Pilot study: Effects of ovariectomy-induced estrogen deficiency on the biomechanical and structural properties of the intact anterior cruciate ligament in a porcine model

Introduction: This pilot study investigated the effects of ovariectomy-induced estrogen deficiency on the biomechanical properties of intact anterior cruciate ligaments (ACLs) in a porcine model, a biological condition that may influence ligament integrity and injury susceptibility. Methods: A bilateral ovariectomy model was used to induce systemic estrogen deficiency. Fourteen two-month-old female pigs were included. Four pigs (8 knees) underwent bilateral ovariectomy (OV group). The left knees of 10 pigs that underwent laparotomy without ovariectomy for a separate study were analyzed as controls (C group). At 12 weeks, knee joints were examined macroscopically, followed by biomechanical testing consisting of cyclic anterior drawer loading and load-to-failure. Results: All ACLs were intact without arthrofibrosis or cartilage degeneration. During cyclic testing, anterior tibial translation was significantly lower in the OV group compared with controls (0.47 ± 0.14 mm vs. 0.82 ± 0.32 mm, P = 0.017). Failure mode differed between groups: all posterolateral bundles in controls avulsed at their insertions, whereas six of eight in the OV group ruptured in the midsubstance (P = 0.0070). No significant between-group differences were observed in yield load, maximum load, stiffness, or elongation at failure. Conclusion: Ovariectomy-induced estrogen deficiency altered ACL failure characteristics and reduced translation without affecting ultimate strength. These findings suggest that ovarian hormone deficiency compromises ligament quality, providing a potential mechanism for increased ACL injury risk in young female athletes. These findings should be interpreted as pilot, hypothesis-generating data. Level of Evidence: Experimental laboratory study.