[Yoda]

Many years ago I broke my left arm quite badly. It healed with a quirk and i think this is making swinging with horizontal hinging very difficult for me.

If I lift my left arm stright out in front of me, with my hand in the karate chop position, I can swivel my forearm so that the top of my hand faces the sky, but if I try to go the other way so that the palm faces the sky, I can only get about 1/5th of the way there.

Is my understanding of the H.Hinge motion all wrong and this infact wouldnt be imparring me at all, or should I give it up and switch to hitting?

Hinge Action is not the problem, Nevermind. Properly understood -- and allowed to happen -- your Rotating Body will automatically produce the Horizontal Hinge Action you seek (with or without your Left Arm 'quirk').

But...

There may well be a problem with your Swivel Action. To diagnose that problem, I need to see you -- or at least photos or video of you. What visuals can you provide?

With or without those visuals, please answer this question:

After Impact, can you Swivel your Left Palm Upinto a 'gimme five' position?