Modified techniques to prevent sagittal imbalance after cervical arthroplasty.
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.
Yi
Seong
S
Department of Neurosurgery; Nanoori Hospital; Seoul, Korea.
Shin
Hyun Chul
HC
Kim
Keung Nyun
KN
Park
Hyang Kwon
HK
Jang
Il Tae
IT
Yoon
Do Heum
DH
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