Aging, vertebral density, and disc degeneration alter the tensile stress‐strain characteristics of the human anterior longitudinal ligament

Abstract

The mechanical properties of the human lumbar anterior longitudinal ligament were investigated, and the influence of aging, disc degeneration, and vertebral bone density on these properties was determined. Tensile mechanical properties of the vertebra-anterior longitudinal ligament-vertebra complex were determined for 16 segments from cadavera of individuals who had been 21-79 years old (mean, 52.1 years) at the time of death. Regional strain patterns associated with three sites across the width and three sites along the length of the anterior longitudinal ligament were measured with use of a video-based motion analysis system. In the young, normal anterior longitudinal ligament, the elastic moduli of the insertion and substance regions of the ligament were similar (approximately 500 MPa). During aging (21-79 years), the elastic modulus of the substance region increased 2-fold, whereas the elastic modulus of the insertion decreased 3-fold; this resulted in an approximately 5-fold difference in elastic modulus between these regions in the older spine. The strength of the bone-ligament complex decreased approximately 2-fold (from 29 to 13 MPa) over this same age range. The outer portion of the anterior longitudinal ligament consistently had the highest peak tensile strains (11.8 +/- 2.7%) in all of the specimens examined. Preparations with nondegenerated discs and high bone density were significantly stronger (66%) and failed in the ligament substance; in contrast, segments from older individuals with degenerated discs and lower bone density failed in the ligament insertion regions.

Failure Properties of Cervical Spinal Ligaments Under Fast Strain Rate Deformations

“…14 -16 Biomechanical studies on the failure in human lumbar spinal ligaments are also rare. [17][18][19] To model failure of ligaments in an impact, ranging from falls to automobile crashes or aircraft ejections, it is imperative to obtain information about the deformation and failure responses of the ligaments at comparable fast strain rates.To the authors' knowledge, only one published study examines rate-sensitive failure properties of cervical spinal ligaments (anterior longitudinal ligament and ligamentum flavum) at deformation rates ranging from 8.89 to 2500 mm/s. 20 There are several gaps in the existing study.…”

Failure Properties and Damage of Cervical Spine Ligaments, Experiments and Modeling

“…In our study, an age-related decrease in the failure load, failure elongation, and stiffness was observed for all three ligaments. To the authors' knowledge, there are only data for the lumbar ALL in the study by Neumann [29], that analyzed the age effect and showed the same tendency of the failure load and failure stress decreasing with age. The age effect has been reported for the LF [30], and our study showed only a 2-time decrease in the LF failure properties, as compared to a 4-time decrease in this study.…”

“…In a few studies, age related changes of isolated spine ligaments have been analyzed (lumbar ALL [29] and LF [30]). …”

“…The impacts of tissue (re)freezing [31], preconditioning [32,33], and donor age [13,29,34] have already been discussed. The inconsistencies in the measured properties complicate the next step of the experimental procedure, which is the constitutive modeling of cervical spine ligaments.…”

Developmental biomechanics of the cervical spine: Tension and compression

“…Tensile mechanics of the adult spine has been evaluated in a number of studies (Panjabi et al, 1978;Cusick et al, 1982;Myklebust et al, 1988;Neumann et al, 1994;Myers and Winkelstein, 1995;Yoganandan et al, 1996), but only sparsely investigated in the immature populace. Miller and Skogland (1982) found that the adolescent spine is 1-10 times more flexible than the adult spine depending upon the applied load.…”