Consequences of the Three-Dimensional Pathoanatomy of Adolescent Idiopathic Scoliosis

Abstract

Scoliosis is a classic orthopedic disorder, a 3D rotational deformity of the spine and trunk with severe consequences for the patient in terms of self-image, pain and treatment options. In most cases, a specific cause is not found, the patients appear otherwise normal, and therefore those cases are called ‘idiopathic’. The most common type, adolescent idiopathic scoliosis (AIS), develops in previously healthy children, most often girls, during early puberty and affects 1-4% of the adolescents. Treatment is always a severe burden and consists of rigid and constraining braces or extensive surgical procedures that carry severe risks such as neurologic damage. Understanding of the true morphology is important to better understand its etiopathogenesis, correctly interpret standard imaging, as well as adequately plan the correction of the curves. The normal human posture and locomotion is unique and differs from other vertebrates. This unique biomechanical sagittal morphology of the spine and pelvis differs between non-scoliotic controls and AIS patients with different curve types, indicating that spinopelvic alignment could play a role in the onset and progression AIS. Furthermore, in the sagittal plane, the spinal column that is longer anteriorly than posteriorly. This anterior-posterior length discrepancy of the primary and secondary scoliotic curves is caused by relative anterior lengthening as well as relative posterior shortening. The 3D deformation of the spine in AIS is predominantly localized in the discs (as a secondary phenomenon to axial rotation) and hardly in the vertebral bodies (as a result of active growth). Additionally, non-idiopathic, neuromuscular scoliosis demonstrates the same pattern of 3D deformation with relative anterior spinal overgrowth and torsion on the different structures as idiopathic scoliosis. This suggests a more generalized passive mechanism that results in the 3D curvature, and that is not the consequence of a local process such as active bony overgrowth or asymmetrical growth. In terms of diagnostic consequences, radiation exposure is a big issue for patients with AIS. 3D ultrasound is a radiation-free modality, that could be used for imaging of patients with AIS. In this thesis, excellent correlations between the ultrasound and radiographic measurements were described. Therefore, the severity of the deformity in AIS patients can be assessed by ultrasound imaging, avoiding hazardous ionizing radiation. Treatment of scoliosis has to restore the coronal, sagittal and transverse alignment and the consequences for the patient. As described in this thesis, the anterior and posterior approaches restore the coronal curve, have a kyphogenic effect and correct the axial rotation. Therefore, the choice of surgical approach depends mostly on the experience of the surgeon. Further knowledge of the 3D morphology, will give more insight in the pathogenesis of AIS and possible risk factors for the onset and progression of AIS, leading to a primary treatment of AIS, instead of restoration of the curve, to decrease the severe consequences for the patient – in terms of self-image, pain and treatment options – as well as the economic burden for the society.