Meniscus: The knee joint has a meniscus on the inner and outer part of the knee, which is basically a shock-absorbing piece of cartilage that also provides some stability to the knee. The meniscus can be injured during a forceful twisting injury or even with long-term "wear and tear". Depending on the type of meniscus tear, the torn piece can get caught in the knee joint during activities, resulting in "catching" or "locking" and can often cause the knee to become painful and swollen. Some meniscus tears can be treated with surgery using medicines, an injections, or physical therapy. For those tears that are more severe or painful, they may require minor arthroscopic surgery to repair or clean up the torn piece of meniscus. Other common terms for this injury include "bucket-handle meniscal tear" or "torn meniscus".
Ligaments: There are four major ligaments that help hold the knee joint together and allow the knee to move properly with activities. Certain injuries can cause these ligaments to stretch or tear, resulting in a painful knee that can feel loose or unstable. Depending on the injury, some ligament injuries do not need much treatment other than a brace and some therapy, whereas some ligaments may require surgery to re-contruct the ligament and restore stability to the knee. Some common terms for these ligament injuries are "anterior cruciate ligament tear", "ACL tear", "posterior cruciate ligament tear", "PCL tear", "medial collateral ligament", "MCL sprain or tear", "lateral collateral ligament", and "LCL sprain or tear".
Patella Tendonitis: The patella tendon attaches the kneecap (patella) to the shin bone (tibia), and certain activities, such as running or jumping, can cause extra stress on this tendon. This can result in a painful condition known as patella tendonitis, which may take awhile to get better. Luckily, most cases of patella tendonitis improve with basic treatment, such rest, braces, therapy, and occasionally injections. Another common term for this condition is "jumper's knee" or "runner's knee".
Patello-Femoral Pain: The kneecap normally runs in smooth groove when the knee bends, but sometimes this area of the knee can be injured during sports, or even with general "wear and tear". Even slight abnormalities in this gliding of the kneecap can cause significant pain and swelling, particularly with going up/down stairs and getting out of a chair. Fortunately, this syndrome of kneecap pain can often be improved with various braces, therapy, and injections. When those treatments don't help, sometimes arthroscopic surgery is required to help treat the kneecap pain. Common terms for this problem are "patella subluxation", "mal-alignment", "patella dislocation", or "chondromalacia patella".
Plica syndrome: The inside of the knee joint is surrounded by a thick lining of tissue that keeps the knee lubricated during movement. Sometimes this lining can become thickened and/or redundant, resulting in tissue that rubs on the knee cartilage during activities, causing pain or swelling. This can occur on the inner or outer part of the knee and be quite painful, particularly during repetitive activities. This can often be relieved with some medications and injection, but occasionally requires minor arthroscopic surgery to remove this extra thickened tissue from within the knee joint, so it can glide smoothly again. Common terms for this condition are "medial plica" or "lateral plica".
Knee Arthritis: Within the knee joint are the ends of the femur and tibia bones, each of which have very smooth cartilage surfaces to allow the knee to glide smoothly with motion. Over time, this cartilage can wear out and become brittle, which exposes the bone below the cartilage. As the cartilage wears out, the knee becomes increasingly painful and swollen, until there is no cartilage remaining, known as "bone on bone" arthritis, which is very painful. During the earlier stages of arthritis, there are many treatments that can help, including medicines, therapy, bracing, and injections. When arthritis becomes more advanced, a total knee replacement may become necessary to remove the destroyed joint surfaces and replace them with metal, which eliminates the pain. Common terms for this condition are "knee osteoarthritis", "degenerative arthritis", "total knee replacement", "total knee arthroplasty".