Modular humeral prosthesis for an inverted shoulder prosthesis

Abstract

The invention relates to a modular humeral prosthesis for an inverse shoulder prosthesis, comprising an anatomical shaft (1) and a separable epiphyseal head (2) which may be angularly orientated by rotation about the longitudinal axis (XX) of the anatomical shaft. The anatomical shaft and the epiphyseal head comprise complementary angular indexing means (11, 28) for relative rotational fixation.

Claims

1. A modular reverse humeral prosthesis for implantation at least in part within a humerus, comprising: an anatomical stem having a longitudinal axis and an axial stem hole parallel to the longitudinal axis, the stem hole having an internally threaded portion; wherein the anatomical stem also has a flared metaphyseal portion; a separable epiphyseal head having a socket configured to receive a cup and a head hole that communicates with the socket, the epiphyseal head being rotatable about the longitudinal axis of the stem such that the epiphyseal head and stem can be assembled at a plurality of angular positions, the head hole configured such that the head hole and the stem hole are aligned when the epiphyseal head and the stem are assembled, the head hole having an internally threaded portion; and a screw comprising a head, a threaded portion having a screw thread that cooperates with the internally threaded portion of the head hole and the internally threaded portion of the stem hole, and a shaft between the threaded portion and the head, the head of the screw configured to be entirely disposed within the head hole of the epiphyseal head when the threaded portion of the screw cooperates with the internally threaded portion of the stem hole; wherein a proximal surface of the stem is planar about the internally threaded portion and a distal surface of the epiphyseal head is planar about the head hole; wherein at least portions of the proximal surface of the stem and the distal surface of the epiphyseal head are in contact when the epiphyseal head and the stem are assembled, and wherein the epiphyseal head comprises a lug that extends from the distal surface, the lug configured to be at least partially disposed within the stem hole when the epiphyseal head and the stem are assembled; and wherein the lug is cylindrical and the head hole extends through the lug.

2. The modular humeral prosthesis of claim 1, wherein one of the proximal surface of the stem and the distal surface of the epiphyseal head has a plurality of notches disposed according to a radial angular distribution about the longitudinal axis, and the other of the proximal surface of the stem and the distal surface of the epiphyseal head comprises a peg extending from said surface configured to cooperate with the plurality of notches.

3. The modular humeral prosthesis of claim 2, wherein, when implanted, the proximal surface of the stem and the distal surface of the epiphyseal head are located inside the humerus.

4. The modular humeral prosthesis of claim 2, wherein the distal surface of the epiphyseal head extends laterally beyond the stem at the plurality of angular positions.

5. The modular humeral prosthesis of claim 2, wherein each of the proximal surface of the stem and the distal surface of the epiphyseal head are substantially perpendicular to the longitudinal axis.

6. The modular humeral prosthesis of claim 1, wherein the stem comprises at least one longitudinal rib for rotational locking.

7. The modular humeral prosthesis of claim 1, wherein the stem hole is aligned with the longitudinal axis.

8. The modular humeral prosthesis of claim 7, wherein the stem hole has a first bore of a first diameter and a second bore that communicates with the first bore, the second bore having a second diameter that is smaller than the first diameter, and the lug is adapted to be at least partially disposed within the first bore of the stem.

9. The modular humeral prosthesis of claim 8, wherein the second bore of the stem hole is threaded.

10. The modular humeral prosthesis of claim 1, wherein the head hole has a first bore of a first diameter and a second bore that communicates with the first bore, the second bore having a second diameter that is smaller than the first diameter.

11. The modular humeral prosthesis of claim 10, wherein at least a portion of the second bore of the head hole is threaded.

12. The modular humeral prosthesis of claim 11, wherein the stem hole has a first bore of a first diameter and a second bore that communicates with the first bore, the second bore having a second diameter that is smaller than the first diameter.

13. The modular humeral prosthesis of claim 12, wherein the at least a portion of the second bore of the stem hole is threaded.

Description

(1) The invention will now be described in greater detail but in a non-limiting manner with reference to the accompanying figures, in which:

(2) FIG. 1 is an exploded view of a modular humeral prosthesis for an inverted shoulder prosthesis,

(3) FIG. 2 is an enlarged view from below of the epiphyseal head and the upper portion of the anatomical rod of a modular humeral prosthesis for an inverted shoulder prosthesis,

(4) FIG. 3 is an exploded schematic section of a modular humeral prosthesis for an inverted shoulder prosthesis in position within a humerus.

(5) FIG. 4 is an enlarged longitudinal section of the upper portion of the modular humeral prosthesis in FIG. 3.

(6) The modular humeral prosthesis for an inverted shoulder prosthesis shown in FIG. 1 comprises an anatomical rod 1, a separable epiphyseal head 2 which is positioned at the upper end (or proximal extremity) of the anatomical rod 1, and a screw 3 for connecting the epiphyseal head 2 to the rod 1.

(7) The anatomical rod of which the shape is known per se comprises a generally cylindrical stem 4 which is extended in its upper portion by a metaphyseal portion 5 which flares upwardly so as to have a shape which is adapted to the form of the epiphyseal joint of a humerus with the metaphysis of this humerus. This head 5 constitutes the proximal extremity of the anatomical rod, the lateral wall of the head 5 of the anatomical rod comprises ribs 6 for blocking in position relative to a humerus in which the rod is implanted.

