Anterior cruciate ligament

The anterior cruciate ligament (or ACL) is one of the four major ligaments of the knee. It connects from a posterio-lateral (back & outside) part of the femur to an anterio-medial (front & inside) part of the tibia.

Treatment

A partially torn ACL will usually be allowed to heal itself. A completely torn ACL will not grow back. It must be replaced or left unattached. The ACL primarily serves to stabilize the knee in an extended position and when surrounding muscles are relaxed, so if the muscles are strong many people can function without it. However, lack of an ACL generally increases the risk of other knee injuries such as torn meniscus.

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There are three options for surgical ACL repair (called ACL reconstruction). In the first, two pieces of hamstring tendon are harvested from the back of the injured knee along with a small, attached chip of bone. These are woven together to form a single piece of connective tissue with pieces of bone at each end. In the second, the middle third of the patellar tendon is harvested from the patella (knee cap) to the tibia (shin). In the third, the patellar tendon is harvested from a cadaver. A fourth option, albeit not commonly performed by most surgeons, is to harvest the bone-patellar tendon-bone graft from the other (normal) knee. This option is typically reserved for revision operations and for some high-performance athletes requiring a faster return to play.

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In all cases the new ligament is threaded through the knee arthroscopically and stapled or screwed into place at each end. Because bone grows much faster than ligaments, the ends of the new ACL becomes attached to the knee in just a few weeks. In about six months, the knee is very close to full strength and after a year or two the knee is generally stronger than before the injury.

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Each method has its own pros and cons. Hamstring grafts are not as strong initially, since two tendons are woven together, but there is not significant clinical evidence that hamstring grafts fail more frequently than others. Patellar grafts are often cited as being stronger, but the site of the harvest is often extremely painful for weeks after surgery and some patients develop chronic patellar tendinitis. Replacement via a posthumous donor involves a slightly higher risk of infection. The risk is estimated to be 1 in 3 million. Additionally, donor grafts eliminate tendon harvesting which, due to improved arthroscopic methods, is responsible for most post-operative pain.

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All treatment options require extensive physical therapy to build up muscle strength around the knee and restore range of motion.

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