Women tend to be knock-kneed because they have wider hips than men, and their thighbones curve inwards more sharply. The angle at which the thighbone, or femur, meets the lower leg bone, or tibia, is larger in women than in men, and is called the "Q angle."
Women’s tendency to be knock-kneed makes them prone to knee injuries. For instance, women are almost four times more likely to suffer from anterior cruciate ligament, or "ACL," tears than men. The risk of ACL injuries is greatest for women who participate in sports that involve pivoting, jumping or rapidly changing direction, such as gymnastics and basketball. This is because women tend to land in a knock-kneed position, which stresses the knees.