  We analyse liquid-crystalline ordering in vertically vibrated monolayers of
cylinders confined in a circular cavity. Short cylinders form tetratic
arrangements with C$_4$ symmetry. This symmetry, which is incompatible with the
geometry of the cavity, is restored by the presence of four point defects with
total topological charge $+4$. Equilibrium Monte Carlo simulations predict the
same structure. A new method to measure the elastic properties of the tetratic
medium is developed which exploits the clear similarities between the vibrated
dissipative system and the thermal equilibrium system. Our observations open up
a new avenue to investigate the formation of defects in response to boundary
conditions, an issue which is very difficult to realize in colloidal or
molecular systems.
