Tensile Failure Properties of the Perinatal, Neonatal, and Pediatric Cadaveric Cervical Spine

Study Design. Biomechanical tensile testing of perinatal, neonatal, and pediatric cadaveric cervical spines to failure. Objective. To assess the tensile failure properties of the cervical spine from birth to adulthood. Summary of Background Data. Pediatric cervical spine biomechanical studies have been few due to the limited availability of pediatric cadavers. Therefore, scaled data based on human adult and juvenile animal studies have been used to augment the limited pediatric cadaver data. Despite these efforts, substantial uncertainty remains in our understanding of pediatric cervical spine biomechanics. Methods. A total of 24 cadaveric osteoligamentous head-neck complexes, 20 weeks gestation to 18 years, were sectioned into segments (occiput-C2 [O-C2], C4-C5, and C6-C7) and tested in tension to determine axial stiffness, displacement at failure, and load-to-failure. Results. Tensile stiffness-to-failure (N/mm) increased by age (O-C2: 23-fold, neonate: 22 +/- 7, 18 yr: 504; C4-C5: 7-fold, neonate: 71 +/- 14, 18 yr: 509; C6-C7: 7-fold, neonate: 64 +/- 17, 18 yr: 456). Load-to-failure (N) increased by age (O-C2: 13-fold, neonate: 228 +/- 40, 18 yr: 2888; C4-C5: 9-fold, neonate: 207 +/- 63, 18 yr: 1831; C6-C7: 10-fold, neonate: 174 +/- 41, 18 yr: 1720). Normalized displacement at failure (mm/mm) decreased by age (O-C2: 6-fold, neonate: 0.34 +/- 0.076, 18 yr: 0.059; C4-C5: 3-old, neonate: 0.092 +/- 0.015, 18 yr: 0.035; C6-C7: 2-fold, neonate: 0.088 +/- 0.019, 18 yr: 0.037). Conclusion. Cervical spine tensile stiffness-to-failure and load-tofailure increased nonlinearly, whereas normalized displacement at failure decreased nonlinearly, from birth to adulthood. Pronounced ligamentous laxity observed at younger ages in the O-C2 segment quantitatively supports the prevalence of spinal cord injury without radiographic abnormality in the pediatric population. This study provides important and previously unavailable data for validating pediatric cervical spine models, for evaluating current scaling techniques and animal surrogate models, and for the development of more biofidelic pediatric crash test dummies.