How did ruffian die?

She broke the sesamoid bones in her right foreleg. After surgery, she thrashed about, undid the surgery, and smashed her other foreleg.

She was in a match race with Foolish Pleasure and her bone snapped in two and pierced her through her skin. Her owners had payed a large amount on a risky surgery and it went very successful however when she woke up she though she was still in the race and was impossible to calm down so they had to put her down. Sadly that was the only race that she never won and never finished.