I'll say right off, that I am in no way a doctor or anything like that. In high school, I managed to burst the bursa sac in each of my elbows while playing football.
If you go to Wikipedia, it gives you a pretty good definition of the purpose of the Bursa Sac:
It provides a cushion between bones and tendons and/or muscles around a joint. This helps to reduce friction between the bones and allows free movement. Bursae are filled with synovial fluid and are found around most major joints of the body.
When you burst the sac, the swelling happens pretty fast and your elbow is pretty tender. It isn't an unbearable pain but it can be painful if you hit the area or apply pressure to it.
Check out this image of an elbow that has a burst bursa sac.
As you can see the swelling is pretty significant. So how does this affect the throwing ability of a QB? Well, try this quick, easy experiment and you can see the restriction.
Extend your arm out so that it is straight. Pinch and hold the excess skin at your elbow. Now, while holding the excess skin, begin to slowly bend your elbow in like you are flexing your bicep. You will notice that while bending the elbow in, the excess skin draws tight until you are left with little or no skin to hold onto.
So, when the bursa sac bursts, the elbow is now filled with fluid. The excess skin is now holding the fluid and your elbow looks like it has an egg in there. That excess skin is now tender and painful if pressure is applied or it is hit.
So when the QB goes through his throwing motion, the most painful part will be right before he begins to actually extend his arm. When he has rared back or wound back his arm to throw the pass. So, if you think about this, the harder he is going to throw a ball, the more pain it is going to cause.
If I'm just tossing a ball around, I'm not going to have to rare back and throw. My elbow will not have to bend as much. Where as, if I am trying to throw the ball with some zip or throw the ball downfield and I want to put something on the throw, my elbow is going to bend in completely and the excess skin will be next to nothing. The tender skin, swelling and fluid will be smashed against my elbow and the pain will increase.
The play that really sticks out to me is when Bert got smashed on the short throw where Ponder's pass seemed to float out there forever. This was the play right before Bert's TD run.
If Ponder's elbow had swelled up then the zip he wanted to put on the ball would have meant he would have been in pain making that pass. It could have caused him to not rare back as much as needed and not put zip on the pass.
I hope this helps us all to realize that Ponder would have been affected by this injury. I still think there were some mental errors on his part. But if his mind was telling him he could make a pass, but his elbow wasn't cooperating, this could account for some of those mistakes.