Clinical Review

Knee Injuries in American Football: An Epidemiological Review

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Football has the highest injury rate amongst popular American sports. Of those injuries that end seasons or careers, the knee is the most common culprit. This is of particular concern because knee injuries are most common in football. This article reviews 4 of the most common knee injuries in American football, with emphasis on epidemiology, risk factors, and treatment outcomes. The injuries reviewed are tears of the anterior cruciate ligament, medial collateral ligament, medial patellofemoral ligament, and posterior cruciate ligament.



Football is one of the most popular sports in the United States. Every year more than 1 million high school males and over 60,000 collegiate males participate in organized football. The number of males who play football is greater than the combined number of males and females who participate in track and field or basketball.1 Football has the highest injury rate amongst popular American sports.2 From 2001 to 2005, there was an estimated 1.1 million emergency room visits as a direct result of football.3 Injuries are more likely to occur during games,1,2,4,5 more likely to require surgery,4 and more likely to end the player’s season or career when compared to other sports.6 Of those injuries that end seasons or careers, the knee is the most common culprit.6 This is of particular concern because knee injuries are most common in football.1,2,5,7 This article reviews the epidemiology of 4 of the most common knee injuries in American football: tears of the anterior cruciate ligament (ACL), medial collateral ligament (MCL), medial patellofemoral ligament (MPFL), and posterior cruciate ligament (PCL).

Anterior Cruciate Ligament

The ACL is the primary structure preventing anterior tibial translation. It is composed of 2 anatomic bundles: the anteromedial and posterolateral bundles. The ACL originates from the posteromedial portion of the lateral femoral condyle and inserts between and slightly anterior to the tibial intercondylar eminence. The bundles are named for their relative insertions onto the tibia.

Injury to the ACL occurs both through noncontact and contact mechanisms. Typical noncontact mechanism is a forceful valgus collapse with the knee close to full extension with combined external or internal rotation of the tibia.8 This is often the result of a sudden deceleration prior to a change in direction.9 Contact injuries to the ACL are the result of a direct blow to the knee causing valgus collapse.9 The majority of ACL injuries amongst all sports are a result of a noncontact mechanism. However, Dragoo and colleagues10 found the majority of football ACL injuries (55%-60%) were from contact. As a result, football players are 4 times more likely to sustain ACL injuries than in other sports.11

ACL injuries are associated with significant time loss from sport. At the high school level, they are the most likely injury to end a season or career.6 Because these are higher-energy injuries, they are frequently associated with damage to additional structures. ACL injuries that occur in football are associated with increased rates of meniscus, chondral, and multi-ligamentous injuries.12,13

The incidence of ACL injuries increases with level of competition. In high school athletes it is 11.1 per 100,000 athlete exposures (AE).1,11 In collegiate football, the rate increases to 14.2 to 18 per 100,000 AE.2,14 Though no incidence data per AE was found in our review of the literature, there were 219 ACL injuries in the National Football League (NFL) from 2010 to 2013.15 In addition, 14.2% of retired NFL athletes in one survey reported a history of ACL injury.16

The most common high-risk positions are running backs and linebackers. Brophy and colleagues17 found that 9.7% of running backs and 8.9% of linebackers participating in the NFL Combine had a history of ACL injury. This may be because both the running back and linebacker are involved in frequent high-energy collisions and often quickly change direction. Other studies have also identified running backs and linebackers as high risk, in addition to tight ends, wide receivers, and interior linemen.13,15,18

Treatment of choice for elite level athletes with ACL injury is reconstruction.19 Of those who undergo ACL reconstruction, the rate of return to play ranges from 63% to 80%.20-22 The average time to return to play is 9 to 13 months. The odds of making a successful return hinges on how successful the athlete was prior to injury. Factors such as prior game experience, position on depth chart, being on scholarship, and draft position for NFL athletes have all been shown to have a positive predictive value on a patient’s chance of returning from ACL reconstruction.20,21

Players who return have variable levels of success afterwards. In a study of NFL quarterbacks who sustained ACL injuries, 12 out of 13 were able to return to game action with no appreciable dropoff in performance based on in-game production.23 Carey and colleagues24 looked specifically at NFL wide receivers and running backs and found an 80% return to play rate but with an approximate decrease in production of one-third upon return. Furthermore, in the Multicenter Orthopaedic Outcomes Network (MOON) cohort study, only 43% of participants felt they returned to their preoperative level.22

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