Support element according to claim 1, wherein said angle α varies between 90° and 155°.

3. Support element according to claim 2, wherein said angle α varies between 140° and 150°.

4. Support element according to claim 1, wherein said angle β varies between 50° and 180°.

5. Support element according to claim 4, wherein said angle β varies between 60° and 80°.

6. Support element according to claim 1, wherein at least one of said arms has an outer rim on the side opposite to ring element—that is rectilinear.

7. Support element according to claim 1, wherein at least two of said arms have an outer rim on the side opposite to ring element that is curvilinear.

8. Support element according to claim 1, wherein said arms have a transversal section tapering from the central body towards the ring element.

9. Support element according to claim 8, wherein the transversal section of said arms at the portion proximal to the ring element is 20-40% smaller than the transversal section at the portion distal from the ring element.

10. Support element according to claim 1, wherein said central body is provided with an internal coaxial threaded blind hole.

11. Support element according to claim 1 wherein said ring element has a trabecular structure.

12. Support element according to claim 1 made of trabecular titanium.

13. Support element for humeral implant comprising a central body extending along an axis and at least three arms extending outwardly from said central body, said arms being transversal to said axis and bearing a ring element at their ends opposite to said central body wherein at least a first and a second pair of arms form different angles, wherein said ring element comprises a first cylindrical portion coaxial to said axis and a second integral cylindrical portion coaxial to a further axis forming an angle γ with said axis.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) A preferred embodiment is hereinafter disclosed for a better understanding of the present invention, by mere way of non-limitative example and with reference to the accompanying drawings, in which:

(2) FIG. 1 is a planar view of the support element according to the present invention;

(3) FIGS. 2 and 3 are perspective views that show the support element according to the present invention;

(4) FIG. 4 is a perspective views that show the support element according to the present invention in its anatomical configuration mounting a male insert;

(5) FIG. 5 is a perspective views that show the support element according to the present invention in its anatomical configuration mounting a male insert and a humeral head;

(6) FIG. 6 is a perspective views that show the support element according to the present invention in its reverse configuration mounting a female insert;

(7) FIG. 7 is a planar view of the humeral implant of FIG. 5 implanted into the humerus;

(8) FIG. 8 is a planar view of the humeral implant of FIG. 6 implanted into the humerus.

BEST MODE FOR CARRYING OUT THE INVENTION

(9) FIGS. 1-3 indicate with numeral 1 as a whole a support element for an humeral implant according to the invention.

(10) The support element 1 comprises a central body 2 extending along an axis H. The central body 2 has three arms 3, 4a and 4b extending outwardly from the central body 2 and transversely positioned with respect to the axis H. The number of the arms may vary from 3 to 5.

(11) The three arms 3, 4a and 4b bear a ring element 5 at their ends opposite to said central body 2. The ring element 5—according to a first embodiment of the invention—comprises a cylindrical tubular body coaxial to axis H. The tubular body is one piece with arms 3, 4a and 4b.

(12) According to a different embodiment (FIG. 4), tubular body comprises a first cylindrical portion 5a coaxial to axis H and a second integral cylindrical portion 5b coaxial to a different axis H1 forming an angle γ with axis H. Arms 3, 4a and 4b and are spaced one with respect to the other along the axis H so that at least a first pair of arms 3-4a or 3-4b and a second pair of arms 4a-4b form different angles α and β with respect the axis H (see FIG. 1). In particular, the angle β is formed between arms 4a and 4b and the angles α are formed between the arms 3 and 4a or 4b. These angles may vary in the range between 50° and 180° for β and between 90° and 155° for α, preferably between 60° and 80° for β and between 140° and 150° for α.

(13) The arm 3 has an outer rim 7 on the side opposite to ring element 5 that is rectilinear and arms 4a, 4b have an outer rim 8a, 8b on the side opposite to ring element 5 that is curvilinear.

(14) All the arms 3, 4a and 4b have a transversal section tapering from the central element 2 towards the ring element 5. In particular, the arms 3, 4a, 4b have, at the portion proximal to the ring element 5, a transversal section that is 20-40% smaller than their transversal section at the portion distal from the ring element 5.

(15) The central body 2 is further provided with an concentric, coaxial with axis H, threaded blind hole 6 that opens on the side facing ring element 5. The blind hole 6 can be used to accommodate a tool (not shown) used for the insertion and removal of the support element 1.

(16) The support element is made of titanium alloy so as to achieve the maximum bio compatibility.

(17) The humeral implant according to the present invention is implanted by resecting one end of the bone, creating cavities to accommodate the arms 3, 4a and 4b and the ring element 5 and placing the support element 1 in the above respective cavities (FIGS. 7 and 8).

(18) The support element is placed with respect to the bone so that to place the arm 3 provided with linear rim 7 in the portion of the humerus head facing the glenoid surface. In this way, an anatomical distribution of the load is achieved.

(19) Accordingly, the ring element 5 allows the peripheral fixation of the implant on the resected humeral head and the arms 3, 4a and 4b allow the fixation to the cortex and the load transmission from the prosthesis to the bone following the natural pattern.

(20) The presence of the ring element 5 and the specific positioning of the arms 3, 4a and 4b allow an improved transmission of loads from the prosthesis to the bone as well as the stability of the implant and the prevention of the rotation.

(21) In the prosthesis of the prior art, the load is transmitted to the spongy bone of the humerus through a central component; the contact between the prosthesis head and the resected surface allows a small load transmission to the peripheral cortex of the bone.

(22) The literature (R. H. Cofield, J. W. Sperling, Revision and complex shoulder arthroplasty, Lippincott Williams and Wilkins Ed) reports that there must be a macrointerlock between the prosthesis and the bone. This means that there must be sufficient bone in all areas to bear stresses: this often requires impaction grafting of the cancellus bone. The distribution of the forces should be such that stress-guided remodelling does not alter the bone significantly with time.

(23) This means also that the best fixation of the prosthesis is the one that allow a transmission of load to the bone that reproduce the natural one.

(24) The load transmission to the bone is related to the distribution of the bone trabeculae. In the humerus is possible to identify five different areas of trabeculae distribution (M. C. Hall, M. Rosser, The structure of the upper end of the humerus with reference to osteoporotic changes in senescence leading to fractures, Canad. Med. Ass. J., Feb. 9, 1663, vol. 88; study performed on osteoporotic humeri).

(25) In case of a prosthesis implantation it is very important to allow the load transmission from the prosthesis to the bone. Indeed if the bone is loaded it remains alive and it is possible to have osteointegration. Otherwise, if the bone is not under load it is possible to have a bone resorption and finally a prosthesis mobilization.

(26) The ring element 5 is able to receive both a male insert 9 or female insert 10. This has in particular the advantage that removal of the humeral implant is not necessary to convert the prosthesis from the anatomical application to the reverse.

(27) In case of the anatomical configuration, as shown in FIGS. 4 and 5, a male insert is mounted on the ring 5. The male insert will then be connected with the humeral head 10.

(28) In case of the inverse configuration, a female insert 11 is mounted on the ring 5, as shown in FIG. 6.

(29) Moreover, the ring element 5 has a trabecular structure in order to increase the primary stability of the support element 1 as well as its osteointegration. In this way the support element 1 may be used also in case of implantation reverse prosthesis, in which the loads to be borne are higher than in case of anatomic prosthesis.

(30) Moreover, in case of conversion from anatomic prosthesis to reverse one, for example because of a cuff tear, it will be possible to leave the osteointegrated support element 1 in its position and simply remove the male insert 9 and connecting female insert 10.