Static and dynamic bending responses of the human cervical spine

The quasi-static and dynamic bending responses of the human mid-lower cervi cal spine were determined using cadaver intervertebral joints fixed at the base to a six-axis load cell. Flexion bending moment was applied to the sup erior end of the specimen using an electrohydraulic piston. Each specimen w as tested under three cycles of quasi-static load-unload and one high-speed dynamic load. A total of five specimens were included in this study. The m aximum intervertebral rotation ranged from 11.0 to 15.4 deg for quasi-stati c tests and from 22.9 to 34.4 deg for dynamic tests. The resulting peak mom ents at the center of the intervertebral joint ranged from 3.8 to 6.9 Nm fo r quasi-static tests and from 14.0 to 31.8 Nm for dynamic tests. The quasi- static stiffness ranged from 0.80 to 1.35 Nm/deg with a mean of 1.03 Nm/deg (+/-0.11 Nm/deg). The dynamic stiffness ranged from 1.08 to 2.00 Nm/deg wi th a mean of 1.50 Nm/deg (+/-0.17 Nm/deg). The differences between the two stiffnesses were statistically significant (p < 0.01). Exponential function s were derived to describe the quasi-static and dynamic moment-rotation res ponses. These results provide input data for lumped-parameter models and va lidation data for finite element models to better investigate the biomechan ics of the human cervical spine.