Biomechanical assessment of the pediatric cervical spine under bending and tensile loading

Study Design. Cadaveric head-neck complexes from pediatric donors aged 2 - 12 years were subjected to a test battery consisting of nondestructive flexion-extension bending, nondestructive tensile step-and-hold tests, and tensile distraction loading to failure. Objective. To characterize the biomechanical response of the pediatric cervical spine in flexion-extension bending, and the response and tolerance of the pediatric cervical spine in tensile distraction loading. Summary of Background Data. Except for a 19th century study on stillborn infants, to our knowledge, there are no published data from human cadaveric studies on the response and tolerance of the pediatric cervical spine. Methods. Ten unembalmed pediatric head-neck complexes with intact ligamentous cervical spines were sectioned from pediatric donors aged 2 - 12 years. Each specimen was potted at the level of T2 and subjected to quasi-static nondestructive flexion-extension bending by a pure moment applied to the neck. Following the flexion-extension testing, each specimen was preconditioned in tension and subjected to a series of nondestructive tensile step-and-hold tests followed by tensile distraction loading to failure using a mini-Bionix MTS machine ( MTS Systems Corp.). Results. The average +/- standard deviation rotational stiffness of the skull - C2, C2 - T2, and skull - T2 spinal segments was 0.72 +/- 0.07, 0.07 +/- 0.02, and 0.04 +/- 0.01 Nm/degree, respectively. Average rotational stiffness was independent of age for the range of pediatric ages tested. In the destructive tensile tests, failure occurred at an average distraction force of 726 +/- 171 N and an average distraction displacement of 20 +/- 3 mm. The average ultimate distraction force recorded for the 2 - 4-year-old specimens ( 595 +/- 143 N) was significantly lower ( P < 0.05) than the corresponding average recorded for the 6 - 12-year-old specimens ( 868 +/- 71 N). Average +/- standard deviation linear stiffness in tensile loading was 34.7 +/- 5.7 N/mm. Pediatric age did not have a statistically significant effect on the average linear stiffness. Conclusions. The current study provides valuable new information on the response and tolerance of the pediatric cervical spine to quasi-static flexion-extension and tensile distraction loading.