title: The Safe Correction Angle of Osteotomy at T12 and L1 for Ankylosing Spondylitis Kyphosis: Patients With 2-level Osteotomy.
abstract: METHODS
  This is a retrospective clinical study.
  
  
  OBJECTIVE
  To investigate the correction angle and safety of the spinal osteotomy at the T12 or L1 vertebra.
  Monosegment subtraction osteotomy cannot effectively correct severe kyphosis in ankylosing spondylitis (AS), generally 2-level spinal osteotomy was taken for achieving expected correction. According to literature, the T12 or L1 were usually taken as the upper spinal osteotomy vertebra. Because of the canalis vertebralis at the T12 and L1 were spinal cord and medullary cone, so the spinal osteotomy at the T12 or L1 vertebra were more dangerous than at lower level. The correction angle and safety of the spinal osteotomy at the T12 or L1 vertebra have not yet been reported.
  
  
  METHODS
  From July 2009 to 2014, 33 patients in our department with severe AS kyphosis underwent 2-level pedicle subtraction osteotomy were studied. Preoperative and postoperative relevant parameters and complications were recorded.
  
  
  RESULTS
  The upper spinal osteotomy was taken at the T12 vertebra for 10 patients. The upper spinal osteotomy was taken at the L1 vertebra for 23 patients. The mean amount of correction of T12 and L1 was 26.230 and 27.952 degrees, respectively. All patients could walk with orthophoria and lie horizontally postoperatively. No deadly vascular and neurological lesion occurred.
  
  
  CONCLUSIONS
  Performing pedicle subtraction osteotomy at T12 and L1 can safely achieve a mean correction of 26.230 and 27.952 degrees, respectively. Two-level osteotomy was safely and advocated for correcting severe AS kyphosis.
  
  
  METHODS
  Level III.
authors.affiliation: *Department of Orthopaedics, Kowloon Hospital of Shanghai Jiaotong University School of Medicine, Suzhou, Jiangsu Province, PR China †Department of Orthopaedics, Chines People's Liberation Army General Hospital, Beijing.
authors.forename: Chao
authors.initials: C
authors.lastname: Liu
authors.forename: Wen
authors.initials: W
authors.lastname: Yu
authors.forename: Guoquan
authors.initials: G
authors.lastname: Zheng
authors.forename: Yue
authors.initials: Y
authors.lastname: Guo
authors.forename: Kai
authors.initials: K
authors.lastname: Song
authors.forename: Xiangyu
authors.initials: X
authors.lastname: Tang
authors.forename: Zheng
authors.initials: Z
authors.lastname: Wang
authors.forename: Yan
authors.initials: Y
authors.lastname: Wang
authors.forename: Yonggang
authors.initials: Y
authors.lastname: Zhang
mesh_terms: D001696:Biomechanical Phenomena; D016063:Blood Loss, Surgical; D006801:Humans; D007738:Kyphosis / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D010027:Osteotomy; D011183:Postoperative Complications / Q000209:etiology; D013167:Spondylitis, Ankylosing / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D013904:Thoracic Vertebrae / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*