Abstract: A hip joint prosthesis including a cup-shaped socket member for being implanted in an acetabular opening, and a ball-shaped member having a shaft attached thereto for being implanted in a femoral opening, wherein after implantation of the socket and ball members, the two members are assembled together for relative movement, and locked in place by an adjustable mechanism. The adjustable mechanism is coupled to the cup-shaped member by springs, wherein forces tending to separate the ball from the socket will be partially absorbed by the springs, thus reducing the likelihood that the cup-shaped member will become dislodged from the acetabular opening.