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Torn ACL (cont.)

Causes of an ACL Tear

In the noncontact injuries, the person is usually changing direction quickly, making a sudden stop or landing from a jump. The injured knee hyperextends (over straightens) and pivots at the same time, stressing the ACL and causing it to stretch and tear. In contact sports, the foot is usually planted and the blow causes knee hyperextension. High-risk sports include football, basketball, soccer, and skiing. The use of cleats also increases the risk of an ACL injury.

Women are at higher risk of sustaining an ACL injury than men. Potential reasons for this increased risk may include differences in anatomy, training, and activity experience. Genetic differences in how muscles contract may also be another reason for the increased risk in females. Furthermore, women have a wider pelvis than men, and this can cause a increased angle (the Q angle) where the femur meets the tibia the knee joint. A wider angle increases the stress on the ACL, increasing the risk of injury.

A narrow femoral notch may increase the risk of ACL injury especially in noncontact situations. The femoral notch is the space between the two condyles that make contact with the tibial plateau in the knee joint. A narrow notch decreases the room where the ACL is located and can pinch the ligament during range of motion of the knee. This is especially true when the knee twists in hyperextension, potentially causing a tear in the ligament. Studies have also found that narrower notches are associated with smaller anterior cruciate ligaments.

Women tend to have less muscle mass than men but tend to perform the same tasks, especially on the field of play. The male's larger quadriceps and hamstring muscle bulk tend to protect and stabilize better than in women if the same stress is placed on the knee joint.

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