The smoking is the part that has a negative effect on spinal fusions. So, it would not matter what type of smoke you were inhaling, it could have a detrimental effect. This is why: smoking decreases your circulation greatly. When this happens, there is less blood flow to the vertebrae in your neck where your surgery was performed. They want lots of bone to form in the area where the fusion was, so that you have a vertebra that is in a sense doubled, and thus becomes more stable. I would not reccommend smoking of any kind after a spinal fusion. If you wish to enjoy the healing benefits from marijuana, might I suggest that you choose a vaporizer or perhaps baking it into brownies instead of actual smoking? You will gain the same benefits, but the health risks are greatly reduced. Feel free to PM me or post back here if you have further questions.