Methods: Retrospective study of 120 patients (223 fusion levels) who underwent ACDF between 2016 and 2021. Spacer types included structural allografts, PEEK, titanium, and ceramic cages. Radiographic measurements of subsidence were obtained from immediate (≤8 weeks) and long-term (≥6 months) postoperative lateral cervical radiographs. Multivariable linear regression was used to assess the association between spacer type and subsidence, adjusting for patient demographics, surgical levels, smoking history, and osteopenia. Results: The mean age of patients was 53.6±10.9 years and 41.7% were male; 47.5% had a smoking history and 20.8% had osteopenia. There were 38 one-level (31.7%), 61 two-level (50.8%), and 21 three-level fusions (17.5%). Spacer distribution included 62 structural allografts (51.7%), 27 PEEK (22.5%), 20 titanium (16.7%), and 11 ceramic (9.2%) cages. On multivariable analysis, PEEK cages were associated with significantly less anterior subsidence (β=−0.972, p <0.001) and posterior subsidence (β=−0.666, p=0.001) compared to allografts, and greater preservation of segmental lordosis (β=1.393, p=0.024). No significant differences in subsidence were found between titanium, ceramic, and allograft spacers. Conclusions PEEK cages showed reduced subsidence and better preservation of cervical lordosis compared to structural allografts, while titanium and ceramic cages did not differ significantly from structural allografts. These results suggest that PEEK cages may help minimize subsidence-related complications and improve outcomes.

The present review presents basic concepts of blood rheology related to vascular diseases. Blood flow in large arteries is dominated by inertial forces exhibited at high flow velocities, while viscous forces (i.e., blood rheology) play an almost negligible role. When high flow velocity is compromised by sudden deceleration as at a bifurcation, endothelial cell dysfunction can occur along the outer wall of the bifurcation, initiating inflammatory gene expression and, through mechanotransduction, the cascade of events associated with atherosclerosis. In sharp contrast, the flow of blood in microvessels is dominated by viscous shear forces since the inertial forces are negligible due to low flow velocities. Shear stress is a critical parameter in microvascular flow, and a force-balance approach is proposed for determining microvascular shear stress, accounting for the low Reynolds numbers and the dominance of viscous forces over inertial forces. Accordingly, when the attractive forces between erythrocytes (represented by the yield stress of blood) are greater than the shear force produced by microvascular flow, tissue perfusion itself cannot be sustained, leading to capillary loss. The yield stress parameter is presented as a diagnostic candidate for future clinical research, specifically, as a fluid dynamic biomarker for microvascular disorders. The relation between the yield stress and diastolic blood viscosity (DBV) is described using the Casson model for viscosity, from which one may be able determine thresholds of DBV where the risk of microvascular disorders is high.
Accounting ; Arteries ; Atherosclerosis ; Blood Viscosity ; Capillaries ; Deceleration ; Endothelial Cells ; Erythrocytes ; Gene Expression ; Hemorheology ; Hydrodynamics ; Microvascular Angina ; Microvessels ; Perfusion ; Rheology ; Vascular Diseases ; Viscosity