Posterior spinal surgery for adolescent idiopathic scoliosis does not induce compensatory increases in distal adjacent segment motion: a prospective gait analysis study

Background Context: Patients with adolescent idiopathic scoliosis (AIS) perform surprisingly well after spinal correction and fusion. It was previously hypothesized that, during gait, certain mechanisms compensate for the loss in spinal motion. Still, previous studies could not identify such compensatory mechanisms in the lower body. Purpose: This study aims to test the hypothesis of a compensatory increased motion of the distal unfused part of the spine during gait after posterior spinal correction and fusion. Study: This is a prospective gait study. Patients and Methods: Twelve patients with AIS were included. Sets of three VICON skin markers were used to measure the 3D motion of the proximal part of the fusion in relation to the pelvis (PFP) and the distal part of the fusion in relation to the pelvis (DFP). By doing so, PFP represents the motion of the fused and unfused parts of the spine, and DFP represents the motion of the unfused part of the spine. Measurements were performed preoperatively and 3 and 12 months after posterior spinal correction and fusion. Results: Surgery resulted in a decrease in PFP transversal plane range of motion (ROM) (8.3° vs. 5.9°, p=.006). No compensatory increase in the ROM of DFP could be identified. Actually, DFP transversal plane ROM also decreased (8.2° vs. 5.6°, p=.019). No improvement over time was observed when comparing the 3- and 12-month postoperative measurements. Conclusions: The hypothesis of a compensatory increase in motion of the distal unfused segments after spinal fusion for AIS is a much researched and controversial topic. This study is the first to study this hypothesis in such detail during gait and could not demonstrate such increase.