Ah I thought I had found it.
But I was wrong.
I've been searching for years for a series/movie that I remembered from when I was young, late 80s/early 90s. Anyhow, I thought it was Robot Jox but what I'm thinking of was a cartoon. It was a group of people who piloted mechs of some sort, it was american animation. I barely remember it because I was so young but what stands out in my mind is a scene in a cave. There was some kind of skeleton badguy/mech that picked up a guy and stuck him in his chest and his ribs became like a cage.
I know thats not alot to go on but I saw someone else's post and you seem to have helped him alot.