There are many medical misconceptions out there, particularly when it comes to fantasy football. One of my least favorite is the idea that football players who display knee valgus during certain movement patterns are more at risk of knee injuries. This is a concept that I hope to debunk and convince our audience is simply not true.
This argument started when fantasy gamers started to fade Jerry Jeudy because of his past medical history of a meniscus tear. Some fantasy analysts further speculated that Jeudy’s excessive knee valgus was a cause for concern and that the fantasy community should proceed with caution while drafting him. This debate sent me down a rabbit hole which eventually led to the column you are reading now.
What is knee valgus?
Knee valgus (Genu Valgum) or collapse is when a person’s knee deviates medially (inward) in relation to their hips and ankles while a person’s feet are in a fixed position. In other words, it is when a knee buckles inward causing someone to have a “knocked knee” appearance.
In the general population this is not an ideal posture, especially when running, jumping, squatting, or turning/pivoting. Knee valgus can be an issue, as multiple orthopedic and sports medicine journals have argued. The results of these studies have shown that increased knee valgus angles (KVAs) are associated with a higher risk of knee injuries – specifically ACL ruptures.
I would argue that when studying the knee valgus posture in professional/high-level athletes, we cannot use the same guidelines set for the general population. Athletes in professional sports have unique profiles and sometimes need to move into this knee valgus position to generate force, power, and speed. In addition to that, I would argue that video analysis alone is not sufficient to predict injury risk or what is the source of the knee valgus.
Video Analysis and Knee Valgus:
I recently tweeted about a new study from the Journal of Orthopedic & Sports Physical Therapy (JOSPT) titled, “There Is No Relationship Between Lower Extremity Alignment During Unilateral and Bilateral Drop Jumps and the Risk of Knee or Ankle Injury: A Prospective Study” which pertained to this specific subject. The authors of the study measured the KVA in over 300 male and females basketball and floorball athletes via video analysis. These researchers followed up with the athletes 12, 24, and 36 months after data collection to measure the frequency and severity of knee and ankle injuries. The results of the study showed that lower extremity alignment (knee valgus) during drop jump tests was not associated with a higher risk of non-contact knee and ankle injuries. This supports my argument that video analysis alone is not sufficient for predicting injury.
My NFL-Specific Knee Valgus Study:
Although the research article from JOSPT bolstered my argument, I was unsatisfied because the demographics included in the research are very different from NFL players. As a result, I investigated whether or not there was any correlation between greater KVAs and ACL tears in NFL WRs. From 2013 I found nine “high-profile” WRs who suffered non-contact ACL tears (A non-contact injury is defined as: an injury that happens spontaneously without contact from another player).
Study Specifics Disclaimer:
If you are interested below this is how I conducted this study. I will admit it is complicated, but I wanted to explain how I measured KVAs. If you are uninterested in this process, then skip down the “Results” section.
The WRs in my study needed to be high-profile players because I needed enough tape to study their movement patterns. I also needed to be able to view the player from the front and have a clear view of their entire leg to accurately record the KVA. The KVA was recorded by measuring three bony landmarks on each player: 1. Anterior superior iliac spine (ASIS) 2. Midpoint of the patella (knee cap) and 3. Midpoint of the ankle joint. The lower limb measured was the knee that the player sustained an ACL rupture in. All measurements were taken prior to when the player suffered the injury. From the game film I measured each player’s KVA in three positions: straight-line running, cutting, and prior to jumping. Using those three measurements, I assigned each player an average KVA.
Lower KVAs (150-179°) indicate excessive knee valgus, while higher KVAs indicate a neutral position (180°). There were some players that displayed knee varus (>180°) which can be seen in the table below. Knee varus is often referred to as “bow-legged” and can be visualized in the first graphic above.
I then compared the composite KVA of the nine NFL WRs with ACL tears to nine other NFL WRs who over their career were relatively healthy and did not have a past medical history of knee injuries in the NFL. To diversify my healthy sample I chose WRs of different ages, sizes and experience. This allowed me to determine if there was an appreciable difference between the KVAs among the two groups (ACL tears vs. non-ACL tears).
Results:
As you can see, there is not much of a difference between the two group KVA averages. The ACL group had an average KVA of 171.33° while the non-ACL group had an average KVA of 171.59°. To determine if the difference in these averages was statistically significant, I asked Undropppables Director of Analytics Blake Hampton (@BlakeAHampton) for help. The main takeaway was that the R Square (r˄2) value was too low at 0.284. R˄2 is the measure of correlation. The value is between 0-1, with 1 being a perfect correlation and 0 being no correlation. In this experiment, the correlation between KVA and ACL tears was small. For medical purposes I would want something much larger (0.5-0.7), especially given my sample size, before I would be comfortable reporting a relationship between KVA and ACL tears via video.
Conclusion:
Based on the JOSPT study and my personal study, I believe that it is unfair to categorize players at a high risk of injury based on the knee valgus angle that is recorded from video. I will admit, both studies are not perfect and have their own limitations. JOSPT did not look at football players and athletes in the age range of most professional athletes and my study had a small sample size of only 18 subjects. Additionally, video of each body position for every NFL WR in this study was hard to find and record a KVA, so there is bound to be some error in my discoveries. With that said, I feel like I am presenting the most objective information on this subject matter and to this point have not seen anything like this in the fantasy football community. For that reason, I am comfortable with my stance that knee valgus angle alone is not substantial information to predict injury.
Circling back to the Jerry Jeudy debate, I believe he should not be avoided because of his knee injuries or his knee valgus. Meniscus tears are commonplace in the NFL, and the surgical procedures to correct them have great outcomes. We should not be avoiding Jeudy (or any player for that matter) because of misconceptions about knee mechanics.
More Information:
If you are interested in more information about this subject matter or want to see a more in depth breakout of Blake Hampton’s stats on the KVA data be sure to go to my twitter account @TheRealAdam_H. Additionally make sure you are visiting The Undroppables website (cantcutlist.com) where our staff has tons of fantasy football information and where you can find more of my medical pieces as well.
