Males have Inferior Achilles Tendon Material Properties Compared to Females in a Rodent Model

Abstract

The Achilles tendon is the most commonly ruptured tendon in the human body. Numerous studies have reported incidence of these injuries to be upwards of five times as common in men than women. Therefore, the objective of this study was to investigate the sex- and hormone-specific differences between Achilles tendon and muscle between female, ovariectomized female (ovarian hormone deficient), and male rats. Uninjured tissues were collected from all groups for mechanical, structural, and histological analysis. Our results showed that while cross-sectional area and failure load were increased in male tendons, female tendons exhibited superior tendon material properties and decreased muscle fiber size. Specifically, linear and dynamic moduli were increased while viscoelastic properties (e.g., hysteresis, percent relaxation) were decreased in female tendons, suggesting greater resistance to deformation under load and more efficient energy transfer, respectively. No differences were identified in tendon organization, cell shape, cellularity, or proteoglycan content. Additionally, no differences in muscle fiber type distribution were observed between groups. In conclusion, inferior tendon mechanical properties and increased muscle fiber size may explain the increased susceptibility for Achilles tendon injury observed clinically in men compared to women.

Aging leads to inferior Achilles tendon mechanics and altered ankle function in rodents

“…Samples (n=11–12/group/protocol) were tested to evaluate quasistatic properties (ramp to failure with optical strain tracking) or viscoelastic, dynamic, and fatigue properties (stress relaxation, low-strain frequency sweep, load-controlled fatigue testing) using one of two previously described protocols (Freedman et al, 2016; Pardes et al, 2016). Briefly, the Achilles tendon was maintained perpendicular to the foot to mimic in vivo loading and submerged in a 1X PBS bath at 37°C.…”

“…Gastrocnemius-soleus muscle mid-belly (n=7/group) was excised at the time of sacrifice, flash frozen, and stored at −80°C until axial cryosectioning at 10μm, as described previously (Pardes et al, 2016). Immunofluorescence imaging was performed on sections stained for laminin and myosin heavy chain (MyHC) types 1, 2a, and 2b.…”

“…Animal models offer a highly controlled system to study Achilles tendon biomechanics, and have demonstrated a potential explanation for the contrasting incidence in Achilles tendon rupture across sex (Pardes et al, 2016). However, it is unknown if aging also alters Achilles tendon mechanical behavior that could help explain the particularly high frequency of Achilles tendon ruptures in middle-aged men.…”

Mechanical, histological, and functional properties remain inferior in conservatively treated Achilles tendons in rodents: Long term evaluation

“…Uninjured age-matched animals (n=10) allowed only cage activity were used as controls. Animals were euthanized 16-weeks post-injury (mass: 618±59g) (CO 2 inhalation), and tissues were harvested for ex vivo assays as described previously (Freedman et al, 2016a; Freedman et al, 2016b; Pardes et al, 2016). …”

“…Full-length images of SAF-O stained tendon sections were obtained by stitching of several smaller images (FOV: 2.14 × 1.61mm) and were evaluated for GAG intensity (1, blue; 2, light red; 3, light to dark red). Additionally, the gastrocnemius/soleus muscle complex was harvested, sectioned axially (10 μm), and stained for antibodies against laminin (L9393, Sigma Aldrich) and myosin heavy chain (MyHC) types 1, 2a, and 2b (type 1: BA-D5; type 2a: SC-71; type 2b: BF-F3), as described (Fryhofer et al, 2016; Pardes et al, 2016). The anti-MyHC antibodies were obtained from the Developmental Studies Hybridoma Bank, created by the National Institute of Child Health and Development of the National Institutes of Health (Schiaffino, S; University of Iowa, Department of Biology; Iowa City, IA).…”