An in vitro evaluation of sagittal alignment in the cervical spine after insertion of supraphysiologic lordotic implants
Cervical spine malalignment can develop as a consequence of degenerative disc disease or following spinal surgery. When normal sagittal alignment of the spine is disrupted, further degeneration may occur adjacent to the deformity. The purpose of this study was to investigate changes in lordosis and sagittal alignment in the cervical spine after insertion of supraphysiologic lordotic implants.
Eight cadaveric cervical spines (Occiput-T1) were tested. The occiput was free to translate horizontally and vertically but constrained from angular rotation. The T1 vertebra was rigidly fixed with a T1 tilt of 23°. Implants with varying degrees of lordosis were inserted starting with single-level constructs (C5–C6), followed by two (C5–C7), and three-level (C4–C7) constructs. Changes in sagittal alignment, Occ-C2 angle, cervical lordosis (C2–7), and segmental lordosis were measured.
Increasing cage lordosis led to global increases in cervical lordosis. As implanted segmental lordosis increased, the axial levels compensated by decreasing in lordosis to maintain horizontal gaze. An increase in cage lordosis also corresponded with larger changes in SVA.
Reciprocal compensation was observed in the axial and sub-axial cervical spine, with the Occ-C2 segment undergoing the largest compensation. Adding more implant lordosis led to larger reciprocal changes and changes in SVA. Implants with supraphysiologic lordosis may allow for additional capabilities in correcting cervical sagittal plane deformity, following further clinical evaluation.
KeywordsCervical spine Biomechanics Cervical lordosis Cervical sagittal alignment Horizontal gaze Supraphysiologic lordotic interbody implants
Compliance with ethical standards
Conflict of interest
Dr. Blaskiewicz is a consultant for NuVasive, Inc., from which he has also received clinical/research support for the study. Dr. Mundis is a consultant and receives royalties for NuVasive, Inc. Dr. Han is a consultant and receives royalties for NuVasive, Inc. Dr. Turner and Mr. Harris are employees of NuVasive, Inc., and own stock in the company.
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