Does estrogen alter the mechanical properties of the anterior cruciate ligament? An experimental study in rabbits.
BACKGROUND
It is well known that anterior cruciate ligament (ACL) injuries are commoner in female athletes. Accordingly, we hypothesized that serum estrogen may play some role in this sex difference. We evaluated the relationship between serum estrogen levels and the mechanical properties of the ACL in rabbits.


METHODS
In 40 ovariectomized rabbits, the serum estrogen levels (SEL) were controlled by intramuscular injection of 17beta-estradiol. The mean SEL in each rabbit was defined as the average of 5 determinations done at 1, 2, 3, 4 and 5 weeks after ovariectomy. The animals were divided into 4 groups according to the dose of estradiol administered (low, medium, high and control: L, M, H and C, respectively) and into 2 groups according to the mean SEL (high-SEL group and low-SEL group). The medial portions of ACL attached to both femur and tibia harvested at 5 weeks after ovariectomy were examined mechanically.


RESULTS
The mean serum estrogen levels in groups C, L, M and H were 37, 50, 60 and 231 pg/mL. Statistically significant differences in the mean serum estrogen levels were seen among the 4 groups, except between groups L and M. Statistically significant differences were found between groups M and H in both the ultimate tensile stress and linear stiffness. In the comparison between 2 groups using the mean SEL value, both ultimate tensile stress and linear stiffness were lower in the high-SEL group. In all animals, a positive correlation was found between ultimate tensile stress and linear stiffness.


CONCLUSIONS
Our findings suggest that high SEL might be one of the factors in the multifactorial pathogenesis of ACL rupture.
Komatsuda
Tatsuro
T
Department of Orthopaedic Surgery, Tohoku Rosai Hospital, Tohoku University Graduate School of Medicine, Sendai, Japan. tkoma@fd5.so-net.ne.jp
Sugita
Takehiko
T
Sano
Hirotaka
H
Kusakabe
Takashi
T
Watanuki
Munenori
M
Yoshizumi
Yusuke
Y
Murakami
Takashi
T
Hashimoto
Minoru
M
Kokubun
Shoichi
S
D000818:Animals; D016118:Anterior Cruciate Ligament / Q000187:drug effects* / Q000502:physiology; D000070598:Anterior Cruciate Ligament Injuries; D004305:Dose-Response Relationship, Drug; D004958:Estradiol / Q000008:administration & dosage*; D004967:Estrogens / Q000097:blood*; D005260:Female; D007273:Injections, Intramuscular; D011817:Rabbits; D012421:Rupture; D012737:Sex Factors; D013314:Stress, Mechanical; D013718:Tensile Strength / Q000187:drug effects
D004967:Estrogens; D004958:Estradiol