I recently saw a physical therapist for a knee rehab program. I injured my ACL years ago and find that as I age, the knee is starting to give out from time to time. The therapist described the way I walk as the “quadriceps avoidance gait pattern.” What does this mean?

The anterior cruciate ligament (ACL) in the knee helps hold the knee together and keeps the lower leg bone (tibia) from sliding too far forward. This forward movement of the tibia is called anterior tibial translation.

After injury, the body tries to make up for the weak or missing ACL. One way to prevent tibial translation is to avoid contracting the quadriceps muscle. This large muscle over the front of the thigh straightens the knee. It pulls the tibia forward.

During walking (gait), the patient with a weak ACL tends to keep the hip extended longer. This keeps the knee in a flexed position, once again avoiding contraction of the quadriceps.

Some studies show that patients may not be avoiding the use of the quadriceps at all. They may be contracting the quadriceps (front of thigh) and the hamstrings (back of the thigh) at the same time. This is called co-contraction.

Measuring the electrical impulses of the muscles shows that the hamstrings are just contracting more than the quadriceps. The hamstrings bend the knee … yet another way the body finds to prevent tibial translation when the ACL is weak or absent.