How do you keep you left elbow straight?

Hi all.
I have been struggling for ages now with very inconsistant ball contact.
My shots are all over the place, I am sure a lot of my problem is my inabillity to keep my left elbow straight on my back swing.

As much as I concentrate on this, I cannot seem to overcome this swing fault, I now find myself using a very short backswing as this is the only way I can get a decent contact with the ball at the moment, trouble is my distance obviously suffering.

In desperation, I have even thought of wearing some kind of neoprene elbow support to try to keep it straight.

Could it be a fault with my grip that is causing it?
Any help or suggestions would be greatly appriciated.