Importance of pelvic compensation in posture and motion after posterior spinal fusion using CD instrumentation for idiopathic scoliosis

Study Design. Posture and motion analysis after a Cotrel-Dubousset instrumentation. Objectives. To investigate the compensation role of pelvis. Summary of Background Data. Few existing studies found no compensation at the lower unfused level but did not investigate the pelvis. Methods. Thirty patients were analyzed before surgery then at short-, medium-, and long-term postoperative follow-up. Calibrated x-rays with three-dimensional reconstruction yielded quantification of pelvic parameters. Noninvasive optoelectronic system allowed analyzing subjects first in standing position, then during flexion-extension, lateral bending, and axial rotation. Skin markers were used to quantify three-dimensional orientation of the shoulders, trunk and pelvis, and their range of motion (ROM). Results. Ten patients among 21 had after surgery more than 5 change of pelvic incidence. In flexion,global ROM decreased from preoperative to postoperative phase (P < 0.05). Global ROM variation was not correlated to that of lower unfused segment, while it was highly correlated to pelvic ROM variation (r(2) = 0.78 at medium follow-up). Conclusion. This study underlines the central role of pelvis in balance and motion of the patients before and after surgery.