Total shoulder replacement with a constrained prosthesis.

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.