Effect of different corrective force directions applied by spinal orthoses on the patients with adolescent idiopathic scoliosis

Abstract

Background Spinal orthoses are commonly prescribed for moderate adolescent idiopathic scoliosis (AIS), however, their effect on three-dimensional correction is not fully investigated. Moreover, the amount of deformity control largely depends on the corrective forces applied via the orthoses, which remains empirically based due to lack of consensus on optimal force application. This study investigated the effects of different corrective force directions exerted by spinal orthoses on the patients with AIS. Methods A retrospective analysis was conducted on 69 subjects. The trunk was segmented into four quadrants using coronal and sagittal planes from a top-down perspective. Each of the left or right posterolateral quadrant (with 90°) was equally subdivided into zones 1–4 from the sagittal to coronal planes. Based on the zone where the resultant corrective force direction fell, the subjects were categorized into Group 1 (zone 1), Group 2 (zone 2), Group 3 (zone 3), or Group 4 (zone 4). The direction of the corrective force was estimated using the modified models of the subjects’ bodies, designed through the computer-aided design and manufacturing system integral to the orthosis fabrication process. The effects of corrective forces in different zones on scoliotic spine were assessed. Results Of the subjects, 17 were in Group 2 and 52 in Group 3, with no subjects meeting the criteria for Groups 1 and 4. Both Groups 2 and 3 showed significant reductions of Cobb angle in the coronal plane and plane of maximum curvature (PMC) following orthosis fitting (p < 0.05). Group 2 displayed a significant decrease > 5º in thoracic kyphosis (p < 0.05), and a more pronounced reduction > 10º in lumbar lordosis compared to Group 3. PMC orientation remained unchanged over time (p > 0.05) but was notably higher in Group 2 after orthosis fitting (p < 0.05). Conclusions Corrective forces, applied by spinal orthoses, in zones 2 and 3 could effectively control the lateral curvature. However, only those in zone 3 did not reduce thoracic kyphosis and did not worsen the deviation of the scoliotic spine from the sagittal plane. Further research is needed to confirm and extend these results. Trial registration: Not available (This is a retrospective study that analyzed the subjects’ spinal images obtained from the database of a local scoliotic center and does not belong to “a clinical trial “ defined by World Health Organization, which is "any research study that prospectively assigns human participants or groups of humans to one or more health-related interventions to evaluate the effects on health outcomes" and is required to be registered in an appropriate registry.)