The Anterior Cruciate Ligament
There are over 200,000 anterior cruciate ligament (ACL) injuries that occur in the United States annually. (3) An anterior cruciate ligament injury is extreme stretching or tearing of the anterior cruciate ligament (ACL) in the knee. An anterior cruciate ligament (ACL) unravels like a braided rope when it's torn and does not heal on its own. (8) This injury can be devided into the partial or complete tearing of the ACL ligament.
ACL tears may be due to contact or non-contact injuries. A blow to the side of the knee, such as may occur during a football tackle, may result in an ACL tear. Contrary to popular beleif, coming to a quick stop, combined with a direction change while running, pivoting, landing from a jump, or overextending the knee joint, can also cause injury to the ACL. One study showed that contact resulted in 93% of injuries in a ground of 226 patients while non-contact sport resulted in the remaining 7%. For recreational athletes, the numbers were much more even. (6) Basketball, football, soccer and skiing are the most common sports in which there are ACL tears.
The biomechanical function of the ACL is complex for it provides
both mechanical stability and proprioceptive feedback to the knee.
In its stabilizing role it has four (main) functions:
Restrains anterior translation of the tibia
Prevents hyperextension of the knee
Acts as a secondary stabilizer to stress, reinforcing the medial collateral ligament
Controls rotation of the tibia on the femur in femoral extensions of 0-30°. (7)
The ACL is widely known as the most important ligament in the knee. Therefore it is often treated with a much more aggressive therapy, especially in competitive athletes. In most cases, the ACL is treated by various surgeries. (See Ligament Surgery for description of the surgery) Sometimes, in the case of patients who are not very active, the ACL is not operated on. This is more common in elderly patients. In competitive athletes, the ACL is reconstructed surgically 90-100% of the time. In a 5 year study of ACL injuries in the National Football League, it was found that 31 out of 31 head physicians recommended operation for all of the ACL injuries that occurred. (4)
For the reconstruction surgeries, portions of the patellar tendon autograft account for most of the ACL surgeries performed in athletes. (2,5,4) Other sources of grafts for reconstruction include hamstring tendon autografts, semitendonosis and gracilis tendon autografts, or achilles tendon allografts. There are many other types of autografts, allografts, engrafts, and prosthetic ligaments which have been used in the population of patients, but the patellar tendon has been adopted as the gold standard for ACL reconstruction therapies for competitive athletes.
In most of the sports analyzed, ACL reconstruction surgery had a recovery time of between 6 and 9 months. After this time, most athletes had returned close to their full level of previous play. Sources showed between 80% and 100% of previous level. In most sports, it was found that around 90% of these athletes returned to play in their respective sports. After the first ACL injury, there is a risk of repeated injury. It is estimated to be between 5 and 15%. (5)
All in all, the tearing or sprain of the anterior cruciate ligament account for a large portion of knee injuries in sports. The standard surgeries and therapies currently in place provide good results and recovery time. A large proportion of athletes which have undergone ACL surgery return to their respective sport at a level close to their previous level of play.