Segmental analysis of the sagittal plane alignment of the normal thoracic and lumbar spines and thoracolumbar junction.

Recent advances in spinal instrumentation have brought about a new emphasis on the three-dimensional spinal deformity of scoliosis and especially on the restoration of normal sagittal plane contours. Normal alignment in the coronal and transverse planes is easily defined; however, normal sagittal plane alignment is not so simple. This retrospective study was undertaken to increase the understanding of the normal alignment of the spine in the sagittal plane, with a special emphasis on the thoracolumbar junction. Measurements were made from the lateral radiographs of 102 subjects with clinically and radiographically normal spines. Cobb measurements of the thoracic kyphosis (T3-T12), the thoracolumbar junction (T10-T12 and T12-L2), and the lumbar lordosis (L1-L5) were determined. The spices of the thoracic kyphosis and lumbar lordosis also were determined. Using a computerized digitalizing table, the segmental angulation was determined at each level from T1-2 to L5-S1. In conclusion, there is a wide range of normal sagittal alignment of the thoracic and lumbar spines. When using composite measurements of the combined frontal and sagittal plane deformity of scoliosis, this wide range of sagittal variance should be taken into consideration. Using norms established here for segmental alignment, areas of hypokyphosis and hypolordosis commonly seen in scoliosis can be more objectively evaluated. The thoracolumbar junction is for all practical purposes straight; lumbar lordosis usually starts at L1-2 and gradually increases at each level caudally to the sacrum.