By Katelyn Perkins, DPT, Physical Therapist

How do ACL injuries happen?

ACL tears are a common and devastating sports injury. Most sports-related ACL injuries occur without contact when the athlete is landing from a jump, planting a foot to cut sharply, or coming to an abrupt stop. When the foot is planted, and the knee twists inward, the tibia (shin bone) can rotate on the femur (thigh bone), resulting in a tear of the ACL.

If you are participating in sports or activities that require jumping or changes in direction, then you are at an increased risk of sustaining an ACL injury. You may know someone-- a family member or teammate-- who has torn their ACL, undergone surgery, and then participated in a lengthy post-operative rehab process. I’m sure they would not recommend it! If you were to tear your ACL, it typically takes a year to fully recover and return to the sport that you love.

What are some known risk factors for ACL injuries?

Gender – Female athletes are at a much higher risk for ACL injuries than their male counterparts. A few of the key differences between females and males are:

-Anatomical (females tend to have a wider pelvis which influences the alignment and mechanics at the knee joint)
-Hormonal (higher estrogen levels may increase ligament and tendon laxity)
-Muscle imbalances (females tend to have stronger quadriceps than hamstrings contributing to poor knee stability)

Alignment – “Knock-kneed” or valgus position where the knees collapse inward in standing predisposes the knee to injury.

Muscle imbalances – Decreased strength and flexibility of muscles in the trunk and legs can hinder your ability to achieve and maintain proper knee alignment.

Poor technique and neuromuscular control— Improper landing or deceleration/cutting techniques directly stress the ACL and contribute to the risk of injury.

Poor conditioning – As your muscles fatigue, your movement patterns are less controlled and increase your risk for injury.

How can you identify if you are at an increased risk for an ACL injury?

There are many great clinical screening tools and tests that can be used to assess your movement patterns and aid in identifying deficits in strength, stability, and mobility that could put you at risk for a knee injury. While a thorough screening by a physical therapist or athletic trainer would be most informative, there are a few relatively simple movement patterns you can videotape yourself doing with your cell phone at home.

Deep Overhead Squat- (Pictured from the front and side) With arms held up overhead, sink down into a deep squat. Key things to note are the ability to hold trunk upright (torso should remain parallel to shin bones), maintain knees apart directly over ankles (do not flare out or allow knees to collapse inward or travel excessively over the toes), toes pointed forward (not outward), and heels on the ground.

Step-down Test- (Pictured from the front) Standing on an 8-10-inch step, step down forward off the step by bending the stance leg until the opposite heel is just about to touch the floor. Then re-straighten your stance leg to return to the step. A single repetition may give you plenty of information. If the first repetition goes well, try to repeat the test for 15 seconds or so. As you fatigue, how do your mechanics hold up? Does your hip drop down? Does your knee collapse inward? Pay close attention to any loss of balance or excessive trunk lean.

Drop-Jump Test- (Pictured from the front) Standing on an 8-10-inch step, jump down off the step and then straight up into a max vertical jump. What happens to your knees when your feet hit the ground? How about as you are going up into your vertical jump? Any flaring out or collapsing inward at the knees indicates that you have poor control of your knee position due to a strength/stability deficit.

Single-Leg Hop for Distance Test- (Pictured from the front) Start by stretching a measuring tape across the floor and lining the toe up to the beginning of the measuring tape. Stand on one leg, then jump forward as far as you can and land on that same leg. If you can stabilize on that leg without touching down with your other foot, then you can mark down the distance hopped. Do three jumps on each leg and take an average of the measures. Both legs should have the same ability. More than a 10-15% difference between sides indicates a higher risk of injury. Also, use the video footage to look at your mechanics. Where do your toes point? What happens at the knees? What is your torso doing-- do you excessively lean or sway to help you balance?

Now, how do I reduce my risk of an ACL injury?

Can you identify with a few of the risk factors mentioned above? Are your squat technique, single leg balance, and jump/land mechanics subpar or asymmetrical side to side? You can do things to minimize your risk of an ACL injury and likely even improve your sports performance along the way. Below are the typical components of an ACL injury prevention program:

Strength and Flexibility of the muscles that control the lower limb (calves, hamstrings, quadriceps, gluteals) to help with the distribution of forces across the knee and ensure that you can get into and maintain proper alignment. Heavy emphasis should be placed on core strength training to create a stable base from which your legs will move.

Neuromuscular Training to improve your body’s ability to recruit the proper muscles in the appropriate sequence to produce the desired movement pattern. Proprioception is your perception or awareness of the position and movement of your body. Working on balance and proprioception training can improve your coordination and ability to react to perturbations or quick changes in direction.

Plyometric Training to improve your ability to land and decelerate the right way.

Jump training should progress in steps to ensure adequate strength and control to handle increased forces. When landing from a jump, you aim to land on the balls of your feet for a soft and quiet landing with low impact. Landing flat-footed is high-impact and means muscles are not active, and you have less control of your knee position. Typically, you would begin jumping with both legs and then advance to a single leg as your strength and control improve.

Deceleration training is also essential and focuses on movements like cutting and pivoting. Just like in jump training, you want to train with a slight knee bend and soft landing, emphasizing proper body position to go safely from full speed to an abrupt stop or change of direction. Deceleration training should be performed in all directions: front/back, side to side, and diagonals.

Strength and flexibility can take weeks to months to develop, and the plyometric and deceleration training takes practice, so don’t wait until the season starts! Instead of playing to get in shape, get in shape to play! Having a large variety of drills in your training program will help your movement patterns become second nature, so you don’t have to think about it when it's game time. Your training should be frequent and consistent before (and ideally during) your season for best results. Verbal and visual feedback can enhance your training and improve your skills more quickly. If you don't have anyone handy that can provide verbal cueing for you, you can always videotape yourself performing a jump or drill and then play it back. You can learn very quickly by seeing how you move and then working to correct it.

Formal ACL injury prevention programs are becoming more popular and successful at reducing ACL injuries. One well-studied and effective ACL prevention program is Sportsmetrics. It was developed over 20 years ago at Cincinnati Sports Medicine by Dr. Frank Noyes and the researchers at the Noyes Knee Institute. It can be used for injury prevention as well as post-recovery/return to play. 

If you are looking for a formal program, The Center For Athletes at the Marsh Brook Rehab in Somersworth has an extensive injury prevention program featuring certified and highly-skilled staff.

About Katelyn Perkins: Katelyn Perkins, DPT, is a Physical Therapist at Marsh Brook Rehab. Katelyn joined the Marsh Brook Rehab team in 2015 and is trained in the Graston Technique and her professional interests include orthopedics as well as sports physical therapy. Katelyn is a graduate of Bates College and earned her Doctorate in Physical Therapy from the University of New England in 2013.