Is Cervical Sagittal Imbalance a Risk Factor for Adjacent Segment Pathomechanics After Multilevel Fusion? Journal Article

Authors: Patwardhan, A. G.; Khayatzadeh, S; Nguyen, N. L.; Havey, R. M.; Voronov, L. I.; Muriuki, M. G.; Carandang, G; Smith, Z. A.; Sears, W.; Lomasney, L. M.; Ghanayem, A. J.
Article Title: Is Cervical Sagittal Imbalance a Risk Factor for Adjacent Segment Pathomechanics After Multilevel Fusion?
Abstract: STUDY DESIGN: A biomechanical study using human spine specimens. OBJECTIVE: To assess whether the presence of cervical sagittal imbalance is an independent risk factor for increasing the mechanical burden on discs adjacent to cervical multilevel fusions. SUMMARY OF BACKGROUND DATA: The horizontal offset distance between the C2 plumbline and C7 vertebral body (C2-C7 SVA) or the angle made with vertical by a line connecting the C2 and C7 vertebral bodies (C2-C7 Tilt Angle), are used as radiographic measures to assess cervical sagittal balance. There is level III clinical evidence that sagittal imbalance caused by kyphotic fusions or global spinal sagittal malalignmernt may increase the risk of adjacent segment pathology. METHODS: Thirteen human cadaveric cervical spines (Occiput-T1; age: 50.6 years; range: 21-67) were tested first in the native intact state and then after instrumentation across C4-C6 to simulate in situ 2-level fusion. Specimens were tested using a previously validated experimental model which allowed measurement of spinal response to prescribed imbalance. The effects of fusion on segmental angular alignments and intradiscal pressures in the C3-C4 and C6-C7 discs, above and below the fusion, were evaluated at different magnitudes of C2-C7 Tilt Angle (or C2-C7 SVA). RESULTS: When compared to the pre-fusion state, in situ fusion across C4-C6 segments required increased flexion angulation and resulted in increased intradiscal pressure at the C6-C7 disc below the fusion in order to accommodate the same increase in C2-C7 Tilt Angle or C2-C7 SVA (P 0.05). The adjacent segment mechanical burden due to fusion became greater with increasing C2-C7 Tilt Angle or SVA. CONCLUSIONS: Cervical sagittal imbalance arising from regional and/or global spinal sagittal malalignment may play a role in exacerbating adjacent segment pathomechanics after multilevel fusion and should be considered during surgical planning. LEVEL OF EVIDENCE: N/A.
Journal Title: Spine
ISSN: 1528-1159; 0362-2436
Publisher: Unknown  
Date Published: 2015
Language: ENG
Notes: LR: 20151203; JID: 7610646; aheadofprint