How To Prevent ACL Injury

Even though ACL injuries can be devastating, a risk of injury can be reduced. There are several strategies that can be used. Since mechanisms of an ACL injury are multi-factorial, the several factors should be considered when implementing a prevention program. Especially those at a higher risk of ACL injury can benefit from the program.

Here are some of the risk factors that can be eliminated or controlled.





Muscle Imbalance

There are two big muscle groups in the thigh, the quads and hamstrings. The quads are usually stronger than the hamstrings. However, if the hamstring strength drops below a certain % of the quad strength, the athlete may be at risk. An intact ACL prevents tibia (shin bone) from shifting forward on femur (thigh bone). When the quads and hamstrings co-contract with the knee straight or slightly bent, the quads pull tibia forward, which also puts stress on ACL, on the other hand, the hamstrings pull it back helping ACL keep tibia from shifting forward. If the hamstring are not strong enough to pull against the quads' counter force, it may put more stress on ACL than the balanced knee. By eliminating the hamstring strength deficit and having balanced muscle groups, a risk of ACL injury can be decreased.





Side-To-Side Difference

Muscle imbalance can also happen between the limbs. This happens when one leg is significantly stronger than the other. When the difference is more than 15%, it is considered significant. This does not necessarily mean that the athlete will get hurt but it means that he/she may be more at risk of injury. This is another risk factor that can eliminated doing some simple strengthening exercises.




Core Stability


Decreased core stability has been linked to lower leg injuries. Core training may not be as simple as strengthening leg muscles. However, it can be easily done without using much equipment and can be implemented as a part of regular training session (as warm-up or cool-down). An athlete may have strong arm and leg muscles, but if he/she does not have stable core, those muscle strength will go wasted. Even an athlete who can move and change directions quickly on the field will not be able to use his/her agility effectively and efficiently without stable core musculature. It will make it a lot harder for those who do not have core stability to defend themselves from an injury when they are off-balance and when they lose a control of their body. The athlete with good core stability will be able to regain their postural control even when it is lost.

Here are some examples of core exercises.








Proprioception


Proprioception is a position sensor located around the joints. If you raise your arm with your eyes closed, you can tell approximately where your arm is. This is because you have proprioceptors giving you information on where your arm is even without any visual feedback. This is the reason why you do not have to be looking at your feet all the time when you play soccer. Good proprioception not only helps athletes' performance but also keeps them from injuries.



Neuromuscular Training


This targets on teaching athletes how to do things the right way in neuromuscular level. Muscles only work when they get a signal from the nervous system. And they respond to it in the way that they are told to. If athletes are introduced to a new skill, the nervous system will send a signal telling the muscles to do what they are supposed to do. It may take some time and practice until they learn to perform the new skill. In the same way, this training focuses on how to use the muscles correctly to do athletic movement patterns the right way so that the athletes will have less risk of injury.

This video shows one exercise that can be used to teach athletes how their legs should be used on landing.

ACL Injury: Who's At More Risk?

There are athletes that are more subject to an ACL injury than the others. Gender, sports they participate in, muscle balance/strength, biomechanics, etc. Some risk factors can be fixed/eliminated, but some may not. Injuries cannot always be avoided, however, it is a lot easier to prevent it than to rehabilitate after surgery.

Female

Female athletes are shown to be 4-6 time more at risk of ACL injuries than male counterparts. This may not sound fair but it is the fact that just being female increases the risk.

Sports

Certain sports have a higher injury rate than others. Those high risk sports include soccer, gymnastics, basketball, football, skiing, etc. ACL injuries can also happen in other sports such as tennis, baseball, and softball, but not as common as in sports listed above.

Previous Injury

Athletes who have had an ACL injury previously may be prone to re-injuring the same or the opposite knee. Some research articles deny it, on the other hand, there are research articles that have proven this is the fact.

Muscle Imbalance

Athletes who have side-to-side muscle imbalance may be more at risk. These athletes have one leg that is stronger than the other. Also, muscle imbalance can occur between two muscle groups (quadriceps and hamstrings). Usually, the quads are stronger than the hamstrings. But if hamstring strength drops below a certain percentage of quad strength, the athlete may be at a higher risk of injury.

Core Strength/Proprioception

Decreased core strength and proprioception have been linked to lower leg injuries. Core strength and proprioception play an important role in postural control and inability to control posture during athletic activities well will put the athletes at risk of injuries.

Biomechanics

There have been numerous research articles that studied biomechanical differences during landing and athletic activities. Athletes with biomechanical deficit are the ones whose knees bend inwardly during landing. This tends to happen more in female athletes. Female athletes also tend to keep their knees straighter compared to male athletes, which is also considered to be a risk factor. As a result, these athletes may not be able to absorb a GRF (ground reaction force) and their knee may be sustaining higher GRF.

Maturation

After growth spur, body weight and height increase drastically. As peak growth occurs, their muscle strength needs to increase in order to support increased body weight. Male athletes seem to successfully be able to get stronger as they grow, however, this adjustment does not seem to happen to females, leading to a gender difference in muscle strength after growth spur. This may be linked to a higher injury rate in female athletes after puberty.


There may be other risk factors. Athletes who participate in high risk sports should be participating in a prevention program as well as those who are considered to be at a higher risk of injury.