A Novel Model of Sacral Obliquity, Iliac Obliquity, and Hip Obliquity in Adolescent Idiopathic Scoliosis

Objective To propose and validate a novel model to explore the potential compensatory mechanism of sacral obliquity and pelvic obliquity in coronal balance. Summary of Background Data Sacral obliquity and pelvic obliquity are common phenomena in adolescent idiopathic scoliosis (AIS). However, their compensatory mechanisms in coronal balance remain unclear. Methods A total of 569 AIS patients were recruited. Coronal pelvic and lower limb parameters, including sacral obliquity (SO), iliac obliquity (IO), and hip obliquity (HO), were measured. Coronal spinal parameters, such as coronal distance (CD), clavicle angle (CA), thoracic curve (T), thoracolumbar/lumbar curve (TL/L), and tilt angle of L2∼L5, were measured. Correlation analysis was performed. Results The mean values of SO, IO, and HO were 3.34±2.81°, 1.40±2.04°, and 0.82±1.79°, respectively. The largest correlation coefficients with SO were L5 and IO (r=0.725, 0.701). The largest correlation coefficients with IO were SO and HO (r=0.701, 0.801). The largest correlation coefficients with HO were SO and IO (r=0.566, 0.801). Conclusion SO, IO, and HO have different implications for coronal balance, and their magnitude and direction can be deduced from the novel model. These parameters could be used to evaluate the compensation of the pelvis and lower limbs in AIS. In the coronal position, the pelvis and lower limbs extend the spinal sequence, similar to vertebrae and intervertebral discs.