Yes cannabis can be very helpful following back surgery. It will help with pain, muscle spasms, inflammation, sleep, mood and other aspects of recovery. Studies have concluded that cannabis can potentiate the effects of opiates. Meaning that if one uses cannabis, less opiates would be required to achieve adequate pain control. I would use a CBD rich whole plant cannabis extract in a sublingual tincture format. Experiment with different ratios and strains. Topicals and suppositories can also provide very direct relief.