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PubMed1991

Strength and motion analysis of the human head-neck complex.

This study was conducted to correlate the pathology of the experimentally tested human cervical spine with biomechanical strength information and localized temporal movements of the various spinal components. Eight fresh human cadaveric head-neck complexes were subjected to compressive forces at a quasistatic rate of 2.5 mm/s until failure. Biomechanical force and deflection data were collected. Localized kinematic data as a function of time were obtained from retroreflective targets placed in the anterior and posterior regions of the vertebral body, facet column, and spinous process at every level of the cervical spine. The specimens were radiographed prior to, during, and following failure; they were then deep frozen at the level of failure to preserve the localized tissue deformations. Specimens underwent computed tomography scanning and sequential sectioning using a cryomicrotome. The failure forces and compressions ranged from 1.3 to 3.6 kN and 0.9 to 3.7 cm. Stiffness and energy-absorbing characteristics ranged from 96.1 to 220.5 kN/m and 12.2 to 53.6 J, respectively. Varying localized temporal motions among spinal components were found to exist at all levels of the head-neck complex. With increasing compressive loads, the specimen components reorient as demonstrated by kinematic changes in the spinal elements; failure was imminent when the structure no longer resisted any further increase in external load. The study demonstrated that an evaluation of the human head-neck complex in a relaxed state, as in clinical observations on posttraumatic radiographs, is often different from that documented immediately following the traumatic insult; this underscores the importance of conducting controlled in vitro investigations to determine the injury biomechanics of the human cervical spine.

Aged↗

PubMed1989

Stiffness and strain energy criteria to evaluate the threshold of injury to an intervertebral joint.

This study is focused to evaluate the threshold of injury to an intervertebral joint based on its mechanical response. The load-deflection behavior of the intervertebral joint indicated non-linear and sigmoidal characteristics with continuously changing stiffness (a measure of the ability to withstand external force). The load corresponding to the point of zero stiffness was identified, according to the classical theories of mechanics, as the maximum load carrying capacity. Further, the initiation of trauma was defined to occur at the point on the load-deflection curve at which the stiffness begins to decrease for the first time. The load, stiffness and energy absorbing capabilities of normal and degenerated intervertebral joints at the initiation of trauma was determined. Axial compressive load experiments were conducted on nine intervertebral joints of fresh human male cadavers and the resulting load-deflection responses were transformed into stiffness-deflection responses using the derivative principle. Energy characteristics were also derived. Load, stiffness and energy at the initiation of trauma were found to be 9.0 kN, 2850 N mm-1, and 10.2 J for normal and 4.4 kN, 1642 N mm-1, and 5.8 J for degenerated segments, respectively. The load and energy values at failure were 11.0 kN, and 18.0 J for normal and 5.3 kN and 5.7 J for degenerated intervertebral joints, respectively.

Biomechanical Phenomena↗