Experimental flexion/extension data corridors for validation of finite element models of the young, normal cervical spine.

Finite element (FE) modeling is an important tool for studying the cervical spine in normal, injured and diseased conditions. To understand the role of mechanical changes on the spine as it goes from a normal to a diseased or injured state, experimental studies are needed to establish the external response of young, normal cervical spinal segments compared to injured or degenerated cervical spinal segments under physiologic loading. It is important to differentiate injured or degenerated specimens from young, normal specimens to provide accurate experimental results necessary for the validation of FE models. This study used seven young, normal fresh adult cadaver cervical spine segments C2-T1 ranging in age from 20 to 51 years. Prior to testing, the spines were graded in three ways: specimen quality, facet degeneration and disc degeneration. Spine segments were tested in flexion/extension, and the range of loads applied to the specimens was 0.33, 0.5, 1.0, 1.5 and 2.0 Nm. These loads resulted in rotations in the direction of loading as the primary response to loading. In general, results for young, normal specimens showed greater flexibility in flexion and less flexibility in extension than results previously reported in the literature. The flexion/extension curves are asymmetric with a greater magnitude in flexion than in extension. These experimental results will be used to validate FE models of young, normal cervical spines.