INFLUENCE OF EARLY OVARIOHYSTERECTOMY ON THE MECHANICAL PROPERTIES OF RABBIT MEDIAL COLLATERAL LIGAMENT

摘要

Female athletes have significantly higher incidence of anterior cruciate ligament (ACL) injuries than males participating in similar sports [1]. To date, no clear explanation has emerged for this disparity. However, hormonal differences may provide an explanation because some ACL injuries have been linked to physiologic fluctuations in estrogen levels over the menstrual cycle [2]. Receptors for estrogen have been identified in rabbit and human ACLs and medial collateral ligaments (MCLs) [3]. Increased estrogen levels caused decreased fibroblast proliferation and collagen synthesis in cell cultures from human and rabbit ACLs [4]. Since fibroblasts maintain collagen production and degradation in ligaments and collagen is the major load-bearing component of ligaments, estrogen may affect knee ligament mechanical properties. Previous studies on estrogen and ligament failure properties have examined the effect of ovariectomy on adult animals, thereby exposing the mature ligament to decreased levels of estrogen. Failure properties of ACLs from ovariectomized adult animals were not different to ACLs from normal animals, as shown in monkeys, rats and sheep [1,5,6]. In young post-pubertal (21-week-old) rabbits, Rasanen and Messner [7] found no effect of ovariectomy on MCL failure properties. The above studies focused on failure properties rather than functionally-relevant mechanical properties, like laxity and creep. Our purpose in this study was to examine the influence of early ovariohysterectomy on the mechanical properties of maturing MCLs, quantifying both low-load (laxity and creep) and high-load (failure) mechanical properties. We performed ovariohysterectomy on adolescent rabbits because both the ovaries and uterus affect estrogen levels. Our hypothesis was that the mechanical properties of maturing ligaments would be influenced by continued lower levels of estrogen that result from ovariohysterectomy in the adolescent rabbit.