Abstract: There is disclosed a surgically implantable prosthetic joint implant adapted for length adjustment after initial surgery to compensate, for example, for growth of a juvenile patient. A stem for bone implantation has a flange for overlying the bone end and a threaded portion for adjusting axially with respect to an overlying sleeve which carries at its extremity an articulating component of the joint. A pin in the sleeve and elongated slot in the stem restrain relative rotation but allow axial relative movement as the stem is urged into or out of the sleeve by rotation of a nut coacting with the threads on the stem while being axially restrained by the sleeve. The nut is described as having a ring of gear teeth to be actuated by an insertable gear-carrying key. An alternative embodiment uses an accessible recessed bolt for moving the stem into or out of the sleeve.