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ACL Injuries

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Diagram of the right knee
Gray's Fig. 347 - Right knee-joint, from the front, showing interior ligaments.
Gray's Fig. 348 - Left knee-joint from behind, showing interior ligaments.

See also Anterior cruciate ligament reconstruction.


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.

ACL Injury

Non-contact tears or ruptures are the most common cause of injury to the ACL. They often occur when athletes moving quickly in one direction make a sharp or sudden change in direction (cutting). In jump sports, ACL failure has been linked to heavy or stiff landing as well as twisting or turning the knee while landing, especially when the knee is in the "valgus" ("knock-knee") position. Studies indicate that women in jumping and cutting sports such as basketball, competitive badminton, volleyball, cheerleading, or football (soccer), are significantly more prone to ACL injuries than men; this is generally believed to be due to differences between the sexes in the angle between the hip and knee called the "Q-angle", general muscular strength, size of the trochlear notch, reaction time of muscle contraction, and possibly training techniques (a new study suggests hormone-induced changes in muscle tension associated with menstrual cycles may be an important factor [1]). Women athletes are being taught safer jumping and landing techniques to better protect them from cruciate injury [2].

Damage to the ACL also occurs with lateral blows to the knee (as happens with a tackle from the side in American football) and often is accompanied by injuries to the medial collateral ligament (MCL) and the medial meniscus, which is attached to the MCL; physicians are taught "...knee injuries come in threes - anterior cruciate, medial collateral, medial meniscus." Clinical studies, however, have noted that a lateral meniscal tear occurs more commonly than the classic "terrible triad" noted previously[3]. A damaged ACL can be confirmed (clinically) by a physician with the anterior drawer test, the Lachman test, or an MRI.

It is one of the most common serious injuries in Association Football (Soccer) and Australian Rules football. ACL injuries are also common in alpine skiing, partially because of improvements in boots. Today's boots have been successful in preventing many of the ankle and leg fractures once caused by accidents; however, the tradeoff has been that the stresses have been transferred to the knees, resulting in many ACL tears.

Symptoms of an ACL injury include the hearing of a sudden popping sound at the time of the injury, swelling, and instability of the knee (i.e., a "wobbly" feeling or a feeling that the knee is not solid). ACL injury is sometimes misdiagnosed as a "knee sprain" by primary care physicians, athletic trainers, or coaches. But the "pop" sound is highly diagnostic for ACL injury. Patients who have experienced this symptom and who are told it is a "sprain" should seek a second opinion. Continued athletic activity on a knee with an ADCL injury can have devastating consequences, resulting in massive cartilage damage, which is likely to lead to osteoarthritis later in life.

An ACL injury can often be debilitating for far longer than a broken leg.


A partially torn ACL will usually be allowed to heal itself. A completely torn ACL will not grow back, probably because the lack of blood supply near the ACL. It must be replaced by surgery 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. The term for non-surgical treatment for ACL rupture is "conservative management, and it often includes physical therapy and use of a knee brace. Lack of an ACL generally increases the risk of other knee injuries such as torn meniscus, so sports with cutting and twisting motions are not recommended. For patients who frequently participate in such sports, surgery is often recommended.

ACL surgery

There are four options for surgical ACL repair (see 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.

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 become 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.

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.

After surgery, the knee joint loses flexibility, and the muscles around the knee tend to atrophy. All treatment options require extensive physical therapy to build up muscle strength around the knee and restore range of motion. For many active patients, the lengthy rehabilitation period is more difficult to deal with than the actual surgery. External bracing is recommended for athletes in contact and collision sports for a period of time after reconstruction. Whether the ACL deficient knee is reconstructed or not, the patient is susceptible to early onset of chronic degenerative joint disease.

See also

External links


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