Is it possible to have a medieval type word where there's no Kings or Queens, only knights that serve as nobles?

The basic idea is that there would be a certain type of order (ex: An Order of the Dragon, Order of the Sword), and only people that become members of this certain order have the rights to certain things like owning land. This would be the case for several orders, each with different requisites (e.g. The Order of the Sword would be war orientated, The Order of the Dragon would be for scholars and so on). The requisites would then be legalized in that this people must maintain the requirements that made them knights to retain their privileges. For example, everyone in the Order of the Sword can't stop being a warrior. Once their privileges are taken away, they can't gain them back. <br><br>Would this system work?