• Limited-efficacy of SDS and MID-C in terms of curve correction maintenance: changes in cobb angle [ Time Frame: Until 1 year post-operative FU ]
  changes in cobb angle on radiographs post-op and at 4 weeks, 3 months and 12 months follow-up (FU). A maximum of 5 degrees increase will be the threshold to define maintenance.
• Incidence of Treatment-Emergent Serious Adverse Events of SDS and MID-C [ Time Frame: Until 1 year post-operative FU ]
  Reported treatment related Serious Adverse Events (SAEs) per-operatively and at 4 weeks, 3 months and 12 months FU.

• Limited-efficacy of SDS and MID-C in terms of spinal length [ Time Frame: Until 1 year post-operative FU ]
  Changes in length of T1-T12, T1-S1 and the instrumented segment in mm on calibrated Anterior Posterior (AP) X-rays post-op and at 4 weeks, 3 months and 12 months FU.
• SDS vs. MID-C with respect to limited-efficacy in terms of curve correction maintenance [ Time Frame: Until 1 year post-operative FU ]
  changes in cobb angle on radiographs post-op and at 4 weeks, 3 months and 12 months FU. A maximum of 5 degrees increase will be the threshold to define maintenance.
• SDS vs. MID-C with respect to limited-efficacy in terms of spinal length [ Time Frame: Until 1 year post-operative FU ]
  Changes in length of T1-T12, T1-S1 and the instrumented segment in mm on calibrated AP X-rays post-op and at 4 weeks, 3 months and 12 months FU.
• SDS vs. MID-C with respect to the incidence of Treatment-Emergent Serious Adverse Events [ Time Frame: Until 1 year post-operative FU ]
  Reported treatment related SAEs per-operatively and at 4 weeks, 3 months and 12 months FU.
• SDS vs. MID-C with respect to surgery time [ Time Frame: Until 1 year post-operative FU ]
  Surgery time in minutes
• SDS vs. MID-C with respect to blood loss during surgery [ Time Frame: Until 1 year post-operative FU ]
  blood loss in cc
• SDS vs. MID-C with respect to length of hospital stay [ Time Frame: Until 1 year post-operative FU ]
  length of hospital stay in days
• SDS vs. MID-C with respect to recovery time [ Time Frame: Until 1 year post-operative FU ]
  recovery time in minutes
• SDS vs. MID-C with respect to bone density [ Time Frame: Until 1 year post-operative FU ]
  Bone density changes of the bypassed vertebrae on Dual Energy X-ray Absorptiometry (DEXA)scan post-op and at 3 months en 12 months FU.
• SDS vs. MID-C with respect to Quality Of Life (QOL) on the Early Onset Scoliosis Questionnaires (EOSQ-24) [ Time Frame: Until 1 year post-operative FU ]
  Parent reported QOL and performance is assessed with the 24-item Early Onset Scoliosis Questionnaires (EOSQ-24) pre-op and at 4 weeks, 3 months and 12 months FU. EOSQ-24 covers the following domains: Child's Health Related Quality of Life (16 items), Family Impact (2 items) and Satisfaction (2 items).
• SDS vs. MID-C with respect to flexibility of the spine [ Time Frame: Until 1 year post-operative FU ]
  Flexibility and 3D rotation of the spine on dynamic echography (Scolioscan)
• SDS vs. MID-C with respect to 3D development of the spine [ Time Frame: Until 1 year post-operative FU ]
  Apical Vertebral Rotation based on MRI
• SDS vs. MID-C with respect to patient appearance [ Time Frame: Until 1 year post-operative FU ]
  sagittal balance on clinical photographs post-op and at 1 year FU

Rationale: EOS is a severe and potentially life-threatening disorder since a disturbance of spinal development leads to impaired development of the trunk, with cardio-respiratory failure as a result, often early in adult life. Several innovative solutions have been developed to treat growing children with severe EOS. The SDS device was developed internally at the dpt. of orthopedics at the UMC Utrecht, the Netherlands, the MID-C device was developed by the company ApiFix Ltd.

Objective: The primary aim of this study is to investigate the limited efficacy of these innovative surgical solutions in treatment of early onset scoliosis in terms of maintaining reduction while maintaining spinal growth. The secondary aim is to compare both devices for these and other parameters as well as safety.

Study design: A feasibility study using two prospective cohorts according to an open label randomized clinical trial (RCT) design. The study will be done in two tertiary referral centers (UMC Utrecht and Amsterdam UMC). Primary endpoints are maintenance of curve correction as well as complications. These data will be compared to a recently described cohort of patients that received a "standard treatment" (Magnetically controlled growing rod (MCGR)). The same endpoints as well as secondary outcomes, will be compared between the two new treatments.

Study population: Children with idiopathic(-like) early onset scoliosis with an indication for a growing rod implant.

• Early-Onset Scoliosis Deformity of Spine (Disorder)
• Idiopathic Scoliosis

• Device: SDS
  The SDS will be added to a traditional growing rod (TGR) of 4.5 or 5.5mm.
• Device: MID-C
  The MID-C system consists of a unilateral one-way ratchet rod that is connected to the spine with polyaxial connectors

• Experimental: Spring Distraction System
  The SDS device will be implanted during a scoliosis correction operation.
  Intervention: Device: SDS
• Experimental: Minimal Invasive Deformity Correction system
  The MID-C device will be implanted during a scoliosis correction operation.
  Intervention: Device: MID-C

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