I actually have the same issue. Broke my elbow in 4th grade, right at the growth plate. I'm now unable to turn my palm all the flat upwards. Because of that I've had to eliminate almost all barbell curls & most preacher machines & such where I can decide the angle of the handle. I really utilize dumbells, specially hammer curls where my palm stays in line with my arm. Cables are good for me too. Can use the rope, single handed cable curls, etc. basically just had to utilize everything that allows me to decide the comfortable angle in which to turn my palm/Lower arm.