A modular prosthesis assembly for insertion in bone, the assembly comprising: a tray element having a first surface including an extension member depending therefrom and an opposite second surface; a first adaptor having first and second ends, the first end having a profile part which receives and retains the extension member; a second adaptor comprising, a first end and a second end; the first end engagable with the second end of the first adaptor; a stem having first and second end, the first end including a formation which allows engagement of the stem with the second end of the second adaptor. The second end of said stem has a profile suitable for insertion in bone.