This happened on the main trail. A buddy and I were descending this way after climbing the E Buttress and found the victim around 5:00pm. The guy blew his knee out and was laying in the snow about 12 switchbacks down from trailcrest and couldn't move. We gave him all the warm gear we had (unfortunately no sleeping bags bc we were dayhiking) and then flaked our rope out on the snow and put one of our backpacks down on top of that, insulating him as much as possible from the snow. After getting some basic info and helping his wife find warm gear with other overnight campers at trailcamp, we continued to hike out. We made it to the car around 8:15 and called 911. I guess rescuers got to him sometime after 10 that night (which leads me to believe somebody was able to get cell reception at trailcrest and start the rescue effort process before we even made it back to the car). It took 6 hours to get him to trail camp where he was airlifted out around 4am. Heard back from the guy and he obviously made it out ok, said he would have to have surgery on the knee.
