The Relationship between Foot Pronation and ACL Injuries
-
I have had plenty of experience treating ACL injuries, both in the subacute phase when surgery is not being considered right now, or in the chronic stage. The chronic stage may be in a patient where the ACL repair still left some laxity, or where no surgery was done in the first place.
When we think about the function of the ACL, it really helps us understand how custom orthotic devices can work with these patients. What are its three main functions and how does that parallel the functional influence of the custom orthotic devices we make on the knee. First, it prevents the tibia from sliding forward on the femur (translation). Think of a pronated foot where the talus slides too far forward on the calcaneus bringing the tibia with it (breaking the Cyma line). Using an orthosis here is crucial at the level of the talus and tibia, and similarly at the level of the tibia on the femur. Generating force to prevent this forward talar position, produces a force that helps the ACL prevent the tibia forward translation on the femur.
The second function of the ACL is perhaps easier to understand the role of custom foot orthoses. The ACL is a restriction against excessive internal rotation of the tibia on the femur. It is important to note that during the contact phase of gait, the entire lower limb is internally rotating. The femur internally rotates (and should), the tibia internally rotates, and the talus across the subtalar joint internally rotates. However, the tibia rotates more than the femur and the talus more than the tibia. This “more” means that the tibia internally rotates on the femur, and when that rotation is excessive, the ACL helps stop that Rotatory Moment or Torque from occurring. It should be easy to see this correlation between the function of the ACL and the function of a custom orthosis in treating excessive pronation.
The final function of the ACL is in keeping the knee from hyperextension. Due to this function, when I treat ACL patients I need rearfoot posts for heel elevation and hamstring super strengthening work with my physical therapy friends. The lower the heel, the more the knee straightens, the higher the heel the more the knee flexes.
I hope this helps you understand why custom foot orthosis can be part of a great ACL program for patients.
