What Causes A Lump In The Knee After A Fall?

i had a basketball game earlier today and i fell right on my knee. ever since then it has been a lump where i fell and it hurts to the touch and hurts to walk or run a little. what is this.? ( i have patellar tendonitis in both of my knees and a possible meniscus tear in my life knee...i fell on my right knee)