X-Stop® implantation effectively limits segmental lumbar extension in-vivo without altering the kinematics of the adjacent levels

Abstract

AIM: To evaluate the in-vivo three-dimensional (3D) vertebral kinematics of the implanted and adjacent segments after implantation of the interspinous process distracting (ISP) device during various functional activities. MATERIAL AND METHODS: Eight patients with lumbar spinal stenosis (LSS) scheduled for X-Stop® surgery were recruited. Prior to surgery, patients were scanned with computed tomography/ magnetic resonance imaging (CT/MRI) in order to construct 3D L2 to S1 vertebral models. The lumbar spines of the patients were then imaged using two fluoroscopes while they performed seven functional activities before and after X-Stop® surgeries. The in-vivo 3D vertebral positions were determined in the dual fluoroscopic images using an established 2D-3D matching method. The vertebral 3D ranges of motion (ROM) of the implanted and cranial-caudal adjacent levels were then measured. RESULTS: Primary ROMs of the implanted segments were significantly decreased (p<0.05) by 50.2% only at torso extension, from preoperative 2.5±1.4° to postoperative 1.1±0.5°, but not significantly (p>0.05) at flexion, twisting and lateral bending. Primary ROM and the coupled translations and rotations of the implanted and the adjacent levels were not significantly changed during each posture. CONCLUSION: X-Stop® implantation reduced the in-vivo range of extension by 50.2% at the implanted segment without disturbing 3D kinematics at the adjacent segments.