MESA Rail™ AIS Study - Preservation of Curve Correction

Inclusion Criteria: * Diagnosis of AIS requiring surgical treatment for selective thoracic/lumbar fusion with a minimum of five (5) instrumented vertebrae between T1-S1 as confirmed by patient history and radiographic studies. AIS cases must be classified as a Lenke type 1 or type 2 curve. No cervical vertebrae are to be incorporated into the construct. * Willingness and ability to comply with the requirements of the protocol including follow-up requirements. * Willing and able to sign a study specific informed consent form or, in the case of a patient who is a minor, provide assent and the minor patient's parent/legal guardian provides written consent to participate. * Age range of ≥ 11 years old and ≤ 21 years old at time of surgery. Exclusion Criteria: * Previous anterior or posterior spine surgery at the index levels. * Previous posterior spine surgery (e.g., posterior element decompression) that destabilizes the cervical/thoracic/lumbar spine. * Active systemic infection or infection at the operative site. * Co-morbid medical conditions of the spine or upper/lower extremities that may affect the thoracic or lumbar spine neurological and/or pain assessment. * Metabolic bone disease such as osteoporosis that contradicts spinal surgery. * History of an osteoporotic fracture. * History of an endocrine or metabolic disorder (e.g., Paget's disease) known to affect bone and mineral metabolism. * Taking medications that may interfere with bony/soft tissue healing including chronic steroid use. * Known allergy to titanium or cobalt chrome. * Rheumatoid arthritis or other autoimmune disease or a systemic disorder such as HIV, active hepatitis B or C or fibromyalgia. * Insulin-dependent type 1 or type 2 diabetes. * Medical condition (e.g., unstable cardiac disease, cancer) that may result in patient death or have an effect on outcomes prior to study completion. * Pregnant, or intend to become pregnant, during the course of the study. * Severe obesity (Body Mass Index \> 40).