Reverse shoulder prosthesis

1. An implant assembly for reverse shoulder arthroplasty, the assembly comprising:

a humeral component having a stem portion and a neck portion, the stem portion being configured for fixation to a humerus of a patient, and the neck portion being angularly oriented relative to the stem portion; and

an adaptor coupled to the humeral component, the adaptor having a first bearing surface and a second bearing surface opposite the first bearing surface;

wherein the first bearing surface of the adaptor interfaces with an articulating surface of the neck portion to allow the humeral component to rotate relative to the adaptor about a rotational axis of the adaptor;

wherein the adaptor and the humeral component form a locking mechanism that prevents the adaptor from decoupling from the humeral component while allowing the humeral component to remain rotatable relative to the adaptor after the implant assembly is implanted in the patient; and

wherein the second bearing surface of the adaptor is configured to interface with a glenosphere component to allow the glenosphere component to articulate relative to the adaptor.

2. The implant assembly of claim 1 , wherein the adaptor comprises a first coupling member matingly engaged with a second coupling member of the neck portion.

3. The implant assembly of claim 2 , wherein the first coupling member comprises a shaft extending from the first bearing surface, and the second coupling member comprises a recess in the neck portion configured to receive the shaft.

4. The implant assembly of claim 2 , wherein the first and the second coupling members are aligned with the rotational axis of the adaptor.

5. The implant assembly of claim 4 , wherein the rotational axis passes through a geometric center of the first bearing surface.

6. The implant assembly of claim 4 , wherein a geometric center of the first bearing surface has a radial offset relative to the rotational axis.

7. The implant assembly of claim 2 , wherein the locking mechanism comprises a tongue-and-groove joint between the adaptor and the humeral component so as to allow rotational movement of the humeral component relative to the adaptor but resist displacement of the adaptor from the plane of rotation.

8. The implant assembly of claim 2 wherein the first coupling member comprises a shank member extending outwardly from the first bearing surface and a keel member angularly extending from the shank member.

9. The implant assembly of claim 8 , wherein the second coupling member comprises a channel and a chamber connected to the channel, wherein the shank is positioned in the channel and the keel is angularly moveable within the chamber.

10. The implant assembly of claim 9 , wherein the chamber has a first angular boundary and a second angular boundary, and the angular movement of the keel within the chamber is limited by the first and second angular boundaries.

11. The implant assembly of claim 10 , wherein the first angular boundary and the second angular boundary defines a circular sector having an angle from about 30° to about 150°.

12. The implant assembly of claim 2 , further comprising a first limiter and a second limiter, the first and second limiters being configured to limit rotational movement of the humeral component relative to the adaptor.

13. The implant assembly of claim 12 , wherein the first limiter is angularly spaced apart from the second limiter from about 30° to about 150° with respect to the rotational axis of the adaptor.

14. The implant assembly of claim 12 , wherein the first and second limiters are disposed on a proximal surface of the neck portion.

15. The implant assembly of claim 12 , further comprising a curved groove located on the first bearing surface of the adaptor and a tab extending outwardly from the articulating surface of the neck portion, the tab being configured to be received in and moveable within the curved groove, wherein a first and second ends of the groove define the respective first and second limiters.

16. The implant assembly of claim 1 , further comprising the glenosphere component, wherein the glenosphere component comprises a base configured for fixation to a glenoid fossa of scapula and a convex surface that articulates against the second bearing surface of the adaptor, wherein the second bearing surface is concave.

17. The implant assembly of claim 1 , wherein the first bearing surface of the adaptor is planar.

18. The implant assembly of claim 1 , wherein the first bearing surface of the adaptor is curved.

19. An implant assembly for reverse shoulder arthroplasty, the assembly comprising:

a humeral component having a stem portion and a neck portion proximal to the stem portion, the stem portion being configured for fixation to a humerus, and the neck portion is angularly oriented relative to the stem portion; and

an adaptor rotatably coupled to the neck portion of the humeral component such that the adaptor rotates relative to the neck portion about a rotational axis;

wherein the rotational axis forms a fixed angle relative to the stem portion of the humeral component; and

wherein the adaptor remains rotatable relative to the humeral component after the implant assembly is implanted in the patient.

20. An implant assembly for reverse shoulder arthroplasty, the assembly comprising:

a humeral component having a stem portion and a neck portion proximal to the stem portion, the stem portion being configured for fixation to a humerus, and the neck portion is angularly oriented relative to the stem portion;

an adaptor rotatably coupled to the neck portion of the humeral component such that the adaptor rotates relative to the neck portion about a rotational axis; and

a glenosphere component having a base and a convex surface, the base configured for fixation to a glenoid fossa of scapula, and the convex surface configured to articulate against a concave surface of the adaptor

wherein the rotational axis forms a fixed angle relative to the stem portion of the humeral component;

wherein the neck portion further comprises a first limiter and a second limiter that are configured to limit rotational movement of the humeral component relative to the adaptor;

wherein the assembly further comprises a locking mechanism configured to allow rotational movement of the humeral component relative to the adaptor but resist displacement of the adaptor along the rotational axis; and

wherein the humeral component remains rotatable relative to the adaptor after the implant assembly is implanted in the patient.