Kneeling post
From wipipedia.org
A kneeling post is a piece of furniture, sometimes found in dungeons, designed to force a captive to remain in a kneeling position.
It consists of a post a few feet high, either firmly fixed to the ground or on a base on which the captive also sits. It has leg cuffs affixed at the bottom, in which the captive's ankles are held. The captive is also secured at various places to the post to ensure that he or she has very little freedom of movement.
