Jordy Nelson, a Super Bowl winning wide-receiver with the Green Bay Packers will miss the entire 2015 season with a torn ACL. There was no contact on the play, which occurred during the second pre-season game of the year for the Packers. Pre-season competition is a valuable way of mentally, physically, and tactically preparing for an upcoming season. With any exposure to high-intensity competition comes the risk of injury. In the NFL, pre-season injuries like Nelson’s are common. Of the injuries sustained, ACL tears are one of the most common. 132 ACL tears have occurred since 2013: 25 of them occurring this year, and 10 occurring during pre-season play (1).
Since 2013 there've been 132 torn ACL's in the NFL. Most = MIA (8) Fewest = HOU, MIN, TB (1 each) pic.twitter.com/txW75IDt8g
— ACL Recovery Club (@ACLrecoveryCLUB) August 27, 2015
"Ligament injuries are scary for elite athletes since the majority will cost an athlete an entire season of training and competition,” said Thomas Roos, Sports Geneticist at Stanford Medical School.
ACL tears are the most common reason for players to miss an entire regular season. Given the high-impact nature of football, you would expect that ACL injuries are caused by big hits and other contact plays, but in fact, the majority of ACL tears are non-contact in nature (2).
There are both environmental and anatomical risk factors for ACL injuries. Environmental factors, such as turf type and weather conditions, contribute to overall injury susceptibility. Anatomical risk factors include structural and biomechanical characteristics of the knee . There is no clear explanation for how these risk factors interact (3). Besides recent investigations into the neuromuscular and biomechanical basis for injury risk, the use of genetic information to identify genetic variants that may predispose an athlete to injury is becoming increasingly popular.
“Ligament injuries are multifactorial with many contributing factors, genetics being one of them. Most scientists would agree that genetics plays a role in structure and function of ligaments,” said Roos.
What do we know now? Variations in the COL5A1 gene are some of the most strongly associated with ligament injury risk. This gene codes for important components of collagen, a primary protein of connective tissue. Similarly, variants in the MMP3 gene appear to be associated with repair and maintenance of connective tissues in tendons (4).
"We are just starting to understand the genetic underpinnings for this injury susceptibility,” adds Roos.
Professional football is incredibly stressful on the body. ACL tears to stars like Nelson, Ryan Clady, and Kelvin Benjamin has opened a lively discussion on the topic of prevention. It is important to recognize that the association between a genetic variant and injury risk does not mean that an injury is caused by an athlete’s genetic makeup; however, knowledge about an athlete’s potential for increased risk allows for individualized care. “The idea that all athletes should be screened for ligament injuries and participate in preventative strength and proprioception programs is becoming more accepted in the sports medicine and sports performance fields,” said Roos.
(1) As of August 26, 2015.
(2) Bradley, et al. (2002). Anterior cruciate ligament injuries in the National Football League. Arthroscopy: The Journal of Arthroscopic & Related Surgery. 18(5), 502–509.
(3) Alentorn-Geli, et al. (2013). Prevention of anterior cruciate ligament injuries in sports - Part I: Systematic review of risk factors in male athletes. Knee Surgery, Sports Traumatology, Arthroscopy. 22(1), 3–15.
(4) Raleigh, et al. (2009). Variants within the MMP3 gene are associated with Achilles tendinopathy: possible interaction with the COL5A1 gene. British Journal of Sports Medicine. 43, 514-20.