title: Corner osteotomy: a modified pedicle subtraction osteotomy for increased sagittal correction in the lumbar spine.
abstract: BACKGROUND
  Sagittal imbalance is a spine deformity with multifactorial etiology, associated with severe low back pain and gait disturbance that worsen deeply patients' quality of life. The amount of correction achievable through PSO is limited by the height of the resection of the posterior wall, causing a ceiling of segmental correction of 30-35°. The aim of this study is to describe and preliminarily evaluate the results of an alternative technique, corner osteotomy (CO), that can increase the amount of correction.
  
  
  METHODS
  From March 2012, every patient examined in our Division, diagnosed with sagittal imbalance to be treated with PSO, underwent CO and fusion. This technique consists in removing the posterior vertebral arch, the pedicle and the posterior-superior corner of the vertebral body; the inferior endplate of the vertebra above is prepared and the superior adjacent disc removed to obtain, when closing the osteotomy, a direct interbody fusion. Ten patients undergoing CO were compared with 20 patients undergoing PSO regarding spinopelvic parameters, operative variables, complications and degree of correction.
  
  
  RESULTS
  Patients undergoing CO obtained higher lordotic angle at the osteotomy than patients undergoing PSO (36.6° ± 8.2° vs 16.5° ± 9.5°, p < 0.001) and had lower postoperative PT and SVA and higher average increase in lordosis. Complications were similar between groups. A trend toward longer surgical time, greater bleeding and higher transfusion rate was observed in the CO group, though this finding could be related to higher complexity of cases or incidence of associated anterior approach.
  
  
  CONCLUSIONS
  Corner osteotomy technique was more effective than the PSO in increasing segmental and lumbar lordosis with modest increase in blood loss and similar complication rate. The CO technique, in addition, proved a good reproducibility. Further studies with larger populations should confirm these preliminary results.
authors.affiliation: IVth Spine Surgery Division, IRCSS Istituto Ortopedico Galeazzi, Via Riccardo Galeazzi, 4, 20161, Milan, Italy, pberjano@gmail.com.
authors.forename: Pedro
authors.initials: P
authors.lastname: Berjano
authors.forename: Matteo
authors.initials: M
authors.lastname: Pejrona
authors.forename: Marco
authors.initials: M
authors.lastname: Damilano
authors.forename: Riccardo
authors.initials: R
authors.lastname: Cecchinato
authors.forename: Maryem-Fama Ismael
authors.initials: MF
authors.lastname: Aguirre
authors.forename: Claudio
authors.initials: C
authors.lastname: Lamartina
mesh_terms: D000368:Aged; D016063:Blood Loss, Surgical; D001803:Blood Transfusion / Q000706:statistics & numerical data; D005260:Female; D065386:Historically Controlled Study; D006801:Humans; D007738:Kyphosis / Q000601:surgery*; D008141:Lordosis / Q000601:surgery; D008159:Lumbar Vertebrae / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D061646:Operative Time; D010027:Osteotomy / Q000379:methods*; D012189:Retrospective Studies; D013123:Spinal Fusion