Innovations in adolescent scoliosis treatment

Background Adolescent idiopathic scoliosis (AIS) is the most common spinal deformity in children, occurring in 2-3% of the population. It consists in a 3D deformity of the spine, including vertebral rotation at the apex, a lateral deviation of the spine, and alteration of the sagittal profile. In case of coronal angle exceeding 45°, a vertebral fusion is indicated. On coronal view, the best fusion strategy should correct the main curve including the less number of vertebrae while straightening the adjacent levels. On sagittal view, the best correction technique should avoid proximal junctional kyphosis and restore a normal thoracic kyphosis (TK), which is related to sagittal parameters as pelvic tilt (PT), lumbar lordosis (LL) and pelvic incidence (PI). The equation TK =2 (PT+LL-PI) was previously validated for adolescents. The use of patient-specific rods (PSR) with measured sagittal curves could improve the congruence between the preoperative plan and the achieved alignment. Part 1) Predictive model of lumbar curve Cobb angle below selective fusion for thoracic AIS. Study design: Longitudinal multicenter descriptive study. Patients: 146 adolescents with Lenke 1 or 2 AIS, surgically treated with posterior selective fusion. Methods: A logistic regression-based prediction model was implemented to identify variables associated with lumbar Cobb angle at last follow-up ≥ 10°. Results: Main curve % correction at last follow-up (p = 0.01) and distal curve angle (p = 0.04) were significantly associated with lumbar Cobb angle at last follow-up ≥ 10°: Part 2) Comparison of four correction techniques for posterior spinal fusion in AIS. Purpose: To compare four techniques -in situ bending (ISB), rod derotation (RD), cantilever (C) and posteromedial translation (PMT)- for the correction of spinal thoracic deformity in AIS. Methods: Multicenter retrospective study including 562 thoracic AIS patients. Outcomes: Main curve correction and thoracic kyphosis (TK) restoration at follow-up ≥ 24 months. Results: Multiregression revealed that correction technique did not influence coronal correction. TK increase was higher in the PMT group (average +13°) than in DR (+3°), while ISB (-3°) and cantilever (-13°) resulted in TK decrease (p <0.001). Part 3) Proximal junctional kyphosis (PJK) after AIS surgery. Purpose: To determine if the difference between TK at follow-up (TKFU) and Calculated TK (CTK)= 2 (PT+LL-PI) plays a role in PJK occurrence after AIS surgery. Patients: 570 thoracic AIS who underwent a posterior thoracic fusion from nine centers. The series was separated in two groups: with and without PJK. Methods: CTK = 2(PT + LL-PI). TK Gap was the difference between TKFU and CTK. Multiple logistic regression was utilized to test the impact of TK Gap. Results: TK Gap had a strong significant influence on PJK (p<0.001). Part 4) Can lumbo-pelvic parameters predict TK at all ages? Purpose: to investigate if the equation CTK =2 (PT+LL-PI) correctly predicts TK regardless of age. Methods: Full-spine radiographs of 2599 individuals without spine pathology were assessed from a national registry. CTK and measured TK (MTK) were compared. Results: Average values were: measured TK 45°, CTK 37°. Average TK gap was 8°: 3.6° for 15-34 years, 5.7° under 15 years and it increased progressively after 35 years with a maximum of 19.9° over 80 years. General conclusion: After selective thoracic fusion for AIS, the main modifiable factor influencing uninstrumented lumbar curve was the correction of main curve. The 4 analyzed surgical techniques had similar ability to correct the coronal deformity. PMT was more effective in restoring TK, particularly in hypokyphotic patients. PJK was related to the insufficient TKFU, compared to CTK. The formula TK=2 (PT+LL-PI) yielded moderate accuracy for adolescents and young adults.