Clinical Review

Knee Injuries in American Football: An Epidemiological Review

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Medial Collateral Ligament

The MCL consists of superficial and deep components. The superficial MCL is the primary restraint to valgus laxity at the knee. The superficial MCL has 1 femoral and 2 tibial attachments. The deep MCL is a thickening of the medial joint capsule and runs deep and parallel to the superficial MCL. The amount of medial joint gapping with a valgus force on examination is used to grade severity of MCL injuries. Grade I is a <5-mm opening; Grade II, 5- to 10-mm opening; and grade III, >10-mm opening.

The MCL is the most common knee injury in high school, collegiate, and professional football.1,18,25-28 Injuries are typically due to contact when a valgus force is applied to the knee.29 The annual incidence of MCL injuries amongst high school football players is 24.2 per 100,000 AE.1 The positions that appear to be at greatest risk for MCL injuries are offensive and defensive linemen.18,30-32 In a review of 5047 collegiate athletes participating in the NFL Combine from 1987 to 2000, 23% of offensive linemen had a history of MCL injury, compared to the overall rate of 16%.33 In a similar study, Bradley and colleagues18 performed medical histories on athletes invited to the 2005 NFL Combine and also found offensive linemen had the highest rate of MCL injury at 33%, compared to the overall rate of 22%. They reasonably hypothesized that “chop blocks” and other players “rolling up” on the outside of linemen’s knees were responsible for these injuries. Albright and colleagues32 found that prophylactic knee braces decreased the incidence of MCL injuries in collegiate offensive lineman. However, additional studies have not been able to reproduce these results and the use of prophylactic knee braces remains controversial.26

Treatment of MCL injuries depends upon the grade of injury, associated injuries, and anatomical location of injury. Management of MCL injuries is for the most part nonsurgical. In 1974, Ellsasser and colleagues34 were the first to publish data on nonoperative management of Grade I and Grade II injuries with immediate motion and rehabilitation instead of cast immobilization. They found 93% of patients returned to football in 3 to 8 weeks.34 Derscheid and Garrick27 observed nonoperative treatment of Grade I and II sprains in collegiate football players, with a time loss of 10.6 days and 19.5 days for Grade I and II injuries, respectively. Holden and colleagues35 evaluated nonoperative management of Grade I and II MCL injuries in collegiate football players and found an average return to play of 21 days.

Grade III injury treatment is more controversial. Indelicato and colleagues36 demonstrated successful nonoperative management of Grade III MCL injuries in collegiate football players, with an average return to play of 64.4 days. Jones and colleagues37 had similar success with high school football players, with an average return to play of 34 days. However, isolated Grade III injuries are rare and therefore treatment is likely to be dictated by concomitant injuries. Fetto and Marshall38 found that 78% of Grade III injuries were associated with an additional ligamentous injury. Of those additional injuries, 95% were ACL tears.

Finally, one must consider the location of the MCL injury. Injuries of the distal MCL at its tibial insertion may result in poor healing, as the ligament is displaced away from its insertion. Therefore, some authors recommend surgical management for these injuries.39,40

Medial Patellofemoral Ligament

The patellofemoral joint is a complex structure in which the patella is stabilized within the trochlear groove of the femur by both bony and soft tissue structures. The MPFL is one of the most important soft tissue stabilizers. The MPFL is the primary restraint to lateral patellar translation within the first 20° of knee flexion, contributing to 60% of the total restraining force.41 The MPFL originates on the medial femoral condyle and inserts on the superomedial aspect of the patella.

Patellar instability is the subluxation or dislocation of the patella out of the trochlear groove. Patellar subluxation and dislocation account for approximately 3% of all knee injuries.42 Patella dislocations are more common in younger populations43-45 with the majority (52%-63%) occurring during sports.43,44,46 Mitchell and colleagues47 reported an incidence of 4.1 patellar subluxations/dislocations per 100,000 AE in high school football players.

Dislocation is most commonly the result of knee flexion with the tibia in a valgus position.44,48 The majority of patellar dislocations occur via a noncontact mechanism.44,48 However, the majority of these injuries in football are from contact (63%).47

Acute patellar dislocations are associated with more soft tissue damage than those with recurrent dislocations.46 In acute patella dislocations, the MPFL is almost always ruptured.44 In contrast, Fithian and colleagues46 found only 38% of recurrent dislocators had MPFL injury. As a result, it is thought that those with recurrent instability dislocate without trauma and do not have the same characteristics as those who dislocate from high-energy trauma in sport. Risk factors for atraumatic dislocation are numerous and have been well described in the literature.49 However, traumatic dislocators usually do not have risk factors.50

Traumatic patella dislocations are higher energy and are associated with chondral injury in up to 95%of cases 51 and osteochondral injury 58% to 76% of the time.52,53 In contrast, people with “articular hypermobility” are less likely to sustain articular damage.54 This concept is important when considering risk for recurrent patella dislocation. The literature reports a 17% to 50% rate of recurrent instability after acute patella dislocation.46,55,56 However, most studies do not distinguish between traumatic and atraumatic injuries. Because the majority of patellar dislocations in football occur through contact mechanisms, the rate of recurrent instability in these athletes may in fact be less than what is reported in the literature.

First-time patella dislocations are generally treated nonoperatively. Mitchell and colleagues47 reported that 72.6% of high school athletes with patella subluxation treated conservatively were able to return to sports within 3 weeks, compared to only 34.1% of those with patellar dislocations. In the same study, patellar dislocations were season-ending 37% of the time.47 Atkin and colleagues50 followed 74 patients treated conservatively for first-time patellar dislocation and noted 58% at 6 months still had difficulty in squatting, jumping, or cutting.

Those who have failed conservative management and have an additional dislocation are 7 times more likely to redislocate.46 Therefore, they are usually treated operatively with MPFL reconstruction. Return to sport ranges from 3 to 6 months,57 with 53% to 77.3% reporting return to their previous functionality.57-59 Overall, 84.1% of patients are able to return to sport with 1.2% risk of recurrent dislocation.60

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