June 16, 2020



Anterior cruciate ligament (ACL) injuries are a major frustration for athletes. Especially frustrating is that 70-84% of all ACL injuries are non-contact(1).

Even in today’s innovative world of surgical interventions and rehabilitation, an ACL injury can sideline an athlete for months to years. On top of this, only 50% of athletes return to play after a year of being sidelined and only 65% return to play after 2 years of being sidelined(3).

What To Expect From This Article

You will learn about modifiable risk factors at the ankle and foot complex and get strategies, including exercise videos (scroll to the bottom of the article), to help reduce the likelihood of an ACL injury.

Although the ankle and foot complex is a big deal when it comes to ACL tears, there are a lot of other risk factors that contribute to ACL injury. In future posts, you will learn about how problems at the knee, hip, and trunk influence ACL integrity.

What Is The ACL & What Does It Do?

Simply put, the ACL is a ligament that stabilizes the knee.

Because the ACL attaches from the medial-posterior side of the lateral femoral condyle and connects to the center of the tibia plateau, it helps control anterior translation of the tibia and rotational forces of the tibia, particularly when the knee is in 30 degrees of knee flexion or less(5). The ACL also helps resist valgus stress (knee abduction) and to extreme degrees, varus stress to the knee.

So What Does The Ankle and Foot Complex Have To Do With The ACL?

The ankle and foot complex assists the ACL in its job to decelerate anterior tibial translation, tibial rotational forces, and tibial abduction.

Let’s explore the ankle and foot complex in detail to better illustrate why the ACL needs this complex to work exceptionally well.

What Does The Ankle and Foot Complex Do?

Impressively, the ankle and foot complex accepts loads of about five times body weight just with walking and around thirteen times body weight when running! All the more impressive is that the ankle and foot complex is less susceptible to osteoarthritis than the knee or hip which both experience less impact forces than the ankle and foot complex(4).

To put it simply, the function of the ankle and foot complex is to deform in a controlled manner to accept load (pronation) when the foot first hits the ground and to take form and become rigid (supination) to push off the ground.

Here’s How the Foot Pronates and Supinates in Complex Detail and How it Ties into the ACL

When pronation occurs at the ankle/foot complex, we get forefoot inversion in the frontal plane, midtarsal dorsiflexion in the sagittal plane, and forefoot abduction in the transverse plane. Essentially, the forefoot moves in a way that allows optimal load acceptance which reduces impact forces.

The opposite is true for supination at the ankle and foot complex in order for the foot to become rigid to push-off of. So under normal circumstances the foot pronates or becomes a bit malleable when the foot first hits the ground. This allows the foot to absorb load to store potential energy which is then used to make the foot rigid (supinate) to push-off the foot from mid-stance to late stance phase while walking or running.

The mechanism that allows the foot to become malleable to store energy and to become rigid to push-off is at the subtalar joint. The subtalar joint has three interfacing condyles that are situated between the calcaneus and the talocrural (ankle) joint and they play an important role in unlocking the foot for successful pronation which then drives tibial internal rotation.

During forefoot push-off, the three interfacing condyles of the subtalar joint, likewise, orient themselves in a way that allows the foot to become rigid and for the tibia to externally rotate. This is why the subtalar joint is known as the torque converter because of its ability to convert frontal and sagittal plane motions at the foot to drive rotational forces up the chain.

This concept is important because the torque converter of the subtalar joint causes the tibia and femur to rotate internally (turn in), and for the knee to abduct (fall in), and it also influences anterior pelvic tilt – all of which are critical to engaging the glute!

It is the rotational forces that occur at the tibia as a result of foot pronation that stimulates the proprioceptors of the ACL to engage the surrounding muscles to help stabilize the knee in order to keep the knee within its normal axis of rotation.

The Ankle and Foot Complex,Tibial Translation in Complex Detail, and How It Ties into the ACL

When the foot first hits the ground, the foot stays fixed in place which allows momentum to carry the tibia forward in the sagittal plane. This action is known as anterior tibial progression (different from anterior tibial translation). In our definition, tibial translation is the shearing force that occurs between the femoral and tibial condyles at the knee.

