Effect of fiber distribution and realignment on the nonlinear and inhomogeneous mechanical properties of human supraspinatus tendon under longitudinal tensile loading

Abstract

Tendon exhibits nonlinear stress-strain behavior that may be partly due to movement of collagen fibers through the extracellular matrix. While a few techniques have been developed to evaluate the fiber architecture of other soft tissues, the organizational behavior of tendon under load has not been determined. The supraspinatus tendon (SST) of the rotator cuff is of particular interest for investigation due to its complex mechanical environment and corresponding inhomogeneity. In addition, SST injury occurs frequently with limited success in treatment strategies, illustrating the need for a better understanding of SST properties. Therefore, the objective of this study was to quantitatively evaluate the inhomogeneous tensile mechanical properties, fiber organization, and fiber realignment under load of human SST utilizing a novel polarized light technique. Fiber distributions were found to become more aligned under load, particularly during the low stiffness toe-region, suggesting that fiber realignment may be partly responsible for observed nonlinear behavior. Fiber alignment was found to correlate significantly with mechanical parameters, providing evidence for strong structure-function relationships in tendon. Human SST exhibits complex, inhomogeneous mechanical properties and fiber distributions, perhaps due to its complex loading environment. Surprisingly, histological grade of degeneration did not correlate with mechanical properties. Keywords: collagen fiber realignment; nonlinear tendon mechanics; structure-function; polarized light; supraspinatus tendon Tendon mechanical behavior is nonlinear and is characterized by an initial low stiffness toe-region, followed by a high stiffness linear-region. This nonlinearity is critical to provide the joint with functional range of motion (low stiffness), as well as stability and force transmission (high stiffness). Restoration of both the nonlinear response and linear stiffness are also crucial for restoring function following repair after injury. The toe-region is commonly associated with the gradual recruitment of crimped collagen fibers and fiber realignment due to interaction between the fibers and extrafibrillar matrix, while in the linear-region, all collagen fibers are believed to be taut and supporting load.

Biaxial mechanics and inter‐lamellar shearing of stem‐cell seeded electrospun angle‐ply laminates for annulus fibrosus tissue engineering

“…[27][28][29] This was then used to calculate stretch in the fiber direction (fiber stretch). In this process, the fiber direction is defined by the initial direction of scaffold fiber alignment (a o ) through the vector:…”

Biaxial tensile testing and constitutive modeling of human supraspinatus tendon

“…Rather than simply running parallel to the tendon's longitudinal axis, collagen fibers follow wide angular distributions that vary across the tendon length and thickness [4][5][6]. The longitudinal tensile modulus, tensile failure stress, and compressive stiffness also exhibit regional variations [6][7][8][9], suggesting a strong relationship between the local structure and function of the supraspinatus tendon. Such complexity likely reflects the multiaxial mechanical environment of the supraspinatus tendon resulting from its position over the humeral head, contact with the acromion, anatomical confluence with the infraspinatus tendon, and the wide range of shoulder motion [10][11][12][13][14][15][16].…”

Effect of partial-thickness tear on loading capacities of the supraspinatus tendon: a finite element analysis

“…We chose this study because it was the only one reporting ultimate failure on complete tendons attached to the greater tubercle, while other studies used morphologically split tendons (Matsuhashi et al 2014) or dissected tendon samples detached from bone (Lake et al 2009(Lake et al , 2010. We observed however a great difference in failure stresses reported by these studies, which could be ascribed to different methods of sample preparation, testing procedure and natural property variation in biological soft tissues.…”

“…We identified the material parameters µ, α, β and w 0 using experimental data from human cadaveric supraspinatus tendons (Lake et al 2009(Lake et al , 2010. Stress-strain curves from a slack position up to failure were available both in the longitudinal and in the transverse direction.…”