However, up until recently, the muscle tones were thought to play little or no role in progression of the disease….but recent findings indicate that abnormal spinal muscle tone does contribute and effect the curve….but it wouldn’t be the initial cause..rather, secondary source which may worsen the existing condition…

As far as back pack safety goes, make sure to wear it on both shoulders, get the ergonomic kind that distributes the weight, and do not carry in it more than 15% of your body weight.

Although heavy back pack wouldn’t cause scoliosis, it could cause other types of postural disturbances like stooping and symptoms such as back pain…

http://myscoliosis.net/scoliosis.aspx

check out above link for more info on scoliosis