(8) The proximal extremity of the anatomical rod 1 is limited by a planar surface 7 which corresponds to a section perpendicular to the longitudinal axis of the anatomical rod. A hole 8 extending within the anatomical rod and parallel to the axis of this rod is drilled perpendicularly to the surface 7 delimiting the proximal extremity. The hole 8 comprises a first bore 9 followed by a screw-threaded hole of smaller diameter 10. Preferably, the hole 8 and the stem 4 of the anatomical rod are coaxial. The surface 7 further comprises a lug 11 which projects longitudinally relative to the metaphyseal rod.

(9) The epiphyseal head 2 is a portion of a sphere delimited by an equatorial plane 21 and a plane forming an acute angle with an equatorial plane. Below the equatorial plane 21, the epiphyseal head 2 comprises a bowl 21A intended to receive a polyethylene or ceramic cup. This cup is the part which is intended to cooperate with the mating portion of the prosthesis which will be fixed to the scapula. The plane forming an acute angle with the equatorial plane defines a polar surface 22 intended to come into contact with the end surface 7 of the anatomical metaphyseal rod 1.

(10) The polar surface 22 comprises a cylindrical lug 23 which projects from the polar surface 22 and is perpendicular thereto. The size of this cylindrical lug 23 is adapted so that it can cooperate with the greater diameter bore 9 of the axial hole 8 in the anatomical rod and thus locate the epiphyseal head relative to the anatomical rod. An axial hole 24 for receiving a screw 3 extends through the cylindrical lug 23, the screw 3 extending both in the hole 24 in the epiphyseal head and in the hole 8 in the anatomical rod so that it will be screwed into the screw-threaded portion 10 of the hole 8. The hole 24 comprises a first portion 25 of greater diameter intended to receive the head 31 of the screw and a portion of smaller diameter 26 intended to receive the body 32 of the screw 3. The cylindrical lug 23 and the hole 8 constitute means for locating and guiding in rotation the epiphyseal head relative to the anatomical rod.

(11) The portion of smaller diameter 26 comprises a first portion 26A of short length having a diameter and a screw thread identical to the diameter and screw thread of the screw-threaded portion 10 of the axial hole 8, the metaphyseal rod and a second portion 26B of greater length extending to the point where the hole emerges at the end of the cylindrical lug 23 and of which the diameter is greater than or equal to the external diameter of the screw-threaded portion of the screw 3. The body 32 of the screw 3 comprises, at its extremity, a screw-threaded end 32A which is capable of cooperating with the screw thread of the screw-threaded portion 10 of the axial hole 8 in the metaphyseal rod, and a stem 32B connecting the head 31 of the screw 3 to the screw-threaded end, and having a diameter smaller than the internal diameter of the first screw-threaded portion 26A of the portion of smaller diameter 26 of the hole 24 in the epiphyseal head.

(12) With this arrangement, the epiphyseal head is completely separated from the anatomical rod by unscrewing the screw. In order to put the screw in position, it first has to be screwed into the screw-threaded portion 26A of the hole in the epiphyseal head. This has the advantage of making the screw integral with this epiphyseal head while leaving it free in rotation and in translation over a specific length and thus facilitates manipulation by the surgeon who is putting the prosthesis in position.

(13) The polar surface 22 comprises a plurality of notches 28 disposed radially relative to the axis of the cylindrical lug 23 and at a distance from this lug such that, when the cylindrical lug 23 is disposed inside the hole 8 of the anatomical rod 1, the lug 11 situated on the surface 7 of the proximal extremity of the anatomical rod 1 can cooperate with a notch 28. These notches are arranged at 10 from one another in a fan and are complemented by markings which allow the position of the epiphyseal head 2 relative to the anatomical rod 1 to be determined when the epiphyseal head is disposed on the anatomical rod and the lug 11 is within a notch 28.

(14) In addition, the plane defining the polar surface 22 is selected so that the diameter of this polar surface is sufficient for the polar surface 22 to extend laterally beyond the surface 7 of the proximal extremity of the anatomical rod, whatever the orientation of the epiphyseal head relative to the anatomical rod. As a result, when the prosthesis is in position in a humerus, the re-growing bone does not form bands which extend beyond the proximal extremity of the anatomical rod and therefore does not prevent extraction of the prosthesis.

(15) Referring to FIG. 4, the epiphyseal head 2 is able to rotate about the longitudinal axis XX of the anatomical rod. The axis YY of the epiphyseal head perpendicular to the equatorial plane 21 intersects the longitudinal axis XX of the anatomical rod 1 at a point A preferably located on a surface defined by the contact between the proximal face 7 of the anatomical rod 1 and the polar face 22 of the epiphyseal head 2.

(16) Finally, FIG. 3 shows that the length of the anatomical rod and the dimensions of the epiphyseal head are selected so that, when the prosthesis is in position, the epiphyseal head is completely included in the epiphysis of the humerus.

(17) In order to put a prosthesis of this type in position, the surgeon begins by preparing the humerus by producing, in a known manner, an axial hole adapted to receive an anatomical humeral rod and an epiphyseal head. Then, using an appropriate gauge, he determines the retroversion which the epiphyseal head will have to perform relative to the anatomical humeral rod.

(18) The surgeon then puts in position the anatomical rod then the epiphyseal head while orientating it at a predetermined angle and immobilises it in rotation by causing the lug 11 of the proximal extremity of the anatomical rod to cooperate with the appropriate groove 28 in the polar surface 22 of the epiphyseal head. He finally tightens the screw 3 to lock the assembly.