The anterior cruciate ligament (ACL) is a cruciate ligament which is one of the four major ligaments of the human knee. In the quadruped stifle (analogous to the knee), based on its anatomical position, it is referred to as the cranial cruciate ligament.

The ACL originates from deep within the notch of the distal femur. Its proximal fibers fan out along the medial wall of the lateral femoral condyle. There are two bundles of the ACL—the anteromedial and the posterolateral, named according to where the bundles insert into the tibial plateau. The ACL attaches in front of the intercondyloid eminence of the tibia, being blended with the anterior horn of the lateral meniscus. These attachments allow it to resist anterior translation and medial rotation of the tibia, in relation to the femur.

Anterior cruciate ligament injury is the most common knee ligament injury, especially in athletes. Lateral rotational movements in sports like these are what cause the ACL to strain or tear. Strains can sometimes be fixed through physical therapy and muscle strengthening, though tears almost always require surgery. The most common method for repairing ACL injuries is arthroscopic surgery. Other common injuries accompanying ACL tears are meniscus, MCL, and knee cartilage tears.

Reconstructive surgeryACL reconstructive surgery can utilize several different tendons and grafts in place of the torn ACL including the hamstring, patellar tendon, semitendinosus tendon, gracillus tendon, and the plantaris.There is great controversy as to which source produces the strongest, most stable ACL replacement. Many orthopedic surgeons prefer to use tendons and grafts from cadavers; therefore the patient does not have to rehabilitate more than just their ACL. Others prefer to use tendons directly from the patient in order to counteract the potential for an immune system rejection of the cadaver tissue. Furthermore surgeons have the choice between several surgical techniques to fixate the ACL replacement to the femoral bone: staple fixation, tying sutures over buttons, and screw fixation.There are several studies currently testing all the variables involved in ACL reconstructive surgery accounting for the lifestyle, age, and future goals of the ACL reconstruction patients. There are no quantitative results as to which combination of ligament and grafts work best with the different surgical techniques for every individual.

The posterior cruciate ligament (or PCL) is one of the four major ligaments of the knee. It connects the posterior intercondylar area of the tibia to the medial condyle of the femur. This configuration allows the PCL to resist forces pushing the tibia posteriorly relative to the femur

Surgery to repair the Posterior Cruciate ligament is controversial due to its placement and technical difficulty.

The function of the PCL is to prevent the femur from sliding off the anterior edge of the tibia and to prevent the tibia from displacing posterior to the femur. Common causes of PCL injuries are direct blows to the flexed knee, such as the knee hitting the dashboard in a car accident or falling hard on the knee, both instances displacing the tibia posterior to the femur.

TreatmentThe PCL does not heal on its own, so surgery is usually required in complete tears of the ligament. Surgery usually takes place after a few weeks, in order to allow swelling to decrease and regular motion to return to the knee. A procedure called ligament reconstruction is used to replace the torn PCL with a new ligament, which is usually a graft taken from the hamstring or Achilles tendon from a host cadaver. An arthroscope allows a complete evaluation of the entire knee joint, including the knee cap (patella), the cartilage surfaces, the meniscus, the ligaments (ACL & PCL), and the joint lining. Then, the new ligament is attached to the bone of the thigh and lower leg with screws to hold it in place