Impact of pelvic obliquity on coronal alignment in patients with adolescent idiopathic scoliosis.

Abstract

Retrospective study. To investigate pelvic obliquity prevalence and its coronal alignment effects in patients with adolescent idiopathic scoliosis (AIS). Pelvic obliquity observed on standing radiographs could affect coronal alignment; however, its incidence or relationship with coronal alignment remains unclear. Data of 141 patients with AIS (11 men, 130 women; mean age, 14.2years) were retrospectively analyzed. Pelvic obliquity (pelvic coronal obliquity angle (PCOA) value ≥ 3°) was evaluated on standing radiographs; PCOAs were classified into two groups: right-upward and left-upward. Cobb angle and flexibility of proximal thoracic, main thoracic, thoracolumbar/lumbar curve, radiographic shoulder height (RSH), L4 tilt, and coronal balance were measured. Iliac crest and femoral head height differences were measured to evaluate correlations between pelvic obliquity and leg length discrepancy. We compared patients with and without pelvic obliquity according to Lenke classifications. Among 141 patients, 33 (23%) showed pelvic obliquity: 12 were type 1, 3 were type 2, 1 was type 3, 13 were type 5, and 4 were type 6. Right-upward obliquity was observed in 25 patients (76%), all B or C curves; left-upward obliquity was observed in 8 (24%) and most were lumbar modifier A curves. PCOA and iliac crest height difference correlated with femoral head height difference. Among patients with Lenke type 1 with and without pelvic obliquity, those with right-upward pelvic obliquity showed significantly greater absolute RSH values, while those with left-upward pelvic obliquity showed significant smaller absolute RSH values. Among patients with Lenke types 5 and 6, those with pelvic obliquity showed significantly greater L4 tilt absolute values. Pelvic obliquity was frequently observed in patients with AIS, especially lumbar scoliosis. Right-upward pelvic obliquity influenced by lumbar curves promoted shoulder imbalance and left-upward obliquity compensated for shoulder imbalance in Lenke type 1. Level 3.