By:
Matthew Matava, MD
Washington University Orthopedics
The anterior cruciate ligament (ACL) is one of the most commonly injured ligaments in the knee. A ligament connects a bone to another bone. The ACL is instrumental in providing rotational stability to the knee during cutting, jumping, or pivoting activities. A young athlete who injures his or her ACL typically does so while cutting or pivoting without direct contact from another player. Girls are up to eight times more commonly injured than boys at all levels due, most likely, to differences in protective muscle firing patterns of the thigh muscles in response to a forceful stress on the knee.
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| Figure 1. MRI of the knee showing a torn ACL |
An ACL tear is usually associated with an audible ‘pop’, an inability to continue play, and knee swelling within 6 hours. Young athletes will injure other structures in the knee, such as the meniscus cartilage, approximately one-half of the time.
The injury is accurately diagnosed by the characteristic injury history, a careful physical examination, and usually an MRI, which stands for magnetic resonance imaging. This highly accurate test is able to obtain internal images of the knee with a high degree of accuracy, without exposure to radiation (Figure 1).
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| Figure 2. Surgical view of a torn ACL being probed |
Most young athletes with an ACL tear elect to have the torn ligament reconstructed in order to prevent recurrent knee instability. Surgery is usually delayed 3-4 weeks from the time of injury to allow any knee swelling to subside and to improve the knee’s range of motion. Surgery to reconstruct a torn ACL takes approximately one hour to complete and is usually done as an out-patient under a general anesthesia (Figure 2). Care is taken in growing children not to injure the growth plates around the knee during the surgical procedure. A graft taken from another tendon around the knee is used to replace the torn ACL without any significant consequences (Figure 3). Any other injuries that are present can also be addressed at the same time.
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| Figure 3. Surgical view of reconstructed ACL graft |
Physical therapy is very important after surgery to allow full return to normal knee function. Children require crutches to walk for up to six weeks following surgery. Young athletes are progressed through a specified sequence of exercises to regain knee motion, strength, and the ability to run, jump, and cut. Most children are able to return to sports approximately six months following ACL surgery with success rates topping 90%.
What was once an injury that doomed an athlete to a premature discontinuation of sports, an ACL tear can now be effectively and safely treated with a high likelihood of success in returning to high-level sports and other activities.
