Abstract: A prosthetic implant for joint structures includes a shell, a head adapted to be secured to a bone leading to the joint structure in which the implant is to be used, an insert member adapted to be received in the shell and also adapted to receive the head, and a locking arrangement associated with the shell. The locking arrangement is adapted for releasably locking the insert member and head received therein in a receptacle in the shell. The locking arrangement preferably includes a ring of resilient material having an opening along part of its circumference for enabling the ring to resiliently expand and collapse. The ring is received in a groove inside the shell receptacle. As the insert member and head received therein are inserted into the shell, the ring expands into the groove allowing the insert member to pass. Once the insert member is fully received in the shell the ring snaps back to contact the insert member and retain it in the shell.