Approximately 100,000 anterior cruciate ligament (ACL) reconstructions occurred last year in the United States alone. 70 to 80 percent of these injuries occurred while the athlete was jumping, landing, cutting, pivoting or running without physical contact from an opposing player. These are called non-contact ACL injuries. These injuries always seem to be a popular subject with our national media. We stay glued to ESPN during the injury reports and pray our local professional and collegiate sports heroes haven’t torn their ACL when they are grimacing on the ground after an injury. So what is an ACL anyway and what is its purpose? To answer that question, we should start by looking at the knee as a whole.
The knee is a joint that is prone to injury due to its complexity and weight-bearing function. Its bony components are the femur, tibia, fibula (non-weight bearing) and the patella. Between the femur and the tibia are the medial and lateral menisci, which are shock absorbing cushions that help distribute weight evenly. Stabilizing the knee are four major ligaments: the lateral collateral ligament (LCL), the medial collateral ligament (MCL) the posterior cruciate ligament (PCL) and the anterior cruciate ligament (ACL). The ACL is the primary knee stabilizer. It is the primary restraint to anterior translation of the tibia and tibia internal rotation in relation to the femur. So how does an ACL tear?
ACL tears are divided into contact tears (20-30%) and non-contact tears (70-80%). Most contact tears occur when an athlete is running or standing with a bent knee and a planted foot. At that point, the athlete is struck forcefully at the outside or lateral aspect of the knee and the knee buckles inward or medially. Usually, these injuries occur with an injury to the MCL as well. Most non-contact injuries occur as a result of improper landing mechanics on an extended (straight) knee. The athlete will usually have pain and immediate instability of the knee. The pain is usually not from tearing the ACL itself but from the powerful impact of the tibia and femur colliding with each other. The integrity of the ACL can be tested with several different physical exams. The Lachman test is the most sensitive. Other exams include the anterior drawer test and the pivot shift test. Although we do not need our ACL to survive, 90% of people have their ACL reconstructed. ACL reconstruction surgeries and post-surgical rehabilitation accounted for over two billion US dollars several years ago.
With such a high rate of non-contact ACL tears, there has been significant research on how to prevent these injuries. Understanding the mechanism of these injuries is quite complicated and has caused serious debate among colleagues in the sports medicine world. Concepts such as ligament dominance vs. quadriceps dominance and core control vs. trunk dominance are hot button topics in the field of ACL tear prevention. Several groups have tried to come up with protocols to help prevent these injuries. One of the most popular among our young athletes has been created by FIFA (Fédération Internationale de Football Association). Their protocol is called the FIFA 11. These are 11 exercises/stretches that should be performed regularly to help create balance and normal firing patterns of the legs and the body core. Other programs emphasize correct landing mechanics to prevent tears. Landing mechanics are especially important in our female athletes. We do know that a combination of prevention programs seems to work better than just one. As long as athletes are aware that these programs are available and they follow the guidelines, ACL injuries will be less likely to occur.
Larry L Benson MD, CAQSM
OOC provider
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