You’re right about smoking’s negative effects on bone fusion surgeries. Smokers generally don’t heal as fast or as well from surgeries to fuse parts of the spine, ankle, or wrist.
In order to grow together to form a solid mass, bones need a decent supply of blood. Blood brings bones the oxygen and nutrients they need, and it discourages the growth of bad cells. Nicotine is thought to get in the way of healing by closing down blood vessels and restricting blood supply, called vasoconstriction. Research has shown that, even in areas such as the wrist that have greater blood supply, smoking impairs bone healing.