Abstract

Pelvic incidence is a parameter of individual measurement which determines pelvic and sacral position and thereby lumbar lordosis and spinal alignment. For additional description of pelvic position, a parameter called pelvic tilt is used. Sacral position, particularly the inclination angle of the S1 upper end-plate, is described by the sacral slope. The sum of pelvic tilt and sacral slope form a constant which is always equal to pelvic incidence, PT + SS = PI. Spinal and pelvic parameters as described in the article are used to assess individual spinal alignment or lateral spinal position. Thoracic kyphosis and lumbar lordosis depend on pelvic parameters. Measurement of lumbar lordosis is approximate to pelvic incidence, LL = PI+/-10º. The sagittal vertical axis is used to describe spinal alignment. When the sagittal vertical axis passes through the S1 upper end-plate, then the spine is balanced. Mismatch between the lumbo-pelvic parameters causes activation of compensatory mechanisms which aim to maintain a balanced posture of the spine. In case compensatory mechanisms are exhausted, the spinal balance is disturbed and the sagittal vertical axis shifts past the femoral heads. In planning spinal surgical treatment, it is recommended to take the spino-pelvic parameters into consideration.