Purpose: Various methods of preoperative planning have been described for the correction of spinal sagittal deformities. They are reliable on condition that the thoracolumbar spine is totally fused and enable only the simulation of pedicle subtraction osteotomy (PSO). In this study, a new theoretical planning that can be used regardless of the etiology of the deformity and the type of osteotomy is described and assessed.
Methods: The spino-pelvic sagittal balance can be expressed by two parameters: pelvic tilt (PT) and center of both acoustic meati (CAM) overhang. These two parameters vary according to the type, number, level, and angulation of osteotomies. The general principle of the planning is to define the surgical program in order to obtain PT and CAM overhang as close as possible to the normal values. The theoretical planning is based on a trigonometric construction which depends on numerous factors and is challenging to use in daily practice without the aid of a software tool. Modifications are proposed if the spine cannot be modeled as a solid beam due to unfused disks allowing relative motion. The SpineView software, which enables analysis and quick visualization of different correction possibilities, is presented. The planning method is assessed in a prospective cohort of 11 patients by comparing planned values of spino-pelvic parameters to postoperative values.
Results: In all, 8 preoperative plans out of 11 were concordant with the postoperative results.
Conclusions: The preoperative planning enables the surgeon to estimate the clinical effects of the different surgical techniques in order to choose the best procedure for a given patient.