The aging disc: using an ovine model to examine age-related differences in the biomechanical properties of the intralamellar matrix of single lamellae
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To determine the effect of age on the biomechanical properties of the intralamellar matrix of single annulus fibrosus (AF) lamellae.
One intervertebral disc (IVD) was excised from five young (<12 months), five middle-aged (2–4 years) and five older (5–7 years) ovine lumbar spines. From each IVD, a maximum of four single AF lamellae samples were harvested: two from the anterior region and two from the posterior region. Tissues were mounted in a tensile testing apparatus such that tension was applied perpendicular to the orientation of the collagen fibers to isolate the intralamellar matrix. Variables of interest from the stress–strain relationship were: end of toe-region strain and corresponding stress, initial failure stress and strain, and elastic stiffness.
When compared to the middle-aged and old samples, the intralamellar matrix of young AF samples displayed significantly higher stress values at the end of the end of toe-region (p = 0.008) and at initial failure (p = 0.002). Further, the young samples were stiffer than both middle-aged and old samples (p = 0.04).
This study was the first to show that the intralamellar matrix of single AF lamellae is weaker and more compliant in middle-aged and old ovine IVDs compared to young IVDs. These findings are likely a result of the remarkable age-related changes that occur that ultimately weaken the IVD as a whole.