ACL Tear

The knee joint is composed of the femur (thigh bone), the tibia (leg bone), and the patella (kneecap). The parts of these bones which face the joint are covered with articular cartilage that allows weight bearing and motion with a very low coefficient of friction. The tibia is also covered by two half-moon shaped soft cartilage (fibrocartilage) structures: medial and lateral menisci that act as shock absorbers and joint stabilizers and provide joint nutrition/lubrication. The anterior cruciate ligament (ACL) attaches the posterior part of the femur to the anterior part of the tibia and prevents the tibia from sliding too far forward and helps with rotational stability.

Most ACL injuries occur during competitive athletics when the knee endures a severe twisting or bending injury. However, the injury can also occur when the knee experiences a sudden change in direction, direct contact with another person, or landing improperly on the ground. Patients who experience an ACL tear will often hear a popping noise, which may or may not be accompanied with great pain. Swelling often follows the injury, and it is unlikely that the person who experiences this injury will be able to continue moving without difficulty.

The most common symptoms of an ACL tear are knee pain, knee instability, swelling, a popping or snapping sensation at the time of the injury, and decreased range of motion. Initially, right after an ACL injury, the symptoms include the inability to bear weight on the knee; gradually, the pain and swelling resolve but instability or buckling of the knee remains.

When checking for an ACL injury, the doctor will perform an examination to look for instability in the knee and whether there is discomfort specific to the injury. The doctor will more likely than not follow-up on the examination with a MRI, which will provide an in-depth and detailed picture of the knee joint. This will show not just damage to the ACL, if it is present, but damage to other knee structures, as well. However, the most definitive and final diagnosis will often only be able to be made during an arthroscopy.