Forty-three shoulder-joint replacements were performed in forty-two
patients using a constrained joint. Twelve material failures were
experienced in the first series of twenty-two shoulders and only two in the
second, modified series (twenty-one shoulders). Loosening of the glenoid
components was not encountered, although radiolucent lines have been
observed about some of the components. A basic feature of the design was to
allow dislocation of the metal head from its cup when excessive motion of
the components is attempted by the patient and a specific torque is
exceeded. A method of insertion and design considerations allowed us to
achieve strong attachment between the metal glenoid and the scapula.