It is important to understand the distinction between the two because when tibial progression occurs during early to midstance phase of gait, it is often accompanied with a degree of knee flexion. The knee flexion moment that occurs during the initial stance phase of gait allows the femoral condyles to rotate or spin posteriorly in the sagittal plane.

When posterior rotation occurs at the femoral condyles, relative anterior translation (anterior shear) of the tibia occurs which lengthens the ACL and turns on its proprioceptors – this proprioceptive activation is what sends information to surrounding muscle groups to help decelerate the anterior tibial translation and thereby protect the ACL.

Ankle and Foot Complex Issues That Contribute To ACL Tears

Now it’s time to look at modifiable risk factors of the ankle when it comes to non-contact ACL injuries.

Excessive Foot Pronation

Excessive foot pronation in an athlete can place excessive stress on the ACL in the transverse and frontal plane. Excessive pronation on impact (when the foot hits the ground) places an excess amount of transverse force on the ACL and, over time, reduces the integrity of the ACL.

In a similar manner, stress on the ACL increases when pronation occurs beyond midstance during gait. This keeps the knee in internal pronation and abduction for too long which means the ACL is under tension for an excessively long period of time.

Uncontrolled Anterior Tibial Translation

Uncontrolled anterior tibial translation places excessive stress on the ACL primarily in the sagittal plane. More often than not, the hamstrings and calves are the primary muscles that fail to help decelerate anterior tibial translation.

Uncontrolled Knee Abduction

Uncontrolled knee abduction also places excessive stress on the ACL in the frontal plane of motion. The attributing factors to uncontrolled knee abduction are often a combination of reduced lower core, glute, and strength in the foot.

How Do Ankle & Foot Complex Issues Relate To An Athlete?

An athlete is most vulnerable to a non-contact ACL injury when landing from a jump or when performing cutting or pivoting motions(3).

Athletes that land on both feet from a jump with excessive subtalar foot pronation put themselves at an increased risk of ACL injury due to excessive tibial internal rotation – this means more time under tension for the ACL (think too much time spent decelerating pronation).

An athlete will be at an even greater risk if they land on one foot with excessive subtalar foot pronation. This is because of the added mass and momentum of impact from landing on one foot.

Repetitive jumps with poor landing mechanics at the ankle/foot complex in a game, over a season, and over an athlete’s career, will cause repetitive strain to the ACL and, worst case scenario, a full rupture.

Pivoting and cutting motions have a similar effect of causing excessive strain to the ACL when the athlete has poor foot pronation control. If the supporting leg has excessive foot pronation, it results in the tibia placing excessive load on the ACL. Again, when cutting and pivoting motions are done repetitively during a match or throughout one’s career, it increases the athlete’s risk of straining or tearing the ACL.

The secondary risk factors that can feed into excessive foot pronation are reduced ankle dorsiflexion and excessive first ray dorsiflexion. The body always finds ways to complete the task at hand even at the expense of less optimal, compensatory motions – this is why secondary risk factors may feed in excessive foot pronation.

When an athlete has limited ankle dorsiflexion, it may start tasking the subtalar joint and midtarsal joints to move through more eversion and inversion motions respectively (these are both components of foot pronation). This is your body’s attempt to increase potential energy of the posterior lower leg extremity muscles (gastrocnemius, soleus, posterior tibialis, fibularis muscles). The compensation’s goal is to help decelerate tibial motion that would usually be directed through ankle dorsiflexion. Increased subtalar eversion and forefoot inversion will influence the tibia to increase its internal rotation moment, exposing the ACL to new ranges of stretch that it may not be able to control without training or support from other systems.

Likewise, excessive dorsiflexion of the first ray puts the ACL at a similar risk of injury. Excessive dorsiflexion of the first ray during stance phase of walking and running influences the torque converter mechanism of the subtalar joint which results in excessive tibial internal rotation. This will increase the ACL’s time under tension which means excessive stretch and increased likelihood of injury.

