ACL injuries are particularly common in sports like soccer, wrestling and basketball.

ACL Injuries: How They Happen and How to Prevent Them

ACL injuries occur when there is damage to the anterior cruciate ligament (ACL), which joins the upper and lower leg bones down the middle of the knee, stabilizing the joint. Injuries can range from mild, such as a small tear to severe, such as when the ligament tears completely or when the ligament and part of the bone separate from the rest of the bone.

Without treatment, the weakened ACL is less able to control knee movement, a condition known as chronic ACL deficiency, says Dr. James Colville, MD, an orthopedic surgeon at Kaiser Permanente San Francisco.

“ACL injuries are particularly common in sports like soccer, wrestling, football, basketball, and other court sports, where you plant your foot, then have to change direction to avoid an opponent or dodge an obstacle,” says Colville. “Any kind of twisting action can lead to ACL tears.” For example, you’re more likely to suffer an ACL injury when pivoting, weaving, landing from a jump, or coming to a sudden stop while running. Your ACL can also tear if sudden force hits your knee while your leg is straight or slightly bent. “Skiing has always led to a lot of ACL tears. Straight-ahead sports like cycling, swimming, triathlons are very vigorous as well, but you’re less at risk because you don’t get twisting to the knees.”

Rates of ACL injuries have been rising among athletes of all ages, as have the number of surgeries required to correct the problem. In 2016, Colville performed more than 100 ACL repairs, a record for both Kaiser Permanente and San Francisco. ACL injury rates are also rising among those in their 40s and older because people now want to stay active, says Colville. And like any other body part, the ACL becomes weaker with age. “In the past, most athletes retired if they developed this injury and we really didn’t think of doing ACL surgeries on people in their 40s and 50s, but now people want to stay active,” says Colville.

Young female athletes seem to be at particular risk for ACL injuries. This may be because of anatomical differences between male and female athletes; for example, some female athletes may have less range of motion in the hip and knee joints or decreased hamstring strength, or because of wider hips may perform playing actions such as cutting with more of a knock-kneed position.

So what can you do to avoid an ACL injury? While playing sports, be aware of your body position while turning, reaching, and jumping, and try not to plant your feet too firmly before executing such maneuvers. Stretching is helpful to increase flexibility, particularly if you have tight hamstrings or hips. However, strength is equally important; in fact, people with loose joints are at increased risk of ACL injury and need to work on stability, Colville says.

Sports programs have had success in reducing the rate of ACL injuries among athletes by teaching new ways to execute common movements, such as landing from a jump. For example, the PEP program from the Santa Monica Sports Medicine Foundation includes a series of training guidelines and exercises.

A strong core gives you the trunk stability you need to protect your knees, so include a program of ab and core exercises in your training. Likewise, strong glutes take pressure off your quads when hopping or jumping. Do agility drills to train your muscles and ligaments to land properly and build power when jumping.

Other factors that raise your risk of ACL are flat feet and having one leg longer than the other; if either of these is true of you, you may wish to consult a trainer or physical therapist and develop compensation strategies.

Melanie Haiken writes about health, wellness and fitness for national magazines and websites. She specializes in discovering and reporting the latest research on diet, nutrition, fitness, weight loss and other health-related topics. Her award-winning stories have appeared in Fitness, Shape, Health, Forbes, and other respected magazines. She also contributes health stories to numerous Kaiser Permanente newsletters and other publications.