While snowboarding through the woods in February 2009, my board and legs tried to go to the right of a tree, while my upper body chose to go to the left of the tree. Tree didn't move, I stopped very quickly. Avulsion fracture of the femur and some other assorted injuries to my knee resulted. First major knee injury in 48 years. Sprained one of my knees 20 years ago while thru-hiking the Appalachian Trail, but have not had any problems since. Broke my leg skiing 44 years ago.
I'm quite fit for my age. 6'3"; 175 lbs. Active hiker year round, snowboard in the winter. Walk minimum of 5 miles a day, 5 days a week with 30 lb pack on rolling dirt roads to keep in shape for search and rescue work in the mountains.
Have a great orthopedic doctor - trust him completely, but have always believed that multiple opinions can either confirm diagnosis and treatment, or cause further questions to be asked and answered. Think of it as "due diligence" that might be done when making a financial transaction!