I was in a car accident on dec 2. my leg was black and blue below the knee on the side. x ray showed no broken bones. today it is still very swollen and red and feels warm to the touch. could a torn ligament cause this?

Prolonged swelling,redness& warmth are worrisome signs and not characteristics of uncomplicated torn knee ligaments. Possibilities include phlebitis, hematoma with cellulitis as well as knee joint injuries.Consult a physician or orthopedic surgeon as soon as possible. In the meantime elevate the leg when sitting & apply warm compresses until you're examined.

It sounds like you have a hematoma. While a torn ligament can cause that the trauma can also cause it. If you haven’t seen your Primary care since the accident it would be a good idea to follow up for an exam and evaluation. In the mean time ice and elevate the leg