ragdoll physics not working properly

Hey I am using a Fuse human model rigged with Mixamo. It automatically made a physics asset for the skeleton when it spawned and I locked the swing motions on the calf and kept the angular motion, then i rotated the green angular constraint so that its range was not possible to bend the knees back but when i simulate physics the knees are able to bend back like a chicken. How do I fix this? Nothing seems to work in the settings I put.

sorry had to bump