Cervical Vertebral Strain Measurements Under Axial and Eccentric Loading

Abstract

The mid to lower cervical spine is a common site for compression related injury. In the present study, we determined the patterns of localized strain distribution in the anterior aspect of the vertebral body and in the lateral masses of lower cervical three-segment units. Miniature strain gages were mounted to human cadaveric vertebrae. Each preparation was line-loaded using a knife-edge oriented in the coronal plane that was moved incrementally from anterior to posterior to induce compression-flexion or compression-extension loading. Uniform compressive loading and failure runs were also conducted. Failure tests indicated strain shifting to "restabilize" the preparation after failure of a component. Under these various compressive loading vectors, the location which resulted in the least amount of deformation for a given force application (i.e., stiffest axis) was quantified to be in the region between 0.5- 1.0 cm anterior to the posterior longitudinal ligament. The location in which line-loading produced no rotation (i.e., balance point) was in this region; it was also close to where the vertebral body strains change from compressive to tensile. Strain values from line loading in this region produced similar strains as recorded under uniform compressive loading, and this was also the region of minimum strain. The region of minimum strain was also more pronounced under higher magnitudes of loading, suggesting that as the maximum load carrying capacity is reached the stiffest axis becomes more well defined.

Deduction of Spinal Loading from Vertebral Body Surface Strain Measurements

“…Our surface strain results are consistent with the literature on lumbar vertebral body surface strains and they were found to result from predictable loading patterns [6,19,60]. Frei et al found axial principal strains of 700-to-840 microstrain for 500 N applied load compared with 582 microstrain (mean) for 400 N applied in the present study.…”

“…This is a trivial task for traditional engineering materials with known geometry, but the application of these methods to the biologic tissues of the lumbar spine is novel. Surface strains on vertebrae have been measured previously [6,19,60]; however, these strains have not been directly correlated with spinal loading and equated with disc health. We have measured distinct relationships between vertebral body surface strain (principal strains) and spinal segment loading (force/moment).…”

Validation of a clinical finite element model of the human lumbosacral spine

“…This study did not quantify the level or degree of validation, a process used in the present study. Furthermore, unlike cervical spine experiments wherein strain data on vertebral body and facet joint have been measured under different loading conditions [26], in the lumbosacral spine, moment-rotation curves appear to be the only response finite element modelers have used for validation. Therefore, it is critical to match these curves as closely as possible during the validation process.…”

Sirsasana (headstand) technique alters head/neck loading: Considerations for safety

“…The discs and their adjacent vertebral segments have articulating surfaces that are designed to absorb and distribute force under compressive loads. Loads transfer anteriorly through the vertebral body and disc and posteriorly through the facets and lateral masses (Pintar, 1995). There are bending moments and shear forces that accompany various movements and create increased mechanical challenges to the spine.…”