The other result, symmetric patients achieved symmetry in part by hopping a shorter distance on the contralateral side. This test is designed to be a way to assess limb symmetry index or the variance between the right side and the left side. Studies have shown (Rhoman et al Am J Sports Med 2015) that norms have a limb symmetry index of 85%. Considering this, it is hypothesized if an athlete has a variance >15% on the right versus the left, then they are at greater risk of injury. Based on the results here, we can make the assumption that this test will not show us who is at risk. Whether consciously or unconsciously, the athlete is modifying effort on the non-involved limb which will misrepresent the true limb symmetry index.
However, the area of biggest focus for most of us is what are the biomechanics at take-off and landing? As the athlete is going into loading the limb for explosive power and begins to explode up, it is usually the transition from loading the limb to explosive movement that you will see the knee move into the dynamic valgus position. This is a focus for most as we know that this motion is the one that will or could potentially lead to increase risk for ACL injury or mensical injury.
If you take the above slide as an example, you will see that based on basic biomechanics that force is determined by both the magnitude of the motion (how much the knee moves into valgus) and speed (how fast it moves into valgus) at which that motion occurs. So the larger the valgus is at loading and the faster that valgus occurs at loading, the greater the risk is that force will be departed to the ACL and the meniscus. This is something we want to measure and quantify. According to Johnston et al Am J Sports Med 2018, based on video review of non-contact ACL injuries in football players, dynamic valgus is the position that causes ACL rupture which led the authors to suggest this should be something that is assessed to identify those at risk.
This same motion is typically observed again at landing. When the athlete’s foot contacts the ground and they have to being to attenuate the force through the foot/ankle, knee and hip. It is typically at this point under high loads that you will again observe the knee move into the dynamic valgus position. Considering the ground reaction forces generated in landing (on a basketball court) is anywhere from 4-8 times body weight, we can understand the importance of controlling this motion during these movements.