Fell on my knee pretty hard?

i fell on my knee really hard when i was scooting around on the sidewalk. I was going pretty fast and the rock i hit made a 8 inch scratch on the pavement. I literally blinked and i hit the pavement. My hand absorbed some of the impact and i went like straight down so i didn't like sc it that much. My hand has 5 deep scs in it but my knee is the problem. I had to sit there swearing for about 5 minutes and i swear it felt like i broke it!! It felt like my knee like had exploded and i couldnt stand up. Then the pain started to subside and my knee was throbbing as i hugged a tree to get up -.- i continued down the block slowly and by the time i got back home my knee hadnt stopped hurting but it wasnt as bad. It seems like i scd my knee but theres just a little bit of scd skin on it. The rest is like a pattern of like big red blotches of skin with a bit of bruising underneath and its only been about 10 minutes. When i make my legs straight up against the wall my knee caps sorta push out a bit and theres like a trench but on my left leg its barely noticable. It looks like its a trench from the first world war on my other right knee and its quite swollen. What did i do? Bruises never swell up for me.. It doesnt really hurt too much but when i extend my knee and that "trench" appears in it then it hurts the most. It doesnt hurt that bad so is it like a bruise or what but im not sure because ive never had a swollen bruise before?! -.- what could it be?