Relationship between distal adding-on phenomenon and vertebral body rotation in Lenke classification type 1A-R cases of adolescent idiopathic scoliosis

• Published in: Journal of Spine Research Vol. 13; no. 12; pp. 1265 - 1270
• Main Authors: Kawamura, Ichiro, Yamamoto, Takuya, Tominaga, Hiroyuki, Sakuma, Daisuke, Tokumoto, Hiroto, Sanada, Masato, Taniguchi, Noboru
• Format: Journal Article
• Language: Japanese
• Published: The Japanese Society for Spine Surgery and Related Research 20.12.2022
• Subjects: adolescent idiopathic scoliosis; Distal adding-on; vertebral body rotation
• ISSN: 1884-7137; 2435-1563
• DOI: 10.34371/jspineres.2022-1210

Introduction: In adolescent idiopathic scoliosis of Lenke type 1A, L4 is subdivided into right tilted 1A-R and left tilted 1A-L, with 1A-R considered to have a high risk of distal adding-on (DA). In this study, we investigated factors related to DA in 1A-R, especially vertebral body rotation.Methods: Included in this analysis were 15 consecutive cases with surgical treatment for Lenke 1A-R. Thirteen cases with both preoperative and 2-year postoperative data were analysed, while two cases were excluded due to an image defect or a lack of follow-up. Patients with and without DA were compared for background, SRS-22, preoperative, immediate postoperative, radiographic parameters 2 years after surgery, and vertebral body rotation using CT.Results: Four cases with postoperative DA were observed (DA+group). In this group, UIV rotation at the first standing tended to be left rotation (p=0.07), and the UIV rotation had resolved 2 years after surgery. Right rotation and wedging occurred in the lower intervertebral space of the LIV vertebral body (p=0.02). This suggests the DA may have been caused by a compensatory mechanism of right rotation and lateral flexion of the LIV to resolve the remnants of UIV rotation. Of note, Lenke type 1A-R has a long C-curve and the vertebral body rotation within the main curve tends to be unidirectional. Since there is no inflection point for vertebral body rotation within the fixed range, this may be a compensatory phenomenon to balance body axis rotation.Conclusion: Our results suggest that DA might occur by lateral rotation around LIV to compensate for convolution in the UIV.