Will a back muscle imbalance cause scoliosis?

Possibly: Muscle imbalances can indeed cause scoliosis, but more likely to occur in the setting of a neuromuscular disease (muscular dystrophy, spina bifida, cerebral palsy, quadriplegia or paraplegia from spinal cord injury, stroke in a young person, multiple sclerosis with paralysis, etc). Existing scoliosis can worsen with certain postures & muscle imbalances. It should be monitored for worsening.

Potentially: There are a number of neuromuscular conditions in which scoliosis is much more common than the general population. Spastic cerebral palsy is just one example. It is believed that the muscular imbalance that these patients have is what makes it more common for them to get scoliosis. Thank you for the question.