Medical science has for years contended that the knee’s anterior cruciate ligament does not heal by simply regenerating. That’s the reason generations of NFL players have had surgery to repair ACL injuries.
Miami Dolphins quarterback Ryan Tannehill went another direction, not having surgery but rather choosing to rehabilitate the partially torn ligament and follow that with stem cell treatments. On Thursday, when Tannehill spoke publicly for the first time since the end of the 2016 season, he said his ACL was indeed healed.
http://www.miamiherald.com/sports/spt-columns-blogs/armando-salguero/article152627619.html
Tannehill's ability to run is by far the biggest news of the preseason