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Anterior Cruciate Ligament (ACL) Injuries

Anterior Cruciate Ligament (ACL) Injuries web based movie


The anterior cruciate ligament (ACL) is one of the four main ligaments in the knee. The ACL connects the thigh bone (femur) to the shin bone (tibia) and functions to stabilize the knee. Although the ACL is not necessary for simple activities, such as walking, a functional ACL is required to participate in activities that require sudden starting and stopping, cutting motions, twisting or pivoting. These higher-level activities include sports like soccer, basketball, and tennis; recreational activities such as hiking and surfing; work activity that requires climbing and work on uneven surfaces.

Injuries to the ACL usually occur due to a sudden twisting motion or hyperextension of the knee. Commonly, the injury does not involve a blow or contact to the knee. ACL injuries are sometimes associated with other injuries to the knee, such as meniscus tears, injury to other knee ligaments, and damage to the articular cartilage.


The symptoms of an ACL injury may involve hearing or feeling a “pop” at the time of injury. There is usually significant swelling that develops in the knee over the first 12-24 hours. Although pain may decrease over time, patients usually report that the knee feels unstable and may give out with certain activities.

The diagnosis of ACL tears is made by a history of the injury and patient’s symptoms combined with findings from a physical examination. X-rays are reviewed to exclude associated fractures. A MRI scan confirms the presence of an ACL tear and any associated injuries to the knee.


The diagnosis of meniscus tears is usually made from a history of the patient’s symptoms and findings from a physical examination. X-rays are reviewed to evaluate the joint for arthritis and other sources of knee pain. A MRI scan reveals the presence and extent of meniscus tears and any associated knee injuries.


Treatment of ACL injuries depends on the age and activity level of the patient. In younger, active patients who want to continue participating in cutting or pivoting sports, surgery is recommended to stabilize the joint. Restoring stability to the knee may prevent further damage to the loose knee joint over time from recurrent “giving way” of the knee.

Due to a variety of factors, including a lack of blood supply and poor quality of the torn ACL tissue, tears of the ACL cannot be repaired to restore normal function. The ACL must be surgically reconstructed using the patient’s own tissue from another location in the knee (termed an autograft) or with donor tissue (termed an allograft). The replacement tissue or graft consists of strong tendon tissue that can withstand the stress normally placed on the native ACL. The graft is place into the knee during a minimally-invasive arthroscopic procedure at the exact location of the native ACL to reconstruct a functional ACL. Common autograft sources include the central third of the patellar tendon in front of the knee, or the hamstring tendons on the inside of the knee.

Several types of allografts can provide excellent strength to use as a reconstruction graft. There are advantages and disadvantages to the different graft types and Dr. Boes will review these with you in detail to determine what type graft is best for you.
Overall, there are few, if any, long-term differences between ACL reconstruction performed either with an autograft or an allograft. Most studies suggest no long-term difference between autografts and allografts with respect to pain, giving way in the knee, measurement of laxity in the knee, rate of re-rupture of the graft, rate of return to sports activity, and overall functional results.

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