ACL Prevention Program
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November 21, 2019
By Mackenzie Simmons, ATC
An anterior cruciate ligament (ACL) tear is one of the most common surgical injuries that occurs in the athletic population. The ACL extends from the lateral femoral condyle to the medial aspect of the tibia, and assists with knee stability, specifically during running, jumping, cutting and pivoting. The positioning of the ACL will also help limit anterior translation of the tibia on the femur. There are several important facts to consider when looking at ACL tears in a patient who wants to keep competing or to maintain an active lifestyle.
- Approximately 25-30 percent of patients who have a primary ACL injury will re-tear their ACL on the surgical leg or the contralateral leg
- The majority (80 percent) of ACL injuries are non-contact
- Female athletes are 4-6 times more likely to tear their ACL in comparison to male athletes
- The highest incidence of ACL tears occurs in soccer, volleyball, handball and basketball, but is evident in all sports
ACL injuries can be sorted into different grades, which distinguishes the tears by the severity. These are listed below.
- Grade 1 – Mild stretching of the ACL, no tear of the ligament and usually has adequate stability in the knee
- Grade 2 – This is a rare injury where the ACL is stretched and partially torn
- Grade 3 – The ACL is completely torn and has instability in the knee
An Athletic Trainer (AT) implementing an ACL injury prevention program can be extremely beneficial for all patients. Keep in mind that this program will not prevent ACL tears from occurring but can help decrease the risk. There are five key steps that should be included in the planning of this program:
Step 1 – Identification
Most ACL injuries occur when an anterior force is applied to the tibia. It is important to identify the risk factors that can contribute to this anterior force to reduce the chance of injury. These can be sorted into modifiable and non-modifiable risk factors.
Modifiable risk factors are sorted into four different categories, including movement and alignment, strength, ground reaction forces (GRFs) and fatigue.
- Movement and alignment – There are certain movement and alignment factors that can predispose a patient to an ACL tear, such as landing from a jump with a small knee flexion angle and larger knee valgus angle, decreased active and passive controls of the knee, and dynamic knee valgus positioning
- Strength – Muscle weakness is another modifiable risk factor, specifically weak gluteus medius, gluteus minimus, quadriceps, hamstrings and hip abductor muscles
- Weakened quadriceps may decrease knee flexion control
- Weak hamstrings and hip abductors may lead to an increased valgus load on the knee
- Weak core musculature will lead to decreased trunk stability and/or lateral pelvic movement
- GRFs – If a patient has weak hamstrings or quadriceps, it may be hard for them to control GRF, which leads to a greater load on the ACL
- Fatigue – Fatigue leads to loss of motor control, especially with the landing phase of a jump
The non-modifiable risk factors list is smaller and are minor considerations when planning an ACL prevention program. These all relate to a patient’s body and the changes that it makes during puberty, such as bone length, body weight and overall height. An increased body mass is also a risk factor for an ACL tear, along with increased knee laxity measures.
Step 2 – Exercises for the ACL Injury Prevention Program
This may vary by sport, gender and competition level of the patient. It is also important to slowly incorporate increased repetitions and resistance to allow the patient to get used to the exercises. It would not be beneficial to fatigue a patient. An active warm-up should be used but can vary by sport. While conducting the exercises in the program, it is imperative to provide frequent cues to the patient to ensure proper form.
- Examples of beginner exercises include bilateral squat, single leg squat, drop vertical jump, bilateral vertical jumps, bilateral line jumps (anterior/posterior, lateral), deadlifts, clamshells, steamboats, bridges, etc.
- Examples of more advanced exercise include single leg squats, single leg bridges, single leg step and hold, bounding, single leg vertical jump, single leg line jumps (anterior/posterior, lateral), squat jumps, bounding, broad jumps with stop, etc.
Step 3 – Training Load and Volume
In this program, load refers to the amount of resistance or weight with each exercise. In a high school setting, some patients will likely start off with no resistance to focus on form of the movements. Volume, in this program, is used as the total number of repetitions for each exercise. This will vary depending on the number of exercises that are selected for the program and the time allotted for the training session.
Step 4 – Training Frequency
This will differ depending on whether the program is for high school or collegiate patients. The National Collegiate Athletic Association has strict regulations on practice time in the off-season, so coaches may not have allotted time for a prevention program. A collegiate AT may have to schedule treatment time for patients who would be interested in this program. When working with high school patients, it may be easier to schedule the program around off-season workouts, either before or after team workouts.
Step 5 – Exercise Timing
Talk with the coaches for the sports and see if it is preferred to do a stand-alone training program, or in conjunction with another training or conditioning session.
Other factors to consider would be to conduct a pre-test and a post-test to show the effectiveness of the ACL program and to ensure patients are showing progress. It also may be helpful to sort a larger group into smaller sections based on their deficiencies or weaknesses. On the pre-test, it would be advantageous to get each patient’s basic demographic information, as well as a pertinent medical history. Following that, assessing form on certain exercises can help evaluate a patient’s weaknesses, such as single leg squats, single leg jumps and drop vertical jumps. If possible, have the same person assess the movement patterns to ensure accuracy. A patient may be considered quad dominant if the knee flexion angle is less than 30 degrees or ligament dominant if they have medial collapse. In addition, a patient may be trunk dominant if they display increased trunk flexion or lateral trunk sway during the exercises, or limb dominant if they lean towards either the right or left side. Depending on the format of the ACL prevention program, agility tests may also be included, such as T-tests or the shuttle run. After the duration of the program, a post-test should be taken, assessing the same exercises. If possible, have the same person that assessed during the pre-test.
There are many different ACL prevention programs used for different sports and different genders. However, the main concepts are the same in identifying areas of weakness and helping to strengthen these areas to prevent injuries. It is easy to use the steps listed above to tailor a program for any sport at any level. Try and incorporate an ACL prevention program into your school or sport this year and see how each patient improves.
Donnell-Fink, Laurel A., et al. "Effectiveness of knee injury and anterior cruciate ligament tear prevention programs: a meta-analysis." PloS one 10.12 (2015): e0144063.
Potach, David, Gregory Myer, and Terry L. Grindstaff. "Special Consideration: Female Athlete and ACL Injury Prevention." The Pediatric Anterior Cruciate Ligament. Springer, Cham, 2018. 251-283.
Prentice, William E. Principles of Athletic Training: A Guide to Evidence-Based Clinical Practice. McGraw-Hill Higher Education, 2017.