What Causes Pain In The Knee Upon Walking Post Injury?

i banged by knee against a coffee table about a month ago which i did not give any thought about, then after about one week after i have been in some pain at the front of the knee and to the left side when walking and standing up and twisting i am a skier and had a major accident three years ago with the other knee with acl and mcl ruptures but no surgery and am now skiing with ski brace, but this recent incident is completely different and without pain and there was no damage to the knee to which i am now having problems with