A.K.
Discipline means to teach. Your son had a bad experience and you're right, he probably had reason to be cranky. But, he needs to LEARN now that he can't act like that any more. You have to be the grown up. If he cries because he doesn't get his way, he cries. You shouldn't be doing things for him that he can do himself. You shouldn't hold him all the time. He may be somewhat afraid of breaking his leg again, but you need to have him do more and regain his confidence. You shouldn't compromise, and you shouldn't bribe (although I have used bribery for the short term, there are some things I won't compromise)
If he can't have something, you just repeat over and over "No, you can't have it" no whys, no compromise, no alternatives. Just no. If he has a tantrum, let him have a tantrum. It bothers you WAY more than it bother him - that's why so many kids have tantrums. They are pretty powerfu. While he is having his tantrum, imagine him at 18 years old. What kind of young man do you want him to be? Someone who is lazy, with a bad attitude, and acts out when he doesn't get his way? Or, a responsible, respectful, young man to be proud of? This is where it starts.
Be strong, it may not be easy, but keep that image of him at 18.