Limited-efficacy Testing of Spring Distraction System (SDS) and Unilateral One-way Rod (MID-C) for Early Onset Scoliosis

Inclusion Criteria: * Ambulant skeletally immature children, 6-12 yrs. of age, with open triradiate cartilages on X-ray * Scoliosis diagnosis prior to the age 10 * Diagnosis of idiopathic or mild syndromic scoliosis (e.g. 22q11DS, Trisomy 21 or 9, Coffin-Siris) * Progressive scoliosis qualified for growth system surgery * One curve for treatment with an apex below Th5 and a proximal end vertebra below Th2 * The primary curve must be between 35 and 75 degrees coronal Cobb angle * The primary curve must be non-rigid (i.e. the curve reduces on bending X-rays to \<35 degrees or reduces \>30% ) * Normal or hypokyphotic sagittal alignment (Th5 -Th12 \< 50 degrees) on lateral X-rays Exclusion Criteria: * Patients with an obvious neuromuscular disease * Patients that are severely mentally retarded * Patients with a scoliosis that extends to the pelvis or the cervicothoracic region * Patients with a main curve of more than 8 vertebra Cobb to Cobb * Patients with a skeletal dysplasia that effects growth (e.g. achondroplasia, SED) * Patients with a systemic disease which severely influences bone quality (e.g. osteogenesis imperfecta, metabolic diseases) * Patients with soft tissue weakness (e.g. Ehler Danlos, Marfan, Neurofibromatosis, Prader Willi) * Patients with an active systemic disease such as Juvenile Idiopathic Arthritis, HIV or oncologic treatment * Patients with a previous surgical fusion of the spine