Question: The medial collateral ligament is contiguous with the knee joint, and therefore causes the knee joint to swell when injured?

Answer: True.

The more closely a ligament is associated with a joint, the more it signals the joint to swell when injured. Some of the fibers of the medial collateral ligament are attached to the joint capsule at the medial side of the knee. Consequently, the knee swells substantially when this ligament is injured. The medial collateral ligament attaches the femur to the tibia and stabilizes the medial aspect of the knee. It functions to limit medial movement of the knees, as in being knock-kneed, and helps keep the knee keep on track as a hinge joint. Its counterpart on the lateral side, the lateral collateral ligament, performs the same function on the lateral aspect of the knee.

This knowledge comes in handy when other structures on the medial side are injured, but cause no swelling. For instance, if one of the medial hamstrings is injured, causing pain at the medial knee, no swelling occurs. This also is true when the portion of the patellar tendon mechanism (the patella retinaculum or the medial quadriceps expansion) on the medial side is injured, causing pain when climbing stairs.

There are several potential causes of knee swelling associated with medial knee pain. The most common cause is a medial collateral ligament sprain. A sprain of the coronary ligament, which holds the medial meniscus in place, is another possible cause. Of course, there may be a more serious injury causing the swelling, such as a torn meniscus, a sprained cruciate ligament or a loose piece of cartilage or bone trapped inside the joint. It's important to note that knee swelling is not indicative of a strained muscle or patellar tendon.