I don't believe that there are any higher incidences of A/MCL injuries today than in the past. Athletic movement in the game is pretty much the same as it's always been with the same amount of stress being placed on the knee and its vital components. I suspect, however, with MRI's being more readily available, teams are able to better diagnose these injuries. Back in the day, an A/MCL tear would've likely been classified a "knee injury" and these players may not have been heard from again because treatment and rehab had not evolved.