The true incidence of MCL injuries is difficult to ascertain because of the wide variation in injury severity. Minor MCL injuries are often never evaluated by a physician. However, injury to the MCL is one of the most common injuries of the knee  and is equally observed in men and women. Due to an age-associated decline in ligament elasticity, adults are more susceptible to MCL injury than children or adolescents. Because MCL injuries are usually related to athletic endeavours, peak incidence occurs in those more likely to engage in these pursuits. Typically this means adults aged 20 to 35 years. Nonetheless, MCL injuries are also observed in older people due to falls. The incidence of MCL injury is highest in sports such as American football (55%),  skiing (15% to 20% of all injuries and 60% of all knee injuries),  and rugby (29%),  where valgus (twisting outwards away from the mid-line) and external rotational forces on the knee are commonly experienced. MCL injuries can also occur in non-contact sports. Finally, the MCL may be injured in conjunction with the anterior cruciate ligament, posterior cruciate ligament, meniscus, bone, and/or lateral complex.