Influence of the shape of the fused spine on the occurrence of proximal junctional kyphosis after posterior spinal fusion for adolescent idiopathic scoliosis.

Background: Proximal Junction Kyphosis (PJK) are mechanical complications of surgical treatment of adolescent idiopathic scoliosis (AIS). It occurs in approximately 7 to 46% of cases. We formulated the hypothesis that the postoperative sagittal profile have an impact on the occurrence of PJK PATIENTS AND

Methods: In our retrospective study 202 pediatric patients aged < 18 years who underwent posterior fusion including the thoracic spine for AIS at a single center between 2013 and 2021 were evaluated (Mean age 15.0 years, 89% female). Biplanar radiographs were analyzed preoperatively, postoperatively and at ≥2 years follow-up. The radiographic parameters analyzed were: Cobb angle, intermediate thoracic kyphosis T5-T9 and distal thoracic kyphosis T9-T12, lumbar lordosis L1-S1 (LL) divided into proximal L1-L4 (PLL) and distal L4-S1 lordosis (DLL), Proximal Junctional kyphosis Angle, Upper Instrumented Vertebrae (UIV) and Lower Instrumented Vertebrae (LIV) The primary outcome was radiographic PJK at final follow-up.

Results: The risk of PJK was significantly associated with an UIV below T2 (OR = 3.11; CI [1.56; 6.18], p = 0.002), with an LIV below L3 (OR = 2.11; CI [1.08;4.52], p = 0.044), with a post-operative T5T12 kyphosis less than 10 ° (OR = 2.8; CI [1.16;6.78], p = 0.035), post-operative distal kyphosis less than 15 ° (OR = 2.13; CI [1.05;4.35], p = 0.047) and an LL greater than the theoretical lordosis (OR = 2.09; CI [1.05;4.17], p = 0.048). At 2 years follow-up, there was a significant relationship between postoperative PLL and proximal junction angle (Pearson Correlation Coefficient R=-0.197, p = 0.005).

Conclusions: PJK is a common complication after posterior fusion. In our study, UIV below T2 and LIV below L3 are associated with the risk of PJK. Postoperative sagittal alignment is associated with the risk of PJK, particularly a T5T12 kyphosis less than 10 ° and an LL greater than the theoretical lordosis. Proximal junction angle was proportional to the PLL. Therefore, it seems important to respect the most physiological posterior alignment to reduce incidence of PJK. Methods: IV; Retrospective study.