The knee is the largest weight-bearing joint in the body. It is a hinge joint that joins the round ends of the femur and the tibia, with the kneecap (patella) in front. Various ligaments hold the bones together and cartilage cushion the force of bending or twisting of the knee.
A disorder that interferes with normal knee movement and mobility is called a derangement. Ligament injuries can be a major cause of this problem, especially when the knee is forced beyond its limits. This can damage the ligaments, the menisci or the patella. Other causes of a derangement include repetitive knee movements that strain the knee, arthritis and other diseases of the joint.
People who play sports may be particularly susceptible to the conditions that can lead to a derangement. For example, a twisting injury can damage the ligaments in the knee or cause the knee to lock up. This may be because a piece of bone or cartilage becomes misplaced in the knee joint and irritates it.
MRI is a diagnostic tool used to examine the knee for ligament and cartilage damage. It can help your doctor diagnose internal derangement of the knee, or IDK, a term that covers several disorders that affect the joints of the knee.