Dynamic Knee Valgus: Villain or Symptom?

Recently, researchers from High Point University proposed a new way of looking at dynamic knee valgus⁽¹⁾. Although long thought the precursor to anterior cruciate ligament (ACL) injury, the research fails to support the thought that increased valgus, observed when landing from a vertical drop jump, predicts the incidence of ACL tear⁽¹⁾. Therefore, the team from High Point suggests that dynamic knee valgus may be a normal movement. Similar to foot supination and pronation, which are normal motions that help with the absorption of ground reaction forces and propulsion, knee valgus may also be a normal motion which athletes travel in and out of during dynamic movement. Also, like foot motion, they suppose that knee valgus only becomes a problem when it is excessive or uncontrolled.

The point made by the researchers is that knee valgus is defined as a movement in a single plane – the frontal plane – and yet bodies move in a three dimensions. Considering what one joint is doing in one plane of movement ignores a great deal about what is happening in the rest of the body. They contend that the triplanar movement of the lumbopelvic complex affects the motion seen at the knee. In unilateral loading, they suggest that the motion of the acetabulum moving over the femur contributes to problematic knee valgus. They coined the term ‘pelvic pronation’ to describe the forward angle downward, anterior tilt, contralateral pelvic drop, and spinal extension/rotation motions that can occur during weight acceptance.

This pelvic pronation contributes to a decrease in musculoskeletal tension throughout the entire body. In essence, it places the fascial and muscular system on slack at a time when the body is attempting to wind up to create power. This wind up is characteristic in movements such as throwing, kicking, and swinging a golf club or bat. The wind up creates tension and stored energy. They liken the musculoskeletal tension in the wind up to a taught rubber band. If the stability in the system breaks, as with a pronating pelvis, then not only is power lost due to the slack, but optimal anatomical alignment and movement as well.

Therefore, when looking at movement patterns, they recommend evaluating the ability of the system to maintain this kinetic chain tension in addition to strength and range of motion. The hypothesis is that if an athlete can maintain the tension, then they will resist injury even if they move into dynamic knee valgus as seen in a drop jump assessment or sporting maneuver. This explains why one might observe an athlete moving in and out of valgus without injury.

This theory impacts rehabilitation as well as prevention. It’s important to maintain pelvic stability post-ACL repair. The incidence of repeated ACL injury is high, even in well-constructed and sturdy grafts, suggesting that there is more to the injury than the integrity of the ligament or graft. Anterior cruciate guru Mick Hughes suggests perturbation training (see Figure 1) as a way of ensuring that the athlete can maintain this stability even when landing or pushed off balance, as was Chuma Okeke when he suffered his recent ACL injury.