THE INFLUENCE OF CONFORMITY AND CONSTRAINT ON TRANSLATIONAL FORCES AND FRICTIONAL TORQUE IN TOTAL SHOULDER ARTHROPLASTY

Glenoid loosening in total shoulder arthroplasty (TSA) may result from translational forces and frictional torque generated at the articular surfaces and transmitted to the fixation interface. The effect of gle nohumeral articular design on the magnitude of these translational for ces and frictional torques has not been evaluated previously. Seven di fferent glenohumeral designs were evaluated on a specially designed fi xture integrated with a materials test system. The degree of conformit y and constraint in the glenohumeral designs directly affected the for ces generated during translation and rotation of the humeral head. Max imum translational forces occurred close to the midline in the more co nforming design. The less conforming designs generated lower translati onal forces and frictional torques. Because frictional torque and tran slational forces at the glenohumeral articulation may contribute to gl enohumeral loosening, the use of less conforming and less constrained designs is advocated where possible to reduce the potential for mechan ical loosening of the glenoid component.