Sagittal Balance Using Position and Orientation of Each Vertebra in an Asymptomatic Population

Abstract

Study design: A monocentric, retrospective radiographic study with 99 asymptomatic volunteers.

Objective: We performed the postural analysis commonly scheduled when evaluating sagittal balance in a vertebra-by-vertebra manner by enrolling an asymptomatic population. We measured the position and angulation of each vertebra to reveal those for which the spatial positioning could be relevant during spinal surgeries.

Methods: We obtained full-spine EOS X-rays of 99 volunteers in the standard free-standing position. We used a validated three-dimensional (3D) reconstruction technique to extract current spinal parameters and the positions and angulations of all vertebrae and lumbar discs. Particular attention was paid to the positions and angulations of the apical and transitional vertebrae.

Results: T1 was the most common transitional cervicothoracic vertebra (in 89.9% of subjects) and was oriented downwards by an average of 22.0° (standard deviation 7.3°, minimum 2.3°, maximum 40.1°). The thoracic apex trio of T5 (22.2%), T6 (28.3%) and T7 (36.4%) were equally found. The transitional thoracolumbar vertebrae were L1 (39.4%) and T12 (33.3%). The lumbar apex was usually the L3L4 disc (36.4%). T1 seemed to be the transitional vertebra (90%) irrespective of the pelvic incidence (PI). For the other relevant vertebrae, the greater the PI, the more cranial the vertebra.

Conclusions: We performed a detailed 3D assessment of overall spinal balance using positional and rotational parameters. The positions and orientations of all vertebrae were specified, particularly the apical and transitional vertebrae.