Long‐term ovariectomy decreases ovine compact bone viscoelasticity

Abstract

Changes in bone mineral density associated with estrogen depletion in humans do not account for all of the associated change in fracture risk, and it is possible that some of this variation may lie in changes of other aspects of bone quality. The purpose of this study was to investigate changes in viscoelastic behavior of compact bone that may be associated with estrogen depletion. Changes in compact bone viscoelastic properties associated with three years of ovariectomy were investigated with dynamic mechanical analysis (low-amplitude 3-point bending at frequencies of 1-20 Hz) using beams milled from the diaphysis of the ovine radius. The viscoelastic storage modulus was significantly (5.2%) lower at the higher frequencies for the ovariectomized animals. The general anatomic variation in storage modulus, in which cranial sectors had higher values than caudal sectors, did not change with ovariectomy. The loss tangent (tan6, a measure of damping) was also greatly decreased (up to 83%) at high frequencies in the ovariectomized animals. Anatomic variation in tan6 at low ( 6 1 2 Hz) frequencies (cranial and caudal sectors having higher values than lateral or medial sectors) was enhanced with ovariectomy. Changes in viscoelastic properties associated with long-term estrogen depletion could be responsible for a significant reduction in the toughness or strength of a bone without concomitant changes in screening modalities used to evaluate bone quality (e.g., DXA, QCT, QUA).

Long-term effects of ovariectomy on the properties of bone in goats

“…Sheep have been widely used as an animal model in orthopedic research (16), and as osteoporosis models in numerous studies (17)(18)(19). However, the time required to establish an accurate osteoporosis model remains inconsistent between studies.…”

“…A number of scholars have proposed that an osteoporosis model can be established within 6 months through the use of various testing methods, such as biomechanical testing, bone histophotometry analysis or DXA (18,(26)(27)(28); however, there are limitations, including a small number of samples and single specimen testing methods. Recent research has demonstrated that the BMD of the vertebral body in ovariectomized sheep exhibits a significant downward trend after 1 year; however, no statistically significant difference was identified when compared with a sham-control group (18).…”

“…Recent research has demonstrated that the BMD of the vertebral body in ovariectomized sheep exhibits a significant downward trend after 1 year; however, no statistically significant difference was identified when compared with a sham-control group (18). It has been suggested that a short-term ovariectomized sheep model should be defined as an osteopenia model, rather than an osteoporosis model (29).…”

The Effects of Variation in Collagen D-Spacing on Compact Bone Viscoelasticity: A Finite Element Analysis

“…Some of the biggest issues with rodents in osteoporosis research are that they are small in size which limits their use in orthopedic analyses, the trabecular remodeling differs from humans, and the osteonal structures that do appear are rare and scattered [72,73]. Many large animal models including dogs, cats, pigs, sheep, and non-human primates have been utilized for osteoporosis research in an effort to avoid some of the small animal model limitations [73] and also incorporate mechanical testing on larger bone structures [8,42,43]. The ewe, or female sheep (Ovis aries), in particular has become a promising large animal model for postmenopausal osteoporosis.…”

“…Many studies have not caused a considerable enough level of bone loss for the specimens to be considered osteoporotic, which may also be due in part to the increased BMD and BMC in ovines [71]. A large number of postmenopausal osteoporosis studies explicitly state that the ewes involved have become osteopenic [6,42,43,71,73]. Nevertheless, important findings have been made that may have significant implications in the osteoporotic condition.…”