There are 200,000 injuries to the anterior cruciate ligament (ACL) per year in the United States, representing a cost of $3 billion.
Three-fourths of all ACL tears are non-contact injuries (think skiing), and typically occur during deceleration, lateral pivoting or landing. Most people who tear an ACL will hear a pop, feel their knee "giving way" and notice immediate pain and swelling.
Female athletes are three to four times more likely to tear an ACL than male athletes playing at similar levels in the same sport. Since passage of Title IX in 1972, female participation in high school sports has increased nine-fold to 2.8 million, while male participation has been steady at 3.8 million. Indeed, there is an epidemic of female athletes tearing their ACLs.
I have also recently seen an increase in young teenagers (12-14 year olds) tearing their ACL, which is concerning. In these young patients, I still recommend fixing their ACLs. Orthopedic knee surgeons used to wait on these kids and try to have them modify their activities; but as kids, they don't, and then they come back when they are done growing at 16-17 and their knees are much worse with bad cartilage injuries and even arthritis.
There are several factors at play, but they are mostly neuromuscular. Women tend to land in a knock-kneed alignment. They also land with their center of gravity being posterior or behind their knee (i.e. "landing in the back seat") and these positions place increased forces on the ACL and can cause it to tear. Women's ACLs are also generally smaller in diameter than males and their tissues are generally more lax. These factors predispose to tearing the ACL.
Women's intercondylar notch at the end of the femur (kind of like the valley through which the ACL passes) is narrower and can more easily pinch the ACL in sports and predispose it to tear. Some experts question whether there are hormonal factors at play, but this is unproven.
Most professional female athletes work hard to keep strong, but more importantly they prevent imbalances in their musculature. Numerous studies comparing athletes who went through neuromuscular training and those who did not demonstrated lower rates of ACL tears in those who participated.
Gluteal (buttock) strengthening is critical as these muscles prevent your knee from falling into that knock-kneed alignment which places increases stresses across the ACL. Core strengthening is also critical so that athletes land directly over their feet and not land in the back seat, which again stresses the ACL.
I recommend preseason and in-season plyometric, strengthening and balance training to reduce the risk of ACL tears. Even 15 minutes of neuromuscular training done once a week for six weeks has shown to help.
> Learn to land on your toes; not your heels.
> Teach yourself to land centered over your skis and avoid landing in the "back seat." If you do find yourself in the back seat, let yourself fall; don't fight it.
> Bend your knees, don't land "stiff legged" or try not to apply pressure to your downhill ski while your knee is extended.
> Avoid your knees falling into a "knock-kneed" position when landing or as you pressure your skis.
> Make sure your ski bindings are adjusted appropriately.
> Injuries tend to happen at the end of the day when your muscles are tired, so maybe skip that last run of the day if you don't feel up to it.
Dr. Rick Cunningham is an orthopaedic specialist with Vail-Summit Orthopaedics. He specializes in ACL reconstruction, sports injuries to knee and shoulder, partial and total knee