By: Dr. Rebecca Van Heuklon, DPT, FAFS, FMR
The anterior cruciate ligament (ACL) is the ligament responsible for stabilizing the knee during pivoting and rotational activities by controlling forward movement and inward rotation of the tibia (shin bone) on the femur (thigh bone). The ACL also helps to control motion at the knee through sensory receptors in the ligament that sense tension and send signals to the brain and spinal cord to activate muscles around the joint to stabilize it.
The ACL is the most commonly torn ligament of the knee, occurring at a rate of 100,000-250,000 tears in the U.S. per year.1 Tears of the ACL can occur in athletes participating in both contact and non-contact sports, but non-contact tears are more common, occurring during deceleration with change of direction like cutting or pivoting. ACL tears may occur in an isolated fashion, but are also frequently accompanied by damage to other structures of the knee as well, such as the medial collateral ligament (MCL) and the medial meniscus. Experiencing an ACL tear can be devastating for athletes, as it results in significant time lost from sports, as well as physical, emotional, and financial stress.
There are a number of non-modifiable factors that put an athlete at risk for having an ACL tear, including:
- Being female,
- Having increased joint laxity or looseness (more common in females, but also genetically influenced),
- Being between the ages of 15-45, and
- Having a previous ACL tear
The primary non-modifiable risk factor is being a female after puberty. Females who participate in running and jumping sports have a 2-10x higher incidence of ACL tears than males playing the same sports.1 There are several anatomical attributes that likely contribute to a higher incidence of ACL tears in women, including females’ wider pelvis and inwardly rotated knees, creating a more knock-kneed position which can increase stress on the ACL.
Modifiable risk factors that make any athlete (male or female) more prone to ACL tears, include the following:
- Poor landing mechanics with jumping;
- Knock-kneed position when landing;
- Weakness and decreased coordination in the core, hips, and legs;
- Decreased sense of body position and movement in the legs;
- Over-reliance on the quadriceps muscles with weakness in the hamstring muscles; and
- Preferred landing technique with more weight on one leg versus the other.
There are also some differences in jumping technique between males and females of the same age that place females at a higher risk of an ACL tear. These differences occur during landing, and include more flat-footed position, decreased flexion or bending of the knees and hips, and rigid foot placement.1 In addition, women tend to run more upright and rely more on their quadriceps muscles rather than their hamstrings to slow down,1 which increases the stress on the ACL when decelerating. These technique differences in running and jumping in females may be attributed to less overall experience in sport or lack of specific training.
By identifying who is at higher injury risk, we can better determine who could benefit most from participation in an injury prevention program. Because having an ACL tear can greatly increase the risk of having functional limitations and early osteoarthritis in the knee even after surgical intervention, the best treatment for ACL tears truly is prevention.1 According to a large study, findings showed that participating in an ACL injury prevention program can reduce the incidence of all types of ACL tears in male and female athletes by 50% and reduction in non-contact tears in females by 67%.2 That’s some fairly supportive data!
So, what does an ACL injury prevention program look like? The goal of the program is to address the modifiable risk factors identified above with emphasis on the individual deficits of each specific athlete. In general, a comprehensive ACL injury prevention program should incorporate plyometric (jumping), strength, and balance exercises.1
Strengthening exercises should target the core, hips, and hamstrings. The program should also incorporate a dynamic warm-up, as well as flexibility, jumping and landing form/technique education and training, and improve sense of body position and movement through sport-specific agility work. It is helpful and more successful for the athlete to have feedback from an athletic trainer, physical therapist, or specially trained coach to encourage excellent posture and technique with the exercises. As with any prevention program, in order to be effective, it requires good compliance and commitment on the part of the athlete, parents, and coaches.
With participation in an ACL injury prevention program, athletes can stay healthy and active throughout their lifespan. To get more information on how physical therapy can help guide you in preventing an ACL injury or properly rehab your ACL injury to prevent it from re-occurring, contact MotionWorks Physical Therapy at 920-215-2050. Stay tuned for next month’s article on specific exercises you can incorporate into your workout routine to reduce the risk of an ACL tear.
1. Hewett TE, Myer GD, Ford KR, et al. 2016. Mechanisms, Prediction, and Prevention of ACL Injuries: Cut Risk with Three Sharpened and Validated Tools. J Ortho Res. 34(11):1843-1855.
2. Webster KE, Hewett TD. 2018. Meta-analysis of Meta-Analyses of Anterior Cruciate Ligament Injury Reduction Training Programs. J Ortho Res. 36(10):2696-2708.