I Have Osteoart In My Knee And If A Torn Ligament Or Muscle Is Damaged, Would It Cause Swelling?

Yes. A torn ligament would cause swelling.
Having osteoarthritis can make you more vulnerable to injuries such as this. Pain would also be a symptom.
Put ice on the knee. Try to stay off of the leg for awhile. Take an antiinflamtory such as advil or motrin.
Contact the doctor if the swelling or pain does not get better after a few days.