Implant assemblies for reverse shoulder arthroplasty are disclosed. In one embodiment, the implant assembly comprises a humeral component, an adaptor fixed to the neck of the humeral component, and a glenosphere bearing component coupled to the adaptor. The glenosphere bearing component comprises a first bearing surface that interfaces with an articulating surface of the adaptor to allow the adaptor to rotate relative to the adaptor and humeral component. The adaptor and the glenosphere bearing component form a locking mechanism that prevents the adaptor from decoupling from the glenosphere bearing component while allowing the adaptor to remain rotatable relative to the glenosphere bearing component after the implant assembly is implanted in the patient The second bearing surface is configured to interface with a glenosphere component to allow the glenosphere bearing component to articulate relative to the glenosphere component.