Knee injury rates for youth sports continue to rise, according to a 2018 study. The rehabilitation can take up to a year in some cases, leading to lost playing time and endless frustration for kids whose positive self-image may be strongly tied to their athletic performance.
About half of these injuries occur due to contact (tackling, being bumped by another player, etc) and are very hard to avoid. Sometimes you just get hit the wrong way at the wrong time.
However, more than half of the severe knee injuries reported came from non-contact events. An athlete simply lands the wrong way after jumping, or makes a cut and their knee buckles.
It is those non-contact injuries that we know have a much better sense of what causes them.
In a study done by PhD's Timothy Hewitt, Kevin Ford, Barbara Hogenboom & Gregory Myer, they identified 4 main risk factors for future knee injury risk. (You can read the full study here, highly recommended).
Risk Factor #1 - Ligament Dominance
This refers to a condition where leg muscles simply are not strong enough to handle the forces placed upon them, so the load is transferred to the ligaments holding the knee together. If a situation occurs where the forces are greater than the strength of the ligament, it snaps.
In particular, weakness in the muscles on the back of the leg (hamstrings, gluteals, and calf muscles) play the largest role in absorbing forces from cutting and landing from jumps. To avoid ligament dominance, strengthening those muscles are a top priority.
You can recognize an athlete prone to knee problems due to ligament dominance by watching to see if their knees (or even just one knee) buckles in when they land from a jump or make a sharp cut.
Risk Factor #2 - Quad Dominance
Developing too much strength in the quadriceps muscles on the front of the thigh compared the the muscles on the back side is another huge risk factor. There is a connection to the ligament dominance here, but it shows itself in a different way.
Athletes with quad dominance will absorb forces primarily by contracting the quads, leading to a straightening of the knee joint(s). Doing this at high speeds creates a shearing force within the knee, in particular putting massive strain on the ACL (Anterior Cruciate Ligament).
Imbalanced strength training (too much quad development vs hamstrings in short range squatting, for example) can create this situation. So can an over-reliance on distance running for speed sports. Athletes and coaches should take care in designing year-round training routines that keep all muscle development in balance.
Risk Factor #3 - Leg Dominance
Very simply, leg dominance refers to using one leg far more than the other to plant, cut, and jump off of. This asymmetrical development for athletes leads to greater risk for knee injuries, among other problems.
Following strength training routines that work each leg independently, and forcing athletes to do drills where they must cut off each leg an equal amount of times are two ways to avoid developing players with a leg dominance risk factor.
Risk Factor #4 - Trunk Dominance
Trunk dominance refers to an inability to control your core in three-dimensional space.
You may be wondering what this has to do with knee injuries, so let's use a real-life example that is common in regards to knee injury cases.
Let's say an athlete goes to make a cut while pushing off their right leg. In this circumstance their upper body and center of gravity should mostly remain over their left leg, referred to as the plant leg.
But someone with poor core stability will struggle to stop the momentum of their upper body, causing it to shift over their push-off leg (right leg in this example). And since the push-off leg is positioned at an angle it isn't set to hold the weight of your body, and may collapse under the extra force placed upon it.
Athletes with better core stability will not shift their weight to the push-off leg, and thus are at lower risk for non-contact knee problems.
We'd be foolish to tell you that all injuries are preventable. Athletic environments are chaotic by nature, especially as you climb the ranks to higher levels of competition.
Yet it is just as foolish to think that none of these injuries are preventable.
With some pre-season screening to determine who has one or more of these risk factors, athletes can train themselves to be at lower risk for future problems, heading off a potential major setback before it ever occurs.