The Hypomobile Foot

A foot that remains in supination when landing or performing cutting and pivoting motions can reduce the integrity of the ACL. If the foot remains in supination, the ankle and foot complex’s ability to absorb load diminishes, forcing the knee and hips to accept more impact. Cutting and pivoting motions with an ankle and foot complex that remains in supination will put an increased amount of stress on the knee structures, including the ACL.

A supinated foot can actually load the ACL via tibia external rotation with same side cutting and pivoting motions, as the ACL will attempt to assist other passive structures to decelerate external rotation at the knee (the femur will internally rotate faster than the tibia now that the rigid foot blocks normal pronation from occurring). Again repetitive movement patterns like these places an increased amount of stress on the knee and ACL.

Fatigue To Ankle Muscles

Fatigue plays a huge role in neuromuscular control of the ankle and foot complex and has been found to increase the risk of an ACL injury(1,2). When the muscles of the ankle and foot complex begin to fatigue (gastrocnemius, soleus, posterior tibialis, fibularis muscles, and intrinsic muscles of the foot), these muscles begin to lose their ability to decelerate motions of the ankle and foot complex which then results in increased tibial internal rotation and abduction of the tibia which leads to increased time that the ACL is under tension – this means greater risk for ACL tears.

Strategies To Reduce The Risk Of ACL Injury Related To Ankle and Foot Complex Issues
Intervention programs that include multiple components (your biomechanics profile, dynamic balance, strengthening, stretching, body awareness and plyometrics) are the most effective way to help reduce ACL tear risk factors related to the ankle and foot complex(2).

Checkout the exercises below to help optimize your ankle and foot complex biomechanics while reducing the risk of ACL tears.

Studies show that preventative exercises can decrease non-contact ACL injuries by 52% in females and 85% in male athletes when done correctly(3)!







To prevent an ACL injury, the ankle and foot complex needs the optimal amount of mobility and stability throughout the subtalar, talocrural, and midtarsal joints that in turn influences motions of the tibia. Being attentive to these motions that you or your athlete lacks or have in excess and addressing them with the appropriate exercises will go a long way to prevent an ACL injury.


​If you need help recovering from an ACL injury or would like to reduce the likelihood of an ACL injury, let one of our ACL specialists help you move and feel better! Call us at (206) 279-2870 or email at hello@forefrontpllc.com. You can also schedule a visit online here.


Most people never fully recover after an injury because they aren’t getting the care they need. At Forefront Physical Therapy, we ensure a full injury recovery by individualizing your care so you can move better and enjoy a pain free life.

​DR. Manny Acheampong, DPT, FAFS
​Forefront Physical Therapy
Belltown & South Lake Union
Seattle, WA


  • Alentorn-Geli, E., Myer, G. D., Silvers, H. J., Samitier, G., Romero, D., Lázaro-Haro, C., & Cugat, R. (2009). Prevention of non-contact anterior cruciate ligament injuries in soccer players. Part 1: Mechanisms of injury and underlying risk factors. Knee surgery, sports traumatology, arthroscopy, 17(7), 705-729.
  • Alentorn-Geli, E., Myer, G. D., Silvers, H. J., Samitier, G., Romero, D., Lázaro-Haro, C., & Cugat, R. (2009). Prevention of non-contact anterior cruciate ligament injuries in soccer players. Part 2: a review of prevention programs aimed to modify risk factors and to reduce injury rates. Knee surgery, sports traumatology, arthroscopy, 17(8), 859-879.
  • Acevedo, R. J., Rivera-Vega, A., Miranda, G., & Micheo, W. (2014). Anterior cruciate ligament injury: identification of risk factors and prevention strategies. Current sports medicine reports, 13(3), 186-191.
  • Brockett, C. L., & Chapman, G. J. (2016). Biomechanics of the ankle. Orthopaedics and trauma, 30(3), 232-238
  • Domnick, C., Raschke, M. J., & Herbort, M. (2016). Biomechanics of the anterior cruciate ligament: Physiology, rupture and reconstruction techniques. World journal of orthopedics, 7(2), 82.


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