Facet Joint Bridging in Adolescent-Onset Adult Idiopathic Scoliosis with Thoracolumbar/Lumbar Curves.

Objective: This study aims to comprehend the natural history of adolescent idiopathic scoliosis (AIS) patients and determine risk factors for facet joint bridging in adolescent-onset adult idiopathic scoliosis with thoracolumbar/lumbar (TL/L) curves.

Methods: We included 50 patients with residual AIS with TL/L curves (3 males, 47 females; age 41.5 ± 17.3 years, TL/L Cobb angle 59.4 ± 11.8°). They were >20 years old and diagnosed with AIS during their adolescence. Radiographic parameters were measured, and facet joint bridging was defined from axial computed tomography images.

Results: The sagittal vertical axis (SVA) significantly increased with age (r = 0.71, P < 0.01). Coronal Cobb angle of the TL/L curve, L4 tilt, C7 translation, lumbar lordosis (LL), pelvic incidence-LL, pelvic tilt, and thoracolumbar kyphosis were also correlated to age (P < 0.05). There were significant differences in age, SVA, pelvic incidence-LL, vertebral bridging, facet tropism, and apical vertebral rotation (AVR) between the facet joint bridging group (n = 10) and the non-facet joint bridging group (n = 40). In the multivariate logistic regression analysis, SVA, vertebral bridging, and AVR emerged as notable risk determinants for facet joint bridging. The threshold for facet joint bridging based on SVA was 2.1 cm (area under the curve: 0.801; sensitivity = 90%; specificity = 65%).

Conclusions: This research revealed that large SVA, the presence of vertebral bridging, and large AVR are associated with facet joint bridging in adolescent-onset adult idiopathic scoliosis patients with TL/L curves. The cutoff value for facet joint bridging based on SVA was 2.1 cm.