The Effect of Estrogen on Ovine Anterior Cruciate Ligament Fibroblasts

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Abstract
Estrogen has been implicated as a causal factor for anterior cruciate ligament injuries in women. Studies have demonstrated a decrease in anterior cruciate ligament fibroblast proliferation and collagen synthesis at supraphysiologic levels of estrogen in a rabbit model. Hypothesis: The authors hypothesized that physiologic levels of estrogen would have no significant effect on anterior cruciate ligament fibroblast proliferation and collagen synthesis in an ovine model. Methods: Anterior cruciate ligament fibroblasts were isolated from sheep knees using routine cell culture methods. The cells were exposed to 17β-estradiol at physiologic concentrations of 2.2, 5, 15, 25, 250, and 2500 pg/ml. Cell proliferation was determined by cell counts on days 4 and 6. Collagen synthesis was determined by 3H-proline incorporation on day 4. Immunohistochemistry was performed to detect estrogen receptors. Results: Immunohistochemistry demonstrated the presence of estrogen receptors in ovine anterior cruciate ligament fibroblasts. There was no significant difference in anterior cruciate ligament fibroblast proliferation or collagen synthesis regardless of 17β-estradiol concentration. Conclusions: Based on results of this study, and given the low turnover of collagen in ligaments, it is unlikely that a 2- to 3-day per month increase in circulating estrogen would result in rapid, clinically significant alterations in material properties ofthe anterior cruciate ligament in vivo. The etiology of noncontact anterior cruciate ligament injuries is complex and multifactorial in nature, meriting further investigation.