3D Sagittal Plane Examination of the Spino-pelvic Complex in Adolescent Idiopathic Scoliosis

Abstract

The spine is a harmonic system of vertebrae joint together like a column, forming a stable but sufficiently mobile frame whose main function is the protection of the spinal cord, bearing of the body’s burdens and enabling the adequate mobility of the trunk, respectively. Due to rapid development in recent past regarding both the field of orthopaedics and diagnostic possibilities, a significant change has occurred also in the assessment and treatment strategy of spinal deformities. Thus an increased demand has risen for the exact mapping of the relation of the joint pelvis and spine and for the evaluation of these anatomic structures as a complex biomechanical unit. A “spine without deformities” or “normal” spine has a relatively straight and regular appearance in the frontal plane, while it takes the shape of a harmonic wave in the sagittal plane, which can be divided into the following four parts: cervical lordosis, thoracic kyphosis, lumbar lordosis and sacral kyphosis. Three pelvic parameters are used for defining the pelvis in the sagittal plane: pelvic tilt (PT), sacral slope (SS) and pelvic incidence (PI). The first two parameters depend on the position of the pelvis, while pelvic incidence is an idiosyncratic and anatomic parameter by definition. The sagittal description of the spine is various in medical literature, thus several terms are applied, such as T1–T12, T4–T12 or T5–T12 for thoracic lordosis and L1–L5 or L1–S1 for lumbar lordosis. The spine and the pelvis form a closely – and also dynamically - attached unit in all three dimensions with the pelvis as a solid base. As a result, the harmonically “curved” spine is approximately ten times more resilient to mechanical impacts than a completely straight spine would be