Cervical Spine Disc Deformation During In Vivo Three-Dimensional Head Movements

Although substantial research demonstrates that intervertebral disc cells respond to mechanical signals, little research has been done to characterize the in vivo mechanical environment in the disc tissue. The objective of this study was to estimate cervical disc strain during three-dimensional head movements. Twenty-nine young healthy adults performed full range of motion flexion/extension, lateral bending, and axial rotation of the head within a biplane radiography system. Three-dimensional vertebral kinematics were determined using a validated model-based tracking technique. A computational model used these kinematics to estimate subject-specific intervertebral disc deformation (C3-4 to C6-7). Peak compression, distraction and shear strains were calculated for each movement, disc level, and disc region. Peak compression strain and peak shear strain were highest during flexion/extension (mean ± 95% confidence interval) (32 ± 3 and 86 ± 8%, respectively), while peak distraction strain was highest during lateral bending (57 ± 5%). Peak compression strain occurred at C4-5 (33 ± 4%), while peak distraction and shear strain occurred at C3-4 (54 ± 8 and 83 ± 11%, respectively). Peak compression, distraction, and shear strains all occurred in the posterior-lateral annulus (48 ± 4, 80 ± 8, and 109 ± 12%, respectively). These peak strain values may serve as boundary conditions for in vitro loading paradigms that aim to assess the biologic response to physiologic disc deformations.