From the article:
In studies on rats, Johns Hopkins Medicine scientists report new evidence that the predominance of the hormone testosterone in males may explain why women are up to 10 times more likely than men to injure the anterior cruciate ligament (ACL) in their knees.
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Explanations for the sex differences include differences in anatomy, strength, reflex times and hormones.
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Eight of the rats were normal, with testosterone levels averaging 3.54 nanograms per milliliter, and eight had been castrated, giving them nearly undetectable levels of the hormone, at 0.14 nanograms per milliliter. The researchers measured the cross-sectional area of each ACL and then connected the bones – with the ACL stretched between them – to a machine that could pull the bones apart, tugging on the ACL. Then, they tested the strength of the ligaments by measuring how much force it took to tear each ACL.
The researchers found that it took more force – 34.5 newtons, compared to 29.2 newtons – to tear the ACLs from mice with normal levels of testosterone, indicating that the ligaments were stronger. Since researchers have generally accepted that a stronger ACL is less prone to injury, the results support a link between testosterone and ACL injuries.