i have something simmilar to your cage thingie. my knee problems stem from injuries back in my days of youth and immortallity though,before MS. when i was young i used to race motocross. i was just never all that good at it and i wrecked alot. and as a result i trashed my knees. now, when they 'go out' on me they wont lock, as it were. and when i walk i cant control when the knee bends for the next step. it just bends when ever it feels like. and yes it does hurt,horrendously to have it bend the wrong way. the first time it did it to me i thought i had broken something.
the brace i have seems to be a different design of the same thingyoure looking at. i got it from a sports medicine place in alexandria,va. the way mine is designed the hinges are supposed to help distribute my weight around my knee while preventing it from snapping back.