title: Modified techniques to prevent sagittal imbalance after cervical arthroplasty.
abstract: METHODS
  Retrospective study of radiographic outcomes in patients undergoing single level cervical arthroplasty with the Bryan cervical disc (Medtronic Sofamor Danek, Memphis, TN).
  
  
  OBJECTIVE
  This study was designed to determine whether modification of disc insertion angle and insertion depth are effective in preventing segmental or whole cervical kyphosis after arthroplasty.
  
  
  BACKGROUND
  Preservation of segmental motion and aggravation of kyphosis are known challenges after arthroplasty. However, there are currently no proven preventative factors for kyphosis. Change in disc insertion angle was only reported effective for avoiding endplate kyphosis. Additionally, it was difficult to predict the effect of insertion angle on overall sagittal alignment. There have been no studies regarding the correlation between insertion depth and sagittal alignment.
  
  
  METHODS
  A total of 41 patients with single-level arthroplasty were evaluated. Radiologic assessment using neutral cervical radiographs at the long-term was performed. Linear regression analysis between insertion angle, insertion depth, postoperative sagittal alignment, functional spinal unit angle, and shell angle were performed.
  
  
  RESULTS
  Disc insertion angle and insertion depth demonstrated significant negative correlation with the postoperative shell angle. Lordotic insertion angle and an anteriorly located disc led to lordosis in the shell angle. Overall sagittal alignment showed a tendency to correlate with insertion angle. By the result of effect of insertion angle ranging from 3.5 degrees to 7.5 degrees on the sagittal alignment and shell angle, we can hypothesize paradoxical biomechanical stress on the other segments.
  
  
  CONCLUSIONS
  Arthroplasty using the Bryan disc provided a favorable clinical and radiologic outcome thus far; however, we should not underestimate emergent adverse outcomes. To prevent postoperative sagittal imbalance after cervical arthroplasty, intentional modification in disc insertion angle and depth would be helpful. Unexpected compensatory biomechanical loads should be elucidated in future studies.
authors: Department of Neurosurgery; Nanoori Hospital; Seoul, Korea.
authors: Seong
authors: S
authors: Yi
authors: Hyun Chul
authors: HC
authors: Shin
authors: Keung Nyun
authors: KN
authors: Kim
authors: Hyang Kwon
authors: HK
authors: Park
authors: Il Tae
authors: IT
authors: Jang
authors: Do Heum
authors: DH
authors: Yoon
mesh_terms: D000328:Adult; D001178:Arthroplasty / Q000295:instrumentation / Q000379:methods*; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery*; D005260:Female; D006801:Humans; D007738:Kyphosis / Q000000981:diagnostic imaging / Q000517:prevention & control*; D008297:Male; D008875:Middle Aged; D011859:Radiography; D012189:Retrospective Studies