Tear It Up

By Peter Galvin, MD

The anterior cruciate ligament (ACL) is a knee ligament that connects the thigh bone (femur) to the shin bone (tibia) and helps control rotational movement of the knee. It also helps prevent, along with the posterior cruciate ligament (PCL), dislocation, or subluxation, of the knee. As a side note, subluxation is a partial dislocation of a joint. Luxation is a complete separation of a joint. The ACL and PCL cross each other, and if viewed from the side, the two ligaments would look like an “X”. Injuries to the ACL include a partial or complete tear (rupture) of the ligament. ACL ruptures can cause acute and chronic knee pain, osteoarthritis, and fear of reinjury. In addition, ACL ruptures lead to time missed from sports activities, and their treatment is associated with significant healthcare costs. Due to the nature of forces at the knee, PCL tears are rare.

It is a biologic fact that males are in general more sturdily built than females, and that includes their ligaments. ACL tears are common sports-related injuries, affecting more than 120,000 individuals in the U.S. every year, but female athletes participating in contact sports (such as basketball and soccer) have a substantially higher risk of ACL tears than males playing the same sports (1.88 vs 0.87 per 10,000 exposures). This is due to anatomical differences between females and males, for example women have a wider pelvis and shorter femur than men. Also, women typically have increased hip internal rotation and torque at the knee compared with men, and this results in less stability of the knee when landing from a jump or suddenly changing direction.

The female sex hormones estrogen and relaxin contribute to decreased strength and increased looseness of ligaments, however the association of these hormones with ACL injury is uncertain. Other potential mechanisms may be related to differing activities in childhood among girls and boys, which can affect muscular strength and physical skills. In addition, women may have inferior-quality sporting grounds and training facilities, which may increase their rates of ACL injury compared to men. Surgery is the recommended treatment for most ACL ruptures, especially for athletes intending to return to a physically demanding sport. ACL reconstruction is typically done arthroscopically, using either the patient’s own tissue (iliotibial band, hamstring, quadriceps, or patellar tendon) or a cadaver tendon.

Despite modern surgical techniques, only about 55% of athletes return to competitive sports after ACL repair, and return rates are lower among females than males. Studies have shown no significant differences in knee pain, graft failure, and osteoarthritis among women and men after ACL surgery. However, in the first 10 years after ACL repair, women report worse functional outcomes such as knee instability, locking or swelling, limping, difficulty with stair climbing and squatting, and overall negative effects on activity levels.

There are low-cost interventions with high-quality evidence that can decrease the risk of ACL injury among female athletes, including neuromuscular training programs that correct imbalances between hamstring and quadriceps strength, plyometric training (which improves the ability to generate rapid muscle forces over shorter time periods), balance training, and stretching routines. For more information go to the website of the American Academy of Orthopaedic Surgeons at www.aaos.org

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