At least there is no arthritis or mini-breaks. This is 12-15 years of bad patellar tendonitis. Mini-tears and periods of inflammation make it a perfect spot for a tear.
Combine that plus a quadricep firing hard to prevent a fall backwards and you get a tear. I felt bad for my kids. They didn't quite know how to handle seeing daddy all hurt. Also, I've been rolling with the kids regularly - Gracies Bullyproof JiuJitsu program. AWESOME stuff. It actually has such great basics that it can help anyone in the Jits game.