When you hear about ACL injuries, you often associate them with impact sports like hockey, soccer, or football. We all remember OBJ going down in the Super Bowl two years ago, getting hurt before he even got tackled! More recently, Kirby Dach of the Montreal Canadians went down with a season-ending injury in mid-October from a hit into the boards.
Did you know that an ACL injury may occur even when there is minimal to no contact at all (1)? How does this happen!?
How Does an ACL Injury Occur?
The main reason this can happen is due to compressive forces on the knee joint that cause your lower leg bone (the tibia) to move slightly forward when we switch from non-weight bearing to weight bearing (1). Think about cutting side to side. When doing this, we have to absorb the forces from the ground to the body.
This is where reactive stability of the foot, ankle, knee, and hip comes into play (1). When the foot is landing on the ground in a near flat-footed position, the foot and ankle complex does not allow for the calf muscles to absorb the ground reaction forces (GRFs) properly (1). There is an increase in ACL ruptures when landing on the heel or a flat foot when hitting the ground compared to landing on the ball of your foot (1). This is because the calf can be in control of the deceleration better when landing on the ball of your foot and allows for sufficient time to absorb the GRFs (1).
How are the hips involved? When looking at ACL injuries, there is a significantly higher degree of hip flexion at ground contact, placing the upper body farther behind the knee (1). To stabilize the body in this position while landing, the quad muscles would need to fire, placing a large amount of torque upon the knee which would strain the ACL (1).
How To Prevent An ACL Tear?
Now that we know how ACL injuries happen, what can we do to prevent them? Thanks to the extensive research done to understand the mechanism of an ACL injury, there are many ACL prevention programs available. Instead of going through every program, I am going to be listing the components needed for a proper ACL prevention program that you can use at home!
The first component is plyometrics (2). This involves a lot of jumping, hopping, and most importantly, landing. These exercises focus on learning how to control our body and build proper techniques to help reduce ligamentous strain when performing explosive and decelerating movements (2). Using plyometrics, you can train the "spring action" of our musculoskeletal system, leading you to be a faster athlete.
The second component is neuromuscular training (2). This type of training is focused on building the mind-body connection. It is used to increase optimal muscle firing patterns, increase joint stability through a range of motion, and perform movement patterns necessary for daily or sport-specific activities (2). Neuromuscular training would include balance and proprioceptive exercises like balancing on uneven surfaces, single-leg stability drills, jump training, and agility drills exercises (2). The main goal of this type of training is to improve postural control, and asymmetries in the lower extremities (2).
Lastly, the third component is strength training (2). After you increase muscle firing patterns with neuromuscular training, it is important to ingrain those patterns with resistance (strength) training. Be aware, according to the research, strength training alone may not be enough to prevent ACL injuries (2).
When going through an ACL prevention program, it is important to have a feedback system in place (2). Focus on external cues, as this aids in the movements becoming automatic and speeds up the learning process (2).
If you play a sport where stopping and starting or changing direction quickly is part of the game, I encourage you to work some preventative training to keep you in the game!
1. Boden, Barry P., et al. "Non-contact ACL injuries: mechanisms and risk factors." The Journal of the American Academy of Orthopaedic Surgeons 18.9 (2010): 520.
2. Nessler, Trent, Linda Denney, and Justin Sampley. "ACL injury prevention: what does research tell us?." Current reviews in musculoskeletal medicine 10.3 (2017): 281-288.
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