By Kateri Kane
Knee injuries are a very common problem that physical therapists see and ACL injuries are one of the more common diagnoses we treat. Whether or not you have any medical background, I am sure that the majority of you have heard of an ACL injury (especially if you follow sports) and know that this condition is associated with the knee. The question then becomes, how much do you know about ACL injuries and what can you do to prevent one?
ACL stands for anterior cruciate ligament. This ligament prevents the tibia (shin bone) from shifting forward on the femur (thigh bone). This ligament, in combination with the PCL (posterior cruciate ligament), also prevents excessive twisting of the tibia inward or the femur outward at the knee joint. The ACL is most commonly injured during sporting activities and is most prominently injured in adolescent female athletes.
Various factors may increase or decrease the risk of injuring the ACL. External factors may include play in which coordination is disrupted just before landing or slowing down (ex. being bumped by another player), wearing a brace, athletic footwear in relation to different surfaces, and the playing surface itself. Internal factors may include hamstring flexibility, increased foot pronation (flat foot), hormonal effects, and variations in nerves and muscles that control knee positioning. Women in particular have a wider pelvis and have a tendency toward being “knock kneed” which increase the risk of an ACL injury.
The majority of ACL injuries are non-contact (70%) meaning that no outside trauma was applied to the knee that caused the injury. Some possible non-contact and contact causes of ACL injury include slowing down suddenly to change direction or pivot with the foot firmly planted, twisting, hyperextending the knee, landing awkwardly from a jump, falling while downhill skiing, a football tackle, or a car accident.
As evidenced by the list of causes, not every ACL injury can be prevented; but there are certain tools and exercises that can decrease your risk of injury. ACL injury prevention programs commonly focus on strength/stability exercises, balance training, and plyometrics. The most important muscles to strengthen are the gluteus medius and the gluteus maximus. Even though these muscles are located along your pelvis and hip, they prevent the knee from rotating inward and creating a “knock kneed” position. Various exercised can be performed to strengthen these muscles including bridging and clamshell exercises as pictured here.
Balance training may include performing activities like weight shifting or squatting while on an unstable surface or throwing a ball while standing on one leg while focusing on form and correct leg position.
Plyometrics consist of exercises where the muscles are lengthened and then immediately shorted again, often in a repeated cycle. These exercises assist with focusing on functional alignment of the knee during activities like jumping off of a box and then immediately jumping again. During plyometrics, proper alignment is a key component, and focus should be placed on landing on the balls of the feet with the knees flexed and the chest over the knees. Plyometric training in particular should be performed more than once a week for at least 6 weeks.
We hope this gives you some insight into the mechanics of an ACL injury and what you can do to help prevent an injury. If you have any questions on this topic or any others in which you are interested feel free to leave any questions, comments, or suggestions. Thank you for reading and stay active.