External Fixators; Lumbar Vertebrae/surgery; Sacrum/surgery; Spinal Fusion/instrumentation; Activities of Daily Living; Adolescent; Adult; Back Pain/epidemiology; Back Pain/etiology; Braces; Child; Female; Follow-Up Studies; Humans; Lumbar Vertebrae/diagnostic imaging; Male; Paralysis/epidemiology; Paralysis/etiology; Postoperative Complications/epidemiology; Pseudarthrosis/etiology; Pseudarthrosis/surgery; Radiography; Reoperation; Retrospective Studies; Sacrum/diagnostic imaging; Sensation Disorders/epidemiology; Sensation Disorders/etiology; Severity of Illness Index; Spinal Diseases/complications; Spinal Diseases/surgery; Spinal Fusion/methods; Treatment Outcome; Urination Disorders/epidemiology; Urination Disorders/etiology