Reverse shoulder prostheses with anti-rotation features

1. A reverse shoulder prosthesis, comprising:

a stem comprising a primary stem axis and an opening in a proximal end of the stem, the proximal opening extending about a metaphyseal axis, the metaphyseal axis at an angle with respect to the primary stem axis;

a metaphysis comprising:

a distal end configured for attachment to the stem, the metaphysis being configured to rotate around the metaphyseal axis when coupled to the stem, the metaphysis configured for attachment to the stem at a plurality of rotational positions of the metaphysis about the metaphyseal axis; and

a proximal end comprising a first interlocking portion having an insert axis that is eccentrically offset from the metaphyseal axis, the first interlocking portion comprising an aperture defining a radially inward facing surface; and

a reverse insert comprising a proximal end and a distal end, wherein the proximal end of the reverse insert comprises a concave cup formed about a cup axis, and wherein the distal end of the reverse insert comprises a second interlocking portion, the second interlocking portion comprising a protrusion having a radially outward facing surface, the radially outward facing surface being continuous around a periphery of the distal end of the reverse insert,

wherein an interface between the first and second interlocking portions has a rotational symmetry about the insert axis, and

wherein the interface between the radially inward facing surface of the first interlocking portion and the radially outward facing surface of the second interlocking portion prevents rotation of the reverse insert relative to the metaphysis about all axes when the reverse insert is engaged with the metaphysis.

2. The prosthesis of claim 1 , wherein the metaphysis is configured for attachment to the stem at any rotational position of the metaphysis about the metaphyseal axis.

3. The prosthesis of claim 1 , wherein the radially outward facing surface of the second interlocking portion has a cross-sectional shape that is rotationally symmetrical about the insert axis when engaged to the radially inward facing surface of the aperture.

4. The prosthesis of claim 3 , wherein the second interlocking portion further comprises a locking lip, and wherein the first interlocking portion further comprises a groove to engage with the locking lip.

5. The prosthesis of claim 4 , wherein the locking lip extends around the protrusion, and wherein the groove extends around the aperture.

6. The prosthesis of claim 1 , wherein the cup axis is aligned with the insert axis.

7. The prosthesis of claim 1 , wherein the cup axis is offset from the insert axis.

8. The prosthesis of claim 1 , wherein the reverse insert is an angled insert for which the cup axis is at an angle with respect to the insert axis, such that the reverse insert is configured to lock with the metaphysis in at least two different positions, wherein the cup axis has a different radial orientation with respect to the metaphyseal axis at each of the at least two different positions.

9. The prosthesis of claim 1 , wherein the rotational symmetry has an order of six, seven, eight, nine, or ten.

10. The prosthesis of claim 1 , wherein the rotational symmetry has an order of eight, a shape of the interface being octagonal.

11. The prosthesis of claim 1 , wherein an interface between the metaphysis and the stem comprises a distal-facing surface of the metaphysis and a proximal-facing surface of the stem.

12. The prosthesis of claim 1 , wherein the metaphysis is configured such that no part of an interface between the metaphysis and the stem extends outside of a bone when the prosthesis is implanted.

13. A kit for a reverse shoulder prosthesis, the kit comprising:

the reverse shoulder prosthesis of claim 1 ;

a second stem comprising a second primary stem axis and a second opening in a proximal end of the second stem, the second opening extending about a second metaphyseal axis, the second metaphyseal axis at a second angle with respect to the second primary stem axis, wherein the second angle is different from the angle;

a second reverse insert having a proximal end and a distal end, wherein the proximal end of the second reverse insert comprises a second concave cup formed about a second cup axis, and wherein the distal end of the second reverse insert comprises a third interlocking portion,

wherein an interface surface between the first and third interlocking portions has a rotational symmetry about the insert axis.

14. The kit of claim 13 , wherein the reverse insert is a first angled insert for which the corresponding cup axis is at a third, non-zero angle with respect to the insert axis, wherein the second reverse insert is a second angled insert for which the corresponding cup axis is at a fourth, non-zero angle with respect to the insert axis, wherein the fourth angle is different from the third angle.

15. The kit of claim 14 , wherein the reverse insert used with the metaphysis and the stem results in a same overall inclination angle as the second reverse insert used with the metaphysis and the second stem.

16. The prosthesis of claim 1 , wherein the first interlocking portion comprising a plurality of teeth.

17. The prosthesis of claim 16 , wherein the metaphysis is configured for attachment to the stem at any rotational position of the metaphysis about the metaphyseal axis.

18. The prosthesis of claim 16 , wherein the cup axis is aligned with the insert axis.

19. The prosthesis of claim 16 , wherein the cup axis is offset from the insert axis.

20. A kit for a reverse shoulder prosthesis, the kit comprising:

the reverse shoulder prosthesis of claim 16 ;

a second stem comprising a second proximal opening and a second primary stem axis, the second opening extending about a second metaphyseal axis, the second metaphyseal axis at a second angle with respect to the second primary stem axis, wherein the second angle is different from the angle;

a second reverse insert having a proximal end and a distal end, wherein the proximal end of the second reverse insert comprises a second concave cup formed about a second cup axis, and wherein the distal end of the second reverse insert comprises a third interlocking portion,

wherein an interface surface between the first and third interlocking portions has a rotational symmetry about the insert axis.

21. The kit of claim 20 , wherein the reverse insert is a first angled insert for which the corresponding cup axis is at a third, non-zero angle with respect to the insert axis, wherein the second reverse insert is a second angled insert for which the corresponding cup axis is at a fourth, non-zero angle with respect to the insert axis, wherein the fourth angle is different from the third angle.

22. The kit of claim 21 , wherein the reverse insert used with the metaphysis and the distal stem results in a same overall inclination angle as the second reverse insert used with the metaphysis and the second distal stem.