Stiff joint disease and the regency of Richard II.
Richard II he was crippled by a mysterious illness during his short reign that gradually took away his bodily mobility and ability to fully rule. His era shows how quickly the formal crown can become separated from the actual exercise of power.
Stiff joint disease
Richard's illness initially manifested as pain and restricted movement, but soon progressed to such profound paralysis that the monarch was unable to act or move normally. At a time when the ruler's authority was still strongly tied to physical presence, this was an extremely dangerous situation.