There is a lot of things that can hurt from bondage, from simple rope burns to damage through lack of blood to the extremities, to asphyxiation and death. Broken limbs can result from falling badly while in bondage and landing badly- if the arm can't move in its normal arc to respond to the impact, the shock will take the next available path of least resistance- and that could be an arm collar bone.
Some can be avoided by making sure you're using suitable materials. I silk rope especially made for bondage is obviously safer than nylon clothesline rope.
Learn your knots. The lark's head is your friend.
You may also want to consider good cuffs which support the wrists and ankles, and tie the ropes through the D rings on there rather than directly on the skin.
Lis x