-symptomatic loosening of glenoid/humeral occurs in 3.5% of those with TSA
-contributing factors include glenoid prep, soft tissue balancing, wear debris, bone reabsorption, prosthetic design, component geometry, and biomaterials
-major concern is eccentric load placed on glenoid by humeral component, particularly if head migrated superiorly
-HH migration bc RC tear, poor humeral fixation, and soft tissue balance
-during arm elevation eccentric load of proximal migrated humeral compt can produce a rocking horse effect on the glenoid that loosens glenoid compt