You may have strained or torn a ligament in your knee also, there are four major ligaments in the knee, most commonly injured is the ACL (anterior cruciate ligament) Lots of athletes get injured there.
This info is from
www.mayoclinic.com (great health info resource!)
Injuries
A knee injury can affect any of the ligaments, tendons or fluid-filled sacs (bursae) that surround your knee joint as well as the bones, cartilage and ligaments that form the joint itself. Some of the more common knee injuries include:
ACL injury. An ACL injury is the tearing of the anterior cruciate ligament (ACL) — one of four ligaments that connect your shinbone to your thighbone. An ACL injury is particularly common in people who play basketball or go downhill skiing, because it's linked to sudden changes in direction.
Torn meniscus. The meniscus is formed of tough, rubbery cartilage and acts as a shock absorber between your shinbone and thighbone. It can be torn if you suddenly twist your knee while bearing weight on it.
Knee bursitis. Some knee injuries cause inflammation in the bursae, the small sacs of fluid that cushion the outside of your knee joint so that tendons and ligaments glide smoothly over the joint.
Patellar tendinitis. Tendinitis is irritation and inflammation of one or more tendons — the thick, fibrous cords that attach muscles to bones. Runners, skiers and cyclists are prone to develop inflammation in the patellar tendon, which connects the quadriceps muscle on the front of the thigh to the shinbone.
Mechanical problems
Loose body. Sometimes injury or degeneration of bone or cartilage can cause a piece of bone or cartilage to break off and float in the joint space. This may not create any problems unless the loose body interferes with knee joint movement — the effect is something like a pencil caught in a door hinge.
Knee 'locking.' This can occur from a cartilage tear. When a portion of cartilage from the tear flips inside the knee joint, you may not be able to fully straighten your knee.
Dislocated kneecap. This occurs when the triangular bone (patella) that covers the front of your knee slips out of place, usually to the outside of your knee. You'll be able to see the dislocation, and your kneecap is likely to move excessively from side to side.
Hip or foot pain. If you have hip or foot pain, you may change the way you walk to spare these painful joints. But this altered gait can interfere with the alignment of your kneecap and place more stress on your knee joint. In some cases, problems in the hip or foot can refer pain to the knee.
Types of arthritis
Osteoarthritis. Sometimes called degenerative arthritis, osteoarthritis is the most common type of arthritis. It's a wear-and-tear condition that occurs when the cartilage in your knee deteriorates with use and age.
Rheumatoid arthritis. The most debilitating form of arthritis, rheumatoid arthritis is an autoimmune condition that can affect almost any joint in your body, including your knees. Although rheumatoid arthritis is a chronic disease, it tends to vary in severity and may even come and go.
Gout. This type of arthritis occurs when uric acid crystals build up in the joint. While gout most commonly affects the big toe, it can also occur in the knee.
Pseudogout. Often mistaken for gout, pseudogout is caused by calcium pyrophosphate crystals that develop in the joint fluid. Knees are the most common joint affected by pseudogout.
Septic arthritis. Sometimes your knee joint can become infected, leading to swelling, pain and redness. There's usually no trauma before the onset of pain. Septic arthritis often occurs with a fever.
Other problems
Iliotibial band syndrome. This occurs when the ligament that extends from the outside of your pelvic bone to the outside of your tibia (iliotibial band) becomes so tight that it rubs against the outer portion of your femur. Distance runners are especially susceptible to iliotibial band syndrome.
Chondromalacia patellae (patellofemoral pain syndrome). This is a general term that refers to pain arising between your patella and the underlying thighbone (femur). It's common in young adults, especially those who have a slight misalignment of the kneecap; in athletes; and in older adults, who usually develop the condition as a result of arthritis of the kneecap.
Osgood-Schlatter disease. This condition affects the softer area of bone near the top of the shinbone, where bone growth occurs. It's most common in boys who play games or sports that involve running or jumping. The discomfort can last a few months and may continue to recur until the child's bones stop growing.
Osteochondritis dissecans. Caused by reduced blood flow to the end of a bone, osteochondritis dissecans is a joint condition in which a piece of cartilage, along with a thin layer of the bone beneath it, comes loose from the end of a bone. It occurs most often in young men, particularly after an injury to the knee.